Issue |
A&A
Volume 459, Number 2, November IV 2006
|
|
---|---|---|
Page(s) | 565 - 576 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20065316 | |
Published online | 12 September 2006 |
The rapidly pulsating subdwarf B star PG 1325+101
II. Structural parameters from asteroseismology
1
UMR 5572, Université Paul Sabatier et CNRS, Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France e-mail: scharpin@ast.obs-mip.fr
2
INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: silvotti@na.astro.it
3
INAF - Osservatorio Astronomico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: [alfio;leccia;afr]@ct.astro.it
4
Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC, H3C 3J7, Canada e-mail: $\!$[ fontaine$\!$;brassard$\!$;bergeron] @astro.umontreal.ca
5
Dept. of Physics and Astronomy, Johns-Hopkins University, 3400 North Charles St., Baltimore, MD 21218-2686, USA e-mail: chayer@pha.jhu.edu
6
Primary affiliation: Dept. of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
7
Steward Observatory, University of Arizona, 933 North Cherry Av., Tucson, AZ 85721, USA e-mail: bgreen@as.arizona.edu
8
INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: bernabei@astbo3.bo.astro.it
9
Danish Asteroseismology Center, Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade, Bygn. 1520, 8000 Aarhus C., Denmark e-mail: kjeldsen@phys.au.dk
10
Institute of Theoretical Physics and Astronomy, Vilnius University, Lithuania e-mail: jr@itpa.lt
11
Isaac Newton Group, S. Cruz de la Palma, Canary Islands, Spain e-mail: roy@ing.iac.es
12
Korea Astronomy and Space Science Institute, South Korea e-mail: [slkim;bgpark]@kasi.re.kr
13
National Astronomical Observatories, Beijing, 100012, PR China e-mail: xjjiang@bao.ac.cn
14
Missouri State University and Baker Observatory, 901 S. National, Springfield, MO 65897, USA e-mail: [MikeReed;gww836f;rsp814f]@missouristate.edu
15
Wise Observatory, Israel e-mail: [yiftah;lili;elia]@wise.tau.ac.il
16
Florida Institute of Technology, USA e-mail: [toswalt;rudkin;kyjohnst]@fit.edu
Received:
29
March
2006
Accepted:
11
May
2006
We present a detailed analysis of the rapidly pulsating
subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits
the outcome of dedicated multisite observations using time-series
photometry that revealed the presence of (at least) 15 periodicities
in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557,
Paper I). Based on high-, medium-resolution spectra obtained at the
Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT
Telescope, new NLTE spectroscopic derivations of the atmospheric
parameters of PG 1325+101 are presented. The mean values of
K,
, and
are in agreement with previous
determinations, but are significantly more accurate. These
improved spectroscopic parameters are essential for isolating a
unique asteroseismic model solution for the observed pulsation spectrum of
PG 1325+101. Using the “forward modeling” approach, our combined
spectroscopic and asteroseismic analysis leads objectively to the
identification of the (k,
) indices of the 12 independent modes
observed in this star, and to the determination of its structural
parameters. The periods correspond to low-order acoustic modes with
adjacent values of k and having degrees
. They define a
band of unstable modes, in agreement with nonadiabatic pulsation
theory. The average dispersion achieved between the observed periods
and the periods of the corresponding theoretical modes of the optimal
model is only ~0.46% (∼0.54 s), comparable to the results
from similar analyses of other EC14026 stars analysed to date. The
inferred structural parameters of PG 1325+101 are
K,
,
,
(i.e.,
close to the canonical mass of extreme horizontal branch stars),
, and
. In
addition, by combining detailed model atmosphere calculations with
, we estimate that this star has an absolute
visual magnitude
and is located at a distance of
pc. Finally, the presence of
fine structure in the observed period spectrum suggests a rotation
period of
days, leading to an equatorial velocity of
km s-1. Hence, asteroseismic evidence
suggests that PG 1325+101 is a slow rotator, a conclusion reinforced by
the limit
km s-1, which we determined by
modeling the He I 4471 line in our 1 Å-resolution
MMT spectrum.
Key words: stars: interiors / stars: oscillations / stars: horizontal-branch / stars: individual: PG 1325+101
© ESO, 2006
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