Search Publications
Local stellar kinematics from HIPPARCOS data
Dehnen, Walter; Binney, James J.
From the parallaxes and proper motions of a kinematically unbiased subsample of the Hipparcos Catalogue, we have re-determined as a function of colour the kinematics of main-sequence stars. Whereas the radial and vertical components of the mean heliocentric velocity of stars show no trend with colour, the component in the direction of Galactic rot…
HIPPARCOS observations of pre-main-sequence stars
Bastian, U.; Krautter, J.; Rucinski, S. M. +2 more
We present first results of Hipparcos observations of nearby low-mass pre-main-sequence (PMS) stars (TTauri and Herbig Ae/Be stars). The data obtained by Hipparcos allow us to derive weighted mean parallaxes for three major nearby star-forming regions (SFRs), Lupus, Chamaeleon I and Taurus-Auriga. Furthermore, results on the isolated objects AB Do…
Refining the Oort and Galactic constants
Merrifield, Michael R.; Olling, Rob P.
The local stellar kinematics of the Milky Way offer a useful tool for studying the rotation curve of the Galaxy. These kinematics - usually parametrized by the Oort constants AB - depend on the local gradient of the rotation curve as well as its absolute value (Theta_0), and the Sun's distance to the Galactic Centre (R_0). The density of interstel…
Fine structure of the red giant clump from HIPPARCOS data, and distance determinations based on its mean magnitude
Salaris, Maurizio; Girardi, Leo; Groenewegen, Martin A. T. +1 more
The I-band brightness M_I of clump stars is a possible distance indicator for stellar populations. Investigations have shown that M_I is almost insensitive to the V-I colour within the clump. Based on this, it was assumed that M_I was insensitive to age and composition of the stellar population and therefore an ideal standard candle, which could b…
A new analysis of the red giant branch `tip' distance scale and the value of the Hubble constant
Salaris, Maurizio; Cassisi, Santi
The theoretical evaluations of the red giant branch tip (TRGB) luminosity presented previously by Salaris & Cassisi are extended to higher metallicities, and compared with analogous independent results recently published. The present sets of stellar models agree quite well in the determination of the TRGB brightness. Relations between TRGB bol…
ΔY/ΔZ from fine structure in the main sequence based on Hipparcos parallaxes
Pagel, B. E. J.; Portinari, L.
The slope ΔY/ΔZ is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate ΔY/ΔZ from fine structure in the main sequence of nearby stars from Hipparcos data for stars with Z<=Zsolar. We find a value of about 3, which is consistent wit…
The distances to the X-ray binaries LSI +61 deg 303 and A0535+262
Coe, M. J.; Steele, I. A.; Negueruela, I. +1 more
Chevalier & Ilovaisky use Hipparcos data to show that the X-ray binary systems LSI+61 deg 303 and A0535+262 are a factor of 10 closer (i.e. d~ few hundred pc) than previously thought (d~kpc). We present high-quality CCD spectra of the systems, and conclude that the spectral types, reddening and absolute magnitudes of these objects are strongly…
Mode switching in the nearby Mira-like variable R Doradus
Bedding, T. R.; Jones, A.; Zijlstra, Albert A. +1 more
We discuss visual observations spanning nearly 70 years of the nearby semiregular variable R Doradus. Using wavelet analysis, we show that the star switches back and forth between two pulsation modes having periods of 332d and about 175d, the latter with much smaller amplitude. Comparison with model calculations suggests that the two modes are the…
The absolute magnitude of field metal-poor horizontal branch stars
Gratton, Raffaele G.
Hipparcos satellite parallaxes for 22 metal-poor field horizontal branch stars with V_0<9 are used to derive their absolute magnitude. The weighted mean value is M_V=+0.69+/-0.10 for an average metallicity of [Fe/H]=-1.41 a somewhat brighter average magnitude of M_V=+0.60+/-0.12 for an average metallicity of [Fe/H]=-1.51 is obtained by eliminat…
HIPPARCOS and the age of the Galactic disc
Jimenez, Raul; Flynn, Chris; Kotoneva, Eira
We use the Hipparcos colour-magnitude diagram of field stars with Tycho colours to make a new minimum age estimate for the Galactic disc. The method is based on fits to the red envelope of subgiants in the Hipparcos colour-magnitude diagram with synthetic isochrones covering the range of disc metal abundance. The colours and luminosities of the is…