A SEARCH FOR GAMMA-DORADUS-TYPE VARIABLE-STARS IN THE HYADES

gamma Doradus stars are photometrically variable early F-type stars on or just above the main sequence in the Hertzsprung-Russell Diagram. T hey vary by as much as 0.1 mag on time-scales an order of magnitude lo nger than the fundamental radial pulsation period. These brightness va riations are presumably due to non-radial gravity-mode pulsations. We obtained high-precision V-band photometry of 8 F0 to F5 stars in the H yades (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 gam ma Dor-type variability. Since gamma Dor-type candidates are found in the Pleiades and in NGC 2516 (having ages of 78 and 137 Myr, respectiv ely) but apparently not in the Hyades (age > 600 Myr), we hypothesize that the gamma Dor phenomenon is a characteristic of relatively young F stars. Two of the stars investigated showed marginal evidence of low -amplitude variability. The +/-3-mmag variability of the F5 star BS 13 19 is most likely due to rotational modulation of star spots, though i t is not impossible that it is a gamma Dor star. Another F5 star, BS 1 459 (Delta V = +/-2 mmag), has a possible period similar to those of d elta Scuti stars, but no firm conclusions should be made concerning it s behaviour unless and until its variability is confirmed.