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Issue A&A
Volume 433, Number 3, April III 2005
Page(s) 787 - 795
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20042357



A&A 433, 787-795 (2005)
DOI: 10.1051/0004-6361:20042357

First microlensing candidate towards M 31 from the Nainital Microlensing Survey

Y. C. Joshi1, 2, A. K. Pandey2, D. Narasimha1, 3 and R. Sagar2

1  Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai - 400 005, India
    e-mail: ycjoshi@tifr.res.in
2  Aryabhatta Research Institute of Observational Sciences (ARIES), Manora peak Nainital - 263129, India
3  Astronomical Institute, Tohoku University, Sendai 980-8578, Japan

(Received 11 November 2004 / Accepted 20 December 2004)

Abstract
We report our first microlensing candidate NMS-E1 towards M 31 from the data accumulated during the four years of Nainital Microlensing Survey. Cousin R and I band observations of $\sim $ $13{'} \times13{'}$ field in the direction of M 31 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 M 31 at $\alpha = 0^{\rm h} 43^{\rm m} 33{\fs}3$ and $\delta = +41^{\circ} 06{'} 44{''}$, about 15.5 arcmin to the South-East direction of the center of M 31. The degenerate Paczynski fit gives a half intensity duration of ~59 days. The photometric analysis of the candidate shows that it reached $R \sim 20.1$ mag at the time of maximum brightness and the colour of the source star was estimated to be $(R-I)_0 \sim 1.1$ mag. The microlensing candidate is blended by red variable stars; consequently the light curves do not strictly follow the characteristic Paczynski shape and achromatic nature. However its long period monitoring and similar behaviour in R and I bands supports its microlensing nature.


Key words: cosmology: dark matter -- Galaxy: halo -- galaxies: Local Group -- gravitational lensing -- methods: data analysis

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