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Astron. Astrophys. 325, 987-993

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B-type pulsators in the open cluster NGC 884 ( Persei)

J. Krzesiski1 and A. Pigulski2

1Mt. Suhora Observatory, Cracow Pedagogical University, ul. Podchorazych 2, PL-30084 Kraków, Poland (sfkrzesi@cyf-kr.edu.pl)
2Wroclaw University Observatory, ul. Kopernika 11, PL-51622 Wroclaw, Poland (pigulski@astro.uni.wroc.pl)

Received 12 November 1996 / Accepted 20 March 1997


We present results of the photometric CCD search for B-type pulsators in the central region of the FORMULA Persei cluster. The most interesting result is the discovery of two FORMULA Cephei stars, Oo 2246 and Oo 2299, the first ones found in FORMULA Persei. Oo 2246 pulsates with two periods equal to 0.184 and 0.171 d. The light of the other FORMULA Cephei star, Oo 2299, varies with a single period of about 0.318 d. This is one of the longest periods known for this type of variable. The photometric Q indices of the two FORMULA Cephei stars fall in the middle of the range covered by all FORMULA Cephei variables. In the HR diagram, the position of Oo 2246 and Oo 2299 coincide with the low-temperature limit of the FORMULA Cephei instability strip in NGC 3293. The pulsational properties of both FORMULA Cephei stars in FORMULA Persei are in agreement with the main sequence stage of evolution.

In addition to the FORMULA Cephei stars, we found nine other variables, including two eclipsing stars, Oo 2301 and Oo 2311. Almost all Be stars in the field turned out to be variable. In the cluster's colour-magnitude diagram, they appear to be slightly redder than non-Be stars of similar spectral type.

Key words: stars: oscillations - stars: Be - stars: variables: FORMULA Cephei - open clusters and associations: individual: NGC 884 ( FORMULA Per)

Send offprint requests to: J. Krzesinski

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998