Search Publications
Ages of Globular Clusters from HIPPARCOS Parallaxes of Local Subdwarfs
Fusi Pecci, Flavio; Carretta, Eugenio; Clementini, Gisella +3 more
We report here initial but strongly conclusive results for absolute ages of Galactic globular clusters (GGCs). This study is based on high-precision trigonometric parallaxes from the HIPPARCOS satellite coupled with accurate metal abundances ([Fe/H], [O/Fe], and [α/Fe]) from high-resolution spectroscopy for a sample of about thirty subdwarfs. Syst…
Astrometric Detection of a Low-Mass Companion Orbiting the Star AB Doradus
White, G. L.; Arenou, F.; Lindegren, L. +19 more
We report submilliarcsecond-precise astrometric measurements for the late-type star AB Doradus via a combination of VLBI (very long baseline interferometry) and HIPPARCOS data. Our astrometric analysis results in the precise determination of the kinematics of this star, which reveals an orbital motion readily explained as caused by gravitational i…
Fundamental Stellar Parameters of γ2 Velorum from HIPPARCOS Data
Schaerer, Daniel; Schmutz, Werner; Grenon, Michel
We report parallax measurements by the HIPPARCOS satellite of γ2 Velorum and a few related objects. The distance of γ2 Vel is d = 258+41-31 pc, significantly smaller than the commonly adopted value to Vela OB2. For ζ Puppis d = 429+120-77 pc is in agreement with the canonical distan…
Hipparcos, VLA, and CCD Observations of Cygnus OB2 No. 5: Solving the Mysteryof the Radio ``Companion''
Badiali, M.; Cardini, D.; Emanuele, A. +4 more
We present accurate optical and radio astrometry for the unresolved contact binary system Cyg OB2 No. 5 and its weaker component to the northeast. While the radio and optical positions of the primary component (taken to be the unresolved contact binary) agree within observational error (~70 mas), we find that the weaker radio component does not ag…
The Nuclear Region of NGC 1068: High-Accuracy Alignment of the Optical and Radio Emission
Macchetto, F. D.; Capetti, A.; Lattanzi, M. G.
We present the results of a campaign to obtain an accurate registration of Hubble Space Telescope (HST) and MERLIN images of NGC 1068, the prototypical Seyfert 2 galaxy. The final registration is accurate to 100 mas.
A strong anticorrelation between radio and optical emission is revealed; in particular, the radio jet lies on a region of relat…Interferometric Angular Diameters of Mira Variables with the Hubble Space Telescope
Munari, Ulisse; Whitelock, Patricia A.; Feast, Michael W. +1 more
This paper presents the first successful interferometric observations of angular diameters with the astrometer Fine Guidance Sensor (FGS) aboard the Hubble Space Telescope, the only optical interferometer operating in space. We report single-epoch angular diameters in visible light for the two Mira-type variables, R Leonis and W Hydrae, along two …
The Mass and Radius of 40 Eridani B from HIPPARCOS: An Accurate Test of Stellar Interior Theory
Provencal, J. L.; Shipman, H. L.; Thejll, P. +1 more
The astrometric satellite HIPPARCOS has determined the distance to the important white dwarf 40 Eridani B with an accuracy surpassing 1%. We use this datum to redetermine the mass and radius of this star and find that M = 0.501 +/- 0.011 Msolar and R = 0.0136 +/- 0.00024 Rsolar. These values, the most accurately determined ma…
Three-Dimensional Orbits of Metal-poor Halo Stars and the Formation of the Galaxy
Yoshii, Yuzuru; Chiba, Masashi
We present the three-dimensional orbital motions of metal-poor stars in conjunction with their metal abundances, for the purpose of getting insight into the formation process of the Galaxy. Our sample stars, which include metal-deficient red giants and RR Lyrae variables observed by the HIPPARCOS satellite, are least affected by known systematics,…
The Age of the Globular Cluster M68
Castellani, V.; Brocato, E.; Piersimoni, A.
Relying on the accurate color-magnitude diagram (CMD) presented by Walker in 1994, we use the fitting of moderately hot horizontal-branch models to the observed CMD to derive suitable information regarding both cluster reddening and distance modulus and to discuss theoretical predictions constraining the absolute age of the metal-poor Galactic glo…
The Extremely Active Single Giant 1E 1751+7046 = ET Draconis: Revised Properties and a Reevaluation of Its Evolutionary Status
Guinan, Edward F.; Hrivnak, Bruce J.; Fekel, Francis C. +1 more
New spectroscopic observations have resulted in significant revisions to several of the orginally published properties of the X-ray bright, chromospherically active star 1E 1751+7046: the spectral classification has been revised from K5 IV to K0 III, v sin i from 30-40 km s-1 to 23 km s-1, and the reported nondetection of the…