MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214

Abstract

We report on the analysis of high-precision space-based photometry of the roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD 134214. All three stars were observed by the MOST satellite for more than 25 days, allowing unprecedented views of their pulsation. We find previously unknown candidate frequencies in all three stars. We establish the rotation period of HD 9289 (8.5 d) for the first time and show that the star is pulsating in two modes that show different mode geometries. We present a detailed analysis of HD 99563's mode multiplet and find a new candidate frequency that appears to be independent of the previously known mode. Finally, we report on 11 detected pulsation frequencies in HD 134214, nine of which have never before been detected in photometry, and three of which are completely new detections. Thanks to the unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214 can be seen to have a well-defined large frequency spacing similar to the well-studied roAp star HD 24712 (HR 1217).

Pulsation models for the roAp star HD 134214

“…This figure indicates that HD 134214 is a relatively cool roAp star and its location in the HRD is similar to that of the prototypical roAp star HD 24712 (=HR 1217). Not only their positions in the HRD are similar, but also their pulsational properties (Gruberbauer et al 2011). We will return to this similarity later in the paper.…”

“…Table 2 lists frequencies and photometric amplitudes obtained by Gruberbauer et al (2011) from MOST photometry, and radial velocity amplitudes of Nd iii lines obtained by Kurtz et al (2007). The first column contains the designations of frequencies by Gruberbauer et al (2011), and the second column lists the corresponding designations by Kurtz et al (2007). No frequencies corresponding to ν 9 and ν 10 were found by Kurtz et al (2007).…”

“… Left‐hand panel: observed pulsation frequencies (mHz) and amplitudes (mmag) of HD 134214 obtained by Gruberbauer et al (2011) from the 2008 MOST photometry. Note that the amplitudes are plotted as log values to accommodate the amplitude of the principal frequency (2.950 mHz), which is an order of magnitude larger than any other.…”

“…In this paper, we compare oscillation frequencies of HD 134214 obtained by Gruberbauer et al (2011) from 2008 MOST photometry to theoretical frequencies of axisymmetric low‐degree modes calculated by the method of Saio (2005), including the effect of dipole magnetic fields.…”

Commission 25: Stellar Photometry and Polarimetry

“…Over the past decade the precision of photometric measurements of stellar brightness has improved to the parts per million level as a result of space-based photometric telescopes, such as the star-tracker on the WIRE mission (e.g., Bruntt et al 2009), the Canadian MOST mission (e.g., Gruberbauer et al 2011), the French-led CoRoT mission (Auvergne et al 2009), and the NASA Kepler mission (Gilliland et al 2011). This precision exceeds the best obtained from the ground (e.g., Kurtz et al 2005) by a factor of 10, and it is in general an improvement of 100 − 1000 times better than traditional ground-based photometric studies.…”