David J. Bell

Non-LTE effects in streams, and mass-transfer rates in three eclipsing binaries

A mass-transferring stream in an eclipsing binary is seen in projection against the hot star in roughly the quarter-period before primary eclipse. At this time a small fraction of the light of the hot star is blocked by the stream, depressing light curves slightly. Five-color observations of such light curves in AQ Cas, RZ Sct, and U Sge are discussed. Non-LTE and LTE predictions of stream-produced light losses with these observations are compared, the validity of this mechanism is discussed, and mass-transfer rates are estimated.

SPECTROPHOTOMETRY OF 15 PLANETARY NEBULAE AND A POSSIBLE SYMBIOTIC STAR

We provide line intensities and limited chemical compositions of a colleciton of planetary nebulae, most of which are within 25 degrees of the Galactic center. Several appear enriched in nitrogen and/or helium. The central star of M 1-51 displays C IV in emission. Ha 1-2 has the spectral characteristics of a symbiotic star.

Photoelectric V and (B-V) for Weistrop stars near the North Galactic pole

V and (B-V) have been obtained for 173 stars near the north Galactic pole. A comparison is made between these photoelectric values and the photographic values obtained by Weistrop (1972). Corrections have been derived which, when applied to (B-V)w and Vw, result in relatively systematic error-free colors and magnitudes.

Detection of Metal-poor Stars in the Direction of the North Galactic Pole

A simple approach to detecting metal-poor stars is to measure a magnesium index, which depends on the Mg H band plus the three nearby Mg b lines and is derived through intermediate-band interference filters. An empirically established line of demarcation in the Mg index versus B-V diagram separates metal-poor stars from solar-abundance stars. A further separation between metal-poor dwarfs and giants depends on B-V; primarily dwarfs for B-V 0.7, with both dwarfs and giants falling in the transition region. For the metal-poor giants the distance from the demarcation line correlates well with [Fe/H], permitting estimates of stellar abundances. Stars in two regions on the sky in the vicinity of the north Galactic pole have been observed with such a set of filters. Eighteen stars (6% of the population of 299) in the sample covering the V range 8.7 to 15.6 and 48 stars (31% of the population of 163) in a deeper probe to V = 19.9 found through this process are suspected metal-poor stars according to their Mg indices. Twenty-three are specifically deemed giants, with [Fe/H] ≤ -1.5.

A spectroscopic study of the three symbiotic stars He 2-171, Ap 1-9, and Ap 1-11

Line intensities of the symbiotic stars He 2-171, Ap 1-9, and Ap 1-11 between 3700 A and 6900 A have been measured; He 2-171 has a particularly rich spectrum filled with the usual forbidden iron lines. Densities estimated from auroral-to-nebular line ratios are high, 2 x 10 to the 6th and 4 x 10 to the 7th/cu cm from forbidden O III for He 2-171 and Ap 1-9, respectively, and 300,000 from forbidden N II for He 2-171, while the nebular forbidden S II ratio gives a much lower density for He 2-171 of 10,000, typical of symbiotic behavior. Comparison with other observations of He 2-171 strongly indicates physical changes in the system over a four-year period. The spectrum of Ap 1-9 has a strong underlying continuum with TiO bands, indicating the presence of an M star.

The quality of photometric information in the Hipparcos Input Catalog

Comparison with independent photoelectric photometry is used to assess the quality of magnitudes and colors in the Hipparcos Input Catalog. These magnitudes and colors will play an important role in the luminosity calibration of Hipparcos stars. We conclude that photoelectric photometry, available for about 37% of the catalog, is of uniformly good quality, and the error estimates in the Catalog are very accurate. On the other hand, colors determined from poor (one-dimensional) spectral classes suffer from very significant errors, also correctly estimated in the Catalog, which make them essentially unsuited for the purpose of luminosity calibration. Only stars with either photoelectric colors or good two-dimensional spectral classes can be used in a high-accuracy luminosity calibration