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Infrared Excesses Around Bright White Dwarfs from Gaia and unWISE. II
Lai, Samuel; Rebassa-Mansergas, Alberto; Xu, Siyi +7 more
Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry…
HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars
Loyd, R. O. Parke; Jackman, James A. G.; Peacock, Sarah +6 more
The ultraviolet (UV) emission from the most numerous stars in the universe, M dwarfs, impacts the formation, chemistry, atmospheric stability, and surface habitability of their planets. We have analyzed the spectral evolution of UV emission from M0-M2.5 (0.3-0.6 M⊙) stars as a function of age, rotation, and Rossby number using Hubble Sp…
Supervirial Temperature or Neon Overabundance? Suzaku Observations of the Milky Way Circumgalactic Medium
Nicastro, Fabrizio; Mathur, Smita; Gupta, Anjali +4 more
We analyzed Suzaku and Chandra observations of the soft diffuse X-ray background toward four sight lines with the goal of characterizing the X-ray emission from the Milky Way circumgalactic medium (CGM). We identified two thermal components of the CGM, one at a uniform temperature of kT = 0.176 ± 0.008 keV and the other at temperatures in the rang…
The Flattening Metallicity Gradient in the Milky Way's Thin Disk
Shen, Juntai; Li, Zhao-Yu; Vickers, John J.
We calculate the ages, orbits and phase-space coordinates for a sample of ~4 million LAMOST and Gaia stars. The ages are cross-matched and compared with values from two other popular age catalogs, which derive the ages using different methods. Of these ~4 million stars, we select a sample of 1.3 million stars and investigate their radial metallici…
New Evidence for Extended He I> Reionization at z ≳ 3.5 from He II Lyman Alpha and Beta Transmission Spikes
Richter, Philipp; Hennawi, Joseph F.; Worseck, Gábor +3 more
We present new high-resolution (R = λ/Δλ ∼ 14,000) spectra of the two brightest He II-transparent quasars in the far-UV at zem > 3.5, HE2QS J2311-1417 (zem = 3.70) and HE2QS J1630+0435 (zem = 3.81), obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. In the predominantly saturated He II …
Metallicity Estimation of RR Lyrae Stars From Their I-Band Light Curves
Grebel, Eva K.; Pojmański, Grzegorz; Dékány, István
We have revisited the problem of metallicity prediction of RR Lyrae stars from their near-infrared light curves in the Cousins I wave band. Our study is based on high-quality time series photometry and state-of-the-art high-resolution spectroscopic abundance measurements of 80 fundamental-mode (RRab) and 24 first-overtone (RRc) stars, spanning ~[-…
The Nature of the Milky Way's Stellar Halo Revealed by the Three Integrals of Motion
Carollo, Daniela; Chiba, Masashi
We developed a new selection method of halo stars in the phase-space distribution defined by the three integrals of motion in an axisymmetric Galactic potential (E, Lz, I3), where I3 is the third integral of motion. The method is used to explore the general chemodynamical structure of the halo based on stellar samp…
Exemplary Merging Clusters: Weak-lensing and X-Ray Analysis of the Double Radio Relic, Merging Galaxy Clusters MACS J1752.0+4440 and ZWCL 1856.8+6616
Dawson, William A.; Jones, Christine; Forman, William R. +8 more
The investigation of merging galaxy clusters that exhibit radio relics is strengthening our understanding of the formation and evolution of galaxy clusters, the nature of dark matter, the intracluster medium, and astrophysical particle acceleration. Each merging cluster provides only a single view of the cluster formation process, and the variety …
A Spatially Resolved Survey of Distant Quasar Host Galaxies. I. Dynamics of Galactic Outflows
Armus, Lee; Larkin, James E.; Wright, Shelley A. +6 more
We present observations of ionized gas outflows in 11 z = 1.39-2.59 radio-loud quasar host galaxies. Data were taken with the integral field spectrograph OSIRIS and the adaptive optics system at the W.M. Keck Observatory targeting nebular emission lines (Hβ, [O III], Hα, [N II], and [S II]) redshifted into the near-infrared (1-2.4 µm). Outfl…
Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
Casey, Andrew R.; Beers, Timothy C.; Lee, Young Sun +7 more
We present the results of spectroscopic follow-up for 1897 low-metallicity star candidates, selected from the Best & Brightest (B&B) Survey, carried out with the GMOS-N/S (Gemini North/South telescopes) and Goodman (SOAR Telescope) spectrographs. From these low-resolution (R ∼ 2000) spectra, we estimate stellar atmospheric parameters, as w…