A Search for $γ$ Doradus-Type Variable Stars in the Hyades

Abstract

$γ$ Doradus stars are photometrically variable early F-type stars on or just above the main sequence in the Hertzsprung-Russell Diagram. They vary by as much as 0.1 mag on time scales an order of magnitude slower than the fundamental radial pulsation period. These brightness variations are presumably due to non-radial gravity-mode pulsations. We obtained high precision $V$-band photometry of 8 F0 to F5 stars in the Hyades (BS 1319, BS 1354, BS 1385, BS 1408, BS 1430, BS 1432, BS 1459, and BS 1472) and found that none of them showed strong evidence of $γ$ Dor-type variability. Since $γ$ Dor-type candidates are found in the Pleiades and in NGC 2516 (having ages of 78 and 137 Myr, repectively) but apparently not in the Hyades (age $>$ 600 Myr), we hypothesize that the $γ$ Dor phenomenon is a characteristic of relatively young F stars. Two of the stars investigated showed marginal evidence of low-amplitude variability. The $\pm$3 mmag variability of the F5 star BS 1319 is most likely due to rotational modulation of star spots, though it is not impossible that it is a $γ$ Dor star. Another F5 star BS 1459 ($ΔV = \pm 2$ mmag) has a possible period similar to $δ$ Scuti stars, but no firm conclusions should be made concerning its behavior unless and until its variability is confirmed.