ROTATION PERIODS OF OPEN-CLUSTER STARS. IIIProsser, Charles F.; Shetrone, Matthew D.; Dasgupta, Amil; Backman, Dana E.; Laaksonen, Bentley D.; Baker, Shawn W.; Marschall, Laurence A.; Whitney, Barbara A.; Kuijken, Konrad; Stauffer, John R.
doi: 10.1086/133541pmid: N/A
We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late-1993/early-1994. Several slow rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleides stars with photometric-periods together with current X-ray vlux measurements, we illustrate the X-ray activity/ortation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P ~6-7 days--in general accordance with previous results using more heterogeneous samples of G/K stars.
THE REMARKABLE VISUAL BINARY SYSTEM VW ARI: CHEMICAL COMPOSITION OF ITS COMPONENTSAndrievsky, S. M.; Chernyshova, I. V.; Usenko, I. A.; Kovtyukh, V. V.; Panchuk, V. E.; Galazutdinov, G. A.
doi: 10.1086/133542pmid: N/A
We present results of a spectroscopic investigation of the A and B components of the visual binary VW Ari. Results are: 1) the atmospheric parameters for the stars are Teff = 7100 K, log g = 3.7 (A component), Teff = 7300 K, log g=4.3, Vt = 1.9 km s-1 (B component); 2) the masses and radii are RA ~ 3.5 Rsun, RB ~ 1.6 Rsun; MA ~2.2 Msun, MB ~ 1.8 Msun; 3) abundances of 16 elements have been determined for VW Ari B. This star shows solar-like chemical composition for most of the elements. 4) Because of the complicated spectrum of VW Ari A (only a few very shallow lines are seen), we were able to estimate only Ca and Fe abundances in its atmosphere: [Ca/H] = -0.73, [Fe/H] = -0.46. The remarkable metallicity difference between the components strongly supports the hypothesis of stellar capture as most probable origin of the VW Ari system.
FAR-ULTRAVIOLET AND OPTICAL SPECTROSCOPY OF THE DETACHED WHITE DWARF-M DWARF BINARY RE J1629+780Sion, Edward M.; Holberg, Jay B.; Barstow, Martin A.; Kidder, Kenneth M.
doi: 10.1086/133544pmid: N/A
We present optical and far ultraviolet observations, including IUE high and low dispersion spectroscopy of the (DA2+dM4-5) close binary, RE J1629+780, a very bright ROSAT EUV source. The optical data reveal emission reversals in the cores of the Balmer lines, which vary in strength but reveal no evidence of wavelength shifts reflecting orbital motion, suggesting that the red dwarf and the white dwarf are widely separated. Thus it is unlikely that irradiation plays a dominant role in the activity of the red dwarf. One dramatic increase in the intensity of the H-beta emission strength in the course of one hour indicates that the observed intensity variations are most likely related to flare activity on the red dwarf. Our analysis of Balmer and Lyman alpha features yield Teff = 42,500 ± 1300K and log g = 7.6 ± 0.3 for the DA2 white dwarf, which is consistent with the overall 900 A to 3200 A energy distribution derived from Voyager and IUE low dispersion spectra. Our analysis of three IUE echelle spectra reveal numerous lines of interstellar origin. Using a total of 13 ISM features we find a mean radial velocity of -13.57 ± 1.66 km/s for the interstellar features. However we found no evidence of trace metal absorbers levitated or accreited in the white dwarf photosphere nor any evidence of circumstellar or wind features. We estimate a lower limit hydrogen layer mass of 2.1 X 10-15 Msun for a stratified atmosphere based upon the non-detection of He II (1640). Tighter constraints on the helium abundance and the hydrogen layer mass, from EUV and X-ray data, are presented for both homogeneous and stratified atmospheric configurations.
THE SPECTRUM OF RY SGR DURING RECOVERY FROM ITS 1993 MINIMUMVanture, Andrew D.; Wallerstein, George
doi: 10.1086/133546pmid: N/A
A spectrum of the RCB star RY Sge in the red and near-IR was obtained during its recovery from a deep minimum. The spectrum shows numerous weak emission lines blueshifted by 20 km/sec relative to the photosphere of the star. In addition to the emission line spectrum, strong, blueshifted Na I D lines are seen in absorption at a velocity of -200 km/sec. an analysis of these lines shows that the column density of Na I in this fast-moving cloud is 2.5 X 1013 cm-2 and that the Na I/K I ratio is substantially enhanced above the solar ratio. The inverse P Cygni profiles of the weak sharp lines are consistent with a picture in which outward moving gas may be interacting with a layer above it to create a weak shock capable of ionizing metals but no C I.
THE HIGH-RESOLUTION CROSS-DISPERSED ECHELLE WHITE PUPIL SPECTROMETER OF THE MCDONALD OBSERVATORY 2.7-M TELESCOPETull, Robert G.; MacQueen, Phillip J.; Sneden, Christopher; Lambert, David L.
doi: 10.1086/133548pmid: N/A
A new high-resolution cross-dispersed echelle spectrometer has been installed at the coude focus of the McDonald Observatory 2.7-m telescope. Its primary goal was to simultaneously gather spectra over as much of the spectral range 3400A to 1 micron as practical, at a resolution R = lambda/delta-lambda ≃ 60,000 with signal-to-noise ratio of ~100 for stars down to magnitude 11, using 1-hour exposures. In the instrument as built, two exposures are all that are needed to cover the full range. Featuring a white-pupil design, fused silica prism ross disperser, and folded Schmidt camera with a Tektronix 2048 X 2048 CCD used at either of two foci, it has been in regularly-scheduled operation since April 1992. Design details and performance will be described.
MEASURING ASTRONOMICAL SEEING: THE DA/IAC DIMMVernin, Jean; Munoz-Tunon, Casiana
doi: 10.1086/133549pmid: N/A
Accurate, absolute and reproducible measurements are the expected qualities of any instrument. A Differential Image Motion Monitor (DIMM) is presented which assesses astronomical seeing with those requirements. It has been designed also to be reliable, simple, trasportable, and to be easy to set up, operate and maintain. Its accuracy has been studied, both from theoretical and experimental points of view, mainly with respect to CCD sampling, photon noise and threshold influence on centroid determination. The DA/IAC DIMM has been cross-calibrated with the existing ESO DIMM. It monitors the seeing with a temporal resolution better than half a minute. This type of instrument is essential for testing new and already existing sites and to ascertain that the surroundings of telescopes do not generate additional turbulence. It is also indispensible to optimize astronomical instrument selection in "flexible scheduling.".
THEORETICAL COLOR CALIBRATION FOR HST FOC ULTRAVIOLET FILTERSYi, Sukyoung; Demarque, Pierre; Oemler, Augustus
doi: 10.1086/133550pmid: N/A
A theoretical color calibration is carried out for three (F140W, F220W, and F342W) of the most heavily used ultraviolet filters, and one visual band filter (F480LP) in the Faint Object Camera on the HST, using the new Kurucz model spectra which became available recently. It is known that the UV filters suffer from the visible leak problem, and it is apparent in this study that the visible leak problem can cause serious trouble to analyses of observed data. We show here that some of the colors defined from these filters do not have a monotonic relation with effective temperature; and thus, the colors fail to indicate a unique effective temperature in certain temperature ranges. This study shows that the problem can be solved by using one of the visual band filters, preferably F480LP, together with the UV filters. The expected model color-magnitude diagrams for a typical globular cluster with the HST ultraviolet colors are also provided.