Friday, April 17, 2009, 12:00 noon, Phillips Auditorium
New Variable Stars from Scanned Moscow Plates
Nikolai Samus (Ed., General Catalog of Variable Stars)
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The oldest sky plates of the Moscow plate stacks were exposed in 1895.
The Moscow plate archive contains more than 60000 well-kept direct sky
photographs from several telescopes. The most valuable part of the
collection are 22500 photographs taken in 1948-1996 with the 40-cm Hoffmeister
astrograph (F=160 cm, 30 cm 30 cm plates covering a field of 1010, the
limiting magnitude being about 17m.5 B for the best plates). In late 2005,
we started our digitization project using two Creo EverSmart Supreme II
flatbed scanners, run at the resolution of 2540 dpi (1733.2 per pixel for
the 40-cm astrograph). Our tests demonstrate serious astrometric problems,
still not completely solved. Effective VaST software was developed for
photometric analysis, making use of the well-known SExtractor code for
star detection and aperture photometry. VaST cross-identifies SExtractor
detections on each plate with the reference plate, one of those with best
quality, and transforms their magnitudes to the system of the reference
plate. In 2008, we performed variable-star search in a 510 field (the
northern half of the field centered at 66 Ophiuchi). We discovered 274
new variable stars in this field, rather well studied in the past, among
them: 2 probable Population II Cepheids, 5 high-amplitude 948 Scuti stars,
82 RR Lyraes, 62 red irregular variables and 41 red semiregular stars,
1 slow irregular variable not red in color. The discoveries were mainly
made in the 13m.516m.5 B range, fainter than numerous discoveries made
in the same field by the ASAS-3 and ROTSE-I/NSVS surveys. We also selected
some 30 variability suspects in the same field for further CCD studies,
4 of them have be confirmed since. 38 variable stars were discovered in
our other studies based on the scans of Moscow plates our MDV (Moscow
Digital Variable) numbering series currently has stars from MDV 1 to
MDV 316. We are finishing a similar study for the stars in the southern
half of the field of 66 Oph it will provide about 180 new discoveries,
the southern part of the field being poorer in stars. Searching for new
variables, we also check information for known variables in the field
several cases of wrong light elements could be detected.
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