scholarly journals Spectra of White-Dwarf Stars at Wavelengths < 3000 A: A Theoretical Perspective

1979 ◽  
Vol 53 ◽  
pp. 86-106 ◽  
Author(s):  
Harry L. Shipman
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Extreme Ultraviolet ◽  
Theoretical Perspective ◽  
Electromagnetic Spectrum ◽  
Dwarf Stars ◽  
X Ray ◽  
Satellite Technology ◽  
White Dwarf Stars ◽  
Current State

Astronomers studying objects outside the solar system first used the ultraviolet, extreme ultraviolet, and x-ray regions of the electromagnetic spectrum in the 1970s. The exploration of these wavelength regions has produced considerable improvements in our understanding of these objects. The achievements of x-ray astronomy are perhaps the best known. With the advance of satellite technology, other wavelength regions begin to play a role, and x-ray astronomy moves into the luminosity domain where quiescent as well as violent astrophysical processes can produce detectable amounts of radiation. This paper reviews the current state of our interpretation of white-dwarf stars at wavelengths less than 3000 A.

scholarly journals The search for planet and planetesimal transits of white dwarfs with the Zwicky Transient Facility

2019 ◽  
Vol 15 (S357) ◽  
pp. 37-40
Author(s):  
Keaton J. Bell
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Metal Pollution ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
Orbital Inclination ◽  
White Dwarf Stars ◽  
Ultimate Fate ◽  
Project Strategy ◽  
Very High

AbstractPlanetary materials orbiting white dwarf stars reveal the ultimate fate of the planets of the Solar System and all known transiting exoplanets. Observed metal pollution and infrared excesses from debris disks support that planetary systems or their remnants are common around white dwarf stars; however, these planets are difficult to detect since a very high orbital inclination angle is required for a small white dwarf to be transited, and these transits have very short (minute) durations. The low odds of catching individual transits could be overcome by a sufficiently wide and fast photometric survey. I demonstrate that, by obtaining over 100 million images of white dwarf stars with 30-second exposures in its first three years, the Zwicky Transient Facility (ZTF) is likely to record the first exoplanetary transits of white dwarfs, as well as new systems of transiting, disintegrating planetesimals. In these proceedings, I describe my project strategy to discover these systems using the ZTF data.

scholarly journals White-dwarf asteroseismology: An update

2019 ◽  
Vol 15 (S357) ◽  
pp. 93-106
Author(s):  
Alejandro H. Córsico
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Theoretical Models ◽  
Space Mission ◽  
Stellar Rotation ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Current State ◽  
Deep Interior ◽  
The Universe

AbstractThe vast majority of stars that populate the Universe will end their evolution as white-dwarf stars. Applications of white dwarfs include cosmochronology, evolution of planetary systems, and also as laboratories to study non-standard physics and crystallization. In addition to the knowledge of their surface properties from spectroscopy combined with model atmospheres, the global pulsations that they exhibit during several phases of their evolution allow spying on the deep interior of these stars. Indeed, by means of asteroseismology, an approach based on the comparison between the observed pulsation periods of variable white dwarfs and the periods predicted by representative theoretical models, we can infer details of the internal chemical stratification, the total mass, and even the stellar rotation profile and strength of magnetic fields. In this article, we review the current state of the area, emphasizing the latest findings provided by space-mission data.

An X-ray survey of hot white dwarf stars - Evidence for a m(He)/n(H) versus Teff correlation

1986 ◽  
Vol 304 ◽  
pp. 356 ◽  
Author(s):  
R. Petre ◽  
H. L. Shipman ◽  
C. R. Canizares
Keyword(s):  
White Dwarf ◽  
Dwarf Stars ◽  
X Ray ◽  
White Dwarf Stars

scholarly journals X-Ray Signatures of Axion Conversion in Magnetic White Dwarf Stars

2019 ◽  
Vol 123 (6) ◽  
Author(s):  
Christopher Dessert ◽  
Andrew J. Long ◽  
Benjamin R. Safdi
Keyword(s):  
White Dwarf ◽  
Dwarf Stars ◽  
X Ray ◽  
White Dwarf Stars

Rotating Magnetic White Dwarf Stars as X-ray Sources

1971 ◽  
Vol 232 (33) ◽  
pp. 153-154 ◽  
Author(s):  
KRISHNA M. V. APPARAO
Keyword(s):  
White Dwarf ◽  
Dwarf Stars ◽  
X Ray ◽  
White Dwarf Stars

scholarly journals The Hot White Dwarf Population in the EUVE Survey

1996 ◽  
Vol 152 ◽  
pp. 193-202
Author(s):  
Stéphane Vennes
Keyword(s):  
Stellar Evolution ◽  
White Dwarf ◽  
Extreme Ultraviolet ◽  
Model Atmosphere ◽  
Asymptotic Giant Branch ◽  
Population Characteristics ◽  
Dwarf Stars ◽  
Origin And Evolution ◽  
White Dwarf Stars ◽  
Main Population

The processes leading to the formation of white dwarf stars are known only in their most general principles; post-asymptotic giant branch evolution, leading to the formation of C-O degenerate cores, is possibly the main formation channel of white dwarf stars. In contrast, observations of hot white dwarf stars and studies of their main population characteristics offer detailed insights into the origin and evolution of these objects. We examine some new facts uncovered in the study of the survey of hot white dwarf stars at extreme ultraviolet (EUV) wavelengths. We describe model atmosphere techniques required to interpret these observations and discuss some implications of our findings for stellar evolution theory.

Exoplanetary oxygen fugacities from polluted white dwarf stars

2019 ◽  
Vol 15 (S357) ◽  
pp. 28-32
Author(s):  
Alexandra E. Doyle ◽  
Beth Klein ◽  
Ben Zuckerman ◽  
Hilke E. Schlichting ◽  
Edward D. Young
Keyword(s):  
Solar System ◽  
Oxygen Fugacity ◽  
White Dwarf ◽  
Terrestrial Planets ◽  
Dwarf Stars ◽  
Elemental Abundances ◽  
White Dwarf Stars ◽  
Solar Composition

AbstractThe intrinsic oxygen fugacity of a planet profoundly influences a variety of its geochemical and geophysical aspects. Most rocky bodies in our solar system formed with oxygen fugacities approximately five orders of magnitude higher than that corresponding to a hydrogen-rich gas of solar composition. Here we derive oxygen fugacities of extrasolar rocky bodies from the elemental abundances in 15 white dwarf (WD) stars polluted by accretion of rocks. We find that the intrinsic oxygen fugacities of rocks accreted by the WDs are similar to those of terrestrial planets and asteroids in our solar system. This result suggests that at least some rocky exoplanets are geophysically and geochemically similar to Earth.

scholarly journals TheEUVEOptical Identification Campaign II: Late-Type and White Dwarf Stars

1996 ◽  
Vol 152 ◽  
pp. 491-496
Author(s):  
N. Craig ◽  
A. Fruscione ◽  
J. Dupuis ◽  
M. Mathioudakis ◽  
J.J. Drake ◽  
...  
Keyword(s):  
White Dwarf ◽  
Extreme Ultraviolet ◽  
Late Type ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Sky Survey ◽  
Deep Survey ◽  
Balmer Lines ◽  
Optical Identifications ◽  
Error Circle

We present optical identifications of nine previously unidentified extreme ultraviolet (EUV) sources discovered during theExtreme Ultraviolet Explorer(EUVE) satellite surveys. The all-sky survey detected four of the sources and the more sensitive deep survey detected the other five sources. Three of the four all-sky survey sources, EUVE_J1918+59.9, EUVE_J2249+58.5, and EUVE_J2329+41.4, are listed in present catalogs as having possible associations with optical counterparts but without spectral class. The first two of these sources are hot DA white dwarfs showing an optical spectrum with broad Balmer lines. The source EUVE_J2329+41.4 is listed as having a possible association with an unclassified M star. We show that a pair of dMe stars are actually optical counterparts located within the error circle of theEUVEsource position. The EUVE_J2114+503 remains unidentified even though all the possible candidates have been studied. Based on the count rates we predict a fainter white dwarf or a cataclysmic variable counterpart for this candidate. All five sources discovered with theEUVEdeep survey, EUVE_J0318+184, EUVE_J0419+217, EUVE_J2053−175, EUVE_J2056−171 and EUVE_J2233−096, have been identified as late-type stars. The spectral classes, distances, visual magnitudes, and estimated hydrogen column densities for theseEUVEsources are presented.

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