The rapidly pulsating subdwarf B star PG 1325+101

I. Oscillation modes from multisite observations

¹ INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: [silvotti;leccia]@na.astro.it
² INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: [alfio;afr]@ct.astro.it
³ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: bernabei@bo.astro.it
⁴ Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC, H3C3J7, Canada e-mail: [fontaine;bergeron;brassard]@astro.umontreal.ca
⁵ UMR 5572, Université Paul Sabatier et CNRS, Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France e-mail: scharpin@ast.obs-mip.fr
⁶ Institut for Fysik og Astronomi (IFA), Aarhus Universitet, 8000 Aarhus, Denmark e-mail: hans@phys.au.dk
⁷ Institute of Theoretical Physics and Astronomy, Vilnius University, Lithuania e-mail: jr@itpa.lt
⁸ Isaac Newton Group, S. Cruz de La Palma, Canary Islands, Spain
⁹ Korea Astronomy and Space Science Institute, South Korea e-mail: [slkim;bgpark]@kasi.re.kr
¹⁰ National Astronomical Observatories, Beijing, 100012, PR China e-mail: xjjiang@bao.ac.cn
¹¹ Missouri State University and Baker Observatory, 901 S. National, Springfield, MO 65897, USA e-mail: [mikereed;rsp814f;gww836f]@missouristate.edu
¹² Wise Observatory, Israel e-mail: [yiftah;lili;elia]@wise.tau.ac.il
¹³ Department of Physics and Space Sciences and the SARA Observatory, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA e-mail: [toswalt;mrudkin;kyjohnst]@fit.edu
¹⁴ Department of Physics and Astronomy, Johns-Hopkins University, 3400 North Charles St., Baltimore, MD 21218-2686, USA e-mail: chayer@pha.jhu.edu
¹⁵ Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
¹⁶ Steward Observatory, University of Arizona, 933 North Cherry Av., Tucson, AZ 85721, USA e-mail: bgreen@as.arizona.edu


Received: 29 March 2006
Accepted: 11 May 2006

Abstract

In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (T_eff = 35 000 K,  = 5.8, N(He)/N(H) = –1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10 μHz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92 μHz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al. 2006b, A&A, 459, 565, Paper II).