Planck’s data acquired during the first 15.4 months of observations towards both the disk and halo of the M31 galaxy are analyzed. We confirm the existence of a temperature asymmetry, previously detected by using the 7-year WMAP data, along the direction of the M31 rotation, therefore indicative of a Doppler-induced effect. The asymmetry extends up to about 10 degrees (about 130 kpc) from the M...

This paper reports the results of the analysis of the second ROSAT PSPC survey of M31 performed in summer 1992. We compare our results with those of the first survey, already published in Supper et al. (1997). Within the ∼ 10.7 deg field of view, 396 individual X-ray sources are detected in the second survey data, of which 164 are new detections. When combined with the first survey, this result...

The two nearby galaxies, M31 and M33, are stepping stones for most of our current efforts to understand the evolving universe at large scales. We are undertaking a long term project, called DIRECT, to improve the direct distance estimate to M31 and M33. The massive photometry we have obtained as part of our project over the past 3 years provides us with very good light curves for known and new ...

We present the discovery of an inhomogenous, low-surface brightness, extended disk-like structure around the Andromeda galaxy (M31) based on a large kinematic survey of more than 2800 stars with the Keck/DEIMOS multi-object spectrograph. The stellar structure spans radii from 15 kpc out to ∼ 40 kpc, with detections out to R ∼ 70 kpc. The constituent stars lag the expected velocity of circular o...

Deep UBRI images of a 15 × 15 field in the outer spheroid of the M31 galaxy obtained using the Kitt Peak National Observatory 4-meter telescope, and I band images obtained with the Keck 10-meter telescope and Low Resolution Imaging Spectrograph, are used to isolate a sample of candidate red giant branch stars located at a projected radial distance of 19 kpc along the minor axis. These stars are...

We report our first microlensing candidate NMS-E1 towards M31 from the data accumulated during the four years of Nainital Microlensing Survey. Cousin R and I band observations of ∼ 13 ′ × 13 ′ field in the direction of M31 have been carried out since 1998 and data is analysed using the pixel technique proposed by the AGAPE collaboration. NMS-E1 lies in the disk of M31 at α = 04333.3 and δ = +41...

We present a color-magnitude diagram (CMD) for a field in the giant tidal stream of the Andromeda galaxy (M31). These observations, taken with the Advanced Camera for Surveys on the Hubble Space Telescope, are 50% complete at V ≈ 30, reaching 1 mag below the oldest main-sequence turnoff. Striking similarities between the stream and a previous spheroid CMD imply they have very similar age and me...

The central bulge of M31 is observed to have two distinct brightness peaks with the separation of ∼ 2 pc. Tremaine (1995) recently proposed a new idea that the M31’s nucleus is actually a single thick eccentric disk surrounding the central super-massive black hole. In order to explore the origin of the proposed eccentric disk, we numerically investigate the dynamical evolution of a merger betwe...

We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M31), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at mV = 30.7 mag. The CMD, constructed from ∼ 3× 105 stars, reaches more than 1...

Near UV HST images of the remnant of SN 1885 (S And) in M31 show a 0. 70 ± 0. 05 diameter absorption disk silhouetted against M31’s central bulge, at SN 1885’s historically reported position. The disk’s size corresponds to a linear diameter of 2.5 ± 0.4 pc at a distance of 725 ±70 kpc, implying an average expansion velocity of 11000 ± 2000 kms over 110 years. Low-dispersion FOS spectra over 320...