Publications of the Astronomical Society of the Pacific

Smith, H. A.; Hesser, J. E.

doi: 10.1086/131158pmid: N/A

Spectra are obtained for nine upper-main-sequence and three blue-straggler stars in the intermediate-age cluster NGC 2477. They are then used in testing the hypothesis that rapid rotation of the turnoff stars gives rise to a discrepancy between the metal abundance given by the uvby-beta photometry of main-sequence stars and by the DDO photometry of red giants. It is found that NGC 2477 turnoff stars are not rotating unusually rapidly relative to their Hyades counterparts. Discrepancies in the photometric metallicity estimates, however, can now be explained through recent revisions in the DDO reddening ratios and through small color corrections to the beta photometry. The spectroscopic and photometric results are all consistent with NGC 2477 being slightly older and slightly metal deficient compared with the Hyades. The mean cluster radial velocity is found to be 6 + or - 10 km/s. It is confirmed spectroscopically that star 'm' is an Am star.

Mihalszki, J. S.; Ferland, G. J.

doi: 10.1086/131159pmid: N/A

In this paper the effects of density and temperature inhomogeneities on the emission-line spectra of planetary nebulae are studied. Model calculations are performed with various density inhomogeneities: three filling factor densities are examined as well as a more realistic sine-wave density variation. In the latter case temperature fluctuations occur in response to changes in the density. Carbon abundances are determined using both the optical recombination lines and the ultraviolet collisionally excited lines although the well-known discrepancy between the two is not reproduced. Peimbert's (1967) temperature fluctuation parameter is found to be justified, although the value which typifies the presented model is often smaller than his preferred value. Since the models and analysis use a consistent set of atomic data, errors normally introduced by uncertainties in the atomic data base do not plague the analysis. It is found that most methods of determining abundance ratios give systematic errors of 0.3 dex.

Sellgren, K.; Soifer, B. T.; Neugebauer, G.; Matthews, K.

doi: 10.1086/131160pmid: N/A

Within the uncertainties, the P-alpha line profile is the same as those of H-beta, L-alpha, and C IV. It is therefore contended that if current models of broad-line-emitting clouds in quasars are correct, then the similarity of the P-alpha line profile to the L-alpha profile argues against a velocity field dominated by radial inflow or outflow. It is noted, however, that if the cloud motions are predominantly due to radial inflow or outflow, then the clouds must radiate more isotropically in L-alpha then current models predict. The observed similarity of the line profiles of P-alpha at 1.875 microns and of C IV at 1550 A leads to the conclusion that there is no differential reddening caused by dust between clouds moving at different velocities within the broad line region of 3C 273.

Wakamatsu, K. -I.

doi: 10.1086/131161pmid: N/A

A new ring galaxy has been discovered in the halo of a nearby rich cluster of galaxies, Abell 1631. The position of the galaxy is alpha = 12h 48 m 27.1s + or - 0.2s, delta = 14 deg 52 arcmin 00 arcsec + or - 3 arcsec. A bright nucleus having a diameter of 3.5 arcsec is located off-center in the ring. The west edge of the ring is slightly bright, which may be due to the presence of giant H II regions. A companion galaxy about one magnitude fainter than the ring galaxy is located nearly on the minor axis of the ring, separated by 14.5 arcsec from the nucleus. Between them, a barely traceable faint bridge can be seen. If the object is assumed to be a cluster member, its absolute magnitude is -20.0 + or - 0.5 on the scale H = 55 km/s/Mpc. The linear diameter of the ring is about 23 kpc, typical of ring galaxies.

Smith, G. H.

doi: 10.1086/131162pmid: N/A

DDO photometry is presented for 13 red stars in the field of IC 4756, ten of which are classified as proper-motion cluster giants. Of these ten, one is found to be a dwarf, in agreement with the uvby photometry of Schmidt (1978). The strength of the delta CN cyanogen excess parameter for five of the giants indicates that the cluster has essentially solar abundance.

Radick, R. R.; Wilkerson, M. S.; Worden, S. P.; Africano, J. L.; Klimke, A.; Ruden, S.; Rogers, W.; Armandroff, T. E.; Giampapa, M. S.

doi: 10.1086/131163pmid: N/A

The authors have observed eleven solar-type main-sequence stars to search for continuum variability. Stars were selected from Wilson's chromospheric activity survey, and were observed for periods of three to six months with intermediate-band Stroemgren uvby photometry. The authors find evidence that two of these eleven stars are variable and that one other may be. Comparison with contemporaneous Ca II H + K emission flux measurements shows that the amplitude of photometric variability correlates strongly with both the mean emission flux and the amplitude of its variation. Variations in continuum light and emission flux tend to correlate in time, as well, with continuum minima coinciding with emission maxima and vice-versa. The authors infer that the surface activity of these stars tends to be confined to localized activity centers that include both emission plages and dark spots, similar to the active regions observed on the sun.

Peters, G. J.

doi: 10.1086/131164pmid: N/A

The discovery of an unusual, periodic, two-component shell phase of short duration in the 'classical' Be star HR2142 (HD41335, MWC133) offered convincing evidence that this object is a mass-transfer binary system. A model based solely on the phase-dependent behavior of the hydrogen shell lines in this 80d.860 binary was developed by Peters and Polidan (1973) and by Peters (1976). The present investigation is concerned with a refinement to the earlier model, taking into account the utilization of an orbital solution obtained from measurements of the wings of the broad photospheric features observed in the rapidly rotating primary. Velocities and equivalent widths from the sharp 'shell' lines, presumably formed in or near the gas stream, provide additional information on the mass flow in the Balmer-line-formation region.

Eaton, J. A.; Wu, C. -C.

doi: 10.1086/131165pmid: N/A

The early-type eclipsing binary Delta Pictoris has been studied with 260 observations in each of five UV bands. These are the most accurate observations to date, and no strong evidence for light-curve complications produced by circumstellar material has been found. Combined light curves from four epochs separated by intervals of six months do not show any strong dips or shoulders as seen in earlier investigations. The strength of th C IV wavelength 1550 line is independent of phase to better than 0.01 m. The root-mean-square scatterer shown by the light curves ranges from 0.006 m to 0.014 and may be evidence that either or both of the components are intrinsically variable. The integrated colors of the system are consistent with a B1 V spectral type and very little interstellar extinction. A detached solution of the light curves for a Roche model well with the spectroscopic mass ratio, but a semidetached solution cannot be ruled out.

Dunham, E. W.; Elliot, J. L.

doi: 10.1086/131166pmid: N/A

The properties of optical photometric data obtainable with the 0.9-meter telescope of the Kuiper Airborne Observatory are described. The major differences between airborne and ground-based data are the absence of scintillation and the increased cosmic-ray background in the airborne data and the large size (≡5 arc sec) and vibration of the airborne images. The underlying cause of the large airborne images is not known although refraction in the turbulent boundary layer of the aircraft is suspected to be the major factor.

Chen, P. C.

doi: 10.1086/131167pmid: N/A

We have developed a digital microprocessor system for high-speed occultation photometry. The principal features are: timekeeping to accuracy of milliseconds, real-time data display, ruggedness, lightweight (1.8 kg), and low cost (250). The observational data can be stored on an ordinary cassette recorder or transferred to a host computer for reduction.