Hipparcos Parallaxes And Distances Of High--Amplitude

. Hipparcos parallaxes of high--amplitude ffi Scuti stars are used to derive a period-- luminosity relation defining a new distance scale which is independent from those of the primary distance indicators, the classical Cepheids and RR Lyrae stars. Thus application of the Hipparcos P--L relation may provide new tests of distances e.g. to globular clusters or the galactic bulge. Comparisons of the Hipparcos P--L relation with several P--L relations based on photometric calibrations to absolute luminosities from the literature, show saticfactory agreement. Data published by the OGLE group for SX Phe variables in ! Centauri are used to derive new independent distances to this globular cluster. 1. Introduction Hipparcos parallaxes (ESA 1997) give accurate distances to a few high--amplitude (amplitude A V 0:3 mag) ffi Scuti stars (HADS in the following). We use these distances to derive a new period--luminosity relation for HADS, which is independent from earlier P--L relations and from ..

MONS and high-amplitude

The important role of high-amplitude ffi Scuti stars (HADS) in asteroseismological tests of model structure and excitation/damping mechanisms of ffi Scuti variables is emphasized. It is suggested that one or two well--studied HADS, e.g. AI Vel and SX Phe as representatives of pop. I and II respectively, should be included in the MONS target list. 1. Introduction The purpose of MONS is to discover oscillations of extremely low amplitude in stars, in particular in solar type stars and ffi Sct variables. Therefore, it can be seen as a paradox that I suggest that we should include high-amplitude ffi Scuti stars (HADS) in the MONS target list. Of course, the purpose of including HADS is not to study the high-amplitude modes with extreme accuracy. The purpose is to discover new low-amplitude modes --- hopefully a considerable number of new modes --- and to use all available modes for asteroseismological studies of these stars. It is known that modes of amplitude 2-10 mmag are present is som..

IRAS Observations of

Introduction Mid-far infrared and radio observations of A-F stars are important for constraining the level of mass loss from these stars. It was theorized by Willson, et al (1987) that mass loss could play a significant role in the evolution of these stars, and could be responsible for shifting a star in the HR diagram by as much as one spectral class. Observations of normal A-F stars at 6 cm by Brown, et al. (1990) and at the IRAS 12, 25, and 60 ¯m bands by Patten and Willson (1991) have shown that extreme mass loss rates (on the order of 10 \Gamma8\Gamma9 M fi yr \Gamma1 ) are not seen in these stars, but lower mass loss rates could still have significant impact on the evolution of these stars [see Guzik and Cox (1995) for example]. King (1990) conducted an infrared study of ffi Scuti stars using the IRAS Point Source Catalog, to try and detect infrared exc

Hipparcos Parallaxes and Period--Luminosity Relations of High--Amplitude

. Hipparcos parallaxes of high-amplitude ffi Scuti stars are used to derive a period-luminosity relation with a scatter of about \Sigma0.1 mag, which is independent from photometric calibrations to absolute luminosities. Comparisons with several P--L relations from the literature show satisfactory agreement, and all deviations from the Hipparcos mean relation can be explained by uncertainties in the data available before Hipparcos. Hipparcos data for a few stars of relatively small and uncertain parallaxes indicate that they may have systematically very low luminosity. However, briefly discussing Lutz--Kelker corrections and considering the full sample of high--amplitude ffi Scuti stars, it is concluded that this sample is homogeneous and has similar basic physical properties as the "normal" low--amplitude ffi Scuti stars. It is emphasized that the Hipparcos P--L relation defines a new distance scale which is independent from those of the classical Cepheids and RR Lyrae stars. Theref..

NEW RADIAL VELOCITY CURVES OF roAp AND

We present new radial velocity curves of the rapidly oscillating Ap (roAp) star, ff Cir, and the ffi Scuti star, FG Vir, obtained from multisite observations with medium-dispersion spectrographs. The velocity curves are found by using a cross-correlation technique on the H ff line and some metal lines, with the (terrestrial) atmospheric absorption band around 6900 A used as a reference. In ff Cir, we have found some unexpected results where the amplitude and phase of the main pulsation mode varies significantly depending on which line is being measured. 1. INTRODUCTION Our inability to identify the oscillation modes, of multi-periodic stars like ffi Scuti, roAp and fi Cephei stars, has prevented useful asteroseismology. Even with 10--20 detected modes (as in FG Vir) the lack of mode identification is striking. From the discussion by Bedding et al. (1996) of different observing methods sensitivity to modes with different l-values as a function of wavelength, this suggests that one can ..

Multisite CCD Photometry of

. The results of a two-site observing campaign of the open cluster NGC 6134 are presented. The observations mainly consist of time series differential CCD photometry with a Johnson V-filter over a period of 10 days. Six, maybe seven, ffi Scuti stars are present in the cluster. Modes have been identified in six stars, and up to 5 modes have been found in a single star. No secure mode identification can be made yet due to lack of sufficient data for the stars, but some ideas about the nature of the modes can be obtained by utilizing the fact that all the variables belong to the same open cluster. Key words: stars: ffi Scuti stars - Blue stragglers - evolution of - oscillations of - clusters: open - photometry 1. Introduction Open clusters are of great importance for testing theories of stellar evolution. They are also very important in the study of pulsating stars as they provide constraints on the luminosities and ages of such stars which are cluster members. Mode identification then ..