Search Publications
A ring of organic molecules around HD 97300
Prusti, T.; Siebenmorgen, R.; Natta, A. +1 more
This paper presents spectro-photometric images of the pre-main-sequence Herbig AeBe star HD 97300 in the mid-IR obtained with ISOCAM on board of ISO. The images show extended emission, an elliptical ring structure of size about 0.045x0.03 pc as well as two peaks of emission, separated by about 3arcsec (240 AU). One of the two peaks coincides with …
Behaviour of calcium abundance in Am-Fm stars with evolution
North, P.; Kunzli, M.
Calcium abundance in the atmosphere of Am stars is examined as a function of their evolutionary state within the main sequence. New spectroscopic abundances as well as abundances obtained photometrically by Guthrie (1987) are used, since they are mutually quite consistent. The main result of this work is that, contrary to earlier suggestions, calc…
Deduced spectrum of interacting protons accelerated after the impulsive phase of the 15 June 1991 solar flare
Kocharov, L.; Rank, G.; Nieminen, P. +6 more
In June 1991 the Sun produced a famous series of six powerful flares. For the solar eruption on 15 June 1991 there exists a rich set of measurements, including in particular >~mma-ray and neutron observations of the COMPTEL instrument on board the COMPTON Gamma Ray Observatory (CGRO) satellite. The >~mma-ray and neutron emissions indicate pr…
HIPPARCOS positioning of Geminga: how and why
Caraveo, P. A.; Bignami, G. F.; Makarov, V. V. +4 more
Accuracy in the absolute position in the sky is one of the limiting factors for pulsar timing, and timing parameters have a direct impact on the understanding of the physics of Isolated Neutron Stars (INS). We report here on a high-accuracy measurement of the optical position of Geminga (mv=25.5), the only known radio-quiet INS. The pro…
The D/H ratio at z=0.7 toward Q 1718+4807
Takahara, Fumio; Levshakov, Sergei A.; Kegel, Wilhelm H.
The apparent discrepancy between low and high D abundances derived from QSO spectra may be caused by spatial correlations in the stochastic velocity field. If one accounts for such correlations, one finds good agreement between different observations and the theoretical predictions for standard big bang nucleosynthesis (SBBN). In particular, we sh…
Very cold dust in the peculiar dwarf elliptical galaxy NGC 205
Haas, Martin
ISO observations of NGC 205 between 120 and 200 mu m resolve the emission from 20-24 K cold dust. It is extended to about 7farcm 5x7farcm 5 with bright concentrations in a 1farcm 5 north-south elongated area, similar to the that seen in HI. Supplemented by IRAS and mm literature data, the photometry of the total galaxy and the central region is di…
A comparison of HIPPARCOS parallaxes with planetary nebulae spectroscopic distances
Pottasch, S. R.; Acker, A.
The Hipparcos satellite has measured the parallax of a small sample of planetary nebulae. In this paper we consider the results for 3 planetary nebulae (PN) for which spectroscopic distances have also been determined from stellar gravities. These gravities in turn have been derived from profile fitting of selected hydrogen and helium lines (Mendez…
Spectroscopic and photometric investigations of MAIA candidate stars
Lehmann, H.; Scholz, G.; Hildebrandt, G. +2 more
Including our own observational material and the Hipparcos photometry data, we investigate the radial velocity and brightness of suspected Maia variable stars which are classified also in some examples as peculiar stars, mainly for the existence of periodic variations with time-scales of hours. The results lead to the following conclusions: (1) Sh…
Beta Hydri (G2 IV): a revised age for the closest subgiant
Lindegren, L.; Vandenberg, D. A.; Dravins, D.
The secular evolution of solar-type atmospheres may be studied through comparisons of the current Sun with old solar-type stars of known age. Among the few such stars in the solar Galactic neighborhood, beta Hydri (G2 IV) stands out as a normal single star with an advanced age. Previous age determinations ( =~ 9.5 Gy) were based on the old ground-…
The hot prominence periphery in EUV lines
Wiehr, E.; Stellmacher, G.; de Boer, C. R.
Two sets of He I and metallic lines were observed with the EUV spectrograph SUMER in a quiescent prominence. H, He, and Ca II lines were observed simultaneously with both German telescopes on Tenerife. The visible lines from elements with different atomic weights yield thermal and non-thermal broadening parameters of 7500 <= Tkin <…