Abstract
Hubble Faint Object Spectrograph (FOS) observations of VW Hyi one day after the end of a normal dwarf nova outburst reveal a heated white dwarf with deep, broad Lyα, narrow metallic absorption features, and evidence of a hotter Keplerian-broadened component manifested in quiescence as a broad continuum hump. Our best reduced χ2 fit to the data reveals (1) a DAZQ white dwarf with Teff= 22,500 ± 500 K, log g = 8, and photospheric abundances C = 0.5 solar, N = 5.0 solar, O = 2.0 solar, Si = 0.2 solar, Fe = 0.5 solar, with all other metals being 0.3 solar, and (2) a rapidly spinning accretion belt with Vrot = 3350 km s-1, Tbelt = 26,000 ± 1000 K, log g = 6.0, and a fractional belt area of approximately 11%. Our earlier FOS spectrum obtained 10 days after superoutburst reveals a cooler DAZQ white dwarf (20,500 ± 1000 K), relatively lower metal abundances, and a smaller fractional area (3%) for the accretion belt. Thus, 1 day after a normal outburst, the white dwarf is ≈2000 K hotter, the accretion belt fractional area is a factor of 3 greater, the accretion belt temperature appears to be cooler than at 10 days post-superoutburst, and the accreted atmosphere has relatively higher metal abundances. Finally, the accretion belt maintained during quiescence may provide a natural explanation for the 14 s soft X-ray oscillations, requires a deeper source of heating (compression and shear mixing), and implies a lower limit to the viscous spin-down timescale of 10 days.
| Original language | English (US) |
|---|---|
| Journal | Astrophysical Journal |
| Volume | 471 |
| Issue number | 1 PART II |
| State | Published - 1996 |
| Externally published | Yes |
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Keywords
- Novae, cataclysmic variables
- Stars: Individual (vw hydri)
- White dwarfs
ASJC Scopus subject areas
- Space and Planetary Science
Cite this
The cooling white dwarf in VW hydri after normal outburst and superoutburst : HST evidence of a sustained accretion belt. / Sion, Edward M.; Cheng, F. U Hua; Huang, Min; Hubeny, Ivan -; Szkody, Paula.
In: Astrophysical Journal, Vol. 471, No. 1 PART II, 1996.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The cooling white dwarf in VW hydri after normal outburst and superoutburst
T2 - HST evidence of a sustained accretion belt
AU - Sion, Edward M.
AU - Cheng, F. U Hua
AU - Huang, Min
AU - Hubeny, Ivan -
AU - Szkody, Paula
PY - 1996
Y1 - 1996
N2 - Hubble Faint Object Spectrograph (FOS) observations of VW Hyi one day after the end of a normal dwarf nova outburst reveal a heated white dwarf with deep, broad Lyα, narrow metallic absorption features, and evidence of a hotter Keplerian-broadened component manifested in quiescence as a broad continuum hump. Our best reduced χ2 fit to the data reveals (1) a DAZQ white dwarf with Teff= 22,500 ± 500 K, log g = 8, and photospheric abundances C = 0.5 solar, N = 5.0 solar, O = 2.0 solar, Si = 0.2 solar, Fe = 0.5 solar, with all other metals being 0.3 solar, and (2) a rapidly spinning accretion belt with Vrot = 3350 km s-1, Tbelt = 26,000 ± 1000 K, log g = 6.0, and a fractional belt area of approximately 11%. Our earlier FOS spectrum obtained 10 days after superoutburst reveals a cooler DAZQ white dwarf (20,500 ± 1000 K), relatively lower metal abundances, and a smaller fractional area (3%) for the accretion belt. Thus, 1 day after a normal outburst, the white dwarf is ≈2000 K hotter, the accretion belt fractional area is a factor of 3 greater, the accretion belt temperature appears to be cooler than at 10 days post-superoutburst, and the accreted atmosphere has relatively higher metal abundances. Finally, the accretion belt maintained during quiescence may provide a natural explanation for the 14 s soft X-ray oscillations, requires a deeper source of heating (compression and shear mixing), and implies a lower limit to the viscous spin-down timescale of 10 days.
AB - Hubble Faint Object Spectrograph (FOS) observations of VW Hyi one day after the end of a normal dwarf nova outburst reveal a heated white dwarf with deep, broad Lyα, narrow metallic absorption features, and evidence of a hotter Keplerian-broadened component manifested in quiescence as a broad continuum hump. Our best reduced χ2 fit to the data reveals (1) a DAZQ white dwarf with Teff= 22,500 ± 500 K, log g = 8, and photospheric abundances C = 0.5 solar, N = 5.0 solar, O = 2.0 solar, Si = 0.2 solar, Fe = 0.5 solar, with all other metals being 0.3 solar, and (2) a rapidly spinning accretion belt with Vrot = 3350 km s-1, Tbelt = 26,000 ± 1000 K, log g = 6.0, and a fractional belt area of approximately 11%. Our earlier FOS spectrum obtained 10 days after superoutburst reveals a cooler DAZQ white dwarf (20,500 ± 1000 K), relatively lower metal abundances, and a smaller fractional area (3%) for the accretion belt. Thus, 1 day after a normal outburst, the white dwarf is ≈2000 K hotter, the accretion belt fractional area is a factor of 3 greater, the accretion belt temperature appears to be cooler than at 10 days post-superoutburst, and the accreted atmosphere has relatively higher metal abundances. Finally, the accretion belt maintained during quiescence may provide a natural explanation for the 14 s soft X-ray oscillations, requires a deeper source of heating (compression and shear mixing), and implies a lower limit to the viscous spin-down timescale of 10 days.
KW - Novae, cataclysmic variables
KW - Stars: Individual (vw hydri)
KW - White dwarfs
UR - http://www.scopus.com/inward/record.url?scp=21444450412&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=21444450412&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:21444450412
VL - 471
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 PART II
ER -