Oscillations on the star Procyon

Stars are sphere of hot gas whose interiors transmit acoustic waves very efficiently. Geologists learn about the interior structure of Earth by monitoring how seismic waves propagate through it and, in a similar way, the interior of a star can be probed using the periodic motions on the surface that arise from such waves. Matthews et al. claim that the star Procyon does not have acoustic surface oscillations of the strength predicted. However, we show here, using ground-based spectroscopy, that Procyon is oscillating, albeit with an amplitude that is only slightly greater than the noise level observed by Matthews et al. using spaced-based photometry

Solar-like oscillations of semiregular variables

Oscillations of the Sun and solar-like stars are believed to be excited stochastically by convection near the stellar surface. Theoretical modeling predicts that the resulting amplitude increases rapidly with the luminosity of the star. Thus one might expect oscillations of substantial amplitudes in red giants with high luminosities and vigorous convection. Here we present evidence that such oscillations may in fact have been detected in the so-called semiregular variables, extensive observations of which have been made by amateur astronomers in the American Association for Variable Star Observers (AAVSO). This may offer a new opportunity for studying the physical processes that give rise to the oscillations, possibly leading to further information about the properties of convection in these stars.Comment: Astrophys. J. Lett., in the press. Processed with aastex and emulateap

Searching for p-modes in MOST Procyon data: Another view

Photometry of Procyon obtained by the MOST satellite in 2004 has been searched for p modes by several groups, with sometimes contradictory interpretations. We explore two possible factors that complicate the analysis and may lead to erroneous reports of p modes in these data. Two methods are used to illustrate the role of subtle instrumental effects in the photometry: time-frequency analysis, and a search for regularly spaced peaks in a Fourier spectrum based on the echelle diagramme approach. We find no convincing evidence of a p-mode signal in the MOST Procyon data. We can account for an apparent excess of power close to the p-mode frequency range and signs of structure in an echelle diagramme in terms of instrumental effects.Comment: Article accepted, to appear in A&

The non-detection of oscillations in Procyon by MOST: is it really a surprise?

We argue that the non-detection of oscillations in Procyon by the MOST satellite reported by Matthews et al. (2004) is fully consistent with published ground-based velocity observations of this star. We also examine the claims that the MOST observations represent the best photometric precision so far reported in the literature by about an order of magnitude and are the most sensitive data set for asteroseismology available for any star other than the Sun. These statements are not correct, with the most notable exceptions being observations of oscillations in alpha Cen A that are far superior. We further disagree that the hump of excess power seen repeatedly from velocity observations of Procyon can be explained as an artefact caused by gaps in the data. The MOST observations failed to reveal oscillations clearly because their noise level is too high, possibly from scattered Earthlight in the instrument. We did find an excess of strong peaks in the MOST amplitude spectrum that is inconsistent with a simple noise source such as granulation, and may perhaps indicate oscillations at roughly the expected level.Comment: 6 pages, accepted for publication in A&A Letter

Asteroseismology of Procyon A with SARG at TNG

We present high precision radial velocity measurements on the F5 IV star alpha CMi obtained by the SARG spectrograph at TNG (Telescopio Nazionale Galileo) exploiting the iodine cell technique. The time series of about 950 spectra of Procyon A taken during 6 observation nights are affected by an individual error of 1.3 m/s. Thanks to the iodine cell technique, the spectrograph contribution to the Doppler shift measurement error is quite negligible and our error is dominated by the photon statistics Brown et al 1994. An excess of power between 0.5 and 1.5 mHz, detected also by Martic et al. 2004 has been found. We determined a large separation frequency Delta nu0 = 56\pm 2 microHz, consistent with both theoretical estimates Chaboyer et al. 1999 and previous observations Martic et al. 2004.Comment: 4 pages, 5 figures, accepted to be published in A&A Letter

Evidence for solar-like oscillations in beta Hydri

We have made a clear detection of excess power, providing strong evidence for solar-like oscillations in the G2 subgiant beta Hyi. We observed this star over five nights with the UCLES echelle spectrograph on the 3.9-m Anglo-Australian Telescope, using an iodine absorption cell as a velocity reference. The time series of 1196 velocity measurements shows an rms scatter of 3.30 m/s, and the mean noise level in the amplitude spectrum at frequencies above 0.5 mHz is 0.11 m/s. We see a clear excess of power centred at 1.0 mHz, with peak amplitudes of about 0.5 m/s, in agreement with expectations for this star. Fitting the asymptotic relation to the power spectrum indicates the most likely value for the large separation is 56.2 microHz, also in good agreement with the known properties of beta Hyi.Comment: Accepted by ApJ Letter

Detection of Solar-like Oscillations in the G7 Giant Star xi Hya

We report the firm discovery of solar-like oscillations in a giant star. We monitored the star xi Hya (G7III) continuously during one month with the CORALIE spectrograph attached to the 1.2m Swiss Euler telescope. The 433 high-precision radial-velocity measurements clearly reveal multiple oscillation frequencies in the range 50 - 130 uHz, corresponding to periods between 2.0 and 5.5 hours. The amplitudes of the strongest modes are slightly smaller than 2 m/s. Current model calculations are compatible with the detected modes.Comment: 4 pages, 4 figures, accepted for publication as a letter in A&

p-mode frequencies in solar-like stars : I. Procyon A

As a part of an on-going program to explore the signature of p-modes in solar-like stars by means of high-resolution absorption lines pectroscopy, we have studied four stars (alfaCMi, etaCas A, zetaHer A and betaVir). We present here new results from two-site observations of Procyon A acquired over twelve nights in 1999. Oscillation frequencies for l=1 and l=0 (or 2) p-modes are detected in the power spectra of these Doppler shift measurements. A frequency analysis points out the dificulties of the classical asymptotic theory in representing the p-mode spectrum of Procyon A

Asteroseismology of Procyon with SOPHIE

This paper reports a 9-night asteroseismic observation program conducted in January 2007 with the new spectrometer Sophie at the OHP 193-cm telescope, on the F5 IV-V target Procyon A. This first asteroseismic program with Sophie was intended to test the performance of the instrument with a bright but demanding asteroseismic target and was part of a multisite network. The Sophie spectra have been reduced with the data reduction software provided by OHP. The Procyon asteroseismic data were then analyzed with statistical tools. The asymptotic analysis has been conducted considering possible curvature in the echelle diagram analysis. These observations have proven the efficient performance of Sophie used as an asteroseismometer, and succeed in a clear detection of the large spacing. An \'echelle diagram based on the 54-$\mu$Hz spacing shows clear ridges. Identification of the peaks exhibits large spacings varying from about 52 $\mu$Hz to 56 $\mu$Hz.Comment: 7 pages, 7 figure