Publications of the Astronomical Society of the Pacific

Vaughan, A. H.; Preston, G. W.

doi: 10.1086/130683pmid: N/A

Fluxes in 1 A bands at the centers of the H and K lines are being measured in main-sequence F-G-K-M stars in the northern half of the Woolley et al. (1970) 'Catalog of stars within twenty-five parsecs of the sun', in a survey not yet completed. Results for 486 stars are presented in the form of flux-color diagrams and discussed in light of evidence that chromospheric activity declines with age in main-sequence stars. Support is noted for the reality of the Sirius moving group. The relative numbers of more-active (Hyades-like) and less-active (solar-like) F-G stars are tolerably in agreement with a nearly constant rate of formation, but there exists an apparent deficiency in the number of F-G stars exhibiting intermediate activity. The possibility that the gap is an accidental characteristic of the sample will be investigated by extending the survey to southern declinations and greater distances.

Vaughan, A. H.

doi: 10.1086/130684pmid: N/A

An analysis of the 91 main-sequence stars studied by Wilson (1978) shows that the behavior of young and old stars is fundamentally different. The stars are plotted in a log S,(B-V) diagram as vertical bars extending over the maximum range of their H-K variations in an eleven year span, revealing a bifurcation in the diagram for young and old stars. In addition, Wilson's time-resolved H-K flux observations for stars in each branch of the diagram are separately arranged in order of a (B-V) color index. The old stars are characterized by smooth, undulating variations in chromospheric H-K emission flux, with a rapidly varying component that increases in the maximum of the cycle; much like solar activity cycles. While young stars exhibit a chaotic behavior occurring over a considerable range of time cycles, with sun-like cycles being the rare exception.

Peterson, C. J.

doi: 10.1086/130685pmid: N/A

From a spectroscopic investigation of the late-type galaxy NGC 4945 (de Vaucouleurs classification SBscd:), we derive the following conclusions: (1) Over the major part of the optical image of the galaxy, the mean rotation curve is linear, with the center of rotation displaced 45" = 1.1 kpc northeast of the apparent optical center of the galaxy, features which are in accord with known kinematical properties of other late-type Sd or Sm galaxies. (2) On the southwest side of the galaxy, velocity data in positions offset from the major axis show strong departures from purely circular motions. This is most easily interpreted in terms of an infall of gas into the galaxy. (3) With regard to the interpretation (de Vaucouleurs 1964a) of NGC 4945 as an asymmetrical barred spiral seen nearly edge-on, there is no evidence for the outward streaming of gas along the bar which has been reported in other galaxies of similar morphological class. In addition, the observed departures from circular motion are not in agreement with those expected in the de Vaucouleurs-Freeman (1973) mass model for asymmetrical systems; thus, if a bar does exist in the galaxy, it can be only a minor perturbation in the mass distribution.Radial velocities and photometry of 15 background galaxies in the vicinity of NGC 4945 are reported in an Appendix.

van den Bergh, S.

doi: 10.1086/130686pmid: N/A

A 3.6-m plate taken in excellent seeing shows that NCC 3928 is not an E0 or S0 galaxy but a miniature spiral galaxy.

Walker, G. A. H.; Yang, S.; Witt, A. N.; Fahlman, G. G.

doi: 10.1086/130687pmid: N/A

The extinction properties of the Be shell star HD 200775 caused by dust in the bright reflection nebula NGC 7023 are discussed on the basis of direct observations of HD 200775. Reddening curves obtained between 5500 and 6800 A by a Reticon linear array are found to differ from any simple curve, lacking diffuse interstellar features except at 6284 and possibly 5780 A and exhibiting a very broad band structure. IUE spectra between wavelengths of 1250 and 3200 A reveal a UV reddening curve in which the 2175-A absorption is weak and the 1540-A feature is absent, although a rapid rise typical of the average extinction curve is present at wavenumbers greater than 6/micron. Comparison of the extinction curve of HD 200775 with that of the shell star Theta 1 Orionis reveals the form of the diffuse absorption bands at 2175 and 1540 A. A three-component dust model consisting of fine grains accounting for UV absorption, large grains for the optical and a volatile mantle responsible for the diffuse absorption features and broadband structure is suggested to account for the observations.

Shields, G. A.

doi: 10.1086/130688pmid: N/A

Planetary nebulae (PN) characteristically show large gas-phase depletions of some refractory elements, with Fe/H and Ca/H concentration ratios approximately equal to -1.5. In contrast, the gas-phase abundance of carbon is large, with a C/H concentration ratio greater than approximately +0.3. This pattern is difficult to understand in terms of grain formation and destruction during PN formation. However, these abundances are consistent with a model (Kwok, Purton, and FitzGerald, 1978) in which the PN shell consists of material expelled as a wind during the red-giant phase and subsequently compressed and accelerated by the impact of a hot stellar wind from the central star.

Auner, G.; Dengel, J.; Weinberger, R.; Hartl, H.

doi: 10.1086/130689pmid: N/A

A hitherto unreported open star cluster of small angular extent (̃2.5 arc min), located within the "ghost" image of Sirius, was identified on the Palomar Sky Survey print no. 1343. The cluster was also examined on a copy of an ESO (B)plate and is found to he rich (n ̃ 140 members), slightly reddened (AV ̃ 1), and distant (d ≳ 4 kpc).

Stone, R. C.

doi: 10.1086/130690pmid: N/A

Photographic UBV magnitudes and colors are presented for 83 stars in the region of the young open cluster NGC 654, which Stone (1977) determined to have nonzero membership probabilities. It is noted that one-third of these stars lie outside the cluster nuclear region, indicating the presence of a stellar corona. Further, the coronal stars can be used to investigate the known variable reddening in a cluster region much larger than considered in previous photometric studies. It is found that over the extended region, the reddening varies from E(B-V) = 0.77 to 1.13 magnitudes with several stars having larger reddenings, and a variable-extinction analysis gives an averaged absorption ratio of R = 2.9 + or - 0.6 (s.e.) which is in good agreement with an earlier study by Turner (1976). In addition, attention is given to the cluster H-R diagram, a study of the nuclear and coronal cluster regions, and a comparison of the cluster luminosity function with the Initial Luminosity Function of Sandage (1957).

Breinhorst, R. A.; Karimie, M. T.

doi: 10.1086/130691pmid: N/A

Details of a recent photoelectric three-color photometry and an unpublished series of earlier UBV observations of the system EM Cep are presented. It is suggested that the previously reported light-curve anomalies result from abrupt transitions between two distinct modes of light variation with different amplitudes rather than from continuous changes of the light curve. An extension of the (O-C) diagram until 1978 is interpreted in terms of only a marginal secular decrease of the period.

Hutchings, J. B.

doi: 10.1086/130692pmid: N/A

HR Del was observed simultaneously with the IUE satellite (low-dispersion spectroscopy), the DAO 1.8-m telescope (medium-dispersion spectroscopy), and the Einstein observatory (X-ray imaging proportional counter) over part or all of one 4-hour orbital cycle. The orbital ephemeris is refined and accurate phases computed for the data. The UV spectra show changes in the C IV P Cygni profile which suggest a spiralling stellar wind. A considerable overabundance of C and N in the wind is indicated. The UV data are also used to determine the continuum flux and temperature, and its variability. Optical spectroscopy shows some small changes since 1978 and confirms the strength of C features in the accretion disk. The X-ray observations yield a marginal detection, indicating a luminosity of 2 x 10 to the 31st erg/sec in the 0.5-3 keV flux. New estimates of the reddening and luminosity are derived.