Variable stars towards the bulge of M 31: The AGAPE catalogue

Abstract

Abstract. We present the AGAPE astrometric and photometric catalogue of 1579 variable stars in a 14 × 10 field centred on M 31. This work is the first survey devoted to variable stars in the bulge of M 31. The R magnitudes of the objects and the B − R colours suggest that our sample is dominated by red long-period variable stars (LPV), with a possible overlap with Cepheid-like type II stars. Fits of the light curves with sinusoids suggest that a large fraction of the stars correspond to periodic or semi-periodic objects with periods longer than 100 days. Twelve nova candidates are identified. Correlations with other catalogues suggest that 2 novae could be recurrent novae and provide possible optical counterparts for 2 supersoft X-ray sources candidates observed with Chandra.

Nainital Microlensing Survey – detection of short period Cepheids in the disk of M 31

“…Therefore, in the present study, we used the pixel method to analyse our data, which relies on the monitoring of pixel light curves and their shape analysis. This method was originally proposed by Baillon et al (1993) and implemented by Ansari et al (1997) and others. In the pixel method, if a star of flux F star is increased, whether due to intrinsic variability or gravitationally lensed, then by subtracting the original flux from the amplified flux of the star, we see an increase in flux equal to (A − 1)F star above the photon noise where A is the flux amplification of the star.…”

“…Cepheids, Miras) and optical transient events. Several groups dedicated to searching for microlensing events in the direction of M 31 have already uncovered a large number of variable stars, most of which are previously unidentified (Joshi et al 2003;Ansari et al 2004;Fliri et al 2006), as well as nova outbursts (Joshi et al 2004, Darnley et al 2004) as a major by-product.These variable stars are of cosmological interest, particularly Cepheids, which are massive (M ∼ 3−20 M ) pulsating stars placed in the instability strip of the Hertzsprung-Russell diagram. They can be identified by their characteristic "saw-tooth" shaped light curves and high intrinsic brightness.…”

Identification of 13 Cepheids and 333 other variables in M 31

“…The NTL images were scaled down or up to MDM pixel size (0.5 × 0.5 arcsec 2 ). These aligned images, in combination with AGAPE observations, will be used to search for microlensing events using the pixel method described in detail by Ansari et al (1997).…”

“…In recent years, the Andromeda galaxy (M 31) has been a target of searches for gravitational microlensing events Ansari et al 1997). To detect lensing events, continuous observations are needed for a long duration though for a short period of time each night.…”

First microlensing candidate towards M 31 from the Nainital Microlensing Survey

“…Therefore, by monitoring a pixel for a long time, one could detect a microlensing event. The pixel technique, which relies on the shape analysis of the light curve to detect microlensing events, is implemented by the AGAPE (Ansari et al 1997) and POINT-AGAPE collaborations (Paulin-Henriksson et al 2002) and have reported more than 10 possible microlensing events towards M 31 (Calchi Novati et al 2002Paulin-Henriksson et al 2002. A similar approach but based on the image subtraction technique was proposed by Crotts (1992) and Tomaney & Crotts (1996) that has been further improved by Alard & Lupton (1998) and Alard (2000) by optimal image subtraction using a space-varying kernel.…”