Kappa effect pulsational instability for hot extreme helium stars

Conference · Mon Jan 01 00:00:00 EST 1990

OSTI ID:6701050

Cox, A N

A long standing problem for the hydrogen deficient stars has been the mechanism for the pulsation instability for the hottest members of this class. The usual {kappa} mechanism works well for stars that are in the hydrogen and helium ionization instability strip, and this strip extends to perhaps 20,000K at high luminosity. However, several stars are definitely hotter. Investigations for another ionization instability strip, such as for carbon, have always shown that there is not enough carbon to produce a rapid enough increase of opacity with temperature to give the well-known {kappa} effect. This is so even though these hydrogen deficient stars do show enhanced carbon in their spectra. A strong stellar wind can produce the observed hydrogen deficiency. Another popular mechanism is mass loss in a binary system through the Roche lobe. It now is possible that the missing pulsational instability mechanism is the rapid increase of iron lines absorption as the temperature increases above about 150,000K in the low density envelopes of these luminous stars. Recent calculations shows that the n = 3 to n = 3 transitions in iron that were assumed unimportant in the earlier Los Alamos calculations can double or triple the opacity suddenly as the iron lines appear in a very sensitive part of the spectrum of the diffusing photons. It has been proposed that these iron lines also cause the many varieties of normal B star pulsations, and the hydrogen deficient stars are merely another example of this new {kappa} effect for pulsating stars. The extreme helium star V2076 Oph at 31,900K, and 38,900 L{sub {circle dot}} for a mass of 1.4 M{sub {circle dot}} pulsates in the radial fundamental model at about 1 day period with a very large linear growth rate when the iron lines more than double the opacity, but is stable otherwise.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: DOE/MA
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6701050
• Report Number(s): LA-UR-90-2368; CONF-9005249-4; ON: DE90014920
• Resource Relation: Conference: Confrontation between stellar pulsation and evolution, Bologna (Italy), 28-31 May 1990
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
PULSARS
INSTABILITY
HELIUM BURNING
IONIZATION
OPACITY
STAR MODELS
COSMIC RADIO SOURCES
MATHEMATICAL MODELS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
STAR BURNING
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources