We present the first results from a study of the X-ray source populations in M81 in the context of their local star-formation histories. We use deep Chandra observations and our multi-band HST maps of M81 in order to detect and classify the X-ray sources, based on their X-ray and optical properties. We compare the different X-ray source populations (Luminosity functions and relative numbers of different source types) for the different regions of the galaxy and for stellar populations in different age ranges (derived from the HST data). This way we can identify High-mass X-ray binaries with Main Sequence and supergiant donors, and we find that their luminosity functions are distinctly different. We also construct the luminosity functions of the X-ray sources associated with globular clusters. Finally we present our results from the spatially resolved star-formation history of M81, based on the study of the color-magnitude diagrams in different regions of the galaxy. We discuss these results in the context of similar studies of star-forming galaxies spanning a wide range of starburst ages.

Context: In the H-R diagram, the intersection of the main sequence and the classical Cepheid instability strip corresponds to a domain where a rich variety of atmospheric phenomena are at play (including pulsation, radiative diffusion, convection). Main-sequence A-type stars are among the best candidates to study the complex interplay between these various phenomena. Aims: We have explored a sample of suspected A-type binaries in a systematic way, both spectroscopically and photometrically. The sample consists of main-sequence A-type stars for which the few existing radial velocity measurements may show variability, but for which other essential information is lacking. Due to their location in the H-R diagram, indications of pulsation and/or chemical peculiarities among these suspected binary (or multiple) systems may be found. Methods: High-resolution spectroscopy obtained with the ELODIE and MUSICOS spectrographs was used in combination with a few nights of differential CCD photometry in order to search for pulsation(s). In order to search as well for chemical peculiarities or for possible hidden component(s), we derived the atmospheric stellar parameters by fitting the observed spectra with LTE synthetic ones. Results: Of the 32 investigated targets, eight are spectroscopic binaries, one of which is a close binary also showing eclipses, and three have been identified as δ Scuti pulsators with rapid line-profile variations. Conclusions: Among the latter stars, HD 217860 reveals interesting multiperiodic photometric and spectroscopic variations, with up to eight frequencies common to two large photometric data sets. We suggest that at least one radial overtone mode is excited among the two most dominant frequencies, on the basis of the computation of the pulsation constants as well as of the predicted frequencies and the expected behaviour of the amplitude ratio and the phase difference in two passbands using adequate theoretical modelling. We furthermore found evidence for a strong modulation of the amplitude(s) and/or the (radial) frequency content of this intriguing δ Scuti star. This work is based on spectroscopic observations made at the Haute-Provence Observatory (OHP), the Observatoire du Pic du Midi (TBL) and the Bulgarian National Astronomical Observatory (NAO, Rozhen). Tables 1, 2, 4, 5 and Fig. 7 are only available in electronic form at http://www.aanda.org

New BVRI CCD observations of the contact binary system HV~Aqr are presented. The new light curves are analyzed with the WD code and new geometric and photometric elements are derived. These elements are combined with the available spectroscopic data to yield the physical parameters of the system. The agreement between the spectroscopically and photometrically determined mass ratios of eclipsing binaries is also discussed.

Radial velocity measurements and sine-curve fits to the orbital radial velocity variations are presented for 10 close binary systems: OO Aql, CC Com, V345 Gem, XY Leo, AM Leo, V1010 Oph, V2612 Oph, XX Sex, W UMa, and XY UMa. Most of these binaries have been observed spectroscopically before, but our data are of higher quality and consistency than in the previous studies. While most of the studied eclipsing pairs are contact binaries, V1010 Oph is probably a detached or semidetached double-lined binary, and XY UMa is a detached, chromospherically active system whose broadening functions clearly show well-defined and localized dark spots on the primary component. A particularly interesting case is XY Leo, which is a member of visually unresolved quadruple system composed of a contact binary and a detached, noneclipsing, active binary with an 0.805 day orbital period. V345 Gem and AM Leo are known members of visual binaries. We found faint visual companions at about 2"-3" from XX Sex and XY UMa. Based on data obtained at the David Dunlap Observatory, University of Toronto.

We present the initial results from a deep HST survey of the nearby spiral galaxy M81 with the HST Advanced Camera for Surveys. The survey consists of B and V band observations of 29 ACS fields, totaling to 38 orbits. These observations, together with archival I-band ACS data, provide complete, deep coverage of the D25 area of the galaxy, down to 26-27 mag. This detection limit probes the bulk of early-type (O,B) stars and the population of star-clusters. The main goal of this survey is to characterize the X-ray source population of M81 in the context of its stellar populations and star-formation history. We discuss the analysis of the ACS data (mosaicing, astrometric registration, photometric analysis) and we present high quality images of the galaxy. We also discuss the initial results from the identification of optical counterparts to the X-ray sources detected in deep Chandra observations of M81, and the preliminary study of the stellar populations in individual fields of the galaxy. This work is supported by HST grant HST-GO-10584.01-A and NASA LTSA grant NAG-5-13056.