Pulsations of B star models by an opacity mechanism

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:7060764

Cox, A N ^[1]; Morgan, S M ^[2]

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1. Los Alamos National Lab., NM (USA)
2. Washington Univ., Seattle, WA (USA). Dept. of Astronomy

The pulsation mechanism for B stars has been sought for 30 years. No proposed radial or nonradial mechanism, either deeply seated or in the surface layers, has been successful in explaining all the observational details. Perhaps the missing piece in the puzzle is the opacity of the stellar material. Many times the first author has tried to make unconventional surface compositions give instability, but none were ever found. We now propose that the sudden appearance of a tremendous number of iron lines, as the temperature rises above about 150,000 K, gives a high sensitivity of the opacity to temperature at the very low densities found in these blue giants. Opacities need to increase quickly to a factor of three or more above the Cox-Tabor (1976) values in the range around 200,000 K. These increases are the same needed to decrease theoretical period ratios of double-mode Cepheids and {delta} Scuti variables to agree better with observations for conventional yellow giant masses. The reason why not all B stars pulsate is that a slight primordial deficit in the iron abundance in the surface layer (1 {times} 10{sup {minus}6} of the mass) can reduce the opacity and its sensitivity to temperature. A slight amount of iron concentration by radiative levitation could make a star pulsate even if it did not originally have enough primordial iron to cause this opacity mechanism to operate. Then any slow slight mixing caused by the unstable nonradial pulsations could restabilize the pulsations as actually observed in {alpha} Vir and {beta} CMa. Rapid levitation and mixing for the very luminous B stars with their very low density envelopes could even explain the puzzling luminous blue variables with this standard {kappa} mechanism. Large amplitude pulsations like those seen in BW Vul would indicate a somewhat larger iron abundance compared to all other B stars.

• Research Organization: Los Alamos National Lab., NM (USA)
• Sponsoring Organization: DOE/MA
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 7060764
• Report Number(s): LA-UR-90-2365; CONF-9005249--5; ON: DE90014923
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIO SOURCES
LUMINOSITY
MATHEMATICAL MODELS
OPACITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PULSARS
PULSATING VARIABLE STARS
STAR MODELS
STARS
VARIABLE STARS