We present new interferometric CO(1-0) and single-dish CO(3-2) observations of the central parts of D478, a large (> 200 pc) dark dust cloud located in a quiescent region of the inner disk of M31 where single-dish CO(1-0) and CO(2-1) observations were previously obtained. Only a small fraction (< 15%) of the CO(1-0) flux previously detected in this region with the single-dish telescope is recor...

The deepest X-ray images of M31, obtained with XMM-Newton, are examined to derive spectral and statistical properties of the population of the softest X-ray sources. Classifying supersoft X-ray sources (SSS) with criteria based on the same hardness ratios defined for recent Chandra observations, a quarter of the selected SSS turn out to be supernova remnants (SNR). Another quarter of SSS are sp...

We report on luminous supersoft X-ray sources (SSSs) in M31. In a survey which was most sensitive to soft sources in four 8×8 regions covered by Chandra’s ACIS-S S3 CCD, we find 33 SSSs that appear to belong to M31. Two of these were first identified as SSSs through ROSAT observations. Two SSSs may be identified with symbiotics, and 2 with supernova remnants. SSSs in the disk are clustered near...

We present a new technique for identifying stellar mass black holes in low mass X-ray binaries (LMXBs), and apply it to XMM-Newton observations of M31. We examine X-ray time series variability seeking power density spectra (PDS) typical of LMXBs accreting at a low accretion rate (which we refer to as Type A PDS); these are very similar for black hole and neutron star LMXBs. Galactic neutron sta...

We present a multiwavelength investigation of the circumnuclear environment of the Andromeda Galaxy (M31), utilizing archival Chandra, FUSE, GALEX, HST and Spitzer data as well as ground-based observations. Based on the Chandra/ACIS data, we tightly constrain the X-ray luminosity of M31, the central supermassive black hole (SMBH) of the galaxy, to be L0.3−7 keV . 1.2 × 10 36 ergs s−1, approxima...

We report new photometry for 10 globular clusters in M31, observed to a uniform depth of four orbits in F5555W(V) and F814W(I) using WFPC2 on board HST. Additionally we have reanalyzed HST archival data of comparable quality, for 2 more clusters. A special feature of our analysis is the extraordinary care taken to account for the effects of blended stellar images and required subtraction of con...

The projected structures and integrated properties of the Andromeda I, II, III, V, VI, VII and Cetus dwarf spheroidal galaxies are analysed based upon resolved counts of red giant branch stars. The observations were taken as part of the Isaac Newton Telescope Wide Field Survey of M31 and its environs. For each object, we have derived isopleth maps, surface brightness profiles, intensity-weighte...

We re-analyze the M31 microlensing event WeCAPP-GL1/Point-AGAPE-S3 taking into account that stars are not point-like but extended. We show that the finite size of stars can dramatically change the self-lensing event rate and (less dramatically) also the halo lensing event rate, if events are as bright as WeCAPP-GL1. The brightness of the brightest events mostly depends on the source sizes and f...

The aim of this thesis is to study the environmental dependence of populations of low-mass X-ray binaries (LMXBs) in early-type galaxies. The dissertation is mainly based on archival data of the Chandra observatory whose unprecedented sub-arcsec angular resolution made it possible to resolve individual compact sources in nearby galaxies. The Chandra data is complemented by the infrared data of ...

Abstract We measure homogeneous distances to M31 and 38 associated stellar systems (?16.8 ? M V ?6.0), using time-series observations of RR Lyrae stars taken as part the Hubble Space Telescope Treasury Survey Satellites. From &gt;700 orbits new/archival Advanced Camera for Surveys imaging, we identify &gt;4700 determine their periods mean magnitudes a typical precision 0.01 day 0.04 mag. Based ...