The d Scuti star FG Virginis II. A search for high pulsation frequencies

Michel Breger, E Serkowitsch, Peter Reegen, Judi L. Provencal, Matt A. Wood, J. Christopher Clemens, M. Sean O'Brien, Beverley J. Winget, R. Edward Nather, Scot J. Kleinman, Antonio Kanaan, Michael H. Montgomery, Paul A. Bradley, Denis J. Sullivan, Elia M. Leibowitz, H Mendelson, J Krzesinski, G Pajdosz, Pawel A. Moskalik, Jan Erik Solheim

Although the d Scuti and roAp variables occupy similar positions on and near the main sequence, d Scuti variables pulsate with lower radial and nonradial overtones and lower frequencies. To test whether high frequencies (as found in the roAp stars) are also present in d Scuti stars, a multisite campaign with the Whole Earth Telescope (WET) was carried out for the star FG Vir. The 96.7 hours of WET photometry were supplemented by measurements made with the Delta Scuti Network (DSN), because the DSN technique includes regular measurements of comparison stars and is better suited to monitoring the low frequencies (= 500 œHz). This made possible the correction for low-frequency variability (10 pulsation frequencies from 106 to 395 œHz and amplitudes from 0.001 to 0.02) in order to prevent spectral leakage into the high-frequency domain. It is shown that such a correction is essential. In the 1-10 mHz region of interest (corresponding to periods between 17 and 1.7 minutes) no significant stellar variability could be detected. The highest peaks in the amplitude spectra ranged from 0.00023 (near 1 mHz) to 0.00012 near 10 mHz, where the amplitudes are expressed in units of fractional intensity. Statistical tests show that these peaks are caused by noise. These results indicate that for FG Vir the multimode pulsations in the low-frequency region (with individual amplitudes up to 0.02) are not accompanied by photometrically detectable high overtone pulsation at high frequencies. This result is consistent with the hypothesis that high-order p-mode pulsations in the millimag range require a large magnetic field, as detected in the roAp stars.

Department of Astrophysics
External organisation(s)
Universität Wien, University of Delaware, Florida Institute of Technology, University of North Carolina at Chapel Hill, Yale University, University of Texas, Austin, Los Alamos National Laboratory, Victoria University of Wellington, Tel Aviv University, Apache Point Observatory, Pedagogical University of Cracow, Polish Academy of Sciences (PAS), University of Oslo (UiO)
Astronomy & Astrophysics
No. of pages
Publication date
Peer reviewed
Austrian Fields of Science 2012
103003 Astronomy
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