Infrared flux excesses from hot subdwarfs^*,**

II. 72 more objects

¹ Universidade de Vigo, Departamento de Física Aplicada, Area de Física da Terra, Astronomía e Astrofísica, Facultade de Ciencias, Campus Marcosende-Lagoas, Apartado Postal 874, E-36200 Vigo, Spain
² Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain
³ Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen, Denmark

Send offprint request to: A. Ulla, ulla@uvigo.es

Received: 19 December 1996
Accepted: 20 March 1998

Abstract

In our search, started in February, 1994, for JHK excess fluxes among the hot subdwarf population as an indicator for the presence of binary companions, results for 72 more hot objects (=63 hot subdwarfs + 1 Horizontal Branch B star + 7 white dwarfs + 1 non-subdwarf object) observed with the Carlos Sánchez CVF IR photometer (in June and October, 1994), are presented. The exact number of binary hot subdwarfs has gained renewed importance after the recent discovery of pulsators with G-F companions. The total number of candidates we propose may help to set some constraints; for example, out of 41 objects with excesses, 13 may have G-type binary companions. From our new sample, 14 discoveries of binary candidates have been found: BD+25 4655, Feige 108, HD 4539, HD 149382, HD 216135, KPD 2109+440, LSI+63 198, LSIV+10 9, LSV+22 38, PG 0011+221, PG 0116+242, PG 0314+103, PG 2151+100 and TON 139. Besides, 2 more from reanalysis of February, 1994, data – BD+37 1977 and BD+48 1777, may now be found to be IR excess candidates. Two suspected binaries, PB 8555 and SB 7, are also confirmed. By fitting Kurucz (1993) model spectra and assuming zero-age main sequence companions, we find upper limits on the subdwarf gravities. The distributions of upper limits on log(g), mostly between about 5.25 and 6.5, are nearly identical for both sdBs and sdOs.