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[1]  arXiv:1705.08452 [pdf, ps, other]
Title: Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-Phase Metallicity Gradients : The Effects of Ram Pressure Stripping
Comments: 17 pages, 21 figures, accepted for publication ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Recent observations of galaxies in a cluster at z=0.35 show that their integrated gas-phase metallicities increase with decreasing cluster-centric distance. To test if ram pressure stripping (RPS) is the underlying cause, we use a semi-analytic model to quantify the "observational bias" that RPS introduces into the aperture-based metallicity measurements. We take integral field spectroscopy of local galaxies, remove gas from their outer galactic disks via RPS, and then conduct mock slit observations of cluster galaxies at z=0.35. Our RPS model predicts a typical cluster-scale metallicity gradient of -0.03 dex/Mpc. By removing gas from the outer galactic disks, RPS introduces a mean metallicity enhancement of +0.02 dex at a fixed stellar mass. This gas removal and subsequent quenching of star formation preferentially removes low mass cluster galaxies from the observed star-forming population. As only the more massive star-forming galaxies survive to reach the cluster core, RPS produces a cluster-scale stellar mass gradient of -0.05 log(M_*/M_sun)/Mpc. This mass segregation drives the predicted cluster-scale metallicity gradient of -0.03 dex/Mpc. However, the effects of RPS alone can not explain the higher metallicities measured in cluster galaxies at z=0.35. We hypothesize that additional mechanisms including steep internal metallicity gradients and self-enrichment due to gas strangulation are needed to reproduce our observations at z=0.35.

[2]  arXiv:1705.08454 [pdf, other]
Title: Comparing Neutron Star Kicks to Supernova Remnant Asymmetries
Authors: Tyler Holland-Ashford (OSU), Laura A. Lopez (OSU), Katie Auchettl (OSU), Tea Temim (STScI), Enrico Ramirez-Ruiz (UCSC)
Comments: 17 pages, 6 figures, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Supernova explosions are inherently asymmetric and can accelerate new-born neutron stars (NSs) to hundreds of km/s. Two prevailing theories to explain NS kicks are ejecta asymmetries (e.g., conservation of momentum between NS and ejecta) and anisotropic neutrino emission. Observations of supernova remnants (SNRs) can give us insights into the mechanism that generates these NS kicks. In this paper, we investigate the relationship between NS kick velocities and the X-ray morphologies of 18 SNRs observed with the Chandra X-ray Observatory and the Rontgen Satellite (ROSAT). We measure SNR asymmetries using the power-ratio method (a multipole expansion technique), focusing on the dipole, quadrupole, and octupole power-ratios. Our results show no correlation between the magnitude of the power-ratios and NS kick velocities, but we find that for Cas A and G292.0+1.8, whose emission traces the ejecta distribution, their NSs are preferentially moving opposite to the bulk of the X-ray emission. In addition, we find a similar result for PKS 1209-51, CTB 109, and Puppis A; however their emission is dominated by circumstellar/interstellar material, so their asymmetries may not reflect their ejecta distributions. Our results are consistent with the theory that NS kicks are a consequence of ejecta asymmetries as opposed to anisotropic neutrino emission. In the future, additional observations to measure NS proper motions within ejecta-dominated SNRs are necessary to constrain robustly the NS kick mechanism.

[3]  arXiv:1705.08455 [pdf, other]
Title: A Reverse Shock and Unusual Radio Properties in GRB 160625B
Comments: 16 pages, 8 figures, 3 tables. Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present multi-wavelength observations and modeling of the exceptionally bright long $\gamma$-ray burst GRB 160625B. The optical and X-ray data are well-fit by synchrotron emission from a collimated blastwave with an opening angle of $\theta_j\approx 3.6^\circ$ and kinetic energy of $E_K\approx 2\times10^{51}$ erg, propagating into a low density ($n\approx 5\times10^{-5}$ cm$^{-3}$) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of $\Gamma_0\gtrsim 100$ and an ejecta magnetization of $R_B\approx 1-100$. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

[4]  arXiv:1705.08456 [pdf, ps, other]
Title: Shell-crossing in quasi one-dimensional flow
Comments: 9 pages, to be submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Blow-up of solutions for the cosmological fluid equations, often dubbed shell-crossing or orbit crossing, denotes the breakdown of the single-stream regime of the cold-dark-matter fluid. At this instant, the velocity becomes multi-valued and the density singular. Shell-crossing is well understood in one dimension (1D), but not in higher dimensions. This paper is about quasi-one-dimensional (Q1D) flow that depends on all three coordinates but differs only slightly from a strictly 1D flow, thereby allowing a perturbative treatment of shell-crossing using the Euler--Poisson equations written in Lagrangian coordinates. The signature of shell-crossing is then just the vanishing of the Jacobian of the Lagrangian map, a regular perturbation problem. In essence the problem of the first shell-crossing, which is highly singular in Eulerian coordinates, has been desingularized by switching to Lagrangian coordinates, and can then be handled by perturbation theory. Here, all-order recursion relations are obtained for the time-Taylor coefficients of the displacement field, and it is shown that the Taylor series has an infinite radius of convergence. This allows the determination of the time and location of the first shell-crossing, which is generically shown to be taking place earlier than for the unperturbed 1D flow.
The time variable used for these statements is not the cosmic time $t$ but the linear growth time $\tau \sim t^{2/3}$. For simplicity, calculations are restricted to an Einstein--de Sitter universe in the Newtonian approximation, and tailored initial data are used. However it is straightforward to relax these limitations, if needed.

[5]  arXiv:1705.08457 [pdf, other]
Title: Episodic mass ejections from common-envelope objects
Comments: 24 pages, 15 figures. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, published by Oxford University Press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

After the initial fast spiral-in phase experienced by a common-envelope binary, the system may enter a slow, self-regulated phase, possibly lasting 100s of years, in which all the energy released by orbital decay can be efficiently transported to the surface, where it is radiated away. If the remaining envelope is to be removed during this phase, this removal must occur through some as-yet-undetermined mechanism. We carried out 1-d hydrodynamic simulations of a low-mass red giant undergoing a synthetic common-envelope event in such a slow spiral-in phase, using the stellar evolutionary code MESA. We simulated the heating of the envelope due to frictional dissipation from a binary companion's orbit in multiple configurations and investigated the response of the giant's envelope. We find that our model envelopes become dynamically unstable and develop large-amplitude pulsations, with periods in the range 3-20 years and very short growth time-scales of similar order. The shocks and associated rebounds that emerge as these pulsations grow are in some cases strong enough to dynamically eject shells of matter of up to 0.1 $\mathrm{M}_{\odot}$, $\sim 10$ % of the mass of the envelope, from the stellar surface at above escape velocity. These ejections are seen to repeat within a few decades, leading to a time-averaged mass-loss rate of order $10^{-3}$ $\mathrm{M}_{\odot} \: \mathrm{yr}^{-1}$ which is sufficiently high to represent a candidate mechanism for removing the entire envelope over the duration of the slow spiral-in phase.

[6]  arXiv:1705.08458 [pdf, ps, other]
Title: Halo Histories vs. Galaxy Properties at z=0, III: The Properties of Star-Forming Galaxies
Comments: 13 pages, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We measure how the properties of star-forming central galaxies correlate with large-scale environment, $\delta$, measured on $10$Mpc/h scales. We use group catalogs to isolate a robust sample of central galaxies with high purity and completeness. The properties we investigate are star formation rate (SFR), exponential disk scale length $R_{\rm exp}$, and Sersic index of the light profile, $n$. We find that, at all stellar masses, there is an inverse correlation between SFR and $\delta$, meaning that above-average star forming centrals live in underdense regions. For $n$ and $R_{\rm exp}$, there is no correlation with $\delta$ at $M_{\rm star}\lesssim 10^{10.5}$ $M_\odot$, but at higher masses there are positive correlations; a weak correlation with $R_{\rm exp}$ and a strong correlation with $n$. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, $\dot{M}_h$. In this model, galaxies are assigned to halos using the abundance matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is assigned to galaxies using the same approach,but $\dot{M}_h$ is used to map onto SFR. The best-fit model requires some scatter in the $\dot{M}_h$-SFR relation. The $R_{\rm exp}$ and $n$ measurements are consistent with a model in which these quantities are correlated with the spin parameter of the halo, $\lambda$. Halo spin does not correlate with $\delta$ at low halo masses, but for higher mass halos, high-spin halos live in higher density environments at fixed $M_h$. Put together with the earlier installments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed properties, are influenced by the details of halo assembly.

[7]  arXiv:1705.08468 [pdf]
Title: Carbon Monoxide Affecting Planetary Atmospheric Chemistry
Comments: 5 figures. Accepted in Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

CO is an important component in many N2/CH4 atmospheres including Titan, Triton, and Pluto, and has also been detected in the atmosphere of a number of exoplanets. Numerous experimental simulations have been carried out in the laboratory to understand the chemistry in N2/CH4 atmospheres, but very few simulations have included CO in the initial gas mixtures. The effect of CO on the chemistry occurring in these atmospheres is still poorly understood. We have investigated the effect of CO on both gas and solid phase chemistry in a series of planetary atmosphere simulation experiments using gas mixtures of CO, CH4, and N2 with a range of CO mixing ratios from 0.05% to 5% at low temperature (~100 K). We find that CO affects the gas phase chemistry, the density, and the composition of the solids. Specifically, with the increase of CO in the initial gases, there is less H2 but more H2O, HCN, C2H5N/HCNO and CO2 produced in the gas phase, while the density, oxygen content, and degree of unsaturation of the solids increase. The results indicate that CO has an important impact on the chemistry occurring in our experiments and accordingly in planetary atmospheres.

[8]  arXiv:1705.08470 [pdf, other]
Title: An upper limit on the mass of the circumplanetary disk for DH Tau b
Comments: accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

DH Tau is a young ($\sim$1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious H${\alpha}$ emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of $17.2\pm1.7\,M_{\oplus}$, which gives a disk-to-star mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42$M_{\oplus}$ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model including heating of the circumplanetary disk by DH Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09$M_{\oplus}$ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.

[9]  arXiv:1705.08476 [pdf, ps, other]
Title: Galactic Sources Detected in the NuSTAR Serendipitous Survey
Authors: John A. Tomsick (SSL/UCB), George B. Lansbury (Cambridge), Farid Rahoui (Harvard), Maica Clavel (SSL/UCB), Francesca M. Fornasini (Harvard-Smithsonian CfA), JaeSub Hong (Harvard-Smithsonian CfA), James Aird (Cambridge), David M. Alexander (Univ. of Durham), Arash Bodaghee (Georgia College), Jeng-Lun Chiu (SSL/UCB), Jonathan E. Grindlay (Harvard-Smithsonian CfA), Charles J. Hailey (Columbia), Fiona A. Harrison (Caltech), Roman A. Krivonos (Space Research Institute, Russian Academy of Sceinces), Kaya Mori (Columbia), Daniel Stern (JPL)
Comments: 16 pages, accepted by ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The Nuclear Spectroscopic Telescope Array (NuSTAR) provides an improvement in sensitivity at energies above 10 keV by two orders of magnitude over non-focusing satellites, making it possible to probe deeper into the Galaxy and Universe. Lansbury and collaborators recently completed a catalog of 497 sources serendipitously detected in the 3-24 keV band using 13 deg2 of NuSTAR coverage. Here, we report on an optical and X-ray study of 16 Galactic sources in the catalog. We identify eight of them as stars (but some or all could have binary companions), and use information from Gaia to report distances and X-ray luminosities for three of them. There are four CVs or CV candidates, and we argue that NuSTAR J233426-2343.9 is a relatively strong CV candidate based partly on an X-ray spectrum from XMM-Newton. NuSTAR J092418-3142.2, which is the brightest serendipitous source in the Lansbury catalog, and NuSTAR J073959-3147.8 are LMXB candidates, but it is also possible that these two sources are CVs. One of the sources is a known HMXB, and NuSTAR J105008-5958.8 is a new HMXB candidate, which has strong Balmer emission lines in its optical spectrum and a hard X-ray spectrum. We discuss the implications of finding these HMXBs for the surface density (logN-logS) and luminosity function of Galactic HMXBs. We conclude that, with the large fraction of unclassified sources in the Galactic plane detected by NuSTAR in the 8-24 keV band, there could be a significant population of low luminosity HMXBs.

[10]  arXiv:1705.08497 [pdf, other]
Title: Discovery of Galactic OIV and OV X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum
Comments: Accepted for publication in Astronomy and Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)

FUV observations have revealed the transition temperature gas (TTG; $\log{T({\mathrm{K}})}$ ~ 5), located in the lower Galactic halo and in the High Velocity Clouds. However, the corresponding X-ray absorption has so far remained mostly undetected. In order to make an improvement in this respect in Galactic X-ray absorption studies, we accumulated very deep (~3 Ms) spectra of the blazar PKS 2155-304 obtained with the spectrometers RGS1, RGS2, LETG/HRC and LETG/ACIS-S and studied the absorption lines due to the intervening Galactic components. The very high quality of the data and the coverage of important wavelengths with at least two independent instruments allowed us to reliably detect ten Galactic lines with better than 99.95% confidence. We discovered significant absorption from blended OIV transitions 1s-2p $^2$S (22.571 \AA ), 1s-2p $^2$P (22.741 \AA ) and 1s-2p $^2$D (22.777 \AA ), and from the OV transition 1s-2p (22.370 \AA ) from TTG at $\log{T({\mathrm{K}})} \thinspace = \thinspace 5.2\pm0.1$. A joint X-ray and FUV analysis indicated that photoionisation is negligible for this component and that the gas is in a cooling transition phase. However, the temperature is high enough that the column density ratio N(OIV)/N(OV) is not significantly different from that in collisional ionisation equilibrium (CIE). Under CIE we obtained $N_{\mathrm{OIV}}$= 3.6$\pm$2.0 $\times 10^{15}$ cm$^{-2}$, corresponding to $N_{\mathrm{H}}$ = 1.0$\pm$0.5 $\times 10^{19} \frac{Z_{\odot}}{Z_{\mathrm{TTG}}}$ cm$^{-2}$.

[11]  arXiv:1705.08512 [pdf]
Title: Low ionospheric reactions on tropical depressions prior hurricanes
Comments: accepted in Advances in Space Research
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We study the reactions of the low ionosphere during tropical depressions (TDs) which have been detected before the hurricane appearances in the Atlantic Ocean. We explore 41 TD events using very low frequency (VLF) radio signals emitted by NAA transmitter located in the USA and recorded by VLF receiver located in Belgrade (Serbia). We found VLF signal deviations (caused ionospheric turbulence) in the case of 36 out of 41 TD events (88%). Additionally, we explore 27 TDs which have not been developed in hurricanes and found similar low ionospheric reactions. However, in the sample of 41 TDs which are followed by hurricanes the typical low ionosphere perturbations seem to be more frequent than other TDs.

[12]  arXiv:1705.08513 [pdf, other]
Title: Extensive Globular Cluster Systems Associated with Ultra Diffuse Galaxies in the Coma Cluster
Comments: Submitted to ApJ Letters. The black and white panels of Figure 1 make the key point of the paper, hopefully
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present Hubble Space Telescope imaging of two ultra diffuse galaxies (UDGs) with measured stellar velocity dispersions in the Coma cluster. The galaxies, Dragonfly 44 and DFX1, have effective radii of 4.7 kpc and 3.5 kpc and velocity dispersions of $47^{+8}_{-6}$ km/s and $30^{+7}_{-7}$ km/s, respectively. Both galaxies are associated with a striking number of compact objects, tentatively identified as globular clusters: $N_{\rm gc}=74\pm 18$ for Dragonfly 44 and $N_{\rm gc}=62\pm 17$ for DFX1. The number of globular clusters is far higher than expected from the luminosities of the galaxies but is consistent with expectations from the empirical relation between dynamical mass and globular cluster count defined by other galaxies. Combining our data for these two objects with previous HST observations of Coma UDGs we find that most have large globular cluster populations for their luminosities, in contrast to a recent study of a similar sample by Amorisco et al. (2017), but consistent with earlier results for individual galaxies. The Harris et al. (2017) relation between globular cluster count and dark matter halo mass implies a median halo mass of $M_{\rm halo}\sim 1.5\times 10^{11}\,{\rm M}_{\odot}$ for the sixteen Coma UDGs that have been observed with HST so far, with the largest and brightest having $M_{\rm halo}\sim 5\times 10^{11}\,{\rm M}_{\odot}$.

[13]  arXiv:1705.08531 [pdf, other]
Title: Properties of the Intergalactic Magnetic Field Constrained by Gamma-ray Observations of Gamma-Ray Bursts
Comments: 8 pages, 6 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The magnetic field in intergalactic space gives important information about magnetogenesis in the early universe. The properties of this field can be probed by searching for radiation of secondary e$^+ $e$^-$ pairs created by TeV photons, that produce GeV range radiation by Compton-scattering cosmic microwave background (CMB) photons. The arrival times of the GeV "echo" photons depend strongly on the magnetic field strength and coherence length. A Monte Carlo code that accurately treats pair creation is developed to simulate the spectrum and time-dependence of the echo radiation. The extrapolation of the spectrum of powerful gamma-ray bursts (GRBs) like GRB 130427A to TeV energies is used to demonstrate how the IGMF can be constrained if it falls in the $10^{-21}$ - $10^{-17}$ G range for 1 Mpc coherence length.

[14]  arXiv:1705.08537 [pdf, ps, other]
Title: The first Baade-Wesselink analysis of Blazhko RR Lyrae stars: discrepancies between photometrically and spectroscopically determined radius variations
Authors: J. Jurcsik, G. Hajdu
Comments: 9 pages, 6 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Society
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The simultaneous photometric and spectroscopic observations of the RR Lyrae variables in the globular cluster, M3, published in Jurcsik et al. (2017, Paper I) made it possible to perform Baade-Wesselink (BW) analysis of a large sample of Blazhko stars for the first time. The BW distances of Blazhko stars turned out to be unreliable, as significantly different distances were obtained for the stars of the Blazhko sample and also for the same star in different modulation phases. Even the results of small modulation-amplitude Blazhko stars may be doubtful. This result warns that the application of the BW method to Blazhko stars is not trustworthy.
Keeping the distance fixed for each Blazhko star in each modulation phase, a significant difference between the spectroscopic and the photometric radius ($R_{\textrm{sp}}$, $R_{\textrm{ph}}$) variations is detected. The phase and amplitude variations of $R_{\textrm{sp}}$ follow the changes of the light curve during the Blazhko cycle but the $R_{\textrm{ph}}$ curve seems to be not (or only marginally) affected by the modulation. The asynchronous behaviour of $R_{\textrm{sp}}$ and $R_{\textrm{ph}}$ supports the interpretation of the Blazhko effect as a depth-dependent phenomenon, as the spectroscopic radius variation reflects the radial displacement of the line-forming region high in the atmosphere, while the photospheric radius variation is derived from the information of the observed visual-band light emitted mostly by the lower photosphere. The stability of $R_{\textrm{ph}}$ may be interpreted as a strong argument against the non-radial-mode explanation of the Blazhko phenomenon.

[15]  arXiv:1705.08543 [pdf, ps, other]
Title: Observing Pulsars with a Phased Array Feed at the Parkes Telescope
Comments: 10 pages, 8 figures, 2 tables. It has been accepted for publication in PASA
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

During February 2016, CSIRO Astronomy and Space Science and the Max-Planck-Institute for Radio Astronomy installed, commissioned and carried out science observations with a phased array feed (PAF) receiver system on the 64m diameter Parkes radio telescope. Here we demonstrate that the PAF can be used for pulsar observations and we highlight some unique capabilities. We demonstrate that the pulse profiles obtained using the PAF can be calibrated and that multiple pulsars can be simultaneously observed. Significantly, we find that an intrinsic polarisation leakage of -31dB can be achieved with a PAF beam offset from the centre of the field of view. We discuss the possibilities for using a PAF for future pulsar observations and for searching for fast radio bursts with the Parkes and Effelsberg telescopes.

[16]  arXiv:1705.08548 [pdf, ps, other]
Title: Detecting the growth of structures in Pure Stellar Disk Models
Comments: 32 pages, 20 figures, Accepted for publication in RMxAA
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We performed a series of 3D N-body simulations where the initial conditions were chosen to get two sets of models; unbarred and barred ones. In this work, we analyze the growth of spirals and bar structures using 1D, and 2D Fourier Transforms FT methods. Spectrograms and diagrams of the amplitude of the Fourier coefficients as a function of time, radius and pitch angle show that the general morphology, of our modeled galaxies, is due to the superposition of structures which have different values of pitch angle and number of arms. Also, we made in barred models a geometric classification of orbits from the bar reference frame showing that the barred potential and the Lagrangian points $L_4$ and $L_5$ catch approximately one-third of the total disk mass.

[17]  arXiv:1705.08555 [pdf, other]
Title: Statistical study of solar dimmings using CoDiT
Comments: this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the results from analyzing the physical and morphological properties of 154 dimmings (transient coronal holes) and the associated flares and coronal mass ejections (CMEs). Each dimming in our 2013 catalog was processed with the semi-automated Coronal Dimming Tracker using Solar Dynamics Observatory AIA 193 A observations and HMI magnetograms. Instead of the typically used difference images, we used our coronal hole detection algorithm to detect transient dark regions "directly" in extreme ultraviolet (EUV) images. This allowed us to study dimmings as the footpoints of CMEs - in contrast with the larger, diffuse dimmings seen in difference images that represent the projected view of the rising, expanding plasma. Studying the footpoint-dimming morphology allowed us to better understand the CME structure in the low corona. While comparing the physical properties of dimmings, flares, and CMEs we were also able to identify relationships between the different parts of this complex eruptive phenomenon. We found that larger dimmings are longer-lived, suggesting that it takes longer to "close down" large open magnetic regions. Also, during their growth phase, smaller dimmings acquire a higher magnetic flux imbalance (i. e., become more unipolar) than larger dimmings. Furthermore, we found that the EUV intensity of dimmings (indicative of local electron density) correlates with how much plasma was removed and how energetic the eruption was. Studying the morphology of dimmings (single, double, fragmented) also helped us identify different configurations of the quasi-open magnetic field.

[18]  arXiv:1705.08556 [pdf, other]
Title: Constraining the Orbit of Supermassive Black Hole Binary 0402+379
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The radio galaxy 0402+379 is believed to host a supermassive black hole binary (SMBHB). The two compact core sources are separated by a projected distance of 7.3 pc, making it the most (spatially) compact resolved SMBHB known. We present new multi-frequency VLBI observations of 0402+379 at 5, 8, 15 and 22 GHz, and combine with previous observations spanning 12 years. A strong frequency dependent core shift is evident, which we use to infer magnetic fields near the jet base. After correcting for these shifts we detect significant relative motion of the two cores at $\beta=v/c=0.0054 \pm 0.0003$ at $PA= -34.4^\circ$. With some assumptions about the orbit, we use this measurement to constrain the orbital period $P\approx 3 \times 10^4$ y and SMBHB mass $M \approx 15 \times 10^9\ M_\odot$. While additional observations are needed to confirm this motion and obtain a precise orbit, this is apparently the first black hole system resolved as a visual binary.

[19]  arXiv:1705.08567 [pdf, other]
Title: Variable stars in the northern Galactic plane from KISOGP
Authors: Noriyuki Matsunaga (on behalf of KISOGP team)
Comments: Conference on wide field variability surveys: a 21st-century perspective, 2 pages in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We have conducted a large-scale survey of the northern plane using Kiso Wide Field Camera attached to Schmidt telescope at Kiso observatory. The KISOGP (KWFC Intensive Survey of the Galactic Plane) project have made 40-70 epoch observations in I band of about 320 sq. degrees for 5 years starting in 2012. The limiting magnitude is around 16.5 in I. In the data analysis so far, we detected a couple of thousands of variable stars including approximately 100 Cepheids and more than 700 Miras. Roughly 90 percent of them were not previously reported as variable stars, indicating that there are still many relatively bright variables to be found in the Galactic plane.

[20]  arXiv:1705.08587 [pdf, ps, other]
Title: Ages and structural and dynamical parameters of two globular clusters in the M81 group
Authors: Jun Ma (1, 2), Song Wang, Zhenyu Wu, Tianmeng Zhang, Hu Zou, Jundan Nie, Zhiming Zhou, Xu Zhou, Xiyang Peng, Jiali Wang, Jianghua Wu, Cuihua Du, Qirong Yuan ((1) Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, (2) College of Astronomy and Space Sciences, University of Chinese Academy of Sciences)
Comments: MNRAS 468, 4513-4528 (2017), 16 pages, 9 figures and 11 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)

GC-1 and GC-2 are two globular clusters (GCs) in the remote halo of M81 and M82 in the M81 group discovered by Jang et al. using the {\it Hubble Space Telescope} ({\it HST}) images. These two GCs were observed as part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey, using 14 intermediate-band filters covering a wavelength range of 4000--10000 \AA. We accurately determine these two clusters' ages and masses by comparing their spectral energy distributions (from 2267 to 20000~{\AA}, comprising photometric data in the near-ultraviolet of the {\it Galaxy Evolution Explorer}, 14 BATC intermediate-band, and Two Micron All Sky Survey near-infrared $JHK_{\rm s}$ filters) with theoretical stellar population-synthesis models, resulting in ages of $15.50\pm3.20$ for GC-1 and $15.10\pm2.70$ Gyr for GC-2. The masses of GC-1 and GC-2 obtained here are $1.77-2.04\times 10^6$ and $5.20-7.11\times 10^6 \rm~M_\odot$, respectively. In addition, the deep observations with the Advanced Camera for Surveys and Wide Field Camera 3 on the {\it HST} are used to provide the surface brightness profiles of GC-1 and GC-2. The structural and dynamical parameters are derived from fitting the profiles to three different models; in particular, the internal velocity dispersions of GC-1 and GC-2 are derived, which can be compared with ones obtained based on spectral observations in the future. For the first time, in this paper, the $r_h$ versus $M_V$ diagram shows that GC-2 is an ultra-compact dwarf in the M81 group.

[21]  arXiv:1705.08588 [pdf, ps, other]
Title: A universal scaling law of black hole activity including gamma-ray bursts
Authors: F. Y. Wang, Z. G. Dai
Comments: 15 pages, 3 figures, 1 table, MNRAS in press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Previous works show that a correlation among radio luminosity, X-ray luminosity, and black hole (BH) mass from stellar-mass BHs in X-ray binaries to supermassive BHs in active galactic nuclei (AGNs), which leads to the so-called fundamental plane of BH activity. However, there are two competing explanations for this fundamental plane, including the jet-dominated model and the disk-jet model. Thus, the physical origin of this fundamental plane remains unknown. In this paper, we show that the X-ray luminosities, radio luminosities and BH masses of gamma-ray bursts (GRBs) and M82 X-1 also show a similar distribution. The universal scaling law among stellar-mass, intermediate and supermassive BH systems, together with the fact that radio and X-ray emission of GRBs originates from relativistic jets, reveals that the fundamental plane of BH activity is controlled by a jet, i.e., the radio and X-ray emission is mainly from the jet. Our work also suggests that the jets are scale-invariant with respect to the BH mass.

[22]  arXiv:1705.08605 [pdf, ps, other]
Title: Transiting Exoplanet Monitoring Project (TEMP). II. Refined System Parameters and Transit Timing Analysis of HAT-P-33b
Comments: Accepted for AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present ten $R$-band photometric observations of eight different transits of the hot Jupiter HAT-P-33b, which has been targeted by our Transiting Exoplanet Monitoring Project (TEMP). The data were obtained by two telescopes at the Xinglong Station of National Astronomical Observatories of China (NAOC) from 2013 December through 2016 January, and exhibit photometric scatter of $1.6-3.0\,\rm{mmag}$. After jointly analyzing the previously published photometric data, radial-velocity (RV) measurements, and our new light curves, we revisit the system parameters and orbital ephemeris for the HAT-P-33b system. Our results are consistent with the published values except for the planet-to-star radius ratio ($R_{P}/R_{*}$), the ingress/egress duration ($\tau$) and the total duration ($T_{14}$), which together indicate a slightly shallower and shorter transit shape. Our results are based on more complete light curves, whereas the previously published work had only one complete transit light curve. No significant anomalies in Transit Timing Variations (TTVs) are found, and we place upper mass limits on potential perturbers, largely supplanting the loose constraints provided by the extant RV data. The TTV limits are stronger near mean-motion resonances, especially for the low-order commensurabilities. We can exclude the existence of a perturber with mass larger than 0.6, 0.3, 0.5, 0.5, and $0.3\,{\rm M_\oplus}$ near the 1:3, 1:2, 2:3, 3:2, and 2:1 resonances, respectively.

[23]  arXiv:1705.08608 [pdf, other]
Title: Formation of solar system analogs I: looking for initial conditions through a population synthesis analysis
Comments: 19 pages, 10 figures, submitted to MNRAS - Paper in review process - minor issues requested by the referee
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Population synthesis models of planetary systems developed during the last $\sim$15 years could reproduce several of the observables of the exoplanet population, and also allowed to constrain planetary formation models. We present our planet formation model, which calculates the evolution of a planetary system during the gaseous phase. The code incorporates relevant physical phenomena for the formation of a planetary system, like photoevaporation, planet migration, gas accretion, water delivery in embryos and planetesimals, a detailed study of the orbital evolution of the planetesimal population, and the treatment of the fusion between embryos, considering their atmospheres. The main goal of this work, unlike other works of planetary population synthesis, is to find suitable scenarios and physical parameters of the disc to form solar system analogs. We are specially interested in the final planet distributions, and in the final surface density, eccentricity and inclination profiles for the planetesimal population. These final distributions will be used as initial conditions for N-body simulations, to study the post-oligarchic formation in a second work. We then consider different formation scenarios, with different planetesimal sizes and different type I migration rates. We find that solar system analogs are favored in massive discs, with low type I migration rates, and small planetesimal sizes. Besides, those rocky planets within their habitables zones are dry when discs dissipate. At last, the final configurations of solar system analogs include information about the mass and semimajor-axis of the planets, water contents, and the properties of the planetesimal remnants.

[24]  arXiv:1705.08610 [pdf, other]
Title: The Southern HII Region Discovery Survey (SHRDS): Pilot Survey
Comments: 19 pages, 5 figures, Astronomical Journal in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Southern HII Region Discovery Survey (SHRDS) is a survey of the third and fourth quadrants of the Galactic plane that will detect radio recombination line and continuum emission at cm-wavelengths from several hundred HII region candidates using the Australia Telescope Compact Array. The targets for this survey come from the WISE Catalog of Galactic HII Regions, and were identified based on mid-infrared and radio continuum emission. In this pilot project, two different configurations of the Compact Array Broad Band receiver and spectrometer system were used for short test observations. The pilot surveys detected radio recombination line emission from 36 of 53 HII region candidates, as well as seven known \hii regions that were included for calibration. These 36 recombination line detections confirm that the candidates are true HII regions, and allow us to estimate their distances.

[25]  arXiv:1705.08612 [pdf, other]
Title: Age spreads and the temperature dependence of age estimates in Upper Sco
Comments: 13 pages, accepted by ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Past estimates for the age of the Upper Sco Association are typically 11-13 Myr for intermediate-mass stars and 4-5 Myr for low-mass stars. In this study, we simulate populations of young stars to investigate whether this apparent dependence of estimated age on spectral type may be explained by the star formation history of the association. Solar and intermediate mass stars begin their pre-main sequence evolution on the Hayashi track, with fully convective interiors and cool photospheres. Intermediate mass stars quickly heat up and transition onto the radiative Henyey track. As a consequence, for clusters in which star formation occurs on a similar timescale as the transition from a convective to a radiative interior, discrepancies in ages will arise when ages are calculated as a function of temperature instead of mass. Simple simulations of a cluster with constant star formation over several Myr may explain about half of the difference in inferred ages versus photospheric temperature; speculative constructions that consist of a constant star formation followed by a large supernova-driven burst could fully explain the differences, including those between F and G stars where evolutionary tracks may be more accurate. The age spreads of low-mass stars predicted from these prescriptions for star formation are consistent with the observed luminosity spread of Upper Sco. The conclusion that a lengthy star formation history will yield a temperature dependence in ages is expected from the basic physics of pre-main sequence evolution and is qualitatively robust to the large uncertainties in pre-main sequence evolutionary models.

[26]  arXiv:1705.08633 [pdf, other]
Title: Discovery of a new branch of the Taurid meteoroid stream as a real source of potentially hazardous bodies
Comments: 24 pages, 22 figures, 5 tables. Accepted in Astronomy and Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Taurid meteor shower produces prolonged but usually low activity every October and November. In some years, however, the activity is significantly enhanced. Previous studies based on long-term activity statistics concluded that the enhancement is caused by a swarm of meteoroids locked in 7:2 resonance with Jupiter. Here we present precise data on 144 Taurid fireballs observed by new digital cameras of the European Fireball Network in the enhanced activity year 2015. Orbits of 113 fireballs show common characteristics and form together a well defined orbital structure, which we call new branch. We found that this branch is characterized by longitudes of perihelia lying between 155.9-160o and latitudes of perihelia between 4.2-5.7o. Semimajor axes are between 2.23-2.28 AU and indeed overlap with the 7:2 resonance. Eccentricities are in wide range 0.80-0.90. The orbits form a concentric ring in the inner solar system. The masses of the observed meteoroids were in a wide range from 0.1 g to more than 1000 kg. We found that all meteoroids larger than 300 g were very fragile, while those smaller than 30 g were much more compact. Based on orbital characteristics, we argue that asteroids 2015 TX24 and 2005 UR, both of diameters 200-300 meters, are direct members of the new branch. It is therefore very likely that the new branch contains also numerous still not discovered objects of decameter or even larger size. Since asteroids of sizes of tens to hundreds meters pose a treat to the ground even if they are intrinsically weak, impact hazard increases significantly when the Earth encounters the Taurid new branch every few years. Further studies leading to better description of this real source of potentially hazardous objects, which can be large enough to cause significant regional or even continental damage on the Earth, are therefore extremely important.

[27]  arXiv:1705.08641 [pdf, ps, other]
Title: Crust-core transition of a neutron star: effects of the symmetry energy and temperature under strong magnetic fields
Comments: 7 pages, 4 figures, submitted for publication in Phys. Rev. C
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We study the simultaneous effects of the symmetry energy and temperature on the crust-core transition of a magnetar. The dynamical and the thermodynamical spinodals are used to calculate the transition region within a relativistic mean-field approach for the equation of state. Quantizing magnetic fields with intensities in the range of $ 2\times 10^{15}<B<5\times 10 ^{16}$G are considered. Under these strong magnetic fields, the crust extension is very sensitive to the density dependence of the symmetry energy, and the properties that depend on the crust thickness could set a constraint on the equation of state. It is shown that the effect on the extension of the crust-core transition is washed out for temperatures above $10^{9}$ K. However, for temperatures below that value, a noticeable effect exists that grows as the temperature decreases and which should be taken into account when the evolution of magnetars is studied.

[28]  arXiv:1705.08642 [pdf, other]
Title: The supernova-regulated ISM. IV. Generation of vorticity, helicity and mean flows
Authors: Maarit J. Käpylä (1 and 2), Frederick A. Gent (2), Miikka S. Väisälä (3 and 2), Graeme G. Sarson (4) ((1) Max-Planck-Institut for Sonnensystemforschung (2) ReSoLVE Center of Excellence, Department of Computer Science, Aalto University (3) Department of Physics, University of Helsinki (4) School of Mathematics and Statistics, Newcastle University)
Comments: 18 pages, 13 figures, submitted to Astronomy and Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The forcing of interstellar turbulence, driven mainly by supernova explosions, is irrotational in nature, but the development of significant amounts of vorticity and helicity, accompanied by large-scale dynamo action, has been reported. Several earlier investigations examined vorticity production in simpler systems; here all the relevant processes can be considered simultaneously. We also investigate the mechanisms for the generation of net helicity and large-scale flow in the system. We use a three-dimensional, stratified, rotating and shearing local simulation domain of the size 1x1x2 kpc$^3$, forced with SN explosions occurring at the rate typical of the solar neighbourhood in the Milky Way. In addition to the nominal simulation run with realistic Milky Way parameters, we vary the rotation and shear rates, but keep the absolute value of their ratio fixed. Reversing the sign of shear vs. rotation allows us to separate the rotation- and shear-generated contributions. As in earlier studies, we find the generation of significant amounts of vorticity, with on average 70% of the kinetic energy being in the rotational modes. The vorticity production can be related to the baroclinicity of the flow, especially in the regions of hot, dilute clustered supernova bubbles. In these regions, the vortex stretching acts as a sink of vorticity. The net helicities produced by rotation and shear are of opposite signs for physically motivated rotation laws, with the solar neighbourhood parameters resulting in the near cancellation of the total net helicity. We also find the excitation of oscillatory mean flows, the strength and oscillation period of which depend on the Coriolis and shear parameters; we interpret these as signatures of the anisotropic kinetic (AKA) effect. We use the method of moments to fit for the turbulent transport coeffcients, and find $\alpha_{\rm AKA}$ values of the order 3-5 km/s.

[29]  arXiv:1705.08662 [pdf]
Title: Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6
Comments: Nature, in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The existence of massive ($10^{11}$ solar masses) elliptical galaxies by redshift z~4 (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z>6 are, with only one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than $10^9$ solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([CII] at a wavelength of 158 micrometres) in four galaxies at z>6 that are companions of quasars, with velocity offsets of less than 600 kilometers per second and linear offsets of less than 600 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [CII] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [CII] brightness, linewidth and implied dynamical masses, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of twenty-five z>6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [CII] luminosity function, then they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density.

[30]  arXiv:1705.08703 [pdf, ps, other]
Title: Modelling polarized light from dust shells surrounding asymptotic giant branch stars
Comments: 9 pages
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Winds of asymptotic giant branch (AGB) stars are commonly assumed to be driven by radiative acceleration of dust grains. For M-type AGB stars, the nature of the wind-driving dust species has been a matter of intense debate. A proposed source of the radiation pressure triggering the outflows is photon scattering on Fe-free silicate grains. This wind-driving mechanism requires grain radii of about 0.1 - 1 micron in order to make the dust particles efficient at scattering radiation around the stellar flux maximum. Grain size is therefore an important parameter for understanding the physics behind the winds of M-type AGB stars. We seek to investigate the diagnostic potential of scattered polarized light for determining dust grain sizes. We have developed a new tool for computing synthetic images of scattered light in dust and gas shells around AGB stars, which can be applied to detailed models of dynamical atmospheres and dust-driven winds. We present maps of polarized light using dynamical models computed with the DARWIN code. The synthetic images clearly show that the intensity of the polarized light, the position of the inner edge of the dust shell, and the size of the dust grains near the inner edge are all changing with the luminosity phase. Non-spherical structures in the dust shells can also have an impact on the polarized light. We simulate this effect by combining different pulsation phases into a single 3D structure before computing synthetic images. An asymmetry of the circumstellar envelope can create a net polarization, which can be used as diagnostics for the grain size. The ratio between the size of the scattering particles and the observed wavelength determines at what wavelengths net polarization switches direction. If observed, this can be used to constrain average particle sizes.

[31]  arXiv:1705.08728 [pdf, ps, other]
Title: Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The solar transition region satisfies the conditions for presence of non-Maxwellian electron energy distributions with high-energy tails at energies corresponding to the ionization potentials of many ions emitting in the EUV and UV portions of the spectrum. We calculate the synthetic Si IV, O IV, and S IV spectra in the far ultra-violet (FUV) channel of the Interface Region Imaging Spectrograph (IRIS). Ionization, recombination, and excitation rates are obtained by integration of the cross-sections or their approximations over the model electron distributions considering particle propagation from the hotter corona. The ionization rates are significantly affected by the presence of high-energy tails. This leads to the peaks of the relative abundance of individual ions to be broadened with pronounced low-temperature shoulders. As a result, the contribution functions of individual lines observable by IRIS also exhibit low-temperature shoulders, or their peaks are shifted to temperatures an order of magnitude lower than for the Maxwellian distribution. The integrated emergent spectra can show enhancements of Si IV compared toO IV by more than a factor of two. The high-energy particles can have significant impact on the emergent spectra and their presence needs to be considered even in situations without strong local acceleration.

[32]  arXiv:1705.08757 [pdf, ps, other]
Title: Expanded solutions of force-Free electrodynamics on general Kerr black holes
Comments: 23 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

In this work, expanded solutions of force-free magnetospheres on general Kerr black holes are derived through a radial distance expansion method. From the regular conditions both at the horizon and at spatial infinity, two previously known asymptotical solutions (one of them is actually an exact solution) are identified as the only solutions that satisfy the same conditions at the two boundaries. Taking them as initial conditions at the boundaries, expanded solutions up to first few orders have been derived by solving the stream equation order by order. It is shown that our extension of the exact solution in such a way can (partially) cure the problems of the solution: it leads to magnetic domination and mostly timelike current for restricted parameters.

[33]  arXiv:1705.08770 [pdf, ps, other]
Title: Far-Ultraviolet Observation of the Globular Cluster NGC 6397
Comments: 13 pages, MNRAS accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present an observational far-UV (FUV) and near-UV (NUV) study of the core region of the globular cluster NGC 6397. The observations were obtained with the Space Telescope Imaging Spectrograph (STIS, FUV), and the Wide Field Camera 3 (WFC3, NUV) on board the Hubble Space Telescope. Here, we focus on the UV bright stellar populations such as blue stragglers (BSs), white dwarfs (WDs) and cataclysmic variables (CVs). We present the first FUV-NUV color-magnitude diagram (CMD) for this cluster. To support our classification of the stellar populations, we compare our FUV-NUV CMD with optical data from the ACS Survey of Galactic Globular Clusters. The FUV-NUV CMD indicates 16 sources located in the WD area, and ten BSs within the 25"x 25" of the STIS FUV data. Eighteen Chandra X-ray sources are located within the FUV field of view. Thirteen of those have a NUV counterpart, of which nine sources also have a FUV counterpart. Out of those, five sources are previously suggested CVs, and indeed all five are located in the WD/CV region in our FUV-NUV CMD. Another CV only has a FUV but no NUV counterpart. We also detect a NUV (but no FUV) counterpart to the MSP located in the core of this cluster. The NUV lightcurves of the CVs and MSP show flickering behaviour typical of CVs. We found that the BSs and CVs are the most centrally concentrated population. This might be an effect of mass segregation or indicate the preferred birth place of BSs and CVs via dynamical interactions in the dense core region of GCs. HB stars are the least centrally concentrated population and absent in the innermost area of the core.

[34]  arXiv:1705.08785 [pdf, other]
Title: Metallicity determination of M dwarfs - Expanded parameter range in metallicity and effective temperature
Comments: 13 pages
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context. Reliable metallicity values for M dwarfs are important for studies of the chemical evolution and advancement of planet formation theory in low-mass environments. Historically the determination of stellar parameters of low-mass stars has been challenging due to the low surface temperature, causing several molecules to form in the photospheric layers. In our work we use the fact that infrared high-resolution spectrographs have opened up a new window for investigating M dwarfs.
Aims. Metallicity determination using high-resolution spectra is more accurate than the use of low-resolution spectra, but rather time-consuming. In this paper we expand our sample analyzed with this precise method both in metallicity and effective temperature in order to build up a calibration sample for a future revised empirical calibration.
Methods. Because of the relatively few molecular lines in the J-band, continuum rectification is possible for high-resolution spectra, allowing the stellar parameters to be determined with greater accuracy than using optical spectra. The metallicity was determined using synthetic spectral fitting of several atomic species.
Results. We have analyzed sixteen targets, with a range of effective temperature from 3350-4550 K. The resulting metallicities lie between -0.5 < [M/H] < +0.4. A few targets have previously been analyzed using low-resolution spectra, and we find a rather good agreement with our values. A comparison with available photometric calibrations shows varying agreement, and the spread within all empirical calibrations is large.
Conclusions. Including the targets from our previous paper, we have analyzed 28 M dwarfs using high-resolution infrared spectra. The targets spread approximately one dex in metallicity and 1400 K in effective temperature. For individual M dwarfs we achieve uncertainties of 0.05 dex and 100 K on average.

[35]  arXiv:1705.08797 [pdf, other]
Title: Conjoined constraints on Modified Gravity from the expansion history and cosmic growth
Comments: 10 pages, 2 figures, 4 tables, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

In this paper we present conjoined constraints on several cosmological models from the expansion history $H(z)$ and cosmic growth $f\sigma_8$. The models we studied include the CPL $w_0w_a$ parametrization, the Holographic Dark Energy (HDE) model, the Time varying vacuum ($\Lambda_t$CDM) model, the Dvali, Gabadadze and Porrati (DGP) and Finsler-Randers (FRDE) model, a power law $f(T)$ model and finally the Hu-Sawicki $f(R)$ model. In all cases we used the best-fit parameters as determined in Basilakos and Nesseris (2016) and we followed the conjoined visualization of $H(z)$ and $f\sigma_8$ as in Linder (2017). Also, we introduce the Figure of Merit (FoM) in the $H(z)-f\sigma_8$ parameter space as a way to constrain models that jointly fit both probes well. In this regard, we used both the latest $H(z)$ and $f\sigma_8$ data, but also LSST-like mocks with $1\%$ measurements. We find that that the conjoined method of constraining the expansion history and cosmic growth simultaneously is able to not only place stringent constraints on these parameters but also provide an easy visual way to discriminate cosmological models. Finally, we found that the FoM in the conjoined parameter space of $H(z)-f\sigma_8(z)$ can be used to discriminate between the $\Lambda$CDM model and certain classes of modified gravity models, namely the DGP and $f(R)$.

[36]  arXiv:1705.08812 [pdf, other]
Title: Self-consistent dynamical model of the Broad Line Region
Comments: Proceeding of the conference "Quasars at all cosmic epochs", held in Padova, April 2-7, 2017. Submitted to Frontiers in Astronomy and Space Sciences
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We develope a self-consistent description of the Broad Line Region based on the concept of the failed wind powered by the radiation pressure acting on dusty accretion disk atmosphere in Keplerian motion. The material raised high above the disk is illuminated, dust evaportes, and the matter falls back towards the disk. This material is the source of emission lines. The model predicts the inner and outer radius of the region, the cloud dynamics under the dust radiation pressure and, subsequently, just the gravitational field of the central black hole, which results in assymetry between the rise and fall. Knowledge of the dynamics allows to predict the shapes of the emission lines as functions of the basic parameters of an active nucleus: black hole mass, accretion rate, black hole spin (or accretion efficiency) and the viewing angle with respect to the symmetry axis. Here we show preliminary results based on analytical approximations to the cloud motion.

[37]  arXiv:1705.08833 [pdf, other]
Title: Measuring solar active region inflows with local correlation tracking of granulation
Comments: 10 pages, 9 figures. Submitted to Astronomy & Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context. Local helioseismology has detected spatially extended converging surface flows into solar active regions. These play an important role in flux-transport models of the solar dynamo.
Aims. We aim to validate the existence of the inflows by deriving horizontal flow velocities around active regions with local correlation tracking of granulation.
Methods. We generate a six-year long-time series of full-disk maps of the horizontal velocity at the solar surface by tracking granules in continuum intensity images provided by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO).
Results. On average, active regions are surrounded by inflows extending up to 10 deg from the center of the active region of magnitudes of 20-30 m/s, reaching locally up to 40 m/s, which is in agreement with results from local helioseismology. By computing an ensemble average consisting of 243 individual active regions, we show that the inflows are not azimuthally symmetric but converge predominantly towards the trailing polarity of the active region with respect to the longitudinally and temporally averaged flow field.

[38]  arXiv:1705.08853 [pdf, ps, other]
Title: Parity fluctuations in stellar dynamos
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Observations of the solar butterfly diagram from sunspot records suggest persistent fluctuation in parity, away from the overall, approximately dipolar structure. We use a simple mean-field dynamo model with a solar-like rotation law, and perturb the $\alpha$-effect. We find that the parity of the magnetic field with respect to the rotational equator can demonstrate what we describe as resonant behaviour, while the magnetic energy behaves in a more or less expected way. We discuss possible applications of the phenomena in the context of various deviations of the solar magnetic field from dipolar symmetry, as reported from analysis of archival sunspot data. We deduce that our model produces fluctuations in field parity, and hence in the butterfly diagram, that are consistent with observed fluctaions in solar behaviour.

[39]  arXiv:1705.08874 [pdf, ps, other]
Title: Integral Field Spectroscopy of the inner kpc of the elliptical galaxy NGC 5044
Comments: 16 pages, 12 figures, accepted by MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We used Gemini Multi-Object Spectrograph (GMOS) in the Integral Field Unit mode to map the stellar population, emission line flux distributions and gas kinematics in the inner kpc of NGC 5044. From the stellar populations synthesis we found that the continuum emission is dominated by old high metallicity stars ($\sim$13 Gyr, 2.5Z$\odot$). Also, its nuclear emission is diluted by a non thermal emission, which we attribute to the presence of a weak active galactic nuclei (AGN). In addition, we report for the first time a broad component (FWHM$\sim$ 3000km$s^{-1}$) in the H$\alpha$ emission line in the nuclear region of NGC 5044. By using emission line ratio diagnostic diagrams we found that two dominant ionization processes coexist, while the nuclear region (inner 200 pc) is ionized by a low luminosity AGN, the filamentary structures are consistent with being excited by shocks. The H$\alpha$ velocity field shows evidence of a rotating disk, which has a velocity amplitude of $\sim$240kms$^{-1}$ at $\sim$ 136 pc from the nucleus. Assuming a Keplerian approach we estimated that the mass inside this radius is $1.9\times10^9$ $M_{\odot}$, which is in agreement with the value obtained through the M-$\sigma$ relation, $ M_{SMBH}=1.8\pm1.6\times10^{9}M_{\odot}$. Modelling the ionized gas velocity field by a rotating disk component plus inflows towards the nucleus along filamentary structures, we obtain a mass inflow rate of $\sim$0.4 M$_\odot$. This inflow rate is enough to power the central AGN in NGC 5044.

[40]  arXiv:1705.08877 [pdf, other]
Title: Testing non-minimally coupled inflation with CMB data: a Bayesian analysis
Comments: 13 pages,7 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use the most recent cosmic microwave background (CMB) data to perform a Bayesian statistical analysis and discuss the observational viability of inflationary models with a non-minimal coupling $\xi$, between the inflaton field and the Ricci scalar. We particularize our analysis to two examples of small and large field inflationary models, namely, the Coleman-Weinberg and the chaotic quartic potentials. We find that (\textit{i})the $\xi$ parameter is closely correlated with the primordial amplitude; (\textit{ii}) although improving the agreement with the CMB data in the $r - n_s$ plane, where $r$ is the tensor-to-scalar ratio and $n_s$ the primordial spectral index, a non-null coupling is strongly disfavoured with respect to the minimally coupled standard $\Lambda$CDM model.