Search Publications
New Insights into the Problem of the Surface Gravity Distribution of Cool DA White Dwarfs
Tremblay, P. -E.; Bergeron, P.; Kalirai, J. S. +1 more
We review at length the longstanding problem in the spectroscopic analysis of cool hydrogen-line (DA) white dwarfs (T eff< 13,000 K) where gravities are significantly higher than those found in hotter DA stars. The first solution that has been proposed for this problem is a mild and systematic helium contamination from convective mix…
Locating the Accretion Footprint on a Herbig Ae Star: MWC 480
Bouret, J. -C.; Ménard, F.; Kim, S. +27 more
Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-ch…
X-ray, FUV, and UV Observations of α Centauri B: Determination of Long-term Magnetic Activity Cycle and Rotation Period
Guinan, E. F.; DeWarf, L. E.; Datin, K. M.
Over the last couple of decades we have been carrying out a study of stellar magnetic activity, dynamos, atmospheric physics, and spectral irradiances from a sample of solar-type G0-5 V stars with different ages. One of the major goals of this program is to study the evolution of the Sun's X-ray through NUV spectral irradiances with age. Of partic…
The Origin and Evolution of the Halo PN BoBn 1: From a Viewpoint of Chemical Abundances Based on Multiwavelength Spectra
Izumiura, Hideyuki; Otsuka, Masaaki; Hyung, Siek +1 more
We have performed a comprehensive chemical abundance analysis of the extremely metal-poor ([Ar/H] < -2) halo planetary nebula (PN) BoBn 1 based on International Ultraviolet Explorer archive data, Subaru/High-Dispersion Spectrograph spectra, VLT/UVES archive data, and Spitzer/IRS spectra. We have detected over 600 lines in total and calculated i…
The Nature of the Hyper-Runaway Candidate Hip 60350
Przybilla, Norbert; Irrgang, Andreas; Heber, Ulrich +2 more
Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B star HIP 60350 to determine which runaway scenario—a supernova expl…
Taming the Invisible Monster: System Parameter Constraints for epsilon Aurigae from the Far-ultraviolet to the Mid-infrared
Stencel, R. E.; Hoard, D. W.; Howell, S. B.
We have assembled new Spitzer Space Telescope IRAC observations of the mysterious binary star epsilon Aurigae, along with archival far-ultraviolet to mid-infrared data, to form an unprecedented spectral energy distribution (SED) spanning 3 orders of magnitude in wavelength from 0.1 µm to 100 µm. The observed SED can be reproduced using…
The Anomalous Accretion Disk of the Cataclysmic Variable RW Sextantis
Szkody, Paula; Sion, Edward M.; Godon, Patrick +2 more
Synthetic spectra covering the wavelength range 900-3000 Å provide an accurate fit, established by a χ2 ν analysis, to a combined observed spectrum of RW Sextantis. Two separately calibrated distances to the system establish the synthetic spectrum comparison on an absolute flux basis but with two alternative scaling factors, …
XMM-Newton and FUSE Tentative Evidence for a WHIM Filament Along the Line of Sight to PKS 0558-504
Papadakis, I.; Elvis, M.; Nicastro, F. +5 more
We present a possible O VIII X-ray absorption line at z = 0.117 ± 0.001 which, if confirmed, will be the first one associated with a broad H I Lyβ (BLB: FWHM = 160+50 -30 km s-1) absorber. The absorber lies along the line of sight to the nearby (z = 0.1372) Seyfert 1 galaxy PKS 0558-504, consistent with being a WHI…
A New Investigation of the Binary HD 48099
Martins, F.; Gosset, E.; Nazé, Y. +5 more
With an orbital period of about 3.078 days, the double-lined spectroscopic binary HD 48099 is, until now, the only short-period O+O system known in the Mon OB2 association. Even though an orbital solution has already been derived for this system, few information are available about the individual stars. We present, in this paper, the results of a …
An Optical-infrared Study of the Young Multipolar Planetary Nebula NGC 6644
Zhang, Yong; Volk, Kevin; Kwok, Sun +2 more
High-resolution Hubble Space Telescope imaging of the compact planetary nebula NGC 6644 has revealed two pairs of bipolar lobes and a central ring lying close to the plane of the sky. From mid-infrared imaging obtained with the Gemini Telescope, we have found a dust torus which is oriented nearly perpendicular to one pair of the lobes. We suggest …