Issue |
A&A
Volume 471, Number 1, August III 2007
|
|
---|---|---|
Page(s) | 255 - 264 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20077514 | |
Published online | 18 June 2007 |
The field high-amplitude SX Phoenicis variable BL Camelopardalis: results from a multisite photometric campaign
I. Pulsation
1
Instituto de Astrofísica de Andalucía, CSIC, PO Box 3004, 18080 Granada, Spain e-mail: eloy@iaa.es
2
Association AstroQueyras, Le Bois de Bardon, Taponnat, 16110 La Rochefoucauld, France e-mail: stephane.fauvaud@wanadoo.fr
3
Groupe Européen d'Observations Stellaires (GEOS), 23 Parc de Levesville, 28300 Bailleau l'Evêque, France
4
Sulphur Flats Observatory, 449 Sulphur Creek Road, Jemez Springs, NM 87025, USA
5
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 China
6
Observatoire de la Côte d'Azur, BP 4229, 06304 Nice cedex 4, France
7
LESIA, Observatoire de Paris-Meudon, UMR 8109, 92190 Meudon, France
8
CRAAG, Algiers Observatory, BP 63 Bouzareah 16340, Algiers, Algeria
9
Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, 3001 Leuven, Belgium
10
Variable Star Section, Norwegian Astronomical Society, PO Box 1029 Blindern, 0315 Oslo, Norway
11
Astronomical Institute, Charles University Prague, V Holesovickach 2, 180 00 Praha 8, Czech Republic
12
Beersel Hills Observatory, B-Beersel, Belgium
13
Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium
14
Ankara University, Science Faculty, Department of Astronomy and Space Sciences, 06100 Ankara, Turkey
15
Department of Physics and Astronomy, Brigham Young University, N283 ESC, Provo, UT 84602, USA
16
Observatory and Planetarium of Johann Palisa, VSB-Technical University, Listopadu 15, 708 33 Ostrava-Poruba, Czech Republic
17
Martin Observatory, Physics Dep., Virginia Polytechnic Institute & State Univ., Blacksburg, VA 24061, USA
18
Astronomical Institute, Academy of Sciences, 251 65 Ondrejov, Czech Republic
19
Club d'Astronomie Lyon Ampère, 37 rue Paul Cazeneuve, 69008 Lyon, France
20
Club Eclipse, 22 rue du Borrégo, Appt 5A4, 75020 Paris, France
21
Ege University Observatory, 35100 Bornova, Izmir, Turkey
22
American Association of Variable Star Observers, 25 Birch St., Cambridge, MA 02138, USA
23
Akdeniz University, Art & Science Faculty, Dep. of Physics, Antalya, Turkey
Received:
20
March
2007
Accepted:
7
June
2007
Context.BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip.
Aims.An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object.
Methods.The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005–2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes.
Results.The detailed frequency analysis revealed a very rich and dense
pulsational content consisting of 25 significant peaks, 22 of them
corresponding to independent modes: one is the already known main
periodicity f0 = 25.5765 cd-1 ( = 153 mmag) and the other
21 are excited modes showing very small amplitudes. Some additional
periodicities are probably still remaining in the residuals.
This represents the most
complex spectrum ever detected in a high-amplitude
pulsator of this type. The
majority of the secondary modes suspected from earlier works are confirmed
here and, additionally, a large number of new peaks are detected.
The amplitude of the main periodicity f0 seems to be stable during decades,
but the majority of the secondary modes show strong amplitude changes
from one epoch to another. The suspected fundamental radial nature of the main
periodicity of BL Cam is confirmed, while the secondary peak
f1 = 25.2523 cd-1 is identified as a nonradial mixed mode g4 with
= 1. The radial double-mode nature, claimed by some authors for the
main two frequencies of BL Cam,
is not confirmed. Nevertheless, the frequency
f6 = 32.6464 cd-1 could correspond to the first radial overtone.
Key words: stars: variables: δ Sct / stars: individual: BL Camelopardalis / stars: oscillations / techniques: photometric
© ESO, 2007
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