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J.P. Magué & B. Ménard

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[1]
Title: Searching for a 0.1-1 keV Cosmic Axion Background
Comments: 4 pages, 2 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Primordial decays of string theory moduli at z \sim 10^{12} naturally generate a dark radiation Cosmic Axion Background (CAB) with 0.1 - 1 keV energies. This CAB can be detected through axion-photon conversion in astrophysical magnetic fields to give quasi-thermal excesses in the extreme ultraviolet and soft X-ray bands. Substantial and observable luminosities may be generated even for axion-photon couplings \ll 10^{-11} GeV^{-1}. We propose that axion-photon conversion may explain the observed excess emission of soft X-rays from galaxy clusters, and may also contribute to the diffuse unresolved cosmic X-ray background. We list a number of correlated predictions of the scenario.

[2]
Title: Modeling the Resolved Disk Around the Class 0 Protostar L1527
Authors: John J. Tobin (NRAO), Lee Hartmann (Michigan), Hsin-Fang Chiang (IfA), David J. Wilner (Harvard CfA), Leslie W. Looney (Illinois), Laurent Loinard (UNAM), Nuria Calvet (Michigan), Paola D'Alessio (UNAM)
Comments: 45 pages, 11 Figures, 7 Tables, Accepted to ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present high-resolution sub/millimeter interferometric imaging of the Class 0 protostar L1527 IRS (IRAS 04368+2557) at 870 micron and 3.4 mm from the Submillimeter Array (SMA) and Combined Array for Research in Millimeter Astronomy (CARMA). We detect the signature of an edge-on disk surrounding the protostar with an observed diameter of 180 AU in the sub/millimeter images. The mass of the disk is estimated to be 0.007 M_sun, assuming optically thin, isothermal dust emission. The millimeter spectral index is observed to be quite shallow at all the spatial scales probed; alpha ~ 2, implying a dust opacity spectral index beta ~ 0. We model the emission from the disk and surrounding envelope using Monte Carlo radiative transfer codes, simultaneously fitting the sub/millimeter visibility amplitudes, sub/millimeter images, resolved L\arcmin\ image, spectral energy distribution, and mid-infrared spectrum. The best fitting model has a disk radius of R = 125 AU, is highly flared (H ~ R^1.3), has a radial density profile rho ~ R^-2.5, and has a mass of 0.0075 M_sun. The scale height at 100 AU is 48 AU, about a factor of two greater than vertical hydrostatic equilibrium. The resolved millimeter observations indicate that disks may grow rapidly throughout the Class 0 phase. The mass and radius of the young disk around L1527 is comparable to disks around pre-main sequence stars; however, the disk is considerably more vertically extended, possibly due to a combination of lower protostellar mass, infall onto the disk upper layers, and little settling of ~1 micron-sized dust grains.

[3]
Title: Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Comments: 16 pages, 10 figures, 10 tables, A&A in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derive an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H]_ZW=-2.01 +- 0.04, or [Fe/H]_UVES=-2.11 +- 0.06, and a distance of 8.32 +- 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 +- 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 +- 1.0 Gyr for M 30.

[4]
Title: Multi-color detection of gravitational arcs: method and new candidates
Comments: 12 pages, 7 figures, 5 tables, A&A submitted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Strong gravitational lensing provides fundamental insights in the understanding of the dark matter distribution in massive galaxies, galaxy clusters and the background cosmology. Despite their importance, the number of gravitational arcs discovered so far is small. The urge for more complete, large samples and unbiased methods of selecting candidates is rising. A number of methods for the automatic detection of arcs have been proposed in the literature, but large amounts of spurious detections retrieved by these methods forces observers to visually inspect thousands of candidates per square degree in order to clean the samples. This approach is largely subjective and requires a huge amount of eye-ball checking, especially considering the actual and upcoming wide field surveys, which will cover thousands of square degrees. In this paper we study the statistical properties of colors of gravitational arcs. We found that most of them lie in a relatively small region of the color-color diagram (g'-r',r'-i'). We support this observational evidence by studying lensing cross section, which peaks for sources at redshift z~1, where the source-galaxy population is dominated by galaxies with large star forming regions and hence well defined colors. The use of this distinctive feature, in combination with an automatic arcfinder, reduces sample contamination by a factor of 6-7. We tested the performance of the method against 37 deg^2 of the CARS survey, detecting 73 new arc candidates.

[5]
Title: Finding a 60.9-day orbital period for the HMXB 4U 1036-56 with the Swift-BAT monitoring
Comments: Submitted to MNRAS Letter; 5 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Since November 2004, the Burst Alert Telescope on board Swift is producing a monitoring of the entire sky in the 15-150 keV band, recording the timing and spectral behavior of the detected sources. In this letter we study the properties of the HMXB 4U 1036-56 using both the BAT survey data and those from a Swift-XRT pointed observation. The timing analysis of the BAT light curve unveils a periodic modulation with a period of ~60.9 days, that we explain as the orbital period of the binary system. The position of 4U 1036-56 on the Corbet diagram and the derived semi-major orbit axis (~180 R_dot) are consistent with the Be nature of its companion star. The intensity orbital profile averaged over 88 months of observations shows a large asymmetric shape with a minimum consistent with zero intensity, that could be related to the occultation of the neutron star by the supergiant companion. The source shows also a strong long term variability, going from high intensity states to quiescent states over a time scale of ~2 years. The broad band 0.2-150 keV spectrum is well modeled with a flat absorbed power law with a cutoff at ~14 keV. Finally, we explore the possibility that 4U~1036--56 is associated to the unidentified source AGL J1037-5708, finding that the BAT light curve does not show any intensity enhancement correlated to the outburst of the Gamma-ray transient.

[6]
Title: Variable jet properties in GRB110721A: Time resolved observations of the jet photosphere
Comments: Contains 11 pages and 9 figures; Accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

{\it Fermi Gamma-ray Space Telescope} observations of GRB110721A have revealed two emission components from the relativistic jet: emission from the photosphere, peaking at $\sim 100$ keV and a non-thermal component, which peaks at $\sim 1000$ keV. We use the photospheric component to calculate the properties of the relativistic outflow. We find a strong evolution in the flow properties: the Lorentz factor decreases with time during the bursts from $\Gamma \sim 1000$ to $\sim 150$ (assuming a redshift $z=2$; the values are only weakly dependent on unknown efficiency parameters). Such a decrease is contrary to the expectations from the internal shocks and the isolated magnetar birth models. Moreover, the position of the flow nozzle measured from the central engine, $r_0$, increases by more than two orders of magnitude. Assuming a moderately magnetised outflow we estimate that $r_0$ varies from $10^6$ cm to $\sim 10^9$ cm during the burst. We suggest that the maximal value reflects the size of the progenitor core. Finally, we show that these jet properties naturally explain the observed broken power-law decay of the temperature which has been reported as a characteristic for GRB pulses.

[7]
Title: Empirical Constraints on the Star Formation & Redshift Dependence of the Lyman Alpha Effective' Escape Fraction
Authors: Mark Dijkstra (MPA), Akila Jeeson-Daniel (Melbourne)
Comments: 9 pages, 3 figures, to be submitted to MNRAS (following 2 rounds of refereeing)
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We derive empirical constraints on the volume averaged effective' escape fraction of Lyman Alpha (Lya) photons from star forming galaxies as a function of redshift, by comparing star formation functions inferred directly from observations, to observed Lya luminosity functions. Our analysis shows that the effective escape fraction increases from f_esc^eff ~ 1-3 % at z=0, to f_esc^eff ~ 10 % at z=3-4, and to f_esc^eff=35-50 % at z=6. Our constraint at z=6 lies above predictions by models that do not include winds, and therefore hints at the importance of winds in the Lya transfer process (even) at this redshift. We can reproduce Lya luminosity functions with an f_esc^eff that does not depend on the galaxies star formation rates (SFR) over up to ~2 orders of magnitude in Lya luminosity. It is possible to reproduce the luminosity functions with an f_esc^eff that decreases with SFR - which appears favored by observations of drop-out galaxies - in models which include a large scatter (~ 1.0 dex) in f_esc^eff, and/or in which star forming galaxies only have a non-zero f_esc^eff for a fraction of their life-time or a fraction of sightlines. We provide a fitting formula that summarizes our findings.

[8]
Title: The 54 days orbital period of AX J1820.5-1434 unveiled by Swift
Comments: Submitted to A&A Letters; 4 pages, 5 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The hard X-ray survey that Swift-BAT has been performing since late 2004 has provided a considerable database for a large number of sources whose hard X-ray emission was poorly known. We are exploiting the BAT survey archive to improve the temporal and spectral characterization of the Galactic hard-X-ray sources. In this letter we focus on the study of the high mass X-ray binary AX J1820.5-1434. All the data relevant to AX J1820.5-1434 have been extracted from the BAT survey archive and analyzed using a folding technique to search for periodical modulations. A broad-band spectral analysis was also performed complementing the BAT spectrum with the available Swift-XRT and XMM-Newton pointed observations. A timing analysis has revealed the detection of a coherent signal at P_0=54.03 +/- 0.07 days, that we interpret as the orbital period of the binary system. When folded with a period of P_0, the light curve shows an asymmetric profile, with a minimum roughly consistent with zero intensity. The broad band spectral analysis performed coupling Swift-XRT, XMM-Newton and Swift-BAT spectra is well modeled with an absorbed power law with a high energy exponential cutoff at ~36 keV.

[9]
Title: Calibrating stellar population models with Magellanic Cloud star clusters
Comments: 15 pages, 6 figures, 2 tables, accepted for publication in ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Stellar population models are commonly calculated using star clusters as calibrators for those evolutionary stages that depend on free parameters. However, discrepancies exist among different models, even if similar sets of calibration clusters are used. With the aim of understanding these discrepancies, and of improving the calibration procedure, we consider a set of 43 Magellanic Cloud (MC) clusters taking age and photometric information from the literature. We carefully assign ages to each cluster based on up-to-date determinations ensuring that these are as homogeneous as possible. To cope with statistical fluctuations, we stack the clusters in five age bins deriving for each of them integrated luminosities and colors. We find that clusters become abruptly red in optical and optical-IR colors as they age from ~0.6 to 1 Gyr, which we interpret as due to the development of a well-populated thermally pulsing asymptotic giant branch (TP-AGB). We argue that other studies missed this detection because of coarser age binnings. Maraston (2005; M05) and Girardi et al. (2010) models predict the presence of a populated TP-AGB at ~0.6 Gyr, with a correspondingly very red integrated color, at variance with the data; Bruzual & Charlot (2003) and Conroy et al. (2009) models run within the error bars at all ages. The discrepancy between the synthetic colors of M05 models and the average colors of MC clusters results from the now obsolete age scale adopted. Finally, our finding that the TP-AGB phase appears to develop between ~0.6-1 Gyr is dependent on the adopted age scale for the clusters and may have important implications for stellar evolution.

[10]
Title: The Turbulence Power Spectrum in Optically Thick Interstellar Clouds
Comments: accepted to ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)

The Fourier power spectrum is one of the most widely used statistical tools to analyze the nature of magnetohydrodynamic turbulence in the interstellar medium. Lazarian & Pogosyan (2004) predicted that the spectral slope should saturate to -3 for an optically thick medium and many observations exist in support of their prediction. However, there have not been any numerical studies to-date testing these results. We analyze the spatial power spectrum of MHD simulations with a wide range of sonic and Alfv\'enic Mach numbers, which include radiative transfer effects of the $^{13}$CO transition. We confirm numerically the predictions of Lazarian & Pogosyan (2004) that the spectral slope of line intensity maps of an optically thick medium saturates to -3. Furthermore, for very optically thin supersonic CO gas, where the density or CO abundance values are too low to excite emission in all but the densest shock compressed gas, we find that the spectral slope is shallower than expected from the column density. Finally, we find that mixed optically thin/thick CO gas, which has average optical depths on order of unity, shows mixed behavior: for super-Alfv\'enic turbulence, the integrated intensity power spectral slopes generally follow the same trend with sonic Mach number as the true column density power spectrum slopes. However, for sub-Alfv\'enic turbulence the spectral slopes are steeper with values near -3 which are similar to the very optically thick regime.

[11]
Title: X-ray view of four high-luminosity Swift/BAT AGN: Unveiling obscuration and reflection with Suzaku
Comments: A&A paper in press, 17 pages
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The Swift/BAT nine-month survey observed 153 AGN, all with ultra-hard X-ray BAT fluxes in excess of 10^-11 erg cm^-2 s^-1 and an average redshift of 0.03. Among them, four of the most luminous BAT AGN (44.73 < Log L(BAT) < 45.31) were selected as targets of Suzaku follow-up observations: J2246.0+3941 (3C 452), J0407.4+0339 (3C 105), J0318.7+6828, and J0918.5+0425. The column density, scattered/reflected emission, the properties of the Fe K line, and a possible variability are fully analyzed. For the latter, the spectral properties from Chandra, XMM-Newton and Swift/XRT public observations were compared with the present Suzaku analysis. Of our sample, 3C 452 is the only certain Compton-thick AGN candidate because of i) the high absorption and strong Compton reflection; ii) the lack of variability; iii) the "buried" nature, i.e. the low scattering fraction (<0.5%) and the extremely low relative [OIII] luminosity. In contrast 3C 105 is not reflection-dominated, despite the comparable column density, X-ray luminosity and radio morphology, but shows a strong long-term variability in flux and scattering fraction, consistent with the soft emission being scattered from a distant region (e.g., the narrow emission line region). The sample presents high (>100) X-to-[OIII] luminosity ratios, confirming the [OIII] luminosity to be affected by residual extinction in presence of mild absorption, especially for "buried" AGN such as 3C 452. Three of our targets are powerful FRII radio galaxies, making them the most luminous and absorbed AGN of the BAT Seyfert survey despite the inversely proportional N_H - L_X relation.

[12]
Title: Fermi LAT Observations of Supernova Remnants Interacting with Molecular Clouds: W41, MSH 17-39, and G337.7-0.1
Comments: 9 pages, 11 figures, submitted to ApJ. arXiv admin note: text overlap with arXiv:1207.1432
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report the detection of gamma-ray emission coincident with three supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. W41, G337.7-0.1, and MSH 17-39 are SNRs known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions and other observational information. SNR shocks are expected to be sites of cosmic ray acceleration, and clouds of dense material can provide effective targets for production of gamma-rays from neutral pion-decay. The observations reveal unresolved sources in the direction of G337.7-0.1, and MSH 17-39, and an extended source coincident with W41. We model their broadband emission (radio to gamma-ray) using a simple one-zone model, and after considering scenarios in which the MeV-TeV sources originate from either neutral pion decay or leptonic emission, we conclude that the gamma-rays must be produced through the hadronic channel.

[13]
Title: Is the black hole in NGC1277 really over-massive?
Authors: Eric Emsellem (ESO)
Comments: 9 pages, 11 Figures; accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

A claim has been made by van den Bosch et al. (2012) that NGC1277 hosts an over-massive BH with a mass larger than half its spheroid mass. We revisit this claim by examining the predictions from dynamical realisations based on new MGE models of NGC1277. We present realisations which fit the observed photometry. M/L is fixed following scaling relations which predict a Salpeter-like IMF. A model without a BH provides a surprisingly good fit of the observed kinematics outside the unresolved central region, but not, as expected, of the central dispersion and h4 values. A model with a MBH of 5 10^9 Msun allows to fit the dispersion profile, consistently with models of the same mass and M/L in vdB+12. It departs from the central h4 values by only about twice the given uncertainty. A slightly varying M/L or the addition of high velocity stars would further lower the need for a very massive BH. These results do not rule out the presence of an over-massive BH at the centre of NGC1277. However, they lead us to advocate the use of 3-sigma confidence intervals for derived MBH as better, more conservative, guidelines for such studies. We caution for the use of ill-defined spheroidal components as an input for scaling relations, and emphasise the fact that a MBH in the range 2-5 10^9 Msun would represent less than 5% of the spheroid mass of our models. This would make the BH in NGC1277 consistent or just twice as large as what a recent version of the MBH-sigma relation predicts. We examine the impact of the presence of a bar by running simulations from the same MGE model but with extreme anisotropies. An inner small bar forms, and an end-on view gets closer to fitting the central dispersion profile without the need for a central BH, while adding a black hole of 2.5 10^9 Msun, in line with the prediction from scaling relations, allows to fit the dispersion peak and h3 profiles. EDITED and ABRIDGED.

[14]
Title: A statistical dynamical study of meteorite impactors: a case study based on parameters derived from the Bosumtwi impact event
Comments: Accepted in Astronomical Notes
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The study of meteorite craters on Earth provides information about the dynamic evolution of bodies within the Solar System. Bosumtwi crater is a well studied, 10.5 km in diameter, ca. 1.07 Ma old impact structure located in Ghana. The impactor was $\sim$ 1 km in diameter, an ordinary chondrite and struck the Earth with an angle between 30$^\circ$ and 45$^\circ$ from the horizontal. We have used a two phase backward integration to constrain the most probable parent region of the impactor. We find that the most likely source region is a high inclination object from the Middle Main Belt.

[15]
Title: The Origin and Chemical Evolution of the Exotic Globular Cluster NGC3201
Comments: 14 pages, 13 figures, 3 tables, accepted for publication in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

NGC3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extraGalactic origin. Our aims are to study NGC3201 in the context of multiple populations (MPs), hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. We present a detailed chemical abundance analysis of eight red giant branch (RGB) stars using high resolution spectroscopy. We measured 29 elements and found [Fe/H]=-1.53+/-0.01, we cannot rule out a metallicity spread of ~0.12 dex, and an alpha-enhancement typical of halo GCs. However significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC3201 appears likely to have had an extraGalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.

[16]
Title: Instrumental Methods for Professional and Amateur Collaborations in Planetary Astronomy
Comments: 123 pages, submitted to Experimental Astronomy
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)

Amateur contributions to professional publications have increased exponentially over the last decades in the field of Planetary Astronomy. Here we review the different domains of the field in which collaborations between professional and amateur astronomers are effective and regularly lead to scientific publications. We discuss the instruments, detectors, softwares and methodologies typically used by amateur astronomers to collect the scientific data in the different domains of interest. Amateur contributions to the monitoring of planets and interplanetary matter, characterization of asteroids and comets, as well as the determination of the physical properties of Kuiper Belt Objects and exoplanets are discussed.

[17]
Title: Galaxy Cluster Bulk Flows and Collision Velocities in QUMOND
Comments: 11 pages, 8 figures, accepted for publication in ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in {\Lambda}CDM simulations. The bulk motions of clusters attain about 1000 km/s by low redshift, comparable to observations whereas {\Lambda}CDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in {\Lambda}CDM, potentially providing an explanation for 'pink elephants' like El Gordo. However, it is not obvious that the cluster mass function can be recovered.

[18]
Title: The future of the Sun: an evolved solar twin revealed by CoRoT
Comments: 5 pages, 4 figures, 1 Table. Accepted to Astrophysical Journal Letters (ApJL): Manuscript #LET30652 press relesae: this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The question of whether the Sun is peculiar within the class of solar-type stars has been the subject of active investigation over the past three decades. Although several solar twins have been found with stellar parameters similar to those of the Sun (albeit in a range of Li abundances and with somewhat different compositions), their rotation periods are unknown, except for 18 Sco, which is younger than the Sun and with a rotation period shorter than solar. It is difficult to obtain rotation periods for stars of solar age from ground-based observations, as a low activity level imply a shallow rotational modulation of their light curves. CoRoT has provided space-based long time series from which the rotation periods of solar twins as old as the Sun could be estimated. Based on high S/N high resolution spectroscopic observations gathered at the Subaru Telescope, we show that the star CoRoT ID 102684698 (CoRoT Sol 1) is a somewhat evolved solar twin with a low Li abundance. Its rotation period is 29 +- 5 days, compatible with its age (6.7 Gyr) and low lithium content A(Li) < 0.85 dex. Interestingly, our CoRoT solar twin seems to have enhanced abundances of the refractory elements with respect to the Sun, a typical characteristic of most nearby twins. With a magnitude V ~14.1, ID 102684698 is the first solar twin revealed by CoRoT, the farthest field solar twin so far known, and the only solar twin older than the Sun for which a rotation period has been determined.

[19]
Title: Ultra compact dwarf galaxy formation by tidal stripping of nucleated dwarf galaxies
Comments: 10 pages, 5 figures, accepted for publication in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA)

Ultra Compact Dwarf Galaxies (UCDs) and dwarf galaxy nuclei have many common properties, such as internal velocity dispersions and colour-magnitude trends, suggesting tidally stripped dwarf galaxies as a possible UCD origin. However, UCDs typically have sizes more than twice as large as nuclei at the same luminosity. We use a GPU-enabled version of the particle-mesh code \textsc{superbox} to study the possibility of turning nucleated dwarf galaxies into UCDs by tidally stripping them in a Virgo-like galaxy cluster. We find that motion in spherical potentials, where close passages happen many times, leads to the formation of compact ($r_h \lesssim 20$ pc) star clusters/UCDs. In contrast, orbital motion where close passages happen only once or twice leads to the formation of extended objects which are large enough to account for the full range of observed UCD sizes. For such motion, we find that dwarf galaxies need close pericentre passages with distances less than 10 kpc to undergo strong enough stripping so that UCD formation is possible. As tidal stripping produces objects with similar properties to UCDs, and our estimates suggest dwarf galaxies have been destroyed in sufficient numbers to explain the observed number of UCDs in M87, we consider tidal stripping to be a likely origin of UCDs. However, comparison with cosmological simulations is needed to determine if the number and spatial distribution of UCDs formed by tidal stripping matches the observations of UCDs in galaxy clusters.

[20]
Title: Stellar population gradients and spatially resolved kinematics in luminous post-starburst galaxies
Comments: accepted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We have used deep integral field spectroscopy obtained with the GMOS instrument on Gemini-North to determine the spatial distribution of the post-starburst stellar population in four luminous E+A galaxies at z<0.04. We find all four galaxies have centrally-concentrated gradients in the young stellar population contained within the central ~1 kpc. This is in agreement with the Balmer line gradients found in local low luminosity E+A galaxies. The results from higher redshift (z~0.1) samples of luminous E+A galaxies have been varied, but in general have found the post-starburst signature to be extended or a galaxy-wide phenomenon or have otherwise failed to detect gradients in the stellar populations. The ubiquity of the detection of a centrally concentrated young stellar population in local samples, and the presence of significant radial gradients in the stellar populations when the E+A galaxy core is well resolved raises the possibility that spatial resolution issues may be important in interpreting the higher redshift results. The two early type E+A galaxies in our sample that can be robustly kinematically classified, using the LambdaR parameter, are fast-rotators. Combined with previous measurements, this brings the total number of E+A galaxies with measurements of LambdaR to twenty-six, with only four being classified as slow-rotators. This fraction is similar to the fraction of the early-type population as a whole and argues against the need for major mergers in the production of E+A galaxies, since major mergers should result in an increased fraction of slow rotators.

[21]
Title: Kepler Observations of Very Low-Mass Stars
Comments: Accepted for publication in Astronomy and Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Observations of very low-mass stars with Kepler represent an excellent opportunity to search for planetary transits and to characterize optical photometric variability at the cool end of the stellar mass distribution. In this paper, we present low-resolution red optical spectra that allow us to identify 18 very low-mass stars that have Kepler light curves available in the public archive. Spectral types of these targets are found to lie in the range dM4.5--dM8.5, implying spectrophotometric distances from 17 pc to 80 pc. Limits to the presence of transiting planets are placed from modelling of the Kepler light curves. We find that the size of the planets detectable by Kepler around these small stars typically lie in the range 1 to 5 Earth radii within the habitable regions (P$\le$10 days). We identify one candidate transit with a period of 1.26 days that resembles the signal produced by a planet slightly smaller than the Moon. However, our pixel by pixel analysis of the Kepler data shows that the signal most likely arises from a background contaminating eclipsing binary. For 11 of these objects reliable photometric periods shorter than 7 days are derived, and are interpreted as rotational modulation of magnetic cool spots. For 3 objects we find possible photometric periods longer than 50 days that require confirmation. H$_\alpha$ emission measurements and flare rates are used as a proxies for chromospheric activity and transversal velocities are used as an indicator of dynamical ages. These data allow us to discuss the relationship between magnetic activity and detectability of planetary transits around very low-mass stars. We show that Super-Earth planets with sizes around 2 Earth radii are detectable with Kepler around about two thirds of the stars in our sample, independently from their level of chromospheric activity.

[22]
Title: Gas kinematics and the Dragged Magnetic Field in the High-mass Molecular Outflow Source G192.16$-$3.84: An SMA View
Comments: 8 pages, 9 figures; ApJ accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

We report the Submillimeter Array (SMA) observations of the polarized 0.88\,mm thermal dust emission and various molecular line transitions toward the early B-type ($L_{*}\sim2\times10^{3}L_{\odot}$) star-forming region G192.16$-$3.84 (IRAS 05553+1631). The peak of the continuum Stokes-I emission coincides with a hot rotating disk/envelope (SO$_{2}$ rotational temperature T$_{rot}^{SO_{2}}$$\sim84^{+18}_{-13}$\,K), with a north-south velocity gradient. Joint analysis of the rotation curve traced by HCO$^{+}$ 4-3 and SO$_{2}$ 19$_{1,19}-18_{0,18}$ suggests that the dense molecular gas is undergoing a spinning-up rotation, marginally bound by the gravitational force of \textbf{an} enclosed mass $M_{*+gas+dust}\sim$11.2-25.2\,$M_{\odot}$. Perpendicular to the rotational plane a $\gtrsim100/\cos(i)$\,km\,s$^{-1}$ ($i\sim63^{\circ}$) high velocity molecular jet, and the $\sim$15-20\,km\,s$^{-1}$ expanding biconical cavity were revealed in the CO 3-2 emission. The polarization percentage of the 0.88\,mm continuum emission decreases toward the central rotating disk/envelope. The polarization angle in the inner $\sim2"$ (0.015\,pc) disk/envelope is perpendicular to the plane of the rotation. The magnetic field lines, which are predominantly in the toroidal direction along the disk plane, are likely to be dragged by the gravitationally accelerated rotation.

[23]
Title: On the magnetisation of gamma-ray burst blast waves
Authors: Martin Lemoine (IAP), Zhuo Li (PKU), Xiang-Yu Wang (NJU)
Comments: 7 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The origin of magnetic fields that permeate the blast waves of gamma-ray bursts is a long-standing problem. The present paper argues that in four GRBs revealing extended emission at >100 MeV, with follow-up in the radio, optical and X-ray domains at later times, this magnetisation can be described as the partial decay of the microturbulence that is generated in the shock precursor. Assuming that the extended high energy emission can be interpreted as synchrotron emission of shock accelerated electrons, we model the multi-wavelength light curves of GRB 090902B, GRB 090323, GRB 090328 and GRB 110731A, using a simplified then a full synchrotron calculation with power law decaying microturbulence \epsilon_B \propto t^{\alpha_t} (t denotes the time since injection through the shock, in the comoving blast frame). We find that these models point to a consistent value of the decay exponent -0.5 < \alpha_t < -0.4.

[24]
Title: Distances to Dwarf Galaxies of the Canes Venatici I Cloud
Comments: 18 pages, 7 figures, 2 tables; published in Astrophysical Bulletin, Volume 68, Issue 2, p.131 (2013)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We determined the spatial structure of the scattered concentration of galaxies in the Canes Venatici constellation. We redefined the distances for 30 galaxies of this region using the deep images from the Hubble Space Telescope archive with the WFPC2 and ACS cameras. We carried out a high-precision stellar photometry of the resolved stars in these galaxies, and determined the photometric distances by the tip of the red giant branch (TRGB) using an advanced technique and modern calibrations. High accuracy of the results allows us to distinguish the zone of chaotic motions around the center of the system. A group of galaxies around M94 is characterized by the median velocity VLG=287 km/s, distance D=4.28 Mpc, internal velocity dispersion sigma=51 km/s and total luminosity LB=1.61x10^10 Lo. The projection mass of the system amounts to Mp=2.56x10^12 Mo, which corresponds to the mass-luminosity ratio of (M/L)p=159 (M/L)o. The estimate of the mass-luminosity ratio is significantly higher than the typical ratio M/LB ~30 for the nearby groups of galaxies. The CVnI cloud of galaxies contains 4-5 times less luminous matter compared with the well-known nearby groups, like the Local Group, M81 and Centaurus A. The central galaxy M94 is at least 1 mag fainter than any other central galaxy of these groups. However, the concentration of galaxies in the Canes Venatici may have a comparable total mass.

[25]
Title: Quintessence with Hybrid Potential
Comments: 10 pages, 4 figures included
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

I present the numerical solution of equations of the evolution of a universe containing background fluids (radiation, dark matter and baryonic matter), plus a scalar matter field with a hybrid potential that is a combination of exponential potential and power-law potential. The plot of the evolution of density parameters is compatible with our universe; and today's values of density parameters of dark energy, dark matter, baryonic matter, and Hubble parameter, and the age and size of our universe, found from this model, are very close to (and some times the same as) measured values.

[26]
Title: Simulated Observations of Young Gravitationally Unstable Protoplanetary Discs
Comments: 12 pages, 15 figures, Accepted by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The formation and earliest stages of protoplanetary discs remain poorly constrained by observations. ALMA will soon revolutionise this field. Therefore, it is important to provide predictions which will be valuable for the interpretation of future high sensitivity and high angular resolution observations. Here we present simulated ALMA observations based on radiative transfer modelling of a relatively massive (0.39 M_solar) self-gravitating disc embedded in a 10 M_solar dense core, with structure similar to the pre-stellar core L1544. We focus on simple species and conclude that C17O 3-2, HCO+ 3-2, OCS 26-25 and H2CO 404-303 lines can be used to probe the disc structure and kinematics at all scales.

[27]
Title: Background simulations for the Large Area Detector onboard LOFT
Comments: 31 pages, 18 figures. Accepted for publication in Experimental Astronomy
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

The Large Observatory For X-ray Timing (LOFT), currently in an assessment phase in the framework the ESA M3 Cosmic Vision programme, is an innovative medium-class mission specifically designed to answer fundamental questions about the behaviour of matter, in the very strong gravitational and magnetic fields around compact objects and in supranuclear density conditions. Having an effective area of ~10 m^2 at 8 keV, LOFT will be able to measure with high sensitivity very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and optimize the design of its main instrument, the Large Area Detector (LAD). In this paper the results of an extensive Geant-4 simulation of the instrument will be discussed, showing the main contributions to the background and the design solutions for its reduction and control. Our results show that the current LOFT/LAD design is expected to meet its scientific requirement of a background rate equivalent to 10 mCrab in 2-30 keV, achieving about 5 mCrab in the most important 2-10 keV energy band. Moreover, simulations show an anticipated modulation of the background rate as small as 10% over the orbital timescale. The intrinsic photonic origin of the largest background component also allows for an efficient modelling, supported by an in-flight active monitoring, allowing to predict systematic residuals significantly better than the requirement of 1%, and actually meeting the 0.25% science goal.

[28]
Title: Lucky Imaging of transiting planet host stars with LuckyCam
Authors: F. Faedi (Warwick), T. Staley (Cambridge), Y.Gomez Maqueo Chew (Warwick/Vanderbilt), D. Pollacco (Warwick), S. Dhital (Vanderbilt), S. C. C. Barros (LAM Marseille), I. Skillen (ING), L. Hebb (Vanderbilt), C. Mackay (Cambridge), C. A. Watson (QUB)
Comments: 13 pages, 9 figures; Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We obtained high-resolution, high-contrast optical imaging in the SDSS $i'$ band with the LuckyCam camera mounted on the 2.56m Nordic Optical Telescope, to search for faint stellar companions to 16 stars harbouring transiting exoplanets. The Lucky Imaging technique uses very short exposures to obtain near diffraction-limited images yielding sub-arcsecond sensitivity, allowing us to search for faint stellar companions within the seeing disc of the primary planet host. Here we report the detection of two candidate stellar companions to the planet host TrES-1 at separations $<6.5\arcsec$ and we confirm stellar companions to CoRoT-2, CoRoT-3, TrES-2, TrES-4, and HAT-P-7 already known in the literature. We do not confirm the candidate companions to HAT-P-8 found via Lucky Imaging by \citet{Bergfors2013}, however, most probably because HAT-P-8 was observed in poor seeing conditions. Our detection sensitivity limits allow us to place constraints on the spectral types and masses of the putative bound companions to the planet host stars in our sample. If bound, the stellar companions identified in this work would provide stringent observational constraints to models of planet formation and evolution. In addition these companions could affect the derived physical properties of the exoplanets in these systems.

[29]
Title: Rapidly evaluating the compact binary likelihood function via interpolation
Comments: 5 pages, 1 figure
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Bayesian parameter estimation on gravitational waves from compact binary coalescences (CBCs) typically requires millions of template waveform computations at different values of the parameters describing the binary. Sampling techniques such as Markov chain Monte Carlo and nested sampling evaluate likelihoods, and hence compute template waveforms, serially; thus, the total computational time of the analysis scales linearly with that of template generation. Here we address the issue of rapidly computing the likelihood function of CBC sources with non-spinning components. We show how to efficiently compute the continuous likelihood function on the three-dimensional subspace of parameters on which it has a non-trivial dependence (the chirp mass, symmetric mass ratio and coalescence time) via interpolation. Subsequently, sampling this interpolated likelihood function is a significantly cheaper computational process than directly evaluating the likelihood; we report improvements in computational time of two to three orders of magnitude while keeping likelihoods accurate to < 0.025 %. Generating the interpolant of the likelihood function over a significant portion of the CBC mass space is computationally expensive but highly parallelizable, so the wall time can be very small relative to the time of a full parameter-estimation analysis.

[30]
Title: Explaining observations of rapidly rotating neutron stars in LMXBs
Comments: 29 pages, 8 figures, 1 table
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We introduce a new scenario that explains the existence of rapidly rotating warm neutron stars (NSs) observed in low-mass X-ray binaries (LMXBs). The scenario takes into account the interaction between the normal (quadrupole) m=2 r-mode and superfluid inertial modes. This interaction can only occur at some fixed resonance' stellar temperatures; it leads to formation of the stability peaks' that stabilize a star in the vicinity of these temperatures. We demonstrate that an NS in LMXB spends a substantial fraction of time on the stability peak, that is in the region of stellar temperatures and spin frequencies, that has been previously thought to be unstable with respect to excitation of r-modes. We also find that the spin frequencies of NSs are limited by the instability of normal (octupole) m=3 r-mode rather than by m=2 r-mode. This result agrees with the predicted value of the cut-off spin frequency ~730 Hz, following from the statistical analysis of the accreting millisecond X-ray pulsars. A comparison of the proposed theory with observations of rotating NSs can impose new important constraints on the properties of superdense matter.

[31]
Title: Unveiling a population of galaxies harboring low-mass black holes with X-rays
Comments: accepted for publication by The Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report the discovery of three low-mass black hole candidates residing in the centers of low-mass galaxies at z<0.3 in the Chandra Deep Field - South Survey. These black holes are initially identified as candidate active galactic nuclei based on their X-ray emission in deep Chandra observations. Multi-wavelength observations are used to strengthen our claim that such emission is powered by an accreting supermassive black hole. While the X-ray luminosities are low at L_X ~ 10^40 erg s^-1 (and variable in one case), we argue that they are unlikely to be attributed to star formation based on H\alpha or UV-fluxes. Optical spectroscopy with Keck/DEIMOS and VLT/FORS allows us to (1) measure accurate redshifts, (2) confirm their low stellar host mass, (3) investigate the source(s) of photo-ionization, and (4) estimate extinction. With stellar masses of M* < 3*10^9 M_\sun determined from HST/ACS imaging, the host galaxies are among the lowest mass systems known to host actively accreting black holes. We estimate BH masses M_BH ~ 2*10^5 M_\sun based on scaling relations between BH mass and host properties for more luminous systems. In one case, a broad component of the H\alpha emission-line profile is detected thus providing a virial mass estimate. Black holes in such low-mass galaxies are of considerable interest as the low-redshift analogs to the seeds of the most massive BHs at high redshift which have remained largely elusive to date. Our study highlights the power of deep X-ray surveys to uncover such low-mass systems.

[32]
Title: Morpho-Kinematical Modelling of Nova Eridani 2009 (KT Eri)
Authors: V. A. R. M. Ribeiro (1), M. F. Bode (2), M. J. Darnley (2), R. M. Barnsley (2), U. Munari (3 and 4), D. J. Harman (2) ((1) Astrophysics, Cosmology and Gravity Centre, Department of Astronomy, University of Cape Town, (2) Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead, CH41 1LD, UK, (3) INAF Astronomical Observatory of Padova, (4) ANS Collaboration)
Comments: 6 pages, 7 figures, 1 table, accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Modelling the morphology of a nova outburst provides valuable information on the shaping mechanism in operation at early stages following the outburst. We performed morpho-kinematical studies, using {\sc shape}, of the evolution of the H\alpha\ line profile following the outburst of the nova KT Eridani. We applied a series of geometries in order to determine the morphology of the system. The best fit morphology was that of a dumbbell structure with a ratio between the major to minor axis of 4:1, with an inclination angle of 58$^{+6}_{-7}$ degrees and a maximum expansion velocity of 2800$\pm$200 km/s. Although, we found that it is possible to define the overall structure of the system, the radial density profile of the ejecta is much more difficult to disentangle. Furthermore, morphology implied here may also be consistent with the presence of an evolved secondary as suggested by various authors.

[33]
Title: Topics in microphysics of relativistic plasmas
Authors: Maxim Lyutikov (Purdue University), Alexandre Lazarian (University of Wisconsin)
Comments: to be published in Space Science Reviews
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Astrophysical plasmas can have parameters vastly different from the more studied laboratory and space plasmas. In particular, the magnetic fields can be the dominant component of the plasma, with energy-density exceeding the particle rest-mass energy density. Magnetic fields then determine the plasma dynamical evolution, energy dissipation and acceleration of non-thermal particles. Recent data coming from astrophysical high energy missions, like magnetar bursts and Crab nebula flares, point to the importance of magnetic reconnection in these objects.
In this review we outline a broad spectrum of problems related to the astrophysical relevant processes in magnetically dominated relativistic plasmas. We discuss the problems of large scale dynamics of relativistic plasmas, relativistic reconnection and particle acceleration at reconnecting layers, turbulent cascade in force-fee plasmas. A number of astrophysical applications are also discussed.

[34]
Title: The effect of rotation and tidal heating on the thermal lightcurves of Super Mercuries
Comments: 15 pages, 13 figures, accepted for publication in Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Short period (<50 days) low-mass (<10Mearth) exoplanets are abundant and the few of them whose radius and mass have been measured already reveal a diversity in composition. Some of these exoplanets are found on eccentric orbits and are subjected to strong tides affecting their rotation and resulting in significant tidal heating. Within this population, some planets are likely to be depleted in volatiles and have no atmosphere. We model the thermal emission of these "Super Mercuries" to study the signatures of rotation and tidal dissipation on their infrared light curve. We compute the time-dependent temperature map at the surface and in the subsurface of the planet and the resulting disk-integrated emission spectrum received by a distant observer for any observation geometry. We calculate the illumination of the planetary surface for any Keplerian orbit and rotation. We include the internal tidal heat flow, vertical heat diffusion in the subsurface and generate synthetic light curves. We show that the different rotation periods predicted by tidal models (spin-orbit resonances, pseudo-synchronization) produce different photometric signatures, which are observable provided that the thermal inertia of the surface is high, like that of solid or melted rocks (but not regolith). Tidal dissipation can also directly affect the light curves and make the inference of the rotation more difficult or easier depending on the existence of hot spots on the surface. Infrared light curve measurement with the James Webb Space Telescope and EChO can be used to infer exoplanets' rotation periods and dissipation rates and thus to test tidal models. This data will also constrain the nature of the (sub)surface by constraining the thermal inertia.

[35]
Title: Saturnian mean motion resonances in meteoroid streams
Comments: 5 pages, 5 figures, 1 table, Accepted by MNRAS Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Many previous works have shown the relevance and dynamics of Jovian mean motion resonances (MMR) in various meteoroid streams. These resonant swarms are known to have produced spectacular meteor displays in the past. In this work we investigate whether any MMR due to Saturn are feasible, and subsequently check whether such effects are strong enough to trap meteoroids so as to cause enhanced meteor phenomena on Earth. Extensive numerical simulations are done on two major meteoroid streams, which are known to exhibit exterior Jovian resonances. The roles of the 1:6 and 5:14 Jovian MMR have already been studied in the Orionids and Leonids respectively. Now we find strong evidence of 1:3 and 8:9 Saturnian MMR in Orionids and Leonids respectively. The presence of compact dust trails in real space due to these two Saturnian resonances is confirmed from our calculations.

[36]
Title: Swinging between rotation and accretion power in a millisecond binary pulsar
Authors: A. Papitto (1), C. Ferrigno (2), E. Bozzo (2), N. Rea (1), L. Pavan (2), S. Campana (3), P. Romano (4), L. Burderi (5), T. Di Salvo (6), A. Riggio (5), D. F. Torres (1,7), M. Falanga (8), J. W. T. Hessels (9,10), M. Burgay (11), J. M. Sarkissian (12), M. H. Wieringa (12), M. D. Filipović (13), G. F. Wong (13) ((1) ICE, IEEC-CSIC Barcelona (2) ISDC Genève (3) INAF OA Brera (4) INAF OA Palermo (5) Univ. of Cagliari (6) Univ. of Palermo (7) ICREA Barcelona (8) ISSI Bern (9) ASTRON (10) Univ. of Amsterdam (11) INAF OA Cagliari (12) CSIRO (13) Univ. of Western Sidney)
Comments: 16 pages, 3 figures, 1 table. Submitted on 2013, May 1. Under refereeing
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)