A driving mechanism for the newly discovered class of pulsating subdwarf B stars

被引:265
作者
Charpinet, S
Fontaine, G
Brassard, P
Chayer, P
Rogers, FJ
Iglesias, CA
Dorman, B
机构
[1] UNIV CALIF BERKELEY,CTR EUV ASTROPHYS,BERKELEY,CA 94720
[2] LAWRENCE LIVERMORE NATL LAB,LIVERMORE,CA 94550
[3] NASA,GODDARD SPACE FLIGHT CTR,ASTRON & SOLAR PHYS LAB,GREENBELT,MD 20771
[4] UNIV VIRGINIA,DEPT ASTRON,CHARLOTTESVILLE,VA 22903
基金
美国国家航空航天局;
关键词
stars; interiors; oscillations; subdwarfs;
D O I
10.1086/310741
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present new calculations that strongly reinforce the idea-originally proposed by Charpinet et al.-that pulsation modes are driven through an opacity bump due to a local enhancement of the iron abundance in the envelopes of sdB stars. Our improved models incorporate nonuniform iron abundance distributions obtained through the condition of diffusive equilibrium between gravitational settling and radiative levitation. They also include special Rosseland opacity tables that take into account the large variations of the iron abundance about the cosmic value that are predicted by equilibrium radiative levitation theory. For representative models with M = 0.48 M. and log g = 5.8, we find strong instabilities for low-order radial and nonradial (p and f) pulsation modes in the range 36,500 K greater than or similar to T-eff greater than or similar to 29,000 K. The four pulsating sdB stars currently known all have effective temperatures in that range. In addition, one of our models with T-eff = 34,000 K has a band of unstable modes with periods in the range 116-195 s, in excellent agreement with those of the known pulsators. We therefore claim that our proposed iron bump mechanism provides a natural explanation for the instabilities found in the newly discovered class of pulsating sdB stars.
引用
收藏
页码:L123 / L126
页数:4
相关论文
共 22 条
[11]   ON NONRADIAL OSCILLATIONS OF B-TYPE STARS [J].
GAUTSCHY, A ;
SAIO, H .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1993, 262 (01) :213-219
[12]  
HEBER U, 1991, IAU S, V145, P363
[13]   Updated OPAL opacities [J].
Iglesias, CA ;
Rogers, FJ .
ASTROPHYSICAL JOURNAL, 1996, 464 (02) :943-953
[14]   A new class of rapidly pulsating star .1. EC 14026-2647, the class prototype [J].
Kilkenny, D ;
Koen, C ;
ODonoghue, D ;
Stobie, RS .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1997, 285 (03) :640-644
[15]  
KILKENNY D, 1997, IN PRESS P 3 C FAINT
[16]   A new class of rapidly pulsating star .2. PB 8783 [J].
Koen, C ;
Kilkenny, D ;
ODonoghue, D ;
VanWyk, F ;
Stobie, RS .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1997, 285 (03) :645-650
[17]  
MOSKALIK P, 1992, ASTRON ASTROPHYS, V256, pL5
[18]   A new class of rapidly pulsating star .4. Oscillations in EC 20117-4014 and atmospheric analyses [J].
ODonoghue, D ;
LynasGray, AE ;
Kilkenny, D ;
Stobie, RS ;
Koen, C .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1997, 285 (03) :657-672
[19]  
ODONOGHUE D, 1997, P 10 EUR WORKSH WHIT
[20]   ROSSELAND MEAN OPACITIES FOR VARIABLE COMPOSITIONS [J].
ROGERS, FJ ;
IGLESIAS, CA .
ASTROPHYSICAL JOURNAL, 1992, 401 (01) :361-366