Peter D. Usher

Faint blue objects at high Galactic latitude. V - Palomar Schmidt field centered on selected area 71

Starlike objects with both blue and ultraviolet excess have been selected from a Palomar 1.2 m Schmidt field centered on Kapteyn selected area 71. The method of selection is that used in the previous papers of this series, but modified to account for the differential reddening that occurs across the field. The color classes, color subclasses, positions, and magnitudes of the selected objects are listed.

A medium-bright quasar sample - New quasar surface densities in the magnitude range from 16.4 to 17.65 for B

A new medium-bright quasar sample (MBQS) is constructed from spectroscopic observations of 140 bright objects selected for varying degrees of blue and ultraviolet excess (B-UVX) in five Palomar 1.2 m Schmidt fields. The MBQS contains 32 quasars with B less than 17.65 mag. The new integral surface densities in the B range from 16.45 to 17.65 mag are approximately 40 percent (or more) higher than expected. The MBQS and its redshift distribution increase the area of the Hubble diagram covered by complete samples of quasars. The general spectroscopic results indicate that the three-color classification process used to catalog the spectroscopic candidates (1) has efficiently separated the intrinsically B-UVX stellar objects from the Population II subdwarfs and (2) has produced samples of B-UVX objects which are more complete than samples selected by (U - B) color alone.

On the light variations of Seyfert galaxy 3C120

The fragmentary light-curve of the Seyfert galaxy 3C120, based on photometry of the bestavailable Harvard plates of the past 60 yr, has been subjected to a periodicity analysis using a method (Appendix) particularly suited to this type of irregularly-spaced data. The analysis yields convincing evidence for a period of about 350 d and some indication of a longer period of about 22.5 yr. The observational data often depart appreciably from the light curve synthesized from the two periodic components. In one comparatively well-documented segment (1934–1939), the agreement between observational data and the synthesized model improves if it is assumed that a pair of oppositelydirected phase shifts have occurred, disturbing the 350-day period and then causing it to recover.

Optical variability of the medium-bright quasar sample

A variability study of the 32-member Medium-Bright Quasar Sample is reported. It is found that the star US 1953 has undergone a noticeable variation in the course of 26 hr. Apparent variations in the extragalactic object US 3498 may be illusory, owing to its partially resolved appearance. No other evidence for variability was detected. 34 refs.

The US Survey and the Incidence of Bright Quasars

The bright quasar sample from the US survey (UBQS) comprises 19 quasars with B 0.3. These subsets and others defined by other morphological criteria currently in use confirm the high incidence of bright US survey quasars previously established with the MB criterion alone. The number count data and the redshift distribution for the bright quasars of the UBQS are found to agree with those of the Hamburg ESO (HES) and Edinburgh quasar surveys (EQS). The number counts in the range 15.5 < B < 16.95 from these three quasar samples are consistently higher than those produced from other published quasar samples in the same magnitude range. These results suggest that the UBQS, HES, and EQS approach statistical completeness within the limits of their respective selection criteria. Surface densities from these three quasar samples favor the semiempirical fit of luminosity-dependent luminosity evolution (LDLE) of LaFranca and Cristiani. An observed excess of quasars in the range 0.5 < z ≤ 0.6 is discussed. The apparent overabundance does not appear to be a result of selection effects. The present data will be useful in recalculating the LDLE fit parameters.

Faint blue objects at high galactic latitude. IV - Palomar Schmidt fields centered on selected areas 55 and 94

Les objets a exces UV ont ete selectionnes dans les champs Palomar Schmidt centres sur les aires selectionnees 55 et 94. On donne les classes de couleur, les sous-classes et les magnitudes et positions approchees des objets selectionnes

FAINT BLUE OBJECTS AT HIGH GALACTIC LATITUDE. VIII. PERFORMANCE CHARACTERISTICS OF THE US SURVEY

The US survey has cataloged 3987 objects in seven high Galactic latitude fields according to their optical colors, magnitudes, and morphologies using photographic techniques. This paper analyzes the effectiveness of the survey at producing finding lists for complete samples of hot stars and quasars that exhibit blue and/or ultraviolet excess (B-UVX) relative to the colors of halo F and G subdwarf stars. A table of 599 spectroscopic identifications summarizes the spectroscopic coverage of the US objects that has been accomplished to date. In addition, some of the survey plates have been reexamined for objects missed during the original selection, and the literature has been searched for all other spectroscopically identified blue stars and quasars with z < 2.2 that have been selected by other surveys within the US survey areas. These results are used to estimate empirically both the accuracy of the US survey selection boundaries (in color, morphology, and brightness) and the completeness of the resulting samples of B-UVX US objects within those boundaries. In particular, it is shown that the reliability of the US color classifications is high and that the previously derived US morphological boundary for the complete selection of unresolved quasars is accurate. The contribution of color and morphological classification errors to B-UVX sample incompleteness is therefore correspondingly small. The empirical tests indicate high levels of completeness (95%) for the samples of US quasars and hot stars isolated within the stated survey selection limits. Errata and improvements to some of the published catalog data are presented in Appendices.

Coordinate stretching and interface location II. A new PL expansion

Abstract An alternative to the perturbation expansion of Poincare and Lighthill is proposed, and a simple method of deriving the new expansion is given, for the case of a nonsingular boundary. The new formulation has the advantage that the process of stretching of the independent coordinate is uncoupled from the rest of the problem, which can then be handled by standard techniques and programs. The method is illustrated by a simple example of pulsational instability in a one-zone approximation to a variable star.

Coordinate stretching and interface location I. Star models in quasi-static equilibrium

Abstract The use of the coordinate stretching procedure of Poincare and Lighthill is investigated for its applicability to the question of interface location in two-point boundary-value problems. The case in which an interface separates zones of convective and radiative equilibrium in star models is used to exemplify the technique. We discuss briefly the necessary conditions for choosing the arbitrary Poincare-Lighthill function, and we formulate the linearized problem by making a particular choice for the function.

On The Problem Of Standard Stars, Extinction, And The Photometric Zero-Point Of Uncalibrated Photographic Plates

Stars of known brightness can be used to estimate the surface brightness of extended objects to a given isophote set by the background sky density on photographic plates. The method requires the digitization of images by the measurement of specular photographic densities. A versatile theory has been proposed by Zou, Chen, and Peterson for which star trails can have arbitrary shape. The method frees observers from the need for spot sensitometry if standard stars of sufficient number and brightness range are in the field. The present formulation is an elaboration which allows for atmospheric extinction and variable background sky density. It permits a solution in principle for the photometric zero-point. A simultaneous solution for the extinction coefficients and the polynomial expansion coefficients can be found by best-fit methods. The photometric zero-point of the standard stars permits calibration of the H-D curve. Energy per pixel area is converted to intensity knowing the exposure time, and the aperture and focal length of the telescope. The incorporation of extinction corrections and variable background should permit photometry of extended objects across wide fields such as those accessible to cameras of the Schmidt design.