Publications of the Astronomical Society of the Pacific

Witt, Adolf N.; Rogers, C.

doi: 10.1086/132835pmid: N/A

BVRI color-difference measurements are reported for the unusual bipolar reflection nebula IC 2220 which surrounds an early-M giant. The data were obtained through BVRI imaging with a CCD detector. Analysis of the color difference between the nebula and the illuminating star HR 3126 indicates that the nebular dust, having formed in the outflow from the star, is similar to average interstellar dust. No evidence is found for the presence of extended red emission in this nebula, although there is an indication of nonequilibrium continuum emission. The Milky Way provides a significant amount of external illumination to IC 2220 in B and U.

Martin, Brian E.; Hube, Douglas P.; Brown, Chris

doi: 10.1086/132836pmid: N/A

The bright star 75 Peg is a close binary ellipsoidal variable with a short period (0.5021035-day) and an extreme mass ratio of 0.104 B, V, and R photometric data, along with previously published radial-velocity data, are analyzed; they suggest that the primary of the 75 Peg system may be, or is very close to, filling its critical Roche lobe.

Hobbs, L. M.; Mathieu, Robert D.

doi: 10.1086/132837pmid: N/A

High-dispersion echelle spectra which include the Li I 6708 A line are reported for four blue stragglers. Two are field Population II stars with Fe/H near -1.4, while the other two are members of the open cluster M 67. The Li I line is not detected in the spectra of any of these four blue stragglers; consequent upper limits on the surface lithium abundances are further deduced from suitable model atmospheres. The upper limits are significantly lower than the initial lithium abundances inferred for the respective stellar populations associated with these blue stragglers. The negative results for the two metal-deficient stars may reveal the existence of a narrow 'lithium gap' along the Population II main sequence. Alternatively, some mechanism associated with the formation and evolution of halo blue stragglers may account for their reduced atmospheric lithium abundance. The negative results in M 67 argue that blue stragglers do not result from delayed star formation, and that blue stragglers do not remain near the main sequence for extended lifetimes as a result of interior mixing, unless the surfaces of such stars are also mixed.

Schulz, Hartmut; Wegner, Gary; Heber, Ulrich

doi: 10.1086/132838pmid: N/A

A coarse spectroscopic analysis is presented of the faint blue stars JL87 and JL111, which are rather different despite their nearly identical UBV colors. JL87 is shown to be a helium-rich subluminous B star. Its abundance ratio nHe/nH = 0.2 is abnormally high compared to the bulk of the sdB stars that have strongly helium-depleted atmospheres relative to the sun. Observers are urged to look for a magnetic field in this star that could have caused the abundance anomaly. The other star, JL111, appears to be a quite normal, slightly hotter sdB.

Gray, David F.; Johanson, Heather L.

doi: 10.1086/132839pmid: N/A

The ratio of line depth for two spectral lines is used to determine stellar temperatures with a precision = 10 K = 0.2 percent. For stars between late-F and early-K spectral types, the V I 6251 to Fe I 6253 depth ratio is easy to measure. It is also applicable to other temperature regimes if suitable lines can be found.

Bopp, Bernard W.; Dempsey, Robert C.; Parsons, Sidney B.

doi: 10.1086/132840pmid: N/A

Optical and ultraviolet spectroscopy is presented for three F + B objects that are members of the first group of strongly interacting, F II + B systems. The data obtained confirm that HD 59771, HD 242257, and CoD -30 5135 are all binary star systems consisting of a luminous F-type component and a B star. Strong, variable H-alpha emission is seen in all the stars. It is found that the UV spectrum of HD 59771 resembles the spectrum of HD 207739. CoD -30 5135 has the most dramatic mid-UV spectrum seen among the scores of observed cool + hot star systems.

Halbedel, Elaine M.

doi: 10.1086/132841pmid: N/A

The star HDE 229189 (BD + 40 4145; in the field, though probably not a member, of the open cluster NGC 6910) has been found to exhibit large photometric changes in V magnitude over relatively short time scales. The total observed range was 0.416 V magnitude. An outburst in 1982 showed an even greater V range (Delta V = 1.66) and concomitant color changes. A coude spectrum of the star taken a week before a minor outburst showed emission at H-alpha but no other unusual lines. The star is likely an A3 (V)e star, an unusual object in itself (since stars as late as A3 seldom show emission at H-alpha), or else possibly a member of a binary system undergoing mass transfer between the members.

Schachter, Jonathan

doi: 10.1086/132842pmid: N/A

The physical processes which produce terrestrial ozone absorption are discussed deriving ozone opacities from laboratory cross sections and published ozone column densities. The ozone opacity decreases from about 1 at 3100 A to about 0.001 at 3500 A. A comparison of model DA white-dwarf spectra absorbed by ozone and actual observed spectra shows good agreement. Therefore, simulated absorbed spectra may be used to remove ozone contamination in ground-based data.

Padin, S.; Scott, S. L.; Woody, D. P.; Scoville, N. Z.; Seling, T. V.; Finch, R. P.; Giovanine, C. J.; Lawrence, R. P.

doi: 10.1086/132843pmid: N/A

The telescopes and signal processing systems of the Owens Valley Millimeter Array are considered, and improvements in the sensitivity and stability of the instrument are characterized. The instrument can be applied to map sources in the 85 to 115 GHz and 218 to 265 GHz bands with a resolution of about 1 arcsec in the higher frequency band. The operation of the array is fully automated. The current scientific programs for the array encompass high-resolution imaging of protoplanetary/protostellar disk structures, observations of molecular cloud complexes associated with spiral structure in nearby galaxies, and observations of molecular structures in the nuclei of spiral and luminous IRAS galaxies.

Babcock, H. W.

doi: 10.1086/132844pmid: N/A

Optical gyroscopes mounted directly on a telescope can provide its precise angular coordinates referred to the fundamental inertial system. Tracking of a star can be accomplished by computing continually in real time its changing apparent place and by applying computer-generated corrections to the telescope to maintain coincidence between the output of the gyros and the apparent place of the star. This system circumvents mechanical imperfections of the mounting and drives of the telescope, thereby promising significant cost reduction as well as improved performance.