We present color magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values ran...

Three different M31 disk fields, spanning a range of stellar populations, were observed by Chandra. We report the X-ray point source luminosity function (LF) of each region, and the LF of M31’s globular clusters, and compare these with each other and with the LF of the galaxy’s bulge. To interpret the results we also consider tracers of the stellar population, such as OB associations and supern...

We point out that the tidal disruption of a giant may leave a luminous (10−10 erg/s), hot (10−100 eV) stellar core. The “supersoft” source (SSS) detected by Chandra at the center of M31 may be such a core; whether or not it is, the observations have shown that such a core is detectable, even in the center of a galaxy. We therefore explore the range of expected observational signatures, and how ...

By applying a digital filtering technique to 1550 deg of the POSS-II in the vicinity of M31, we found two previously unidentified very low surface brightness dwarf galaxies which we designate And V and VI. Follow-up imaging with the KPNO 4-m telescope resolved these into stars easily. The V and Iband images of And V indicate a distance similar to that of M31, and <[Fe/H]> ∼ –1.5. All evidence s...

We provide a set of microlensing event rate maps for M31, the Andromeda Galaxy. Rates for Andromeda microlensing were calculated on the basis of a four component model of the lens and source populations: disk and bulge sources lensed by bulge, disk, M31 halo and Galactic halo lenses. We confirm the high rate gradient along the M31 minor axis due to a dark halo of lenses. Furthermore, we compute...

We have performed Chandra observations during the past 3 years of 5 of the M31 supersoft X-ray sources discovered with ROSAT. Surprisingly, only one of these sources has been detected, despite a predicted detection of about 20-80 counts for these sources. This has motivated a thorough check of the ROSAT M31 survey I data, including a relaxation of the hardness ratio requirement used to select s...

We report spectroscopic observations of the nova M31N-2007-06b, which was found to be spatially coincident with the M31 globular cluster Bol 111. This nova is the first out of more than 700 discovered in M31 over the past century to be associated with one of the galaxy’s globular clusters. A total of three spectra of the nova were obtained 3, 6, and 36 days post discovery. The data reveal broad...

The photometric evolution of M31-RV has been investigated on 1447 plates of the Andromeda galaxy obtained over half a century with the Asiago telescopes. M31-RV is a gigantic stellar explosion that occurred during 1988 in the Bulge of M31 and that was characterized by the appearance for a few months of an M supergiant reaching Mbol = −10. The 1988 outburst has been positively detected on Asiago...

We present here the results of a 325 MHz radio survey of M31, conducted with the A-configuration of the Very Large Array. The survey covered an area of 7.6 deg, and a total of 405 radio sources between .6 and 170 in extent were mapped with a resolution of 6 and a 1σ sensitivity of ∼0.6 mJy beam. For each source, its morphological class, major axis θM , minor axis θm, position angle θPA, peak fl...

ABSTRACT Our goal is to estimate the mass of Local Group (LG) and individual masses its primary galaxies,the M31 Milky Way (MW). We do this by means a supervised machine learning algorithm, gradient boosted decision trees (GBDT) using observed distance relative velocity two as input parameters. The GBDT applied sample 2148 mock LGs drawn from set 5 dark matter (DM)-only simulations, ran withing...