Variable quasi-stellar objects. II. Photometry and completeness of faint blue objects in the Sandage-Luyten survey field 15h10m, +24 .
Abstract
Optical variability is investigated for 381 faint blue LB objects in the Sandage-Luyten survey field at a(l 855) = 1 5h10rn, 8(1855) = +240; the investigation is based on a plate series initiated by Sandage. Mean magnitudes are derived for all but a few of the bluest (color class I) objects, and for a complete sample of 82 redder objects of color classes II and III. Priorities on variability have been established based on statistical criteria developed previously, and on subjective perception. Current success rates for the discovery of QSOs through variability are on the order of 60%-80%. Of the 22 known QSOs discovered by random selection of candidates among the LB objects in the 8h field (Paper I) and the 1 5h field, none has a 2 probability of variability less than 80%, which suggests that nearly complete QSO populations can be discovered above this significance level. The incidence of variables among the two redder classes is much less than among the color class I population. The morphology of all sources has been investigated, resulting in three color class I and two color class II LB sources that appear to be resolved. Five other cases of contiguous nebulosities are noted. The factor by which numbers of color class I objects in the center of the field must be multiplied to achieve completeness is estimated to be 1.15 for B brighter than 18.6 mag, and is negligibly small for B brighter than 18.4 mag. The completeness factor for the edges of the field is probably much larger. Positions, estimated colors, mean magnitudes, and finding charts for additional blue objects are given. Seven of these are judged to be variable. With the present time base and sampling rate, the distribution of amplitudes of variability appears to diminish from the detectability threshold near 0.4 mag to about 0.8 mag, with some sources of larger amplitude up to 1.2 mag. Known QSOs in the field are fully compatible with the Bmax Hubble diagram. Three single-line LB objects found to be QSOs by Schmidt are consistent with the Bmax Hubble diagram when their lines are identified with Mg ii A2798; at the suggested red shifts these sources also appear to have properties similar to others at the same absolute magnitude. Some evidence emerges from the Bmax Hubble diagram that collisionally dominated excitation spectra become less frequent with increasing luminosity of QSOs in their quiescent states. Subject headings: quasars - cosmology
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1978
- DOI:
- 10.1086/156230
- Bibcode:
- 1978ApJ...223....1U
- Keywords:
-
- Astronomical Photography;
- Quasars;
- Stellar Spectrophotometry;
- Variable Stars;
- Color;
- Cosmology;
- Photographic Plates;
- Standard Deviation;
- Statistical Distributions;
- Visibility;
- Astronomy;
- Blue Objects:Photometry;
- Quasi-Stellar Objects: Variations