Abstract
We are currently monitoring up to 40 Kepler candidate δ Scuti-γ Doradus (resp. γ Doradus-δ Scuti) hybrid stars in radial velocity in order to identify the physical cause behind the low frequencies observed in the periodograms based on the ultra-high ac- curacy Kepler space photometry. The presence of low frequency variability in unevolved or slightly evolved oscillating A/F-type stars can generally be explained in three ways: either 1) the star is an (un)detected binary or multiple system, or 2) the star is a g-mode pulsator (i.e. a genuine hybrid), or 3) the star's atmosphere displays an asymmetric in- tensity distribution (caused by spots, i.e. chemical anomalies, or by (very) high rotation), which is detected through rotational modulation. Our targets were selected from the glob- ally characterized variable A/F-type stars of the Kepler mission (7). We observe each star at least 4 times unevenly spread over a time lapse up to 2 months with the HERMES spectrograph (6). In the case of composite, multiple-lined spectra, these observations also provide the atmospheric properties of each component. Our principal goal is to estimate the fraction of short-period, spectroscopic systems in the sample.
Highlights
Among the latest discoveries regarding A-F type stars, the detection of many candidate pulsating hybrid stars based on the analysis of CoRoT and Kepler data is surprising
We are addressing the question of the physical mechanism responsible for the low frequencies observed in their periodograms, especially because we don’t know their true binary fraction
We initiated a programme to collect complementary spectroscopy for a sample of 40 brighter candidate targets [7]. These observations are conducted in the high-resolution mode (R ∼ 85.000) with the echelle spectrograph HERMES attached to the 1.2-m Mercator telescope at the observatory Roque de los Muchachos (La Palma, Spain) [6]
Summary
Among the latest discoveries regarding A-F type stars, the detection of many candidate pulsating hybrid stars based on the analysis of CoRoT and Kepler data is surprising. We initiated a programme to collect complementary spectroscopy for a sample of 40 brighter candidate targets [7]. These observations are conducted in the high-resolution mode (R ∼ 85.000) with the echelle spectrograph HERMES attached to the 1.2-m Mercator telescope at the observatory Roque de los Muchachos (La Palma, Spain) [6]
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