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Variability of Disk Emission in Pre-Main-Sequence and Related Stars. I. HD 31648 and HD 163296: Isolated Herbig Ae Stars Driving Herbig-Haro Flows
Polomski, Elisha F.; Russell, Ray W.; Sitko, Michael L. +13 more
Infrared photometry and spectroscopy covering a time span of a quarter-century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically…
Modeling Ultraviolet Wind Line Variability in Massive Hot Stars
Blomme, R.; Lobel, A.
We model the detailed time-evolution of discrete absorption components (DACs) observed in P Cygni profiles of the Si IV λ1400 resonance doublet lines of the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption that the DACs are caused by corotating interaction regions (CIRs) in the stellar wind. We perform 3D radiative trans…
Detection of a Hot Subdwarf Companion to the Be Star FY Canis Majoris
Gies, Douglas R.; Peters, Geraldine J.; Grundstrom, Erika D. +1 more
The rapid rotation of Be stars may be caused in some cases by past mass and angular momentum accretion in an interacting binary in which the mass donor is currently viewed as a small, hot subdwarf stripped of its outer envelope. Here we report on the spectroscopic detection of such a subdwarf in the Be binary system FY Canis Majoris from the analy…
Constraining Cosmic Evolution of Type Ia Supernovae
Becker, A. C.; Sollerman, J.; Spyromilio, J. +27 more
We present a large-scale effort of creating composite spectra of high-redshift SNe Ia and comparing them to low-redshift counterparts in an attempt to understand possible cosmic evolution of SNe Ia, which has major implications for studies of dark energy. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with exc…
Binarity in Cool Asymptotic Giant Branch Stars: A GALEX Search for Ultraviolet Excesses
Sahai, R.; Sánchez Contreras, C.; Gil de Paz, A. +1 more
The search for binarity in AGB stars is of critical importance for our understanding of how planetary nebulae acquire the dazzling variety of aspherical shapes which characterizes this class. However, detecting binary companions in such stars has been severely hampered due to their extreme luminosities and pulsations. We have carried out a small i…
Stellar Wind Variations during the X-Ray High and Low States of Cygnus X-1
Crenshaw, D. M.; Kaper, L.; Herrero, A. +10 more
We present results from Hubble Space Telescope ultraviolet spectroscopy of the massive X-ray and black hole binary system, HD 226868 = Cyg X-1. The spectra were obtained at both orbital conjunction phases in 2002 and 2003, when the system was in the X-ray high/soft state. The UV stellar wind lines suffer large reductions in absorption strength whe…
Luminosity Indicators in the Ultraviolet Spectra of Type Ia Supernovae
Filippenko, Alexei V.; Foley, Ryan J.; Jha, Saurabh W.
We present a complete sample of International Ultraviolet Explorer and Hubble Space Telescope ultraviolet (UV) spectra of Type Ia supernovae (SNe Ia) through 2004. We measure the equivalent width (EW) and blueshifted velocity of the minimum of the one strong UV feature, Fe II λ3250. We also quantify the slope of the near-UV spectra using a new par…
A Spectroscopic Orbit for Regulus
Rivinius, Th.; Štefl, S.; Baade, D. +8 more
We present a radial velocity study of the rapidly rotating B star Regulus that indicates the star is a single-lined spectroscopic binary. The orbital period (40.11 days) and probable semimajor axis (0.35 AU) are large enough that the system is not interacting at present. However, the mass function suggests that the secondary has a low mass (M…
Characterizing the Near-UV Environment of M Dwarfs
Hawley, Suzanne L.; Johns-Krull, Christopher M.; Walkowicz, Lucianne M.
We report the results of our Hubble Space Telescope (HST) snapshot survey with the ACS HRC PR200L prism, designed to measure the near-UV emission in a sample of nearby M dwarfs. Thirty-three stars were observed, spanning the mass range from 0.1 to 0.6 solar masses (Teff ~ 2200-4000 K) where the UV energy distributions vary widely betwee…
Rotational Feature of Vega Revealed from Spectral Line Profiles
Takeda, Yoichi; Kawanomoto, Satoshi; Ohishi, Naoko
In order to establish Vega's absolute rotational velocity, ve, as distinct from the inclination angle, i, we conducted a detailed profile study on a large number (~200) of weak lines based on very high signal-to-noise ratio spectrum data, making use of the fact that the lines' characteristic shapes may contain information about rotation…