Related papers: M31-RV evolution and its alleged multi-outburst pa…
M31 RV is a luminous red variable star that appeared for several months in the bulge of M31 during 1988. Unlike classical novae, M31 RV was cool throughout its outburst. Interest in this object has revived recently because of its strong…
M31 RV is a red transient that erupted in 1988 in the Andromeda bulge, reaching a luminosity intermediate between novae and supernovae. It was cool throughout its outburst, unlike a normal classical nova. In 2006, Bond & Siegel examined…
We report photometry and spectroscopy of the evolution of Nova Sagittarii 1994 #1 (V4332 Sagittarii) during outburst. We compare the photometric and spectral evolution of this outburst to known classes of outbursts -- including classical…
We discuss various models and scenarios proposed to explain the nature of the V838 Mon type eruptions. In this class of eruptive objects we include: M31 RV (erupted in 1988), V4332 Sgr (erupted in 1994) and V838 Mon (erupted in 2002). We…
The Andromeda galaxy (M31) hosts a central super-massive black hole (SMBH), known as M31$^\ast$, which is remarkable for its mass ($\sim$$10^8{\rm~M_\odot}$) and extreme radiative quiescence. Over the past decade, the Chandra X-ray…
M31-RV was an extraordinarily luminous (~10^6 Lsun) eruptive variable, displaying very cool temperatures (roughly 1000 Kelvins) as it faded. The photometric behavior of M31-RV (and several other very red novae, i.e. luminous eruptive red…
In 1994 V4332 Sgr underwent a mysterious eruption. Somehow its fast evolution towards a red giant star was, lacking alternative classifications, connected to the red variable M31 RV, which had its eruption in 1988. The red eruptive variable…
The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia…
Insight into the origin of unusual events like the eruption of V838 Mon can be obtained from studies of the stellar populations from which they arise. V838 Mon lies in an intriguing region of the Galaxy, toward the warped outer edge of the…
V838 Mon is marking one of the most mysterious stellar outbursts on record. The spectral energy distribution of the progenitor resembles an under-luminous F main sequence star (at V=15.6 mag), that erupted into a cool supergiant following a…
M31-2015-LRN is a likely stellar merger discovered in the Andromeda Galaxy in 2015. We present new optical to mid-infrared photometry and optical spectroscopy for this event. Archival data shows that the source started to brighten $\sim$2…
We present a photometric study of the Andromeda XVIII dwarf spheroidal galaxy associated with M31, and situated well outside of the virial radius of the M31 halo. The galaxy was resolved into stars with Hubble Space Telescope/Advanced…
We present spectroscopic observations of red giant branch (RGB) stars over a large expanse in the halo of the Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck II 10-m telescope. Using a combination of five…
We report the discovery and multicolor (VRIW) photometry of a rare explosive star MASTER OT J004207.99+405501.1 - a luminous red nova - in the Andromeda galaxy M31N2015-01a. We use our original light curve acquired with identical MASTER…
Although the proximity of the Andromeda galaxy (M31) offers an opportunity to understand how mergers affect galaxies, uncertainty remains about M31's most important mergers. Previous studies focused individually on the giant stellar stream…
V838 Mon underwent, after a first nova-like outburst in January and a usual decline, a second outburst after one month, and a third weak one again a month later. Moreover a very small increase of the temperature at the beginning of April…
We confirm our earlier tentative detection of M31* in X-rays and measure its light-curve and spectrum. Observations in 2004-2005 find M31* rather quiescent in the X-ray and radio. However, X-ray observations in 2006-2007 and radio…
We revisit a notable AGN known as `Sharov21', seen to undergo a dramatic outburst in 1992, brightening by a factor of thirty over a period of approximately one year. A simple microlensing model fit to the event lightcurve provides a…
We present spectroscopy and discuss the photometric history of a previously obscure star in M31. The spectrum of the star is an extremely close match to that of P Cygni, one of the archetypes of Luminous Blue Variables (LBVs). The star has…
We have identified a major global enhancement of star formation in the inner M31 disk that occurred between 2-4 Gyr ago, producing $\sim$60% of the stellar mass formed in the past 5 Gyr. The presence of this episode in the inner disk was…