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The helium isotopic ratio in the solar wind and ion fractionation in the corona by inefficient Coulomb drag
Bochsler, Peter; Bodmer, Roland
Using data obtained between 1991 and 1996 with the SWICS instrument (Solar Wind Ion Composition Spectrometer) aboard the Ulysses spacecraft, a long time average of the ((4) He / (3) He ) isotopic ratio of 2450 +/- 460 in coronal hole dominated solar wind is derived. To assess the influence of inefficient Coulomb friction in the inner corona and to…
X-ray activity and evolutionary status of late-type giants
Schmitt, J. H. M. M.; Schroeder, K. -P.; Huensch, M.
We study the evolution of stellar activity in a volume-limited sample of single giants within 35 pc distance from the Sun as measured by the amount of soft X-ray emission. This sample of 36 stars is assumed to be complete for absolute magnitude M_V la 3.0 and for X-ray luminosities L_x ga 1.5 x 10(28) erg s(-1) . We use ROSAT data to determine ste…
Kinematics of T Tauri stars in Chamaeleon
Brandner, Wolfgang; Covino, Elvira; Frink, Sabine +2 more
We study the kinematics of T Tauri stars (TTS) located in the cores of the Chamaeleon clouds as well as far off these clouds. Our sample comprises 2 early type stars known to be related to Cha i, 6 classical (CTTS) and 6 weak-line T Tauri stars (WTTS) known before the ROSAT mission, and 8 bona-fide pre-main sequence (PMS) stars as well as 23 presu…
Detection of UIR bands in an isolated local interstellar cirrus cloud
Lemke, D.; Laureijs, R. J.; Lehtinen, K. +4 more
The unidentified infrared (UIR) emission bands at 7.7 and 11.3 mu m have been detected in the emission of an isolated cirrus cloud externally heated by the typical interstellar radiation field (ISRF) of the solar neighbourhood. For the observations we used ISOPHOT, the photometer aboard ISO. The detected UIR bands have absolute intensities ~ 1/100…
ISO observations of Uranus: The stratospheric distribution of C_2H_2 and the eddy diffusion coefficient
Kessler, M. F.; Lellouch, E.; Feuchtgruber, H. +7 more
The infrared spectrum of Uranus has been recorded between 7 and 16.5mu m with the grating mode of the Short-Wavelength Spectrometer of ISO, with a resolving power of 1500. The 6-12mu m spectrum of Uranus has also been recorded at lower resolution (R=90) by the PHOT instrument in spectroscopic mode. The spectra show no signatures other than the C_2…
The galactic globular cluster NGC 1851: its dynamical and evolutionary properties
Saviane, I.; Zaggia, S.; Piotto, G. +3 more
We have completely mapped the Galactic globular cluster NGC 1851 with large-field, ground-based VI CCD photometry and pre-repair HST/WFPC1 data for the central region. The photometric data set has allowed a V vs. (V-I) colour-magnitude diagram for ~ 20500 stars to be constructed. >From the apparent luminosity of the horizontal branch (HB) we de…
Multi-line analysis of the spectra of Herbig Ae/Be stars
Bouret, J. -C.; Catala, C.
We present the results of the study of four Herbig Ae/Be stars (AB Aur, BD+46(deg) 3471, HD250550, BD+61(deg) 154). For each of them, semi-empirical models of the structure of their winds have been constructed; we then calculated the Hα line, the Balmer discontinuity, as well as the C IV 1548 Angstroms and Mg II h or k resonance lines. Thanks to c…
HIPPARCOS parallaxes and period-luminosity relations of high-amplitude delta Scuti stars
Hog, E.; Petersen, J. O.
Hipparcos parallaxes of high-amplitude delta Scuti stars are used to derive a period-luminosity relation with a scatter of about +/-0.1 mag, which is independent from photometric calibrations to absolute luminosities. Comparisons with several P-L relations from the literature show satisfactory agreement, and all deviations from the Hipparcos mean …
Young star clusters in the Antennae: a clue to their nature from evolutionary synthesis
Fritze-v. Alvensleben, Uta
We analyse the population of bright star clusters in the interacting galaxy pair NGC 4038/39 detected with HST WFPC1 by Whitmore & Schweizer (1995). Making use of our spectrophotometric evolutionary synthesis models for various initial metallicities we derive the ages of these star clusters and calculate their future luminosity evolution. This…
Starcounts in the flanking fields of the Hubble Deep Field. The faint end of the disc stellar luminosity function and its scale-height
Mendez, R. A.; Guzman, R.
We present instrumental (F606W, F814W) and calibrated (V, I) photometry and astrometry for point-like sources in the Hubble Deep Field and its flanking fields from combined HST and Keck direct imaging. From this data, a complete sample of stars in the range 18 <= V ~ 25 is derived and compared to the predictions of a galactic structure model. T…