Astronomy & Astrophysics

Table of contents

A&A 477, 67-78 (2008)
DOI: 10.1051/0004-6361:20078288

A systematic search for novae in M 31 on a large set of digitized archival Schmidt plates

M. Henze¹, H. Meusinger¹, and W. Pietsch²

¹ Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
e-mail: henze@tls-tautenburg.de
² Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany

(Received 16 July 2007 / Accepted 14 September 2007)

Abstract
Aims.This paper reports on the detection of optical novae in our neighbour galaxy M 31 based on digitized historical Tautenburg Schmidt plates. The accurate positions of the detected novae lead to a much larger database when searching for recurrent novae in M 31.
Methods.We conducted a systematic search for novae on 306 digitized Tautenburg Schmidt plates covering a time span of 36 years from 1960 to 1996. From the database of both ${\sim}3 \times 10^5$ light curves and $\gtrsim$ 10⁶ detections on only one plate per colour band, nova candidates were efficiently selected by automated algorithms and subsequently individually inspected by eye.
Results.We report the detection of 84 nova candidates. We found 55 nova candidates from the automated analysis of the light curves. Among these, 22 were previously unknown, 12 were known but not identified on Tautenburg Schmidt plates before, and 21 novae had been discovered previously on Tautenburg plates. An additional 29 known novae could be confirmed by the detailed investigation of single detections. One of our newly discovered nova candidates shows a high position coincidence with a nova detected about 30 years earlier. Therefore, this object is likely to be a recurrent nova. Furthermore, we re-investigated all 41 nova candidates previously found on Tautenburg plates and confirm all but two. Positions are given for all nova candidates with a typical accuracy of ${\sim} 0\,\farcs4$ . We present light curves and finding charts as online material.
Conclusions.The analysis of the plates has shown the wealth of information still buried in old plate archives. Extrapolating from this survey, digitization of other historical M 31 plate archives (e.g. from the Mount Wilson or Asiago observatories) for a systematic nova search looks very promising.

Key words: galaxies: individual: M 31 -- novae, cataclysmic variables -- catalogs