Surveys of ultraviolet-excess quasar candidates in large fields

in Astronomy and Astrophysics. Supplement Series (1997), 123

We describe the results of a survey for moderately bright quasars performed in a 20.6-square-degree field around the galaxy NGC 450. The quasar candidates were selected on the basis of their ultraviolet ... [more ▼]

We describe the results of a survey for moderately bright quasars performed in a 20.6-square-degree field around the galaxy NGC 450. The quasar candidates were selected on the basis of their ultraviolet excess: by comparative visual inspection of the double image of each single object on a U/B dual-exposure Schmidt photographic plate, 95 primary and 45 secondary quasar candidates were selected on the basis of their $U$ image being too bright. The spectroscopic identification of the primary candidates led to the discovery of 59 bona fide quasars (out of which 6 were previously known). The Palomar Schmidt plate was digitised using the MAMA measuring machine and the outcoming data reduced using ad hoc procedures. A photometric calibration allowed us to derive values for the limiting magnitudes and for the U-B index selection threshold of the survey. A catalogue containing 60 quasars is presented with accurate positions, magnitudes and additional information such as redshifts. We studied the spatial distribution of the objects and detected, for the quasars of our sample, a significant deviation from randomness in the form of a propensity to cluster in pairs on the celestial sphere with a typical scale of about 10 arcmin. We also formally detected a tendency towards a 3-D clustering, but this result is induced by a single pair of quasars. A forthcoming paper will deal with a similar work performed in a field around NGC 520; the latter field is located directly to the North of the present one and slightly overlaps it. Based on observations acquired at the Mount Palomar and Las Campanas Observatories as well as at the European Southern Observatory. Also based on Schmidt-plate digitisations performed with the MAMA measuring machine of C.A.I. (I.N.S.U., Paris). [less ▲]

Discovery of a quadruply lensed quasar - The 'clover leaf' H1413 + 117

in Nature (1988), 334

The authors report the discovery of a second gravitational lens system in the broad absorption line quasar H1413+117. Four images of comparable brightness are seen, separated by â ¡1 arcsec. The unique ... [more ▼]

The authors report the discovery of a second gravitational lens system in the broad absorption line quasar H1413+117. Four images of comparable brightness are seen, separated by â ¡1 arcsec. The unique configuration of the images, together with the fairly rare occurrence of this type of quasar, makes it incontrovertible that this is a lensed system, not a cluster of quasars. (See also 159.062). [less ▲]

Observations of the new gravitational lens system UM 673 = Q 0142-100

in Astronomy and Astrophysics (1988), 198

The authors have recently initiated a high resolution direct imaging survey of a selected sample of highly luminous quasars (HLQs). The observations are carried out with the 2.2 m telescope at ESO, and ... [more ▼]

The authors have recently initiated a high resolution direct imaging survey of a selected sample of highly luminous quasars (HLQs). The observations are carried out with the 2.2 m telescope at ESO, and with the VLA at the NRAO, New Mexico. Following the first observing run at ESO, the authors have reported the discovery of a new gravitational lens system for the HLQ UM 673 = Q 0142-100. Additional observations supporting this interpretation are discussed here. Application of gravitational optometry to this system is given: a value of M[SUB]0[/SUB] = 2.4×10[SUP]11[/SUP]M_sun; is derived for the mass of the lensing galaxy located between UM 673 A and B and a most likely estimate of Deltat = 7 weeks is found for the expected delay between the arrival times of a similar variability event in the two lensed images of the quasar (H[SUB]0[/SUB] = 75 km s[SUP]-1[/SUP]Mpc[SUP]-1[/SUP], q[SUB]0[/SUB] = 0). [less ▲]

Photoelectric photometry of the peculiar emission-line star GG Carinae

in Astronomy and Astrophysics. Supplement Series (1984), 55

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of ... [more ▼]

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of 767 independent measurements leads to the determination of a period P = 31[SUP]d[/SUP].020 for the light variations. Different physical arguments based on the analysis of the present photoelectric - as well as previous photographic - data clearly indicate, however, that the true period is P = 62[SUP]d[/SUP].039. The resulting composite lightcurve displays two distinct maxima and minima with a total light amplitude Deltam â ¡ 0.5 mag. Additional interesting features are noticed in the mean lightcurve. Although it is not possible to classify GG Carinae among any known type of variable stars, the light variations of this object are similar to those observed for beta Lyrae-type systems. [less ▲]