Recovery of p-modes in the combined 2004-2005 MOST observations of Procyon

Abstract

Procyon A, a bright F5 IV-V Sun-like star, is justifiably regarded as a prime asteroseismological target. This star was repeatedly observed by MOST, a specialized microsatellite providing long-term, non-interrupted broadband photometry of bright targets. So far, the widely anticipated p modes eluded direct photometric detection, though numerous independent approaches hinted for the presence of signals in the f~0.5-1.5 mHz range. Implementation of an alternative approach in data processing, as well as combination of the MOST data from 2004 and 2005 (264189 measurements in total) helps to reduce the instrumental noise affecting previous reductions, bringing the 3-sigma detection limit down to ~5.5 part-per-million in the f=0.8-1.2 mHz range. This enables to cross-identifiy 16 p-mode frequencies (though not their degrees) which were previously detected via high-precision radial velocity measurements, and provides an estimate of the large spacing, delta_nu =0.0540 mHz at f~1 mHz. The relatively low average amplitude of the detected modes, a=5.8+/-0.6 ppm, closely matches the amplitudes inferred from the ground-based spectroscopy and upper limits projected from WIRE photometry. This also explains why such low-amplitude signals eluded the direct-detection approach which exclusively relied on the MOST 2004 (or 2005) data processed by a standard pipeline.