Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center

Abstract

Far-ultraviolet photometry is presented for 121 objects in a 20 diameter field centered on ρ Oph and for 649 objects in a field covering the Galactic center. Broadband magnitudes with effective wavelengths of 1375 Å and 1781 Å are given. The Galactic center field overlaps two fields which were discussed in an earlier paper. Eighty- eight percent of the ultraviolet objects in the ρ Oph field were identified with visible stars using the SIMBAD database, while only 9% of the objects are blends of early-type stars too close together to separate with our resolution. The photometric calibration was studied in detail, and corrections for nonlinearity were derived for the fields analyzed earlier as well as those discussed here. For stars in common between the Galactic center field and the previous fields, a comparison of the magnitudes yielded estimates of the internal errors of the magnitudes of σ₁₃₇₅ = 0.13 mag and σ₁₇₈₁ = 0.21 mag. A collated list of stars in the fields covering the Galactic center and incorporating the revised calibration is presented and compared with the S20l data of the same region. The properties of the sample of ultraviolet objects in the σ Oph field are briefly commented upon.