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According to Koo et al.(1987), the astrometry was performed at six epochs over a 10 year baseline. With the 4 meter Mayall Telescope (Kitt Peak) they surveyed three 0.3 square degree areas centered at : SA 57 (1305+30), SA 68 (00015+15) and Hercules No.1 (1720+50) and using UV excess criterion they find 76 QSO candidates in SA57 and 65 candidates in SA68 down to J=22.5. Their astrometry is accurate to 0.2 arcsec/century, which they claim is sufficient to determine typical halo subdwarf proper motions at 2 to 3 sigma. Majewski et al. (1991), using the same raw data claim that QSO proper motion of up to 3.5 sigma is not significant. This contradicts their original selection criterion for rejecting halo dwarfs if their motion exceeds 2 sigma ! So what happened to the QSO with 7 sigma proper motion in this confusing game of statistical juggling ?
A literature search reveals about 20 papers by Richard G. Kron over the last 20 years relating to digitized sky survey analysis. The following are four of the papers where QSO proper motion in SA57 is explicitly mentioned in the abstract:
The field of SA 57 is surveyed for faint QSOs by studying the properties of stars which lack detectable proper motion. In principle, the method is capable of avoiding selection effects intrinsic to other search techniques. The zero-proper-motion criterion is generally successful, but all of the QSOs that have been studied would have been found with some other conventional technique, so that evidently no significant population of stellar-appearing extragalactic objects has remained undiscovered. After combining the results of several techniques, a surface density of QSOs is obtained which supersedes, but is completely consistent with, the previous point on the log N-m diagram at B = 21.4.
A catalog of 77 quasar candidates at the north Galactic pole is presented to a blue magnitude limit of 22.5 and over an area of 0.3 square degree. The data and the selection of the candidates are discussed along with the reduction procedures for the photometry, astrometry, and variability included in the catalog. The data are analyzed in terms of the counts, color indices, proper motions, and variability of faint quasar candidates. The findings strengthen the conclusion that the pure density evolution model of quasars is incorrect, that most faint quasars are not at redshifts higher than 2.5, that the soft X-ray background will not be exceeded by proposing quasars as one of the dominant constituents, and that primeval galaxies with quasar color indices and image structures are rare.
We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.
A survey of proper motions and variability was conducted of all 1185 stellar objects to J = 22.5 or F = 21.5 in the North Galactic Pole field SA57. None of the confirmed QSOs and narrow emission line galaxies in the sample was misidentified as a star due to spuriously detected proper motion larger than 3.5 sigma. Variability was detected in 30 of the 31 previously confirmed QSOs and it was concluded that all QSOs are variable over a 16 year baseline. It is shown that a search for objects which are both variable and stationary is a powerful technique for efficiently finding QSOs with no selection bias with regard to color, redshift, spectral index, or emission line equivalent widths. QSOs with the color of normal stars may be missed by conventional multicolor searches and it was concluded that multicolor surveys are from 11 to 34 percent incomplete.
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