Search Publications
A Search for Helium in Ultramassive White Dwarfs
Vennes, Stéphane; Chayer, Pierre; Dupuis, Jean
We have obtained extreme ultraviolet (EUV) spectra of eight hot, ultramassive white dwarfs (M=0.9-1.3Msolar) with the Extreme Ultraviolet Explorer. The stars are, on average, twice as massive as normal white dwarfs. The relatively high turnout of ultramassive white dwarfs in EUV surveys is difficult to explain in the context of single-s…
Microwave Detection of Shock and Associated Electron Beam Formation
Reiner, M.; Shibasaki, K.; Karlický, M. +1 more
We use complementary European and Japanese solar radio ground-based observations, together with Yohkoh soft X-ray and SOHO extreme-UV images, to search for the signature of flare-related waves at different heights above the Sun. The key data set for event selection is 40-800 MHz dynamic radio spectra from the Potsdam Astrophysical Institute, whose…
Ultraviolet Imaging Polarimetry of the Peculiar Seyfert 2 Galaxy Markarian 477
Cohen, Ross D.; Antonucci, Robert; Kishimoto, Makoto +3 more
We present the results of UV imaging polarimetry of the Seyfert 2 galaxy Mrk 477 taken by the Faint Object Camera on board the Hubble Space Telescope (HST). From a previous HST UV image (λ~2180 Å), Mrk 477 has been known to have a pointlike bright UV hot spot in the central region, peculiar among nearby Seyfert 2 galaxies. There are also claims of…
Infrared Space Observatory Observations of Hickson Compact Group 31 with the Central Wolf-Rayet Galaxy NGC 1741
Hanlon, L.; McBreen, B.; Metcalfe, L. +5 more
Hickson Compact Group (HCG) 31, consisting of the Wolf-Rayet galaxy NGC 1741 and its irregular dwarf companions, was observed using the Infrared Space Observatory. The deconvolved ISOCAM maps of the galaxies using the 7.7 and 14.3 µm (LW6 and LW3) filters are presented, along with ISOPHOT spectrometry of the central starburst region of NGC 1…
Ultraviolet Observations of Periodic Annular Intensity Fluctuations Propagating around Sunspots
Muglach, K.; Georgakilas, A. A.; Christopoulou, E. B.
We analyze UV observations of an isolated sunspot taken with the Transition Region and Coronal Explorer. We produced ``space/time slice images,'' which reveal periodic, inward-propagating, intensity fluctuations in the inner photospheric penumbra and periodic, outward-propagating, annular intensity fluctuations in the outer penumbra and the area a…
The Rate of Visual Binaries among the Brightest X-Ray Stars
Makarov, Valeri V.
Using the Tycho Double Star Catalogue and the Hipparcos Catalogue, I compare the rates of occurrence of resolved visual doubles among the brightest X-ray stars from the ROSAT All-Sky Survey Bright Source Catalog (RASS-BSC) and generally in these two catalogs. A strong correlation between visual binarity and brightness in X-rays is found. The rate …
Is There Evidence for Rotation or Horizontal Motions in Hot DB White Dwarfs?
Bergeron, P.; Wesemael, F.; Dufour, P.
In a recent analysis of Goddard High Resolution Spectrograph observations of three hot DB white dwarfs, Provencal et al. suggested that the C II λ1335 doublet in two such objects is abnormally broadened. This was interpreted as the signature of rotation, or perhaps of pulsation-related horizontal motions, at a velocity of v~60kms-1. Our…
Artifacts at 4.5 and 8.0 Microns in Short-Wavelength Spectra from the Infrared Space Observatory
Price, S. D.; Sloan, G. C.; Kraemer, K. E.
Spectra from the Short-Wavelength Spectrometer (SWS) on board the Infrared Space Observatory exhibit artifacts at 4.5 and 8 µm. These artifacts appear in spectra from a recent data release, OLP 10.0, as spurious broad emission features in the spectra of stars earlier than approximately F0, such as α CMa. Comparison of absolutely calibrated s…
XMM-Newton Spectroscopy of the Galactic Microquasar GRS 1758-258 in the Peculiar Off/Soft State
Wijnands, R.; Miller, J. M.; Lewin, W. H. G. +5 more
We report on an XMM-Newton Reflection Grating Spectrometer observation of the black hole candidate and Galactic microquasar GRS 1758-258. The source entered a peculiar ``off/soft'' state in 2001 late February in which the spectrum softened while the X-ray flux-and the inferred mass accretion rate-steadily decreased. We find no clear evidence for e…
The Effect of High-lying Levels on Atomic Models Relevant to Spectroscopic Analyses of Solar Extreme-Ultraviolet Spectra
Bhatia, A. K.; Doschek, G. A.; Feldman, U. +2 more
In this work we investigate the effect of including high-lying configurations in the collisional-radiative models used to calculate spectral line intensities recorded by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on board the SOHO satellite. Many of the emission lines observed by SUMER are attributed to transitions…