Stars, Interstellar Medium and the Galaxy Commons^™

The Frb 121102 Host Is Atypical Among Nearby Fast Radio Bursts, Ye Li, Bing Zhang, Kentaro Nagamine, Jingjing Shi

Physics & Astronomy Faculty Research

We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure DMhost of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and …

A Global View Of The Inner Accretion And Ejection Flow Around Super Massive Black Holes, Margherita Giustini, Daniel Proga

Physics & Astronomy Faculty Research

Context. Understanding the physics and geometry of accretion and ejection around super massive black holes (SMBHs) is important to understand the evolution of active galactic nuclei (AGN) and therefore of the large scale structures of the Universe. Aims. We aim at providing a simple, coherent, and global view of the sub-parsec accretion and ejection flow in AGN with varying Eddington ratio, ṁ, and black hole mass, MBH. Methods. We made use of theoretical insights, results of numerical simulations, as well as UV and X-ray observations to review the inner regions of AGN by including different accretion and ejection modes, with …

Polar Alignment Of A Protoplanetary Disc Around An Eccentric Binary – Iii. Effect Of Disc Mass, Rebecca G. Martin, Stephen H. Lubow

Physics & Astronomy Faculty Research

An initially sufficiently misaligned low-mass protoplanetary disc around an eccentric binary undergoes damped nodal oscillations of tilt angle and longitude of ascending node. Dissipation causes evolution towards a stationary state of polar alignment in which the disc lies perpendicular to the binary orbital plane with angular momentum aligned to the eccentricity vector of the binary. We use hydrodynamic simulations and analytical methods to investigate how the mass of the disc affects this process. The simulations suggest that a disc with non-zero mass settles into a stationary state in the frame of the binary, the generalized polar state, at somewhat lower …

Wallaby Early Science − V. Askap Hi Imaging Of The Lyon Group Of Galaxies 351, B. Q. For, L. Staveley-Smith, T. Westmeier, M. Whiting, S. -H. Oh, B. Koribalski, J. Wang, O. I. Wong, G. Bekiaris, L. Cortese, A. Elagali, D. Kleiner, K. Lee-Waddell, Juan P. Madrid, A. Popping, J. Rhee, T. N. Reynolds, J. D. Collier, C. J. Phillips, M. A. Voronkov, O. Mueller, H. Jerjen

Physics and Astronomy Faculty Publications and Presentations

We present an HI study of the galaxy group LGG 351 usingWidefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early science data observed with the Australian Square Kilometre Array Pathfinder (ASKAP). LGG 351 resides behind the M 83 group at a velocity range (cz) of ∼3500–4800 km s−1 within the rich Hydra-Centaurus overdensity region. We detect 40 sources with the discovery of a tidally interacting galaxy pair and two new HI sources that are not presented in previous optical catalogues. 23 out of 40 sources have new redshifts derived from the new HI data. This study is the largest WALLABY …

Photoionization Calculations Of The Radiation Force Due To Spectral Lines In Agns, Randall C. Dannen, Daniel Proga, Timothy R. Kallman, Tim Waters

Physics & Astronomy Faculty Research

One of the main mechanisms that could drive mass outflows in active galactic nuclei (AGNs) is radiation pressure due to spectral lines. Although straightforward to understand, the actual magnitude of the radiation force is challenging to compute because the force depends on the physical conditions in the gas, as well as the strength, spectral energy distribution (SED), and geometry of the radiation field. We present results from our photoionization and radiation transfer calculations of the force multiplier, M(ξ, t), using the same radiation field to compute the gas photoionization and thermal balance. We assume low gas density (n = 104 …

The Hubble Pancet Program: An Extensive Search For Metallic Ions In The Exosphere Of Gj 436 B, Leonardo A. Dos Santos, David Ehrenreich, Vincent Bourrier, Alain Lecavelier Des Etangs, Mercedes López-Morales, David K. Sing, Gilda E. Ballester, Lofti Ben-Jaffel, Lars A. Buchhave, Antonio García Muñoz, Gregory W. Henry, Tiffany Kataria, Baptiste Lavie, Panayotis Lavvas, Nikole K. Lewis, Thomas Mikal-Evans, Jorge Sanz-Forcada, Hannah R. Wakeford

Information Systems and Engineering Management Research Publications

Context. The quiet M2.5 star GJ 436 hosts a warm Neptune that displays an extended atmosphere that dwarfs its own host star. Predictions of atmospheric escape in such planets state that H atoms escape from the upper atmosphere in a collisional regime and that the flow can drag heavier atoms to the upper atmosphere. It is unclear, however, what astrophysical mechanisms drive the process.

Aims. Our objective is to leverage the extensive coverage of observations of the far-ultraviolet (FUV) spectrum of GJ 436 obtained with the Cosmic Origins Spectrograph (COS) to search for signals of metallic ions in the upper …

Viewing Angle Constraints On S190425z And S190426c And The Joint Gravitational-Wave/Gamma-Ray Detection Fractions For Binary Neutron Star Mergers, Hao-Ran Song, Shun-Ke Ai, Min-Hao Wang, Nan Xing, He Gao, Bing Zhang

Physics & Astronomy Faculty Research

The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo scientific collaboration (LVC) detected two binary neutron star (BNS) merger candidates, S190425z and S190426c. The Fermi-Gamma-ray Burst Monitor (GBM) observed 55.6% (for S190425z) and 100% (for S190426c) of the probability regions of both events at the respective merger times, but no gamma-ray burst (GRB) was detected in either case. The derived luminosity upper limits suggest that a short GRB similar to GRB 170817A would not be detectable for both cases due to their distances, which are larger than that of GW170817. Assuming that the jet profile obtained from GW170817/GRB 170817A is quasi-universal …

Type I Outbursts In Low-Eccentricity Be/X-Ray Binaries, Alessia Franchini, Rebecca G. Martin

Physics & Astronomy Faculty Research

Type I outbursts in Be/X-ray binaries are usually associated with the eccentricity of the binary orbit. The neutron star accretes gas from the outer parts of the decretion disk around the Be star at each periastron passage. However, this mechanism cannot explain type I outbursts that have been observed in nearly circular orbit Be/X-ray binaries. With hydrodynamical simulations and analytic estimates we find that in a circular orbit binary, a nearly coplanar disk around the Be star can become eccentric. The extreme mass ratio of the binary leads to the presence of the 3:1 Lindblad resonance inside the Be star …

The Frequency Of Kozai–Lidov Disc Oscillation Driven Giant Outbursts In Be/X-Ray Binaries, Rebecca G. Martin, Alessia Franchini

Physics & Astronomy Faculty Research

Giant outbursts of Be/X-ray binaries may occur when a Be-star disc undergoes strong eccentricity growth due to the Kozai–Lidov (KL) mechanism. The KL effect acts on a disc that is highly inclined to the binary orbital plane provided that the disc aspect ratio is sufficiently small. The eccentric disc overflows its Roche lobe and material flows from the Be star disc over to the companion neutron star causing X-ray activity. With N-body simulations and steady state decretion disc models we explore system parameters for which a disc in the Be/X-ray binary 4U 0115+634 is KL unstable and the resulting time-scale …

Using Optical And Near-Infrared Photometry To Test Macho Lens Candidates, Ted Von Hippel, Et Al.

Ted von Hippel

We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars and adjacent LMC field regions. After combining our near-IR photometry with Hubble Space Telescope/PC BVRI optical photometry, we compared the MACHO objects to the adjacent field stars in a variety of color-magnitude and color-color diagrams. These diagnostic diagrams were chosen to be sensitive to our hypothesis that at least some of the MACHO lenses were foreground Galactic disk or thick-disk M dwarfs. For the five lensed objects we studied, our hypothesis could be ruled out for main-sequence lens masses ≥0.1 M☉ for distances out to …

Virgo’S Intracluster Globular Clusters As Seen By The Advanced Camera For Surveys, Benjamin F. Williams, Robin Ciardullo, Ted Von Hippel, Et Al.

Ted von Hippel

We report the discovery of four candidate intracluster globular clusters (IGCs) in a single deepHST ACS field of the Virgo Cluster. We show that each cluster is roughly spherical, has a magnitude near the peak of the Virgo globular cluster luminosity function, has a radial profile that is best fitted by a King model, and is surrounded by an excess of point sources that have the colors and magnitudes of cluster red giant stars. Despite the fact that two of our IGC candidates have integrated colors redder than the mean of the M87 globular cluster system, we propose that …

Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.

Ted von Hippel

We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (T_eff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict T_eff with an accuracy of σ(T_eff) = 135-150 K over the range 4250 ≤ T_eff ≤ 6500 K, log g with an accuracy …

The White Dwarf Age Of Nfc 2477, Elizabeth J. Jeffery, Ted Von Hippel, Et Al.

Ted von Hippel

We present deep photometric observations of the open cluster NGC 2477 using HST/WFPC2. By identifying seven cluster white dwarf candidates, we present an analysis of the white dwarf age of this cluster, using both the traditional method of fitting isochrones to the white dwarf cooling sequence, and by employing a new Bayesian statistical technique that has been developed by our group. This new method performs an objective, simultaneous model fit of the cluster and stellar parameters (namely, age, metallicity, distance, reddening, as well as individual stellar masses, mass ratios, and cluster membership) to the photometry. Based on this analysis, …

The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider

Ted von Hippel

A sample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematicsmodels are used to understand and correct for velocity-dependent selection biases.A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to Mbol=15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars …

Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.

Ted von Hippel

We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135-150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy of σ(log …

The Power Of Principled Bayesian Methods In The Study Of Stellar Evolution, Ted Von Hippel, David Van Dyk, David Stenning, Elliot Robinson, Elizabeth Jeffery, Nathan Stein, William Jefferys, Erin M. O'Malley

Ted von Hippel

It takes years of effort employing the best telescopes and in- struments to obtain high-quality stellar photometry, astrometry, and spectroscopy. Stellar evolution models contain the experience of life- times of theoretical calculations and testing. Yet most astronomers fit these valuable models to these precious datasets by eye. We show that a principled Bayesian approach to fitting models to stellar data yields substantially more information over a range of stellar astrophysics. We highlight advances in determining the ages of star clusters, mass ratios of binary stars, limitations in the accuracy of stellar models, post-main-sequence mass loss, and the ages of individual …

The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.

Ted von Hippel

We present 4.5 and 8 µm photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with Teᶠᶠ < 6000 K show slightly depressed mid-infrared fluxes relative to white dwarf models. In addition, another white dwarf with a peculiar optical and near-infrared spectral energy distribution (LHS 1126) is found to display significant flux deficits in Spitzer observations. These mid-infrared flux deficits are not predicted by the current white dwarf models including collision-induced absorption due to molecular hydrogen. We postulate that either the collision-induced absorption calculations are incomplete or there are other unrecognized physical processes occurring in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with effective temperature well in excess of 105 K. This implies that the source of this flux deficit is probably not molecular absorption but some other process.

Thirty-Five New Pulsating Da White Dwarf Stars, Anjum S. Mukadam, Ted Von Hippel, Et Al.

Ted von Hippel

We present 35 new pulsating DA (hydrogen atmosphere) white dwarf stars discovered from the Sloan Digital Sky Survey (SDSS) and the Hamburg Quasar Survey (HQS). We have acquired high-speed time series photometry of preselected DA white dwarfs with a prime focus CCD photometer on the 2.1 m telescope at McDonald Observatory over 15 months. We selected these stars on the basis of prior photometric and spectroscopic observations by the SDSS and HQS. For the homogeneous SDSS sample, we achieve a success rate of 80% for finding new variables at a detection threshold of 0.1%-0.3%. With 35 newly discovered DA variable …

The Resolved Stellar Populations Of A Dwarf Spheroidal Galaxy In The Virgo Cluster, Patrick R. Durell, Ted Von Hippel, Et Al.

Ted von Hippel

We report on the discovery of a faint (MV ~ -10.6 ± 0.2) dwarf spheroidal galaxy on deep F606W and F814W Hubble Space Telescope images of a Virgo intracluster field. The galaxy is easily resolved in our images, as our color magnitude diagram (CMD) extends 1 magnitude beyond the tip of the red giant branch (RGB). Thus, it is the deepest CMD for a small dwarf galaxy inside a cluster environment. Using the colors of the RGB stars, we derive a metal abundance for the dwarf of [M/H] = -2.3 ± 0.3 and show that the metallicity dispersion …

The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al.

Ted von Hippel

We describe a new survey for cool white dwarfs that supplements Sloan Digital Sky Survey photometry with USNO proper motions and followup spectroscopy. To date we have discovered and spectroscopically confirmed 80 new moderate temperature and cool white dwarfs. We have also found a handful of high-velocity white dwarfs and we expect a sizable fraction of these to be thick disk or possibly halo objects. Our survey is designed to find 104 new white dwarfs, although only 60 will be among the faintest white dwarfs (MV 16), where most of the age-sensitivity resides. We discuss an extension of our survey …