Search Publications

Surface gravities of very metal-poor stars from HIPPARCOS parallaxes

Fuhrmann, Klaus

We discuss some consequences for the determination of the surface gravity parameter of very metal-poor halo dwarfs in the new light shed upon these objects from the Hipparcos astrometry. Whereas it has become clear that standard spectroscopic LTE iron ionization equilibria are prone to systematic errors, in the sense, that stages of evolution are …

Effective temperature of detached eclipsing binaries from HIPPARCOS parallax

Ribas, I.; Jordi, C.; Torra, J. +2 more

Effective temperatures of detached eclipsing binaries computed through Hipparcos trigonometric parallaxes are compared with the photometric determinations. The former are based on the values of the radius, the apparent visual magnitude and the bolometric correction of the star, whereas the latter are obtained from standard calibrations using Strom…

The Age Range of Hyades Stars

Eggen, Olin J.

On the basis of canonical models, the age of Hyades supercluster stars, whether in the Hyades and Praesepe clusters or the noncluster field, ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallax derived from the supercluster motion and that obtained from Hipparcos observations has a dispersion only twice that of the mean dispers…

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XII. The Discovery of Cepheids and a New Distance to NGC 2541

Illingworth, Garth D.; Madore, Barry F.; Freedman, Wendy L. +17 more

We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). A total of 25 exposures (divided into 13 epochs) were obtained using the F555W filter (transformed to Johnson V), and nine exposures were obtained (divided in…

Time-dependent structure in ultraviolet absorption lines of the rapid rotators HD 64760 (B0Ib) and HD 93521 (O9.5V)

Massa, D.; Prinja, R. K.; Howarth, Ian D. +5 more

Cross-correlation provides an effective line-averaging function for spectra containing many line features, a result which can be exploited in order to perform time-series and spatial-domain analyses of absorption-line variability in data of (relatively) poor quality. We apply this method to high-resolution IUE spectra. For the known non-radial pul…

A Spherical Non-LTE Line-blanketed Stellar Atmosphere Model of the Early B Giant epsilon Canis Majoris

Hauschildt, P. H.; Baron, E.; Shore, S. N. +1 more

We use a spherical non-LTE fully line-blanketed model atmosphere to fit the full multiwavelength spectrum, including the extreme-ultraviolet (EUV) continuum observed by the Extreme Ultraviolet Explorer, of the B2 II star ɛ Canis Majoris (CMa). The available spectrophotometry of ɛ CMa from 350 Å to 25 µm is best fitted with model parameters T…

Discovery of extended radio emission in the young cluster Wd1

Waters, L. B. F. M.; Steele, I. A.; Fender, R. P. +4 more

We present 10-µm ISO-SWS and Australia Telescope Compact Array observations of the region in the cluster Wd1 in Ara centred on the B[e] star Ara C. An ISO-SWS spectrum reveals emission from highly ionized species in the vicinity of the star, suggesting a secondary source of excitation in the region. We find strong radio emission at both 3.5 …

The First Definitive Binary Orbit Determined with the Hubble Space Telescope Fine Guidance Sensors: Wolf 1062 (Gliese 748)

Nelan, Edmund P.; Henry, Todd J.; Kirkpatrick, J. Davy +15 more

The M dwarf binary, Wolf 1062 (Gliese 748), has been observed with the Hubble Space Telescope (HST) Fine Guidance Sensor 3 in the transfer function scan mode to determine the apparent orbit. This is the first orbit defined fully and exclusively with HST, and is the most accurate definitive orbit for any resolved, noneclipsing system. The orbital p…

Regression of Martian North Polar Cap: 1990-1997 Hubble Space Telescope Observations

Wolff, Michael J.; Cantor, Bruce A.; James, Philip B. +1 more

Hubble Space Telescope imaging of Mars from December 13, 1990, through April 17, 1997, has resulted in the synoptic monitoring of parts of four consecutive martian north polar cap regressional cycles spanningL_s= 335.65° toL_s= 144.56°. The 1990-1993 observations were obtained with the Wide Field Planetary Camera 1 (WFPC1) inst…

DeHoffmann-Teller Analysis

Sonnerup, Bengt U. Ö.; Khrabrov, Alexander V.