Search Publications
An analysis of DA white dwarfs from the Hamburg Quasar Survey
Reimers, D.; Dreizler, S.; Heber, U. +5 more
Follow-up spectroscopy of several hundred hot stars detected by the Hamburg Quasar Survey (HQS) has been carried out between 1989 and 1996. We present the analysis of 80 DA white dwarfs using model atmospheres and theoretical cooling tracks to derive the atmospheric parameters T_eff and log g, masses and absolute magnitudes. The HQS turned out to …
A reliable transformation of HIPPARCOS H_p magnitudes into Johnson V and B magnitudes
Harmanec, P.
A comparison of accurate UBV magnitudes, derived from numerous observations at Hvar and SkalnatePleso, and of the mean Hipparcos \hp magnitudes for a number of constant stars showed a very good mutual correspondence of these two data sets. Simple transformation formul\ae\ are presented which allow calculating Johnson V and B magnitudes from the \h…
A Search for Ultraviolet Emission from LINERs
Filippenko, Alexei V.; Ho, Luis C.; Barth, Aaron J. +1 more
We have obtained Hubble Space Telescope Wide Field and Planetary Camera 2 ultraviolet (UV) 2200 Å and optical V-band images of 20 low-luminosity active galactic nuclei, most of which are spectroscopically classified as LINERs, in order to search for a possible photoionizing continuum. Six (30%) of the galaxies are detected in the UV. Two of the de…
Comparison of two different extinction laws with HIPPARCOS observations
Carraro, G.; Vergely, J. L.; Chen, B. +1 more
Interstellar absorption in the galactic plane is highly variable from one direction to another. In this paper colour excesses and distances from a new open cluster sample are used to investigate the spatial distribution of the interstellar extinction. An inverse method (Tarantola & Valette, 1982) is used to construct the extinction map in the …
On the Far-Infrared Emission of Quasars
Haas, Martin; Meisenheimer, Klaus; Chini, Rolf +4 more
Infrared spectral energy distributions between 4.8 and 200 µm are presented for a subsample of 10 quasars and radio galaxies from the European Central Quasar Programme observed with the Infrared Space Observatory. For three of the sources, this represents the first far-infrared detection. The spectral energy distributions (SEDs) reveal signa…
On the relationship between coronal mass ejections and magnetic clouds
Thompson, B. J.; Nitta, N.; Steinberg, J. T. +9 more
We compare the substructures of the 1997 February 07 coronal mass ejection (CME) observed near the Sun with a corresponding event in the interplanetary medium to determine the origin of magnetic clouds (MCs). We find that the eruptive prominence core of the CME observed near the Sun may not directly become a magnetic cloud as suggested by some aut…
Acoustic Power Maps of Solar Active Regions
Brown, Timothy M.; Hindman, Bradley W.
Using observations made by the Michelson Doppler Imager (MDI), we find that within solar active regions the spatial distributions of Doppler velocity power and continuum intensity power differ. The oscillation power within any pixel is a strong function of the magnetic field strength within that pixel. The amplitudes of oscillations with frequenci…
Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of alpha Orionis
Dupree, A. K.; Gilliland, R. L.; Uitenbroek, H.
Spatially resolved UV spectra of the supergiant alpha Orionis (Betelgeuse) obtained in 1995 March with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST) show that the chromospheric emission in the Mg II h and k (around 280 nm) lines reaches a diameter of at least ~270 milliarcseconds, about twice the size of…
Hubble Space Telescope observations of the nucleus and inner coma of comet 19P/1904 Y2 (Borrelly)
Weaver, Harold A.; Toth, Imre; Lamy, Philippe L.
The nucleus of comet 19P/Borrelly was detected using the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST). During the time of our observations, the comet was 0.62 AU from the Earth, 1.40 AU from the Sun, and had a solar phase angle of 38°. The high spatial resolution of the HST images allowed us to discriminate clearly between the sign…
Mass Segregation in Young Large Magellanic Cloud Clusters. I. NGC 2157
Mateo, Mario; Pryor, Carlton; Fischer, Philippe +2 more
We have carried out Wide Field Planetary Camera 2 V- and I-band imaging of the young LMC cluster NGC 2157. Construction of a color-magnitude diagram and isochrone fitting yield an age of tau = 10^8 yr, a reddening E(B - V) = 0.1, and a distance modulus of 18.4 mag. Our data cover the mass range 0.75 M_⊙ <= m <= 5.1 M_⊙. We find that the clus…