2009/07/11 by D. Huber, Daniel Huber, J. M. Matthews +19
Mathematics · Physics and Astronomy · #Amplitude #Asteroseismology #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Binary number #Biology #Context (archaeology) #Effective temperature #Light curve #Mathematics #Metallicity #Optics #Photometry (optics) #Physics #Spectral line #Stars #Starspot #Stellar rotation #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/200912139
11 pages, 9 figures, accepted for publication in A&A
arxiv created 2009/07/11 · openalex publication_date 2009/08/03 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Context. <i/>Asteroseismology has great potential for the study of metal-poor stars due to its sensitivity to determine stellar ages. Solid detections of oscillation frequencies in stars with well constrained fundamental parameters, combined with a known rotation period, should significantly advance our understanding of stellar structure and evolution in context with metallicity effects.<i>Aims. <i/>Our goal was to detect p-mode oscillations in the metal-poor sub-dwarf 85 Peg A and to search for variability on longer timescales.<i>Methods. <i/>We have obtained continuous high-precision optical photometry of the binary system 85 Pegasi with the MOST (Microvariability & Oscillations of STars) space telescope in two seasons (2005 & 2007). The light curves were analyzed using traditional Fourier techniques. Furthermore, we redetermined for 85 Peg A using high resolution spectra obtained through the ESO archive, and used photometric spot modeling to interpret long periodic variations.<i>Results. <i/>Our frequency analysis yields no convincing evidence for p-modes significantly above a noise level of 4 ppm. Using simulated p-mode patterns we provide upper rms amplitude limits for 85 Peg A. After removal of instrumental trends the light curve shows evidence for variability with a period of about 11 d and this periodicity is also seen in the follow up run in 2007; however, as different methods to remove instrumental trends in the 2005 run yield vastly different results, the exact shape and periodicity of the 2005 variability remain uncertain. Our re-determined value for 85 Peg A is comparable to previous studies and we provide realistic uncertainties for this parameter. Using these values in combination with simple photometric spot models we are able to reconstruct the observed variations.<i>Conclusions. <i/>The null-detection of p-modes in 85 Peg A is consistent with theoretical values for pulsation amplitudes in this star. The detected long-periodic variation in the 85 Peg system must await confirmation by further observations with similar or better precision and long-term stability. If the 11 d periodicity is real, rotational modulation of surface features on one of the components is the most likely explanation.