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[1]  arXiv:1407.5992 [pdf, ps, other]
Title: Transparent Helium in Stripped Envelope Supernovae
Comments: Submitted for publication in The Astrophysical Journal Letters, 4 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

The light curves and velocity evolution of core-collapse supernovae (SNe) provide important clues to help constrain their progenitors. This may be especially important for stripped envelope SNe (Type Ib, Ic, and IIb), which have been elusive in providing direct connections with the massive stars that give rise to these explosions. Using simple arguments based on photometric light curves, we propose that many of these stripped envelope SNe show evidence that a significant fraction their helium is effectively transparent during the majority of their light curve evolution. This means that the helium should not contribute to the shaping of the main SN light curve and thus the total helium mass may be difficult to constrain from simple light curve modeling. Conversely, such modeling may be more useful for constraining the mass of the carbon/oxygen core of the SN progenitor. We discuss ways in which similar analysis can provide insights into the differences and similarities between SNe Ib and Ic, which will help lead to a better understanding of their respective formation mechanisms.

[2]  arXiv:1407.5993 [pdf]
Title: Stellar intensity interferometry over kilometer baselines: Laboratory simulation of observations with the Cherenkov Telescope Array
Comments: 18 pages, 11 figures; Presented at SPIE conference on Astronomical Telescopes + Instrumentation in Montreal, Quebec, Canada, June 2014. To appear in SPIE Proc.9146, Optical and Infrared Interferometry IV (J.K.Rajagopal, M.J.Creech-Eakman, F.Malbet, eds.), 2014
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

A long-held astronomical vision is to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, show their evolution over time, and reveal interactions of stellar winds and gas flows in binary star systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and used also for intensity interferometry. With no optical connection between the telescopes, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are on the order of one meter, making the method practically insensitive to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths. Theoretical modeling has shown how stellar surface images can be retrieved from such observations and here we report on experimental simulations. In an optical laboratory, artificial stars (single and double, round and elliptic) are observed by an array of telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations are cross correlated between up to a hundred baselines between pairs of telescopes, producing maps of the second-order spatial coherence across the interferometric Fourier-transform plane. These experiments serve to verify the concepts and to optimize the instrumentation and observing procedures for future observations with (in particular) CTA, the Cherenkov Telescope Array, aiming at order-of-magnitude improvements of the angular resolution in optical astronomy.

[3]  arXiv:1407.5994 [pdf, ps, other]
Title: Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel-ATLAS
Comments: 10 pages, 6 figures. Resubmitted to MNRAS after addressing referee's comments
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report an unexpected variation in the positional offset distributions between Herschel-ATLAS sub-millimetre (submm) sources and their optical associations, depending on both 250-{\mu}m signal-to-noise ratio and 250/350-{\mu}m colour. We show that redder and brighter submm sources have optical associations with a broader distribution of positional offsets than would be expected if these offsets were due to random positional errors in the source extraction. The observation can be explained by two possible effects: either red submm sources trace a more clustered population than blue ones, and their positional errors are increased by confusion; or red submm sources are generally at high redshifts and are frequently associated with low-redshift lensing structures which are identified as false counterparts. We perform various analyses of the data, including the multiplicity of optical associations, the redshift and magnitude distributions in H-ATLAS in comparison to HerMES, and simulations of weak lensing, and we conclude that the effects are most likely to be explained by widespread weak lensing of Herschel-SPIRE sources by foreground structures. This has important consequences for counterpart identification and derived redshift distributions and luminosity functions of submm surveys.

[4]  arXiv:1407.5995 [pdf, ps, other]
Title: On the Feeding Zone of Planetesimal Formation by the Streaming Instability
Comments: AASTeX preprint, 21 pages, including 7 figures. Accepted by ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The streaming instability is a promising mechanism to overcome the barriers in direct dust growth and lead to the formation of planetesimals. Most previous studies of the streaming instability, however, were focused on a local region of a protoplanetary disk with a limited simulation domain such that only one filamentary concentration of solids has been observed. The characteristic separation between filaments is therefore not known. To address this, we conduct the largest-scale simulations of the streaming instability to date, with computational domains up to 1.6 gas scale heights both horizontally and vertically. The large dynamical range allows the effect of vertical gas stratification to become prominent. We observe more frequent merging and splitting of filaments in simulation boxes of high vertical extent. We find multiple filamentary concentrations of solids with an average separation of about 0.2 local gas scale heights, much higher than the most unstable wavelength from linear stability analysis. This measures the characteristic separation of planetesimal forming events driven by the streaming instability and thus the initial feeding zone of planetesimals.

[5]  arXiv:1407.5996 [pdf, ps, other]
Title: Clumping factors of HII, HeII and HeIII
Authors: Akila Jeeson-Daniel (1,2,3), Benedetta Ciardi (2), Luca Graziani (2) ((1) Melbourne, (2) MPA, (3) CAASTRO)
Comments: 12 pages, 10 figures, 1 table. Accepted by MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

Estimating the intergalactic medium ionization level of a region needs proper treatment of the reionization process for a large representative volume of the universe. The clumping factor, a parameter which accounts for the effect of recombinations in unresolved, small-scale structures, aids in achieving the required accuracy for the reionization history even in simulations with low spatial resolution.
In this paper, we study for the first time the redshift evolution of clumping factors of different ionized species of H and He in a small but very high resolution simulation of the reionization process. We investigate the dependence of the value and redshift evolution of clumping factors on their definition, the ionization level of the gas, the grid resolution, box size and mean dimensionless density of the simulations.

[6]  arXiv:1407.5998 [pdf, ps, other]
Title: Monitoring the Variability of Intrinsic Absorption Lines in Quasar Spectra
Comments: 33 pages, including 30 figures; accepted for publication in the Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We have monitored 12 intrinsic narrow absorption lines (NALs) in five quasars and seven mini-broad absorption lines (mini-BALs) in six quasars for a period of 4-12 years (1-3.5 years in the quasar rest-frame). We present the observational data and the conclusions that follow immediately from them, as a prelude to a more detailed analysis. We found clear variability in the equivalent widths (EWs) of the mini-BAL systems but no easily discernible changes in their profiles. We did not detect any variability in the NAL systems nor in narrow components that are often located at the center of mini-BAL profiles. Variations in mini-BAL EWs are larger at longer time intervals, reminiscent of the trend seen in variable broad absorption lines. If we assume that the observed variations result from changes in the ionization state of the mini-BAL gas, we infer lower limits to the gas density $\sim$ 10$^3$-10$^5$ cm$^{-3}$ and upper limits on the distance of the absorbers from the central engine of order a few kpc. Motivated by the observed variability properties, we suggest that mini-BALs can vary because of fluctuations of the ionizing continuum or changes in partial coverage while NALs can vary primarily because of changes in partial coverage.

[7]  arXiv:1407.6001 [pdf, other]
Title: Optical Confirmation and Redshift Estimation of the Planck Cluster Candidates overlapping the Pan-STARRS Survey
Comments: 10 pages, 9 figures, submitted to MNRAS, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We report results of a study of Planck Sunyaev-Zel'dovich effect (SZE) selected galaxy cluster candidates using the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) imaging data. We first examine 150 Planck confirmed galaxy clusters with spectroscopic redshifts to test our algorithm for identifying optical counterparts and measuring their redshifts; our redshifts have a typical accuracy of $\sigma_{z/(1+z)} \sim 0.022$ for this sample. We then examine an additional 237 Planck galaxy cluster candidates that have no redshift in the source catalogue. Of these 237 unconfirmed cluster candidates we are able to confirm 60 galaxy clusters and measure their redshifts. A further 83 candidates are so heavily contaminated by stars due to their location near the Galactic plane that we do not attempt to identify counterparts. For the remaining 94 candidates we find no optical counterpart but use the depth of the Pan-STARRS1 data to estimate a redshift lower limit $z_{\text{lim}(10^{15})}$ beyond which we would not have expected to detect enough galaxies for confirmation. Scaling from the already published Planck sample, we expect that $\sim$12 of these unconfirmed candidates may be real clusters.

[8]  arXiv:1407.6003 [pdf, other]
Title: Distributed Low-Mass Star Formation in the IRDC G34.43+00.24
Comments: 15 pages, 16 figures. Accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically-verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in K-band which comes from excited H2 in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow linewidth SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.

[9]  arXiv:1407.6004 [pdf, ps, other]
Title: A New Method to Calibrate the Stellar Color/Surface-Brightness Relation
Authors: Andrew Gould
Comments: Submitted to Journal of The Korean Astronomical Society; 6 pages, 1 figure
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

I show that the standard microlensing technique to measure the angular radius of a star using color/surface-brightness relations can be inverted, via late-time proper motion measurements, to calibrate these relations. The method is especially useful for very metal-rich stars because such stars are in short supply in the solar neighborhood where other methods are most effective, but very abundant in Galactic bulge microlensing fields. I provide a list of eight spectroscopically identified high-metallicity bulge stars with the requisite finite-source effects, seven of which will be suitable calibrators when the Giant Magellan Telescope comes on line. Many more such sources can be extracted from current and future microlensing surveys.

[10]  arXiv:1407.6005 [pdf, other]
Title: Being WISE I: Validating Stellar Population Models and M/L ratios at 3.4 and 4.6 microns
Comments: 11 pages, 6 figures, submitted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Using data from the WISE mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 micron (W2) photometry of stellar populations have been examined.
We find that the W1 - W2 colors of intermediate and old (> 2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 - W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 micron bandpass with metallicity.
Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

[11]  arXiv:1407.6006 [pdf, other]
Title: The Mass Dependence of Dwarf Satellite Galaxy Quenching
Comments: 8 pages, 3 figures. Accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic clouds. While almost all of the low mass ($M_\star \lesssim 10^7$ $M_\odot$) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40-50%. This change in the quenched fraction is large, and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell in to their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

[12]  arXiv:1407.6009 [pdf, other]
Title: Proper Motions of Young Stellar Outflows in the Mid-Infrared with Spitzer. II. HH 377/Cep E
Authors: A. Noriega-Crespo, (1,3), A. C. Raga, (2), A. Moro-Martin, (3), N. Flagey, (4,6) S. J. Carey, (5) ((1) IPAC, (2) ICN-UNAM, (3) STSCI, (4) JPL, (5) SSC, (6) IfA)
Comments: Accepted for publication in New Journal of Physics (Special Issue article)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

We have used multiple mid-infrared observations at 4.5 micron obtained with the Infrared Array Camera, of the compact (~1.4 arcmin) young stellar bipolar outflow Cep E to measure the proper motion of its brightest condensations. The images span a period of ~6 yr and have been reprocessed to achieve a higher angular resolution (~0.8 arcsec) than their normal beam (2 arcsec).
We found that for a distance of 730 pc, the tangential velocities of the North and South outflow lobes are 62+/-29 and 94+/-6 km/s respectively, and moving away from the central source roughly along the major axis of the flow. A simple 3D hydrodynamical simulation of the H2 gas in a precessing outflow supports this idea. Observations and model confirm that the molecular Hydrogen gas, traced by the pure rotational transitions, moves at highly supersonic velocities without being dissociated. This suggests either a very efficient mechanism to reform H2 molecules along these shocks or the presence of some other mechanism (e.g. strong magnetic field) that shields the H2 gas.

[13]  arXiv:1407.6011 [pdf, other]
Title: Hot super-Earths and giant planet cores from different migration histories
Comments: 16 pages, 16 figures. Accepted in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Planetary embryos embedded in gaseous protoplanetary disks undergo Type I orbital migration. Migration can be inward or outward depending on the local disk properties but, in general, only planets more massive than several $M_\oplus$ can migrate outward. Here we propose that an embryo's migration history determines whether it becomes a hot super-Earth or the core of a giant planet. Systems of hot super-Earths (or mini-Neptunes) form when embryos migrate inward and pile up at the inner edge of the disk. Giant planet cores form when inward-migrating embryos become massive enough to switch direction and migrate outward. We present simulations of this process using a modified N-body code, starting from a swarm of planetary embryos. Systems of hot super-Earths form in resonant chains with the innermost planet at or interior to the disk inner edge. Resonant chains are disrupted by late dynamical instabilities triggered by the dispersal of the gaseous disk. Giant planet cores migrate outward toward zero-torque zones, which move inward and eventually disappear as the disk disperses. Giant planet cores migrate inward with these zones and are stranded at ~1-5 AU. Our model reproduces several properties of the observed extra-solar planet populations. The frequency of giant planet cores increases strongly when the mass in solids is increased, consistent with the observed giant exoplanet - stellar metallicity correlation. The frequency of hot super-Earths is not a function of stellar metallicity, also in agreement with observations. Our simulations can reproduce the broad characteristics of the observed super-Earth population.

[14]  arXiv:1407.6012 [pdf, ps, other]
Title: The Star-Formation Rate and Stellar Mass Relation of Galaxies at 3.5 $\le z\le$ 6.5 in CANDELS
Comments: 28 pages, 22 figures, resubmitted to ApJ after responding to referee report
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Distant star-forming galaxies show a correlation between their star-formation rates (SFR) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR$-$stellar mass relation for galaxies at $3.5\leq z\leq 6.5$ using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star-formation histories that are constant or rising with time, and different dust attenuation prescriptions (starburst and Small Magellanic Cloud). From $z$=6.5 to $z$=3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR $\sim$ $M_\star^\alpha$ with $\alpha = 0.54 \pm 0.16$ at $z\sim 6$ and $0.70 \pm 0.21$ at $z\sim 4$. This evolution requires a star-formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The measured scatter in the SFR$-$stellar mass relation is tight, $\sigma(\log \mathrm{SFR}/\mathrm{M}_\odot$ yr$^{-1})< 0.3 -$0.4 dex, for galaxies with $\log M_\star/\mathrm{M}_\odot > 9$ dex. Assuming that the SFR is tied to the net gas inflow rate (SFR $\sim$ $\dot{M}_\mathrm{gas}$), then the scatter in the gas inflow rate is also smaller than 0.3$-$0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star-formation. We further show that the implied star-formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR$-$stellar mass relation.

[15]  arXiv:1407.6016 [pdf, other]
Title: LRS2: the new facility low resolution integral field spectrograph for the Hobby-Eberly Telescope
Comments: 26 pages, 14 figures, 3 tables. To be published in Proc. SPIE, 2014, "Ground-Based and Airborne Instrumentation for Astronomy V", 9147-9. arXiv admin note: text overlap with arXiv:1207.6118
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The second generation Low Resolution Spectrograph (LRS2) is a new facility instrument for the Hobby-Eberly Telescope (HET). Based on the design of the Visible Integral-field Replicable Unit Spectrograph (VIRUS), which is the new flagship instrument for carrying out the HET Dark Energy Experiment (HETDEX), LRS2 provides integral field spectroscopy for a seeing-limited field of 12 x 6 arcseconds. For LRS2, the replicable design of VIRUS has been leveraged to gain broad wavelength coverage from 370 nm to 1 micron, spread between two fiber-fed dual-channel spectrographs, each of which can operate as an independent instrument. The blue spectrograph, LRS2-B, covers 370-470 nm and 460-700 nm at fixed resolving powers of ~1900 and ~1100, respectively, while the red spectrograph, LRS2-R, covers 650-842 nm and 818-1050 nm with both of its channels having a resolving power of ~1800. In this paper, we present a detailed description of the instrument's design in which we focus on the departures from the basic VIRUS framework. The primary modifications include the fore-optics that are used to feed the fiber integral field units at unity fill-factor, the cameras' correcting optics and detectors, and the volume phase holographic grisms. We also present a model of the instrument's sensitivity and a description of specific science cases that have driven the design of LRS2, including systematically studying the spatially resolved properties of extended Lyman-alpha blobs at 2 < z < 3. LRS2 will provide a powerful spectroscopic follow-up platform for large surveys such as HETDEX.

[16]  arXiv:1407.6041 [pdf, ps, other]
Title: On the Nature of the Extreme-Ultraviolet Late Phase of Solar Flares
Comments: Accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The extreme-ultraviolet (EUV) late phase of solar flares is a second peak of warm coronal emissions (e.g., Fe XVI) for many minutes to a few hours after the GOES soft X-ray peak. It was first observed by the EUV Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO). The late phase emission originates from a second set of longer loops (late phase loops) that are higher than the main flaring loops. It is suggested as being caused by either additional heating or long-lasting cooling. In this paper, we study the role of long-lasting cooling and additional heating in producing the EUV late phase using the "enthalpy-based thermal evolution of loops" (EBTEL) model. We find that a long cooling process in late phase loops can well explain the presence of the EUV late phase emission, but we cannot exclude the possibility of additional heating in the decay phase. Moreover, we provide two preliminary methods based on the UV and EUV emissions from the Atmospheric Imaging Assembly (AIA) on board SDO to determine whether an additional heating plays some role or not in the late phase emission. Using nonlinear force-free field modeling, we study the magnetic configuration of the EUV late phase. It is found that the late phase can be generated either in hot spine field lines associated with a magnetic null point or in large-scale magnetic loops of multipolar magnetic fields. In this paper, we also discuss why the EUV late phase is usually observed in warm coronal emissions and why the majority of flares do not exhibit an EUV late phase.

[17]  arXiv:1407.6042 [pdf, other]
Title: Methanol Maser Associated Outflows: Detection statistics and properties
Authors: H. M. de Villiers (1), A. Chrysostomou (1), M. A. Thompson (1), S. P. Ellingsen (2), J. S. Urquhart (3), S. L. Breen (4), M. G. Burton (5), T. Csengeri (3), D. Ward-Thompson (6) ((1) Centre for Astrophysics Research, University of Hertfordshire, Hatfield, United Kingdom, (2) School of Physical Science, University of Tasmania, Hobart, TAS, Australia, (3) Max-Planck-Institut für Radioastronomie, Bonn, Germany, (4) CSIRO Astronomy and Space Science, Australia Telescope National Facility, Epping, Australia, (5) School of Physics, University of New South Wales, Sydney, Australia, (6) Jeremiah Horrocks Institute, University of Central Lancashire, Preston, United Kingdom)
Comments: Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We have selected the positions of 54 6.7GHz methanol masers from the Methanol Multibeam Survey catalogue, covering a range of longitudes between $20^{\circ}$ and $34^{\circ}$ of the Galactic Plane. These positions were mapped in the J=3-2 transition of both the $\rm{^{13}CO}$ and $\rm{C^{18}O}$ lines. A total of 58 $\rm{^{13}CO}$ emission peaks are found in the vicinity of these maser positions. We search for outflows around all $\rm{^{13}CO}$ peaks, and find evidence for high-velocity gas in all cases, spatially resolving the red and blue outflow lobes in 55 cases. Of these sources, 44 have resolved kinematic distances, and are closely associated with the 6.7GHz masers, a sub-set referred to as Methanol Maser Associated Outflows (MMAOs). We calculate the masses of the clumps associated with each peak using 870 $\rm{\mu m}$ continuum emission from the ATLASGAL survey. A strong correlation is seen between the clump mass and both outflow mass and mechanical force, lending support to models in which accretion is strongly linked to outflow. We find that the scaling law between outflow activity and clump masses observed for low-mass objects, is also followed by the MMAOs in this study, indicating a commonality in the formation processes of low-mass and high-mass stars.

[18]  arXiv:1407.6044 [pdf, other]
Title: Astrophysical Tests of Modified Gravity: Stellar and Gaseous Rotation Curves in Dwarf Galaxies
Comments: 8 pages, 2 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Chameleon theories of gravity predict that the gaseous component of isolated dwarf galaxies rotates with a faster velocity than the stellar component. In this paper, we exploit this effect to obtain new constraints on the model parameters using the measured rotation curves of six low surface brightness galaxies. For $f(R)$ theories, we rule out values of $f_{R0}>10^{-6}$. For more general theories, we find that the constraints from Cepheid variable stars are currently more competitive than the bounds we obtain here but we are able to rule out self-screening parameters $\chi_c>10^{-6}$ for fifth-force strengths (coupling of the scalar to matter) as low as $0.05$ the Newtonian force. This region of parameter space has hitherto been inaccessible to astrophysical probes. We discuss the future prospects for improving these bounds.

[19]  arXiv:1407.6045 [pdf, ps, other]
Title: Imaging survey of subsystems in secondary components to nearby southern dwarfs
Authors: Andrei Tokovinin
Comments: Accepted by the Astronomical Journal; 7 pages, 7 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

To improve the statistics of hierarchical multiplicity, secondary components of wide nearby binaries with solar-type primaries were surveyed at the SOAR telescope for evaluating the frequency of subsystems. Images of 17 faint secondaries were obtained with the SOAR Adaptive Module that improved the seeing; one new 0.2" binary was detected. For all targets, photometry in the g', i', z' bands is given. Another 46 secondaries were observed by speckle interferometry, resolving 7 close subsystems. Adding literature data, the binarity of 95 secondary components is evaluated. We found that the detection-corrected frequency of secondary subsystems with periods in the well-surveyed range from 10^3 to 10^5 days is 0.21+-0.06, same as the normal frequency of such binaries among solar-type stars, 0.18. This indicates that wide binaries are not produced by dynamical ejection from compact N-body systems during their early evolution, but are rather formed by fragmentation.

[20]  arXiv:1407.6054 [pdf, ps, other]
Title: H2O abundances in the atmospheres of three hot Jupiters
Authors: Nikku Madhusudhan (IoA, Cambridge), Nicolas Crouzet (Dunlap Institute), Peter R. McCullough (STScI), Drake Deming (U. Maryland), Christina Hedges (IoA, Cambridge)
Comments: ApJ Letters, in press
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The core accretion theory for giant planet formation predicts enrichment of elemental abundances in planetary envelopes caused by runaway accretion of planetesimals, which is consistent with measured super-solar abundances of C, N, P, S, Xe, and Ar in Jupiter's atmosphere. However, the abundance of O which is expected to be the most dominant constituent of planetesimals is unknown for solar system giant planets, owing to the condensation of water in their ultra-cold atmospheres, thereby posing a key unknown in solar system formation. On the other hand, hundreds of extrasolar hot Jupiters are known with very high temperatures (>~1000 K) making them excellent targets to measure H2O abundances and, hence, oxygen in their atmospheres. We constrain the atmospheric H2O abundances in three hot Jupiters (HD 189733b, HD 209458b, and WASP-12b), spanning a wide temperature range (1200-2500 K), using their near-infrared transmission spectra obtained using the HST WFC3 instrument. We report conclusive measurements of H2O in HD 189733b and HD 209458b, while that in WASP-12b is not well constrained by present data. The data allow nearly solar as well as significantly sub-solar abundances in HD 189733b and WASP-12b. However, for HD 209458b, we report the most precise H2O measurement in an exoplanet to date that suggests a ~20-135 sub-solar H2O abundance. We discuss the implications of our results on the formation conditions of hot Jupiters and on the likelihood of clouds in their atmospheres. Our results highlight the critical importance of high-precision spectra of hot Jupiters for deriving their H2O abundances.

[21]  arXiv:1407.6068 [pdf, other]
Title: The SAMI Galaxy Survey: Early Data Release
Comments: 16 pages, 20 figures. Galaxy datacubes and related data available from this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of ~3400 low-redshift (z<0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters.
In the Early Data Release, we publicly release the fully calibrated datacubes for a representative selection of 107 galaxies drawn from the GAMA regions, along with information about these galaxies from the GAMA catalogues. All datacubes for the Early Data Release galaxies can be downloaded individually or as a set from the SAMI Galaxy Survey website.
In this paper we also assess the quality of the pipeline used to reduce the SAMI data, giving metrics that quantify its performance at all stages in processing the raw data into calibrated datacubes. The pipeline gives excellent results throughout, with typical sky subtraction residuals of 0.9-1.2 per cent, a relative flux calibration uncertainty of 4.1 per cent (systematic) plus 4.3 per cent (statistical), and atmospheric dispersion removed with an accuracy of 0."09, less than a fifth of a spaxel.

[22]  arXiv:1407.6069 [pdf, other]
Title: Rapid Change of Field Line Connectivity and Reconnection in Stochastic Magnetic Fields
Comments: Accepted for publication in Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph); Space Physics (physics.space-ph)

Magnetic fields without a direction of continuous symmetry have the generic feature that neighboring field lines exponentiate away from each other and become stochastic, hence the ideal constraint of preserving magnetic field line connectivity becomes exponentially sensitive to small deviations from ideal Ohm's law. The idea of breaking field line connectivity by stochasticity as a mechanism for fast reconnection is tested with numerical simulations based on reduced magnetohydrodynamics equations with a strong guide field line-tied to two perfectly conducting end plates. Starting from an ideally stable force-free equilibrium, the system is allowed to undergo resistive relaxation. Two distinct phases are found in the process of resistive relaxation. During the quasi-static phase, rapid change of field line connectivity and strong induced flow are found in regions of high field line exponentiation. However, although the field line connectivity of individual field lines can change rapidly, the overall pattern of field line mapping appears to deform gradually. From this perspective, field line exponentiation appears to cause enhanced diffusion rather than reconnection. In some cases, resistive quasi-static evolution can cause the ideally stable initial equilibrium to cross a stability threshold, leading to formation of intense current filaments and rapid change of field line mapping into a qualitatively different pattern. It is in this onset phase that the change of field line connectivity is more appropriately designated as magnetic reconnection. Our results show that rapid change of field line connectivity appears to be a necessary, but not a sufficient condition for fast reconnection.

[23]  arXiv:1407.6095 [pdf, other]
Title: Synthetic Stellar Photometry. I-General considerations and new transformations for broad-band systems
Comments: MNRAS, accepted. Tables and programs to generate synthetic colours and bolometric corrections in various photometric systems and for different combination of E(B-V), [Fe/H], [alpha/Fe], Teff and logg available at this https URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

After a pedagogical introduction to the main concepts of synthetic photometry, colours and bolometric corrections in the Johnson-Cousins, 2MASS, and HST-ACS/WFC3 photometric systems are generated from MARCS synthetic fluxes for various [Fe/H] and [alpha/Fe] combinations, and virtually any value of reddening E(B-V) < 0.7. The successes and failures of model fluxes in reproducing the observed magnitudes are highlighted. Overall, extant synthetic fluxes predict quite realistic broad-band colours and bolometric corrections, especially at optical and longer wavelengths: further improvements of the predictions for the blue and ultraviolet spectral regions await the use of hydrodynamic models where the microturbulent velocity is not treated as a free parameter. We show how the morphology of the colour-magnitude diagram (CMD) changes for different values of [Fe/H] and [alpha/Fe]; in particular, how suitable colour combinations can easily discriminate between red giant branch and lower main sequence populations with different [alpha/Fe], due to the concomitant loops and swings in the CMD. We also provide computer programs to produce tables of synthetic bolometric corrections as well as routines to interpolate in them. These colour-Teff-metallicity relations may be used to convert isochrones for different chemical compositions to various bandpasses assuming observed reddening values, thus bypassing the standard assumption of a constant colour excess for stars of different spectral type. We also show how such an assumption can lead to significant systematic errors. The MARCS transformations presented in this study promise to provide important constraints on our understanding of the multiple stellar populations found in globular clusters (e.g., the colours of lower main sequence stars are predicted to depend strongly on [alpha/Fe]) and of those located towards/in the Galactic Bulge.

[24]  arXiv:1407.6098 [pdf, other]
Title: EUNHA: a new cosmological hydro simulation code
Comments: 12 pages, 10 figures, published in JKAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We have developed a parallel cosmological hydrodynamic simulation code designed for the study of formation and evolution of cosmological structures. The gravitational force is calculated using the TreePM method and the hydrodynamics is implemented based on the smoothed particle hydrodynamics. The initial displacement and velocity of simulation particles are calculated according to second-order linear perturbation theory using the power spectra of dark matter and baryonic matter. The initial background temperature is given by Recfast and the temperature uctuations at the initial particle position are determined by the adiabatic model. We use a time-limiter scheme over the individual time steps to capture shock-fronts and to ease the time-step tension between the shock and preshock particles. We also include the astrophysical gas processes of radiative heating/cooling, star formation, metal enrichment, and supernova feedback. We have tested the code in several standard cases such as one-dimensional Riemann problems, Kelvin-Helmholtz, and Sedov blast wave instability. Star formation on the galactic disk is investigated to check whether the Schmidt-Kennicutt relation is properly recovered. We also study global star formation histories at different simulation resolutions and compare them with observations.

[25]  arXiv:1407.6143 [pdf, other]
Title: A six-part collisional model of the main asteroid belt
Comments: Accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

In this work, we construct a new model for the collisional evolution of the main asteroid belt. Our goals are to test the scaling law of Benz and Asphaug (1999) and ascertain if it can be used for the whole belt. We want to find initial size-frequency distributions (SFDs) for the considered six parts of the belt (inner, middle, 'pristine', outer, Cybele zone, high-inclination region) and to verify if the number of synthetic asteroid families created during the simulation matches the number of observed families as well. We used new observational data from the WISE satellite (Masiero et al., 2011) to construct the observed SFDs. We simulate mutual collisions of asteroids with a modified version of the Boulder code (Morbidelli et al., 2009), where the results of hydrodynamic (SPH) simulations of Durda et al. (2007) and Benavidez et al. (2012) are included. Because material characteristics can significantly affect breakups, we created two models - for monolithic asteroids and for rubble-piles. To explain the observed SFDs in the size range D = 1 to 10 km we have to also account for dynamical depletion due to the Yarkovsky effect. The assumption of (purely) rubble-pile asteroids leads to a significantly worse fit to the observed data, so that we can conclude that majority of main-belt asteroids are rather monolithic. Our work may also serve as a motivation for further SPH simulations of disruptions of smaller targets (with a parent body size of the order of 1 km).

[26]  arXiv:1407.6145 [pdf, ps, other]
Title: A Northern Sky Survey for Point-Like Sources of EeV Neutral Particles with the Telescope Array Experiment
Comments: 27 pages, 10 figures, 3 tables, submitted to the ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report on the search for steady point-like sources of neutral particles around 10$^{18}$ eV between 2008 May and 2013 May with the surface detector of the Telescope Array experiment. We found overall no significant point-like excess above 0.5 EeV in the northern sky. Subsequently, we also searched for coincidence with the Fermi bright Galactic sources. No significant coincidence was found within the statistical error. Hence, we set an upper limit at the 95% confidence level on the neutron flux that corresponds to an averaged flux of 0.07 km$^{-2}$ yr$^{-1}$ above 1 EeV in the northern sky. This is the most stringent flux upper limit in a northern sky survey assuming point-like sources. The upper limit at the 95% confidence level on the neutron flux from Cygnus X-3 is also set to 0.2 km$^{-2}$ yr$^{-1}$ above 0.5 EeV. This is an order of magnitude smaller than previous flux measurements.

[27]  arXiv:1407.6148 [pdf, ps, other]
Title: Roche tomography of cataclysmic variables - VI. Differential rotation of AE Aqr - Not tidally locked!
Comments: 17 pages, 18 figures, 5 tables, Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present Roche tomograms of the K4V secondary star in the cataclysmic variable AE Aqr, reconstructed from two datasets taken 9 days apart, and measure the differential rotation of the stellar surface. The tomograms show many large, cool starspots, including a large high-latitude spot and a prominent appendage down the trailing hemisphere. We find two distinct bands of spots around 22$^{\circ}$ and 43$^{\circ}$ latitude, and estimate a spot coverage of 15.4-17% on the northern hemisphere. Assuming a solar-like differential rotation law, the differential rotation of AE Aqr was measured using two different techniques. The first method yields an equator-pole lap time of 269 d and the second yields a lap time of 262 d. This shows the star is not fully tidally locked, as was previously assumed for CVs, but has a co-rotation latitude of $\sim 40^{\circ}$. We discuss the implications that these observations have on stellar dynamo theory, as well as the impact that spot traversal across the first Lagrangian point may have on accretion rates in CVs as well as some of their other observed properties. The entropy landscape technique was applied to determine the system parameters of AE Aqr. For the two independent datasets we find M$_1$ = 1.20 and 1.17 M$_{\odot}$, M$_2$ = 0.81 and 0.78 M$_{\odot}$, and orbital inclinations of $50^{\circ}$ to $51^{\circ}$ at optimal systemic velocities of {\gamma} = -64.7 and -62.9 kms$^{-1}$.

[28]  arXiv:1407.6150 [pdf, other]
Title: Diffusion of cosmic rays at EeV energies in inhomogeneous extragalactic magnetic fields
Comments: 16 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Ultra-high energy cosmic rays can propagate diffusively in cosmic magnetic fields. When their propagation time is comparable to the age of the universe, a suppression in the flux relative to the case in the absence of magnetic fields will occur. In this work we find an approximate parametrization for this suppression at energies below $\sim$ Z EeV using several magnetic field distributions obtained from cosmological simulations of the magnetized cosmic web. We assume that the magnetic fields have a Kolmogorov power spectrum with the field strengths distributed according to these simulations. We show that, if magnetic fields are coupled to the matter distribution, low field strengths will fill most of the volume, making the suppression milder compared to the case of a constant magnetic field with strength equal to the mean value of this distribution. We also derive upper limits for this suppression to occur for some models of extragalactic magnetic fields, as a function of the coherence length of these fields.

[29]  arXiv:1407.6157 [pdf, ps, other]
Title: Atmospheric parameters and carbon abundance for hot DB white dwarfs
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25000K are extremely difficult to determine from optical spectroscopy. This is particularly unfortunate, because this is the range of variable DBV or V777 Her stars. Accurate atmospheric parameters are needed to help or confirm the asteroseismic analysis of these objects. Another important aspect is the new class of white dwarfs - the hot DQ - detected by Dufour et al. (2007), with spectra dominated by carbon lines. The analysis shows that their atmospheres are pure carbon. The origin of these stars is not yet understood, but they may have an evolutionary link with the hotter DBs as studied here. Our aim is to determine accurate atmospheric parameters and element abundances and study the implications for the evolution white dwarfs of spectral classes DB and hot DQ. High resolution UV spectra of five DBs are studied with model atmospheres. We determine stellar parameters and abundances or upper limits of C and Si. These objects are compared with cooler DBs below 20000K. We find photospheric C and no other heavy elements - with extremely high limits on the C/Si ratio - in two of the five hot DBs. We compare various explanations for this unusual composition, which have been proposed in the literature: accretion of interstellar or circumstellar matter, radiative levitation, carbon dredge-up from deeper interior below the helium layer, and a residual stellar wind. None of these explanations is completely satisfactory, and the problem of the origin of the hot DQ remains an open question.

[30]  arXiv:1407.6159 [pdf, ps, other]
Title: Distributions of Gamma-Ray Bursts and Blazars in the $L_{\rm p}-E_{\rm p}$ Plane and Possible Implications for their Radiation Physics
Comments: 23 pages, 2 tables, 2 figures. Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a spectral analysis for a sample of redshift known GRBs observed with {\em Fermi}/GBM. Together with the results derived from our systematical spectral energy distribution modeling with the leptonic models for a {\em Fermi}/LAT blazar sample, we compare the distributions of the GRBs and the blazars by plotting the synchrotron peak luminosity ($L_{\rm s}$) and the corresponding peak photon energy $E_{\rm s}$ of blazars in the $L_{\rm p}-E_{\rm p}$ plane of GRBs, where $L_{\rm p}$ and $E_{\rm p}$ are the peak luminosity and peak photon energy of the GRB time-integrated $\nu f_\nu$ spectrum, respectively. The GRBs are in the high-$L_{\rm p}$, high-$E_{\rm p}$ corner of the plane and a tight $L_{\rm p}-E_{\rm p}$ relation is found, i.e., $L_{\rm p}\propto E_{\rm p}^{2.13^{+0.54}_{-0.46}}$. Both FSRQs and LBLs are clustered in the low-$E_{\rm p}$, low-$L_{\rm p}$ corner. IBLs and HBLs have $E_{\rm s}\sim 2\times 10^{-3} - 10^{2}$ keV and $L_{\rm s} \sim 10^{44} - 10^{47}$ erg s$^{-1}$, but no dependence of $L_{\rm s}$ on $E_{\rm s}$ is found. We show that the tight $L_p-E_p$ relation of GRBs is potentially explained with the synchrotron radiation of fast-cooling electrons in a highly magnetized ejecta, and the weak anti-correlation of $L_{\rm s}-E_{\rm s}$ for FSRQs and LBLs may be attributed to synchrotron radiation of slow-cooling electrons in a moderately magnetized ejecta. The distributions of IBLs and HBLs in the $L_{\rm p}-E_{\rm p}$ plane may be interpreted with synchrotron radiation of fast-cooling electrons in a matter-dominated ejecta. These results may present a unified picture for the radiation physics of relativistic jets in GRBs and blazars within the framework of the leptonic synchrotron radiation models.

[31]  arXiv:1407.6163 [pdf, ps, other]
Title: White paper: Gaia and the end states of stellar evolution
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

This is the product of a Gaia GREAT workshop on "Gaia and the end states of stellar evolution" held at the University of Leicester in April 2011.

[32]  arXiv:1407.6193 [pdf, other]
Title: A new sample of X-ray selected narrow emission-line galaxies. I. The nature of optically elusive AGN
Comments: 13 pages, 13 figues, accepted for publication in A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

Using the 3XMM catalogue of serendipitous X-ray sources, and the SDSS-DR9 spectroscopic catalogue, we have obtained a new sample of X-ray selected narrow emission line galaxies. The standard optical diagnostic diagram and selection by hard X-ray luminosity expose a mismatch between the optically-based and X-ray-based classifications. The nature of these misclassified elusive AGN can be understood in terms of their broader X-ray and optical properties and leads to a division of this sub-sample into two groups. A little more than half are likely to be narrow-line Seyfert 1s (NLS1s), so misclassified because of the contribution of the Broad Line Region (BLR) to their optical spectra. The remainder have some of the properties of Seyfert 2 (Sy2) AGN; their optical elusiveness can be explained by optical dilution from the host galaxy plus a star-formation contribution and by their underluminous optical emission due to low accretion rates. Because some of the Sy2 sources have very low accretion rates, are unabsorbed, plus the fact that they lack broad optical emission lines, they are good candidates to be True Sy2 AGN.

[33]  arXiv:1407.6197 [pdf, ps, other]
Title: Smooth halos in the cosmic web
Authors: Jose Gaite
Comments: 17 pages, 7 figures, JCAP style
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of equality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in $N$-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these "smoothness sizes" have no direct relation to the virial radii.

[34]  arXiv:1407.6212 [pdf, other]
Title: Accretion discs as regulators of stellar angular momentum evolution in the ONC and Taurus-Auriga
Comments: Accepted for publication in MNRAS on 23rd July 2014, 22 pages, 12 figures, 5 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In light of recent substantial updates to spectral type estimations and newly established intrinsic colours, effective temperatures, and bolometric corrections for pre-main sequence (PMS) stars, we re-address the theory of accretion-disc regulated stellar angular momentum (AM) evolution. We report on the compilation of a consistent sample of fully convective stars within two of the most well-studied and youngest, nearby regions of star formation: the Orion Nebula Cluster (ONC) and Taurus-Auriga. We calculate the average specific stellar AM ($j_{\star}$) assuming solid body rotation, using surface rotation periods gathered from the literature and new estimates of stellar radii and ages. We use published Spitzer IRAC fluxes to classify our stars as Class II or Class III and compare their $j_{\star}$ evolution. Our results suggest that disc dispersal is a rapid process that occurs at a variety of ages. We find a consistent $j_{\star}$ reduction rate between the Class II and Class III PMS stars which we interpret as indicating a period of accretion disc-regulated AM evolution followed by near-constant AM evolution once the disc has dissipated. Furthermore, assuming our observed spread in stellar ages is real, we find the removal rate of $j_{\star}$ during the Class II phase is more rapid than expected by contraction at constant stellar rotation rate. A much more efficient process of AM removal must exist, most likely in the form of an accretion-driven stellar wind or other outflow from the star-disc interaction region or extended disc surface.

[35]  arXiv:1407.6223 [pdf, other]
Title: A Consistency Relation for the CMB B-mode Polarization in the Squeezed Limit
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

A large-scale temperature perturbation has a non-zero correlation with the power spectrum of B-modes of cosmological origin on short scales while the corresponding correlation is expected to be zero for B-modes sourced by galactic foregrounds. We thus compute the squeezed limit of a three-point function in which one correlates the temperature fluctuations at large scales with two polarization modes at small scales. In the particular case of the B-mode polarization we obtain a relation that connects the squeezed limit of the $TBB$ three-point function with the cosmological B-mode power spectrum, which can be used as a consistency relation. This could in principle help to distinguish a primordial signal from that induced by inter-stellar dust.

[36]  arXiv:1407.6229 [pdf, ps, other]
Title: The ALMA view of the protostellar system HH212 - The wind, the cavity, and the disk
Comments: Astronomy & Astrophysics Letter, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context: Because it is viewed simply edge-on, the HH212 protostellar system is an ideal laboratory for studying the interplay of infall, outflow, and rotation in the earliest stages of low-mass star formation. Aims: We wish to exploit the unmatched combination of high angular resolution, high sensitivity, high-imaging fidelity, and spectral coverage provided by ALMA to shed light on the complex kinematics of the innermost central regions of HH212. Methods: We mapped the inner 10" (4500 AU) of the HH212 system at about 0.5 arcsec resolution in several molecular tracers and in the 850 $\mu$m dust continuum using the ALMA interferometer in band 7 in the extended configuration of the Early Science Cycle 0 operations. Results: Within a single ALMA spectral set-up, we simultaneously identify all the crucial ingredients known to be involved in the star formation recipe namely: (i) the fast, collimated bipolar SiO jet driven by the protostar, (ii) the large-scale swept-up CO outflow, (iii) the flattened rotating and infalling envelope, with bipolar cavities carved by the outflow (in C$^{17}$O(3--2)), and (iv) a rotating wide-angle flow that fills the cavities and surrounding the axial jet (in C$^{34}$S(7--6)). In addition, the compact high-velocity C$^{17}$O emission ($\pm$ 1.9--3.5 km s$^{-1}$ from systemic) shows a velocity gradient along the equatorial plane consistent with a rotating disk of about 0.2 arcsec = 90 AU around a $\simeq 0.3 \pm 0.1 M_{\rm \odot}$ source. The rotating disk is possibly Keplerian. Conclusions: HH212 is the third Class 0 protostar with possible signatures of a Keplerian disk of radius $\geq 30 AU$. The warped geometry in our CS data suggests that this large keplerian disk might result from misaligned magnetic and rotation axes during the collapse phase. The wide-angle CS flow suggests that disk winds may be present in this source.

[37]  arXiv:1407.6231 [pdf, ps, other]
Title: Modeling SNR G1.9+0.3 as a Supernova Inside a Planetary Nebula
Authors: Danny Tsebrenko, Noam Soker (Technion, Israel)
Comments: 16 pages, 7 figures. Submitted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

Using 3D numerical hydrodynamical simulations we show that a type Ia supernova (SN Ia) explosion inside a planetary nebula (PN) can explain the observed shape of the G1.9+0.3 supernova remnant (SNR), and its X-ray morphology. The SNR G1.9+0.3 morphology can be generally described as a sphere with two small and incomplete lobes protruding on opposite sides of the SNR, termed "ears", a structure resembling many elliptical PNe. Observations show the synchrotron X-ray emission to be much stronger inside the two ears than in the rest of the SNR. We numerically show that a spherical SN Ia explosion into a circumstellar matter (CSM) with the structure of an elliptical PN with ears can explain the X-ray properties of SNR G1.9+0.3. While the ejecta has already collided with the PN shell in most of the SNR and its forward shock has been slowed down, the ejecta is still advancing inside the ears. The fast forward shock inside the ears explains the stronger X-ray emission there. SN Ia inside PNe (SNIPs) seem to comprise a non-negligible fraction of resolved SN Ia remnants.

[38]  arXiv:1407.6235 [pdf, ps, other]
Title: A state-dependent influence of the type-I bursts on the accretion in 4U 1608--52?
Comments: 10 pages, 5 figures, accepted by ApJ Letter
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigated the possible feedback of type-I burst to the accretion process during the spectral evolution of the atoll source 4U 1608--52. By fitting the burst spectrum with a blackbody and an adjustable, persistent spectral component, we found that the latter is significant state-dependent. In the banana state the persistent flux increases along the burst evolution, while in the island state this trend holds only when the bursts are less luminous and starts to reverse at higher burst luminosities. We speculate that, by taking into account both the Poynting-Robertson drag and radiation pressure, these phenomena may arise from the interactions between the radiation field of the type-I burst and the inner region of the accretion disc.

[39]  arXiv:1407.6249 [pdf, other]
Title: A LEKID-based CMB instrument design for large-scale observations in Greenland
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present the results of a feasibility study, which examined deployment of a ground-based millimeter-wave polarimeter, tailored for observing the cosmic microwave background (CMB), to Isi Station in Greenland. The instrument for this study is based on lumped-element kinetic inductance detectors (LEKIDs) and an F/2.4 catoptric, crossed-Dragone telescope with a 500 mm aperture. The telescope is mounted inside the receiver and cooled to $<\,4$ K by a closed-cycle $^4$He refrigerator to reduce background loading on the detectors. Linearly polarized signals from the sky are modulated with a metal-mesh half-wave plate that is rotated at the aperture stop of the telescope with a hollow-shaft motor based on a superconducting magnetic bearing. The modular detector array design includes at least 2300 LEKIDs, and it can be configured for spectral bands centered on 150~GHz or greater. Our study considered configurations for observing in spectral bands centered on 150, 210 and 267~GHz. The entire polarimeter is mounted on a commercial precision rotary air bearing, which allows fast azimuth scan speeds with negligible vibration and mechanical wear over time. A slip ring provides power to the instrument, enabling circular scans (360 degrees of continuous rotation). This mount, when combined with sky rotation and the latitude of the observation site, produces a hypotrochoid scan pattern, which yields excellent cross-linking and enables 34\% of the sky to be observed using a range of constant elevation scans. This scan pattern and sky coverage combined with the beam size (15~arcmin at 150~GHz) makes the instrument sensitive to $5 < \ell < 1000$ in the angular power spectra.

[40]  arXiv:1407.6253 [pdf, ps, other]
Title: High-precision photometry by telescope defocussing. VI. WASP-24, WASP-25 and WASP-26
Comments: Accepted for publication in MNRAS. 14 pages, 10 figures, 8 tables. Data and supplementary information are available on request
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We present time-series photometric observations of thirteen transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three systems have orbital obliquity measurements, WASP-24 and WASP-26 have been observed with Spitzer, and WASP-25 was previously comparatively neglected. Our light curves were obtained using the telescope-defocussing method and have scatters of 0.5 to 1.2 mmag relative to their best-fitting geometric models. We used these data to measure the physical properties and orbital ephemerides of the systems to high precision, finding that our improved measurements are in good agreement with previous studies. High-resolution Lucky Imaging observations of all three targets show no evidence for faint stars close enough to contaminate our photometry. We confirm the eclipsing nature of the star closest to WASP-24 and present the detection of a detached eclipsing binary within 4.25 arcmin of WASP-26.

[41]  arXiv:1407.6254 [pdf, ps, other]
Title: Spectral State Transitions of the Ultraluminous X-ray Source IC 342 X-1
Comments: 10 pages, 5 Figures. MNRAS: Accepted 2014 July 22
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We observed the Ultraluminous X-ray Source IC 342 X-1 simultaneously in X-ray and radio with Chandra and the JVLA to investigate previously reported unresolved radio emission coincident with the ULX. The Chandra data reveal a spectrum that is much softer than observed previously and is well modelled by a thermal accretion disc spectrum. No significant radio emission above the rms noise level was observed within the region of the ULX, consistent with the interpretation as a thermal state though other states cannot be entirely ruled out with the current data. We estimate the mass of the black hole using the modelled inner disc temperature to be $30~\mathrm{M_{\odot}} \lesssim M\sqrt{\mathrm{cos}i}\lesssim200~\mathrm{M_{\odot}}$ based on a Shakura-Sunyaev disc model. Through a study of the hardness and high-energy curvature of available X-ray observations, we find that the accretion state of X-1 is not determined by luminosity alone.

[42]  arXiv:1407.6263 [pdf]
Title: Analysis of the time series in the space maser signals
Comments: 5 pages, 6 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We analyze the data of the observations of the radio sources frequently found in space. They are believed to be the sets of molecular condensations each of which works as a maser, so that the whole set produces a characteristic spectrum. It turns out that in some cases the intensity of one of the components of such spectrum corresponding to a single condensation changes periodically with a period of dozens of minutes or of hours.

[43]  arXiv:1407.6269 [pdf, ps, other]
Title: Modified pulsar current analysis: probing magnetic field evolution
Authors: A.P. Igoshev (Nijmegen), S.B. Popov (Sternberg Astronomical Institute, Russia)
Comments: Accepted for publication in MNRAS. 11 pages, 11 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We use a modified pulsar current analysis to study magnetic field decay in radio pulsars. In our approach we analyse the flow, not along the spin period axis as has been performed in previous studies, but study the flow along the direction of growing characteristic age, $\tau=P/(2\dot P)$. We perform extensive tests of the method and find that in most of the cases it is able to uncover non-negligible magnetic field decay (more than a few tens of per cent during the studied range of ages) in normal radio pulsars for realistic initial properties of neutron stars. However, precise determination of the magnetic field decay timescale is not possible at present. The estimated timescale may differ by a factor of few for different sets of initial distributions of neutron star parameters. In addition, some combinations of initial distributions and/or selection effects can also mimic enhanced field decay. We apply our method to the observed sample of radio pulsars at distances $<10$ kpc in the range of characteristic ages $8 \times 10^4 < \tau < 10^6$ years where, according to our study, selection effects are minimized. By analysing pulsars in the Parkes Multibeam and Swinburne surveys we find that, in this range, the field decays roughly by a factor of two. With an exponential fit this corresponds to the decay time scale $\sim 4 \times 10^5$ yrs. With larger statistics and better knowledge of the initial distribution of spin periods and magnetic field strength, this method can be a powerful tool to probe magnetic field decay in neutron stars.

[44]  arXiv:1407.6271 [pdf, ps, other]
Title: Six Faint Gamma-ray Pulsars Seen with the Fermi Large Area Telescope -- Towards a Sample Blending into the Background
Comments: 12 pages, 5 figures. Accepted to A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Context: GeV gamma-ray pulsations from over 140 pulsars have been characterized using the Fermi Large Area Telescope, enabling improved understanding of the emission regions within the neutron star magnetospheres, and the contributions of pulsars to high energy electrons and diffuse gamma rays in the Milky Way. The first gamma-ray pulsars to be detected were the most intense and/or those with narrow pulses. Aims: As the Fermi mission progresses, progressively fainter objects can be studied. In addition to more distant pulsars (thus probing a larger volume of the Galaxy), or ones in high background regions (thus improving the sampling uniformity across the Galactic plane), we detect pulsars with broader pulses or lower luminosity. Adding pulsars to our catalog with inclination angles that are rare in the observed sample, and/or with lower spindown power, will reduce the bias in the currently known gamma-ray pulsar population. Methods: We use rotation ephemerides derived from radio observations to phase-fold gamma rays recorded by the Fermi Large Area Telescope, to then determine the pulse profile properties. Spectral analysis provides the luminosities and, when the signal-to-noise ratio allows, the cutoff energies. We constrain the pulsar distances by different means in order to minimize the luminosity uncertainties. Results: We present six new gamma-ray pulsars with an eclectic mix of properties. Three are young, and three are recycled. They include the farthest, the lowest power, two of the highest duty-cycle pulsars seen, and only the fourth young gamma-ray pulsar with a radio interpulse. We discuss the biases existing in the current gamma-ray pulsar catalog, and steps to be taken to mitigate the bias.

[45]  arXiv:1407.6282 [pdf, ps, other]
Title: Adaptive Weighting in Radio Interferometric Imaging
Authors: Sarod Yatawatta
Comments: MNRAS Accepted 2014 July 22. Received 2014 July 15; in original form 2014 June 26
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Radio interferometers observe the Fourier space of the sky, at locations determined by the array geometry. Before a real space image is constructed by a Fourier transform, the data is weighted to improve the quality of reconstruction. Two criteria for calculation of weights are maximizing sensitivity and minimizing point spread function (PSF) sidelobe levels. In this paper, we propose a novel weighting scheme suitable for ultra deep imaging experiments. The proposed weighting scheme is used to maximize sensitivity while minimizing PSF sidelobe variation across frequency and multiple epochs. We give simulation results that show the superiority of the proposed scheme compared with commonly used weighting schemes in achieving these objectives.

[46]  arXiv:1407.6284 [pdf, ps, other]
Title: Stellar tidal disruption candidates found by cross-correlating the ROSAT Bright Source Catalogue and XMM-Newton observations
Comments: Accepted for publication in MNRAS; 13 pages, 9 figures, 4 tables
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We performed a systematic search for stellar tidal disruption events (TDE) by looking for X-ray sources that were detected during the ROSAT All Sky Survey and faded by more than an order of magnitude over the next two decades according to XMM-Newton serendipitous observations. Besides a number of highly variable persistent X-ray sources (like active galactic nuclei and cataclysmic variables), we found three sources that are broadly consistent with the TDE scenario: 1RXS J114727.1+494302, 1RXS J130547.2+641252, and 1RXS J235424.5-102053. A TDE association is also acceptable for the fourth source, 1RXS J112312.7+012858, but an AGN origin cannot be ruled out either. This statistics implies a TDE rate of $ \sim 3\times 10^{-5} $ yr$ ^{-1} $ per galaxy in the Universe within $z\sim 0.18$, which is broadly consistent with the estimates of the TDE rate in the more local Universe obtained previously.

[47]  arXiv:1407.6291 [pdf, ps, other]
Title: The Enigma of the Open Cluster M29 (NGC 6913) Solved
Comments: 13 pages, 7 figures Astronomical Journal, accepted on 2014 July 17
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Determining the distance to the open cluster M29 (NGC 6913) has proven difficult, with distances determined by various authors differing by a factor of two or more. To solve this problem, we have initiated a new photometric investigation of the cluster in the Vilnius seven-color photometric system supplementing it with available data in the BV and JHK_s photometric systems, and spectra of the nine brightest stars of spectral classes O and B. Photometric spectral classes and luminosities of 260 stars in a 15 arcmin x 15 arcmin area down to V = 19 mag are used to investigate the interstellar extinction run with distance and to estimate the distance of the Great Cygnus Rift, 800 pc. The interstellar reddening law in the optical and near-infrared regions is found to be close to normal, with the ratio of extinction to color excess R(BV) = 2.87. The extinction A(V) of cluster members is between 2.5 to 3.8 mag, with a mean value of 2.97 mag or E(B-V) = 1.03. The average distance of eight stars of spectral types O9-B2 is 1.54 +- 0.15 kpc. Two stars from the seven brightest ones are field stars: HDE 229238 is a background B0.5 supergiant and HD 194378 is a foreground F star. In the intrinsic color-magnitude diagram, seven fainter stars of spectral classes B3-B8 are identified as possible members of the cluster. The 15 selected members of the cluster of spectral classes O9--B8 plotted on the log L/L(sun) vs. log T(eff) diagram, together with the isochrones from the Padova database, give the age of the cluster as 5 +- 1 Myr.

[48]  arXiv:1407.6300 [pdf]
Title: Model-Independent Plotting of the Cosmological Scale Factor as a Function of Lookback Time
Comments: Accepted Astronomical Journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In the present work we describe a model-independent method of developing a plot of scale factor versus lookback time from the usual Hubble diagram of modulus data against redshift. This is the first plot of this type. We follow the model-independent methodology of Daly and Djorgovski (2004) used for their radio-galaxy data. Once the data plot is completed, any model can be applied and will display accordingly as described in standard literature. We then compile an extensive data set to z = 1.8 by combining SNe Ia data from SNLS3 of Conley et al. (2011), High-z SNe data of Riess et al. (2004) and radio-galaxy data of Daly & Djorgovski (2004) to be used to validate the new plot. We first display these data on a standard Hubble diagram to confirm the best fit for LCDM cosmology and thus validate the joined data set. The scale factor plot is then developed from the data and the LCDM model is again displayed from a least-squares fit. The fit parameters are in agreement with the Hubble diagram fit confirming the validity of the new plot. Of special interest is the transition-time of the universe which in the scale factor plot will appear as an inflection point in the data set. Noise is more visible on this presentation which is particularly sensitive to inflection points of any model displayed on the plot unlike on a modulus-z diagram where there are no inflection points and the transition-z is not at all obvious by inspection. We obtain a lower limit of z >0.6. It is evident from this presentation that there is a dearth of SNe data in the range, z = 1-2, exactly the range necessary to confirm a LCDM transition-z in the neighborhood of z = 0.76.

[49]  arXiv:1407.6301 [pdf, other]
Title: Extended Warm Gas in the ULIRG Mrk273: Galactic Outflows and Tidal Debris
Comments: Accepted for Publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present new HST ACS medium- and narrow-band images and long-slit, optical (4000 - 7200A) spectra obtained using the Isaac Newton Telescope (INT) on La Palma, of the merging system Mrk273. The HST observations sample the [OIII]4959,5007 emission from the galaxy and the nearby continuum. The images show that the morphologies of the extended continuum and the ionised gas emission from the galaxy are decoupled, extending almost perpendicular to each other. In particular, we detect for the first time a spectacular structure of ionised gas in the form of filaments extending ~23 kpc to the east of the nuclear region. The quiescent ionised gas kinematics at these locations suggests that these filaments are tidal debris left over from a secondary merger event that are illuminated by an AGN in the nuclear regions. The images also reveal a complex morphology in the nuclear region of the galaxy for both the continuum and the [OIII] emission. Kinematic disturbance, in the form of broad (FWHM > 500 km s-1) and/or strongly shifted (abs(\DeltaV) >150 km s-1) emission line components, is found at almost all locations within a radius of ~4 kpc to the east and west of the northern nucleus. We fit the profiles of all the emission lines of different ionisation with a kinematic model using up to 3 Gaussian components. From these fits we derive diagnostic line ratios that are used to investigate the ionisation mechanisms at the different locations in the galaxy. We show that, in general, the line ratios are consistent with photoionization by an AGN as the main ionisation mechanism. Finally, the highest surface brightness [OIII] emission is found in a compact region that is coincident with the so-called SE nuclear component. The compactness, kinematics and emission line ratios of this component suggest that it is a separate nucleus with its own AGN.

[50]  arXiv:1407.6349 [pdf, other]
Title: Atmospheric dynamics of terrestrial exoplanets over a wide range of orbital and atmospheric parameters
Comments: 18 pages, 20 figures, submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The recent discoveries of terrestrial exoplanets and super Earths extending over a broad range of orbital and physical parameters suggests that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone---including transitions to Snowball-like states and runaway-greenhouse feedbacks---depend on the equator-to-pole temperature differences, pattern of relative humidity, and other aspects of the dynamics. Here, using an idealized moist atmospheric general circulation model (GCM) including a hydrological cycle, we study the dynamical principles governing the atmospheric dynamics on such planets. We show how the planetary rotation rate, planetary mass, surface gravity, heat flux from a parent star, optical thickness and atmospheric mass affect the atmospheric circulation and temperature distribution on such planets. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. We elucidate the possible climatic regimes and diagnose the mechanisms controlling the formation of atmospheric jet stream, Hadley and Ferrel cells and latitudinal temperature differences. Finally, we discuss the implications for understanding how the atmospheric circulation influences the global climate.