Search Publications
Rising Near-ultraviolet Spectra in Stellar Megaflares
Notsu, Yuta; Kowalski, Adam F.; Maehara, Hiroyuki +5 more
Flares from M dwarf stars can attain energies up to 104 times larger than solar flares but are generally thought to result from similar processes of magnetic energy release and particle acceleration. Larger heating rates in the low atmosphere are needed to reproduce the shape and strength of the observed continua in stellar flares, whic…
Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime
Brandt, W. N.; Shen, Yue; Ho, Luis C. +9 more
Over three decades of reverberation mapping (RM) studies on local broad-line active galactic nuclei (AGNs) have measured reliable black hole (BH) masses for >100 AGNs. These RM measurements reveal a significant correlation between the Balmer broad-line region (BLR) size and AGN optical luminosity (the R–L relation). Recent RM studies for AGN sa…
The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions
Gies, Douglas R.; Klement, Robert; Rivinius, Thomas +8 more
Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs …
Expanded Sample of Small Magellanic Cloud Ultraviolet Dust Extinction Curves: Correlations between the 2175 Å Bump, q PAH, Ultraviolet Extinction Shape, and N(H I)/A(V)
Murray, Claire E.; Gordon, Karl D.; Fitzpatrick, E. L. +7 more
The Small Magellanic Cloud (SMC) shows a large variation in ultraviolet (UV) dust extinction curves, ranging from Milky Way (MW) like to significantly steeper curves with no detectable 2175 Å bump. This result is based on a sample of only nine sight lines. From Hubble Space Telescope Space Telescope Imaging Spectrograph and IUE spectra of OB stars…
An Angular Diameter Measurement of β UMa via Stellar Intensity Interferometry with the VERITAS Observatory
Benbow, W.; Feng, Q.; Furniss, A. +45 more
We use the Very Energetic Radiation Imaging telescope Array System (VERITAS) imaging air Cherenkov telescope array to obtain the first measured angular diameter of β UMa at visual wavelengths using stellar intensity interferometry (SII) and independently constrain the limb-darkened angular diameter. The age of the Ursa Major moving group has been …
The Orbit and Mass of the Cepheid AW Per
Mérand, Antoine; Lanthermann, Cyprien; Anugu, Narsireddy +17 more
The Cepheid AW Per is a component in a multiple system with a long-period orbit. The radial velocities of Griffin cover the 38 yr orbit well. An extensive program of interferometry with the Center for High Angular Resolution Astronomy array is reported here, from which the long-period orbit is determined. In addition, a Hubble Space Telescope high…
ϵ Sagittarii: An Extreme Rapid Rotator with a Decretion Disk
Lewis, Fiona; Bailey, Jeremy; Cotton, Daniel V. +3 more
We report high-precision, multiwavelength linear-polarization observations of the bright B9 (or A0) star ϵ Sagittarii. The polarization shows the distinctive wavelength dependence expected for a rapidly rotating star. Analysis of the polarization data reveals an angular rotation rate ω (=Ω/Ωcrit) of 0.995 or greater, the highest yet mea…
Expanding the Ultracompacts: Gravitational-wave-driven Mass Transfer in the Shortest-period Binaries with Accretion Disks
Kulkarni, S. R.; Rappaport, Saul A.; Riddle, Reed +35 more
We report the discovery of three ultracompact binary white dwarf systems hosting accretion disks, with orbital periods of 7.95, 8.68, and 13.15 minutes. This significantly augments the population of mass-transferring binaries at the shortest periods, and provides the first evidence that accretors in ultracompacts can be dense enough to host accret…
Wind-line Variability and Intrinsic Errors in Observational Mass-loss Rates
Massa, Derck; Oskinova, Lidia M.; Prinja, Raman K.
UV wind-line variability in OB stars appears to be universal. In order to quantify this variation and to estimate its effect on a mass-loss rate determined from a single observation, we use the International Ultraviolet Explorer archive to identify nonpeculiar OB stars with well-developed but unsaturated Si IV λ1400 doublets and at least 10 indepe…
Revealing the Elusive Companion of the Red Giant Binary 2MASS J05215658+4359220 from UV HST and Astrosat/UVIT Data
Hutchings, John; Thilker, David; Bianchi, Luciana +2 more
Black hole (BH) demographics in different environments is critical in view of recent results on massive star binarity, and of the multimessenger detectability of compact object mergers. But the identification and characterization of noninteracting BHs are elusive, especially in the sparse field stellar population. A candidate noninteractive BH + r…