Search Publications
Solar irradiances and radiances of UV and EUV lines during the minimum of sunspot activity in 1996
Wilhelm, K.; Curdt, W.; Lemaire, P. +6 more
Full Sun observations in UV and EUV emission lines were performed by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (Solar and Heliospheric Observatory) in 1996. The radiometric pre-flight calibration of SUMER is traceable to a primary radiometric source standard - the electron storage ring BESSY. Based on this calibration, th…
The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Hamann, W. -R.; Koesterke, L.
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTE radiation transfer calculations are performed which account for helium and nitrogen. Grids of theoretical models are presented for the whole relevant parameter range. The WN classification criteria are employed in order to identify the subtype domains, and inconsistencies are disc…
Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
van der Hucht, K. A.; Moffat, A. F. J.; van den Heuvel, E. P. J. +9 more
Reliable systemic radial velocities are almost impossible to secure for Wolf-Rayet stars, difficult for O stars. Therefore, to study the motions - both systematic in the Galaxy and peculiar - of these two related types of hot, luminous star, we have examined the Hipparcos proper motions of some 70 stars of each type. We find that (a) both groups f…
The nucleus and inner coma of Comet 46P/Wirtanen
Jorda, L.; Lamy, P. L.; Toth, I. +2 more
We report the detection of the nucleus of comet 46P/Wirtanen from analysis of images taken with the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed us to separate the signal of the nucleus from that of the coma and to …
Faint [O iv] emission from starburst galaxies
Lutz, D.; Kunze, D.; Spoon, H. W. W. +1 more
We report the detection of faint emission in the high-excitation [O iv] 25.90mu m line in a number of starburst galaxies, from observations obtained with the Short Wavelength Spectrometer (SWS) on board ISO. Further observations of M 82 spatially resolve the [O iv] emitting region. Detection of this line in starbursts is surprising since it is not…
ISO-SWS observations of infrared absorption bands of the diffuse interstellar medium: The 6.2 MU M feature of aromatic compounds
de Graauw, Th.; Morris, P. W.; van Dishoeck, E. F. +8 more
We present ISO-SWS spectroscopy of eight strong infrared sources with large extinction through the diffuse interstellar medium. These are five late-type Wolf-Rayet stars, the blue hypergiant Cyg OB2 #12 and the Galactic Center Sources 3 and 4. The spectra show a number of absorption features that can be ascribed to interstellar dust and gas. Featu…
A model of solar total and spectral irradiance variations
Solanki, S. K.; Unruh, Y. C.; Fligge, M. +2 more
We model solar spectral irradiance variations under the assumption that they are produced by sunspots and faculae alone. The model is based on three components, i.e. quiet Sun, assumed to be temporally invariant, sunspots and faculae whose temporal variations are mimicked using time series of sunspot areas and Mg II core-to-wing ratios. The detail…
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…
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 …