Identification of 13 Cepheids and 333 other variables in M 31

Abstract

Abstract. We present Cousins R and I band photometry of variable stars in a ∼13 × 13 region in the disk of M 31 galaxy, obtained during 141 nights. Of the 26 Cepheid variables present in the region, two are newly discovered, 11 are classified as Cepheids for the first time and 13 are confirmed as Cepheids. The extensive photometry of these Cepheids enabled us to determine precise phase and amplitude of pulsation which ranges from 0.11 to 0.48 mag in R band. The period of variability ranges from ∼7.5 to 56 days. The period-luminosity diagram is used to derive a distance modulus of 24.49 ± 0.11 mag for M 31 galaxy. We also report variability in 333 other stars, of them, 115 stars appear to be long period variables, 2 suspected eclipsing binaries and remaining 216 are irregular variables.

Long-term photometric study of a faint W UMa binary in the direction of M31

“…Several surveys aimed to find microlensing events towards M31 have already unearthed thousands of variable stars as a major by-product, most of which were previously unknown (Ansari et al 2004, Darnley et al 2004, Fliri et al 2006, Lee et al 2012, Soszyńksi et al 2016. Apart from detecting microlensing events in the NMS data (Joshi et al 2005), we have detected Cepheids (Joshi et al 2003(Joshi et al , 2010 and classical novae (Joshi et al 2004) in M31. In continuation of our efforts to identify variables in the archival data taken under the survey, we searched for eclipsing binary stars in the target field of M31.…”

“…Unlike our earlier study (Joshi et al 2003(Joshi et al , 2005(Joshi et al , 2010, we have not combined the frames on a nightly basis in the present analysis but carried out photometry on each individual frame in order to increase W UMa W UMa Fig. 1 A 13 ′ × 13 ′ finding chart centered at (0:42:59.33, +41:06:29.3).…”

First microlensing candidate towards M 31 from the Nainital Microlensing Survey

“…The average seeing during the observations was ∼2.2 arcsec. A detailed overview of the observations is given in Joshi et al (2003). …”

“…In regions like M 31, which is at ∼780 kpc (Stanek & Garnovich 1998;Joshi et al 2003), microlens monitoring is a cumbersome process due to the large background of unresolved stars of M 31 where the typical stellar density is as high as few hundred stars per arcsec 2 . To deal with this problem, Baillon et al (1993) proposed to monitor pixels of the CCD rather than the stars themselves.…”

“…Since the search for gravitational microlensing events requires monitoring of millions of stars over a few years to yield a significant number of detections as well as to test their uniqueness, we started multi-band observations of M 31 in the autumn of 1998 under a program Nainital Microlensing Survey at the ARIES, Nainital, India in collaboration with the AGAPE (Joshi 2004). The details of our observations are given in the next section while the pixel technique and its implementation is described in Sect.…”