QSO ABSORPTION LINE SYSTEMS AND EARLY CHEMICAL EVOLUTIONLauroesch, J. T.; Truran, J. W.; Welty, D. E.; York, D. G.
doi: 10.1086/133780pmid: N/A
Heavy element absorption line systems in spectra of QSOs represent unique probes of gas and high redshifts. An understanding of these systems will be important for theories of galaxy formation and large-scale structure. By using spectroscopic studies to obtain abundances in QSO absorption line systems at different redshifts, it is possible to observe clues to the nucleosynthetic history of objects, at a large range in redshift, that are presumably at different points in their evolution. In principle, one could imagine using abundance ratios to identify absorbing gas in which the heavy elements are predominantly those produced in Type II SNe (as are the Galactic halo and oldest disk stars) and those which have a mixture of the products of Type I and Type II SNe (like the gas and young stars of the Galatic disk). We review the present state of abundance measurements in damped Lyman-alpha systems, as well as recent results of studies of Galactic halo star and interstellar abundances. We also briefly discuss the results of imaging studies of fields around QSOs showing absorption by intervening gas, and the results of statistical analyses of the change in number of observed QSO absorption line systems with redshift. The range of overall abundances (10-0.5 to 10-3 solar) found in the absorbers (at redshifts of 0.6-3.4) overlaps the range found in Galactic halo stars. Specific, measurable tracers of supernova activity and dust grain formation in the absorber population are identified. As yet, however, there is no evidence of a system with [O/Zn]> 0 , [S/Zn]> 0, or [Si/Zn]> 0, the most distinguishing characteristic of Galactic halo star abundances. Dust-free gas with halo star abundances and solar metallicity gas with a Galactic cold-cloud depletion pattern are excluded by existing data. Additional observations of absorption line systems with 1019 < N(H I)< 1022 to obtain abundances of Al, Si, S, Mn, Fe, and Zn are needed. High spectral resolution is critical so that H I and H II regions may be identified and separated; otherwise the derived abundances are only upper limits. Future observations of O, N, Ca, Ti and Cr should shed new light on the origin of the elements and of grains in the absorbers. Observed cosmic timescales for elemental buildup can lead to specific predictions for the typical rates of Type I and Type II SNe as a function of redshift.
THE BLAZHKO EFFECT OF THE RR LYRAE STAR V421 HERCULISLee, Kevin; Gay, Pamela; Smith, Horace A.
doi: 10.1086/133781pmid: N/A
We have obtained new V-band photometry of the RR Lyrae Star V421 Her to test the suggestion of Tsessevich and Mandel (1985) that V421 Her is a double model RR Lyrae with the unusual period ratio of 0.79. We confirm the finding of Tsessevich and Mandel that the light curve of V421 Her is not well described by a single period. However, although the primary period we find agrees well with that of Tsessevich and Mandel, we are unable to confim their 0.43812 day secondary period. Instead, we suggest that V421 Her exhibits the classical Blazhko effect.
AN O VIII SEQUENCE FOR PLANETARY NEBULA NUCLEIFeibelman, Walter A.
doi: 10.1086/133782pmid: N/A
The detection of O VIII emission lines in ultraviolet and optical spectra of high-excitation planetary nebula central stars suggests an "O VIII Sequence" for these object. Emission lines of O VII are also detected. Seven out of ten central stars for these planetaries are known to be nonradial g-mode pulsators. The stars form a narrow strip when plotted on the log L*/Lsun - log Teff H-R diagram.
UV OBSERVATIONS OF THREE LMC BE-STAR/X-RAY BINARIESSchmidtke, P. C.; Cowley, A. P.; Hauschildt, P. H.; Ponder, A. L.; McGrath, T. K.; Frattare, L. M.; Franklin, B. E.
doi: 10.1086/133783pmid: N/A
This paper describes IUE ultraviolet observations of three Be-star/X-ray binaries in the LMC: CAL 9, CAL E, and RX J0520.5-6932. Because the optical spectra show evidence of an overlying continuum source, ultraviolet spectra were obtained to further investigate its properties, but no UV emission lines are found. The UV spectra have been compared to models indicating that the stellar temperatures are near 30000 K (for log g = 4.0). This is in agreement with the temperatures suggested by the spectral type determined in the optical region. Thus, there is no clear evidence in either the optical or UV regions of the gas being accreted by the unseen compact companion which must give rise to the X-ray emission. Optical photometry shows these systems undergo irregular variations of up to a few tenths of a magnitude.
DDO METAL ABUNDANCES OF HIGH-LUMINOSITY LATE-TYPE STARS IN GALACTIC OPEN CLUSTERSClaria, Juan J.; Piatti, Andres E.; Osborn, Wayne
doi: 10.1086/133784pmid: N/A
Results from UBV and DDO photometry are presented for 54 high-luminosity late-type stars in the fields of 23 open clusters. The probability of cluster membership for each observed star is evaluated using two independent photometric criteria. It is found that 32 stars are very likely cluster members, the remaining ones being almost certainly field objects. The recently improved calibrations of the DDO system have been used to derive MK spectral types, effective temperatures, and metallicities, while E(B-V) color excesses have been determined through known photometric and spectroscopic procedures. The DDO metallicities range between values typical of moderately metal-poor ([Fe/H]≃ -0.3) to moderately metal-rich ([Fe/H] ≃ 0.2) clusters. The masses of the cluster giants range between 1 and 4 solar masses, with the scatter within a cluster being less than 1 solar mass.
THE DIVERSE OPTICAL/ULTRAVIOLET SPECTRA OF THE GLOBULAR CLUSTER X-RAY SOURCES IN NGC 7078 AND NGC 6712Downes, Ronald A.; Anderson, Scott F.; Margon, Bruce
doi: 10.1086/133786pmid: N/A
Among the about one dozen luminous X-ray bursters in the cores of globular clusters, only three have optical/UV counterparts unambiguously identified. We have observed two of these counterparts spectroscopically with the low resolution optical and UV gratings of the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope (HST), yielding broad (1150-2500A and 3600-7000A) wavelength coverage in each case. For the counterpart AC211 to the X-ray source in NGC 7078/M15, our small aperture FOS data reveal both strong absorption and emission features, as well as a broad spectral energy distribution (SED), that are akin to those determined from earlier ground-based and IUE spectra, but with some important differences. These differences suggest that only the HST spectra of AC211 are free of significant contamination from nearby cluster stars. Our FOS data for the counterpart "Star S" in NGC 6712 permit an investigation of the SED for this second object as well; in this case a composite (and/or variable) SED is indicated. However, intriguingly in the case of "Star S", we find little evidence for any identifiable features--emission or absorption--attributable to the system, although features as strong as those seen for AC211 would be readily detected. These HST optical and UV spectra of AC211 and "Star S" may presage a spectral diversity among the counterparts to X-ray bursters in globular cluster cores.
GALACTIC MODEL COMPARISONS WITH THE HST GUIDE STAR CATALOGHershey, John L.; Ratnatunga, Kavan
doi: 10.1086/133787pmid: N/A
The HST Guide Star Catalog provides magnitudes and positions, and is nearly complete down to fourteenth magnitude for high and intermediate Galactic latitudes. The limitation in types of information is offset in some degree by the size of the Catalog, with 15 million stars. Experiments using the Galactic structure software, "IASG:, show that the IASG models can represent the Catalog very closely with small changes to the IASG old-disk default density and scale height, in clear preference to a single component disk model. The density, scale-height combinations were explored to bracket the region of agreement. An increase of 20% in both the old-disk density normalization to 0.13 and scale height to 0.8 kpc generates star numbers which very closely follow the numbers in the Catalog starcount histograms and are suggested as an optimal fit, although some trade-off between these two parameters can also represent the data well.
THE TELESCOPE POINT SPREAD FUNCTIONRacine, Rene
doi: 10.1086/133788pmid: N/A
New observations are used to accurately define the stellar point spread function produced by atmospheric turbulence at the focus of large telescopes and to compare its profile to those computed from wavefronts characterized by various structure functions. Excellent agreement is found with the PSF expected from Kolmogorov statistics, except for the presence of an extended aureole of light which appears to results from a combination of instrumental and atmospheric light scattering. Simple yet accurate analytic fits are developed to represent the PSF profile over a range of 15 magnitudes in surface brightness. The relation between the Strehl ratio S of the PSF and the value of the parameter D/r0 is re-discussed, both for a natural wavefront and for a wavefront whose variance DeltaN is reduced by an adaptive optics systems. A simple expression for S(D/r0, DeltaN) is proposed and shown to yield essentially correct Strehl ratios for any value of the parameters.
THE PERUGIA UNIVERSITY AUTOMATIC OBSERVATORYTosti, Gino; Pascolini, Sergio; Fiorucci, Massimo
doi: 10.1086/133789pmid: N/A
In this paper we describe the hardware and software architecture of the Automatic Imaging Telescope (AIT), recently developed at the Perugia University Observatory. It is based on an existing 0.4 m telescope which was transformed into an automatic device. During the night, all the observatory functions are controlled by two PCs in an unattended mode. The system is equipped with an autoguider and the software was designed to allow the automatic reduction of the data at the end of the night. Since October 1994 the AIT has been collecting a large amount of BVRcIc data for about 30 blazars.