In the last ten years a significant step forward has been made toward a better understanding of the evolutionary status and unusual nature of the R Coronae Borealis (RCB) stars, a rare class of hydrogen-poor and carbon-rich variable stars. More detailed abundance analyses of the majority of RCB stars, and objects related to them, have become available in the last couple of years. In addition to this, recent theoretical studies of the most popular evolutionary models (“Double Degenerate” and “Final Flash”) provide a new insight into the origin of these stars. Regarding the nature of the RCB declines, more observations from the light maxima and the decline phase are now available, including more data from space. However, the characteristics of the various emission lines appearing during the RCB declines, and the nature of their emitting regions, are still not entirely understood.

We report the angular diameter measurements of seven classical Cepheids, X Sgr, η Aql, W Sgr, ζ Gem, β Dor, Y Oph, and l Car, that we have obtained with the VLT Interferometer Commissioning Instrument, installed at ESO’s VLT Interferometer. For four of these stars, η Aql, W Sgr, β Dor, and l Car, we detect the pulsational variation of their angular diameter. This enables us to compute directly their distances using a modified version of the Baade-Wesselink method. For X Sgr, ς Gem, and Y Oph, we apply a hybrid method that makes use of published estimates of their linear diameters to derive their distances.

We have utilized the latest stellar models of the Y2 (Yonsei-Yale) collaborators and color-magnitude diagrams of globular clusters to infer ages and absolute magnitudes of their horizontal branches (HB). The intrinsic (B – V) color indices of the turn-offs, of the globular clusters were used to find ages. For 47 clusters that appear to be coeval (within ±0.7 Gyr), we find an average age of 12.5 Gyr. We adopt this age and infer the absolute magnitudes of the turn-offs, from the clusters [Fe/H] values. The absolute magnitude of the horizontal branches or RR Lyrae stars are then determined from the difference between the apparent magnitudes of the horizontal branches (or RR Lyrae stars) and the apparent magnitude of the turn-offs, VTO. We conclude: 1) The slope of the MV(HB), [Fe/H] relation is ~0.3 for clusters with [Fe/H] values between —0.5 to —1.5. The relation has zero slope for [Fe/H] values smaller than −1.5. 2) For [Fe/H] < -1.3, the MV(HB) or MV values of RRLyrae stars are not only a function of [Fe/H], but the horizontal-branch type in the sense that the clusters with the blue horizontal branches have more luminous horizontal branches than clusters with red horizontal branches. The same results are found by inferring the luminosities of the HBs from pulsating blue stragglers.

Studying classical novae in the Magellanic Clouds has at least three huge advantages: (1) their distances are well-known; (2) the interstellar extinction is small and reasonably well known; and (3) an abundance of novae (47 as of 2003 September 15) have been discovered in the two clouds. Consequently, we will investigate in this paper one of the most important characteristics of novae: the relationship between the absolute magnitudes of the nova outbursts at maximum brightness and their rate of decline, often referred to as the MMRD.

We report a new series of high-precision Stokes V profiles and longitudinal magnetic field measurements of RR Lyrae, obtained with the MuSiCoS spectropolarimeter over a period of four years. These data provide no evidence whatsoever for a strong magnetic field in the photosphere of RRLyrae, which is consistent with Preston’s (1967) results, but inconsistent with apparent magnetic field detections by Babcock (1958) and Romanov et al. (1987, 1994). Following discussion of these disparate results, we conclude that RR Lyrae is a bona fide non-magnetic star, a conclusion which leads to the general falsification of models of the Blazkho effect requiring strong photospheric magnetic fields.

Results from a three-site photometric and spectroscopic campaign of the hottest known extreme helium star V2076 Oph are presented. V2076 Oph shows complex multiple periods ranging from 0.3 to 3 d. However for the two campaigns in 1982 and 2000, no definitive single period can be identified in both datasets. Some of the extracted periods appear to be one-day aliases of others. The two most convincing periods are 0.52 d (22.28 mHz) and 2.75 d (4.21 mHz). The spectral lines identified in V2076 Oph were He I, He II, C II (emission), C III (both emission and absorption), C IV and N III. These lines showed profile variations that could not be linked to the photometric variations. Individual line velocities vary by species and ionisation level. The spectral lines vary in phase with an amplitude of ~25 kms−1 – the exception is the strong C III emission line at 5696 Å which shows different behaviour and has the lowest observed average velocity. This indicates that this emission line originates in the stellar wind rather than the photosphere.

By phasing using the minimum of the acceleration curve of a selection of Type II Cepheids of a range of periods, a clearer understanding of the pulsational dynamics of the stars is obtained. BVRI photometry and a selection of metallic line velocities and Hα equivalent widths are presented using this phasing.

A Bayesian model of Cepheid kinematics has been applied to the Hipparcos parallaxes and proper motions to obtain an independent estimate of the Galactic Cepheid Period-Luminosity relation for visual magnitudes. The resulting estimate includes a slope that differs significantly from those of Magellanic Cloud Cepheids, suggestive of a lack of universality amongst galaxies in Cepheid P-L calibration.

The COROT project has been developed in the framework of the CNES small satellite programme, with European and Brazilian cooperation. It will be launched in 2006. It is dedicated to seismology and detection of telluric planets. It will perform relative broad-band photometry in visible light during very long (150 d) observing runs in the same direction, plus a number of short (10-20 d) observing runs. Both programmes will work simultaneously on the same region of the sky. The seismology programme aims to map the HR diagram and study in detail approximately 50 targets brighter than magnitude 9. The exoplanet programme will search for telluric planets slightly larger than the Earth orbiting around stars of magnitude 12 to 16, located in the habitable zone and closer. The data collected will also allow valuable seismic studies. A number of additional scientific programmes will also be conducted. The mission characteristics derived from the scientific objectives, the instrument and its performances for seismology, as well as preliminary observing plans, are presented.

The different research teams involved in the study of δ Sct stars have slightly changed their strategy in the past years. The observational effort to secure worldwide coverage of case studies has been continued, but the requirements have become more severe, especially about target characterization and frequency resolution.

After the successful launch of the Canadian satellite MOST, which will be the pioneer of asteroseismology from space, the future missions are programmed to properly take into account the need for adequate frequency resolution: COROT will spent 30 and 150 d (additional and core programs, respectively) on the target, while EDDINGTON will spend up to 3yr. Such a requirement is a direct consequence of the observational results on δ Sct, γ Dor, SPB, and other stars obtained from ground. It should be noted that without these results (see Poretti 2000 for a review about δ Sct stars) the scientific background of the space missions would be much less defined and the risks of incomplete results (owing to inaccurate selection of targets, insufficient resolution, underestimate of the influence of the rotation) much higher.

The CNES/European space mission COROT will monitor asteroseismic targets located in selected fields to probe stellar interiors. Therefore, suitable candidate targets have to be searched for in order to optimize the scientific return of the mission. However, to be able to use the asteroseismic tools on the stars, their physical parameters must be known in advance. In this work, we detail the process of building a photometric database of all the stars brighter than V = 8.0 in the field of view of COROT and the process of selecting suitable δ Sct and γ Dor-type stars for the mission.

For an optimal selection of the seismology targets (for both COROT programs devoted to asteroseismology, i.e., the core and exploratory ones), it is essential to gather a priori as much information as possible on all potential candidates. With this aim, Strömgren-Crawford uvby-Hβ and Ca II H&K photometry were obtained for all of them. These data have been used to derive estimates of their effective temperatures, surface gravities and metallicities. These observations, together with high resolution echelle spectroscopy and high angular resolution imaging observations, are components of an ambitious ground-based program.

For hot and rapidly rotating stars, the considerably wide line profile is spread over several echelle orders and thus a precise data reduction before merging several spectral orders together is required to obtain reliable results. As we show, the usage of automatic pipelines or wrong application of general reduction procedures may result in periodic ripple disturbances in the shape of the apparent stellar continuum and by this way introduce considerable errors into the determination of fundamental astrophysical quantities as gravity and mass of the stars.

A collection of computer programs called the Hercules Reduction Software Package (HRSP) has been developed in the Department of Physics and Astronomy, University of Canterbury, for the data reduction of échelle spectra obtained with the Hercules spectrograph. The main goal in writing a dedicated software package for Hercules was to achieve a highly-optimized reduction process that would provide the basis of a pipeline reduction performed at the Mt John University Observatory. Since the spectrograph has no moving parts, the spectrum produced in the focal plane does not move or change, so that the same reduction procedure can be applied to all CCD images. An optimized routine written especially for Hercules is always much more efficient and reliable than any general-purpose software available. HRSP is written in C and the whole reduction procedure is performed on standard FITS files. A standard échelle reduction is applied, including the background and cosmic ray subtraction, order extraction, flat-fielding, normalization and wavelength rebinning. A special feature is the radial velocity determination by cross-correlation, which has been tested extensively over the past two years proving that Hercules is capable of delivering the high-precision radial velocities needed for detailed studying of binary stars, stellar pulsations, extra-solar planets and other related fields.