Solar-like oscillations in the G9.5 subgiant beta Aquilae

TL;DR

This study detects and analyzes solar-like oscillations in the G9.5 IV star beta Aquilae using high-precision radial velocity measurements, identifying p-mode frequencies and deriving key asteroseismic parameters for the first time.

Contribution

First detection and detailed analysis of p-mode oscillations in beta Aquilae, including the derivation of large and small frequency separations.

Findings

Identified six high S/N p-modes with l=0,2

Derived the large frequency separation  = 29.56 1 0.10 5Hz

Estimated the small separation   2.55 1 0.71 5Hz

Abstract

An interesting asteroseismic target is the G9.5 IV solar-like star beta Aql. This is an ideal target for asteroseismic investigations, because precise astrometric measurements are available from Hipparcos that greatly help in constraining the theoretical interpretation of the results. The star was observed during six nights in August 2009 by means of the high-resolution \'echelle spectrograph SARG operating with the TNG 3.58 m Italian telescope on the Canary Islands, exploiting the iodine cell technique. We present the result and the detailed analysis of high-precision radial velocity measurements, where the possibility of detecting time individual p-mode frequencies for the first and deriving their corresponding asymptotic values will be discussed. The time-series analysis carried out from \sim 800 collected spectra shows the typical p-mode frequency pattern with a maximum centered at 416 \muHz. In the frequency range 300 - 600 \muHz we identified for the first time six high S/N (\gtrsim 3.5) modes with l = 0,2 and 11 < n < 16 and three possible candidates for mixed modes (l = 1), although the p-mode identification for this type of star appears to be quite difficult owing to a substantial presence of avoided crossings. The large frequency separation and the surface term from the set of identified modes by means of the asymptotic relation were derived for the first time. Their values are \Delta \nu = 29.56 \pm 0.10 \muHz and \epsilon = 1.29 \pm 0.04, consistent with expectations. The most likely value for the small separation is \delta\nu_{02} = 2.55 \pm 0.71 \muHz.