Case Low-Dispersion Northern Sky Survey. Thirteen of them are quasars, ranging in redshift from 0.0786 to 2.67, with a median redshift of 2. CSO 203 is a broad absorption-line quasar, and CSO 38 may have substantial associated absorption in the cores of emission lines. Several other objects show some intervening absorption, and all of them are bright enough to make the follow-up studies practical. CSO 251 is a bright (~15m), previously uncataloged quasar. The remaining objects are Galactic stars, five subdwarfs, and one hot white dwarf (CSO 160)

Djorgovski, S.

Thompson, D. J.

Weir, W. N.

Caltech Authors - Main

Publications of the Astronomical Society of the Pacific 
101: 1065-1071, December 1989 
PUBLICATIONS OF THE 
ASTRONOMICAL SOCIETY OF THE PACIFIC 
Vol. 101 December 1989 No. 646 
SPECTROSCOPY OF QUASAR CANDIDATES FROM THE CASE 
LOW-DISPERSION SURVEY 
D. J. THOMPSON, S. DJORGOVSKI,* AND W. N. WEIR 
Palomar Observatory, California Institute of Technology, Pasadena, California 91125 
Received 1989 August 4, revised 1989 August 30 
ABSTRACT 
We present long-slit CCD spectra of 19 stellar objects selected from the Case Low-Dispersion 
Northern Sky Survey. Thirteen of them are quasars, ranging in redshift from 0.0786 to 2.67, with a 
median redshift of 2. CSO 203 is a broad absorption-line quasar, and CSO 38 may have substantial 
associated absorption in the cores of emission lines. Several other objects show some intervening 
absorption, and all of them are bright enough to make the follow-up studies practical. CSO 251 is a 
bright (~ 15m), previously uncataloged quasar. The remaining objects are Galactic stars, five 
subdwarfs, and one hot white dwarf (CSO 160). 
Key words: galaxies: redshifts-quasars-redshifts-spectroscopy-stars: subdwarf 
1. Introduction 
The Case Low-Dispersion Northern Sky Survey is a 
slitless spectroscopy survey for blue and emission-line 
objects, with the limiting magnitude B ~ 18 (Pesch and 
Sanduleak 1983, 1986, 1988, 1989, and references 
therein; Sanduleak and Pesch 1984). The survey has pro- 
duced many interesting objects: quasars, active and star- 
forming galaxies, rare types of stars, etc. Stellar objects 
selected in this survey are usually designated as CSO, a 
convention which we follow. The information obtained 
from the survey plates is rather limited, and redshifts are 
seldom determined for quasars; follow-up slit spec- 
troscopy is necessary in most cases. 
The principal advantage of the Case and similar surveys 
in selecting quasars is that the objects are relatively 
bright. That makes them particularly useful for absorp- 
tion-line studies, if the redshifts are sufficiently large. 
Bright, high-redshift quasars are also good candidates for 
gravitational lenses, as witnessed by the success of sur- 
veys conducted by Surdej and collaborators (Surdej et al. 
1989, and references therein; Djorgovski and Meylan 
1989). Yet, the Case survey seems to be somewhat ne- 
glected: The Hewitt and Burbidge (1987) catalog lists only 
15 CSO objects as confirmed quasars. 
We have undertaken a follow-up slit spectroscopy pro- 
* Alfred P. Sloan Foundation fellow. 
gram of bright CSO quasar candidates at Palomar Obser- 
vatory, as a marginal weather backup project. Our goal is 
to measure the redshifts and identify objects worth pursu- 
ing in more detail. 
2. Data and Results 
The observations reported here were done on UT 1988 
January 10 and 11 and UT 1988 March 10 and 11, using 
the Double Spectrograph (Oke and Gunn 1982) mounted 
in the Cassegrain focus on the Hale 200-inch (5-m) tele- 
scope. The conditions were nonphotometric, with vari- 
able transparency, and the seeing was never better than 
about 2 or 3 arc sec (FWHM). The slit width used was 2 
arc sec and the effective spectral resolution (FWHM) was 
about 10 A. The wavelength range covered was different 
for different nights, but typically was 3700 Â-7400 Â, or 
3600 Â-9000 Â; on the night of UT 1988 January 10 there 
was a gap of about 500 A in the coverage between the blue 
and the red sides of the spectrograph. The exposure times 
were in the range of 900-2000 sec. 
Exposures of arc lamps were used to obtain the disper- 
sion solutions, giving the wavelength calibration rms of ~ 
1 A. Dome flat fields and exposures of standard stars from 
Oke and Gunn (1983) were used to correct for the instru- 
ment response and to provide a crude flux calibration, and 
we estimate the zero-point uncertainties to be of the 
order of 0T5. The data were reduced using standard pro- 
cedures. 
1065 
1 
.5 
O 
4 
2 
O 
1 
.5 
O 
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.5 
O 
0 2, 
THOMPSON, DJORGOVSKI, AND WEIR 
abjects were observed, 13 of which 
ars, and six Galactic stars, including 
one white dwarf (CSO 160). An emission-line foreground 
galaxy was found near CSO 259. Figures 1-4 show the 
4000 
4000 
4000 
5000 
5000 
5000 
1
 r 
! CSO 151 
6000 7000 
6000 7000 
6000 7000 
a> o a> 
S 
1 1 
4000 5000 
X (Â) 
6000 7000 
CSO 38, CSO 139, and CSO 151, with emission lines identified. The flux calibration zero point is uncertain by as much as 
ifferent objects. See the text for further details. 
(m
Jy
) 
F„
 
(m
Jy
) 
F„
 
(m
Jy
) 
F„
 
(m
Jy
) 
SPECTROSCOPY OF QUASAR CANDIDATES 1067 
spectra of the AGNs spectroscopically identified here with the features labeled. 
4000 5000 6000 7000 
4000 5000 6000 7000 
4000 5000 6000 7000 8000 9000 
x (A) 
Fig. 2-As in Figure 1, but for CSO 199, CSO 203, CSO 239, and CSO 261. 
(m
Jy
) 
F„
 
(m
Jy
) 
F„
 
(m
Jy
) 
F„
 
(m
Jy
) 
1068 THOMPSON, DJORGOVSKI, AND WEIR 
9000 
4000 5000 6000 7000 
X (A) 
Fig. 3-As in Figure 1, but for CSO 259, foreground galaxy nearby, CSO 282, and CSO 340. 
(m
Jy
) 
F„
 
(m
Jy
) 
SPECTROSCOPY OF QUASAR CANDIDATES 1069 
4000 5000 6000 7000 
Fig. 4-Spectra of CSO 251 (top) and CSO 352 (bottom), with features labeled. Solid lines correspond to the nominal flux calibration, and dotted lines 
are the spectra multiplied by a factor of 6, in order to show the detail. CSO 251 is an unusually bright object, with ~ 15m. 
1070 THOMPSON, DJORGOVSKI, AND WEIR 
3. Comments on Individual Objects 
CSO 2 = 0844+295: Also known as Ton 11. A 17m 
quasar or an N-galaxy at % = 0.660 ± 0.001. Pesch and 
Sanduleak (1983) noted a possible weak emission line near 
4360 Â, which we identify as Mg n 2799. 
CSO 24 = 0950+294: A 16m subdwarf star with narrow 
absorption lines, probably sdF or later. 
CSO 38 = 1009+299: A 16m quasar at z = 2.62 ± 0.01. 
Pesch and Sanduleak (1983) noted a possible emission line 
near 4450 A, which we identify as Lyman-a. The stubby 
shape of the emission lines suggests a considerable associ- 
ated absorption (the C ill] line is affected by telluric ab- 
sorption as well, but that is probably a minor effect). Most 
of the absorption features seen blueward of the La are 
real. 
CSO 139 = 1224+290: A 17m quasar at * = 2.25 ± 
0.01. Sanduleak and Pesch (1984) noted a possible emis- 
sion line near 3960 A, which we identify as La. 
CSO 151 = 1231 ± 294: Also known as Ton 621. A 16m 
quasar at % = 2.011 ± 0.001. Sanduleak and Pesch (1984) 
noted a possible weak emission line near 4640 A which is 
not covered by our spectra, but it corresponds to the C iv 
X1549 line expected from our redshift identification. Note 
the absorption feature at 6065 A. 
CSO 160 = 1240+326: A hot, 17m white dwarf, proba- 
bly DB. From the red continuum slope we estimate TBB ~ 
20,000 K. 
CSO 186 = 0819+363: A 17m subdwarf star with nar- 
row absorption lines, probably sdF or later. 
CSO 199 = 0838+359: A 16m quasar at z = 1.775 ± 
0.002. The feature at 5195 A is probably an artifact corre- 
sponding to the spectrograph dichroic split. The absorp- 
tion features near 5225 A and 6170 A are probably real. 
CSO 203 = 0842+345: Broad absorption-line quasar 
(BALQ)at% = 2.126 ± 0.003, 17m. The broad absorption 
features, and the emission line near 3825 A (identified 
here as La), were already noted by Pesch and Sanduleak 
(1986). 
CSO 239 = 0952+338: Also known as Ton 1125. A 17m 
quasar at z = 2.500 ± 0.001. Pesch and Sanduleak (1986) 
noted the emission line near 4210 A, identified here as 
La. Note the weak absorption features at 5940 A, 6035 A, 
6555 Â, and 6590 Â. 
CSO 241 = 0954+341: A 16m subdwarf star with nar- 
row absorption lines, probably sdF or later. 
CSO 251 = 1010+361: Also known as Ton 1187. A 
very bright (~ 15m) quasar at % = 0.0786 ± 0.0002 (from 
the hydrogen lines alone: 0.07845, from the [O III] lines 
alone: 0.07887; the difference is marginally significant). 
The lines are very luminous, and the spectrum is quite 
rich (see Fig. 4). It is remarkable that this object was not 
(to the best of our knowledge) previously noted in any of 
the quasar surveys or catalogs. Pesch and Sanduleak 
(1986) noted the emission lines near 4620 A (Hy) and 
5240 Â (Hß). It is the only CSO object without a pub- 
lished finding chart, but at 15th mag one is hardly neces- 
sary. 
CSO 259 = 1016+359: A 17m quasar at z = 1.552 ± 
0.004. It is not clear whether the absorption features on 
the blue side of the C iv X1549 line are real. There is a 
foreground galaxy ~ 45 arc sec away in P. A. = 207°, at z = 
0.055 ± 0.001, with a fairly blue continuum and a low- 
ionization, emission-line spectrum (Fig. 3), suggestive of 
a starburst galaxy. There is also an IRAS point source 
about 3 arc min to the east from the quasar. Pesch and 
Sanduleak (1988) note the “proximity of a group of galax- 
ies”. 
CSO 261 = 1016+359: A 17m quasar at % = 2.67 ± 
0.01. Pesch and Sanduleak (1988) suggested that this 
object is a BALQ, but we find no evidence for it. 
CSO 282 = 1036+355A: A 17m quasar at % = 1.999 ± 
0.002. Pesch and Sanduleak (1988) noted a possible emis- 
sion line near 3660 A, which according to our redshift 
determination must be La. 
CSO 283 = 1036+355B: An 18m subdwarf star with 
weak narrow absorption lines, probably sdF. 
CSO 340 = 1123+356: A 17m quasar at % = 1.285 ± 
0.004. Pesch and Sanduleak (1988) note that the object is 
“located in the midst of a small group of galaxies”, un- 
doubtedly foreground. The quasar may be gravitationally 
(micro?) lensed. 
CSO 352 = 1131+358: A 17m quasar at z = 0.2035 ± 
0.0005. The iron blends are prominent in the spectrum 
(Fig. 4). Pesch and Sanduleak (1988) note that the object 
is “about 5 arc sec south of a faint galaxy”; we were not 
successful in obtaining its spectrum. Given the relatively 
low redshift of the quasar, the two may be physically 
associated. 
CSO 362 = 1141+362: A moderately hot, 17m sub- 
dwarf star, sdA or sdF. The Bahner series is very promi- 
nent. 
4. Concluding Remarks 
Our impression is that the CSO lists provide a good 
yield of quasars compared to some other, similar surveys 
(e.g., Kiso, or even UM). However, our source selection 
was biased toward objects for which the original papers 
indicated a (possible) presence of emission lines. 
Probably the most interesting objects found here are 
CSO 251 (because of its brightness) and CSO 38 and CSO 
203 (because of the absorption features). Several other 
objects noted above show absorption lines, possibly Mg II 
X2799 from intervening galaxies, and may be worth fol- 
lowing up with a higher spectral resolution. 
We are indebted to the staff of Palomar Observatory for 
their expert help and in particular to Juan Carrasco, Dave 
Tennant, John Henning, and Skip Staples. We also thank 
Helen Johnston, Alain Picard, and Georges Meylan for 
their assistance with the observations and Charles Steidel 
SPECTROSCOPY OF QUASAR CANDIDATES 1071 
for useful comments on the manuscript. This work was 
supported in part by a Caltech Institute Institute Fellow- 
ship (D. J.T.), the Alfred P. Sloan Foundation and Califor- 
nia Institute of Technology (S.D.), and an NSF Fellow- 
ship (W.N.W.). 
REFERENCES 
Djorgovski, S., and Meylan, G. 1989, in Gravitational Lenses, Lecture Notes 
in Physics, 330, ed. J. Moran et al. (Berlin: Springer Verlag), p. 173. 
Hewitt, A., and Burbidge, G. 1987, Ap. J. Suppl., 63, 1. 
Oke, J. B., and Gunn, J. E. 1982, Pub. A.S.P., 94, 586. 
  1983, Ap./., 266, 713. 
Pesch, P., and Sanduleak, N. 1983, Ap. J. Suppl., 51, 171. 
  1986, Ap./. Suppl, 60, 543. 
  1988, Ap./. Suppl, 66, 297. 
  1989, Ap. J. Suppl, 70, 173. 
Sanduleak, N., and Pesch, P. 1984, Ap. /. Suppl, 55, 517. 
Surdej, J. et al. 1989, ESO Messenger, No. 55, 8. 


Spectroscopy of quasar candidates from the case low-dispersion survey

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Spectroscopy of quasar candidates from the case low-dispersion survey

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