A Multisite Campaign to Measure Solar‐like Oscillations in Procyon. I. Observations, Data Reduction, and Slow Variations

Abstract

We have carried out a multi-site campaign to measure oscillations in the F5 star Procyon A. We obtained high-precision velocity observations over more than three weeks with eleven telescopes, with almost continuous coverage for the central ten days. This represents the most extensive campaign so far organized on any solar-type oscillator. We describe in detail the methods we used for processing and combining the data. These involved calculating weights for the velocity time series from the measurement uncertainties and adjusting them in order to minimize the noise level of the combined data. The time series of velocities for Procyon shows the clear signature of oscillations, with a plateau of excess power that is centred at 0.9 mHz and is broader than has been seen for other stars. The mean amplitude of the radial modes is 38.1 ± 1.3 cm s −1 (2.0 times solar), which is consistent with previous detections from the ground and by the WIRE spacecraft, and also with the upper limit set by the MOST spacecraft. The variation of the amplitude during the observing campaign allows us to estimate the mode lifetime to be 1.5 +1.9 −0.8 d. We also find a slow variation in the radial velocity of Procyon, with good agreement between different telescopes. These variations are remarkably similar to those seen in the Sun, and we interpret them as being due to rotational modulation from active regions on the stellar surface. The variations appear to have a period of about 10 days, which presumably equals the stellar rotation period or, perhaps, half of it. The amount of power in these slow variations indicates that the fractional area of Procyon covered by active regions is slightly higher than for the Sun.

Probing tiny convective cores with the acoustic modes of lowest degree

“…These satellites and high-precision, ground-based, campaigns conducted in the past few years (e.g. Arentoft et al 2008) have allowed the study of a number of bright solar-type stars. Yet, the recent launch of the NASA Kepler satellite (Gilliland et al 2010) is expected to completely change the current picture, increasing to over a thousand the number of solar-like pulsators for which excellent seismic data sets will be available.…”

Prospects for asteroseismology

“…Evidence for a power excess associated with solar-like oscillations was found already by Brown et al (1991); however, several subsequent observations have failed to make an unambiguous identification of the modes of oscillation, and doubt was even raised on the reality of the oscillations on the basis of observations from the MOST satellite (Matthews et al 2004) (see, however, Bedding et al 2005). A very extensive observing campaign, involving 11 telescopes, was carried out by Arentoft et al (2008). This confirmed beyond any doubt that Procyon exhibited solar-like oscillations; the mode identification has proven to be difficult but is now close to being completed (Bedding et al, in preparation).…”

Triennial Report (2012-2015): The Legacy Issue

“…Ground-based multi-side spectroscopic campaigns such as the ones for Ophiuchi (G9. 5III, De Ridder et al 2006) 420 DIVISION G COMMISSION 27 with two telescopes and Procyon (Arentoft et al 2008) with eleven telescopes were the state-of-the-art up to the photometric space revolution of the CoRoT and Kepler missions.…”