The classification of frequencies in the γ Doradus/δ Scuti hybrid star HD 49434★

Abstract

Hybrid stars of the γ Doradus and δ Scuti pulsation types have great potential for asteroseismic analysis to explore their interior structure. To achieve this, mode identifications of pulsational frequencies observed in the stars must be made, a task which is far from simple. In this work we begin the analysis by scrutinizing the frequencies found in the CoRoT photometric satellite measurements and ground-based high-resolution spectroscopy of the hybrid star HD 49434. The results show almost no consistency between the frequencies found using the two techniques and no characteristic period spacings or couplings were identified in either dataset. The spectroscopic data additionally show no evidence for any long term (5 year) variation in the dominant frequency. The 31 spectroscopic frequencies identified have standard deviation profiles suggesting multiple modes sharing (l, m) in the δ Scuti frequency region and several skewed modes sharing the same (l, m) in the γ Doradus frequency region. In addition, there is a clear frequency in the γ Doradus frequency region that appears to be unrelated to the others. We conclude HD 49434 remains a δ Scuti/ γ Doradus candidate hybrid star but more sophisticated models dealing with rotation are sought to obtain a clear picture of the pulsational behaviour of this star.

Detection of Solar-Like Oscillations, Observational Constraints, and Stellar Models for Θ Cyg, the Brightest Star Observed by the Kepler Mission

“…It is possible that γ Dor modes may be visible in high-resolution spectroscopic observations, but not in photometry. Brunsden et al (2015) find that,for = V 5.74 magnitude δSct/γ Dor hybrid star HD 49434, some g modes found via high-resolution spectroscopy were not detected in CoRoT photometry, and vice versa. Another possibility discussed by Guzik et al (2000) is that shear dissipation from turbulent viscosity near the convection zone base or in an overshooting region below the convection zone may be comparable to the driving, and may quench the pulsations.…”

Spectroscopic mode identification of γ Doradus stars

“…There is not presently good agreement between ground-based and space-based observations (e.g., [2]), although only a few stars have such observations.…”

Asteroseismology of hybridδScuti-γDoradus pulsating stars

“…Among them, we mention HD 114839 (King et al 2006) and BD+18-4914 (Rowe et al 2006), both detected by the MOST satellite. Furthermore, hybrid δ Sct-γ Dor stars discovered with CoRoT observations are CoRoT 102699796 (Ripepi et al 2011), CoRoT 105733033 (Chapellier et al 2012), CoRoT 100866999 (Chapellier & Mathias 2013), and HD 49434 Brunsden et al (2015). Finally, among hybrid stars discovered with the Kepler mission, we mention KIC 6761539 (Herzberg et al 2012), KIC 11145123 (Kurtz et al 2014), KIC 8569819 (Kurtz et al 2015), KIC 9244992 (Saio et al 2015), KIC 9533489 (Bognár et al 2015) and KIC 10080943 (Keen et al 2015).…”

“…In this section we will describe our asteroseismological analysis of the hybrid δ Sct-γ Dor stars KIC 11145123 (Kurtz et al 2014), KIC 9244992 (Saio et al 2015), HD 49434 (Brunsden et al 2015), CoRoT 105733033 (Chapellier et al 2012) and CoRoT 100866999 (Chapellier & Mathias 2013). As we shall see, we take fully advantage of the information contained in both the acoustic-and the gravity-mode period spectra offered by these target stars.…”

“…In particular, we make full use of the valuable property that some hybrid stars offer, that is, the value of the mean period spacing (∆Π) of g modes. Specifically, we perform asteroseismic modelling of the hybrid δ Sct-γ Dor stars CoRoT 105733033 (Chapellier et al 2012), CoRoT 100866999 (Chapellier & Mathias 2013), KIC 11145123 (Kurtz et al 2014), KIC 9244992 (Saio et al 2015) and HD 49434 Brunsden et al (Brunsden et al 2015). The use of ∆Π allows us to discard a large portion of the grid of models; those that do not reproduce the observed period spacing.…”