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J.P. Magué & B. Ménard



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[1]  arXiv:1701.04402 [pdf, other]
Title: Understanding Systematic Errors Through Modeling of ALMA Primary Beams
Comments: 13 pages, 5 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Many aspects of the Atacama Large Millimeter Array (ALMA) instrument are still unknown due to its young age. One such aspect is the true nature of the primary beam of each baseline, and how changes to the individual primary beams affect astronomical observations when said changes are ignored during imaging. This paper aims to create a more thorough understanding of the strengths and weaknesses of ALMA through realistic modeling of the primary beams and simulated observations, which in turn can inform the user of the necessity of implementing more computationally costly algorithms, such as A-Projection, and when simpler, quicker algorithms will suffice. We quantify our results by examining the dynamic range of each observation, along with the ability to reconstruct the Stokes I amplitude of the test sources. These tests conclude that for dynamic ranges of less than 1000, for point sources and sources much smaller than the main lobe of the primary beam, the accuracy of the primary beam model beyond the physical size of the aperture simply doesn't matter. In observations of large extended sources, deconvolution errors dominate the reconstructed images and the individual primary beam errors were indistinguishable from each other.

[2]  arXiv:1701.04406 [pdf, other]
Title: Evidence for the Stochastic Acceleration of Secondary Antiprotons by Supernova Remnants
Comments: 5 pages, 3 figures and 4 tables
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); Space Physics (physics.space-ph)

The antiproton-to-proton ratio in the cosmic-ray spectrum is a sensitive probe of new physics. Using recent measurements of the cosmic-ray antiproton and proton fluxes in the energy range of 1-1000 GeV, we study the contribution to the $\bar{p}/p$ ratio from secondary antiprotons that are produced and subsequently accelerated within individual supernova remnants. We consider several well-motivated models for cosmic-ray propagation in the interstellar medium and marginalize our results over the uncertainties related to the antiproton production cross section and the time-, charge-, and energy-dependent effects of solar modulation. We find that the increase in the $\bar{p}/p$ ratio observed at rigidities above $\sim$ 100 GV cannot be accounted for within the context of conventional cosmic-ray propagation models, but is consistent with scenarios in which cosmic-ray antiprotons are produced and subsequently accelerated by shocks within a given supernova remnant. In light of this, the acceleration of secondary cosmic rays in supernova remnants is predicted to substantially contribute to the cosmic-ray positron spectrum, accounting for a significant fraction of the observed positron excess.

[3]  arXiv:1701.04407 [pdf, ps, other]
Title: The catastrophic effect of mergers on the angular momentum and morphology of galaxies in EAGLE
Authors: Claudia del P. Lagos (ICRAR, CAASTRO), Adam R.H. Stevens (Swinburne), Richard G. Bower (Durham), Timothy A. Davis (Cardiff), Sergio Contreras (PUC), Nelson D. Padilla (PUC), Danail Obreschkow (ICRAR), Darren Croton (Swinburne), James W. Trayford (Durham), Charlotte Welker (ICRAR), Tom Theuns (Durham)
Comments: Submitted to MNRAS. 21 pages, 21 figures. Main body of the paper is 16 pages with 5 of appendices. Comments are welcomed
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use EAGLE to explore the effect galaxy mergers have on the stellar specific angular momentum of galaxies, $j_{\rm stars}$. We characterise mergers into: dry (gas-poor)/wet (gas-rich), major/minor, and by different spin alignments and orbital parameters. Our wet (dry) mergers have an average neutral gas fraction (i.e. the ratio between the neutral gas and the stellar masses of the merging system) of $1.1$ ($0.02$), while minor (major) mergers are those with stellar mass ratios between the secondary and primary galaxy in the range $0.1-0.3$ ($\ge 0.3$). We correlate the positions of galaxies in the $j_{\rm stars}$-stellar mass plane at $z=0$ with their merger history, and find that galaxies of low spins suffered dry mergers, while galaxies of normal/high spins suffered predominantly wet mergers, if any at all. The radial $j_{\rm stars}$ profiles of galaxies that went through dry mergers are deficient by $\approx 0.3$~dex at $r\lesssim 10\,r_{50}$ compared to galaxies that went through wet mergers. By studying galaxies before and after mergers, we find that dry mergers reduce $j_{\rm stars}$ by $\approx 30$%, while wet mergers increase it by $\approx 10$%, on average. The latter is connected to the build-up of the central stellar over-density by newly formed stars of high rotational speed. Moving from minor to major mergers mostly accentuates the effects above. When the spin vectors of the galaxies prior to the dry merger are misaligned, $j_{\rm stars}$ decreases to a greater magnitude, while in wet mergers, co-rotation and high orbital angular momentum lead to the largest $j_{\rm stars}$ increase. We make predictions for what would be the observational signatures in the mean $j_{\rm stars}$ profiles driven by dry mergers: (i) shallow radial profiles and (ii) profiles that continue to rise beyond $\approx 10\,r_{50}$, both of which are significantly different from spiral galaxies.

[4]  arXiv:1701.04408 [pdf, other]
Title: Large 21 cm signals from AGN-dominated reionization
Authors: Girish Kulkarni (Cambridge), Tirthankar Roy Choudhury (NCRA), Ewald Puchwein (Cambridge), Martin G. Haehnelt (Cambridge)
Comments: 10 pages, 5 figures; submitted to MNRAS; comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present here predictions for the spatial distribution of 21 cm brightness temperature fluctuations from high-dynamic-range simulations for AGN-dominated reionization histories that have been tested against available Lyman-alpha and CMB data. We model AGN by extrapolating the observed M-sigma relation to high redshifts and assign them ionizing emissivities consistent with recent UV luminosity function measurements. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen 21 cm spin temperature is significantly larger than the CMB temperature. Our AGN-dominated reionization histories increase the variance of the 21 cm emission by a factor of up to ten compared to similar reionization histories dominated by faint galaxies, to values close to 100 mK^2 at scales accessible to experiments (k < 1 h/cMpc). This is lower than the sensitivity claimed to have been already reached by ongoing experiments by only a factor of about two or less. When reionization is dominated by AGN, the 21 cm power spectrum is enhanced on all scales due to the enhanced bias of the clustering of the more massive haloes and the peak in the large scale 21 cm power is strongly enhanced and moved to larger scales due to bigger characteristic bubble sizes. AGN dominated reionization should be easily detectable by LOFAR (and later HERA and SKA1) at their design sensitivity, assuming successful foreground subtraction and instrument calibration. Conversely, these could become the first non-trivial reionization scenarios to be ruled out by 21 cm experiments, thereby constraining the contribution of AGN to reionization.

[5]  arXiv:1701.04410 [pdf, other]
Title: A rumble in the dark: signatures of self-interacting dark matter in Super-Massive Black Hole dynamics and galaxy density profiles
Comments: 10 pages, 6 figures, submitted to MNRAS, comments welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of Super-Massive Black Hole (SMBH) formation and evolution is used, as in Tremmel et al.(2015, 2016), allowing to explicitly follow SMBH dynamics at the center of galaxies. A high SIDM constant cross-section is chosen, $\sigma$=10 $\rm cm^2/gr$, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in CDM, with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80$\%$ of the SMBH population is off-centered in the SIDM case, as opposed to the CDM case in which $\sim$90$\%$ of SMBHs have reached their host's centre. SMBHs are found as far as $\sim$9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction timescale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in 'core stalling'. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to SMBH physics to study their influence on galaxy formation.

[6]  arXiv:1701.04411 [pdf, other]
Title: Using photo-ionisation models to derive carbon and oxygen gas-phase abundances in the rest UV
Comments: 7 pages, 4 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a new method to derive oxygen and carbon abundances using the ultraviolet (UV) lines emitted by the gas-phase ionised by massive stars. The method is based on the comparison of the nebular emission-line ratios with those predicted by a large grid of photo-ionisation models. Given the large dispersion in the O/H - C/O plane, our method firstly fixes C/O using ratios of appropriate emission lines and, in a second step, calculates O/H and the ionisation parameter from carbon lines in the UV. We find abundances totally consistent with those provided by the direct method when we apply this method to a sample of objects with an empirical determination of the electron temperature using optical emission lines. The proposed methodology appears as a powerful tool for systematic studies of nebular abundances in star-forming galaxies at high redshift.

[7]  arXiv:1701.04412 [pdf, other]
Title: A test for skewed distributions of dark matter and a detection in galaxy cluster Abell 3827
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Simulations of self-interacting dark matter (SIDM) predict that dark matter should lag behind galaxies during a collision. If the interaction is mediated by a high-mass force carrier, the distribution of dark matter can also develop asymmetric dark matter tails. To search for this asymmetry, we compute the gravitational lensing properties of a mass distribution with a free skewness parameter. We apply this to the dark matter around the four central galaxies in cluster Abell 3827. In the galaxy whose dark matter peak has previously been found to be offset, we measure skewness $s=0.23^{+0.05}_{-0.22}$ in the same direction as the peak offset. Our method may be useful in future gravitational lensing analyses of colliding galaxy clusters and merging galaxies.

[8]  arXiv:1701.04414 [pdf, other]
Title: Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation?
Comments: 10 pages, 8 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud's envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to $\approx$ 0.25 according to $\alpha$, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.

[9]  arXiv:1701.04415 [pdf, other]
Title: Uncertainty in the visibility mask of a survey and its effects on the clustering of biased tracers
Comments: 23 pages, 6 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The forecasted accuracy of upcoming surveys of large-scale structure cannot be achieved without a proper quantification of the error induced by foreground removal (or other systematics like 0-point photometry offset). Because these errors are highly correlated on the sky, their influence is expected to be especially important at very large scales. In this work we quantify how the uncertainty in the visibility mask of a survey influences the measured power spectrum of a sample of tracers of the density field and its covariance matrix. We start from a very large set of 10,000 catalogs of dark matter halos in periodic cosmological boxes, produced with the PINOCCHIO approximate method. To make an analytic approach feasible, we assume luminosity-independent halo bias and an idealized geometry for the visibility mask. We find that the power spectrum of these biased tracers can be expressed as the sum of a cosmological term, a mask term and a term involving their convolution. The mask and convolution terms scale like $P\propto l^2\sigma_A^2$, where $\sigma_A^2$ is the variance of the uncertainty on the visibility mask. With $l=30-100$ Mpc$/h$ and $\sigma_A=5-20$\%, the mask term can be significant at $k\sim0.01-0.1\ h/$Mpc, and the convolution term can amount to $\sim 1-10$\% of the total. For the power spectrum covariance, the coupling of the convolution term with the other two gives rise to several mixed terms, that we quantify by difference using the mock catalogs. These are found to be of the same order of the mask covariance, and to introduce non-diagonal terms at large scales. Then, the power spectrum covariance matrix cannot be expressed as the sum of a cosmological and of a mask term. Our results lie down the theoretical bases to quantify the impact that uncertainties in the mask calibration have on the derivation of cosmological constraints from large spectroscopic surveys. [Abridged]

[10]  arXiv:1701.04416 [pdf]
Title: Analogs of primeval galaxies two billion years after the Big Bang
Comments: 25 pages, 8 figs, 2 tables. Accepted for publication
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Deep observations are revealing a growing number of young galaxies in the first billion year of cosmic time. Compared to typical galaxies at later times, they show more extreme emission-line properties, higher star formation rates, lower masses, and smaller sizes. However, their faintness precludes studies of their chemical abundances and ionization conditions, strongly limiting our understanding of the physics driving early galaxy build-up and metal enrichment. Here we study a rare population of UV-selected, sub$-L^{*}$(z=3) galaxies at redshift 2.4$<z<$3.5 that exhibit all the rest-frame properties expected from primeval galaxies. These low-mass, highly-compact systems are rapidly-forming galaxies able to double their stellar mass in only few tens million years. They are characterized by very blue UV spectra with weak absorption features and bright nebular emission lines, which imply hard radiation fields from young hot massive stars. Their highly-ionized gas phase has strongly sub-solar carbon and oxygen abundances, with metallicities more than a factor of two lower than that found in typical galaxies of similar mass and star formation rate at $z\lesssim$2.5. These young galaxies reveal an early and short stage in the assembly of their galactic structures and their chemical evolution, a vigorous phase which is likely to be dominated by the effects of gas-rich mergers, accretion of metal-poor gas and strong outflows.

[11]  arXiv:1701.04417 [pdf, other]
Title: Ecology of dark matter haloes -II. Effects of interactions on the alignment of halo pairs
Authors: Benjamin L'Huillier (1,2), Changbom Park (1), Juhan Kim (1) ((1) Korea Institute for Advanced Study, (2) Korea Astronomy and Space Science Institute)
Comments: Accepted for Publication in MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use the Horizon Run 4 cosmological N -body simulation to study the effects of distant and close interactions on the alignments of the shapes, spins, and orbits of targets haloes with their neighbours, and their dependence on the local density environment and neighbour separation. Interacting targets have a significantly lower spin and higher sphericity and oblateness than all targets. Interacting pairs initially have anti-parallel spins, but the spins develop parallel alignment as time goes on. Neighbours tend to evolve in the plane of rotation of the target, and in the direction of the major axis of prolate haloes. Moreover, interactions are preferentially radial, while pairs with non-radial orbits are preferentially prograde. The alignment signals are stronger at high-mass and for close separations, and independent on the large-scale density. Positive alignment signals are found at redshifts up to 4, and increase with decreasing redshifts. Moreover, the orbits tend to become prograde at low redshift, while no alignment is found at high redshift (z = 4).

[12]  arXiv:1701.04418 [pdf, other]
Title: Characterization of star-forming dwarf galaxies at 0.1 $\lesssim z \lesssim$ 0.9 in VUDS: Probing the low-mass end of the mass-metallicity relation
Comments: 24 Figures, 3 Tables. Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the discovery and spectrophotometric characterization of a large sample of 164 faint ($i_{AB}$ $\sim$ $23$-$25$ mag) star-forming dwarf galaxies (SFDGs) at redshift $0.13$ $\leq z \leq$ $0.88$ selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We investigate their integrated physical properties and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. We use optical VUDS spectra in the COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multiwavelength photometry, to derive stellar masses, star formation rates (SFR) and gas-phase metallicities. The VUDS SFDGs are compact (median $r_{e}$ $\sim$ $1.2$ kpc), low-mass ($M_{*}$ $\sim$ $10^7-10^9$ $M_{\odot}$) galaxies with a wide range of star formation rates (SFR($H\alpha$) $\sim 10^{-3}-10^{1}$ $M_{\odot}/yr$) and morphologies. Overall, they show a broad range of subsolar metallicities (12+log(O/H)=$7.26$-$8.7$; $0.04$ $\lesssim Z/Z_{\odot} \lesssim$ $1$). The MZR of SFDGs shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift. We find the scatter of the MZR partly explained in the low mass range by varying specific SFRs and gas fractions amongst the galaxies in our sample. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a "closed-box" model, but those from a gas regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation.

[13]  arXiv:1701.04421 [pdf, ps, other]
Title: MOSiC: an analysis tool for IRIS spectral data
Authors: Reza Rezaei
Comments: The program is available on the GitHub page (this https URL)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

This is a manual for the MOSiC package. MOSiC is a collection of IDL programs for profile analysis and Gaussian fitting of the Mg II h/k lines along with Gaussian fitting of the C II 133.5 nm line pair, the O I 135.6, the Cl I 135.2, the Si IV 139.7 and 140.3 and the O IV 140.0 nm lines observed with the IRIS near UV and far UV spectrograph. It was tested by analyzing over a hundred different IRIS data sets (quiet Sun, sunspot, ...). It works for off limb data, although it is still experimental. MOSiC analyzes different spectral lines separately and returns line intensity, width, and velocity for each line. A few sample profiles and maps are included in this manual.

[14]  arXiv:1701.04422 [pdf, ps, other]
Title: Population gradient in Sextans dSph: Comprehensive mapping of a dwarf galaxy by Suprime-Cam
Comments: 11pages, 12 figures, Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the deep and wide $V$ and $I_c$ photometry of the Sextans dwarf spheroidal galaxy (dSph) taken by Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius. The colour-magnitude diagram (CMD) reaches two magnitudes below the main sequence (MS) turn-off, showing a steep red giant branch, blue and red horizontal branch (HB), sub-giant branch (SGB), MS, and blue stragglers (BS). We construct the radial profile of each evolutionary phase and demonstrate that blue HB stars are more spatially extended, while red HB stars are more centrally concentrated than the other components. The colour distribution of SGB stars also varies with the galactocentric distance; the inner SGB stars shift bluer than those in the outskirt. The radial differences in the CMD morphology indicate the existence of the age gradient. The relatively younger stars ($\sim10$ Gyr) are more centrally concentrated than the older ones ($\sim13$ Gyr). The spatial contour maps of stars in different age bins also show that the younger population has higher concentration and higher ellipticity than the older one. We also detect the centrally concentrated bright BS stars, the number of which is consistent with the idea that a part of these stars belongs to the remnant of a disrupted star cluster discovered in the previous spectroscopic studies.

[15]  arXiv:1701.04429 [pdf, other]
Title: Enabling Radiative Transfer on AMR grids in CRASH
Authors: N.Hariharan (MPA/Intel), L. Graziani (MPA/OAR), B. Ciardi (MPA), F. Miniati (ETH), H.-J. Bungartz (TUM)
Comments: 19 pages, 17 figures. MNRAS, in press
Journal-ref: MNRAS 2017
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We introduce CRASH-AMR, a new version of the cosmological Radiative Transfer (RT) code CRASH, enabled to use refined grids. This new feature allows us to attain higher resolution in our RT simulations and thus to describe more accurately ionisation and temperature patterns in high density regions. We have tested CRASH-AMR by simulating the evolution of an ionised region produced by a single source embedded in gas at constant density, as well as by a more realistic configuration of multiple sources in an inhomogeneous density field. While we find an excellent agreement with the previous version of CRASH when the AMR feature is disabled, showing that no numerical artifact has been introduced in CRASH-AMR, when additional refinement levels are used the code can simulate more accurately the physics of ionised gas in high density regions. This result has been attained at no computational loss, as RT simulations on AMR grids with maximum resolution equivalent to that of a uniform cartesian grid can be run with a gain of up to 60% in computational time.

[16]  arXiv:1701.04445 [pdf]
Title: A Deep Mixing Solution to the Aluminum and Oxygen Isotope Puzzles in Presolar Grains
Comments: 10 pages, 3 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present here the application of a model for a mass circulation mechanism in between the H-burning shell and the base of the convective envelope of low mass AGB stars, aimed at studying the isotopic composition of those presolar grains showing the most extreme levels of 18O depletion and high concentration of 26Mg from the decay of 26Al. The mixing scheme we present is based on a previously suggested magnetic-buoyancy process, already shown to account adequately for the formation of the main neutron source for slow neutron captures in AGB stars. We find that this scenario is also capable of reproducing for the first time the extreme values of the 17O/16O, the 18O/16O, and the 26Al/27Al isotopic ratios found in the mentioned oxide grains, including the highest amounts of 26Al there measured.

[17]  arXiv:1701.04453 [pdf, other]
Title: Pairwise velocities in the "Running FLRW" cosmological model
Comments: 10 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the "Running Friedmann-Lema\^itre-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends {\Lambda}CDM with a time-evolving vacuum energy density. To enforce local conservation of matter a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and {\sigma}_8 at z=0 for almost all scenarios considered, which remains even when we look back to epochs as early as z=2. We also investigate various Coupled Dark Energy models, some of which show minimal degeneracy, and reveal interesting deviations from {\Lambda}CDM which could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.

[18]  arXiv:1701.04454 [pdf, ps, other]
Title: Gamma-ray and Optical Oscillations of PKS 0716+71, MRK 421, and BL Lac
Comments: 7 pages, 8 figure. Accepted for publication on Astronomy and Astrophysics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We examine the 2008-2016 gamma-ray and optical light curves of three bright BL Lac objects, PKS 0716+71, MRK 421, BL Lac, which exhibit large structured variability. We searched for periodicities by using a fully Bayesian approach. For two out of three sources investigated no significant periodic variability was found. In the case of BL Lac we detected a periodicity of ~ 680 days. Although the signal related to this is modest, the coincidence of the periods in both gamma and optical bands is indicative of a physical relevance. Considering previous literature results, possibly related gamma-ray and optical periodicities of about one year time scale are proposed in 4 bright gamma-ray blazars out of the 10 examined in detail. Comparing with results from periodicity search of optical archives of quasars, the presence of quasi-periodicities in blazars might be more frequent by a large factor. This suggests the intriguing possibility that the basic conditions for their observability are related to the relativistic jet in the observer direction, but the overall picture remains uncertain.

[19]  arXiv:1701.04459 [pdf, other]
Title: Photodissociation and photoionisation of atoms and molecules of astrophysical interest
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

A new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic processes involved. These have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (ISRF) and wavelength-dependent radiation fields. The new ISRF rates generally agree within 30% with our previous compilations, with a few notable exceptions. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic C, and self-shielding column densities. The relative importance of shielding types depends on the species in question and the dust optical properties. The new data are publicly available from the Leiden photodissociation and ionisation database.
Sensitivity of rates to variation of temperature and isotope, and cross section uncertainties, are tested. Tests were conducted with an interstellar-cloud chemical model, and find general agreement (within a factor of two) with the previous iteration of the Leiden database for the ISRF, and order-of-magnitude variations assuming various kinds of stellar radiation. The newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. Under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. The partial cross sections for H2O and NH3 photodissociation forming OH, O, NH2 and NH are also evaluated and lead to radiation-field-dependent branching ratios.

[20]  arXiv:1701.04501 [pdf, ps, other]
Title: Ultraviolet and Optical Emission-line Outflows in the Heavily Obscured Quasar SDSS J000610.67+121501.2: At the Scale of the Dusty Torus and Beyond
Comments: 26 pages, 7 figures, submited to the ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Broad emission-line outflows of active galactic nuclei (AGNs) have been proposed for many years but are very difficult to quantitatively study because of the coexistence of the gravitationally-bound and outflow emission. We present detailed analysis of a heavily reddened quasar, SDSS J000610.67+121501.2, whose normal ultraviolet (UV) broad emission lines (BELs) are heavily suppressed by the Dusty Torus as a natural "Coronagraph", thus the blueshifted BELs (BBELs) can be reliably measured. The physical properties of the emission-line outflows are derived as follows: ionization parameter $U \sim 10^{-0.5}$, column density $N_{\rm H}\sim 10^{22.0}$ cm$^{-2}$, covering fraction of $\sim 0.1$ and upper limit density of $n_{\rm H}\sim 10^{5.8}$ cm$^{-3}$. The outflow gases are located at least 41 pc away from the central engine, which suggests that they have expanded to the scale of the dust torus or beyond. Besides, Lya shows a narrow symmetric component, to our surprise, which is undetected in any other lines. After inspecting the narrow emission-line region and the starforming region as the origin of the Lya narrow line, we propose the end-result of outflows, diffusing gases in the larger region, acts as the screen of Lya photons. Future high spatial resolution spectrometry and/or spectropolarimetric observation are needed to make a final clarification.

[21]  arXiv:1701.04514 [pdf, ps, other]
Title: Performance of a prototype active veto system using liquid scintillator for a dark matter search experiment
Comments: Submitted to Nuclear Instruments and Methods in Physics Research Section A
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

We report the performance of an active veto system using a liquid scintillator with NaI(Tl) crystals for use in a dark matter search experiment. When a NaI(Tl) crystal is immersed in the prototype detector, the detector tags 48% of the internal K-40 background in the 0-10 keV energy region. We also determined the tagging efficiency for events at 6-20 keV as 26.5 +/- 1.7% of the total events, which corresponds to 0.76 +/- 0.04 events/keV/kg/day. According to a simulation, approximately 60% of the background events from U, Th, and K radioisotopes in photomultiplier tubes are tagged at energies of 0-10 keV. Full shielding with a 40-cm-thick liquid scintillator can increase the tagging efficiency for both the internal K-40 and external background to approximately 80%.

[22]  arXiv:1701.04523 [pdf, other]
Title: Photospheric Emission of Gamma-Ray Bursts
Comments: 29 pages, 10 figures, accepted to Space Science Reviews, chapter in ISSI book "Jets and Winds in Pulsar Wind Nebulae and Gamma-ray Bursts"
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We review the physics of GRB production by relativistic jets that start highly opaque near the central source and then expand to transparency. We discuss dissipative and radiative processes in the jet and how radiative transfer shapes the observed nonthermal spectrum released at the photosphere. A comparison of recent detailed models with observations gives estimates for important parameters of GRB jets, such as the Lorentz factor and magnetization. We also discuss predictions for GRB polarization and neutrino emission.

[23]  arXiv:1701.04536 [pdf, other]
Title: Design of the telescope truss and gondola for the balloon-borne X-ray polarimeter X-Calibur
Comments: 19 pages, 20 figures, submitted to Journal of Astronomical Instrumentation
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

X-ray polarimetry has seen a growing interest in recent years. Improvements in detector technology and focusing X-ray optics now enable sensitive astrophysical X-ray polarization measurements. These measurements will provide new insights into the processes at work in accreting black holes, the emission of X-rays from neutron stars and magnetars, and the structure of AGN jets. X-Calibur is a balloon-borne hard X-ray scattering polarimeter. An X-ray mirror with a focal length of 8 m focuses X-rays onto the detector, which consists of a plastic scattering element surrounded by Cadmium-Zinc-Telluride detectors, which absorb and record the scattered X-rays. Since X-rays preferentially scatter perpendicular to their polarization direction, the polarization properties of an X-ray beam can be inferred from the azimuthal distribution of scattered X-rays. A close alignment of the X-ray focal spot with the center of the detector is required in order to reduce systematic uncertainties and to maintain a high photon detection efficiency. This places stringent requirements on the mechanical and thermal stability of the telescope structure. During the flight on a stratospheric balloon, X-Calibur makes use of the Wallops Arc-Second Pointer (WASP) to point the telescope at astrophysical sources. In this paper, we describe the design, construction, and test of the telescope structure, as well as its performance during a 25-hour flight from Ft. Sumner, New Mexico. The carbon fiber-aluminum composite structure met the requirements set by X-Calibur and its design can easily be adapted for other types of experiments, such as X-ray imaging or spectroscopic telescopes.

[24]  arXiv:1701.04538 [pdf, other]
Title: SETIBURST: A Robotic, Commensal, Realtime Multi-Science Backend for the Arecibo Telescope
Comments: 13 pages; Accepted for publication in The Astrophysical Journal Supplement Series
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Radio astronomy has traditionally depended on observatories allocating time to observers for exclusive use of their telescopes. The disadvantage of this scheme is that the data thus collected is rarely used for other astronomy applications, and in many cases, is unsuitable. For example, properly calibrated pulsar search data can, with some reduction, be used for spectral line surveys. A backend that supports plugging in multiple applications to a telescope to perform commensal data analysis will vastly increase the science throughput of the facility. In this paper, we present 'SETIBURST', a robotic, commensal, realtime multi-science backend for the 305-m Arecibo Telescope. The system uses the 1.4 GHz, seven-beam Arecibo L-band Feed Array (ALFA) receiver whenever it is operated. SETIBURST currently supports two applications: SERENDIP VI, a SETI spectrometer that is conducting a search for signs of technological life, and ALFABURST, a fast transient search system that is conducting a survey of fast radio bursts (FRBs). Based on the FRB event rate and the expected usage of ALFA, we expect 0-5 FRB detections over the coming year. SETIBURST also provides the option of plugging in more applications. We outline the motivation for our instrumentation scheme and the scientific motivation of the two surveys, along with their descriptions and related discussions.

[25]  arXiv:1701.04557 [pdf, other]
Title: Perspectives for observing hot massive stars with XMM-Newton in the years 2017 -- 2027
Authors: Gregor Rauw
Comments: To appear in a special issue of Astronomical Notes. Proceedings of the workshop "XMM-Newton: The Next Decade", (ESAC, Villafranca del Castillo, Spain, 9-11 May 2016)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects helped us gain a deeper insight into the physics of single massive stars with or without magnetic fields, as well as of massive binary systems, where the stellar winds of both stars interact. These observations also revealed a number of previously unexpected features that challenge our understanding of the dynamics of the stellar winds of massive stars. I briefly summarize the results obtained over the past 15 years and highlight the perspectives for the next decade. It is anticipated that coordinated (X-ray and optical or UV) monitoring and time-critical observations of either single or binary massive stars will become the most important topics in this field over the coming years. Synergies with existing or forthcoming X-ray observatories (NuSTAR, Swift, eROSITA) will also play a major role and will further enhance the importance of XMM-Newton in our quest for understanding the physics of hot, massive stars.

[26]  arXiv:1701.04572 [pdf, ps, other]
Title: Searching for a pair of accreting supermassive black holes in J1425+3231
Comments: 4 pages, 1 figure. Accepted for publication in the Proceedings of the IAU Symposium No. 324, New Frontiers in Black Hole Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In hierarchical structure formation scenarios, merging galaxies are expected to be seen in different phases of their coalescence. Simulations suggest that simultaneous activity of the supermassive black holes (SMBHs) in the centres of the merging galaxies may be expected at kpc-scale separations. Currently, there are no direct observational methods which allow the selection of a large number of such dual active galactic nuclei (AGN) candidates. SDSS J142507.32+323137.4 was reported as a promising candidate source based on its optical spectrum. Here we report on our sensitive e-MERLIN observations performed at $1.6$ and at $5$ GHz, which show that the optical spectrum of the source can be more straightforwardly explained with jet-cloud interactions instead of the dual AGN scenario.

[27]  arXiv:1701.04573 [pdf, other]
Title: New astrophysical bounds on ultralight axionlike particles (ULALPs)
Comments: 14 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Motivated by tension between the predictions of ordinary cold dark matter (CDM) and observations at galactic scales, ultralight axionlike particles (ULALPs) with mass of the order $10^{-22}~{\rm eV}$ have been proposed as an alternative CDM candidate. We consider cold and collisionless ULALPs produced in the early universe by the vacuum realignment mechanism and constituting most of CDM. The ULALP fluid is commonly described by classical field equations. However, we show that, like QCD axions, the ULALPs thermalize by gravitational self-interactions and form a Bose-Einstein condensate (BEC), a quantum phenomenon. ULALPs, like QCD axions, explain the observational evidence for caustic rings of dark matter because they thermalize and go to the lowest energy state available to them. This is one of rigid rotation on the turnaround sphere. By studying the heating effect of infalling ULALPs on galactic disk stars and the thickness of the nearby caustic ring as observed from a triangular feature in the IRAS map of our galactic disk, we obtain lower mass bounds on the ULALP mass of order $10^{-23}~{\rm eV}$ and $10^{-20}~{\rm eV}$ respectively.

[28]  arXiv:1701.04578 [pdf, ps, other]
Title: Korean VLBI Network Calibrator Survey (KVNCS): 1. Source Catalog Of KVN Single Dish Flux Density Measurement In The K And Q Bands
Comments: Aaccepted for publication in ApJS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present the catalog of the KVN Calibrator Survey (KVNCS). This first part of the KVNCS is a single dish radio survey conducted at 22 (K band) and 43 GHz (Q band) simultaneously using the Korean VLBI Network (KVN) from 2009 to 2011. A total 2045 sources selected from the VLBA Calibrator Survey (VCS) with an extrapolated flux density limit of 100 mJy at K band. The KVNCS contains 1533 sources in the K band with a flux density limit of 70 mJy and 553 sources in the Q band with a flux density limit of 120 mJy; it covers the whole sky down to $-32.^\circ5$ in declination. Five hundred thirteen sources were detected in the K and Q bands, simultaneously; $\sim76\%$ of them are flat-spectrum sources ($-0.5 \leq \alpha \leq 0.5$). From the flux--flux relationship, we anticipated that the most of the radiation of many of the sources comes from the compact components. Therefore, the sources listed in the KVNCS are strong candidates for high frequency VLBI calibrators.

[29]  arXiv:1701.04580 [pdf, other]
Title: Modified evolution of stellar binaries from supermassive black hole binaries
Authors: Bin Liu (SHAO, USTC), Yi-Han Wang (USTC), Ye-Fei Yuan (USTC)
Comments: 12 pages, 9 figures, MNRAS in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The evolution of main sequence binaries resided in the galactic centre is influenced a lot by the central super massive black hole (SMBH). Due to this perturbation, the stars in a dense environment are likely to experience mergers or collisions through secular or non-secular interactions. In this work, we study the dynamics of the stellar binaries at galactic center, perturbed by another distant SMBH. Geometrically, such a four-body system is supposed to be decomposed into the inner triple (SMBH-star-star) and the outer triple (SMBH-stellar binary-SMBH). We survey the parameter space and determine the criteria analytically for the stellar mergers and the tidal disruption events (TDEs). For a relative distant and equal masses SMBH binary, the stars have more opportunities to merge as a result from the Lidov-Kozai(LK) oscillations in the inner triple. With a sample of tight stellar binaries, our numerical experiments reveal that a significant fraction of the binaries, ~70 per cent, experience merger eventually. Whereas the majority of the stellar TDEs are likely to occur at a close periapses to the SMBH, induced by the outer Kozai effect. The tidal disruptions are found numerically as many as ~10 per cent for a close SMBH binary that is enhanced significantly than the one without the external SMBH. These effects require the outer perturber to have an inclined orbit (>=40 degree) relatively to the inner orbital plane and may lead to a burst of the extremely astronomical events associated with the detection of the SMBH binary.

[30]  arXiv:1701.04594 [pdf, ps, other]
Title: Numerical Simulations of Torsional Alfvén Waves in Axisymmetric Solar Magnetic Flux Tubes
Comments: Submitted to Solar Physics (accepted)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We investigate numerically Alfv\'en waves propagating along an axisymmetric and non-isothermal solar flux tube embedded in the solar atmosphere. The tube magnetic field is current-free and diverges with height, and the waves are excited by a periodic driver along the tube magnetic field lines. The main results are that the two wave variables, the velocity and magnetic field perturbations in the azimuthal direction, behave differently as a result of gradients of physical parameters along the tube. To explain these differences in the wave behavior, the time evolution of the wave variables and the resulting cutoff period for each wave variable are calculated, and used to determine regions in the solar chromosphere where strong wave reflection may occur.

[31]  arXiv:1701.04608 [pdf, ps, other]
Title: Abundances of the light elements from UV (HST) and red (ESO) spectra in the very old star HD 84937
Comments: 8 pages, 9 figures
Journal-ref: 2017, Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In order to provide a better basis for the study of mechanisms of nucleosynthesis of the light elements beyond hydrogen and helium in the oldest stars, the abundances of C, O, Mg, Si, P, S, K, and Ca have been derived from UV-HST and visible-ESO high resolution spectra in the old, very metal-poor star HD 84937, at a metallicity that is 1/200 that of the Sun's. For this halo main-sequence turnoff star, the abundance determination of P and S are the first published determinations. The LTE profiles of the lines were fitted to the observed spectra. Wherever possible, we corrected the derived abundances for non-LTE effects. Three-dimensional (3D) CO5BOLD model atmospheres have been used to determine the abundances of C and O from molecular CH and OH bands. The abundances of these light elements in HD 84937 are found to agree well with the abundances in classical metal-poor stars. Our HD 84937 carbon abundance determination points toward a solar (or mildly enhanced) value of [C/Fe]. The modest overabundance of the alpha elements of even atomic number Z, typical of halo turnoff stars, is confirmed in this example. The odd-Z element P is found to be somewhat deficient in HD 84937, at [P/Fe]=-0.32, which is again consistent with the handful of existing determinations for turnoff stars of such low metallicity. We show that the abundance of oxygen, deduced from the OH band from 3D computations, is not compatible with the abundance deduced from the red oxygen triplet. This incompatibility is explained by the existence of a chromosphere heating the shallow layers of the atmosphere where the OH band, in 3D computations, is mainly formed. The abundance ratios are compared to the predictions of models of galactic nucleosynthesis and evolution

[32]  arXiv:1701.04620 [pdf, ps, other]
Title: Measurement of the muon-induced neutron seasonal modulation with LVD
Authors: N. Yu. Agafonova (on behalf of the LVD Collaboration)
Comments: XXV ECRS 2016 Proceedings - eConf C16-09-04.3
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

Cosmic ray muons with the average energy of 280 GeV and neutrons produced by muons are detected with the Large Volume Detector at LNGS. We present an analysis of the seasonal variation of the neutron flux on the basis of the data obtained during 15 years. The measurement of the seasonal variation of the specific number of neutrons generated by muons allows to obtaine the variation magnitude of of the average energy of the muon flux at the depth of the LVD location. The source of the seasonal variation of the total neutron flux is a change of the intensity and the average energy of the muon flux.

[33]  arXiv:1701.04621 [pdf, other]
Title: V-type candidates and Vesta family asteroids in the Moving Objects VISTA (MOVIS) Catalogue
Comments: In press in Astronomy & Astrophysics. 9 pages, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Basaltic asteroids (V-types) are believed to be fragments of large differentiated bodies. The majority of them are found in the inner part of the asteroid belt, and are current or past members of the Vesta family. Recently, some V-type asteroids have been discovered far from the Vesta family supporting the hypothesis of the presence of multiple basaltic asteroids in the early solar system. The discovery of basaltic asteroids in the outer belt challenged the models of the radial extent and the variability of the temperature distribution in the early solar system. We aim to identify new basaltic V-type asteroids using near-infrared colors of ~40000 asteroids observed by the VHS-VISTA survey and compiled in the MOVIS-C catalogue. We also want to study their near-infrared colors and to study the near-infrared color distribution of the Vesta dynamical family. We performed a search in the MOVIS-C catalogue of all the asteroids with (Y-J) and (J-Ks) in the range (Y-J) > 0.5 and (J-Ks) < 0.3, associated with V-type asteroids, and studied their color distribution. We have also analyzed the near-infrared color distribution of 273 asteroid members of the Vesta family and compared them with the albedo and visible colors from WISE and SDSS data. We determined the fraction of V-type asteroids in the family. We found 477 V-type candidates in MOVIS-C, 244 of them outside the Vesta dynamical family. We identified 19 V-type asteroids beyond the 3:1 mean motion resonance, 6 of them in the outer main belt, and 16 V-types in the inner main belt with proper inclination i_p < 3.0deg, well below the inclination of the Vesta family. We computed that ~85% of the members of the Vesta dynamical family are V-type asteroids, and only 1-2% are primitive class asteroids and unlikely members of the family. This work almost doubles the sample of basaltic asteroid candidates in regions outside the Vesta family.

[34]  arXiv:1701.04627 [pdf, other]
Title: Global Evolution of an Accretion Disk with Net Vertical Field: Coronal Accretion, Flux Transport, and Disk Winds
Comments: 27 pages, 28 figures, Submitted to the AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We report new global ideal MHD simulations for thin accretion disks threaded by net vertical magnetic fields. Our computations span three orders of magnitude in radius, extend all the way to the pole, and are evolved for more than one viscous time over the inner decade in radius. Static mesh refinement is used to properly resolve MRI. We find that:(1) inward accretion occurs mostly in the upper magnetically dominated regions of the disk, similar to the "coronal accretion" in previous GRMHD simulations. Rapid inflow in the upper layers combined with slow outflow at the midplane creates strong $R\phi$ and $z\phi$ stresses in the mean field; the vertically integrated $\alpha\sim 0.5-1$ when the initial field has $\beta_{0}=10^3$ at the midplane. (2) A quasi-static global field geometry is established in which flux transport by inflows at the surface is balanced by turbulent diffusion. The field is strongly pinched inwards at the surface. A steady-state advection-diffusion model, with turbulent magnetic Prandtl number of order unity, reproduces this geometry well. (3) Weak unsteady disk winds are launched at $z/R\sim1$ with the Alfven radius $R_{A}/R_{0}\sim3$. Although the wind is episodic, the time averaged properties are well described by steady wind theory. Wind is not efficient at transporting angular momentum. Even with $\beta_{0}=10^3$, only 5% of the angular momentum transport is driven by torque from the wind, and the wind mass flux from the inner decade of radius is only $\sim$ 0.4% of the mass accretion rate. With weaker fields or thinner disks, the wind contributes even less. (4) Most of the disk accretion is driven by the $R\phi$ stress from the MRI and global magnetic fields. Our simulations may shed light on high $\alpha$ in CVs, high near-IR flux in Herbig stars, fast inflow in transitional disks, outflow in FUors, and the transport of chondrites in our solar system.

[35]  arXiv:1701.04640 [pdf, ps, other]
Title: Rotational spectroscopy, tentative interstellar detection, and chemical modelling of N-methylformamide
Comments: Accepted for publication in A&A. 41 pages, 30 figures, 13 tables. The abstract has been shortened to comply with the size limit set by arXiv
Subjects: Astrophysics of Galaxies (astro-ph.GA)

N-methylformamide, CH3NHCHO, may be an important molecule for interstellar pre-biotic chemistry because it contains a peptide bond. The rotational spectrum of the most stable trans conformer of CH3NHCHO is complicated by strong torsion-rotation interaction due to the low barrier of the methyl torsion. We use two absorption spectrometers in Kharkiv and Lille to measure the rotational spectra over 45--630 GHz. The analysis is carried out using the Rho-axis method and the RAM36 code. We search for N-methylformamide toward the hot molecular core Sgr B2(N2) using a spectral line survey carried out with ALMA. The astronomical results are put into a broader astrochemical context with the help of a gas-grain chemical kinetics model. The laboratory data set for the trans conformer of CH3NHCHO consists of 9469 line frequencies with J <= 62, including the first assignment of the rotational spectra of the first and second excited torsional states. All these lines are fitted within experimental accuracy. We report the tentative detection of CH3NHCHO towards Sgr B2(N2). We find CH3NHCHO to be more than one order of magnitude less abundant than NH2CHO, a factor of two less abundant than CH3NCO, but only slightly less abundant than CH3CONH2. The chemical models indicate that the efficient formation of HNCO via NH + CO on grains is a necessary step in the achievement of the observed gas-phase abundance of CH3NCO. Production of CH3NHCHO may plausibly occur on grains either through the direct addition of functional-group radicals or through the hydrogenation of CH3NCO. Provided the detection of CH3NHCHO is confirmed, the only slight underabundance of this molecule compared to its more stable structural isomer acetamide and the sensitivity of the model abundances to the chemical kinetics parameters suggest that the formation of these two molecules is controlled by kinetics rather than thermal equilibrium.

[36]  arXiv:1701.04641 [pdf, other]
Title: Hydrodynamic simulations of moonlet induced propellers in Saturn's rings: Application to Bleriot
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Small moons (moonlets) embedded in the rings of Saturn cause S-shaped density structures in their close vicinity called propellers. These structures have been predicted by Spahn and Sremcevic (2000) and Sremcevic et al. (2002). N-body simulations later not only confirmed the formation of a propeller but additionally showed the appearance of wakes induced by the moonlet in the region adjacent to the S-shaped gaps (Seiss et al., 2005; Sremcevic et al., 2007; Lewis and Stewart, 2009). One of the biggest successes of the Cassini mission is the detection of propeller structures in images taken by the Imaging Science Subsystem (ISS) of the spacecraft (Tiscareno et al., 2006).
Here, we present isothermal hydrodynamic simulations of moonlet induced propellers in the A ring of Saturn. These allow for a combined treatment of gravitational scattering and diffusion and denote a further development of the original model (Spahn and Sremcevic, 2000; Sremcevic et al., 2002) where gravitational scattering of particles by the moonlet (creating the structure) and diffusion described by the hydrodynamic equations (smearing out the structure) had to be treated separately. We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirmed the scaling laws predicted by Spahn and Sremcevic (2000) and an analytical solution derived by Sremcevic et al. (2002). Finally, we match results from hydrodynamic simulations of the giant propeller Bleriot to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS). Best fits of the optical depth profiles are achieved using a Hill radius of 600 m and a kinematic shear viscosity of the surrounding ring material of 350cm$^2$/s. The results imply a moonlet diameter of about 900 m.

[37]  arXiv:1701.04647 [pdf, other]
Title: Outflows, infall and evolution of a sample of embedded low-mass protostars. The William Herschel Line Legacy (WILL) survey
Comments: Accepted to A&A, version after language editor corrections. 47 pages, 18 figures, 15 tables. The figures have been converted to pdf due to file-size considerations, which may lead to some degradation
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

[Abridged] We present spectroscopic observations in H$_{2}$O, CO and related species with \textit{Herschel} HIFI and PACS, as well as ground-based follow-up with the JCMT and APEX in CO, HCO$^{+}$ and isotopologues, of a sample of 49 nearby ($d<$500\,pc) candidate protostars. These data are used to study the outflow and envelope properties of these sources. We also compile their continuum SEDs in order to constrain their physical properties. Water emission is dominated by shocks associated with the outflow, rather than the cooler, slower entrained outflowing gas probed by ground-based CO observations. These shocks become less energetic as sources evolve from Class 0 to Class I. The fraction of mass in the outflow relative to the total envelope (i.e. $M_{\mathrm{out}}/M_{\mathrm{env}}$) remains broadly constant between Class 0 and I. The median value ($\sim$1$\%$) is consistent with a core to star formation efficiency on the order of 50$\%$ and an outflow duty cycle on the order of 5$\%$. Entrainment efficiency, as probed by $F_{\mathrm{CO}}/\dot{M}_{\mathrm{acc}}$, is also invariant with source properties and evolutionary stage. The median value (6.3\kms{}) suggests an entrainment efficiency of between 30 and 60$\%$ if the wind is launched at $\sim$1AU. $L$[O\,{\sc i}] is strongly correlated with $L_{\mathrm{bol}}$ but not with $M_{\mathrm{env}}$, while low-$J$ CO is more closely correlated with the latter than the former. This suggests that [O\,{\sc i}] traces the present-day accretion activity while CO traces time-averaged accretion over the dynamical timescale of the outflow. $L$[O\,{\sc i}] does not vary from Class 0 to Class I, unlike CO and H$_{2}$O. This is likely due to the ratio of atomic to molecular gas in the wind increasing as the source evolves, balancing out the decrease in mass accretion rate. Infall signatures are detected in HCO$^{+}$ and H$_{2}$O in a few sources.

[38]  arXiv:1701.04669 [pdf, ps, other]
Title: A new look at the molecular gas in M42 and M43; possible evidence for cloud-cloud collision which triggered formation of the OB stars in the Orion Nebula Cluster
Comments: 30 pages, 17 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Orion Nebula Cluster toward the HII region M42 is the most outstanding young cluster at the smallest distance 410pc among the rich high-mass stellar clusters. By newly analyzing the archival molecular data of the 12CO(J=1-0) emission at 21" resolution, we identified at least three pairs of complementary distributions between two velocity components at 8km/s and 13km/s. We present a hypothesis that the two clouds collided with each other and triggered formation of the high-mass stars, mainly toward two regions including the nearly ten O stars, theta1 Ori and theta2 Ori, in M42 and the B star, NU Ori, in M43. The timescale of the collision is estimated to be ~0.1Myr by a ratio of the cloud size and velocity corrected for projection, which is consistent with the age of the youngest cluster members less than 0.1Myr. The majority of the low-mass cluster members were formed prior to the collision in the last one Myr. We discuss implications of the present hypothesis and the scenario of high-mass star formation by comparing with the other eight cases of triggered O star formation via cloud-cloud collision.

[39]  arXiv:1701.04687 [pdf, other]
Title: Application of Association rule analysis to study the evolution of halos in Cosmological N-Body simulations
Authors: B. Hareesh Gautham (1), Rahul Nigam (1) ((1) Birla Institute of Technology and Science-Pilani, Hyderabad Campus)
Comments: 8 pages, 12 figures. For code related to the article, see this https URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Merger trees track the evolution of halos across multiple snapshots. They assign for halos of a particular snapshot, the set of halos from previous snapshots they possibly originated from. In this work, Association rule analysis a well known technique from data mining has been used to build halo merger trees. Association rule analysis tries to find associations between different halos(in same as well as in snapshots) using the particle IDs of the particles which the halos are made of. Associations are expressed in the form of association rules. Merger trees are one of the several useful results one can obtain from the output of association rule analysis. Other results including halo substructure and halo splitting can also be extracted. Each type of output to be extracted from the association rule analysis output correspond to a pattern in association rules. Merger trees were formed and tested using the above technique. Dark matter simulations were run using Gadget-2 for 128^3 particles. Halos were extracted from the simulation snapshots using Amiga Halo Finder. Halo accretion history was plotted and compared against those formed using AHF merger tree builder.

[40]  arXiv:1701.04706 [pdf, other]
Title: On the Detection of Extrasolar Moons and Rings
Authors: René Heller
Comments: invited review, 16 pages, 4 figures (3 col, 1 b/w)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Since the discovery of a planet transiting its host star in the year 2000, thousands of additional exoplanets and exoplanet candidates have been detected, mostly by NASA's Kepler space telescope. Some of them are almost as small as the Earth's moon. As the solar system is teeming with moons, more than a hundred of which are in orbit around the eight local planets, and with all of the local giant planets showing complex ring systems, astronomers have naturally started to search for moons and rings around exoplanets in the past few years. We here discuss the principles of the observational methods that have been proposed to find moons and rings beyond the solar system and we review the first searches. Though no exomoon or exoring has been unequivocally validated so far, theoretical and technological requirements are now on the verge of being mature for such discoveries.

[41]  arXiv:1701.04712 [pdf, other]
Title: SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium
Comments: 30 pages. Accepted for publication in A&A. Abstract slightly shortened due to arXiv requirements
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. The SEDIGISM survey covers 78 deg^2 of the inner Galaxy (-60 deg < l < +18 deg, |b| < 0.5 deg) in the J=2-1 rotational transition of 13CO. This isotopologue of CO is less abundant than 12CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13CO(2-1) and C18O(2-1) lines, plus several transitions from other molecules. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. Preliminary results based on a science demonstration field covering -20 deg < l < -18.5 deg are presented. Analysis of the 13CO(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ~30".

[42]  arXiv:1701.04713 [pdf, ps, other]
Title: Neutrino Fluxes from a Core-Collapse Supernova in a Model with Three Sterile Neutrinos
Comments: 16 pages, 9 figures
Journal-ref: Astronomy Letters, 2016, Vol. 42, 12, pp. 800-814
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics - Phenomenology (hep-ph)

The characteristics of the gravitational collapse of a supernova and the fluxes of active and sterile neutrinos produced during the formation of its protoneutron core have been calculated numerically. The relative yields of active and sterile neutrinos in core matter with different degrees of neutronization have been calculated for various input parameters and various initial conditions. A significant increase in the fraction of sterile neutrinos produced in superdense core matter at the resonant degree of neutronization has been confirmed. The contributions of sterile neutrinos to the collapse dynamics and the total flux of neutrinos produced during collapse have been shown to be relatively small. The total luminosity of sterile neutrinos is considerably lower than the luminosity of electron neutrinos, but their spectrum is considerably harder at high energies.

[43]  arXiv:1701.04716 [pdf, other]
Title: Morphology and the Color-Mass Diagram as Clues to Galaxy Evolution at z~1
Journal-ref: 2017, ApJ, 835, 22
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the significance of mergers in the quenching of star formation in galaxies at z~1 by examining their color-mass distributions for different morphology types. We perform two-dimensional light profile fits to GOODS iz images of ~5000 galaxies and X-ray selected active galactic nucleus (AGN) hosts in the CANDELS/GOODS-north and south fields in the redshift range 0.7<z<1.3. Distinguishing between bulge-dominated and disk-dominated morphologies, we find that disks and spheroids have distinct color-mass distributions, in agreement with studies at z~0. The smooth distribution across colors for the disk galaxies corresponds to a slow exhaustion of gas, with no fast quenching event. Meanwhile, blue spheroids most likely come from major mergers of star-forming disk galaxies, and the dearth of spheroids at intermediate green colors is suggestive of rapid quenching. The distribution of moderate luminosity X-ray AGN hosts is even across colors, in contrast, and we find similar numbers and distributions among the two morphology types with no apparent dependence on Eddington ratio. The high fraction of bulge-dominated galaxies that host an AGN in the blue cloud and green valley is consistent with the scenario in which the AGN is triggered after a major merger, and the host galaxy then quickly evolves into the green valley. This suggests AGN feedback may play a role in the quenching of star formation in the minority of galaxies that undergo major mergers.

[44]  arXiv:1701.04717 [pdf, other]
Title: Episodic Torque-Luminosity Correlations and Anticorrelations of GX 1+4
Authors: M.M. Serim (1), S. Sahiner (1), D. Cerri-Serim (1), S.C. Inam (2), A. Baykal (1) ((1) METU, Ankara, Turkey (2) Baskent University, Ankara, Turkey)
Comments: 4 pages, 1 figure, 11th INTEGRAL Conference Gamma-Ray Astrophysics in Multi-Wavelength Perspective, 10-14 October 2016, Amsterdam, The Netherlands
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

We analyse archival CGRO-BATSE X-ray flux and spin frequency measurements of GX 1+4 over a time span of 3000 days. We systematically search for time dependent variations of torque luminosity correlation. Our preliminary results indicate that the correlation shifts from being positive to negative on time scales of few 100 days.

[45]  arXiv:1701.04727 [pdf, other]
Title: The Tunka Radio Extension, an antenna array for high-energy cosmic-ray detection
Comments: XXV ECRS 2016 Proceedings - eConf C16-09-04.3
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

This article presents the first results of the combined measurements of Tunka-Rex and Tunka-Grande as well as studies of the antenna alignment effect and an overview of the recent Tunka-Rex results.

[46]  arXiv:1701.04728 [pdf, ps, other]
Title: Observations and light curve solutions of the W UMa binaries V796 Cep, V797 Cep, CSS J015341.9+381641 and NSVS 3853195
Comments: 13 pages, 4 figures, 8 tables. Accepted for publication in Research in Astronomy and Astrophysics (RAA)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Photometric observations in Sloan g' and i' bands of four W UMa binaries, V796 Cep, V797 Cep, CSS J015341.9+381641 and NSVS 3853195, are presented. Our observations showed that CSS J015404.1+382805 and NSVS 3853195 are the same star. We determined the initial epochs T_{0} of all targets and improved the period of NSVS 3853195. The light curve solutions of our data revealed that the components of each target are almost the same in mass, temperature, radius and luminosity. The stellar components are of G and K spectral types and undergo partial eclipses. All systems have barely-overcontact configurations and belong to H subtype W UMa binaries. We established that the relation between the luminosity ratio l_{2}/l_{1} and mass ratio q of our targets is approximately l_{2}/l_{1} = q^{1.5}.

[47]  arXiv:1701.04729 [pdf, ps, other]
Title: A Long-Term Decrease of the Mid-Size Segmentation Lengths Observed in the HeII 30.4 nm Solar EUV Emission
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Power spectra of segmentation-cell length (a dominant length scale of EUV emission in the transition region) from full-disk HeII extreme ultraviolet (EUV) images observed by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during periods of quiet Sun conditions for a time interval from 1996 to 2015 were analyzed. The spatial power as a function of the spatial frequency from about 0.04 to 0.27 (EIT) or up to 0.48 (AIA) 1/Mm depends on the distribution of the observed segmentation-cell dimensions, -- a structure of the solar EUV network. The temporal variations of the spatial power reported by Didkovsky and Gurman (Solar Phys., 289, 153) were suggested as decreases at the mid-spatial frequencies for the compared spectra when the power curves at the highest spatial frequencies of 0.5 1/pix were adjusted to match each other. That approach has been extended in this work to compare spectral ratios at high spatial frequencies expressed in the solar spatial frequency units of 1/Mm. Based on this approach we represent these ratio changes as a long-term network transformation which may be interpreted as a continuous dissipation of mid-size network structures to the smaller-size structures in the transition region. In contrast to expected cycling of the segmentation-cell dimension structures and associated spatial power in the spectra with the solar cycle, the spectra demonstrate a significant and steady change of the EUV network. The temporal trend across these structural spectra is not critically sensitive to any long-term instrumental changes, e.g. degradation of sensitivity, but to the change of the segmentation-cell dimensions of the EUV network structure.

[48]  arXiv:1701.04731 [pdf, ps, other]
Title: The optimal on-source region size for detections with counting-type telescopes
Authors: Stefan Klepser
Comments: 6 pages, 2 figures. Accepted for publication in Astropart. Phys
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Source detection in counting type experiments such as Cherenkov telescopes often involves the application of the classical Eq. 17 from the paper of Li & Ma (1983) to discrete on- and off-source regions. The on- source region is typically a circular area with radius {\theta} in which the signal is expected to appear with the shape of the instrument point spread function (PSF). This paper addresses the question of what is the {\theta} that maximises the probability of detection for a given PSF width and background event density. In the high count number limit and assuming a Gaussian PSF profile, the optimum is found to be at $\zeta_\infty^2 \approx 2.51$ times the squared PSF width $\sigma_\mathrm{PSF39}^2$. While this number is shown to be a good choice in many cases, a dynamic formula for cases of lower count numbers, which favour larger on-source regions, is given. The recipe to get to this parametrisation can also be applied to cases with a non-Gaussian PSF. This result can standardise and simplify analysis procedures, reduce trials and eliminate the need for experience-based ad hoc cut definitions or expensive case-by-case Monte Carlo simulations.

[49]  arXiv:1701.04751 [pdf, other]
Title: The circumstellar disk response to the motion of the host star
Comments: 17 pages, 20 figures, accepted for publication in Astronomy & Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Grid-based hydrodynamics simulations of circumstellar disks are often performed in the curvilinear coordinate system, in which the center of the computational domain coincides with the motionless star. However, the center of mass may be shifted from the star due to the presence of any non-axisymmetric mass distribution. As a result, the system exerts a gravity force on the star, causing the star to move in response, which can affect the evolution of the circumstellar disk. We aim at studying the effects of stellar motion on the evolution of protostellar and protoplanetary disks. In protostellar disks, a non-axisymmetric distribution of matter in the form of spiral arms or massive clumps can form due to gravitational instability. Protoplanetary disks can also feature non-axisymmetric structures caused by a high-mass planet or a large-scale vortex. We use 2D grid-based hydrodynamic simulations to explore the effect of stellar motion. We adopt a non-inertial polar coordinate system centered on the star, in which the stellar motion is taken into account by calculating the indirect potential caused by the non-axisymmetric disk, a high-mass planet, or a large-scale vortex. We found that the stellar motion has a moderate effect on the evolution history in protostellar disks, reducing somewhat the disk size and mass, while having a profound effect on the collapsing envelope, changing its inner shape from an initially axisymmetric to a non-axisymmetric configuration. Protoplanetary disk simulations show that the stellar motion slightly reduces the width of the gap opened by a high-mass planet, decreases the planet migration rate, and strengthens the large-scale vortices formed at the viscosity transition. We conclude that the inclusion of the indirect potential is recommended in grid-based hydrodynamics simulations of circumstellar disks which use the curvilinear coordinate system.

[50]  arXiv:1701.04758 [pdf, other]
Title: The VLT-FLAMES Tarantula Survey XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus
Comments: 39 pages, 12 figures in the main text, 12 figures in the appendix. Accepted for publication in A&A. Tables C1-C5 will be available at the CDS. The full version of Appendix E will be available on A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The Tarantula region in the Large Magellanic Cloud contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and mass-loss properties. Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model {{\sc fastwind}} with the genetic fitting algorithm {{\sc pikaia}} to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by Brott et al. (2011) and K\"{o}hler et al. (2015). Except for five stars, the helium abundance of our sample stars is in agreement with the initial LMC composition. The aforementioned five stars present moderate projected rotational velocities (i.e., $v_{\mathrm{e}}\,\sin\,i\,<\,200\,\mathrm{km\,s^{-1}}$) and hence do not agree with current predictions of rotational mixing in main-sequence stars. Adopting theoretical results for the wind velocity law, we find modified wind momenta for LMC stars that are $\sim$0.3 dex higher than earlier results. [Due to the limitation of characters, the abstract appearing here is slightly shorter than that in the PDF file.]

[51]  arXiv:1701.04760 [pdf, ps, other]
Title: VLBI observations of four radio quasars at $z>4$: blazars or not?
Comments: 11 pages, 4 figures, 5 tables, MNRAS accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift $z>4$ with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134$-$0419 is firmly confirmed as a blazar with our VLBI observations, due to its relativistically beamed radio emission. Its radio jet extended to $\sim$10 milli-arcsec scale makes this source a promising target for follow-up VLBI observations to reveal any apparent proper motion. Another target, J0839+5112 shows a compact radio structure typical of quasars. There is evidence for flux density variability and its radio "core" has a flat spectrum. However, the EVN data suggest that its emission is not Doppler-boosted. The remaining two blazar candidates (J1420+1205 and J2220+0025) show radio properties totally unexpected from radio AGN with small-inclination jet. Their emission extends to arcsec scales and the Doppler factors of the central components are well below 1. Their structures resemble that of double-lobed radio AGN with large inclination to the line of sight. This is in contrast with the blazar-type modeling of their multi-band spectral energy distributions. Our work underlines the importance of high-resolution VLBI imaging in confirming the blazar nature of high-redshift radio sources.

[52]  arXiv:1701.04762 [pdf, other]
Title: Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole
Authors: Tal Alexander (Weizmann Institute of Science)
Comments: 41 pp. 6 figures. Author's original version. To appear in Annual Review of Astronomy and Astrophysics. See final published version in ARA&A website: www.annualreviews.org/doi/10.1146/annurev-astro-091916-05530
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Most galactic nuclei harbor a massive black hole (MBH), whose birth and evolution are closely linked to those of its host galaxy. The unique conditions near the MBH: high velocity and density in the steep potential of a massive singular relativistic object, lead to unusual modes of stellar birth, evolution, dynamics and death. A complex network of dynamical mechanisms, operating on multiple timescales, deflect stars to orbits that intercept the MBH. Such close encounters lead to energetic interactions with observable signatures and consequences for the evolution of the MBH and its stellar environment. Galactic nuclei are astrophysical laboratories that test and challenge our understanding of MBH formation, strong gravity, stellar dynamics, and stellar physics. I review from a theoretical perspective the wide range of stellar phenomena that occur near MBHs, focusing on the role of stellar dynamics near an isolated MBH in a relaxed stellar cusp.

[53]  arXiv:1701.04787 [pdf, other]
Title: Searching for the QCD Axion with Gravitational Microlensing
Comments: 5 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph)

The phase transition responsible for axion dark matter production can create large amplitude isocurvature perturbations which collapse into dense objects known as axion miniclusters. We use microlensing data from the EROS survey, and from recent observations with the Subaru Hyper Suprime Cam to place constraints on the minicluster scenario. We compute the microlensing event rate for miniclusters treating them as spatially extended objects with an extended mass function. Using the published bounds on the number of microlensing events we bound the fraction of DM collapsed into miniclusters, $f_{\rm MC}$. For an axion with temperature dependent mass consistent with the QCD axion we find $f_{\rm MC}<0.22(m_a/100\,\mu\text{eV})^{-0.57}$, which represents the first observational constraint on the minicluster fraction. We forecast that a high-efficiency observation of ten nights with Subaru would be sufficient to constrain $f_{\rm MC}\lesssim 0.1$ over the entire QCD axion mass range. We make various approximations to derive these constraints and dedicated analyses by the observing teams of EROS and Subaru are necessary to confirm our results. If accurate theoretical predictions for $f_{\rm MC}$ can be made in future then microlensing can be used to exclude, or discover, the QCD axion. Further details of our computations are presented in a companion paper.

[54]  arXiv:1701.04791 [pdf, ps, other]
Title: Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations
Comments: 17 pages, 13 figures, accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Asteroseismic parameters allow us to measure the basic stellar properties of field giants observed far across the Galaxy. Most of such determinations are, up to now, based on simple scaling relations involving the large frequency separation, \Delta\nu, and the frequency of maximum power, \nu$_{max}$. In this work, we implement \Delta\nu\ and the period spacing, {\Delta}P, computed along detailed grids of stellar evolutionary tracks, into stellar isochrones and hence in a Bayesian method of parameter estimation. Tests with synthetic data reveal that masses and ages can be determined with typical precision of 5 and 19 per cent, respectively, provided precise seismic parameters are available. Adding independent information on the stellar luminosity, these values can decrease down to 3 and 10 per cent respectively. The application of these methods to NGC 6819 giants produces a mean age in agreement with those derived from isochrone fitting, and no evidence of systematic differences between RGB and RC stars. The age dispersion of NGC 6819 stars, however, is larger than expected, with at least part of the spread ascribable to stars that underwent mass-transfer events.

[55]  arXiv:1701.04802 [pdf, ps, other]
Title: Complex Organic Molecules tracing shocks along the outflow cavity in the high-mass protostar IRAS20126+4104
Comments: accepted in MNRAS. Figures of Appendix A upon request to first author
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We report on subarcsecond observations of complex organic molecules (COMs) in the high-mass protostar IRAS20126+4104 with the Plateau de Bure Interferometer in its most extended configurations. In addition to the simple molecules SO, HNCO and H2-13CO, we detect emission from CH3CN, CH3OH, HCOOH, HCOOCH3, CH3OCH3, CH3CH2CN, CH3COCH3, NH2CN, and (CH2OH)2. SO and HNCO present a X-shaped morphology consistent with tracing the outflow cavity walls. Most of the COMs have their peak emission at the putative position of the protostar, but also show an extension towards the south(east), coinciding with an H2 knot from the jet at about 800-1000 au from the protostar. This is especially clear in the case of H2-13CO and CH3OCH3. We fitted the spectra at representative positions for the disc and the outflow, and found that the abundances of most COMs are comparable at both positions, suggesting that COMs are enhanced in shocks as a result of the passage of the outflow. By coupling a parametric shock model to a large gas-grain chemical network including COMs, we find that the observed COMs should survive in the gas phase for about 2000 yr, comparable to the shock lifetime estimated from the water masers at the outflow position. Overall, our data indicate that COMs in IRAS20126+4104 may arise not only from the disc, but also from dense and hot regions associated with the outflow.

[56]  arXiv:1701.04815 [pdf, ps, other]
Title: Testing the young neutron star scenario with persistent radio emission associated with FRB 121102
Comments: 6 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Recently a repeating fast radio burst (FRB) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. While other possibilities are not ruled out, the emission properties are broadly consistent with theoretical suggestions of Murase et al. (2016) for quasi-steady nebula emission from a pulsar-driven supernova remnant as a counterpart of FRBs. Here we constrain the model parameters of such a young neutron star scenario for FRB 121102. If the associated supernova has a conventional ejecta mass of $M_{\rm ej}\gtrsim{\rm a \ few}\ M_\odot$, a neutron star with an age of $t_{\rm age} \sim 10-100 \ \rm yrs$, an initial spin period of $P_{\rm i} \lesssim$ a few ms, and a dipole magnetic field of $B_{\rm dip} \sim 10^{12-13} \ \rm G$ can be compatible with the observations. However, in this case, the magnetically-powered scenario may be more favored as an FRB energy source because of the efficiency problem in the rotation-powered scenario. On the other hand, if the associated supernova is an ultra-stripped one with $M_{\rm ej} \sim 0.1 \ M_\odot$, a younger neutron star with $t_{\rm age} \sim 1-10$ yrs can be the persistent radio source and might produce FRBs with the spin-down power. These possibilities could be distinguished by the decline rate of the quasi-steady radio counterpart.