Engineering topics

Gunn, James E.

Publications and source records attributed to Gunn, James E..

24 records · Page 2

NASA NTRS1989

A study of ten quasars with redshifts greater than four

Four quasars with redshifts greater than four were detected in a low-resolution CCD grism survey. CCD photometry and high S/N, moderate resolution spectra are presented for these quasars and the six other known quasars with redshifts above 4. The M sub B values of nine of the objects are between -27.5 and -25, with the tenth quasar having an M sub B value of -29. The emission lines and shapes of the continua of these ten quasars are similar to those of lower-redshift quasars. The results suggest that the C IV emission lines in high-redshift quasars may be weaker than those in lower-redshift quasars. The continua of all of the high-redshift quasars display strong depressions blueward of the Ly-alpha emission line.

Schneider, Donald P.↗

NASA NTRS1988

A new convergent point and distance modulus for the Hyades from radial velocities

The dynamics of the Hyades open star cluster is investigated analytically on the basis of the photoelectric radial velocities reported by Griffin et al. (1988). The methods used to determine the radial-velocity gradient, convergent point, and distance modulus are described, and the results are presented in tables and graphs and characterized in detail. Findings reported include convergent-point alpha = 98.2 + or - 1.1 deg and delta = 6.1 + or - 1.0 deg, space motion 48.0 + or - 0.27 km/s, distance to cluster center 45.4 + or - 2.1 pc, distance modulus 3.28 + or - 0.10, and cluster velocity dispersion 230 m/s.

Gunn, James E.↗

NASA NTRS1987

PC 0910 + 5625 - An optically selected quasar with a redshift of 4.04

The discovery of the second quasar with a redshift greater than 4 is reported. This object, which has an r magnitude of 21.0, was detected on a CCD grism survey. The spectrum of the quasar has strong, relatively narrow (but resolved) emission lines; there is a deep absorption trough about 100 A wide on the blue wing of the Lyman-alpha line; and the continuum at wavelengths shorter than the absorption feature is far weaker than the level present redward of Lyman-alpha.

Schmidt, Maarten↗

NASA NTRS1987

Four-shooter - A large format charge-coupled device camera for the Hale telescope

The Hale telescope has employed an astronomical camera using four 800x800 CCDs in an optical arrangement that allows the imaging of a contiguous 1600-pixel-square region of the sky; reimaging optics are then used to yield a scale of 0.33 arcsec/pixel. Optical coatings are incorporated to yield a throughput at peak efficiency of nearly 50 percent, including telescope losses. This camera can be used in a scanning mode, in which the telescope tracking rate is offset and the charge is clocked in the chips in such a way that the charge image remains aligned with the optical image. Attention is given to the results of a survey for high-redshift quasars using this equipment, which has produced images for the most distant galaxy clusters yet discovered.

Gunn, James E.↗

NASA NTRS1987

Nine optically selected quasars with redshifts larger than 3

The detection of nine quasars with redshifts between 3.0 and 3.8 is reported. The quasars were all found in a grism survey from their Lyman-alpha emission line. The r magnitudes of the quasars range from 18.5 to 21.7. The strengths of the Lyman-alpha lines are comparable to the values observed in other quasars (rest equivalent widths from 40 to 160 A). The spectrum of one of the objects possesses complex broad absorption features, similar to those seen in PHL 5200. A preliminary evaluation of these findings suggests that the comoving quasar density declines gradually beyond z = 3.

Schmidt, Maarten↗

NASA NTRS1986

Spectroscopic CCD surveys for quasars at large redshift. II - A Pfuei transit survey

A CCD transit survey has been carried out with the 200 in. telescope of a strip of sky 5 arcmin wide and 9 hr long. Direct images and slitless spectra of over 43,000 objects were obtained on two successive nights. An automatic search for emission lines of given minimum equivalent width and signal-to-noise ratio yielded 52 candidate sources. Slit spectra revealed that 24 were emission-line galaxies with z less than 0.4 and eight were quasars with 2 between 1.00 and 2.76. The number of quasars detect agrees with that predicted from luminosity function models for z less than 2.9. The models also indicate that between 30 and 62 quasars with z less than 2.9 should have been found in this survey, but none were detected. This result reconfirms that there is a redshift cutoff near or below redshift three. The apparent conflict of this measurement with the known existence of dozens of quasars with redshifts larger than three is discussed.

Schmidt, Maarten↗