Search Publications
Chemical Analysis of Two Extremely Metal-poor Stars HE 2148-2039 and HE 2155-2043
Goswami, Aruna; Purandardas, Meenakshi
We present elemental abundance results for HE 2148-2039 and HE 2155-2043 based on a detailed high-resolution spectroscopic analysis. The high-resolution Subaru/High Dispersion Spectrograph (HDS) spectra used for our analysis have a resolution of R ∼ 60,000. Although limited information based on photometry and low-resolution spectroscopy is availab…
Cooling Models for the Most Massive White Dwarfs
Schwab, Josiah
We present a set of ultramassive white dwarf models, focused on masses above 1.3 M⊙. Given the uncertainties about the formation and compositions of such objects, we construct parameterized model sequences, guided by evolutionary calculations including both single star and double white dwarf merger formation channels. We demonstrate tha…
The ACTIONFINDER: An Unsupervised Deep Learning Algorithm for Calculating Actions and the Acceleration Field from a Set of Orbit Segments
Famaey, Benoit; Ibata, Rodrigo; Monari, Giacomo +1 more
We introduce the ACTIONFINDER, a deep learning algorithm designed to transform a sample of phase-space measurements along orbits in a static potential into action and angle coordinates. The algorithm finds the mapping from positions and velocities to actions and angles in an unsupervised way, by using the fact that points along the same orbit have…
The Mass and Age Distribution of Halo White Dwarfs in the Canada-France Imaging Survey
Gwyn, Stephen D. J.; McConnachie, Alan W.; Cuillandre, Jean-Charles +6 more
We present optical spectroscopy for 18 halo white dwarfs identified using photometry from the Canada-France Imaging Survey and Pan-STARRS1 DR1 3π survey combined with astrometry from Gaia DR2. The sample contains 13 DA, 1 DZ, 2 DC, and 2 potentially exotic types of white dwarf. We fit both the spectrum and the spectral energy distribution in order…
The QuaStar Survey: Detecting Hidden Low-velocity Gas in the Milky Way's Circumgalactic Medium
Werk, Jessica K.; Zheng, Yong; Peek, Joshua +2 more
From our position embedded within the Milky Way's interstellar medium, we have limited ability to detect gas at low relative velocities in the extended Galactic halo because those spectral lines are blended with much stronger signals from dense foreground gas. As a result, the content of the Milky Way's circumgalactic medium (CGM) is poorly constr…
Revealing a New Black Widow Binary 4FGL J0336.0+7502
Kong, Albert K. H.; Li, Kwan-Lok; Jane Yap, Y. X. +1 more
We report on the discovery of a promising candidate for a black widow (BW) millisecond pulsar binary, 4FGL J0336.0+7502, which shows many pulsar-like properties in the 4FGL-DR2 catalog. Within the 95% error region of the LAT source, we identified an optical counterpart with a clear periodicity at Porb = 3.718178(9) hr using the Bohyunsa…
Data-driven Stellar Models
Rix, Hans-Walter; Fouesneau, Morgan; Zucker, Catherine +7 more
We developed a data-driven model to map stellar parameters (Teff, $\mathrm{log}g$ , and $\left[\mathrm{Fe}/{\rm{H}}\right]$ ) accurately and precisely to broadband stellar photometry. This model must, and does, simultaneously constrain the passband-specific dust reddening vector in the Milky Way, R. The model uses a neural network to le…
Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at 300 Myr from Optical Through Mid-infrared Spectrophotometry
Metchev, Stanimir; Marley, Mark S.; Saumon, Didier +2 more
We present Spitzer IRS 5-14 µm spectra and 16 µm and 22 µm photometry of the T2.5 companion to the ~300 Myr old G0V star HN Peg. We incorporate previous 0.8-5 µm observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Ga…
Peeking Between the Pulses: The Far-UV Spectrum of the Previously Unseen White Dwarf in AR Scorpii
Garnavich, Peter; Littlefield, Colin; Lyutikov, Maxim +1 more
The compact object in the interacting binary AR Sco has widely been presumed to be a rapidly rotating, magnetized white dwarf (WD), but it has never been detected directly. Isolating its spectrum has proven difficult because the spin-down of the WD generates pulsed synchrotron radiation that far outshines the WD's photosphere. As a result, a previ…
A Luminous X-Ray Transient in SDSS J143359.16+400636.0: A Likely Tidal Disruption Event
Riddle, Reed; Stern, Daniel; Gezari, Suvi +9 more
We present the discovery of a luminous X-ray transient, serendipitously detected by Swift's X-ray Telescope on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 at z = 0.099 (luminosity distance DL = 456 Mpc). The transient was observed to reach a peak luminosity of ∼1044 erg s-1 in the…