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Mon. Not. R. Astron. Soc. 000, 116 (2006) Printed 23 June 2006 (MN LATEX style file v2.2) Fe-bump instability: the excitation of pulsations in
 

Summary: Mon. Not. R. Astron. Soc. 000, 116 (2006) Printed 23 June 2006 (MN LATEX style file v2.2)
Fe-bump instability: the excitation of pulsations in
subdwarf B and other low-mass stars
C.S. Jeffery & H. Saio
Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
Astronomical Institute, School of Science, Tohoku University, Sendai 980-8578, Japan
Accepted ..... Received ..... ; in original form .....
ABSTRACT
We consider the excitation of radial and non-radial oscillations in low-mass B stars by
the iron-bump opacity mechanism. The results are significant for the interpretation
of pulsations in subdwarf B stars, helium-rich subdwarfs and extreme helium stars,
including the EC14026 and PG1716 variables.
We demonstrate that, for radial oscillations, the driving mechanism becomes ef-
fective by increasing the contrast between the iron-bump opacity and the opacity from
other sources. This can be achieved either by increasing the iron abundance or by de-
creasing the hydrogen abundance. The location of the iron-bump instability boundary
is found to depend on the mean molecular weight in the envelope and also on the ra-
dial order of the oscillation. A bluer instability boundary is provided by increasing the
iron abundance alone, rather than the entire metal component, and is required to ex-
plain the observed EC14026 variables. A bluer instability boundary is also provided by

  

Source: Armagh Observatory

 

Collections: Physics