Search Publications
New periodic variables from the Hipparcos epoch photometry
Koen, Chris; Eyer, Laurent
Two selection statistics are used to extract new candidate periodic variables from the epoch photometry of the Hipparcos catalogue. The primary selection criterion is a signal-to-noise ratio. The dependence of this statistic on the number of observations is calibrated using about 30000 randomly permuted Hipparcos data sets. A significance level of…
K dwarfs and the chemical evolution of the solar cylinder
Chiappini, Cristina; Matteucci, Francesca; Flynn, Chris +1 more
K dwarfs have lifetimes older than the present age of the Galactic disc, and are thus ideal stars for investigating the chemical evolution of the disc. We have developed several photometric metallicity indicators for K dwarfs, based on a sample of accurate spectroscopic metallicities for 34 disc and halo G and K dwarfs. The photometric metalliciti…
The status of Galactic field λ Bootis stars in the post-Hipparcos era
Kamp, I.; Paunzen, E.; Iliev, I. Kh. +1 more
The λ Bootis stars are Population I, late B- to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). To put constraints on the various existing theories that try to explain these peculiar stars, we investigate the observational p…
Globular clusters and the Mira period-luminosity relation
Feast, Michael; Whitelock, Patricia; Menzies, John
A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of MK for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period-luminosity (PL) relation, PL(K), in good agreement with that derived fr…
Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars
Lambert, David L.; Lyubimkov, Leonid S.; Rostopchin, Sergey I. +1 more
Effective temperatures Teff, surface gravities logg and interstellar extinctions AV are found for 107 B stars. Distances d of the stars, which are based on the derived Teff, logg and AV values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the Teff and logg v…
Discovery of the `missing' mode in HR1217 by the Whole Earth Telescope
Kepler, S. O.; Kawaler, S. D.; Winget, D. E. +35 more
HR1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6µHz, with a sixth mode at a problematic spacing of 50.0µHz (which equals to the high-frequency side. As…
Hipparcos open clusters and stellar evolution
Prada Moroni, P. G.; Degl'Innocenti, S.; Castellani, V. +1 more
By relying on recently improved Hipparcos parallaxes for the Hyades, Pleiades and Ursa Major clusters we find that stellar models with updated physical inputs reproduce nicely the location in the colour-magnitude diagram of main-sequence stars of different metallicities. Stars in the helium-burning phase are also discussed, showing that the lumino…
UBV(RI)C photometry of Hipparcos red stars
Kilkenny, D.; Marang, F.; Koen, C. +2 more
We present homogeneous and standardized UBV(RI)C photometry for nearly 550 M stars selected from the Hipparcos satellite data base using the following selection criteria: lack of obvious variability (no Hipparcos variability flag); δ<+10°(V-I)>1.7 and V magnitude fainter than about 7.6. Comparisons are made between the current pho…
The Galactic distribution of asymptotic giant branch stars
Knapp, G. R.; Ivezić, Željko; Jackson, Tom
We study the Galactic distribution of ~10000 candidate asymptotic giant branch (AGB) stars selected by IRAS colours and variability index. The distance to each star is estimated by assuming a narrow luminosity function and a model-derived bolometric correction. The characteristic AGB star luminosity, LAGB, is determined from the conditi…
Luminosity-metallicity relation for stars on the lower main sequence
Jimenez, Raul; Flynn, Chris; Kotoneva, Eira
We present a comparison of the predictions of stellar models with the luminosity of the lower main sequence (5.5 < MV < 7.3) using K dwarfs in the Hipparcos catalogue. The parallaxes of our comparison stars are known to better than 15 per cent and metallicities have been recently determined from photometry. A major advantage of ou…