Publications of the Astronomical Society of the Pacific

Graham, J. A.; Heyer, Mark H.

doi: 10.1086/132725pmid: N/A

During a survey for faint H-alpha emission-line stars in Tau, a pair of on-line, off-line frames of the L1551-HH30-HL Tau region was obtained with an 800 x 800 CCD detector mounted on the Burrell Schmidt telescope at KPNO. Potentially important optical features unnoticed in most previous studies are discussed. In the L1551 core region there is a cluster of HH objects W of HH28 which on the average are larger and more diffuse than those which are closer to the source IRS5. In the SW and NE corners of the 20-arcmin field, new outlying HH objects are found. The evidence favors association with the second FIR source to the NE of IRS5 (L1551NE).

Schmidt, Edward G.; Gross, Bradley A.

doi: 10.1086/132726pmid: N/A

The General Catalogue of Variable Stars gives periods of slightly less than three-quarters of a day for the stars NO Cas and CN Tau. However, new photometry demonstrates that their periods are actually 2.6 and 1.8 days, respectively, and they are thus classical Cepheids. Fourier decompositions of their light curves are performed, and they are found to be members of a class of Cepheids with periods less than three days which may be related to the s-Cepheids. These two stars represent the shortest and longest known members of this class and thus are very useful in defining its properties in the Fourier diagrams.

Evans, Nancy Remage; Szabados, Laszlo; Udalska, Joanna

doi: 10.1086/132727pmid: N/A

IUE spectra have been used to search for companions of FN Aql and RX Aur, two classical Cepheids which have been tentatively identified as binary stars on the basis of cyclic variations in their pulsation periods. Three other Cepheids, FM Aql, Y Lac, and RS Ori, suspected of having blue companions from the (U-B), (B-V) diagram, have also been investigated. There is no indication of a companion of FM Aql, FN Aql, and RX Aur. If these stars have companions, they must be at least as cool as A0 V, Al V, and A1 V, respectively.

Caillault, Jean-Pierre

doi: 10.1086/132728pmid: N/A

The M-dwarf contribution to the soft X-ray background has been redetermined using new optical photometry for a previous sample of M dwarfs and additional Einstein X-ray survey data. The result, which is obtained from a sample area more than double the size of that previously used, is a conservative upper limit: M dwarfs contribute less than 10 percent to the soft XRB. This limit is consistent with that obtained in a similar X-ray-selected sample analysis by Caillault et al. (1986) and is more than a factor of two less than the estimate obtained by Rosner et al. (1981) from an optically selected sample of stars.

Samec, Ronald G.

doi: 10.1086/132729pmid: N/A

Observations made of the short-period eclipsing binary system V728 Her using a photoelectric telescope on four nights in June 1988 at Lowell Observatory are presented. Three times of minimum light were revealed by observations covering the eclipse portions of the light curves. A period study covering 80 years of observations indicates that a drastic period increase may have recently occurred, while indications such as a possible reversal of eclipse depths may suggest that V728 Her is magnetically active. Standard magnitudes derived for V728 Her and for comparison and check stars indicate that V728 Her is approximately of spectral type F3 while the comparison and check stars are K type. A preliminary light-curve solution indicates that the system consists of two nearly equal temperature components in the spectral class F3 to F4 in contact with a substantial fillout of near 20 percent and a mass ratio of about 0.4. This degree of contact is supported by the position of V728 Her on the period, color plane of Eggen. The period increase may indicate a mass exchange from the secondary to the primary component or a catastrophic angular-momentum loss due to an episode of massive stellar wind expulsion along lines of a corotating magnetic field.

Joner, Michael D.; Taylor, Benjamin J.

doi: 10.1086/132730pmid: N/A

Cousins VRI data for 19 standard stars in the M 67 dipper asterism are presented. With one exception, the values of sigma per mean for these data are lsss than 10 mmag. Because these stars are close together in the sky, they can be used with economy of effort in standardizing CCD images. New Cousins VRI photometry is reported for 23 M 67 stars. For 22 additional cluster stars, new V magnitudes are reported. It is found that some published V data for the Hyades and M 67 must be corrected by small amounts to recover the Landolt (1983) zero point. In addition, faint-star M 67 measurements by Eggen and Sandage (1964) display scatter which is not easily interpreted. The same is true for the (largely) bright-star M 67 data of Johnson and Sandage (1955). The photomultiplier colors of Janes and Smith (1984) and the CCD data of Schild (1983, 1985) are also considered.

Lopez, Carlos E.; Girard, Terrence M.

doi: 10.1086/132731pmid: N/A

Improved positions for 950 confirmed variable and 368 suspected variable stars located south of -67 deg have been determined by measuring the first-epoch plates of the Yale-San Juan southern proper-motion survey. The new positions, referred to the system of the SRS, have an average standard error of 0.7 arcsec in both R.A. and Dec. Some of the differences with the coordinates quoted in the GCVS are as large as 1 deg.

Lester, John B.

doi: 10.1086/132732pmid: N/A

A small systematic error that can affect the determination of stellar abundances is described. When the structure of the atmosphere of a star is represented by a line-blanketed model, the general line opacity should also be included in the calculation of the equivalent width of each individual line. The failure to do this makes the line too deep, and a given, observed equivalent width is matched by an abundance that is less than the correct value. Tests of the dependence of this systematic effect on line strength, wavelength, surface gravity, effective temperature, and spectral resolution are presented. The error can be avoided by analyzing each line by spectral synthesis, by using a portion of an opacity distribution function to represent general line blanketing in the computation of each line profile, or by making a careful differential abundance analysis.