Search Publications
Calibrating horizontal-branch stars with Hipparcos.
de Boer, K. S.; Tucholke, H. -J.; Schmidt, J. H. K.
Parallaxes from the Hipparcos satellite allow for the first time to calibrate parameters of horizontal-branch (HB) like stars based on geometric distances. The authors present absolute magnitudes and luminosities for 8 such stars. Using Teff and log g values available from the literature, they also can calculate the mass of the HB stars…
Macromolecules, Very Small Grains, and Large Dust Particles in the Whirlpool Galaxy M51 and Its Companions: A Unified View
Sauvage, Marc; Elmegreen, Bruce G.; Stockton, Alan +1 more
A combined image using optical and mid-infrared ISOCAM data of the galaxy M51 and its companion reveals a unified view of the distribution of dust grains of all sizes. The image shows the large grains in extinction at blue light and the small grains in emission at 15 µm. Much of the emission from small grains coincides with extinction from l…
UV Spectral Classification of O and B Stars in the Small Magellanic =
Bruhweiler, Frederick C.; Smith Neubig, Margaret M.
We present an ultraviolet classification system for 0 and B stars of the Small Magellanic Cloud (SMC). This system is defined by a set of standard, low resolution, International Ultraviolet Explorer (JUE) spectra. This UV classification system results from the development of spectral sequences demonstrating systematic patterus of UV spectral featu…
Accretion and UV Variability in BP Tauri
Gómez de Castro, Ana I.; Franqueira, M.
BP Tau is one of the few classical T Tauri stars for which the presence of a hot spot in the surface has been reported without ambiguity. The most likely source of heating is gravitational energy released by the accreting material as it shocks with the stellar surface. This energy is expected to be radiated mainly at UV wavelengths. In this work w…
Third Interplanetary Network Localization, Time History, Fluence, Peak Flux, and Distance Lower Limit of the 1997 February 28 Gamma-Ray Burst
Frontera, F.; Orlandini, M.; Cline, T. +9 more
The gamma-ray burst of 1997 February 28 was localized using the arrival time analysis method with the Ulysses, BeppoSAX, and WIND spacecraft. The result is a +/-31.5" (3 σ) wide annulus of possible arrival directions that intersects both the position of the burst determined independently by the BeppoSAX Wide Field Camera and the position of a fadi…
Ultraviolet Emission from the Liner Nucleus of NGC 6500
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +3 more
As a step towards clarifying the ionization mechanism of LINERs, we have used the Hubble Space Telescope Faint Object Spectrograph to obtain an ultraviolet spectrum of the nucleus of NGC 6500. This is the first time that such a spectrum has been taken of a "LINER 2" nucleus-that is, a LINER lacking broad permitted emission lines like those in Type…
Excess heating of 4He2+ and O6+ relative to H+ downstream of interplanetary shocks
Mall, Urs; Gloeckler, George; Geiss, Johannes +1 more
Using observations made by the solar wind ion composition spectrometer on Ulysses during its trip in the ecliptic plane to Jupiter, we examined the temperature ratios T(4He2+)/T(H+) and T(O6+)/T(H+) across 15 shocks, including forward and reverse shock pairs as well as isolated shocks. The mea…
Mass Segregation and Equipartition of Energy in Two Globular Clusters with Central Density Cusps.
Sosin, Craig
We begin by presenting the analysis of a set of deep B- and V-band images of the central density cusp of the globular cluster M30 (NGC 7099), taken with the Faint Object Camera aboard the Hubble Space Telescope. These images are the first to resolve lower-mass main-sequence stars in the cluster's central 10". From the positions of individual stars…
Abundances of the ^3^He star 3 CEN A (B5 IIIp) from ultraviolet IUE spectra.
Hack, M.; Parthasarathy, M.; Castelli, F.
High resolution (0.010-0.025nm) IUE ultraviolet spectra of the peculiar ^3^He star 3 Cen A were analyzed in the whole 120-320nm region. Abundances were derived from the comparison of the observed and computed spectra. For computing spectra a Kurucz ATLAS9 model with parameters T_eff_=17500K, logg=3.8, and microturbulent velocity ξ=0km/s was adopte…
Analyzing X-ray variability by linear state space models
Timmer, J.; Konig, M.
In recent years, autoregressive models have had a profound impact on the description of astronomical time series as the observation of a stochastic process. These methods have advantages compared with common Fourier techniques concerning their inherent stationarity and physical background. However, if autoregressive models are used, it has to be t…