Results from the Central Hyades Survey

Abstract

As participants in the HEAO-2 (Einstein Observatory) guest investigator program, we have conducted a soft x-ray survey of the central ~5° of the Hyades cluster. Using the Imaging Proportional Counter (IPC) on Einstein, over 40 discrete sources were detected, most of which have bright (V≲10) stars as optical counterparts. X-ray luminosities (L_X) for these stars are in the range 10^28.5 - 10³⁰ erg s ^-1. From the fraction of Hyades detected (≳50%), and the observed range of L_X, we may infer that stellar coronae are common phenomena in the cluster. The level of x-ray emission among the late F and early G stars in the Hyades is ~30 times that of the sun viewed as a star. The relative youth and thus higher rotational velocities of the Hyades dwarfs compared to the sun is probably the most significant factor in producing such enhanced coronal activity. Comparison of our survey results with data in other wavelength regions and with other stellar surveys on Einstein is beginning to prove fruitful in understanding physical processes in coronae.