Search Publications
An Outburst Detected in the Spectrum of Hd 6226
Šlechta, Miroslav; Škoda, Petr
HD 6226 is a bright binary Be star at visual magnitude 6.81 (Hipparcos database). The emission and absorption phases occur in cycles, which are probably not periodic. The suspected period of about 630 days (derived from photometric measurements) is not confirmed by our spectroscopic survey. The latest emission phase developed in the beginning of 2…
Multiwavelength Study of two Unidentified γ-ray Sources
Caraveo, Patrizia; La Palombara, Nicola; Bignami, Giovanni F. +3 more
Most counterparts of the identified low-latitude γ-ray sources are isolated neutron stars (INSs). Since INSs are characterized by an extremely high value of f X/f opt, a systematic X-ray/optical coverage of the fields of unidentified low-latitude γ-ray sources is the best way to unveil INS counterparts of unidentified sources…
Towards an Understanding of Radial Velocity Shift in Uv Spectra of Symbiotic Stars
Friedjung, Michael; Mikołajewska, Joanna
A systematic redshift of high ionization resonance emission lines relative to the intercombination lines was found by Friedjung et al. (1883, A & A126, 4071983) in the UV spectra of a number of symbiotic binaries. The interpretation was not then clear. We present a study of archival IUE and GHRS/HST spectra of the symbiotic binary CI Cyg. The …
The Density and Masses of Obscured Black Holes
Comastri, Andrea; Fiore, Fabrizio
Recent Chandra and XMM-Newton surveys have uncovered a large fraction of the obscured AGN responsible of the hard X-ray background. One of the most intriguing results of extensive programs of follow-up observations concerns the optical and near-infrared properties of the hard X-ray sources counterparts. More specifically, for a significant fractio…
HST/STIS observations of sdBV stars: testing diffusion and pulsation theory
Heber, U.; Chayer, P.; Fontaine, G. +3 more
We present the initial results of an abundance analysis of echelle UV spectra of five hot subdwarf B (sdB) stars. These stars have been identified as core helium burning objects on the extreme Horizontal Branch. Around 5% of sdBs show short-period acoustic-mode oscillations. Models predict that these oscillations are due to an opacity bump caused …
A new mechanism for the crab fingers
Carlqvist, P.
Images of the outer filamentary parts of the Crab Nebula, earlier obtained with the Hubble Space Telescope WFPC2, are reconsidered. On inspection of the images it is found that most of the mainly radially oriented fingers possess an internal structure, usually in the form of two or more filaments. For some of the fingers there are clear signs that…
Photometric analysis of EL Aqr
Wadhwa, Surjit S.; Zealey, William J.
We present an analysis of the Hipparcos and ASAS photometry of the W UMa star EL Aqr. The Wilson-Devinney code is employed in conjunction with recent spectroscopic mass ratio of 0.203 to model the V band light curve. We confirm that the system is an A type contact binary however our analysis suggests that it is over massive for its spectral class …
Evidence for an Ionized Rotating Structure Around RW Aur
Gómez de Castro, Ana I.; Verdugo, Eva
Profiles of the UV semiforbidden lines of C III and Si III of RW Aur have been obtained with the HST/STIS. The C III profile shows two high velocity components at v = +/- 170 km s-1 and a central one. The Si III profile is very broad (FWHM = 293 km s-1) and the high velocity components are unresolved. It is shown that the hig…
X-rays from the Local Bubble
Freyberg, Michael J.
Thermal plasma emission in the soft X-ray band (0.1–2.0 keV)is believed to be responsible for the bulk of the X-ray intensityseen from the Local Bubble, a low-density cavity extending over∼ 70–200 pc around the Sun. The state of the hot plasmais still a matter of discussion as previous instrumentation like aboardROSAT was not able to unambiguously…
Diffuse Baryons in Cosmic Structures
Cavaliere, Alfonso
I review the processes that govern the amount and the thermal state of the hot plasma pervading clusters and groups of galaxies: the gravitational heating driven by the DM merging histories, the radiative cooling of baryons, and the energy fed back by SNe and by AGNs or quasars. I argue that the X-ray emissions and the entropy levels now observed …