Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20918203w&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #182.03; Bulletin of the American Astronomical Society,
Other
4
Scientific paper
The subclass of symbiotic stars that has been suggested to be one of the sources of supernovae of type Ia is the repeating novae. Spectroscopic orbits of TCrB and RS Oph indicate that the white dwarfs in those systems have masses close to 1.4 MSun and hence they are vulnerable to catastrophic collapse if they accumulate additional mass from their red giant companions.
To investigate the nature of their companions we obtained high res (35,000) spectra of both RS Oph and TCrB in 2004 with the echelle spectrograph of the Apache Point 3.5-m telescope. The purpose was to derive as much information about the red giant component that has been losing mass, some of which has probably been captured by the white dwarf. Of particular interest is the possibility that the red giant has lost much of its hydrogen envelope which might indicate that the mass-transfer process had reached the point that a supernova outburst (rather than just a repeat of the nova outburst) is imminent. Standard methods were used to derive the effective temperature and gravity of the cool star. Using model atmospheres we have been able to derive the metallicity of the stars. Using lines of Si, Ti, Fe and Ni we found RS Oph to show small metal excess. A small metal deficiency was found for TCrB. Within the uncertainties a solar metallicity is possible for both stars. Both stars show a strong Li line. For 41 other symbiotic stars observed at the Asiago Observatory, 28 showed no Li line and 13 were too severely blended to make a judgment. It is not clear if the lithium in the two repeating nova systems is due to processes within the red giant or to capture by the red giant of Li produced in the nova explosions.
Harrison Tanya
Munari Ulisse
Wallerstein George
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