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Abteilung Astronomie

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Preprint H/03

A Whole Earth Telescope campaign (Xcov17) on the pulsating subdwarf B binary system PG1336-018 (NY Vir)

Kilkenny D. (1), Reed M.D. (2,3), O'Donoghue D. (1), Kawaler S.D. (3), Mukadam A. (4), Kleinman S.J. (3,5), Nitta A. (4,5), Metcalfe T.S. (4,6), Provencal J.L. (7), Watson T.K. (8), Sullivan D.J. (9), Sullivan T. (9), Shobbrook R. (10), Jiang X.J. (11), Joshi S. (12), Ashoka B.N. (13), Seetha S. (13), Leibowitz E. (14), Ibbetson P. (14), Mendelson H. (14), Meistas E. (15), Kalytis R. (15), Alisuaskas D. (16), Martinez P. (1), van Wyk F. (1), Stobie R.S. (1), Marang F. (1), Zola S. (17), Krzesinski J. (18), Ogloza W. (18), Moskalik P. (19), Silvotti R. (20), Piccioni A. (21), Vauclair G. (22), Dolez N. (22), Cheverton M. (23), Dreizler S. (24), Schuh S.L. (24), Deetjen J.L. (24), Solheim J.-E. (25), Gonzalez Perez J.M. (25), Ulla A. (26), Oestensen R. (27), Manteiga M. (28), Suarez O. (28), Burleigh M. (29), Kepler S.O. (30), Kanaan A. (31), Giovanni O. (32)

(1) South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
(2) Department of Physics, Astronomy and Material Science, SW Missouri State University, 901 S. National, Springfield, MO 65804, USA
(3) Department of Physics and Astronomy, Iowa State University, Ames IA 50011, USA
(4) Department of Astronomy, University of Texas, Austin, TX 78712, USA
(5) Apache Point Observatory, PO Box 59, Sunspot, NM 88349, USA
(6) Harvard-Smithsonian Center for Astrophysics, 60, Garden Street, Cambridge MA 02138, USA
(7) University of Delaware, Newark, DE 19716, USA
(8) Southwestern University, 1001 E. University Avenue, Georgetown, Texas 78626, USA
(9) School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand
(10) Chatterton Astronomy Department, School of Physics, University of Sydney, NSW 2006, Australia
(11) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
(12) State Observatory, Manora Peak, Naini Tal 263 129, India
(13) Indian Space Research Organisation, Airport Road, Vimanapura, Bangalore 560 017, India
(14) Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel
(15) Institute of Theoretical Physics and Astronomy, Gostauto 12, Vilnius 2600, Lithuania
(16) Institute of Materials Research and Applied Sciences, Vilnius University, Ciurlionio 29, Vilnius 2009, Lithuania
(17) Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland
(18) Mt. Suhora Observatory, Krakow Pedagogical University, ul. Podchorczych 2, Krakow, Poland
(19) Nicolas Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland
(20) Osservatorio Astronomica di Capodimonte, Via Moiariello 16, I-80131, Napoli, Italy
(21) Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
(22) Universite Paul Sabatier, Observatoire Midi-Pyrenees, CNRS/UMR5572, 14 av. E. Belin, 31400 Toulouse, France
(23) Observatoire de Paris-Meudon, DAEC, 92195 Meudon, France
(24) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(25) Institutt for Fysikk, Universitetet i Tromsoe, N-9037 Tromsoe, Norway
(26) Universidade di Vigo, Depto. de fisisca Aplicada, Facultade de Ciencias, Campus Marcosende-Logoas, 36200, Vigo, Spain
(27) Isaac Newton Group of Telescopes, E-37800 Santa Cruz de la Palma, Canary Islands, Spain
(28) Depto. de Ciencias de la Navegacion y de la Tierra E.S. Marina, Civil. Univ. de Coruna, Pasoe de ronda 51, E-15011 A, Coruna, Spain
(29) Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, United Kingdom
(30) Instituto de fissica, UFRGS, 91501-900 Porto Alegre, RS, Brazil
(31) Universidade federal de Santa Catarina, Florianoplois, SC, Brazil
(32) Departamento de Fisica e Quimica, Universidade de Caxias do Sul, CEP 95001-970 caxias do Sul, RS, Brazil

MNRAS 345, 834 (2003)

Abstract. We present results from a multisite (`Whole Earth Telescope') photometric campaign on PG 1336-018, the close eclipsing binary system containing a pulsating subdwarf B (sdB) star. The main part of the campaign (1999 April) resulted in ~172 h of observations, representing a coverage of about 47 per cent, and additional data were obtained outside the core campaign. Periodogram analysis shows that the light variations are dominated by three frequencies near 5757, 5585 and 5369 ?Hz (~174, 179 and 186 s, respectively), although many frequencies are present, particularly in the range 5000-6000 ?Hz (~200-170 s). We identify, with some confidence, 28 frequencies down to a semi-amplitude of 0.0005 in fractional intensity (equivalent to about 0.5 mmag). It is clear that the pulsation frequencies of PG 1336-018 have changed substantially since the 1996 discovery observations were made, and that amplitude changes occur, at least in the dominant three frequencies, on relatively short time-scales (of the order of a day). On the assumption that the pulsating star is phase-locked in the binary system, we have searched for rotational splitting of frequencies near the orbital and half of the orbital period, but the results are confused by aliasing at those frequencies (due to the data gaps caused by the eclipses). A preliminary model qualitatively matches the distribution of frequencies in PG 1336-018, with some good individual correspondences, but cannot be considered adequate because geometric cancellation should hide some of the modes which are apparently detected. Analysis of the pulsations during eclipse recovers three of the strongest modes, but the limited eclipse data - which can, at best, be only about 9 per cent of the total - do not allow mode identification at this stage. Simulations indicate that an overall coverage of about 80 per cent would be required for this to be viable. An attempt was made to determine phase shifts in the pulsation frequencies as a way of directly measuring the size of the binary orbit, but the uncertainties in the method are comparable to the light travel time across the orbit (probably less than a second).

Key words: stars: individual: PG1336-018, stars: oszillations, stars: varaibles: other


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