2007A&A...476.1317R


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.08CET01:25:08

2007A&A...476.1317R - Astronomy and Astrophysics, volume 476, 1317-1329 (2007/12-4)

Observations and asteroseismic analysis of the rapidly pulsating hot B subdwarf PG 0911+456.

RANDALL S.K., GREEN E.M., VAN GROOTEL V., FONTAINE G., CHARPINET S., LESSER M., BRASSARD P., SUGIMOTO T., CHAYER P., FAY A., WROBLEWSKI P., DANIEL M., STORY S. and FITZGERALD T.

Abstract (from CDS):

The principal aim of this project is to determine the structural parameters of the rapidly pulsating subdwarf B star PG 0911+456 from asteroseismology. Our work forms part of an ongoing programme to constrain the internal characteristics of hot B subdwarfs with the long-term goal of differentiating between the various formation scenarios proposed for these objects. So far, a detailed asteroseismic interpretation has been carried out for 6 such pulsators, with apparent success. First comparisons with evolutionary theory look promising, however it is clear that more targets are needed for meaningful statistics to be derived. The observational pulsation periods of PG 0911+456 were extracted from rapid time-series photometry using standard Fourier analysis techniques. Supplemented by spectroscopic estimates of the star's mean atmospheric parameters, they were used as a basis for the ``forward modelling'' approach in asteroseismology. The latter culminates in the identification of one or more ``optimal'' models that can accurately reproduce the observed period spectrum. This naturally leads to an identification of the oscillations detected in terms of degree l and radial order k, and infers the structural parameters of the target. The high S/N low- and medium resolution spectroscopy obtained led to a refinement of the atmospheric parameters for PG 0911+456, the derived values being Teff=31940±220K, logg=5.767±0.029, and logHe/H=-2.548±0.058. From the photometry it was possible to extract 7 independent pulsation periods in the 150-200 s range with amplitudes between 0.05 and 0.8% of the star's mean brightness. There was no indication of fine frequency splitting over the ∼68-day time baseline, suggesting a very slow rotation rate. An asteroseismic search of parameter space identified several models that matched the observed properties of PG 0911+456 well, one of which was isolated as the ``optimal'' model on the basis of spectroscopic and mode identification considerations. All the observed pulsations are identified with low-order acoustic modes with degree indices l=0,1,2 and 4, and match the computed periods with a dispersion of only ∼0.26%, typical of the asteroseismological studies carried out to date for this type of star. The inferred structural parameters of PG 0911+456 are Teff=31940±220K (from spectroscopy), logg=5.777±0.002, M*/M=0.39±0.01, logMenv/M*=-4.69±0.07, R/R=0.133±0.001 and L/L=16.4±0.8. We also derive the absolute magnitude MV=4.82±0.04 and a distance d=930.3±27.4pc.

Abstract Copyright:

Journal keyword(s): stars: individual: PG 0911+456 - stars: interiors - stars: horizontal-branch - stars: oscillations

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 PG 0014+068 HS* 00 16 54.2524890907 +07 04 30.045980038   15.3       sdO 69 1
2 HS 0039+4302 HS* 00 42 42.3972448465 +43 19 00.852852583   15.1       sdB 25 0
3 V* DT Lyn HS* 09 14 55.3782483821 +45 23 41.396924047   14.92       sdBO 26 0
4 V* UY Sex HS* 10 50 02.8264873492 -00 00 36.880346331 12.063 13.184 13.474 13.606 13.769 sdO9VIIHe6 151 0
5 Feige 48 HS* 11 47 14.4977747924 +61 15 31.790488292   13.12 13.28     sdB 111 0
6 PG 1219+534 HS* 12 21 29.0915970330 +53 04 36.796970097   12.41       sdB 79 1
7 PG 1325+102 HS* 13 27 48.5602550889 +09 54 51.048576366   13.73 13.98 14.29   sdBO 54 1
8 KPD 1930+2752 HS* 19 32 14.8086352823 +27 58 35.444970697 12.80 13.75 13.82     sdB 146 0
9 CD-40 13747 HS* 20 15 04.7874862110 -40 05 44.113745580 11.91 12.09 11.82     sdO 44 0
10 KPD 2109+4401 HS* 21 11 47.6446188582 +44 13 50.621291301 12.14 13.11 13.30 13.64   sdB 63 0
11 Balloon 90100001 HS* 23 15 21.4810383697 +29 05 01.429272894   11.90 12.30     sdB 79 0

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