Jr.
January 1976~ No. 1440
C. H. Costain, L. A. Higgs, J. M. MacLeod, and R. S. Roger Dominion Radio Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, Penticton, B.C.,
Synthesis observations to 2-aremin resolution of the 1420-MHz continuum emission from six extragalactic sources are described. Two of the sources are unresolved: 3C66A, a QSO, is found to be 80% more intense than previously reported and may be variable; the other, OM591, is tentatively identified with a stellar-type object. 3C66B is shown to have extended structure very similar to that observed at 408 MHz. OM588, the major component of 4C55.22, itself comprises at least two extended components, one of which is coincident with a 16-mag galaxy. A map of the halo of 3C274 (M87) is given and its relation to the optical and x-ray halos is considered. A suspected halo surrounding 3C103 was not detected at the 4% level.
of the spatial coefficients, truncated at 20%, produces a synthesized beamwidth of 1.94 arcmin in right ascension by (1.94 csc 8) arcmin in declination. Inten- sities are scaled with respect to an assumed flux den- sity for 3C48 at 1420 MHz of 15.3 Jy (1 Jy=1 jansky -10-26 W m Hz-1) (epoch 1973.8). The rms noise level on the maps for a 10-spacing grating survey is (6 sin 8) mJy/beam area.
HE synthesis radio telescope at the Dominion THE Radio Astrophysical Observatory (Roger, Costain, Lacey, Landecker, and Bowers 1973) has been used to map the continuum emission at 1420 MHz from several extended radio sources. The sources are mem- bers of complete samples at 1420 MHz [i.e., samples of extragalactic sources in excess of a given flux den- sity, e.g., Galt and Kennedy (1968); Bridle, Davis, Fomalont, and Lequeux (1972)] which either have not been mapped at high resolution near 1420 MHz by the Cambridge instruments (e.g., Macdonald Kenderdine, and Neville 1968; Mackay 1969), or which could possess extended components not detected by their particular choice of grating interval. It is of Both components of 3C66 were measured at 1.4 GHz some importance to collect accurate information on such sources. Observations of six sources, 3C66A 3C66B, 3C103, OM588, OM591, and 3C274, are de scribed. Maps of brightness distribution are presented for the three extended sources.
We consider each of the sources in turn.
A. 3C66A
, 3C66A has been identified (Wills and Wills 1974) with a 15-mag quasistellar object with a continuous spectrum, possibly of the OJ287 type.
1. THE OBSERVATIONS
The radio telescope is sensitive to left-circular po- larization and measures the emission within a 15-MHz band centered on 1420.1 MHz. Notch filters exclude galactic H1 emission. Except where noted the mea- surement of each source consisted of a 12-h observa- tion at each of 10 spacings at a grating interval of 30 m. This ensures no reduction in amplitude for EW structure finer than 12 arcmin. A Gaussian grading
*Present address: Herzberg Institute of Astrophysics, National Research Council of Canada, Ottawa, Ontario, Canada.
by Macdonald, Neville, and Ryle (1966) who reported , that the unresolved component 3C66A has a flux - density of 1.3 Jy, comprising 13% of the total emission. Fomalont (1968) measured 2.0 Jy for this component at the same frequency. The observations reported here (epoch 1973 January) yield a value of 2.4±0.3 Jy which amounts to over 20% of the total emission from 3C66. Because the source is quasistellar and variability was suspected, the survey was repeated in September 1974. No significant change is apparent in the 20-month interval. However, measurements at the Algonquin Radio Observatory at 10.7 GHz by MacLeod and Harvey (personal communication) during the period May 1974-July 1975 indicate that the source is variable at the 10% level.
Figure 1 is a plot of the flux densities of 3C66A at frequencies where the observations allow a separa- tion from 3C66B (see Table I). The value at 89 GHz
Copyright 1976 by the American Astronomical Society.
core .5R disk
s i n sew
60%
SUPPRESSION OF BAH DIKTABILITY
along the terms try and histo
wchangeably at times Figure 1 shum the
Skip The total mass of the duck plus core/hal 2X M
Figure 3 shows the wafution of an lly balanced disk of stars under the influence of snd nire-halo with radius 13 times the initial of the disk The time to given in units of etarial period of the uniformly rotating disk o core-hale omponent), Over most of the drak the ct of the core balo is entisily that of a point mass at the center of the system. Par a core halo oss of o e of the total system ma, the disk approaches an axisymmetric shape and does not form a bar For a core-halo base of 30% or less, the disk quickly a bar
The relative magnitude of the radial gravitational el component of the fived halo and the self-con atent disk components are shown in Fig. 3. Note that for 13 kpe the fixed force component domi les For both cases, with 40% and 50% of the tal mass in the disk stars there is a tendency of the disk star distribution to become more centrally condensed. This can be seen by comparing the radial gravitational field for the disk stars at 10 and 4. The actual increase in the surface mass density is about 50% in the central region (<5 kpe) with a siderable decrease of surface mass density between- Scr<20. At 2-4 the surface mass density for r>5 kpc approximating an exponential distribution. Even though the disk containing 40% of the system mass in Fig. 2 does not form a bar, there is still a con- siderable increase in the velocity dispersion. For both cases shown in Fig. 2 the value of e,/.. has in-
creased from the initial value of 1 to a final value
F. 6 Copa of the hard dicks shown in Fig tational held co companenix for and all dial gravi
the ring region. At 1-4, the value of ./ ranges up to 2 for the 20 disk stars system and up the 60% system. Figure 6 shows the relative mag nitude of the nixed core-halo and self-consistent disk radial gravitational field components. The self-con- sistent disk star field at 7-4 indicates the increased mass concentrations in rings near 10 kpc. As the system evolves further in time the initially nearly axisymmetric ring instability will result in nonac- symmetric (bar formation) evolution as indicated at 4 for the 60% system in Fig. 5. For all four sys tems shown in Fig. 5, the ratio of the random to rotational kinetic energy increases at a nearly uniform rate for / up to 4.
Figure 7 shows the evolution of four disks of stars
(at 4) slightly above 2 for > 10 kpc. The central under the influence of a spherical halo with radius
core of the two disks has values of ./..mt reaching equal to the initial disk radius. For a halo mass of
up to & with / beginning to increase for 40% or more of the total system mass, bar formation
10 kpc and 6 kpe for 50% and 40% disk star is prevented, whereas for a halo mass of 30% or less systems, respectively. The evolution of the ratio of the random kinetic energy to the rotational kinetic the systems shown in Fig. 7, the fixed component of energy for the two cases is shown in Fig. 4. Note the gravitational field is very much smaller than the that for the case where a bar forms (50% disk Note stars) the energy ratio continues to increase whereas remains nearly constant after 2 for the non-bar- forming disk. After four rotations (at 1-4) the bar- forming, 50% disk population system, has a random/ rotational energy ratio 61% larger than the 40% symmetric system. These results show that the bar instability causes considerable heating in the central part of the disk.
of the total
mass, a bar quickly forms. Note that lor
self-consistent com component. This is displayed in Fig. 8. it For all four systems shown there is a a considerable increase in the central surface mass density of the disk stars. The central mass density increases by factor of 3.7 for the 50% system and by a factor of about 5 for the other three systems. It is surprising that for the systems shown in Fig. 7,
a fixed core-halo component of 40% is sufficient to stabilize the system against bar formation, whereas, for the system shown in Fig. 2, a core-halo: com- ponent of 60% is needed to stabilize the disk. This is because the fixed-to-self-consistent field ratio for the disks in Fig. 2 is much larger than for the disks in Fig. 7.
Using a normal mode analysis, Kalnajs (1972) de- termined the susceptability of uniformly rotating disks
The spatial evolution of disks of stars with the fixed spherical core-halo radius equal to one-half the disk radius is shown in Fig. 5. Only half of the stars are displayed to increase the resolution. As can be seen, a ring instability forms for all three systems shown. This instability causes considerable heating in
20%
CONTENTS
THE ASTRONOMICAL JOURNAL
JANUARY 1976-No. 1440
VOLUME 81, NUMBER 1
Articles
Continuum observations of six extragalactic radio sources at 1420 MHz C. H. Costain, L. A. Higgs, J. M. Macleod, and R. S. Roger 1
Optical behavior of 64 extragalactic radio sources
R. L. Scott,
R. J. Leacock, B. Q. McGimsey, A. G. Smith, P. L. Edwards, K. R. Hackney, and R. L. Hackney
Photometry of SO galaxies. III. NGC 524
Paul Hodge and Paul Steidl 20
The structure of NGC 147.
Paul Hodge 25
Suppression of bar instability by a massive halo
F. Hohl 30
Carl Heiles and G. Katz 37
The absence of systematic kinematics in dust clouds
Rediscussion of the local space density of M dwarf stars
S. M. Faber, David Burstein, Beatrice Tinsley, and Ivan R. King 45
Suspected subluminous A stars in the solar neighborhood
Thomas D. Griess: 53
Photometric evidence of circumstellar gas and orbital elements for the Algol system Edward F. Guinan, George P. McCook, Peter J. Bachmann, and William G. Bistline 57
Minor planets and related objects. XIX. Shape and pole orientation of (39) Laetitia R. E. Sather 67
Radii and albedos of 84 asteroids from visual and infrared photometry. Olay L. Hansen 74
Erratum: "NGC 3114: Another open cluster possibly rich in peculiar stars" [Astron. J. 80, 807 (1975)]... Hugo Levato and Stella Malaroda 85
Plates
Plate I (Hodge).
87
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CONTENTS
FEBRUARY 1976-No. 1441
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 2
Articles
. George F. Benedict
89
Surface photometry of Virgo Cluster galaxies NGC 4321.
David G. Turner 97
Importance of random scatter to variable-extinction analyses.
Sidney van den Bergh 104
UBV observations of the x-ray nova in Monoceros
. Sidney van den Bergh 106.
UBV observations of Nova Scuti 1975.
Gary E. Mechler 107
ubvy 3 study of A- and F-type visual binaries. I.
O stars and supergiants south of declination -53.0°. Nancy Houk, Mark R. Hartoog, and Anne P. Cowley 116
Observations of comets, minor planets, Pluto, and satellites
G. Van Biesbroeck, C. D. Vesely, K. Aksnes, and B. G. Marsden 122
Orbits of comets 1892 VI and 1911 V.
G. Van Biesbroeck, C. D. Vesely, and B. G. Marsden 125
Discussion of the photographic observations of the Galilean satellites in the period 1930-1970
. S. Ferraz-Mello and L. R. de Paula 127
New treatment of the critical argument in resonance problems
William H. Jefferys 132
Algorithm for the restoration of infrared raster scans
Theodore Simon 135
Plate I (Benedict)
Plates
Plate II (van den Bergh)
Plate III (van den Bergh)
139
141
143
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 4
APRIL 1976-No. 1443
Articles
A. de Vaucouleurs, R. R. Shobbrook, and A. Strobel 219
New redshifts of bright galaxies. II.
2290-MHz flux densities of 52 high-declination radio sources Alan W. Harris, Robert A. Preston, Donovan J. Spitzmesser, Martin A. Slade, and Lyle J. Skjerve 222
Finding list and spectral classifications for southern luminous stars. D. J. MacConnell and W. P. Bidelman 225
Broad-band photometry of G and K stars: The C, M, T₁, T: photometric system
R. Canterna 228
MK classification for visual binary components.
Terry W. Edwards 245
Eclipsing binary system SZ Piscium.
S. Jakate, G. A. Bakos, J. D. Fernie, and J. F. Heard 250
Parallaxes of 31 stars determined from plates taken with the McCormick 26-in. refractor
Philip A. Ianna, Ronald G. Probst, and George E. Martin 257
Minor planets and related objects. XX. Polarimetric evidence for the albedos and compositions of 94 asteroids
B. Zellner and J. Gradie 262
Secular variation of the obliquity of the ecliptic. R. L. Duncombe and T. C. Van Flandern 281
Oversampling of digitized images.
David Fischel 285
Plates I-III (Fischel).
289
Plates
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CONTENTS
THE ASTRONOMICAL JOURNAL
MAY 1976-No. 1444
LANCASTER PRESS, INC., LANCASTER, PA.
VOLUME 81, NUMBER 5
Articles
Detection at 2=0.5 of a 21-cm absorption line in AO 0235+164: The first coincidence of large radio and
optical redshifts M. S. Roberts, R. L. Brown, W. D. Brundage, A. H. Rots, M. P. Haynes, and A. M. Wolfe 293
On the intraday variability of OJ 287
H. R. Miller, D. W. Wingert, B. Q. McGimsey, E. S. Anderson, T. L. Mullikin, and G. H. Folsom 298
CO emission associated with compact continuum sources in dark clouds L1613 and L1640
A. G. Kislyakov and B. E. Turner 302
Infrared surveys of dark-cloud complexes. I. The Lynds 1630 dark cloud ..... K. M. Strom, S. E. Strom, and F. J. Vrba 308
Infrared surveys of dark-cloud complexes. II. The NGC 1333 region. S. E. Strom, F. J. Vrba, and K. M. Strom 314
Infrared surveys of dark-cloud complexes. III. The R Corona Austrina dark cloud
F. J. Vrba, S. E. Strom, and K. M. Strom 317
Infrared surveys of dark-cloud complexes. IV. The Lynds 1517 and Lynds 1551 clouds
.. K. M. Strom, S. E. Strom, and F. J. Vrba 320
Multichannel spectrophotometry and the luminosities of white dwarfs.
. Jesse L. Greenstein 323
Photometry of stars near 3U1700-37-HD153919 and 3U0900-40-HD77581.
C. T. Bolton and William Herbst 339
Catalog of probable dwarf stars of type M3 and later in the direction of the north galactic pole.......
N. Sanduleak 350
Charles A. Dean 364
Proper motion membership analysis of the Orion Nebula cluster
Bernard J. McNamara 375
Kinematic properties of the carbon stars
Erratum: "Search for circular polarization in compact radio sources at a wavelength of 2.2 cm" [Astron. J. 79, 918 (1974)]. E. R. Seaquist, P. C. Gregory, and T. R. Clarke 383
Erratum and Addendum: "Eclipses by an elliptical torus" [Astron. J. 80, 719 (1975)]... R. E. Wilson 383
Plates
Plate I (Strom, Strom, and Vrba).
Plate II (Strom, Vrba, and Strom)
Plate III (Vrba, Strom, and Strom).
Plates IV-V (Strom, Strom, and Vrba)
Plates VI-VII (Bolton and Herbst).
Plates VIII-X (McNamara).
385
387
389
391
393
395
CONTENTS
THE ASTRONOMICAL JOURNAL
JUNE 1976-No. 1445
VOLUME 81, NUMBER 6
Articles
P. E. Clegg, M. Rowan Robinson, and R. A. R. Ade 399
Millimeter observations of Galactic sources
.... Julius H. Cahn 407
Interstellar extinction: A calibration by planetary nebulae.
D. L. Crawford and C. L. Perry 419
Four-color and H3 photometry for open clusters. XI. The Pleiades
Donna Weistrop 427
Photometric parallaxes for faint red dwarf stars.
D. C. Backer and R. A. Sramek 430
Proper motion of pulsars by radio interferometry
B. A. Goldberg, G. A. H. Walker, and G. J. Odgers 433
The variations of BW Vulpeculae
Diffraction calculation of occultation light curves in the presence of an isothermal atmosphere
Richard G. French and Peter J. Gierasch 445
Gravitational deflection of light: solar eclipse of 30 June 1973 I. Description of procedures and final results
Texas Mauritanian Eclipse Team 452
Gravitational deflection of light: solar eclipse of 30 June 1973 II. Plate reductions. Burton F. Jones 455
Mutual phenomena of the Galilean satellites in 1973.
III. Final results from 91 light curves
K. Aksnes and F. A. Franklin 464
Observations of the fortnightly nutation terms and the "dynamical variation of latitude" with photographic zenith tubes
Denins D. McCarthy 482
Perturbation theory for strongly perturbed dynamical systems. II. Canonical coordinates
William H. Jeffreys 485
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 7
JULY 1976-No. 1446
Articles
Search for correlated radio and optical events in long-term studies of extragalactic sources. R. B. Pomphrey, A. G. Smith, R. J. Leacock, C. N. Olsson, R. L. Scott, J. T. Pollock, Patricia Edwards, and W. A. Dent 489
Near-infrared observations of the edge-on spiral galaxy NGC 4565 ...... M. Frankston and R. Schild 500
Study of CO in Lynds 134 M. J. Mahoney, W. H. McCutcheon, and W. L. H. Shuter 508
Recombination-line and continuum observations of compact H 11 regions at 10.5 GHz ......M. R. Viner, J. N. Clarke, and V. A. Hughes 512
Membership and internal motions in the globular cluster M15.
Kyle M. Cudworth 519
Variable 19 in NGC 5466: An anomalous cepheid in a globular cluster. Robert Zinn and Conard C. Dahn 527
Optical counterparts of AFCRL infrared sources.
M. J. Lebofsky and S. G. Kleinmann 534 Harry H. Guetter 537 Spectral classification in the belt of Ori OB1
Visual multiples. II. The y Velorum group. Helmut A. Abt, Arlo U. Landolt, Saul G. Levy, and Stefan Mochnacki 541
Astrometric constants for £282, BD+75° 325, BD+66° 550, Ross 142, and selected stars in those regions
Jane Russell, George Gatewood, and John W. Stein 545
Parallaxes and proper motions of Me V stars from plate taken with the Sproul 61-cm refractor..........
Sarah Lee Lippincott and Michael D. Worth 548
Parallaxes and proper motions. XI. Double-star measures
S. E. Burt and E. W. Weis 551
Parallaxes of 33 stars
W. D. Heintz 554
Plates
Plate I (Frankston and Schild).
559
Plate II (Mahoney, McCutcheon, and Shuter). 561
Plate III (Cudworth). Plate IV (Zinn and Dahn). 563
565
567
Plates V-VII (Lebofsky and Kleinmann).
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 8
AUGUST 1976-No. 1447
Articles
Pencil beam observations of Abell clusters of galaxies II. 775 and 968 MHz.
Frazer N. Owen 571
Radio two-color diagram for QSOs, spiral galaxies, and BL Lac objects
Erich Pacht 574
Radio emission and optical morphology in Markarian galaxies
Jack W. Sulentic 582
Radial velocities of galaxies and star clusters from interference filter scans
G. de Vaucouleurs and A. de Vaucouleurs 595
Radio source positions from very-long-baseline interferometry observations. T. A. Clark, L. K. Hutton, G. E. Marandino, C. C. Counselman, D. S. Robertson, I. I. Shapiro, J. J. Wittels, H. E. Hinterregger, C. A. Knight, A. E. E. Rogers, A. R. Whitney, A. E. Niell, B. O. Rönnäng, and O. E. H. Rydbeck $99.
Distribution of BS-A3 stars near the galactic plane II. Galactic longitudes 270° to 300°
S. W. McCuskey and S. G. Lee 604
Studies of globular clusters. I. Star counts in 23 clusters.
Charles J. Peterson 617
Variable stars in the globular cluster NGC 5634
Martha H. Liller and Helen Sawyer Hogg 628
Multicolor photometry of the open cluster NGC 4755
C. B. Franklin Jr., A. U. Landolt, and D. L.. Crawford 632
C. L. Perry,
Infrared surveys of dark cloud complexes V. The NGC 7129 region and the Serpens dark cloud
S. E. Strom, F. J. Vrba, and K. M. Strom 638
Wavelength dependence of polarization. XXXI. Cool stars.
A. Kruszewski and G. V. Coyne 641
Photoelectric measurements of lunar occultations. VIII
.... John L. Africano, David S. Evans, Francis C. Fekel, and Gary J. Ferland 650
Visual multiples. III. ADS 11745 (3 Lyrae group)
Helmut A. Abt and Saul G. Levy 659
Photoelectric photometry of 20 Canum Venaticorum
Period study and UBV light curves of MN Cassiopeia
.J. Scott Shaw 661
Albert D. Grauer, J. Don Bell, Charles A. Cecchini, Hubert L. Dawson, Mike T. Durban, Claud F.
Elliott Jr., William B. Hankins III, Catherine J. Jones, George C. Jones, David W. Maffett,
Michael L. Medley, Charles E. Pittman, Kurt W. Stone, Charles K. Tipton, and Terrell L. Tribble 665
Microwave line transitions in the 3-mm wavelength range in Comet Kohoutek (1973f)
W. F. Huebner, D. Buhl, and L. E. Snyder 671
G. P. Horedt 675
Capture of planetary satellites
Plates
Plates I-II (Strom, Vrba, Strom).
679
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 9
SEPTEMBER 1976-No. 1448
Articles
J. A. Graham 681
Integrated B and V photometry of Sc I and Sc II galaxies.
Motion of the Galaxy and the Local Group determined from the velocity anisotropy of distant Sc I galaxies. I.
The data Vera C. Rubin, W. Kent Ford Jr., Norbert Thonnard, Morton S. Roberts, and John A. Graham 687
Motion of the Galaxy and the Local Group determined from the velocity anisotropy of distant Sc I galaxies. II. The analysis for the motion.
Vera C. Rubin, Norbert Thonnard, W. Kent Ford Jr., and Morton S. Roberts 719
Linear polarization and flux density variations in the radio galaxy 3C120 Hugh D. Aller, E. T. Olsen, and Margo R. Aller 738
The brightest stars in nearby galaxies. I. The color-magnitude diagram and luminosity function for IC 1613
Photoelectric UBV sequences in the fields of extragalactic sources
Allan Sandage and Basil Katem 743
B. Q. McGimsey, H. R. Miller, and R. M. Williamon 750
Optical position for planetary nebulae. II.
D. K. Milne 753
Further comments on the evidence for a high density of red dwarf stars.
Donna Weistrop 759
Broad-band 20- photometry of 50 stars
Theodore Simon 764
Photoelectric radial velocities II. The RRS stars
G. W. Van Citters Jr. 766
HR 1099: A new bright RS CVn variable
Bernard W. Bopp and Francis Fekel Jr. 771
Parallaxes and proper motions of four multiple stars determined with the 61-cm Sproul refractor.
Peter van de Kamp and Sarah Lee Lippincott 775
Minor planets and related objects. XXI. Photometry of eight asteroids
R. C. Taylor, T. Gehrels, and R. C. Capen 778
On the stability of the solar system
Paul E. Nacory 787
Erratum: "Discussion of the photographic observations of the Galilean satellites in the period 1930-1970"
[Astron. J. 81, 127 (1976)].
S. Ferraz-Mello and L. R. de Paula 792
Plates
Plate I (Sandage and Katem)
793
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 11
NOVEMBER 1976-No. 1450
Articles
Image-tube photography of a complete sample of 4C radio sources
Alan K. Uomoto, Beverley J. Wills, and D. Wills 905
Optical identifications of sources in the Parkes 2.7-GHz selected-areas surveys ....J. J. Condon, T. J. Balonek, and D. L. Jauncey
913
Variability of extragalactic sources at 2.7 GHz. I. Results of a 2-yr monitoring program.
.. M. J. L. Kesteven, A. H. Bridle, and G. W. Brandie
919
Time-dependent radio fine structure of the quasar 3C 345
J. J. Wittels,
1. I. Shapiro, W. D. Cotton, C. C. Counselman, H. F. Hinteregger, C. A. Knight, A. E. E. Rogers, A. R. Whitney, T. A. Clark, L. K. Hutton, A. E. Niell, B. Ö. Rönnäng, and O. E. H. Rydbeck 933
VLBI detection of compact central components in 17 extended radio sources.
R. T. Schilizzi 946
The Zwicky catalogue magnitude scale: A comparison with photoelectric magnitudes of faint galaxies and
with the magnitudes of Holmberg and de Vaucouleurs.
. John Huchra
952
High-latitude reflection nebulosities illuminated by the galactic plane.
Allan Sandage 954
Magnetic field structure in the vicinity of five dark cloud complexes.
Frederick J. Vrba, Stephen E. Strom, and Karen M. Strom 958
Interstellar polarization in front of the young cluster NGC 7380
R. S. McMillan 970
Membership and internal motions in the globular cluster M92 Kyle M. Cudworth 975
On the dynamics and shapes of star clusters
William H. Jefferys 983
Spectrophotometry of barium, CH, and R-type carbon stars
Charles E. Gow 993
Intrinsic linear polarization of the eclipsing binary AO Gas.
. Raymond J. Pfeiffer
1000
Astrometric observations of satellites of Jupiter and Saturn during 1973
J. Derral Mulholland, Peter J. Shelus, and Richard I. Abbot 1007
Trajectories and orbits from the NASA-NMSU meteor observatory I.
. Edward F. Tedesco and Gale A. Harvey 1010
Erratum: "Radio continuum measurements of compact H II regions and other sources" [Astron. J. 81,
172 (1976)]
D. N. Matsakis, N. J. Evans II, T. Sato, and B. Zuckerman 1014
Plates
1015
Plates I-II (Uomoto, Wills, Wills).
Plates III-IV (Condon, Balonek, and Jauncey).
Plates V-VI (Sandage). . .
Plates VII-XV (Vrba, Strom, and Strom).
1017
1019
1021
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CONTENTS
THE ASTRONOMICAL JOURNAL
VOLUME 81, NUMBER 12
DECEMBER 1976
Articles
Optical identifications of radio sources using accurate radio and optical positions. II. . Beverely J. Wills 1031
Variations of extragalactic sources at 7.9 GHz.
William A. Dent and John E. Kapitzky 1053
Observations of variable radio sources at 18-cm wavelength. J. C. Webber, L. K. DeNoyer, K. S. Yang, and G. W. Swenson Jr. 1069
Calibration radio sources for radio astronomy: Precision flux-density measurements at 2295 MHz
M . J. Klein and C. T. Stelzried 1078
Measurements of the flux densities and spectra of discrete radio sources at centimeter wavelengths. V. The observations at 14.9 GHz (2 cm). R. Genzel, I. I. K. Pauliny-Toth, E. Preuss, and A. Witzel 1084
Discovery of an extended (85 pc) molecular cloud associated with the M17 star-forming complex
. Bruce G. Elmegreen and Charles J. Lada 1089
Spatial structure of the globular cluster system and the distance to the galactic center.
William E. Harris 1095
Further observations of faint M stars in the direction of the north galactic pole.
Peter Pesch 1117
Spectral classification of stars in Lac OBI
. Harry H. Guetter 1120
New determinations of R in open clusters.
D. G. Turner 1125
Photometric study of CW Canis Majoris.
Richard M. Williamon 1134
On the period variations in AR Lacertae. Douglas S. Hall, Terry R. Richardson, and Carlson R. Chambliss 1138
Parallaxes and proper motions. XII.
E. W. Weis and A. R. Upgren 1144
Preliminary results from the occultation of & Geminorum by Mars on 8 April 1976. G. de Vaucouleurs, R. E. Nather, and P. J. Young 1147
Gravity field of Jupiter and its satellites from Pioneer 10 and Pioneer 11 tracking data... G. W. Null 1153 1162
Far-ultraviolet albedo of the Moon.
R. L. Lucke, R. C. Henry, and W. G. Fastie
Plate I (Wills).
1171
Plates
Subject Classification Scheme.
Indexes
Subject Index.
Author Index.
1179
1180
1186
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