Completeness of the FBS

The Catalogue of mean UBV data on stars (Mermilliod & Mermilliod 1994) contains 102 stars in the FBS area, with 11.0 < V < 16.5 (bright stars are saturated on the FBS plates and are therefore missed) and U - B < -0.50; 53 are included in the FBS catalogue suggesting that, in this magnitude interval, the completeness of the FBS is 52% (53/102). The completeness of the survey increases from $\sim$ 20% at U - B $\sim$ -0.6 to $\sim$ 80% for U - B < -1.0. The QSO U - B colour changes with z; but most of the changes, at least for z < 2.2, are due to the presence of an emission line in one of the two filters. The U - B colour of the continuum is in the range -0.9 < U - B < -0.7. Slitless spectroscopic surveys are sensitive to the colour of the continuum, unaffected by the emission lines. There are 58 known stars with 14.0 < V < 16.5 and U - B < -0.70 in the FBS area; 39 (67%) have been found by the FBS; we shall adopt this value for the completeness of the FBS.

 

Figure: Spectra of the six newly discovered QSOs.

The PG and FBS samples have about 2250 deg² in common. Out of the 1103 FBS objects, 618 are within the PG fields, 276 being in the PG sample. Thirty-six PG objects have not been found in the FBS. So 88% (276/312) of the PG objects have been discovered. The 36 undiscovered objects have been examined on the FBS plates; 24 have a weak UV excess (the PG survey finds a significant fraction of stars with U - B $\sim$ -0.4, while the FBS is relatively insensitive for U - B > -0.7). From this, we conclude that the FBS is $\sim$ 95% complete for U - B < -0.5. This is significantly larger than the 67% success rate obtained from the UBV stars; it is probably due to the fact that, in principle, the PG survey contains only objects brighter than B = 16.2. There are 25 PG QSOs in the FBS area, 23 of them have been found, confirming that the FBS is very efficient in discovering bright QSOs.

 

FBS name Mag. O (1) (2) b     z

0732+396 16.0 14.70 X 10 20 N 25.1 0.118

1112+668 17.0 16.53 X 10  4 Y 47.9 0.544

1150+334 16.2 16.30 R  0.8  1.2 Y 76.0 1.40

1235+699 17.9 17.96 x  5  4 Y 47.4 0.522 ?

1255+447 16.5 16.48 X 10 13 Y 72.6 0.300

1324+448 17.0 18.09 X  8  9 Y 71.1 0.331 ?

X: in the RASS-BSC; x: in the WGACAT; R: in the NVSS; (1): error of the ROSAT or VLA position (in arcsec); (2): distance between the FBS and ROSAT or VLA positions (in arcsec); Y: in the PG area; N: not in the PG area; O: APS O magnitudes.