Regular frequency patterns in the young [delta] Scuti star HD 261711 observed by the CoRoT and MOST satellites

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 HD261711, a rather hot [delta] Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS [delta] Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 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 [delta] 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 [delta] 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[subscript eff]) was derived to be 8600 [plus or minus] 200 K, log g is 4.1 [plus or minus] 0.2, and the projected rotational velocity ([upsilon] sin i) is 53 [plus or minus] 1 km s[superscript −1]. Using our T[subscript eff] value and the radius of 1.8 [plus or minus] 0.5 R[subscript circled dot] derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L[subscript circled dot] of 1.20 [plus or minus] 0.14 which agrees well to the seismologically determined values of 1.65 R[subscript circled dot] and, hence, a log L/L[subscript circled dot] of 1.13. The radial velocity of 14 [plus or minus] 2 km s[superscript −1] we derived for HD261711, confirms the star’s membership to NGC2264. Conclusions. Our asteroseismic models suggest that HD261711 is a [delta] Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M[subscript circled dot]. 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.