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J.P. Magué & B. Ménard



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[1]  arXiv:1410.6155 [pdf, ps, other]
Title: Exceptional AGN-driven turbulence inhibits star formation in the 3C 326N radio-galaxy
Comments: Accepted for publication in A&A. 15 pages, 8 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We detect bright [CII]158$\mu$m line emission from the radio galaxy 3C 326N at z=0.09, which shows weak star formation ($SFR<0.07$M$_{\odot}$~yr$^{-1}$) despite having strong H$_2$ line emission and $2\times 10^9$M$_{\odot}$ of molecular gas. The [CII] line is twice as strong as the 0-0S(1) 17$\mu$m H$_2$ line, and both lines are much in excess what is expected from UV heating. We combine infrared Spitzer and Herschel data with gas and dust modeling to infer the gas physical conditions. The [CII] line traces 30 to 50% of the molecular gas mass, which is warm (70<T<100K) and at moderate densities $700<n_{H}<3000$cm$^{-3}$. The [CII] line is broad with a blue-shifted wing, and likely to be shaped by a combination of rotation, outflowing gas, and turbulence. It matches the near-infrared H$_2$ and the Na D optical absorption lines. If the wing is interpreted as an outflow, the mass loss rate would be larger than 20M$_{\odot}$/yr, and the depletion timescale shorter than the orbital timescale ($10^8$yr). These outflow rates may be over-estimated because the stochastic injection of turbulence on galactic scales can contribute to the skewness of the line profile and mimic outflowing gas. We argue that the dissipation of turbulence is the main heating process of this gas. Cosmic rays can also contribute to the heating but they require an average gas density larger than the observational constraints. We show that strong turbulent support maintains a high gas vertical scale height (0.3-4kpc) in the disk and can inhibit the formation of gravitationally-bound structures at all scales, offering a natural explanation for the weakness of star formation in 3C 326N. To conclude, the bright [CII] line indicates that strong AGN jet-driven turbulence may play a key role in enhancing the amount of molecular gas (positive feedback) but yet can prevent star formation on galactic scales (negative feedback).

[2]  arXiv:1410.6156 [pdf, other]
Title: Insights into gas heating and cooling in the disc of NGC 891 from Herschel far-infrared spectroscopy
Comments: Accepted for publication in A&A. 25 pages, including 17 figures and 3 tables, abstract abridged for arXiv
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby edge-on spiral galaxy, NGC 891: [CII] 158 $\mu$m, [NII] 122, 205 $\mu$m, [OI] 63, 145 $\mu$m, and [OIII] 88 $\mu$m. We find that the photoelectric heating efficiency of the gas, traced via the ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ ratio, varies from a mean of 3.5$\times$10$^{-3}$ in the centre up to 8$\times$10$^{-3}$ at increasing radial and vertical distances in the disc. A decrease in ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ but constant ([CII]+[OI]63)/$F_{\mathrm{PAH}}$ with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891's disc have hydrogen densities of 1 < log ($n$/cm$^{-3}$) < 3.5 experiencing an incident FUV radiation field with strengths of 1.7 < log $G_0$ < 3. Although these values we derive for most of the disc are consistent with the gas properties found in PDRs in the spiral arms and inter-arm regions of M51, observed radial trends in $n$ and $G_0$ are shown to be sensitive to varying optical thickness in the lines, demonstrating the importance of accurately accounting for optical depth effects when interpreting observations of high inclination systems. With an empirical relationship between the MIPS 24 $\mu$m and [NII] 205 $\mu$m emission, we estimate an enhancement of the FUV radiation field strength in the far north-eastern side of the disc.

[3]  arXiv:1410.6158 [pdf, other]
Title: The Survey of Lines in M31 (SLIM): Investigating the Origins of [CII] Emission
Comments: 19 pages, 9 figures, 5 tables, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The [CII] 158 micron line is one of the strongest emission lines observed in star-forming galaxies, and has been empirically measured to correlate with the star formation rate (SFR) globally and on ~kpc scales. However, due to the multi-phase origins of [CII], one might expect this relation to break down at small scales. We investigate the origins of [CII] emission by examining high spatial resolution observations of [CII] in M31, with the Survey of Lines in M31 (SLIM). We present five ~700x700 pc (3"x3") Fields mapping the [CII] emission, Halpha emission, combined with ancillary infrared (IR) data. We spatially separate star-forming regions from diffuse gas and dust emission on ~50 pc scales. We find that the [CII] - SFR correlation holds even at these scales, although the relation typically has a flatter slope than found at larger (~kpc) scales. While the Halpha emission in M31 is concentrated in the SFR regions, we find that a significant amount (~20-90%) of the [CII] emission comes from outside star-forming regions, and that the total IR (TIR) emission has the highest diffuse fraction of all SFR tracers. We find a weak correlation of the [CII]/TIR to dust color in each Field, and find a large scale trend of increasing [CII]/TIR with galactocentric radius. The differences in the relative diffuse fractions of [CII], Halpha and IR tracers are likely caused by a combination of energetic photon leakage from HII regions and heating by the diffuse radiation field arising from older (B-star) stellar populations. However, we find that by averaging our measurements over ~kpc scales, these effects are minimized, and the relation between [CII] and SFR found in other nearby galaxy studies is retrieved.

[4]  arXiv:1410.6159 [pdf, ps, other]
Title: HST Emission Line Galaxies at z ~ 2: The Mystery of Neon
Comments: 15 pages, 8 figures, accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use near-IR grism spectroscopy from the Hubble Space Telescope to examine the strength of [Ne~III] 3869 relative to H-beta, [O~II] 3727 and [O~III] 5007 in 236 low mass (7.5 < log (Mstar/Msolar) < 10.5) star-forming galaxies in the redshift range 1.90 < z < 2.35. By stacking the data by stellar mass, we show that the [Ne~III]/[O~II] ratios of the z ~ 2 universe are marginally higher than those seen in a comparable set of local SDSS galaxies, and that [Ne~III]/[O~III] is enhanced by ~0.2 dex. We consider the possible explanations for this ~4-sigma result, including higher oxygen depletion out of the gas-phase, denser H~II regions, higher production of Ne22 via Wolf-Rayet stars, and the existence of a larger population of X-ray obscured AGN at z ~ 2 compared to z ~ 0. None of these simple scenarios, alone, are favored to explain the observed line ratios. We conclude by suggesting several avenues of future observations to further explore the mystery of enhanced [Ne~III] emission.

[5]  arXiv:1410.6160 [pdf, other]
Title: What is the probability that direct detection experiments have observed Dark Matter?
Comments: 22 pages, 5 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

In Dark Matter direct detection we are facing the situation of some experiments reporting positive signals which are in conflict with limits from other experiments. Such conclusions are subject to large uncertainties introduced by the poorly known local Dark Matter distribution. We present a method to calculate an upper bound on the joint probability of obtaining the outcome of two potentially conflicting experiments under the assumption that the Dark Matter hypothesis is correct, but completely independent of assumptions about the Dark Matter distribution. In this way we can quantify the compatibility of two experiments in an astrophysics independent way. We illustrate our method by testing the compatibility of the hints reported by DAMA and CDMS-Si with the limits from the LUX and SuperCDMS experiments. The method does not require Monte Carlo simulations but is mostly based on using Poisson statistics. In order to deal with signals of few events we introduce the so-called "signal length" to take into account energy information without the need of binning data. The signal length method provides a simple way to calculate the probability to obtain a given experimental outcome under a specified Dark Matter and background hypothesis.

[6]  arXiv:1410.6161 [pdf, ps, other]
Title: Galactic Tides and the Shape and Orientation of Dwarf Galaxy Satellites
Comments: 16 pages, 13 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use cosmological N-body simulations from the Aquarius Project to study the tidal effects of a dark matter halo on the shape and orientation of its substructure. Although tides are often assumed to enhance asphericity and to stretch subhaloes tangentially, these effects are short lived: as in earlier work, we find that subhaloes affected by tides become substantially more spherical and show a strong radial alignment toward the centre of the host halo. These results, combined with a semi-analytic model of galaxy formation, may be used to assess the effect of Galactic tides on the observed population of dwarf spheroidal (dSph) satellites of the Milky Way and Andromeda galaxies. If, as the model suggests, the relatively low dark matter content of luminous dSphs such as Fornax and Leo I is due to tidal stripping, then their gravitational potential must be substantially more spherical than that of more heavily dark matter-dominated systems such as Draco or Carina. The model also predicts a tidally-induced statistical excess of satellites whose major axis aligns with the direction to the central galaxy. We find tantalizing evidence of this in the M31 satellite population, which suggests that tides may have played an important role in its evolution.

[7]  arXiv:1410.6166 [pdf, ps, other]
Title: Reconstructing the Accretion History of the Galactic Stellar Halo from Chemical Abundance Ratio Distributions
Comments: Article contains 18 pages total (16 pages of main text + 2 pages of Appendix) with 12 figures; article submitted to ApJ for publication
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Observational studies of halo stars during the last two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2-D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven "MW-like" halos to generate satellite template sets of 2-D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of $\sim10^{3-4}$ mock observations of stellar chemical abundance ratios ([$\alpha$/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs - precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide $\sim6-9$ dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history - and the luminosity function of infalling dwarf galaxies - across cosmic time.

[8]  arXiv:1410.6168 [pdf, other]
Title: Discovery of a New Galactic Center Excess Consistent with Upscattered Starlight
Comments: 5 pages, 3 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

We present a new extended gamma ray excess toward the Galactic Center that traces the 3.4 micron infrared emission morphology. Combined with its measured spectrum, this new extended source is consistent with inverse Compton emission from a high-energy electron-positron population with energies up to about 10 GeV. Previously detected emissions tracing the 20 cm radio, interpreted as bremsstrahlung radiation, and the Galactic Center Extended emission tracing a spherical distribution and peaking at 2 GeV, are also detected. We show that the inverse Compton and bremsstrahlung emissions are likely due to the same source of electrons and positrons. All three extended emissions may be explained within the framework of a model where the dark matter annihilates to leptons or a model with unresolved millisecond pulsars in the Galactic Center.

[9]  arXiv:1410.6169 [pdf, ps, other]
Title: Early flattening of dark matter cusps in dwarf spheroidal galaxies
Authors: Carlo Nipoti (1), James Binney (2) ((1) Bologna University, (2) Oxford University)
Comments: 9 pages, 3 figures, MNRAS in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Simulations of the clustering of cold dark matter yield dark-matter halos that have central density cusps, but observations of totally dark-matter dominated dwarf spheroidal galaxies imply that they do not have cuspy central density profiles. We use analytic calculations and numerical modelling to argue that whenever stars form, central density cusps are likely to be erased. Gas that accumulates in the potential well of an initially cuspy dark-matter halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clouds are massive enough to transfer energy to the dark-matter particles via dynamical friction on a short time-scale. The halo's central cusp is heated to form a core with central logarithmic density slope gamma=0 before stellar feedback makes its impact. Since star formation is an inefficient process, the clouds are disrupted by feedback when only a small fraction of their mass has been converted to stars, and the dark matter dominates the final mass distribution.

[10]  arXiv:1410.6170 [pdf, ps, other]
Title: The G+M eclipsing binary V530 Orionis: A stringent test of magnetic stellar evolution models for low-mass stars
Authors: G. Torres (1), C. H. Sandberg Lacy (2), K. Pavlovski (3), G. A. Feiden (4), J. A. Sabby (5), H. Bruntt (6), J. V. Clausen (7) ((1) CfA, (2) Univ. of Arkansas, (3) Univ. of Zagreb, (4) Uppsala Univ., (5) Southern Illinois Univ., (6) Aarhus Univ., (7) Niels Bohr Inst.)
Comments: 17 pages in emulateapj format, including figures and tables. To appear in The Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report extensive photometric and spectroscopic observations of the 6.1-day period, G+M-type detached double-lined eclipsing binary V530 Ori, an important new benchmark system for testing stellar evolution models for low-mass stars. We determine accurate masses and radii for the components with errors of 0.7% and 1.3%, as follows: M(A) = 1.0038 +/- 0.0066 M(sun), M(B) = 0.5955 +/- 0.0022 M(sun), R(A) = 0.980 +/- 0.013 R(sun), and R(B) = 0.5873 +/- 0.0067 R(sun). The effective temperatures are 5890 +/- 100 K (G1V) and 3880 +/- 120 K (M1V), respectively. A detailed chemical analysis probing more than 20 elements in the primary spectrum shows the system to have a slightly subsolar abundance, with [Fe/H] = -0.12 +/- 0.08. A comparison with theory reveals that standard models underpredict the radius and overpredict the temperature of the secondary, as has been found previously for other M dwarfs. On the other hand, models from the Dartmouth series incorporating magnetic fields are able to match the observations of the secondary star at the same age as the primary (3 Gyr) with a surface field strength of 2.1 +/- 0.4 kG when using a rotational dynamo prescription, or 1.3 +/- 0.4 kG with a turbulent dynamo approach, not far from our empirical estimate for this star of 0.83 +/- 0.65 kG. The observations are most consistent with magnetic fields playing only a small role in changing the global properties of the primary. The V530 Ori system thus provides an important demonstration that recent advances in modeling appear to be on the right track to explain the long-standing problem of radius inflation and temperature suppression in low-mass stars.

[11]  arXiv:1410.6171 [pdf, ps, other]
Title: Suzaku Monitoring of Hard X-ray Emission from Eta Carinae over a Single Binary Orbital Cycle
Comments: 19 pages, 6 figures
Journal-ref: Astrophysical Journal, 2014, 795, 119
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

The Suzaku X-ray observatory monitored the supermassive binary system Eta Carinae 10 times during the whole 5.5 year orbital cycle between 2005-2011. This series of observations presents the first long-term monitoring of this enigmatic system in the extremely hard X-ray band between 15-40 keV. During most of the orbit, the 15-25 keV emission varied similarly to the 2-10 keV emission, indicating an origin in the hard energy tail of the kT ~4 keV wind-wind collision (WWC) plasma. However, the 15-25 keV emission declined only by a factor of 3 around periastron when the 2-10 keV emission dropped by two orders of magnitude due probably to an eclipse of the WWC plasma. The observed minimum in the 15-25 keV emission occurred after the 2-10 keV flux had already recovered by a factor of ~3. This may mean that the WWC activity was strong, but hidden behind the thick primary stellar wind during the eclipse. The 25-40 keV flux was rather constant through the orbital cycle, at the level measured with INTEGRAL in 2004. This result may suggest a connection of this flux component to the gamma-ray source detected in this field. The Helium-like Fe Kalpha line complex at ~6.7 keV became strongly distorted toward periastron as seen in the previous cycle. The 5-9 keV spectra can be reproduced well with a two-component spectral model, which includes plasma in collision equilibrium (CE) and a plasma in non-equilibrium ionization (NEI) with tau ~1e11 cm-3 s-1. The NEI plasma increases in importance toward periastron.

[12]  arXiv:1410.6175 [pdf, ps, other]
Title: Instability of Magnetized Ionization Fronts Surrounding H II Regions
Authors: Jeong-Gyu Kim, Woong-Tae Kim (Seoul National University, Korea)
Comments: 35 pages, 6 figures; Accepted for publication in the ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

An ionization front (IF) surrounding an H II region is a sharp interface where a cold neutral gas makes transition to a warm ionized phase by absorbing UV photons from central stars. We investigate the instability of a plane-parallel D-type IF threaded by parallel magnetic fields, by neglecting the effects of recombination within the ionized gas. We find that weak D-type IFs always have the post-IF magnetosonic Mach number $\mathcal{M}_{\rm M2} \leq 1$. For such fronts, magnetic fields increase the maximum propagation speed of the IFs, while reducing the expansion factor $\alpha$ by a factor of $1+1/(2\beta_1)$ compared to the unmagnetized case, with $\beta_1$ denoting the plasma beta in the pre-IF region. IFs become unstable to distortional perturbations due to gas expansion across the fronts, exactly analogous to the Darrieus-Landau instability of ablation fronts in terrestrial flames. The growth rate of the IF instability is proportional linearly to the perturbation wavenumber as well as the upstream flow speed, and approximately to $\alpha^{1/2}$. The IF instability is stabilized by gas compressibility and becomes completely quenched when the front is D-critical. The instability is also stabilized by magnetic pressure when the perturbations propagate in the direction perpendicular to the fields. When the perturbations propagate in the direction parallel to the fields, on the other hand, it is magnetic tension that reduces the growth rate, completely suppressing the instability when $\mathcal{M}_{\rm M2}^2 < 2/(\beta_1 - 1)$. When the front experiences an acceleration, the IF instability cooperates with the Rayleigh-Taylor instability to make the front more unstable.

[13]  arXiv:1410.6187 [pdf, ps, other]
Title: Whistler mode waves and the electron heat flux in the solar wind: Cluster observations
Comments: The Astrophysical Journal, 2014, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)

The nature of the magnetic field fluctuations in the solar wind between the ion and electron scales is still under debate. Using the Cluster/STAFF instrument, we make a survey of the power spectral density and of the polarization of these fluctuations at frequencies $f\in[1,400]$ Hz, during five years (2001-2005), when Cluster was in the free solar wind. In $\sim 10\%$ of the selected data, we observe narrow-band, right-handed, circularly polarized fluctuations, with wave vectors quasi-parallel to the mean magnetic field, superimposed on the spectrum of the permanent background turbulence. We interpret these coherent fluctuations as whistler mode waves. The life time of these waves varies between a few seconds and several hours. Here we present, for the first time, an analysis of long-lived whistler waves, i.e. lasting more than five minutes. We find several necessary (but not sufficient) conditions for the observation of whistler waves, mainly a low level of the background turbulence, a slow wind, a relatively large electron heat flux and a low electron collision frequency. When the electron parallel beta factor $\beta_{e\parallel}$ is larger than 3, the whistler waves are seen along the heat flux threshold of the whistler heat flux instability. The presence of such whistler waves confirms that the whistler heat flux instability contributes to the regulation of the solar wind heat flux, at least for $\beta_{e\parallel} \ge$ 3, in the slow wind, at 1 AU.

[14]  arXiv:1410.6196 [pdf, other]
Title: On the Anisotropic Nature of MRI-Driven Turbulence in Astrophysical Disks
Authors: Gareth C. Murphy, Martin E. Pessah (Niels Bohr Institute)
Comments: 13 pages, 13 figures, submitted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The magnetorotational instability is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is related to both the strength of the amplitudes of the fluctuations on various scales and the degree of anisotropy of the underlying turbulence. This has motivated several studies of the distribution of turbulent power in spectral space. In this paper, we investigate the anisotropic nature of MRI-driven turbulence using a pseudo-spectral code and introduce novel ways to robustly characterize the underlying turbulence. We show that the general flow properties vary in a quasi-periodic way on timescales comparable to 10 inverse angular frequencies motivating the temporal analysis of its anisotropy. We introduce a 3D tensor invariant analysis to quantify and classify the evolution of the anisotropic turbulent flow. This analysis shows a continuous high level of anisotropy, with brief sporadic transitions towards two- and three-component isotropic turbulent flow. This temporal-dependent anisotropy renders standard shell-average, especially when used simultaneously with long temporal averages, inadequate for characterizing MRI-driven turbulence. We propose an alternative way to extract spectral information from the turbulent magnetized flow, whose anisotropic character depends strongly on time. This consists of stacking 1D Fourier spectra along three orthogonal directions that exhibit maximum anisotropy in Fourier space. The resulting averaged spectra show that the power along each of the three independent directions differs by several orders of magnitude over most scales, except the largest ones. Our results suggest that a first-principles theory to describe fully developed MRI-driven turbulence will likely have to consider the anisotropic nature of the flow at a fundamental level.

[15]  arXiv:1410.6212 [pdf, ps, other]
Title: Sample of optically unidentified X-ray binaries in the Galactic bulge. Constraints on the physical nature from infrared photometric surveys
Authors: Ivan Zolotukhin (1, 2), Mikhail Revnivtsev (3) ((1) CNRS, IRAP, Toulouse, France, (2) Sternberg Astronomical Institute, Moscow, Russia, (3) IKI, Moscow, Russia)
Comments: 11 pages, 5 figures, accepted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report on the archival near-infrared and mid-infrared observations of 7 persistent X-ray sources situated in the Galactic bulge using data from the UKIRT Infrared Deep Sky Survey (UKIDSS), Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and the Wide-field Infrared Survey Explorer (WISE) all-sky survey. We were able to successfully identify, or provide upper flux limits for the systems SAX J1747.0-2853, IGR J17464-2811, AX J1754.2-2754, IGR J17597-2201, IGR J18134-1636, IGR J18256-1035, Ser X-1 and constrain the nature of these systems. In the case of IGR J17597-2201 we present arguments that the source accretes matter from the stellar wind rather than via Roche lobe overflow of the secondary. We suggest that, at its X-ray luminosity of $10^{34-35}$ erg s$^{-1}$, we are probing the poorly known class of wind-fed low-mass X-ray binaries (LMXBs).

[16]  arXiv:1410.6224 [pdf, other]
Title: First detection of surface magnetic fields in Post-AGB stars : the cases of U Monocerotis and R Scuti
Comments: 11 pages, 4 figures and 4 tables. Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

While several observational investigations have revealed the presence of magnetic fields in the circumstellar envelopes, jets and outflows of post-Asymptotic Giant Branch stars (PAGBs) and planetary nebulae (PNe), none has clearly demonstrated their presence at the stellar surface. The lack of information on the strength of the surface magnetic fields prevents us from performing any thorough assessment of their dynamic capability (i.e. material mixing, envelope shaping, etc). We present new high resolution spectropolarimetric (Stokes V ) observations of a sample of PAGB stars, realised with the instruments ESPaDOnS and Narval, where we searched for the presence of photospheric magnetic fields. Out of the seven targets investigated the RV Tauri stars U Mon and R Sct display a clear Zeeman signature and return a definite detection after performing a least squares deconvolution (LSD) analysis. The remaining five PAGBs show no significant detection. We derived longitudinal magnetic fields of 10.2 +/- 1.7 G for U Mon and 0.6 +/- 0.6 G for R Sct. In both cases the Stokes profiles point towards an interaction of the magnetic field with the atmosphere dynamics. This first discovery of weak magnetic fields (i.e. ~10 gauss level) at the stellar surface of PAGB stars opens the door to a better understanding of magnetism in evolved stars.

[17]  arXiv:1410.6241 [pdf, ps, other]
Title: The Narrow Line Region in 3D: mapping AGN feeding and feedback
Comments: 6 pages, 4 figures. To appear in IAU Symposium No. 309, "Galaxies in 3D across the Universe", B. L. Ziegler, F. Combes, H. Dannerbauer, M. Verdugo, Eds. (Cambridge: Cambridge Univ. Press)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Early studies of nearby Seyfert galaxies have led to the picture that the Narrow Line Region (NLR) is a cone-shaped region of gas ionized by radiation from a nuclear source collimated by a dusty torus, where the gas is in outflow. In this contribution, I discuss a 3D view of the NLR obtained via Integral Field Spectroscopy, showing that: (1) although the region of highest emission is elongated (and in some cases cone-shaped), there is also lower level emission beyond the "ionization cone", indicating that the AGN radiation leaks through the torus; (2) besides outflows, the gas kinematics include also rotation in the galaxy plane and inflows; (3) in many cases the outflows are compact and restricted to the inner few 100pc; we argue that these may be early stages of an outflow that will evolve to an open-ended, cone-like one. Inflows are observed in ionized gas in LINERs, and in warm molecular gas in more luminous AGN, being usually found on hundred of pc scales. Mass outflow rates in ionized gas are of the order of a few solar masses per year, while the mass inflow rates are of the order of tenths of solar masses per year. Mass inflow rates in warm molecular gas are ~4-5 orders of magnitude lower, but these inflows seem to be only tracers of more massive inflows in cold molecular gas that should be observable at mm wavelengths.

[18]  arXiv:1410.6244 [pdf, ps, other]
Title: L'-band AGPM vector vortex coronagraph's first light on LBTI/LMIRCam
Comments: 9 pages, 4 figures, SPIE proceedings
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present the first observations obtained with the L'-band AGPM vortex coronagraph recently installed on LBTI/LMIRCam. The AGPM (Annular Groove Phase Mask) is a vector vortex coronagraph made from diamond subwavelength gratings. It is designed to improve the sensitivity and dynamic range of high-resolution imaging at very small inner working angles, down to 0.09 arcseconds in the case of LBTI/LMIRCam in the L' band. During the first hours on sky, we observed the young A5V star HR\,8799 with the goal to demonstrate the AGPM performance and assess its relevance for the ongoing LBTI planet survey (LEECH). Preliminary analyses of the data reveal the four known planets clearly at high SNR and provide unprecedented sensitivity limits in the inner planetary system (down to the diffraction limit of 0.09 arcseconds).

[19]  arXiv:1410.6245 [pdf]
Title: MAXI: all-sky observation from the International Space Station
Comments: 6 pages, 7 figures, SPIE Astronomical Telescopes and Instrumentation
Journal-ref: Proceedings of the SPIE, Volume 9144, id. 91441O (2014)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Monitor of All-sky X-ray Image (MAXI) is mounted on the International Space Station (ISS). Since 2009 it has been scanning the whole sky in every 92 minutes with ISS rotation. Due to high particle background at high latitude regions the carbon anodes of three GSC cameras were broken. We limit the GSC operation to low-latitude region around equator. GSC is suffering a double high background from Gamma-ray altimeter of Soyuz spacecraft. MAXI issued the 37-month catalog with 500 sources above ~0.6 mCrab in 4-10 keV. MAXI issued 133 to Astronomers Telegram and 44 to Gammaray burst Coordinated Network so far. One GSC camera had a small gas leak by a micrometeorite. Since 2013 June, the 1.4 atm Xe pressure went down to 0.6 atm in 2014 May 23. By gradually reducing the high voltage we keep using the proportional counter. SSC with X-ray CCD has detected diffuse soft X-rays in the all-sky, such as Cygnus super bubble and north polar spur, as well as it found a fast soft X-ray nova MAXI J0158-744. Although we operate CCD with charge-injection, the energy resolution is degrading. In the 4.5 years of operation MAXI discovered 6 of 12 new black holes. The long-term behaviors of these sources can be classified into two types of the outbursts, 3 Fast Rise Exponential Decay (FRED) and 3 Fast Rise and Flat Top (FRFT). The cause of types is still unknown.

[20]  arXiv:1410.6280 [pdf, ps, other]
Title: B-mode in CMB polarization. What's that and why it is interesting
Authors: A.D. Dolgov
Comments: 9 pages, 4 figures; Invited talk at the XXX Int. Workshop on HIgh Energy Physics "Particle and Astroparticle Physics, Gravitation and Cosmology:Predictions, Observations and New Projects. Protvino, June, 23-27, 2014
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Generation of the B-mode of CMB polarization by background of relic gravitational wave is discussed in connection with the BICEP2 measurements. Description of the polarization maps in terms of the eigenvectors of the polarization matrix is considered.

[21]  arXiv:1410.6281 [pdf, other]
Title: Area and Flux Distributions of Active Regions, Sunspot Groups, and Sunspots: A Multi-Database Study
Comments: Accepted for publication in the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this work we take advantage of eleven different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are better fitted by different distributions (as has been reported previously in the literature). However, we find that all our databases can be reconciled by the simple application of a proportionality constant, and that, in reality, different databases are sampling different parts of a composite distribution. This composite distribution is made up by linear combination of Weibull and log-normal distributions -- where a pure Weibull (log-normal) characterizes the distribution of structures with fluxes below (above) $10^{21}$Mx ($10^{22}$Mx). Additionally, we demonstrate that the Weibull distribution shows the expected linear behaviour of a power-law distribution (when extended into smaller fluxes), making our results compatible with the results of Parnell et al.\ (2009).

[22]  arXiv:1410.6283 [pdf, ps, other]
Title: Oscillation modes in the rapidly rotating Slowly Pulsating B-type star $\bmu$ Eridani
Comments: accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present results of a search for identification of modes responsible for the six most significant frequency peaks detected in the rapidly rotating SPB star $\mu$ Eridani. All published and some unpublished photometric data are used in our new analysis. The mode identification is carried out with the method developed by Daszy\'nska-Daszkiewicz et al. employing the phases and amplitudes from multi-band photometric data and relying on the traditional approximation for the treatment of oscillations in rotating stars.
Models consistent with the observed mean parameters are considered. For the five frequency peaks, the candidates for the identifications are searched amongst unstable modes. In the case of the third frequency, which is an exact multiple of the orbital frequency, this condition is relaxed. The systematic search is continued up to a harmonic degree $\ell =6$.
Determination of the angular numbers, $(\ell,m)$, is done simultaneously with the rotation rate, $V_{\rm rot}$, and the inclination angle, $i$, constrained by the spectroscopic data on the projected rotational velocity, $V_{\rm rot}\sin i$, which is assumed constant. All the peaks may be accounted for with g-modes of high radial orders and the degrees $\ell\le 6$. There are differences in some identifications between the models. For the two lowest--amplitude peaks the identifications are not unique. Nonetheless, the equatorial velocity is constrained to a narrow range of (135, 140) km/s.
Our work presents the first application of the photometric method of mode identification in the framework of the traditional approximation and we believe that it opens a new promising direction in studies of SPB stars.

[23]  arXiv:1410.6291 [pdf, ps, other]
Title: Globular Cluster Systems in Brightest Cluster Galaxies: A Near-Universal Luminosity Function?
Comments: To appear in Astrophysical Journal, December 2014
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the first results from our HST Brightest Cluster Galaxy (BCG) survey of seven central supergiant cluster galaxies and their globular cluster (GC) systems. We measure a total of 48000 GCs in all seven galaxies, representing the largest single GC database. We find that a log-normal shape accurately matches the observed luminosity function (LF) of the GCs down to the GCLF turnover point, which is near our photometric limit. In addition, the LF has a virtually identical shape in all seven galaxies. Our data underscore the similarity in the formation mechanism of massive star clusters in diverse galactic environments. At the highest luminosities (log L > 10^7 L_Sun) we find small numbers of "superluminous" objects in five of the galaxies; their luminosity and color ranges are at least partly consistent with those of UCDs (Ultra-Compact Dwarfs). Lastly, we find preliminary evidence that in the outer halo (R > 20 kpc), the LF turnover point shows a weak dependence on projected distance, scaling as L_0 ~ R^-0.2, while the LF dispersion remains nearly constant.

[24]  arXiv:1410.6307 [pdf, ps, other]
Title: Flipping minor bodies: what comet 96P/Machholz 1 can tell us about the orbital evolution of extreme trans-Neptunian objects and the production of near-Earth objects on retrograde orbits
Comments: 9 pages, 8 figures, 1 table. Accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Nearly all known extreme trans-Neptunian objects (ETNOs) have argument of perihelion close to 0 degrees. An existing observational bias strongly favours the detection of ETNOs with arguments of perihelion close to 0 degrees and 180 degrees yet no objects have been found at 180 degrees. No plausible explanation has been offered so far to account for this unusual pattern. Here, we study the dynamical evolution of comet 96P/Machholz 1, a bizarre near-Earth object (NEO) that may provide the key to explain the puzzling clustering of orbits around argument of perihelion close to 0 degrees recently found for the population of ETNOs. Comet 96P/Machholz 1 is currently locked in a Kozai resonance with Jupiter such that the value of its argument of perihelion is always close to 0 degrees at its shortest possible perihelion (highest eccentricity and lowest inclination) and about 180 degrees near its shortest aphelion (longest perihelion distance, lowest eccentricity and highest inclination). If this object is a dynamical analogue (albeit limited) of the known ETNOs, this implies that massive perturbers must keep them confined in orbital parameter space. Besides, its future dynamical evolution displays orbital flips when its eccentricity is excited to a high value and its orbit turns over by nearly 180 degrees, rolling over its major axis. This unusual behaviour, that is preserved when post-Newtonian terms are included in the numerical integrations, may also help understand the production of NEOs on retrograde orbits.

[25]  arXiv:1410.6322 [pdf, ps, other]
Title: The almost ubiquitous association of 6.7 GHz methanol masers with dust
Authors: J. S. Urquhart (1), T. J. T. Moore (2), K. M. Menten (1), C. König (1), F. Wyrowski (1), M. A. Thompson (3), T. Csengeri (1), S. Leurini (1), D. J. Eden (2,4) ((1) MPIfR, (2) Liverpool John Moores, (3) University of Hertfordshire, (4) Observatoire astronomique de Strasbourg)
Comments: Accepted by MNRAS. 17 pages, 17 figures and 5 tables. The full version of Figs. 3 and 5 are only available in electronic form of the journal while the full versions of Tables 1, 2 and 4 will only be available through CDS. A complete version of the paper is available on request
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report the results of 870-$\mu$m continuum observations, using the Large APEX Bolometer Camera (LABOCA), towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol Multibeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with compact dense clumps identified from the ATLASGAL survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99% for the full MMB catalogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find median clump masses of a few 10$^3$ M$\odot$ and that all but a handful of sources satisfy the mass-size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ~2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump-formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.

[26]  arXiv:1410.6329 [pdf, ps, other]
Title: Extended HCN and HCO$^{+}$ emission in the starburst galaxy M82
Comments: 10 pages, 6 figures, 5 tables. Accepted for publication in the ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We mapped 3 mm continuum and line emission from the starburst galaxy M82 using the Combined Array for Research in Millimeter-wave Astronomy. We targeted the HCN, HCO$^{+}$, HNC, CS and HC$_{3}$N lines, but here we focus on the HCN and HCO$^{+}$ emission. The map covers a field of 1.2' with a ~5" resolution. The HCN and HCO$^{+}$ observations are combined with single dish images. The molecular gas in M82 had been previously found to be distributed in a molecular disk, coincident with the central starburst, and a galactic scale outflow which originates in the central starburst. With the new short spacings-corrected maps we derive some of the properties of the dense molecular gas in the base of the outflow. From the HCN and HCO$^{+}$ J=(1-0) line emission, and under the assumptions of the gas being optically thin and in local thermodynamic equilibrium, we place lower limits to the amount of dense molecular gas in the base of the outflow. The lower limits are $7\times10^{6}$ $M_{\odot}$ and $21\times10^{6}$ $M_{\odot}$, or $\gtrsim2\%$ of the total molecular mass in the outflow. The kinematics and spatial distribution of the dense gas outside the central starburst suggests that it is being expelled through chimneys. Assuming a constant outflow velocity, the derived outflow rate of dense molecular gas is $\geq0.3$ $M_{\odot}$ yr$^{-1}$, which would lower the starburst lifetime by $\geq5\%$. The energy required to expel this mass of dense gas is $(1-10)\times10^{52}$ erg.

[27]  arXiv:1410.6332 [pdf, ps, other]
Title: Consistent neutron star models with magnetic field dependent equations of state
Comments: 13 pages, 8 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)

We present a self-consistent model for the study of the structure of a neutron star in strong magnetic fields. Starting from a microscopic Lagrangian, this model includes the effect of the magnetic field on the equation of state, the interaction of the electromagnetic field with matter (magnetisation), and anisotropies in the energy-momentum tensor, as well as general relativistic aspects. We build numerical axisymmetric stationary models and show the applicability of the approach with one example quark matter equation of state (EoS) often employed in the recent literature for studies of strongly magnetised neutron stars. For this EoS, the effect of inclusion of magnetic field dependence or the magnetisation do not increase the maximum mass significantly in contrast to what has been claimed by previous studies.

[28]  arXiv:1410.6334 [pdf, other]
Title: Is PLANCK consistent with primordial deuterium measurements ?
Comments: 10 pages, 7 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The recent measurements of the Cosmic Microwave Background Anisotropies provided by the Planck satellite experiment have significantly improved the constraints on several cosmological parameters. In this brief paper we point out a small but interesting tension present between recent values of the primordial deuterium measured from quasar absorption line systems and the same value inferred, albeit indirectly, from the Planck measurements assuming {\Lambda}CDM and Big Bang Nucleosynthesis. Here we discuss this tension in detail investigating the possible new physics that could be responsible for the tension. We found that, among 8 extra parameters, only an anomalous lensing component and a closed universe could change the Planck constraint towards a better consistency with direct deuterium measurements.

[29]  arXiv:1410.6343 [pdf, other]
Title: Pore evolution in interstellar ice analogues: simulating the effects of temperature increase
Comments: 9 pages, 8 figures Accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Context. The level of porosity of interstellar ices - largely comprised of amorphous solid water (ASW) - contains clues on the trapping capacity of other volatile species and determines the surface accessibility that is needed for solid state reactions to take place. Aims. Our goal is to simulate the growth of amorphous water ice at low temperature (10 K) and to characterize the evolution of the porosity (and the specific surface area) as a function of temperature (from 10 to 120 K). Methods. Kinetic Monte Carlo simulations are used to mimic the formation and the thermal evolution of pores in amorphous water ice. We follow the accretion of gas-phase water molecules as well as their migration on surfaces with different grid sizes, both at the top growing layer and within the bulk. Results. We show that the porosity characteristics change substantially in water ice as the temperature increases. The total surface of the pores decreases strongly while the total volume decreases only slightly for higher temperatures. This will decrease the overall reaction efficiency, but in parallel, small pores connect and merge, allowing trapped molecules to meet and react within the pores network, providing a pathway to increase the reaction efficiency. We introduce pore coalescence as a new solid state process that may boost the solid state formation of new molecules in space and has not been considered so far.

[30]  arXiv:1410.6358 [pdf, ps, other]
Title: Three WASP-South transiting exoplanets: WASP-74b, WASP-83b & WASP-89b
Comments: Submitted to AJ, 12 pages
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We report the discovery of three new transiting hot Jupiters by WASP-South together with the TRAPPIST photometer and the Euler/CORALIE spectrograph.
WASP-74b orbits a star of V = 9.7, making it one of the brighter systems accessible to Southern telescopes. It is a 0.95 M_Jup planet with a moderately bloated radius of 1.5 R_Jup in a 2-d orbit around a slightly evolved F9 star.
WASP-83b is a Saturn-mass planet at 0.3 M_Jup with a radius of 1.0 R_Jup. It is in a 5-d orbit around a fainter (V = 12.9) G8 star.
WASP-89b is a 6 M_Jup planet in a 3-d orbit with an eccentricity of e = 0.2. It is thus similar to massive, eccentric planets such as XO-3b and HAT-P-2b, except that those planets orbit F stars whereas WASP-89 is a K star. The V = 13.1 host star is magnetically active, showing a rotation period of 20.2 d, while star spots are visible in the transits. There are indications that the planet's orbit is aligned with the stellar spin. WASP-89 is a good target for an extensive study of transits of star spots.

[31]  arXiv:1410.6365 [pdf, other]
Title: Constraining the shaping mechanism of the Red Rectangle through spectro-polarimetry of its central star
Comments: accepted in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We carried out high-sensitivity spectropolarimetric observations of the central star of the Red Rectangle proto-planetary nebula with the aim of constraining the mechanism that gives its biconical shape. The stellar light of the central binary system is linearly polarised since it is scattered on the dust particles of the nebula. Surprisingly, the linear polarisation in the continuum is aligned with one of the spikes of the biconical outflow. Also, the observed Balmer lines as well as the Ca II K lines are polarised. These observational constraints are used to confirm or reject current theoretical models for the shaping mechanism of the Red Rectangle. We propose that the observed polarisation is very unlikely generated by a uniform biconical stellar wind. Also, the hypothesis of a precessing jet does not completely match the observations since it will require a jet aperture larger than that of the nebula.

[32]  arXiv:1410.6366 [pdf, ps, other]
Title: Chemical modeling of water deuteration in IRAS16293-2422
Comments: 20 pages, 15 figures. This version is slightly different from the published one because of language editor's modifications
Journal-ref: Monthly Notices of the Royal Astronomical Society 2014 445 (1)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

IRAS 16293-2422 is a well studied low-mass protostar characterized by a strong level of deuterium fractionation. In the line of sight of the protostellar envelope, an additional absorption layer, rich in singly and doubly deuterated water has been discovered by a detailed multiline analysis of HDO. To model the chemistry in this source, the gas-grain chemical code Nautilus has been used with an extended deuterium network. For the protostellar envelope, we solve the chemical reaction network in infalling fluid parcels in a protostellar core model. For the foreground cloud, we explored several physical conditions (density, cosmic ionization rate, C/O ratio). The main results of the paper are that gas-phase abundances of H2O, HDO and D2O observed in the inner regions of IRAS16293-2422 are lower than those predicted by a 1D dynamical/chemical (hot corino) model in which the ices are fully evaporated. The abundance in the outer part of the envelope present chaotic profiles due to adsorption/evaporation competition, very different from the constant abundance assumed for the analysis of the observations. We also found that the large abundances of gas-phase H2O, HDO and D2O observed in the absorption layer are more likely explained by exothermic surface reactions rather than photodesorption processes.

[33]  arXiv:1410.6368 [pdf, other]
Title: Discovery of a stellar tidal stream around the Whale galaxy, NGC 4631
Authors: David Martinez-Delgado (ARI, Heidelberg), Elena D'Onghia (Univ. Wisconsin), Taylor S. Chonis (Univ. Texas, Austin), Rachael L. Beaton (OCI, Pasadena), Karel Teuwen (ROSA Observatory), R. Jay GaBany (Black Bird Observatory II), Eva K. Grebel (ARI, Heidelberg), Gustavo Morales (ARI, Heidelberg)
Comments: 8 pages, 5 figures.Submitted to The Astronomical Journal. A high resolution version of the paper is available from the following link: this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report the discovery of a giant stellar tidal stream in the halo of NGC 4631, a nearby edge-on spiral galaxy interacting with the spiral NGC 4656, in deep images taken with a 40-cm aperture robotic telescope. The stream has two components: a bridge-like feature extended between NGC 4631 and NGC 4656 (stream_SE) and an overdensity with extended features on the opposite side of the NGC 4631 disk (stream_NW). Together, these features extend more than 85 kpc and display a clear (g-r) colour gradient. The orientation of stream_SE relative to the orientations of NGC 4631 and NGC 4656 is not consistent with an origin from interaction between these two spirals, and is more likely debris from a satellite encounter. The stellar tidal features can be qualitatively reproduced in an N-body model of the tidal disruption of a single, massive dwarf satellite on a moderately eccentric orbit (e=0.6) around NGC 4631 over $\sim$ 3.5 Gyr, with a dynamical mass ratio (m1:m2) of ~40. Both modelling and inferences from the morphology of the streams indicate these are not associated with the complex HI tidal features observed between both spirals, which likely originate from a more recent, gas-rich accretion event. The detailed structure of stream_NW suggests it may contain the progenitor of the stream, in agreement with the N-body model. In addition, stream_NW is roughly aligned with two very faint dwarf spheroidal candidates. The system of dwarf galaxies and the tidal stream around NGC 4631 can provide an additional interesting case for exploring the anisotropy distribution of satellite galaxies recently reported in Local Group spiral galaxies by means of future follow-up observations.

[34]  arXiv:1410.6379 [pdf, other]
Title: The K2-TESS Stellar Properties Catalog
Authors: Keivan G. Stassun (1,2), Joshua A. Pepper (3,1), Martin Paegert (1), Nathan De Lee (4,1), Roberto Sanchis-Ojeda (5), ((1) Vanderbilt University, (2) Fisk University, (3) Lehigh University, (4) University of Northern Kentucky, (5) MIT)
Comments: 7 pages, 3 figures. This brief report is provided for the community on arxiv only
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

We introduce a catalog of stellar properties for stars observed by the Kepler follow-on mission, K2. We base the catalog on a cross-match between the K2 Campaign target lists and the current working version of the NASA TESS target catalog. The resulting K2-TESS Stellar Properties Catalog includes value-added information from the TESS Target Catalog, including stellar colors, proper motions, and an estimated luminosity class (dwarf/subgiant versus giant) for each star based on a reduced-proper-motion criterion. Also included is the Guest Observer program identification number(s) associated with each K2 target. The K2-TESS Stellar Properties Catalog is available to the community as a freely accessible data portal on the Filtergraph system at: this http URL .

[35]  arXiv:1410.6391 [pdf, ps, other]
Title: Multiwavelength observations of Mrk 501 in 2008
Comments: Accepted for publication in A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. Our goal is to characterize in detail the source gamma-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE gamma-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity.

[36]  arXiv:1410.6411 [pdf, other]
Title: On Magnetic Activity Band Overlap, Interaction, and the Formation of Complex Solar Active Regions
Comments: 14 pages, 5 figures, accepted to appear in ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); Popular Physics (physics.pop-ph)

Recent work has revealed an phenomenological picture of the how the $\sim$11-year sunspot cycle of Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22-year magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle we anticipate that those complex active regions may be particular susceptible to profoundly catastrophic breakdown---producing flares and coronal mass ejections of most severe magnitude.

[37]  arXiv:1410.6415 [pdf, ps, other]
Title: The Gaia-ESO Survey: α-abundances of metal-poor stars
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We performed a detailed study of the ratio of low-{\alpha} to high-{\alpha} stars in the Galactic halo as observed by the Gaia-ESO Survey. Using a sample of 381 metal-poor stars from the second internal data release, we found that the value of this ratio did not show evidence of systematic trends as a function of metallicity, surface gravity, Galactic latitude, Galactic longitude, height above the Galactic plane, and Galactocentric radius. We conclude that the {\alpha}-poor/{\alpha}-rich value of 0.28 $\pm$ 0.08 suggests that in the inner halo, the larger portion of stars were formed in a high star formation rate environment, and about 15% of the metal-poor stars originated from much lower star formation rate environments.

[38]  arXiv:1410.6422 [pdf, ps, other]
Title: Stellar parameters and chemical abundances of 223 evolved stars with and without planets
Comments: 49 pages, 31 figures, Accepted for publication in A&A, abstract shortened
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~ 0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 Msun. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a $\lesssim$ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a $\lesssim$ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M < 1.5 Msun, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs.

[39]  arXiv:1410.6428 [pdf, other]
Title: Star formation around the mid-infrared bubble CN 148
Comments: 20 pages, 10 figures, 3 tables. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a multi-wavelength study to analyse the star formation process associated with the mid-infrared bubble CN 148 (H II region G10.3-0.1), which harbors an O5V-O6V star. The arc-shaped distribution of molecular CO(2-1) emission, the cold dust emission, and the polycyclic aromatic hydrocarbon features trace a photodissociation region (PDR) around the H II region. We have identified 371 young stellar objects (YSOs) in the selected region and, interestingly, their spatial distribution correlates well with the PDR. 41% of these YSOs are present in 13 clusters, each having visual extinction larger than 16 mag. The clusters at the edges of the bubble (both northeast and southwest) are found to be relatively younger than the clusters located further away from the bubble. We also find that four 6.7 GHz methanol masers, two Extended Green Objects, an ultra-compact H II region, and a massive protostar candidate (as previously reported) are spatially positioned at the edges of the bubble. The existence of an apparent age gradient in YSO clusters and different early evolutionary stages of massive star formation around the bubble suggest their origin to be influenced by an H II region expanding into the surrounding interstellar medium. The data sets are suggestive of triggered star formation.

[40]  arXiv:1410.6435 [pdf, ps, other]
Title: Ultraluminous Infrared Galaxies in the AKARI All Sky Survey
Comments: 31 pages, 19 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a new catalog of 118 Ultraluminous Infrared Galaxies (ULIRGs) and one Hyperluminous Infrared Galaxy (HLIRG) by crossmatching AKARI all-sky survey with the Sloan Digital Sky Survey Data Release 10 (SDSS DR10) and the Final Data Release of the Two-Degree Field Galaxy Redshift Survey (2dFGRS). 40 of the ULIRGs and one HLIRG are new identifications. We find that ULIRGs are interacting pair galaxies or ongoing/post mergers. This is consistent with the widely accepted view: ULIRGs are major mergers of disk galaxies. We confirm the previously known positive trend between the AGN fraction and IR luminosity. We show that ULIRGs have a large off-set from the 'main sequence' up to z~1; their off-set from the z~2 'main sequence' is relatively smaller. We find a consistent result with the previous studies showing that compared to local star forming SDSS galaxies of similar mass, local ULIRGs have lower oxygen abundances. We for the first time demonstrate that ULIRGs follow the fundamental metallicity relation (FMR). The scatter of ULIRGs around the FMR (0.09 dex - 0.5 dex) is comparable with the scatter of z~2-3 galaxies. Their optical colors show that ULIRGs are mostly blue galaxies and this agrees with previous findings. We provide the largest local (0.050 < z < 0.487) ULIRG catalog with stellar masses, SFRs, gas metallicities and optical colors. Our catalog provides us active galaxies analogous to high-z galaxies in the local Universe where they can be rigorously scrutinized.

[41]  arXiv:1410.6441 [pdf, ps, other]
Title: Searching for A Generic Gravitational Wave Background via Bayesian Nonparametric Analysis with Pulsar Timing Arrays
Authors: Xihao Deng
Comments: Accepted for publication in Physical Review D. arXiv admin note: text overlap with arXiv:1404.0663
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Gravitational wave background results from the superposition of gravitational waves generated from all sources across the Universe. Previous efforts on detecting such a background with pulsar timing arrays assume it is an isotropic Gaussian background with a power law spectrum. However, when the number of sources is limited, the background might be non-Gaussian or the spectrum might not be a power law. Correspondingly previous analysis may not work effectively. Here we use a method --- Bayesian Nonparametric Analysis --- to try to detect a generic gravitational wave background, which directly sets constraints on the feasible shapes of the pulsar timing signals induced by a gravitational wave background and allows more flexible forms of the background. Our Bayesian nonparametric analysis will infer if a gravitational wave background is present in the data, and also estimate the parameters that characterize the background. This method will be much more effective than the conventional one assuming the background spectrum follows a power law in general cases. While the context of our discussion focuses on pulsar timing arrays, the analysis itself is directly applicable to detect and characterize any signals that arise from the superposition of a large number of astrophysical events.

[42]  arXiv:1410.6446 [pdf, ps, other]
Title: A revised upper limit to energy extraction from a Kerr black hole
Comments: submitted to PRL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

We present a new upper limit on the energy that may be extracted from a Kerr black hole by means of particle collisions in the ergosphere (i.e., the "Penrose process"). Earlier work on this subject has focused largely on particles with critical values of angular momentum falling into an extremal Kerr black hole from infinity and colliding just outside the horizon. While these collisions are able to reach arbitrarily high center-of-mass energies, it is very difficult for the reaction products to escape back to infinity, effectively limiting the peak efficiency of such a process to roughly $130\%$. When we allow one of the initial particles to have $\ell > 2M$, and thus not get captured by the horizon, it is able to collide along outgoing trajectories, greatly increasing the chance that the products can escape. For equal-mass particles annihilating to photons, we find a greatly increased peak energy of $E_{\rm out} \approx 6\times E_{\rm in}$. For Compton scattering, the efficiency can go even higher, with $E_{\rm out} \approx 14\times E_{\rm in}$, and for repeated scattering events, photons can both be produced $and$ escape to infinity with Planck-scale energies.

[43]  arXiv:1410.6462 [pdf, ps, other]
Title: The Contribution of Millisecond Pulsars to the Galactic Cosmic-Ray Lepton Spectrum
Comments: 19 pages, 3 figures, submitted to Advances in Space Research
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Pulsars are believed to be sources of relativistic electrons and positrons. The abundance of detections of gamma-ray millisecond pulsars by Fermi Large Area Telescope coupled with their light curve characteristics that imply copious pair production in their magnetospheres, motivated us to investigate this old pulsar population as a source of Galactic electrons and positrons and their contribution to the enhancement in cosmic-ray positron flux at GeV energies. We use a population synthesis code to predict the source properties (number, position, and power) of the present-day Galactic millisecond pulsars, taking into account the latest Fermi and radio observations to calibrate the model output. Next, we simulate pair cascade spectra from these pulsars using a model that invokes an offset-dipole magnetic field. We assume free escape of the pairs from the pulsar environment. We then compute the cumulative spectrum of transported electrons and positrons at Earth, following their diffusion and energy losses as they propagate through the Galaxy. Our results indicate that the predicted particle flux increases for non-zero offsets of the magnetic polar caps. Comparing our predicted spectrum and positron fraction to measurements by AMS-02, PAMELA, and Fermi, we find that millisecond pulsars are only modest contributors at a few tens of GeV, after which this leptonic spectral component cuts off. The positron fraction is therefore only slightly enhanced above 10 GeV relative to a background flux model. This implies that alternative sources such as young, nearby pulsars and supernova remnants should contribute additional primary positrons within the astrophysical scenario.

[44]  arXiv:1410.6463 [pdf, ps, other]
Title: Probing the Structure of the Accretion Region in a Sample of Magnetic Herbig Ae/Be Stars
Comments: 8 pages, 5 figures, to appear in the proceedings of the conference "Physics and Evolution of Magnetic and Related Stars"
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the results of a study of the temporal behaviour of several diagnostic lines formed in the region of the accretion-disk/star interaction in the three magnetic Herbig Ae stars HD101412, HD104237, and HD190073. More than 100 spectra acquired with the ISAAC, X-shooter, and CRIRES spectrographs installed at the VLT-8m telescope (ESO, Chile), as well as at other observatories (OHP, Crimean AO) were analyzed. The spectroscopic data were obtained in the He I lambda10830, Pa gamma and He I lambda5876 lines. We found that the temporal behaviour of the diagnostic lines in the spectra of all program stars can be widely explained by a rotational modulation of the line profiles generated by a local accretion flow. This result is in good agreement with the predictions of the magnetospheric accretion model. For the first time, the rotation period of HD104237 (P_rot = 5.37+-0.03 days), as well as the inclination angle (i = 21+-4deg) were determined. Additional analysis of the HARPSpol spectra of HD104237 and HD190073, taken from the ESO archive, with the use of the SVD method shows that the magnetic field structure of HD190073 is likely more complex than a simple dipole and contains a circumstellar component. For the first time, the magnetic field of the secondary component of the binary system HD104237 was also detected (<B_z> = 128+-10G).

[45]  arXiv:1410.6465 [pdf, other]
Title: Particle acceleration at a reconnecting magnetic separator
Comments: 17 pages, 12 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph)

While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. The effect upon particle behaviour of initial position, pitch angle and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains several free parameters and we study the effect of changing these parameters upon particle acceleration, in particular in view of the final particle energy ranges which agree with observed energy spectra.

[46]  arXiv:1410.6473 [pdf, ps, other]
Title: OGLE-2013-SN-079: a lonely supernova consistent with a helium shell detonation
Comments: ApJ Letter submitted. 8 pages, 3 figures. Comments are welcome
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of z=0.07 implies an absolute magnitude in the rest-frame I-band of M$_{I}\sim-17.6$ mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths <5000 \AA. To date, this is the only reported SN showing Ti-dominated spectra. Our multi band and bolometric lightcurves, as well as the spectral evolution, are in reasonable agreement with the predictions of models for the pure detonation of a helium shell around a low-mass CO white dwarf and "double-detonation" models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.