Publications of the Astronomical Society of the Pacific

Deutsch, Eric W.

doi: 10.1086/133489pmid: N/A

Recent-epoch positions and proper motions of nine dwarf carbon star candidates are presented along with finding charts for each object. Measurements are obtained from digitized POSS and Quick V plate archives at the Space Telescope Science Institute, and from recent CCD images.

Fernie, J. D.; Seager, S.

doi: 10.1086/133490pmid: N/A

Two hundred and three nights of UBV APT data are reported for R CrB in the years 1992 and 1993. An additional twenty-one nights of photometry from this observatory are also reported, and previously reported visual estimates are included to sketch the early stages of a deep decline at the end of the 1993 season. Through most of these two seasons R CrB reached peak brightness and showed well-developed pulsations of 0.25 mag amplitude and period 35.3 ± 0.2 days. To within the observational errors these maintained phase-coherence across the two seasons. The deep decline began near the minimum phase of pulsation, whereas in 1985 the deep decline began nearer to the maximum phase of pulsation, casting some doubt on the role of pulsation in triggering deep declines.

Patterson, Joseph; Skillman, David R.

doi: 10.1086/133491pmid: N/A

We report photometry of the cataclysmic variabla V795 Herculis during 1990-94. Comparison of recent with previously published data shows that the 2.78 hr periodicity has essentially disappeared; the amplitude has diminished by a factor of at least 10. In its place, there is a low-amplitude signal near the radial-velocity (orbital?) period of 2.60 hr. During 1983-89, the star did show an obvious 2.78 hr signal. We study the published data on this signal, together with our own data under the (questionable) assumption that the signal still exists with an amplitude too small to survive the rigors of unbiased period detection. The data are really too sparse and too poorly distributed to decide the issue of phase stability. But since the photometric signal is transient and exceeds the likely orbital period by ~8%, the photometric waves are likely to be yet another example of "superhumps," the phenomenon made famous by dwarf novae in superoutburst. At high frequencies, the star shows a quasi-periodic signal with P ~1160 s, and possibly also a stable signal with P = 1310.2 s (or 1330.4 s, the one-day alias). The beat period between these signals could be the orbital period, or that of the vanished superhump.

Greason, M. R.; Offenberg, Joel D.; Cornett, Robert H.; Hill, R. S.; Stecher, Theodore P.

doi: 10.1086/133492pmid: N/A

The Ultraviolet Imaging Telescope cameras include two-stage magnetically focussed image intensifiers that introduce small but significant geometrical distortions to the data. These distortions, which create positional offsets as large as 25 arcseconds at the field edges, are corrected by the procedure described here to 2-3 arcseconds, approximately the resolution of the images. The distortion is measured by comparing and correcting UIT images to digitized Guidestar survey plates of the same fields. Two-dimensional third-order polynomials are used to model the distortion. The models assume that the distortion is an instrumental effect, independent of mission elapsed time and target, and that the effect of distortion in the center of each field is minimal. The models are used to improve computed astrometric plate solutions and to remove the geometric distortion while transforming the image to a standard north-up, east-left orientation.

Lissandrini, C.; Cristiani, S.; La Franca, F.

doi: 10.1086/133493pmid: N/A

The sky subtraction performance of multi-fiber spectrographs are discussed, analyzing in detail the case of the OPTOPUS system at the 3.6 meter ESO telescope at La Silla. A standard technique, based on flat-fields obtained with a uniformly illuminated screen on the dome, provides poor results. A new method has been developed, using the [O I] emission line at 5577 A as a calibrator of the fiber transmittance, taking into account the diffuse light and the influence of each fiber on the adjacent ones, and correcting for the effects of the image distortions on the sky sampling. In this way the accuracy of the sky subtraction improves from 2-8% to 1.3-1.6%.

Sturmann, Laszlo

doi: 10.1086/133494pmid: N/A

In this paper, we discuss how the Time Delay and Integration (TDI) method can be applied to observations of lunar occultations. The TDI method allows us to track the diffraction pattern of an occulted star by stepping the photon generated charge packages in a CCD array synchronously with the moving diffraction pattern. The use of TDI should considerably improve the signal-to-noise ratio that can be reached in occultation observations compared with that which can be obtained currently using conventional high speed photometers. The TDI method could extend lunar occultation studies to faint stars and telescopes with large apertures without sacrificing angular resolution. We show that observers can achieve 1 mas angular resolution in observations of stars as faint as mV~8 with a 5-m class telescope.

Jablonski, F.; Baptista, R.; Barroso, J.; Gneiding, C. D.; Rodrigues, F.; Campos, R. P.

doi: 10.1086/133495pmid: N/A

We describe the characteristics and performance of a high-speed multicolor photometer, FOTRAP, which has been used since 1988 at LNA, Laboratorio Nacional de Astrofisicas/CNPq, Brazil. The opto-mechanical concepts, electronics and software are outlined. We discuss the quality and consistency of the transformations from the natural system to the UBVRI standard system. We give particular attention to the problem of transforming to the standard system observations of objects with blue spectra, like cataclysmic variables. We compare the results of our UBVRI measurements for a few spectrophotometric standards with the values published in the literature.

Gutierrez-Moreno, A.; Heathcote, S.; Moreno, H.; Hamuy, M.

doi: 10.1086/133496pmid: N/A

Observations of the planetary nebula Me 2-1 are used to discuss some effects of contamination produced by the second order ultraviolet spectrum in the first order red, longer than approximately 6200 A. It is found that this contamination is present with some instrument set-ups, and that the contaminating lines are displaced in wavelength with respect to the predictions from diffraction theory by an amount which varies slightly for different set-ups. From the theoretical and empirical analysis of these displacements, it is concluded that the shift in wavelength is due to the presence of chromatic difference in magnification in spectrograph cameras including any transmission element, as is the case in teh semi-solid Schmidt-Cassegrain cameras used in our observations.