Precise radial velocities with BOES

Abstract

We present the first results from a high-precision radial velocity study of the K2 III giant star α Ari. Observations were acquired over 6 nights in 2004 using the new high-resolution spectrograph BOES (Bohyunsan Observatory Echelle Spectrograph) of the 1.8-m telescope. A high radial-velocity precision was achieved by using the high-resolution (R = 90 000) mode of BOES and an iodine gas absorption cell. The radial velocity measurements made during JD = 2 452 948−2 452 950 show coherent, low-amplitude variations with a period of P 1 = 0.571 days (or aliases at 0.445 or 0.821 days), and an amplitude of 18.9 m s −1 . Observations of τ Cet over this same interval are constant to within 3 m s −1 . After subtracting the contribution of the 0.57-day period, we find evidence for a second period, P 2 = 0.190 days. Observations made on a second run during JD = 2 452 975−2 452 981 show that the radial velocity variations are indeed present, but on shorter time-scales and with a lower amplitude. Two probable periods fit the radial velocity measurements from the second run reasonably well: 0.185 days or an alias of 0.256 days. The shorter period coincides with the secondary one found in the earlier measurements. We conclude that, similar to other K-giant pulsating stars, α Ari shows unstable acoustic pulsations or mode switching on time scales of tens of days. The calculated pulsation constants for the dominant 0.571-day period is consistent with third-overtone pulsations, while the secondary periodicity found in both data runs corresponds to a high overtone (n ≥ 12).

A likely exoplanet orbiting the oscillating K-giantαArietis

“…We also confirmed the short-period oscillations previously found in α Ari (Kim et al 2006). We found no evidence of the correlation between the 381 day RV variation and the EWs of H α lines or the Hipparcos photometry.…”

“…In previous publication, we (Kim et al 2006) reported multiperiodic oscillations in α Ari with periods P 1 = 0.571 day (or aliases at 0.445 or 0.871 days) observed during November to December 2003. The average amplitude variation ranges ∼±20 m s −1 just overnight.…”

Detection of a planetary companion around the giant star γ1Leonis

“…Results from the first 3 years of our survey show that the majority (more than 90%) of our sample of K-giants show RV dariations. Among them, we found spectroscopic binaries, pulsating variables (see Kim et al 2006), and several periodic RV variable stars. Our survey confirmed an exoplanet around β Gem (Han et al 2008) discovered by Hatzes et al (2006) and Reffert et al (2006).…”

Detection of an exoplanet around the evolved K giant HD 66141

“…We have reported two new exoplanets (Han et al 2010;Lee et al 2011) and confirmed an exoplanet ) and an oscillating star (Kim et al 2006).…”

“…We solved the matrix equation using singular value decomposition instead of the maximum entropy method adopted by Endl et al (2000). The code has been used in several cases (Kim et al 2006;Han et al 2008Han et al , 2010Lee et al 2008Lee et al , 2011.…”