The field high-amplitude SX Phoenicis variable BL Camelopardalis: results from a multisite photometric campaign
Instituto de Astrofísica de Andalucía, CSIC, PO Box 3004, 18080 Granada, Spain e-mail: firstname.lastname@example.org
2 Association AstroQueyras, Le Bois de Bardon, Taponnat, 16110 La Rochefoucauld, France e-mail: email@example.com
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
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