scholarly journals Far Ultraviolet Observations of Hot DA White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 139-143 ◽  
Author(s):  
David Finley ◽  
Gibor Basri ◽  
Stuart Bowyer
Keyword(s):  
Wavelength Range ◽  
White Dwarfs ◽  
Time Dependent ◽  
Flux Correction ◽  
V Band ◽  
International Ultraviolet Explorer ◽  
Effective Temperatures ◽  
Far Ultraviolet ◽  
Ultraviolet Observations ◽  
Flux Calibration

AbstractFar ultraviolet (FUV) fluxes have been used for determining the effective temperatures of a number of DA white dwarfs hotter than 20,000 K. The spectra were obtained with the International Ultraviolet Explorer (IUE). The analysis consisted of comparing the observed FUV fluxes with model fluxes scaled to the V-band flux. After suitable corrections were performed for the time-dependent sensitivity degradation of the IUE, it was found that the available flux calibrations for the IUE were insufficiently accurate for precise temperature determinations. Accordingly, we used seven white dwarfs for which accurate, independent temperature determinations have been made from line profile analyses to improve the accuracy of the IUE flux calibration. The correction to the original calibration was as great as 20% in individual 5-Å wavelength bins, while the average over the IUE wavelength range was 5%. We present both our IUE flux correction and the temperatures obtained for the hot white dwarfs.

Far Ultraviolet Observations of Disks, Winds, and White Dwarfs in Cataclysmic Variables

2009 ◽  
Author(s):  
Knox S. Long ◽  
Michael E. Van Steenberg ◽  
George Sonneborn ◽  
H. Warren Moos ◽  
William P. Blair
Keyword(s):  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

scholarly journals Future Possibilities for Ultraviolet Observations of Interstellar Molecules

1980 ◽  
Vol 87 ◽  
pp. 613-614
Author(s):  
George R. Carruthers
Keyword(s):  
Wavelength Range ◽  
Interstellar Molecules ◽  
International Ultraviolet Explorer ◽  
Ultraviolet Observations

Ultraviolet observations of interstellar molecules are currently being obtained primarily with two astronomical satellites, Copernicus (OAO-3) and International Ultraviolet Explorer (IUE). The former covers the wavelength range down to 900 Å with 0.05 or 0.2 Å resolution. IUE can observe fainter or more highly reddened stars than Copernicus, with 0.1 Å resolution, but its wavelength range does not include the resonance absorptions of the important interstellar molecules H2, HD, and N2.

scholarly journals Middle- and Far-Ultraviolet Observations of Hot White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 109-113
Author(s):  
S. B. Parsons ◽  
J. D. Wray ◽  
K. G. Henize
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Star ◽  
Low Resolution ◽  
Objective Prism ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

Several hot subluminous stars were first recognized as such from low-resolution spectra obtained with the ultraviolet objective-prism survey from Skylab, Experiment S-019. About 9 percent of the sky was photographed, 3 percent with unwidened spectra. Two hot subdwarf stars have been reported previously, HDE 283048 (Laget et al. 1978) and the companion to HR 3080 (Parsons et al. 1976a). Papers on two other subdwarfs are in preparation. One previously unrecognized white dwarf star was found, HD 149499 B, and new observations (Wray, Parsons and Henize 1979) show it to be probably the hottest white dwarf known.

scholarly journals Extreme Ultraviolet Observations of Hot White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 66-85 ◽  
Author(s):  
Stuart Bowyer
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Thermal Emission ◽  
Extreme Ultraviolet ◽  
Upper Atmosphere ◽  
Wavelength Band ◽  
Upper Limits ◽  
Effective Temperatures ◽  
Ultraviolet Observations ◽  
The Universe

The term extreme ultraviolet (EUV or XUV) is employed in upper atmosphere physics and in solar work where it usually denotes the wavelength band between 100 and 1000 Å. Since thermal emission with 30,000 ≲ T ≲ 300,000 K peaks in this band, it might be expected that studies at these wavelengths would be especially useful for objects with effective temperatures in this range. In fact9 few such studies have been carried out. The reason for this anomaly is that very few EUV studies have been made at all, particularly because of unreasonably pessimistic estimates of the opacity of the interstellar medium and partially because of instrumental difficulties encountered at these wavelengths. The first search for extreme ultraviolet emitting objects was carried out in 1975 with instrumentation on the Apollo spacecraft in the Apollo-Soyuz mission. Four of approximately thirty preselected objects were detected with this instrumentation. The objects detected unquestionably are more a reflection of the prejudices of the investigators than they are a sampling of the contents of the universe. Nonetheless, two of the four objects detected were hot white dwarfs: HZ 43 and Feige 24. In addition, upper limits which turned out to be extremely useful were obtained on the Sirius A/B system. These results, plus more recent results obtained on hot white dwarfs will be discussed in this review.

scholarly journals Far Ultraviolet Observations of Dwarf Novae made with the Hopkins Ultraviolet Telescope

1996 ◽  
Vol 158 ◽  
pp. 233-241
Author(s):  
Knox S. Long
Keyword(s):  
Steady State ◽  
Wavelength Range ◽  
White Dwarf ◽  
Space Shuttle ◽  
Higher Order ◽  
Stellar Model ◽  
Dwarf Novae ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

AbstractObservations with the Hopkins Ultraviolet Telescope on the Astro-1 and Astro-2 space shuttle missions have provided the first set of moderate (3 Å) resolution far ultraviolet (FUV) spectra of dwarf novae to include the wavelength range between Lyα and the Lyman limit. Important lines which are detected in the HUT spectra of dwarf novae in this wavelength range include S VI λλ933,945, C III λ977, O VI λλ1032,1038, P V λλ1118,1128 and C III λ1176, as well as the higher order Lyman lines. The observations confirm earlier IUE observations that two dwarf novae – U Gem and VW Hyi – have quiescent FUV spectra dominated by the white dwarf, but suggest that the quiescent FUV emission from three other dwarf novae – SS Cyg, WX Hyi and YZ Cnc – are dominated by emission from a hot portion of the disk or a disk corona. The spectra obtained of the dwarf novae Z Cam and EM Cyg in outburst and also of the nova-like variable IX Vel can be modeled reasonably successfully in terms of steady state disks constructed by adding appropriately-weighted stellar model spectra.

scholarly journals Ultraviolet Observations of Some Close Binary Systems by the Astronomical Netherlands Satellite-Ans

1976 ◽  
Vol 73 ◽  
pp. 213-223
Author(s):  
Chi-Chao Wu
Keyword(s):  
Binary Systems ◽  
Hot Spot ◽  
Close Binary ◽  
Spectral Energy ◽  
Dwarf Novae ◽  
Energy Distributions ◽  
Primary Star ◽  
Higher Temperature ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

Observations of δ Pic, a β Lyr type of eclipsing binary and seven dwarf novae are reported. The ultraviolet light curves of δ Pic indicate the accumulation of matter at the triangular Lagrangian points L4 and L5, the presence of a hot spot and a higher temperature for the primary star. The implication is that the cooler secondary fills its Roche lobe and is transfering mass to the primary; mass loss to the circumstellar space and possibly to the system may also be appreciable. The temperatures of dwarf novae are derived by comparing their ultraviolet spectral energy distributions with those for normal stars of luminosity classes IV and V. Piecing together observations for different objects, the SSCyg systems have temperatures of 28 500 K, 10 000 K and 9500 K, respectively, when they are at minimum, immediately before outburst and at the beginning of rise to maximum. At maximum, the temperature is 22 500 K or 17 300 K depending on the interstellar reddening correction for AR And. Immediately before outburst, there is a large excess of flux in the far ultraviolet as indicated by the large value of the ratio of flux at 1550 Å to that at 1800 Å. The observations of Z Cam during standstill gives a temperature of 14 900 K. No excess of flux in the far ultraviolet was observed during the maximum of AR And and the standstill of Z Cam.

scholarly journals Ultraviolet Observations of Cataclysmic Variables

1987 ◽  
Vol 93 ◽  
pp. 205-205 ◽  
Author(s):  
F. Verbunt
Keyword(s):  
Orbital Period ◽  
Cataclysmic Variables ◽  
Type Systems ◽  
Terminal Velocity ◽  
Dwarf Novae ◽  
Preliminary Results ◽  
System Type ◽  
International Ultraviolet Explorer ◽  
Flux Level ◽  
Ultraviolet Observations

AbstractThe preliminary results of the analysis of more than 1000 spectra of cataclysmic variables in the archive of the International Ultraviolet Explorer were presented at the meeting. To characterize the slope of the spectra I use F = log(f1460Å/f2880Å). For most spectra F lies between 0.2 and 0.7. No correlation of F with orbital period, inclination, system type or (for dwarf novae) length of the interoutburst interval are found, apart from somewhat lower values of F for DQ Her type systems. Out of 16 dwarf novae for which spectra both at outburst maximum and minimum are available 11 show no large difference in F between maximum and minimum, and in 5 F declines with the flux level. Out of 6 dwarf novae 5 show very red spectra during the rise to maximum, and 1 shows slopes during rise similar to those during decline.In the ultraviolet resonance lines, due to a wind from the disc, no correlation is found between inclination and terminal velocity.

scholarly journals Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations

2021 ◽  
Vol 911 (2) ◽  
pp. L25
Author(s):  
Meredith A. MacGregor ◽  
Alycia J. Weinberger ◽  
R. O. Parke Loyd ◽  
Evgenya Shkolnik ◽  
Thomas Barclay ◽  
...  
Keyword(s):  
Short Duration ◽  
Far Ultraviolet ◽  
Ultraviolet Observations
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