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The HB Narrowband Comet Filters: Standard Stars and Calibrations
We present results concerning the development and calibration of a newset of narrowband comet filters, designated the HB filter set, which wasdesigned and manufactured to replace aging IHW filters. Information isalso presented about the design and manufacturing of the filters,including the reasoning that was used for deciding the final wavelengthsand bandpasses. The new filters are designed to measure five differentgas species (OH, NH, CN, C2, C3), two ions(CO+, H2O+), and four continuum points.An improved understanding of extended wings from emission bands in cometspectra, gained since the development of the IHW filters, wasincorporated into the new design, so that contamination from undesiredspecies is significantly reduced compared to previous filters. Inaddition, advances in manufacturing techniques lead to squarertransmission profiles, higher peak transmission and UV filters withlonger lifetimes. We performed the necessary calibrations so that dataobtained with the filters can be converted to absolute fluxes, allowingfor, among other things, accurate subtraction of the continuum from thegas species. Flux standards and solar analogs were selected andobserved, and the data were used to establish a magnitude system for theHB filters. The star measurements were also used to evaluate which solaranalogs were best representatives of the Sun and to explore how the fluxstandards differed in the UV with respect to their spectral type. Newprocedures were developed to account for the non-linear extinction inthe OH filter, so that proper extrapolations to zero airmass can beperformed, and a new formalism, which can account for mutualcontaminations in two (or more) filters, was developed for reducingcomet observations. The relevant equations and reduction coefficientsare given, along with detailed instructions on how to apply them. Wealso performed a series of tests involving factors that can affecteither the filter transmission profiles or the distribution of theemission lines in the gas species to determine how these effectspropagate through to the calibration coefficients. The results indicatethat there are only two factors that are a concern at a level of morethan a few percent: f-ratios smaller than f/4, and a few individualfilters whose transmission profiles are significantly different from thefilters used in the calibrations.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Hubble Space Telescope and Ground-based Observations of I ZW 1 and MRK 486 and the Variability of Polarization in Radio-quiet Active Galactic Nuclei
Hubble Space Telescope UV spectropolarimetry and new ground-basedoptical observations of the Seyfert 1/QSO I Zw 1 and highly polarizedSeyfert 1 Mrk 486 are presented. I Zw 1 is found to be a polarimetricvariable. Our data show that the polarization position angle has changedby ~50 deg compared to measurements obtained 10--15 yr ago. There isevidence that the degree of optical linear polarization may be variableas well, but for lambda >~ 4000 Angstroms, P remained less than 1%.Optical/UV synchrotron radiation can be ruled out as the cause of theobserved polarized flux and variations because the permitted lines arepolarized. The optical polarization increases dramatically to the blue.In contrast, the UV polarization is roughly constant with wavelength at~1% and falls far below the polarization level expected fromground-based observations. The overall wavelength dependence of theoptical and UV polarization can be reconciled if the effect of starlightfrom the luminous host galaxy is taken into account. The strong increasein the optical polarization with decreasing wavelength for Mrk 486continues into the UV and reaches nearly 8% by 2000 Angstroms. Thissuggests that dust scattering may be the dominant polarizing mechanismin this object. Spectropolarimetry of H alpha and H beta reveals complexpolarization structure across the lines (mostly in the polarizationposition angle), leading to the conclusion that at least some of thescattering material is located within the broad-line region (BLR). Theseresults are consistent with the BLR being composed of two distinctline-emitting regions: (1) a region of width ~1500 km s-1- (FWHM)polarized at P.A. 150 deg--160 deg, and (2) a region of width ~3000 kms-1- polarized at P.A. 100 deg--110 deg. Identification of thesedistinct regions in the BLR by their differing polarizationsdemonstrates the existence of an intermediate-line region in alow-luminosity AGN. Associated C IV absorption is detected in the UVspectrum of Mrk 486, in keeping with the general trend that highpolarization in radio-quiet AGNs is somehow linked to the presence ofabsorbing gas. The object also shows evidence for variations inpolarization. Observations acquired at two separate telescopes during1994--1995 reveal a decrease of ~10 deg in polarization P.A. comparedwith earlier measurements. The polarization variability of these twoobjects, along with the deduced proximity of the scattering region tothe nucleus of Mrk 486, argues that the structure of the scatteringand/or emission-line regions in at least some radio-quiet AGNs evolve onrelatively short time scales (a few years or less).
| Photometry of faint blue stars. IV - Some 'very definitely blue' PHL stars
Photometry on the uvby system is presented for 56 faint blue stars,mostly from the Palomar-Haro-Luyten 'very definitely blue' list. Themajority of these stars are hot subdwarfs.
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
| Four-colour and H beta photometry of southern B stars at high galactic latitudes
Four-color and H beta photometry has been obtained for 105 early-type HDstars with galactic latitudes less than -45 deg. They are mostly late Bstars of luminosity class V to III. Two new Am stars and several Ap orBp stars are detected photometrically. Absolute magnitudes aredetermined from the photometry and from MK types where available. Theinterstellar reddening of many of the more distant stars is very small,suggesting either the existence of undetected peculiar stars in thesample or that there are areas of effectively zero reddening at highsouthern galactic latitudes.
| On the transfer of photometric systems
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....12..442M&db_key=AST
| Faint blue stars in the region near the South Galactic Pole.
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