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J.P. Magué & B. Ménard

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[1]  arXiv:1605.07606 [pdf, other]
Title: Limits on Fast Radio Bursts from Four Years of the V-FASTR Experiment
Comments: Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The V-FASTR experiment on the Very Long Baseline Array was designed to detect dispersed pulses of milliseconds duration, such as fast radio bursts (FRBs). We use all V-FASTR data through February 2015 to report V-FASTR's upper limits on the rates of FRBs, and compare these with re-derived rates from Parkes FRB detection experiments. V-FASTR's operation at lambda=20 cm allows direct comparison with the 20 cm Parkes rate, and we derive a power-law limit of \gamma<-0.4 (95% confidence limit) on the index of FRB source counts, N(>S)\propto S^\gamma. Using the previously measured FRB rate and the unprecedented amount of survey time spent searching for FRBs at a large range of wavelengths (0.3 cm > \lambda > 90 cm), we also place frequency-dependent limits on the spectral distribution of FRBs. The most constraining frequencies place two-point spectral index limits of \alpha_{20cm}^{4cm} < 5.8 and \alpha_{90cm}^{20cm} > -7.6, where fluence F \propto f^\alpha if we assume true the burst rate reported by Champion et al. (2016) of R(F~0.6 Jy ms) = 7 x 10^3 sky^{-1} day^{-1} (for bursts of ~3 ms duration). This upper limit on \alpha suggests that if FRBs are extragalactic but non-cosmological, that on average they are not experiencing excessive free-free absorption due to a medium with high optical depth (assuming temperature ~8,000 K), which excessively invert their low-frequency spectrum. This in turn implies that the dispersion of FRBs arises in either or both of the intergalactic medium or the host galaxy, rather than from the source itself.

[2]  arXiv:1605.07612 [pdf, ps, other]
Title: Electrical conductivity of warm neutron star crust in magnetic fields
Comments: 18 pages + 8 pages supplementary tables, 19 figures, uses RevTex
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)

We study the electrical conductivity of finite-temperature crust of a warm compact star which may be formed in the aftermath of a supernova explosion or a binary neutron star merger as well as when a cold neutron star is heated by accretion of material from a companion. We focus on the temperature-density regime where plasma is in the liquid state and, therefore, the conductivity is dominated by the electron scattering off correlated nuclei. The dynamical screening of this interaction is implemented in terms of polarization tensor computed in the hard-thermal-loop effective field theory of QED plasma. The correlations of the background ionic component are accounted for via a structure factor derived from Monte-Carlo simulations of one-component-plasma. With this input we solve the Boltzmann kinetic equation in relaxation time approximation taking into account the anisotropy of transport due to the magnetic field. The electrical conductivity tensor is studied numerically as a function of temperature and density for carbon and iron nuclei as well as density-dependent composition of zero-temperature dense matter in weak equilibrium with electrons. We also provide accurate fit formulas to our numerical results which can be used in dissipative magneto-hydrodynamics simulations of warm compact stars.

[3]  arXiv:1605.07616 [pdf, other]
Title: Far-UV bow shock nebula around PSR J0437-4715
Comments: submitted to the Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Pulsars traveling at supersonic speeds are often accompanied by cometary bow shocks seen in Halpha. We report on the first detection of a pulsar bow shock in the far-ultraviolet (FUV). We detected it in FUV images of the nearest millisecond pulsar J0437-4715 obtained with the Hubble Space Telescope. The images reveal a bow-like structure positionally coincident with part of the previously detected Halpha bow shock, with an apex at 10'' ahead of the moving pulsar. Its FUV luminosity, L(1250-2000 A) ~ 5x10^28 erg/s, exceeds the Halpha luminosity from the same area by a factor of 10. The FUV emission could be produced by the shocked ISM matter or, less likely, by relativistic pulsar wind electrons confined by strong magnetic field fluctuations in the bow shock. In addition, in the FUV images we found a puzzling extended (~3'' in size) structure overlapping with the limb of the bow shock. If related to the bow shock, it could be produced by an inhomogeneity in the ambient medium or an instability in the bow shock. We also report on a previously undetected X-ray emission extending for about 5'' ahead of the pulsar, possibly a pulsar wind nebula created by shocked pulsar wind, with a luminosity L(0.5-8 keV) ~ 3x10^28 erg/s.

[4]  arXiv:1605.07617 [pdf, ps, other]
Title: The dynamical state of the galaxy cluster: Theoretical insights from cosmological simulations
Comments: 11 pages, 4 figures, MNRAS submitted, comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Following the work of Cui et al. (2016b, hereafter Paper I), we investigate the dynamical state of the galaxy clusters from the theoretical point of view. After extending to vrial radius $R_{vir}$, we reselect out 123 clusters with $\log(M_{DM, vir}) \le 14.5$ from the galaxy cluster samples in Paper I, here DM indicate the dark-matter-only run. These clusters from the two hydro-dynamical runs are matched to the dark-matter-only run using the unique dark matter particle ID. We investigate 4 independent parameters, which are normally used to classify the cluster dynamical state. We find that the virial ratio $\eta$ from both hydro-dynamical runs is $\sim$ 10 per cent lower than from the dark-matter-only run; there is no clear bimodal distribution between the relaxed and un-relaxed clusters for all investigated parameters. Further, using the velocity dispersion deviation parameter $\zeta$ , which is defined as the ratio between cluster velocity dispersion $\sigma$ and the theoretical prediction $\sigma_t = \sqrt{G M_{total}/R}$, we find that there is a linear correlation between the virial ratio $\eta$ and the velocity dispersion deviation parameter $\zeta$. We propose to use this $\zeta$ parameter, which can be derived easily from observed clusters, as a substitute of the $\eta$ parameter to quantify the cluster dynamical state.

[5]  arXiv:1605.07618 [pdf, other]
Title: Chemistry and radiative shielding in star forming galactic disks
Comments: 21 Pages, 15 figures. Submitted to MNRAS. Comments welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

To understand the conditions under which dense, molecular gas is able to form within a galaxy, we post-process a series of three-dimensional galactic-disk-scale simulations with ray-tracing based radiative transfer and chemical network integration to compute the equilibrium chemical and thermal state of the gas. In performing these simulations we vary a number of parameters, such as the ISRF strength, vertical scale height of stellar sources, cosmic ray flux, to gauge the sensitivity of our results to these variations. Self-shielding permits significant molecular hydrogen (H2) abundances in dense filaments around the disk midplane, accounting for approximately ~10-15% of the total gas mass. Significant CO fractions only form in the densest, n>~10^3 cm^-3, gas where a combination of dust, H2, and self-shielding attenuate the FUV background. We additionally compare these ray-tracing based solutions to photochemistry with complementary models where photo-shielding is accounted for with locally computed prescriptions. With some exceptions, these local models for the radiative shielding length perform reasonably well at reproducing the distribution and amount of molecular gas as compared with a detailed, global ray tracing calculation. Specifically, an approach based on the Jeans Length with a T=40K temperature cap performs the best in regards to a number of different quantitative measures based on the H2 and CO abundances.

[6]  arXiv:1605.07619 [pdf, other]
Title: Systematic biases in low frequency radio interferometric data due to calibration: the LOFAR EoR case
Comments: Submitted to MNRAS, 14 pages, 11 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The redshifted 21 cm line of neutral hydrogen is a promising probe of the Epoch of Reionization (EoR). However, its detection requires a thorough understanding and control of the systematic errors. We study two systematic biases observed in the LOFAR EoR residual data after calibration and subtraction of bright discrete foreground sources. The first effect is a suppression in the diffuse foregrounds, which could potentially mean a suppression of the 21 cm signal. The second effect is an excess of noise beyond the thermal noise. The excess noise shows fluctuations on small frequency scales, and hence it can not be easily removed by foreground removal or avoidance methods. Our analysis suggests that sidelobes of residual sources due to the chromatic point spread function and ionospheric scintillation can not be the dominant causes of the excess noise. Rather, both the suppression of diffuse foregrounds and the excess noise can occur due to calibration with an incomplete sky model containing predominantly bright discrete sources. We show that calibrating only on bright sources can cause suppression of other signals and introduce an excess noise in the data. The levels of the suppression and excess noise depend on the relative flux of sources which are not included in the model with respect to the flux of modeled sources. We discuss possible solutions such as using only long baselines to calibrate the interferometric gain solutions as well as simultaneous multi-frequency calibration along with their benefits and shortcomings.

[7]  arXiv:1605.07620 [pdf, ps, other]
Title: II. Apples to apples $A^2$: cluster selection functions for next-generation surveys
Comments: 12 pages, 10 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present the cluster selection function for three of the largest next-generation stage-IV surveys in the optical and infrared: Euclid-Optimistic, Euclid-Pessimistic and the Large Synoptic Survey Telescope (LSST). To simulate these surveys, we use the realistic mock catalogues introduced in the first paper of this series.
We detected galaxy clusters using the Bayesian Cluster Finder (BCF) in the mock catalogues. We then modeled and calibrated the total cluster stellar mass observable-theoretical mass ($M^*_{\rm CL}-M_{\rm h}$) relation using a power law model, including a possible redshift evolution term. We find a moderate scatter of $\sigma_{M^*_{\rm CL} | M_{\rm h}}$ of 0.124, 0.135 and 0.136 $\rm dex$ for Euclid-Optimistic, Euclid-Pessimistic and LSST, respectively, comparable to other work over more limited ranges of redshift. Moreover, the three datasets are consistent with negligible evolution with redshift, in agreement with observational and simulation results in the literature.
We find that Euclid-Optimistic will be able to detect clusters with $>80\%$ completeness and purity down to $8\times10^{13}M_{\odot}$ up to $z<1$. At higher redshifts, the same completeness and purity are obtained with the larger mass threshold of $2\times10^{14}M_{\odot}$ up to $z=2$. The Euclid-Pessimistic selection function has a similar shape with $\sim10\%$ higher mass limit. LSST shows $\sim 5\%$ higher mass limit than Euclid-Optimistic up to $z<0.7$ and increases afterwards, reaching values of $2\times10^{14}M_{\odot}$ at $z=1.4$. Similar selection functions with only $80\%$ completeness threshold have been also computed. The complementarity of these results with selection functions for surveys in other bands is discussed.

[8]  arXiv:1605.07621 [pdf, other]
Title: Lens Models Under the Microscope: Comparison of Hubble Frontier Field Cluster Magnification Maps
Comments: 20 pages, 18 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Using the power of gravitational lensing magnification by massive galaxy clusters, the Hubble Frontier Fields provide deep views of six patches of the high redshift Universe. The combination of deep Hubble imaging and exceptional lensing strength has revealed the greatest numbers of multiply-imaged galaxies available to constrain models of cluster mass distributions. However, even with O(100) images per cluster, the uncertainties associated with the reconstructions are not negligible. The goal of this paper is to present a quantitative and visual impression of the diversity of model magnification predictions. We examine 7 and 9 mass models of Abell 2744 and MACS J0416, respectively, submitted to the Mikulski Archive for Space Telescopes for public distribution in September 2015. The dispersion between model predictions increases from 20% at common low magnifications (\mu~2) to 70% at rare high magnifications (\mu~40). MACS J0416 exhibits smaller dispersions than Abell 2744 for 2<\mu<10. We show that magnification maps based on different lens inversion techniques typically differ from each other by more than their quoted statistical errors. This suggests that some models probably underestimate the true uncertainties, which are primarily due to various lensing degeneracies. Though the exact mass sheet degeneracy is broken, its approximate counterpart is not broken at least in Abell 2744. Other, local degeneracies are also present in both clusters. The comparison of models in this paper is complementary to the exercise of comparing reconstructions of known synthetic mass distributions. By focusing here on a comparison of actual observed clusters, we can identify the clusters that are best constrained, and therefore provide the clearest view of the distant Universe.

[9]  arXiv:1605.07623 [pdf, ps, other]
Title: A cautionary note about composite Galactic star formation relations
Authors: Genevieve Parmentier (ARI/ZAH)
Comments: 12 pages, 7 figures; accepted for publication in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We explore the pitfalls which affect the comparison of the star-formation (SF) relation for nearby molecular clouds with that for distant compact molecular clumps. We show that both relations behave differently in the ($\Sigma_{gas}$, $\Sigma_{SFR}$) space, where $\Sigma_{gas}$ and $\Sigma_{SFR}$ are, respectively, the gas and SF rate surface densities, even when the physics of star formation is the same. This is because the SF relation of nearby clouds relates gas and star surface densities measured locally, that is, within a given interval of gas surface density, or at a given protostar location. We refer to such measurements as local measurements, and the corresponding SF relation as the local relation. In contrast, the stellar content of a distant molecular clump remains unresolved. Only the mean SF rate can be obtained from e.g. the clump infrared luminosity. One clump therefore provides one single point to the ($\Sigma_{gas}$, $\Sigma_{SFR}$) space, that is, its mean gas surface density and SF rate surface density. We refer to this SF relation as a global relation since it builds on the global properties of molecular clumps. Its definition therefore requires an ensemble of cluster-forming clumps. We show that, although the local and global relations have different slopes, this per se cannot be taken as evidence for a change in the physics of SF with gas surface density. It therefore appears that great caution should be taken when physically interpreting a composite SF relation, that is, a relation combining together local and global measurements.

[10]  arXiv:1605.07626 [pdf, ps, other]
Title: Suppressing star formation in quiescent galaxies with supermassive black hole winds
Comments: To be published in Nature on May 26th, 2016
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above $M_{*}\sim 2 \times 10^{10}~M_{\odot}$, where their numbers have increased by a factor of $\sim25$ since $z\sim2$. Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss or mergers that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centers of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized gas velocity gradients from which we infer the presence of centrally-driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as $10\%$ of the population at $M_* \sim 2 \times 10^{10}~ M_{\odot}$. In a prototypical example, we calculate that the energy input from the galaxy's low-level active nucleus is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

[11]  arXiv:1605.07632 [pdf, other]
Title: The space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics
Comments: Accepted to A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics

[12]  arXiv:1605.07635 [pdf, other]
Title: Zombie Vortex Instability. II. Thresholds to Trigger Instability and the Properties of Zombie Turbulence in the Dead Zones of Protoplanetary Disks
Comments: Submitted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In Zombie Vortex Instability (ZVI), perturbations excite critical layers in stratified, rotating shear flow (as in protoplanetary disks), causing them to generate vortex layers, which roll-up into anticyclonic zombie vortices and cyclonic vortex sheets. The process is self-sustaining as zombie vortices perturb new critical layers, spawning a next generation of zombie vortices. Here, we focus on two issues: the minimum threshold of perturbations that trigger self-sustaining vortex generation, and the properties of the late-time zombie turbulence on large and small scales. The critical parameter that determines whether ZVI is triggered is the magnitude of the vorticity on the small scales (and not velocity), the minimum Rossby number needed for instability is $Ro_{crit}\sim0.2$ for $\beta\equiv N/\Omega = 2$, where $N$ is the Brunt-V\"ais\"al\"a frequency. While the threshold is set by vorticity, it is useful to infer a criterion on the Mach number, for Kolmogorov noise, the critical Mach number scales with Reynolds number: $Ma_{crit}\sim Ro_{crit}Re^{-1/2}$. In protoplanetary disks, this is $Ma_{crit}\sim10^{-6}$. On large scales, zombie turbulence is characterized by anticyclones and cyclonic sheets with typical Rossby number $\sim$0.3. The spacing of the cyclonic sheets and anticyclones appears to have a "memory" of the spacing of the critical layers. On the small scales, zombie turbulence has no memory of the initial conditions and has a Kolmogorov-like energy spectrum. While our earlier work was in the limit of uniform stratification, we have demonstrated that ZVI works for non-uniform Brunt-V\"ais\"al\"a frequency profiles that may be found in protoplanetary disks.

[13]  arXiv:1605.07638 [pdf, other]
Title: Coherent magneto-elastic oscillations in superfluid magnetars
Comments: 16 pages, 12 figures, accepted by MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)

We study the effect of superfluidity on torsional oscillations of highly magnetised neutron stars (magnetars) with a microphysical equation of state by means of two-dimensional, magnetohydrodynamical- elastic simulations. The superfluid properties of the neutrons in the neutron star core are treated in a parametric way in which we effectively decouple part of the core matter from the oscillations. Our simulations confirm the existence of two groups of oscillations, namely continuum oscillations that are confined to the neutron star core and are of Alfv\'enic character, and global oscillations with constant phase and that are of mixed magneto-elastic type. The latter might explain the quasi-periodic oscillations observed in magnetar giant flares, since they do not suffer from the additional damping mechanism due to phase mixing, contrary to what happens for continuum oscillations. However, we cannot prove rigorously that the coherent oscillations with constant phase are normal modes. Moreover, we find no crustal shear modes for the magnetic field strengths typical for magnetars.We provide fits to our numerical simulations that give the oscillation frequencies as functions of magnetic field strength and proton fraction in the core.

[14]  arXiv:1605.07640 [pdf, other]
Title: Deep wideband single pointings and mosaics in radio interferometry - How accurately do we reconstruct intensities and spectral indices of faint sources?
Comments: 12 pages, 12 figures (accepted to AJ)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Many deep wide-band wide-field radio interferometric surveys are being designed to accurately measure intensities, spectral indices and polarization properties of faint source populations. In this paper we compare various wideband imaging methods to evaluate the accuracy to which intensities and spectral indices of sources close to the confusion limit can be reconstructed. We simulated a wideband single-pointing (C-array, L-Band (1-2GHz)) and 46-pointing mosaic(D-array, C-Band (4-8GHz)) JVLA observation using realistic brightness distribution ranging from $1\mu$Jy to $100m$Jy and time-,frequency-, polarization- and direction-dependent instrumental effects. The main results from these comparisons are (a) errors in the reconstructed intensities and spectral indices are larger for weaker sources even in the absence of simulated noise, (b) errors are systematically lower for joint reconstruction methods (such as MT-MFS) along with A-Projection for accurate primary beam correction, and (c) use of MT-MFS for image reconstruction eliminates Clean-bias (which is present otherwise). Auxiliary tests include solutions for deficiencies of data partitioning methods (e.g. the use of masks to remove clean bias and hybrid methods to remove sidelobes from sources left undeconvolved), the effect of sources not at pixel centers and the consequences of various other numerical approximations within software implementations. This paper also demonstrates the level of detail at which such simulations must be done in order to reflect reality, enable one to systematically identify specific reasons for every trend that is observed and to estimate scientifically defensible imaging performance metrics and the associated computational complexity of the algorithms/analysis procedures.

[15]  arXiv:1605.07667 [pdf, other]
Title: Exploring the mass assembly of the early-type disc galaxy NGC3115 with MUSE
Comments: 16 pages, 15 figures, accepted in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present MUSE integral field spectroscopic data of the S0 galaxy NGC 3115 obtained during the instrument commissioning at the ESO Very Large Telescope (VLT). We analyse the galaxy stellar kinematics and stellar populations and present two dimensional maps of their associated quantities. We thus illustrate the capacity of MUSE to map extra-galactic sources to large radii in an efficient manner, i.e., ~4 Re, and provide relevant constraints on its mass assembly. We probe the well known set of substructures of NGC 3115 (its nuclear disc, stellar rings, outer kpc-scale stellar disc and spheroid) and show their individual associated signatures in the MUSE stellar kinematics and stellar populations maps. In particular, we confirm that NGC 3115 has a thin fast rotating stellar disc embedded in a fast rotating spheroid, and that these two structures show clear differences in their stellar age and metallicity properties. We emphasise an observed correlation between the radial stellar velocity, V, and the Gauss-Hermite moment, h3, creating a "butterfly" shape in the central 15" of the h3 map. We further detect the previously reported weak spiral and ring-like structures, and find evidence that these features can be associated with regions of younger mean stellar ages. We provide tentative evidence for the presence of a bar, despite the fact that the V-h3 correlation can be reproduced by a simple axisymmetric dynamical model. Finally, we present a reconstruction of the two dimensional star formation history of NGC 3115 and find that most of its current stellar mass was formed at early epochs (>12Gyr ago), while star formation continued in the outer (kpc-scale) stellar disc until recently. Since z~2, and within ~4 Re, we suggest that NGC 3115 has been mainly shaped by secular processes.

[16]  arXiv:1605.07668 [pdf, other]
Title: First axion bounds from a pulsating helium-rich white dwarf star
Comments: 17 pages, 6 figures, 2 tables, prepared for submission to JCAP
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics - Phenomenology (hep-ph)

The Peccei-Quinn mechanism proposed to solve the CP problem of Quantum Chromodynamics has as consequence the existence of axions, hypothetical weakly interacting particles whose mass is constrained to be on the sub-eV range. If these particles exist and interact with electrons, they would be emitted from the dense interior of white dwarfs, becoming an important energy sink for the star. Due to their well known physics, white dwarfs are good laboratories to study the properties of fundamental particles such as the axions. We study the general effect of axion emission on the evolution of helium-rich white dwarfs and on their pulsational properties. To this aim, we calculate evolutionary helium-rich white dwarf models with axion emission, and asses the pulsational properties of this models. Our results indicate that the rates of change of pulsation periods are significantly affected by the existence of axions. We are able for the first time to independently constrain the mass of the axion from the study of pulsating helium-rich white dwarfs. To do this, we use an estimation of the rate of change of period of the pulsating white dwarf PG 1351+489 corresponding to the dominant pulsation period. From an asteroseismological model of PG 1351+489 we obtain $g_{ae}<3.3\times10^{-13}$ for the axion-electron coupling constant, or $m_a\cos^2{\beta}\lesssim$ 11.5 meV for the axion mass. This constraint is relaxed to $g_{ae}<5.5\times10^{-13}$ ($m_a\cos^2{\beta}\lesssim$ 19.5 meV), when no detailed asteroseismological model is adopted for the comparison with observations.

[17]  arXiv:1605.07677 [pdf, other]
Title: Analysis of intermittency in submillimeter radio and Hard X-Rays during the impulsive phase of a solar flare
Comments: Submitted to Solar Physics, the editor accepted for publication. 16 pages, 6 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present an analysis of intermittent processes occurred during the impulsive phase of the flare SOL2012-03-13, using hard X-rays and submillimeter radio data. Intermittency is a key characteristic in turbulent plasmas and have been a analyzed recently for Hard X-rays data only. Since in a typical flare the same accelerated electron population is believed to produce both Hard X-rays and gyrosynchrotron, we compare both time profiles searching for intermittency signatures. For that we define a cross-wavelet power spectrum, that is used to obtain the Local Intermittency Measure or LIM. When greater than 3, the square LIM coefficients indicate a local intermittent process. The LIM$^2$ coefficient distribution in time and scale helps to identify avalanche or cascade energy release processes. We find two different and well separated intermittent behaviors in the submillimeter data: for scales greater than 20 s, a broad distribution during the rising and maximum phases of the emission seems to favor a cascade process; for scales below 1 s, short pulses centered on the peak time, are representative of avalanches. When applying the same analysis to Hard X-rays, we find only the scales above 10 s producing a distribution related to a cascade energy fragmentation. Our results suggest that different acceleration mechanisms are responsible for tens of keV and MeV energy ranges of electrons.

[18]  arXiv:1605.07687 [pdf, other]
Title: A Protostellar Jet Emanating from a Hypercompact HII Region
Comments: Accepted in the Astrophysical Journal. 36 pages, 9 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 made using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact HII region. By comparing with images taken 6 yr earlier at 5 and 9 GHz using the same telescope, we assess the proper motions of the radio sources. The outer West and East lobes exhibit proper motions of $64\pm12$ and $48\pm13$ milliarcsec yr$^{-1}$, indicating velocities projected in the plane of the sky and receding from G345.4938+01.4677 of $520$ and $390$ km s$^{-1}$, respectively. The internal radio lobes also display proper motion signals consistently receding from the HMYSO, with magnitudes of $17\pm11$ and $35\pm10$ milliarcsec yr$^{-1}$ for the inner West and East lobes, respectively. The morphology of the outer West lobe is that of a detached bow shock. At 17 and 19 GHz, the outer East lobe displays an arcuate morphology also suggesting a bow shock. These results show that disk accretion and jet acceleration --- possibly occurring in a very similar way compared with low-mass protostars --- is taking place in G345.4938+01.4677 despite the presence of ionizing radiation and the associated hypercompact HII region.

[19]  arXiv:1605.07691 [pdf]
Title: The Use of Extraterrestrial Resources to Facilitate Space Science and Exploration
Comments: Accepted for publication in Astronomy and Geophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

To-date, all human economic activity has depended on the resources of a single planet, and it has long been recognized that developments in space exploration could in principle open our closed planetary economy to external resources of energy and raw materials. Recently, there has been renewed interest in these possibilities, with several private companies established with the stated aim of exploiting extraterrestrial resources. Space science and exploration are among the potential beneficiaries of space resources because their use may permit the construction and operation of scientific facilities in space that will be unaffordable if all the required material and energy resources have to be lifted out of Earth's gravity. Examples may include the next generation of large space telescopes, sample return missions to the outer Solar System, and human research stations on the Moon and Mars. These potential scientific benefits of extraterrestrial resource utilisation were the topic of a Royal Astronomical Society specialist discussion meeting held on 8 April 2016 and summarised here.

[20]  arXiv:1605.07718 [pdf, other]
Title: Atmospheric nitrogen evolution on Earth and Venus
Authors: R. D. Wordsworth
Comments: 12 pages, 5 figures, published in EPSL
Journal-ref: Earth and Planetary Science Letters, vol. 447, 2016, pp. 103-111
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Nitrogen is the most common element in Earth's atmosphere and also appears to be present in significant amounts in the mantle. However, its long-term cycling between these two reservoirs remains poorly understood. Here a range of biotic and abiotic mechanisms are evaluated that could have caused nitrogen exchange between Earth's surface and interior over time. In the Archean, biological nitrogen fixation was likely strongly limited by nutrient and/or electron acceptor constraints. Abiotic fixation of dinitrogen becomes efficient in strongly reducing atmospheres, but only once temperatures exceed around 1000 K. Hence if atmospheric N2 levels really were as low as they are today 3.0 - 3.5 Ga, the bulk of Earth's mantle nitrogen must have been emplaced in the Hadean, most likely at a time when the surface was molten. The elevated atmospheric N content on Venus compared to Earth can be explained abiotically by a water loss redox pump mechanism, where oxygen liberated from H2O photolysis and subsequent H loss to space oxidises the mantle, causing enhanced outgassing of nitrogen. This mechanism has implications for understanding the partitioning of other Venusian volatiles and atmospheric evolution on exoplanets.

[21]  arXiv:1605.07741 [pdf, other]
Title: Stellar rotation effects in polarimetric microlensing
Authors: Sedighe Sajadian
Comments: 12 pages, 13 figures, accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

It is well known that the polarization signal in microlensing events of hot stars is larger than that of main-sequence stars. Most hot stars rapidly rotate around their stellar axes. The stellar rotation makes ellipticity and gravity-darkening effects which break the spherical symmetry of the source shape and the circular symmetry of the source surface brightness respectively. Hence, it causes a net polarization signal for the source star. This polarization signal should be considered in polarimetry microlensing of fast rotating stars. For moderate rotating stars, lensing can magnify or even characterize small polarization signals due to the stellar rotation through polarimetry observations. The gravity-darkening effect due to a rotating source star makes asymmetric perturbations in polarimetry and photometry microlensing curves whose maximum happens when the lens trajectory crosses the projected position of the rotation pole on the sky plane. The stellar ellipticity makes a time shift (i) in the position of the second peak of the polarimetry curves in transit microlensing events and (ii) in the peak position of the polarimetry curves with respect to the photometry peak position in bypass microlensing events. By measuring this time shift via polarimetry observations of microlensing events, we can evaluate the ellipticity of the projected source surface on the sky plane. Given the characterizations of the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT) telescope, the probability of observing this time shift is so small. The more accurate polarimeters of the next generation may likely measure these time shifts and evaluate the ellipticity of microlensing source stars.

[22]  arXiv:1605.07742 [pdf]
Title: Carrying a Torch for Dust in Binary Star Systems
Comments: 12 pages, 5 figures, 1 table. Accepted for publication in 2016, in Proc. 15th Aust. Space Res. Conf. (ASRC15), Wayne S., Graziella C., eds, National Space Society of Australia (NSSA), Australia
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Young stars are frequently observed to host circumstellar disks, within which their attendant planetary systems are formed. Scattered light imaging of these proto-planetary disks reveals a rich variety of structures including spirals, gaps and clumps. Self-consistent modelling of both imaging and multi-wavelength photometry enables the best interpretation of the location and size distribution of disks' dust. Epsilon Sagittarii is an unusual star system. It is a binary system with a B9.5III primary that is also believed to host a debris disk in an unstable configuration. Recent polarimetric measurements of the system with the High Precision Polarimetric Instrument (HIPPI) revealed an unexpectedly high fractional linear polarisation, one greater than the fractional infrared excess of the system. Here we develop a spectral energy distribution model for the system and use this as a basis for radiative transfer modelling of its polarisation with the RADMC-3D software package. The measured polarisation can be reproduced for grain sizes around 2.0 microns.

[23]  arXiv:1605.07752 [pdf, other]
Title: Approximated methods for the generation of dark matter halo catalogs in the age of precision cosmology
Authors: Pierluigi Monaco
Comments: Submitted to Galaxies, special issue: "Dark Matter: Large versus Small Scale Structures", ed. J. Gaite & A. Diaferio. 37 pages. Comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Precision cosmology has recently triggered new attention on the topic of approximate methods for the clustering of matter on large scales, whose foundations date back to the period from late '60s to early '90s. Indeed, although the prospect of reaching sub-percent accuracy in the measurement of clustering poses a challenge even to full N-body simulations, an accurate estimation of the covariance matrix of clustering statistics requires usage of a large number (hundreds in the most favourable cases) of simulated (mock) galaxy catalogs. Combination of few N-body simulations with a large number of realizations performed with approximate methods, combined with the shrinkage technique or a similar tool, gives the most promising approach to solve this problem with a reasonable amount of resources. In this paper I review this topic, starting from the foundations of the methods, then going through the pioneering efforts of the '90s, and finally presenting the latest extensions and a few codes that are now being used in present-generation surveys and thoroughly tested to assess their performance in the context of future surveys.

[24]  arXiv:1605.07764 [pdf, ps, other]
Title: Vacuum ultraviolet photolysis of hydrogenated amorphous carbons. III. Diffusion of photo-produced H2 as a function of temperature
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Hydrogenated amorphous carbon (a-C:H) has been proposed as one of the carbonaceous solids detected in the interstellar medium. Energetic processing of the a-C:H particles leads to the dissociation of the C-H bonds and the formation of hydrogen molecules and small hydrocarbons. Photo-produced H2 molecules in the bulk of the dust particles can diffuse out to the gas phase and contribute to the total H2 abundance. We have simulated this process in the laboratory with plasma-produced a-C:H and a-C:D analogs under astrophysically relevant conditions to investigate the dependence of the diffusion as a function of temperature. Plasma-produced a-C:H analogs were UV-irradiated using a microwave-discharged hydrogen flow lamp. Molecules diffusing to the gas-phase were detected by a quadrupole mass spectrometer, providing a measurement of the outgoing H2 or D2 flux. By comparing the experimental measurements with the expected flux from a one-dimensional diffusion model, a diffusion coefficient D could be derived for experiments carried out at different temperatures. Dependance on the diffusion coefficient D with the temperature followed an Arrhenius-type equation. The activation energy for the diffusion process was estimated (ED(H2)=1660+-110 K, ED(D2)=2090+-90 K), as well as the pre-exponential factor (D0(H2)=0.0007+0.0013-0.0004 cm2 s-1, D0(D2)=0.0045+0.005-0.0023 cm2 s-1) The strong decrease of the diffusion coefficient at low dust particle temperatures exponentially increases the diffusion times in astrophysical environments. Therefore, transient dust heating by cosmic rays needs to be invoked for the release of the photo- produced H2 molecules in cold PDR regions, where destruction of the aliphatic component in hydrogenated amorphous carbons most probably takes place.

[25]  arXiv:1605.07780 [pdf, other]
Title: Determining protoplanetary disk gas masses from CO isotopologues line observations
Comments: 20 pages, 15 figures, A&A accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Despite intensive studies of protoplanetary disks, there is still no reliable way to determine their total mass and their surface density distribution, quantities that are crucial for describing both the structure and the evolution of disks up to the formation of planets. The goal of this work is to use less abundant CO isotopologues, whose detection is routine for ALMA, to infer the gas mass of disks. Isotope-selective effects need to be taken into account in the analysis, because they can significantly modify CO isotopologues line intensities. CO isotope-selective photodissociation has been implemented in the physical-chemical code DALI and 800 disk models have been run for a range of disk and stellar parameters. Dust and gas temperature structures have been computed self-consistently, together with a chemical calculation of the main species. Both disk structure and stellar parameters have been investigated. Total fluxes have been ray-traced for different CO isotopologues and for various transitions for different inclinations. A combination of 13CO and C18O total intensities allows inference of the total disk mass, although with non-negligible uncertainties. These can be overcome by employing spatially resolved observations, i.e. the disk's radial extent and inclination. Comparison with parametric models shows differences at the factor of a few level, especially for extremely low and high disk masses. Finally, total line intensities for different CO isotopologue and for various low-J transitions are provided and are fitted to simple formulae. The effects of a lower gas-phase carbon abundance and different gas/dust ratios are investigated as well, and comparison with other tracers is made. Disk masses can be determined within a factor of a few by comparing CO isotopologue lines observations with the simulated line fluxes, modulo the uncertainties in the volatile elemental abundances.

[26]  arXiv:1605.07781 [pdf, ps, other]
Title: The Oxygen Features in Type Ia Supernovae and the Implications for the Nature of Thermonuclear Explosions
Authors: Xulin Zhao (1,2), Keiichi Maeda (2), Xiaofeng Wang (1), Lifan Wang (3), Hanna Sai (1), Jujia Zhang (4), Tianmeng Zhang (5), Fang Huang (1), Liming Rui (1) ((1) Tsinghua University, (2) Kyoto University, (3) PMO and Texas A&M University, (4) Yunnan Astronomical Observatories of China, (5) National Astromomical Observatories of China)
Comments: 37 pages, 10 figures, accepted for publication in the Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The absorption feature O I 7773 is an important spectral indicator for type Ia supernovae (SNe~Ia) that can be used to trace the unburned material at outer layers of the exploding white dwarf. In this work, we use a large sample of SNe~Ia to examine this absorption at early phases (i.e., -13 days <t <-7 days), and make comparisons with the absorption features of Si~II 6355 and Ca~II near-infrared (NIR) triplet. We show that for a subgroup of spectroscopically normal SNe with normal photospheric velocities (i.e., v_si < 12,500 km s^{-1} at optical maximum), the line strength of high velocity feature (HVF) of O~I is inversely correlated with that of Si~II (or Ca~II), and this feature also shows a negative correlation with the luminosity of SNe Ia. This finding, together with other features we find for the O~I HVF, reveal that for this subgroup of SNe~Ia explosive oxygen burning occurs at the outermost layer of supernova and difference in burning there could lead to the observed diversity, which are in remarkable agreement with the popular delayed-detonation model of Chandrasekhar mass WD.

[27]  arXiv:1605.07782 [pdf, ps, other]
Title: Discs in misaligned binary systems
Comments: 15 pages, 16 figures, 1 table, accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We perform SPH simulations to study precession and changes in alignment between the circumprimary disc and the binary orbit in misaligned binary systems. We find that the precession process can be described by the rigid-disc approximation, where the disc is considered as a rigid body interacting with the binary companion only gravitationally. Precession also causes change in alignment between the rotational axis of the disc and the spin axis of the primary star. This type of alignment is of great important for explaining the origin of spin-orbit misaligned planetary systems. However, we find that the rigid-disc approximation fails to describe changes in alignment between the disc and the binary orbit. This is because the alignment process is a consequence of interactions that involve the fluidity of the disc, such as the tidal interaction and the encounter interaction. Furthermore, simulation results show that there are not only alignment processes, which bring the components towards alignment, but also anti-alignment processes, which tend to misalign the components. The alignment process dominates in systems with misalignment angle near 90 degrees, while the anti-alignment process dominates in systems with the misalignment angle near 0 or 180 degrees. This means that highly misaligned systems will become more aligned but slightly misaligned systems will become more misaligned.

[28]  arXiv:1605.07800 [pdf, ps, other]
Title: The chemical composition of Galactic ring nebulae around massive stars
Comments: 26 pages, 12 pages, 13 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C$^{++}$ and O$^{++}$ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O$^{++}$. The ADFs are larger than the typical ones of normal HII regions but similar to those found in the ionised gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 solar masses seem to reproduce the observed abundance ratios of most of the nebulae.

[29]  arXiv:1605.07825 [pdf, other]
Title: Chemical complexity in protoplanetary disks in the era of ALMA and Rosetta
Authors: Catherine Walsh
Comments: Conference proceedings from The 6th Zermatt ISM Symposium: Conditions and Impact of Star Formation
Journal-ref: EAS publications series, 75-76 (2015), 315-320
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Comets provide a unique insight into the molecular composition and complexity of the material in the primordial solar nebula. Recent results from the Rosetta mission, currently monitoring comet 67P/Churyumov-Gerasimenko in situ, and ALMA (the Atacama Large Millimeter/submillimeter Array), have demonstrated a tantalising link between the chemical complexity now confirmed in disks (via the detection of gas-phase CH3CN; Oberg et al. 2015) and that confirmed on the surface of 67P (Goesmann et al. 2015), raising questions concerning the chemical origin of such species (cloud or inheritance versus disk synthesis). Results from an astrochemical model of a protoplanetary disk are presented in which complex chemistry is included and in which it is assumed that simple ices only are inherited from the parent molecular cloud. The model results show good agreement with the abundances of several COMs observed on the surface of 67P with Philae/COSAC. Cosmic-ray and X-ray-induced photoprocessing of predominantly simple ices inherited by the protoplanetary disk is sufficient to generate a chemical complexity similar to that observed in comets. This indicates that the icy COMs detected on the surface of 67P may have a disk origin. The results also show that gas-phase CH3CN is abundant in the inner warm disk atmosphere where hot gas-phase chemistry dominates and potentially erases the ice chemical signature. Hence, CH3CN may not be an unambiguous tracer of the complex organic ice reservoir. However, a better understanding of the hot gas-phase chemistry of CH3CN is needed to confirm this preliminary conclusion.

[30]  arXiv:1605.07840 [pdf, ps, other]
Title: Mid-infrared vibrational study of deuterium-containing PAH variants
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long proposed to be a major carrier of 'Unidentified Infrared' (UIR) emission bands that have been observed ubiquitously in various astrophysical environments. These molecules can potentially be an efficient reservoir of deuterium. Once the infrared properties of the deuterium- containing PAHs are well understood both experimentally and theoretically, the interstellar UIR bands can be used as a valuable tool to infer the cause of the deuterium depletion in the ISM.
Density Functional Theory (DFT) calculations have been carried out on deuterium-containing ovalene variants to study the infrared properties of these molecules. These include deuterated ovalene, cationic deuterated ovalene, deuteronated ovalene and deuterated-deuteronated ovalene. We present a D/H ratio calculated from our theoretical study to compare with the observationally proposed D/H ratio.

[31]  arXiv:1605.07842 [pdf, ps, other]
Title: Slow blue nuclear hypervariables in PanSTARRS-1
Comments: Submitted to MNRAS, 44 pages, 27 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

We discuss 76 large amplitude transients (Delta-m>1.5) occurring in the nuclei of galaxies, nearly all with no previously known AGN. They have been discovered as part of the Pan-STARRS1 3pi survey, by comparison with SDSS photometry a decade earlier, and then monitored with the Liverpool Telescope. We also have optical spectroscopy for 51/76 of the objects. Based on colours, light curve shape, and spectra, these transients seem to fall into four groups. Some (~13%) turned out to be misclassified stars or objects of unknown type. Of the remainder, some (~21%$) are red/fast transients and are known or likely nuclear supernovae of various types. A few (~9%) are either radio sources or erratic variables and so likely blazars. However the majority (~66%) are blue and evolve slowly, on a timescale of years. Spectroscopy shows that these objects are AGN at z~ 0.3 - 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that most of these objects were in fact AGN a decade ago, but somewhat too weak to have been recognised as such by SDSS. These objects could then be classed as "hypervariable" AGN. In at least one case, the object has transitioned from a Type 1.9 to a Type 1 AGN. By searching the SDSS Stripe 82 quasar database, we find 15 comparison AGN which have changed over ~10 years by at least a factor 4, some of these seem to be blazars, but others are like the objects presented here, evolving smoothly over several years. We discuss several possible explanations for these slow blue hypervariables - (i) unusually luminous tidal disruption events, (ii) extinction events, (iii) changes in accretion state, and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon.

[32]  arXiv:1605.07846 [pdf, other]
Title: Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Aims. The formation and properties of star clusters at the edge of H II regions are poorly known, partly due to limitations in angular resolution and sensitivity, which become particularly critical when dealing with extragalactic clusters. In this paper we study the stellar content and star-formation processes in the young N159W region in the Large Magellanic Cloud.
Methods. We investigate the star-forming sites in N159W at unprecedented spatial resolution using JHKs-band images obtained with the GeMS/GSAOI instrument on the Gemini South telescope. The typical angular resolution of the images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent completeness). Photometry from our images is used to identify candidate young stellar objects (YSOs) in N159W. We also determine the H-band luminosity function of the star cluster at the centre of the H II region and use this to estimate its initial mass function (IMF).
Results. We estimate an age of 2 + or - 1 Myr for the central cluster, with its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 , and with a total estimated mass of 1300 solar mass. We also identify 104 candidate YSOs, which are concentrated in clumps and subclusters of stars, principally at the edges of the H II region. These clusters display signs of recent and active star-formation such as ultra-compact H II regions, and molecular outflows. This suggests that the YSOs are typically younger than the central cluster, pointing to sequential star-formation in N159W, which has probably been influenced by interactions with the expanding H II bubble.

[33]  arXiv:1605.07882 [pdf, ps, other]
Title: The injection of ten electron/$^{3}$He-rich SEP events
Comments: 8 pages, 4 figures, 1 table
Journal-ref: Astronomy & Astrophysics, Volume 585, A119, 2016
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (

We have derived the particle injections at the Sun for ten good electron/$^{3}$He-rich solar energetic particle (SEP) events, using a 1.2 AU particle path length (suggested by analysis of the velocity dispersion). The inferred solar injections of high-energy ($\sim$10 to 300 keV) electrons and of $\sim$MeV/nucleon ions (carbon and heavier) start with a delay of 17$\pm$3 minutes and 75$\pm$14 minutes, respectively, after the injection of low-energy ($\sim$0.4 to 9 keV) electrons. The injection duration (averaged over energy) ranges from $\sim$200 to 550 minutes for ions, from $\sim$90 to 160 minutes for low-energy electrons, and from $\sim$10 to 30 minutes for high-energy electrons. Most of the selected events have no reported H$\alpha$ flares or GOES SXR bursts, but all have type III radio bursts that typically start after the onset of a low-energy electron injection. All nine events with SOHO/LASCO coverage have a relatively fast ($>$570km/s), mostly narrow ($\lesssim$30$^{\circ}$), west-limb coronal mass ejection (CME) that launches near the start of the low-energy electron injection, and reaches an average altitude of $\sim$1.0 and 4.7 $R_{S}$, respectively, at the start of the high-energy electron injection and of the ion injection. The electron energy spectra show a continuous power law extending across the transition from low to high energies, suggesting that the low-energy electron injection may provide seed electrons for the delayed high-energy electron acceleration. The delayed ion injections and high ionization states may suggest an ion acceleration along the lower altitude flanks, rather than at the nose of the CMEs.

[34]  arXiv:1605.07883 [pdf, other]
Title: A dispersive wave pattern on Jupiter's fastest retrograde jet at $20^\circ$S
Comments: 19 pages, 11 figures, article accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

A compact wave pattern has been identified on Jupiter's fastest retrograding jet at 20S (the SEBs) on the southern edge of the South Equatorial Belt. The wave has been identified in both reflected sunlight from amateur observations between 2010 and 2015, thermal infrared imaging from the Very Large Telescope and near infrared imaging from the Infrared Telescope Facility. The wave pattern is present when the SEB is relatively quiescent and lacking large-scale disturbances, and is particularly notable when the belt has undergone a fade (whitening). It is generally not present when the SEB exhibits its usual large-scale convective activity ('rifts'). Tracking of the wave pattern and associated white ovals on its southern edge over several epochs have permitted a measure of the dispersion relationship, showing a strong correlation between the phase speed (-43.2 to -21.2 m/s) and the longitudinal wavelength, which varied from 4.4-10.0 deg. longitude over the course of the observations. Infrared imaging sensing low pressures in the upper troposphere suggest that the wave is confined to near the cloud tops. The wave is moving westward at a phase speed slower (i.e., less negative) than the peak retrograde wind speed (-62 m/s), and is therefore moving east with respect to the SEBs jet peak. Unlike the retrograde NEBn jet near 17N, which is a location of strong vertical wind shear that sometimes hosts Rossby wave activity, the SEBs jet remains retrograde throughout the upper troposphere, suggesting the SEBs pattern cannot be interpreted as a classical Rossby wave. Cassini-derived windspeeds and temperatures reveal that the vorticity gradient is dominated by the baroclinic term and becomes negative (changes sign) in a region near the cloud-top level (400-700 mbar) associated with the SEBs, suggesting a baroclinic origin for this meandering wave pattern. [Abr]

[35]  arXiv:1605.07900 [pdf, ps, other]
Title: The Red Supergiant Content of M31
Comments: Accepted for publication in the Astronomical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We investigate the red supergiant (RSG) population of M31, obtaining radial velocities of 255 stars. These data substantiate membership of our photometrically-selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B-V, V-R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar-metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25-30 Mo stars, while the vast majority evolved from stars with initial masses of 20 Mo or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is only partially reflected in the evolutionary tracks, although that might be due to the mis-match in metallicities between the solar Geneva models and the higher-than-solar metallicity of M31. As the luminosities increase the median spectral type also increases; i.e., the higher mass RSGs spend more time at cooler temperatures than do those of lower luminosities, a result which is new to this study. Finally we discuss what would be needed observationally to successfully build a luminosity function that could be used to constrain the mass-loss rates of RSGs as our Geneva colleagues have suggested.

[36]  arXiv:1605.07901 [pdf, ps, other]
Title: Towards an analytical theory of the third-body problem for highly elliptical orbits
Comments: Proceedings of the International Symposium on Orbit Propagation and Determination - Challenges for Orbit Determination and the Dynamics of Artificial Celestial Bodies and Space Debris, Lille, France, 2011
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Mathematical Physics (math-ph); Space Physics (

When dealing with satellites orbiting a central body on a highly elliptical orbit, it is necessary to consider the effect of gravitational perturbations due to external bodies. Indeed, these perturbations can become very important as soon as the altitude of the satellite becomes high, which is the case around the apocentre of this type of orbit. For several reasons, the traditional tools of celestial mechanics are not well adapted to the particular dynamic of highly elliptical orbits. On the one hand, analytical solutions are quite generally expanded into power series of the eccentricity and therefore limited to quasi-circular orbits [17, 25]. On the other hand, the time-dependency due to the motion of the third-body is often neglected. We propose several tools to overcome these limitations. Firstly, we have expanded the disturbing function into a finite polynomial using Fourier expansions of elliptic motion functions in multiple of the satellite's eccentric anomaly (instead of the mean anomaly) and involving Hansen-like coefficients. Next, we show how to perform a normalization of the expanded Hamiltonian by means of a time-dependent Lie transformation which aims to eliminate periodic terms. The difficulty lies in the fact that the generator of the transformation must be computed by solving a partial differential equation involving variables which are linear with time and the eccentric anomaly which is not time linear. We propose to solve this equation by means of an iterative process.

[37]  arXiv:1605.07917 [pdf, ps, other]
Title: A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau
Comments: 61 pages, 13 figures, accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in its radial velocity (RV) variations measured at infrared (IR) and optical wavelengths. We find that these observations are consistent with a massive planet in a ~9-day period orbit. These results are based on 71 IR RV measurements of this system obtained over 5 years, and on 26 optical RV measurements obtained over 9 years. CI Tau was also observed photometrically in the optical on 34 nights over ~one month in 2012. The optical RV data alone are inadequate to identify an orbital period, likely the result of star spot and activity induced noise for this relatively small dataset. The infrared RV measurements reveal significant periodicity at ~9 days. In addition, the full set of optical and IR RV measurements taken together phase coherently and with equal amplitudes to the ~9 day period. Periodic radial velocity signals can in principle be produced by cool spots, hot spots, and reflection of the stellar spectrum off the inner disk, in addition to resulting from a planetary companion. We have considered each of these and find the planet hypothesis most consistent with the data. The radial velocity amplitude yields an Msin(i) of ~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the circumstellar disk inclination from the literature, we find a planet mass of ~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.

[38]  arXiv:1605.07920 [pdf, ps, other]
Title: Effect of planet ingestion on low-mass stars evolution: the case of 2MASS J08095427--4721419 star in the Gamma Velorum cluster
Comments: Accepted for publication in MNRAS. 13 pages, 3 tables, 9 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We analysed the effects of planet ingestion on the characteristics of a pre-MS star similar to the Gamma Velorum cluster member 2MASS J08095427--4721419 (#52). We discussed the effects of changing the age $t_0$ at which the accretion episode occurs, the mass of the ingested planet and its chemical composition. We showed that the mass of the ingested planet required to explain the current [Fe/H]^#52 increases by decreasing the age $t_0$ and/or by decreasing the Iron content of the accreted matter.
We compared the predictions of a simplified accretion method -- where only the variation of the surface chemical composition is considered -- with that of a full accretion model that properly accounts for the modification of the stellar structure. We showed that the two approaches result in different convective envelope extension which can vary up to 10 percent. We discussed the impact of the planet ingestion on a stellar model in the colour-magnitude diagram, showing that a maximum shift of about 0.06 dex in the colour and 0.07 dex in magnitude are expected and that such variations persist even much later the accretion episode. We also analysed the systematic bias in the stellar mass and age inferred by using a grid of standard non accreting models to recover the characteristics of an accreting star. We found that standard non accreting models can safely be adopted for mass estimate, as the bias is <= 6 percent, while much more caution should be used for age estimate where the differences can reach about 60 percent.

[39]  arXiv:1605.07923 [pdf, ps, other]
Title: Non-thermal line-broadening in solar prominence
Journal-ref: 2015A&A...581..141S
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We show that the line broadening in quiescent solar prominences is mainly due to non-thermal velocities. We have simultaneously observed a wide range of optically thin lines in quiescent prominences, selected for bright and narrow Mg\,b emission without line satellites from macro-shifts. We find a ratio of reduced widths of H-gamma and H-delta of 1.05 +-0.03 which can hardly be attributed to saturation, since both are optically thin for the prominences observed: tau(gamma)<0.3 ; tau(delta)<0.15. We confirm the ratio of reduced widths of He4772(triplet) and He5015(singlet of 1.1 +-0.05 at higher significance and detect a width ratio of Mgb2 and Mg4571 (both from the triplet system) of 1.3 +-0.1. The discrepant widths of lines from different atoms, and even from the same atom, cannot be represented by a unique pair [T_kin ; V_nth]. Values of T_kin deduced from observed line radiance using models, indicate low temperatures down to T_kin~5000K. Non-thermal velocities, related to different physical states of the respective emitting prominence region, seem to be the most important line broadening mechanism.

[40]  arXiv:1605.07927 [pdf, other]
Title: Population Properties of Brown Dwarf Analogs to Exoplanets
Comments: Accepted for Publication in ApJs. 84 pages, 43 Figures, 19 Tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 8 parallaxes, 38 radial velocities, and 19 proper motions. We find 39 objects to be high-likelihood or bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. We find that gravity classification and photometric color separate 5-150 Myr sources from > 3 Gyr field objects, but they do not correlate one-to-one with the narrower 5 -150 Myr age range. The absolute magnitudes of low-gravity sources from J band through W3 show a flux redistribution when compared to equivalent field sources that is correlated with spectral subtype. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On CMDs, the latest-type low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M_J but are consistent with or brighter than the elbow at M_W1 and M_W2. Furthermore, there is an indication on CMD's (such as M_J versus (J-W2) of increasingly redder sequences separated by gravity classification. Examining bolometric luminosities for planets and low-gravity objects, we confirm that young M dwarfs are overluminous while young L dwarfs are normal compared to the field. This translates into warmer M dwarf temperatures compared to the field sequence while lower temperatures for L dwarfs.

[41]  arXiv:1605.07938 [pdf, other]
Title: Determining the midplane conditions of circumstellar discs using gas and dust modelling: a study of HD 163296
Comments: 17 pages, 11 figures, accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The mass of gas in protoplanetary discs is a quantity of great interest for assessing their planet formation potential. Disc gas masses are however traditionally inferred from measured dust masses by applying an assumed standard gas to dust ratio of $g/d=100$. Furthermore, measuring gas masses based on CO observations has been hindered by the effects of CO freeze-out. Here we present a novel approach to study the midplane gas by combining C$^{18}$O line modelling, CO snowline observations and the spectral energy distribution (SED) and selectively study the inner tens of au where freeze-out is not relevant. We apply the modelling technique to the disc around the Herbig Ae star HD 163296 with particular focus on the regions within the CO snowline radius, measured to be at 90 au in this disc. Our models yield the mass of C$^{18}$O in this inner disc region of $M_{\text{C}^{18}\text{O}}(<90\,\text{au})\sim 2\times10^{-8}$ M$_\odot$. We find that most of our models yield a notably low $g/d<20$, especially in the disc midplane ($g/d<1$). Our only models with a more ISM-like $g/d$ require C$^{18}$O to be underabundant with respect to the ISM abundances and a significant depletion of sub-micron grains, which is not supported by scattered light observations. Our technique can be applied to a range of discs and opens up a possibility of measuring gas and dust masses in discs within the CO snowline location without making assumptions about the gas to dust ratio.

[42]  arXiv:1605.07958 [pdf, other]
Title: Asteroseismic modelling of the two F-type hybrid pulsators KIC10080943A and KIC10080943B
Comments: 13 pages, 14 figures, 3 tables, accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Pulsating binary stars are ideal targets for testing the theory of stellar structure and evolution. Fundamental parameters can be derived from binary modelling to high precision and provide crucial constraints for seismic modelling. High-order gravity modes are sensitive to the conditions near the convective core and therefore allow for a determination of parameters describing interior physics, especially the convective-core overshooting parameter. KIC 10080943 is a binary system, which contains two gravity- and pressure-mode hybrid pulsators. A detailed observational study has provided fundamental and seismic parameters for both components. We aim to find a model, which is able to predict the observed g-mode period spacings and stellar parameters of both components of KIC 10080943. By calculating model grids with the stellar evolution code MESA and the seismic code GYRE, we can compare theoretical properties to the observed mean period spacing and position in the Hertzsprung-Russell diagram. The masses of our best models are somewhat below the values estimated from binarity, which is a consequence of the low observed mean g-mode period spacing. We find that the amount of core overshooting and of diffusive mixing can be well constrained by the equal-age requirement for the two stars. However, we find no significant difference for different shapes of the core overshooting. The measured rotation rates are within the limit of validity for the first-order perturbation approximation. We can find a good fit by using the traditional approximation for the pulsations, when taking slightly younger models with a higher asymptotic period spacing. This is because the zonal modes experience a slight shift due to the Coriolis force, which the first-order perturbation approximation ignores.

[43]  arXiv:1605.07973 [pdf, other]
Title: An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ436 b
Comments: 15 pages, 5 figures Accepted for publication in A&A (in press)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The warm Neptune GJ436b was observed with HST/STIS at three different epochs in the stellar Ly-alpha line, showing deep, repeated transits caused by a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas. Yet by itself it cannot explain the time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and stellar wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and stellar properties through the direct comparison of simulated and observed spectra. Our simulations match the last two epochs well. The observed sharp early ingresses come from the abrasion of the planetary coma by the stellar wind. Spectra observed during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the stellar wind). We find similar properties at both epochs for the planetary escape rate (2.5x10$^{8}$ g/s), the stellar photoionization rate (2x10$^{-5}$ /s), the stellar wind bulk velocity (85 km/s), and its kinetic dispersion velocity (10 km/s). We find high velocities for the escaping gas (50-60 km/s) that may indicate MHD waves that dissipate in the upper atmosphere and drive the planetary outflow. In the last epoch the high density of the stellar wind (3x10$^{3}$ /cm3) led to the formation of an exospheric tail mainly composed of neutralized protons. The observations of GJ436 b allow for the first time to clearly separate the contributions of radiation pressure and stellar wind and to probe the regions of the exosphere shaped by each mechanism.

[44]  arXiv:1605.07979 [pdf, ps, other]
Title: Radial motions in disk stars: ellipticity or secular flows?
Comments: 6 pages, accepted to be published in AJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Average stellar orbits of the Galactic disk may have some small intrinsic ellipticity which breaks the exact axisymmetry and there may also be some migration of stars inwards or outwards. Both phenomena can be detected through kinematic analyses. We use the red clump stars selected spectroscopically from APOGEE (APO Galactic Evolution Experiment), with known distances and radial velocities, to measure the radial component of the Galactocentric velocities within 5 kpc$<R<$16 kpc, $|b|<5^\circ$ and within 20 degrees from the Sun-Galactic center line. The average Galactocentric radial velocity is $V_R=(1.48\pm 0.35)[R({\rm kpc})-(8.8\pm 2.7)]$ km/s outwards in the explored range, with a higher contribution from stars below the Galactic plane. Two possible explanations can be given for this result: i) the mean orbit of the disk stars is intrinsically elliptical with a Galactocentric radial gradient of eccentricity around 0.01 kpc$^{-1}$; or ii) there is a net secular expansion of the disk, in which stars within $R\approx 9-11$ kpc are migrating to the region $R\gtrsim 11$ kpc at the rate of $\sim 2$ M$_\odot $/yr, and stars with $R\lesssim 9$ kpc are falling toward the center of the Galaxy. This migration ratio would be unattainable for a long time and it should decelerate, otherwise the Galaxy would fade away in around 1 Gyr. At present, both hypotheses are speculative and one would need data on the Galactocentric radial velocities for other azimuths different to the center or anticenter in order to confirm one of the scenarios.

[45]  arXiv:1605.07987 [pdf, other]
Title: Reconstructing the high energy irradiation of the evaporating hot Jupiter HD 209458b
Comments: Submitted to MNRAS. 8 pages, 3 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The atmosphere of the exoplanet HD 209458b is undergoing sustained mass loss, believed to be caused by X-ray and extreme-ultraviolet (XUV) irradiation from its star. The majority of this flux is not directly observable due to interstellar absorption, but is required in order to correctly model the photo-evaporation of the planet and photo-ionisation of the outflow. We present a recovered high energy spectrum for HD\,209458 using a Differential Emission Measure (DEM) retrieval technique. We construct a model of the stellar corona and transition region for temperatures between 10$^{4.1}$ and 10$^{8}$ K which is constrained jointly by ultraviolet line strengths measured with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) and X-ray flux measurements from XMM-Newton. The total hydrogen ionising luminosity ($\lambda < 912$ \AA) is found to be 10$^{28.26}$ erg s$^{-1}$, which is similar to the value for the mean activity level of the Sun. This luminosity is incompatible with energy limited mass loss rates estimated from the same COS dataset, even the lower bound requires an uncomfortably high energetic efficiency of >40%. However, our luminosity is compatible with early estimates of the mass loss rate of HD 209458b based on results from the HST Space Telescope Imaging Spectrograph (STIS). Precisely reconstructed XUV irradiation is a key input to determining mass loss rates and efficiencies for exoplanet atmospheres.

[46]  arXiv:1605.08022 [pdf, ps, other]
Title: Radiative transfer simulations of magnetar flare beaming
Comments: 17 pages, 8 figures, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Magnetar giant flares show oscillatory modulations in the tails of their light curves, which can only be explained via some form of beaming. The fireball model for magnetar bursts has been used successfully to fit the phase-averaged light curves of the tails of giant flares, but so far no attempts have been made to fit the pulsations. We present a relatively simple numerical model to simulate beaming of magnetar flare emission. In our simulations, radiation escapes from the base of a fireball trapped in a dipolar magnetic field, and is scattered through the optically thick magnetosphere of the magnetar until it escapes. Beaming is provided by the presence of a relativistic outflow, as well as by the geometry of the system. We find that a simple picture for the relativistic outflow is enough to create the pulse fraction and sharp peaks observed in pulse profiles of magnetar flares, while without a relativistic outflow the beaming is insufficient to explain giant flare rotational modulations.

[47]  arXiv:1605.08026 [pdf, other]
Title: Star formation activity in a young galaxy cluster at z=0.866
Comments: Accepted for publication in ApJ. 12 pages, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The galaxy cluster RXJ1257$+$4738 at $z=0.866$ is one of the highest redshift clusters with a richness of multi-wavelength data, and thus a good target to study the star formation-density relation at early epochs. Using a sample of spectroscopically-confirmed cluster members, we derive the star formation rates of our galaxies using two methods, (I) the relation between SFR and total infrared luminosity extrapolated from the observed \textit{Spitzer} MIPS 24$\mu$m imaging data, and (II) spectral energy distribution (SED) fitting using the MAGPHYS code, including eight different bands.
We show that, for this cluster, the SFR-density relation is very weak and seems to be dominated by the two central galaxies and the SFR presents a mild dependence on stellar mass, with more massive galaxies having higher SFR. However, the specific SFR (SSFR) decreases with stellar mass, meaning that more massive galaxies are forming less stars per unit of mass, and thus suggesting that the increase in star-forming members is driven by cluster assembly and infall.
If the environment is somehow driving the SF, one would expect a relation between the SSFR and the cluster centric distance, but that is not the case. A possible scenario to explain this lack of correlation is the contamination by infalling galaxies in the inner part of the cluster which may be on their initial pass through the cluster center. As these galaxies have higher SFRs for their stellar mass, they enhance the mean SSFR in the center of the cluster.

[48]  arXiv:1605.08030 [pdf, other]
Title: Doppler shifts on the spin period of the intermediate polar FO Aqr with K2
Authors: S. Scaringi (1), C. Knigge (2), T.J. Maccarone (3) ((1) MPE, (2) Soton, (3) TTU)
Comments: 10 pages, 10 figures, 2 tables. Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We analyse the K2 short cadence data of the intermediate polar FO Aqr and provide accurate and updated orbital and spin periodicities. We additionally find small spin period changes as a function of orbital phase of ~0.02 seconds translating to velocities of ~ a few km/s. The obtained orbital-folded velocity profile displays two clear maxima and minima, and cannot be explained by the radial velocity of the orbiting white dwarf. Instead we propose that the observed velocities are the sum of the radial velocities of both the white dwarf and of the stellar surface facing the white dwarf which reprocesses the WD spin pulses. This combination can explain the observed low velocities in FO Aqr. However asymmetries in the orbital configuration are required to explain the double peaked velocity profile. One possible scenario would invoke binary eccentricity. We thus developed a simple binary model to explain and fit our observations, and find a small binary eccentricity of e=0.03. Although small, persistent eccentricity in a close interacting binary would induce enhanced mass transfer occurring preferentially at periastron passages. We thus discuss alternative scenarios where other asymmetries might explain our observations assuming circular orbits. Since FO Aqr is the first system where the combined radial velocities of both the WD and secondary surface have been measured, it is possible that other mass-transferring binaries also display similar velocity curves when observed with Kepler. These will provide additional valuable tests to either confirm or rule out small eccentricities in similar systems.