Opacity Effects on the Pulsations of 20 Solar Mass Models

Details Opacity Effects on the Pulsations of 20 Solar Mass Models Opacity Effects on the Pulsations of 20 Solar Mass Models

Sep 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aspc..332..265g&link_type=abstract

The Fate of the Most Massive Stars, ASP Conference Series, Vol. 332, Proceedings of the conference held 23-28 May, 2004 in Grand

Astronomy and Astrophysics

Astronomy

Scientific paper

In earlier studies (see Guzik et al. poster, Guzik et al. 1997, 1998, 1999) we used a nonlinear hydrodynamics pulsation code (Cox & Ostlie 1993) to explore the behavior of massive star models (Mo=50 and 80 M&sun;). The calculations are difficult due to the near instability of the envelopes of these stars that are approaching or exceed the Eddington limit in deeper layers. Here we study the pulsation behavior for more well-behaved lower-mass models (20 M&sun;) with Teff˜22,000 K near the red edge of the β Cep instability region, to examine trends in behavior with changes in Teff and composition (Y, Z). Pulsations with periods of about a day are driven by ionization of Fe-group elements in the envelope near 200,000 K. We initiated the models in the radial fundamental mode with radial velocity amplitude 5 km/sec. We find that for our nominal model with Teff=22,000 K, Y=0.28, Z=0.02, the amplitude grows slowly to radial velocity ˜50 km/sec. The radial velocity amplitudes decrease for lower Teff=20,000 K, and grow quickly for higher Teff =24,000 K. Pulsations also grow rapidly for higher Z (0.03), and damp quickly for lower Z (0.01) due to the increase or decrease in opacity in the driving region. Pulsations grow slowly with decreased He abundance (Y=0.24), due to increased opacity and modified envelope structure, and damp rapidly with increased Y (0.30). These are the same trends indicated earlier for the more massive models (Guzik et al. poster), but were difficult to verify. More information on these models can be found in Austin et al. (2004).

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