Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii

Abstract

We report Chandra detections of coronal X-rays from the early G supergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD 204867: G0 Ib). Previous ROSAT observations of these archetypical ``hybrid chromosphere'' stars were inconclusive, in the case of α Aqr owing to a 38' mispointing, and for β Aqr because of a small positional discrepancy of the apparent source. The Chandra High Resolution Camera (HRC-I), with its superior spatial resolution and sensitivity, has obtained a positive detection of α Aqr and recovered faint emission at the location of β Aqr, now well separated from the stronger source to the southeast that dominated the earlier ROSAT image. The coronal LX/L<sub>C IV</sub> luminosity ratios of both supergiants are extremely depressed relative to early G main-sequence stars, continuing the ``X-ray deficiency syndrome'' originally identified in late F/early G luminosity class III giants of the Hertzsprung gap.