Pulsational analysis of V 588 Mon and V 589 Mon observed with the MOST and CoRoT satellites

The Astrophysical Journal (Impact Factor: 6.73). 01/2011; 729(1). DOI: 10.1088/0004-637X/729/1/20
Source: arXiv

ABSTRACT The two pulsating pre-main sequence (PMS) stars V 588 Mon and V 589 Mon were
observed by CoRoT for 23.4 days in March 2008 during the Short Run SRa01 and in
2004 and 2006 by MOST for a total of ~70 days. We present their photometric
variability up to 1000 $\mu$ Hz and down to residual amplitude noise levels of
23 and 10 ppm of the CoRoT data for V 588 Mon and V 589 Mon, respectively. The
CoRoT imagette data as well as the two MOST data sets allowed for detailed
frequency analyses using Period04 and SigSpec. We confirm all previously
identified frequencies, improve the known pulsation spectra to a total of 21
frequencies for V 588 Mon and 37 for V 589 Mon and compare them to our PMS
model predictions. No model oscillation spectrum with l = 0, 1, 2, and 3
p-modes matches all the observed frequencies. When rotation is included we find
that the rotationally split modes of the slower rotating star, V 589 Mon, are
addressable via perturbative methods while for the more rapidly rotating star,
V 588 Mon, they are not and, consequently, will require more sophisticated
modeling. The high precision of the CoRoT data allowed us to investigate the
large density of frequencies found in the region from 0 to 300 $\mu$Hz. The
presence of granulation appears to be a more attractive explanation than the
excitation of high-degree modes. Granulation was modeled with a superposition
of white noise, a sum of Lorentzian-like functions and a Gaussian. Our analysis
clearly illustrates the need for a more sophisticated granulation model.

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    ABSTRACT: We concentrate on an asteroseismological study of HD 261711, a rather hot delta 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 pre-main sequence delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in 4 separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. 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 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 was derived to be 8600$\pm$200 K, log g is 4.1$\pm$0.2, and the projected rotational velocity is 53$\pm$1km/s. Using our Teff value and the radius of 1.8$\pm$0.5 Rsun derived from SED fitting, we get a log L/Lsun of 1.20$\pm$0.14 which agrees well to the seismologically determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial velocity of 14$\pm$2 km/s we derived for HD 261711, confirms the star's membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning.
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    ABSTRACT: Information on 72 confirmed or candidate pre-main-sequence delta-Scuti stars is collected and analysed to varying degree of sophistication and completeness. A systematic asteroseismic analysis of around 40 of these stars is performed, putting significant luminosity constraints on many of them simply by comparing the pulsation spectra of the stars to the fundamental and acoustic cut-off frequencies of a dense grid of stellar models. One star in particular, V1366 Ori, appears to be pulsating at or near the acoustic cut-off frequency. Many stars are found to otherwise defy proper asteroseismic analysis, in that matches between observed pulsation spectra and computed values are not able to be found. A simple test reveals that the most likely cause for these problems are the high stellar-rotation rates typically found in this class of star, with v sin i most typically between 60 and 200 km/s. The high rotation rates are found to significantly modify the pulsation spectrum of a star compared to a non-rotating star. These collective results reveal the richness and variety of phenomena within this group of stars, with stars pulsating anywhere from the lowest to the highest possible radial orders, including radial orders just below the acoustic cut-off frequency of some stars. Pulsation in non-radial orders is the normal case, not the exception to the rule, with all stars displaying low-amplitude delta-Scuti variability only.
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    ABSTRACT: The satellites MOST and CoRoT have observed the young open cluster NGC 2264 in 2006 and 2008, respectively. The resulting high-precision time-series photometry has been used to investigate the pulsational properties of pre-main sequence (PMS) cluster members. We present a highlight of this study.

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