Photometric and UV spectroscopic observations of 22 VUL at eclipse : observational evidence for an extended chromosphere of a solar type G supergiant.

Abstract

The solar spectral type supergiant (G3 Ib-II) of the 22 Vul binary has been observed photometrically and spectroscopically during its recent eclipse of the B9 V companion. From the new photometric observations the eclipse data given by Parsons and Ake (1984) can be slightly improved (period = 249.21 ± 0.2 days, mideclipse: JD 2446191.6 ± 0.2). The UV spectra obtained from IUE enable us to determine the extension and density of the chromosphere. The extension of the chromosphere is of the order of one giant radius (lR_G). The column density of hydrogen at a projected distance of one eclipse radius from the photosphere is log N_H = 21.6 ± 0.3, which is almost the same as the column density of the extended chromosphere of 32 Cyg (a K5 supergiant) at 1 R_K.