Search Publications
HST observations of the QSO pair Q1026-0045A,B
Petitjean, Patrick; Smette, Alain; Surdej, Jean +3 more
The spatial distribution of the Lyalpha forest is studied using new HST data for the quasar pair Q 1026-0045 A and B at z_em = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and corresponds to transverse linear separations between lines of sight of ~ 300h(-1}_{50) kpc (q_o = 0.5) over the redshift range 0.833 < z < 1.438. …
Spectral analyses of WC stars in the LMC
Hillier, D. J.; Hamann, W. -R.; Koesterke, L. +1 more
Spectra of six Wolf-Rayet stars in the Large Magellanic Cloud (LMC) of the subtype WC4, the dominant WC spectral type in the LMC, are taken with the Faint Object Spectrograph (FOS) on board the Hubble Space Telescope (HST). They are analyzed by means of non-LTE models for spherically expanding atmospheres computed using standard assumptions. Compl…
Halo stars in the immediate solar neighbourhood
Jahreiß, H.; Fuchs, B.
We have searched the Fourth Catalogue of Nearby Stars for halo stars and identified 15 subdwarfs and a high velocity white dwarf in the solar neighbourhood. This search was motivated mainly by the recent determinations of MACHO masses of about 0.5cal M_sun, which are typical for halo dwarfs. The local mass density of these stars is 1.5*10(-4) cal …
Small-scale structures in the far-infrared background
Laureijs, R. J.; Klaas, Ulrich; Herbstmeier, Uwe +6 more
Four fields with areas ranging from 80 to 2000 arcmin(2) have been mapped with the photometer on board of the Infrared Space Observatory (ISO) at 90 and around 180mu m in regions of bright and faint cirrus. We examined the spatial characteristics of the infrared background emission with high spatial resolution and found that the fluctuations in th…
Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Torra, J.; Comeron, F.; Gomez, A. E.
Proper motions measured by Hipparcos confirm the large anomalous velocities of the OB associations located around the Cygnus Superbubble (Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organized expanding pattern in Canis Major OB1. At the distances of these associations, the organized velocity patterns imply LSR velocities of up to ~ 60 km …
On the accuracy of helioseismic determination of solar helium abundance
Dziembowski, W. A.; Goode, Philip R.; Richard, O. +1 more
The Helium abundance in the solar envelope is one of the most important seismic observables. We investigate the accuracy of its determination taking into account uncertainties in the data and in the inversion procedure. Our best value for the helium abundance in the photosphere is Ysun=0.248. The estimated uncertainty of 0.002 is domina…
Temperature and density diagnostics of quiet Sun and active regions observed with CDS NIS
Landini, M.; Landi, E.
We study the Differential Emission Measure distribution of two pairs of active and quiet regions of the solar atmosphere, observed by CDS Normal Incidence Spectrometer (NIS) on SOHO, and investigate their temperature and density structure . Use is made of the Arcetri Method (Landi & Landini 1997) for DEM and density diagnostics. An iterative m…
HIPPARCOS results for ROSAT-discovered young stars
Brandner, Wolfgang; Neuhauser, Ralph
Out of ~ 500 Lithium-rich ROSAT counterparts, which were presumed to be low-mass pre-main sequence stars, 21 stars have been observed by HIPPARCOS. We study their parallaxes, proper motions, and photometric data. For 7 out of 10 Taurus and Lupus stars in our sample, proper motions and parallaxes are not inconsistent with membership to these associ…
Near-IR images of the torus and micro-spiral structure in NGC 1068 using adaptive optics
Rouan, D.; Doyon, R.; Gendron, E. +5 more
We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system Pueo at CFHT. The achieved resolution (0.12") reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. ~ 102°, beginnin…
Do SI stars undergo any rotational braking?
North, P.
The old question of rotational braking of Ap Si stars is revisited on the empirical side, taking advantage of the recent Hipparcos results. Field stars with various evolutionary states are considered, and it is shown that the loose correlation between their rotational period and their surface gravity is entirely compatible with conservation of ang…