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Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV-bright Underlying Source 2-4 Yr Post-discovery
Kilpatrick, Charles D.; Drout, Maria R.; Foley, Ryan J. +4 more
In this second of a two-paper series, we present a detailed analysis of three Hubble Space Telescope observations taken ~2-4 yr post-discovery, examining the evolution of a UV-bright underlying source at the precise position of AT 2018cow. While observations at ~2-3 yr post-discovery revealed an exceptionally blue (L ν ∝ ν 1.99
Understanding the Early Stages of Galaxy Formation Using Very Metal-poor Stars from the Hamburg/ESO Survey
Carollo, Daniela; Christlieb, Norbert; Tissera, Patricia B. +1 more
We explore the chemodynamical properties of a sample of very metal-poor (VMP) stars selected from the Hamburg/ESO survey, matched with Gaia EDR3, in the phase space identified by the three integrals of motion (L z , E, I 3). Disk and halo orbits are separated by using the criteria defined in Carollo & Chiba. We found 26 …
Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II
Li, Ting S.; Simon, Joshua D.; Pace, Andrew B. +3 more
In this paper, we present a chemical and kinematic analysis of two ultrafaint dwarf galaxies (UFDs), Aquarius II (Aqu II) and Boötes II (Boo II), using Magellan/IMACS spectroscopy. We present the largest sample of member stars for Boo II (12), and the largest sample of red giant branch members with metallicity measurements for Aqu II (eight). In b…
UV and Hα HST Observations of Six GASP Jellyfish Galaxies
Scarlata, Claudia; Mingozzi, Matilde; Calzetti, Daniela +17 more
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medi…
The SOFIA Massive (SOMA) Star Formation Survey. IV. Isolated Protostars
Law, Chi-Yan; Telkamp, Zoie; Yang, Yao-Lun +13 more
We present ~10-40 µm SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 µm imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build…
High-resolution Spectroscopic Metallicities of Milky Way Cepheid Standards and Their Impact on the Leavitt Law and the Hubble Constant
Riess, Adam G.; Macri, Lucas M.; Marconi, Marcella +10 more
Milky Way Cepheid variables with accurate Hubble Space Telescope photometry have been established as standards for primary calibration of the cosmic distance ladder to achieve a percent-level determination of the Hubble constant (H 0). These 75 Cepheid standards are the fundamental sample for investigation of possible residual systemati…
Solar Flare Ribbon Fronts. I. Constraining Flare Energy Deposition with IRIS Spectroscopy
Polito, Vanessa; Xu, Yan; Kerr, Graham S. +2 more
Spectral lines formed at lower atmospheric layers show peculiar profiles at the "leading edge" of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He I λ10830 line, as well as broad and centrally reversed profiles in the spectra of the Mg II and C II lines observed by the IRIS satellite, has been reported. In this w…
Coronal Heating Rate in the Slow Solar Wind
Telloni, Daniele; Zank, Gary P.; Adhikari, Laxman +59 more
This Letter reports the first observational estimate of the heating rate in the slowly expanding solar corona. The analysis exploits the simultaneous remote and local observations of the same coronal plasma volume, with the Solar Orbiter/Metis and the Parker Solar Probe instruments, respectively, and relies on the basic solar wind magnetohydrodyna…
The Fast X-Ray Transient XRT 210423 and Its Host Galaxy
Bauer, F. E.; Dhillon, V. S.; Littlefair, S. P. +8 more
Fast X-ray Transients (FXTs) are X-ray flares with durations ranging from a few hundred seconds to a few hours. Possible origins include the tidal disruption of a white dwarf by an intermediate-mass black hole, a supernova shock breakout, or a binary neutron star merger. We present the X-ray light curve and spectrum as well as deep optical imaging…
Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ -3) Regime
Lee, Young Sun; Chiappini, Cristina; Limberg, Guilherme +6 more
In this work, we study the phase-space and chemical properties of the Sagittarius (Sgr) stream, the tidal tails produced by the ongoing destruction of the Sgr dwarf spheroidal (dSph) galaxy, focusing on its very metal-poor (VMP; [Fe/H] < -2) content. We combine spectroscopic and astrometric information from SEGUE and Gaia EDR3, respectively, wi…