Regular frequency patterns in the young δ Scuti  star HD 261711 observed by the CoRoT and MOST satellites^{⋆,⋆⋆,⋆⋆⋆}

¹ Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: konstanze.zwintz@ster.kuleuven.be
² University of Vienna, Institute of Astronomy, Türkenschanzstrasse 17, 1180 Vienna, Austria
³ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ Department of Astronomy and Physics, St. Mary’s University, Halifax, NS B3H 3C3, Canada
⁵ Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 119017 Moscow, Russia
⁶ LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon, France
⁷ The University of Texas at Austin, McDonald Observatory, 82 Mt. Locke Rd., McDonald Observatory, Texas 79734, USA
⁸ Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
⁹ Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁰ Départment de Physique, Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, QC H3C 3J7, Canada
¹¹ NASA-Ames Research Park, MS-244-30, Moffett Field, CA 94035, USA
¹² Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
¹³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 17 December 2012
Accepted: 19 February 2013

Abstract

Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars.

Aims. We concentrate on an asteroseismological study of HD 261711, a rather hot δ Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a PMS δ Scuti  star using the time series photometry obtained by the MOST satellite in 2006.

Methods. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star’s fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis.

Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the δ Scuti  variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new δ Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T_eff) was derived to be 8600 ± 200 K, log g  is 4.1 ± 0.2, and the projected rotational velocity (υsini) is 53 ± 1 km s^-1. Using our T_eff  value and the radius of 1.8 ± 0.5 R_⊙  derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L_⊙  of 1.20 ± 0.14 which agrees well to the seismologically determined values of 1.65 R_⊙  and, hence, a log L/L_⊙  of 1.13. The radial velocity of 14 ± 2 km s^-1 we derived for HD 261711, confirms the star’s membership to NGC 2264.

Conclusions. Our asteroseismic models suggest that HD 261711 is a δ Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M_⊙. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.