Publications of the Astronomical Society of the Pacific

Wallerstein, G.; Cox, A. N.

doi: 10.1086/131406pmid: N/A

Several of the spectral and dynamic characteristics of Population II Cepheids are described, based on a number of recent observations. The stars are categorized according to period distribution, light curves, velocity curves, chemical composition, galactic kinematics, atmospheric shock waves, and location in the color-magnitude diagram. The relationship of normal Population II Cepheids to similar variable stars such as the RV Tauri is also discussed.

Jones, B.; Worrall, D. M.; Rodriguez-Espinosa, J. M.; Stein, W. A.; Gillett, F. C.

doi: 10.1086/131407pmid: N/A

Observations carried out with a 8-13 micron grating-spectrometer of Mrk 231 and NGC 4151 are reported. The Mrk 231 data can be fitted to various thermal dust emission models or a single power law, with dust extinction. In all the model fits, except for that of graphite and silicon carbide grain emission, a component of silicate absorption of optical depth of not more than 0.7 is required. Confirming published work, the absorption being at the redshift of the low-redshift absorption-line system is ruled out. The high values of silicate optical depth absorption do not give ratios to the galaxy's visual extinction which are comparable to those of galactic H II regions. Weak evidence for a 10-micron absorption feature in NGC 4151 is also reported. This is somewhat contrary to expectation, since the visual extinction of NGC 4151 is lower than that of Mrk 231, and since there is evidence to support a nonthermal rather than thermal dust origin for the infrared continuum emission.

Worrall, D. M.; Puschell, J. J.; Bruhweiler, F. C.; Miller, H. R.; Aller, M. F.; Aller, H. D.

doi: 10.1086/131391pmid: N/A

The authors present single-epoch multifrequency data for the radio-quiet low-redshift QSO Ton 1542, spanning radio through ultraviolet wavelengths. They measure a 3σ upper limit of 9.2 mJy for the 20.3 GHz flux density. The first ultraviolet spectrum of this object is presented and discussed. The authors find a particularly strong excess of flux density at ≡3000 Å, which is likely to be dominated by Balmer continuum emission. They also find a Lα/Hβ flux ratio of ≡17, which is higher than that usually observed in QSOs.

Corso, G. J.; Purcell, B.; Giroux, M.; Schultz, J.

doi: 10.1086/131408pmid: N/A

A table is presented listing the photographically-determined blue magnitudes of OJ 287 obtained in the F/15 Cassegrain focus with the Northwestewn University 1-meter reflecting telescope. The observations were carried out using a standard GG13 filter and 103a-0 emulsion. A secular trend is found in the average brightness of OJ 287 during the 1982-83 observing season, amounting to about 0.004 m per day. This secular trend is similar to that present during other seasons when OJ 287 is not at its base level of luminosity. The amplitude of the total range of optical variations of OJ 287 during the 1982-83 observing season was about 1.5 magnitudes, which is about 0.25 magnitude larger than that reported for most previous seasons.

Duncan, D. K.; Frazer, J.; Lanning, H. H.; Baliunas, S. L.; Noyes, R. W.; Vaughan, A. H.

doi: 10.1086/131409pmid: N/A

The identity of chromospheric Ca II H- and K-line emission has been monitored for two seasons in a large sample of Hyades F and G dwarfs. Mean emission levels vary smoothly with spectral type, suggesting that the rotation rate at a given spectral type varies relatively little, and that the rotation rate decreases smoothly as a function of mass. In this case the mechanism which controls pre-main-sequence angular momentum loss in late-type stars must be self-regulating to a high degree.

Lockwood, G. W.; Thompson, D. T.; Radick, R. R.; Osborn, W. H.; Baggett, W. E.; Duncan, D. K.; Hartmann, L. W.

doi: 10.1086/131410pmid: N/A

High-precision differential photometric observations of 32 Hyades stars, spectral type F4 V to K1 V, were obtained at Lowell Observatory over a five-month season during late 1982 and early 1983. Contemporaneous Ca II H+K emission flux measurements for 30 of these stars were made at Mount Wilson Observatory. Fifteen (possibly 18) of these stars, all later than type F7 V, were found to be photometrically variable. Highly significant correlations between continuum and Ca II emission variations were found in several cases. The photometric variations for nine of the stars were periodic. The authors have interpreted this as rotational modulation, since the measured periods agreed well with rotation periods predicted from measurements of the mean chromospheric emission fluxes for these stars.

Geisler, D.

doi: 10.1086/131411pmid: N/A

The DDO 51 filter has been added to the Washington photometric system. The strong surface gravity sensitivity of the Mg I "b" triplet and MgH bands which it monitors allows the system to easily discriminate between dwarfs and giants of late G and K spectral type. The system is especially suited as a membership criterion for abundance studies of distant cluster giants. The Mg index is insensitive to surface gravity variations among G giants. The metallicity sensitivity among giants is also relatively weak. Population I and II giants can be distinguished but no further differentiation is evident.

Rice, J. B.; Wehlau, W. H.; Khokhlova, V. L.

doi: 10.1086/131412pmid: N/A

Spectra of Theta Aur taken in rapid succession at several phases showed no real variations, with an upper limit of 0.5 percent of the continuum. Variations above the noise level which were found for four spectra at one epoch are explained as the result of a spot on the Reticon detector.

Forbes, D.; Scarfe, C. D.

doi: 10.1086/131413pmid: N/A

Three-color photometry of the 1981 eclipse of the long-period binary RZ Oph is presented. The data are combined with those of Baldwin (1978) to improve the determination of the times of contacts. A solution assuming i = 90°, similar to Baldwin's, leads to the conclusion that the cooler star does not fill its Roche lobe. A solution similar to Smak's (1981), which assumes that this star does fill its lobe, is also possible, but leads to a value of k = 0.022±0.001, which is hard to reconcile with the stars' spectral types, relative visual luminosities, and bolometric corrections. This leaves unanswered the questions of the origin of the material in the disk surrounding the hotter star, and of the evolutionary state of the system.

Vardya, M. S.

doi: 10.1086/131414pmid: N/A

Empirical and semiempirical expressions for the rate of mass loss, derived for O and B stars, have been examined vis-a-vis R136a. The best expression has been used to predict the rate of mass loss for some R136a-type objects. The change in predicted values, when these objects are not single stars but are composed of a dense cluster of similar stars has been discussed.