Issue |
A&A
Volume 471, Number 3, September I 2007
|
|
---|---|---|
Page(s) | 893 - 900 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20066541 | |
Published online | 26 June 2007 |
Synthetic properties of bright metal-poor variables
II. BL Hercules stars
1
INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: marcella@na.astro.it
2
Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
3
INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
4
INAF – Osservatorio Astronomico di Collurania, via Maggini, 64100 Teramo, Italy
Received:
11
October
2006
Accepted:
16
May
2007
We investigate the properties of the so-called BL Her stars,
i.e., Population II Cepheids with periods shorter than 8 days, using
updated pulsation models and evolutionary tracks computed by adopting a
metal abundance in the range of Z = 0.0001 to Z = 0.004. We derive
the predicted period-magnitude (PM) and period-Wesenheit (PW)
relations at the various photometric bands and we show that the
slopes of these relations are in good agreement with the slopes
determined by observed variables in Galactic globular clusters,
independently of the adopted MV(RR)-[Fe/H] relation to get the
cluster RR Lyrae-based distance. Moreover, we show that the
distances provided by the predicted PM and PW relations for BL Her stars agree within the errors with the RR Lyrae-based values. Using the predicted relations with W Vir stars, which are
Population II Cepheids with periods longer than 8 days, provides no
clear evidence for or against a change in the PM and PW slopes
around 10 days.
Key words: stars: evolution / stars: population II / stars: variables: general
© ESO, 2007
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