A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. V. NGC 2169

Details A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. V. NGC 2169 A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. V. NGC 2169

Jun 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aca....53..151j&link_type=abstract

Acta Astronomica, v.53, pp.151-165, (2003).

Other

6

Stars: Early-Type, Stars: Oscillations, Open Clusters And Associations: Individual: Ngc 2169

Scientific paper

We present results of a search for variable stars in the field of the young open cluster NGC 2169. The General Catalogue of Variable Stars (GCVS, http://www.sai.msu.su/groups/cluster/gcvs/) lists four variable stars in the field we observed, viz., two beta Cep stars, V 916 and V 917Ori, an alpha^2CVn variable, V 1356Ori, and an RRc variable, V 1154Ori. We find V 916 and V 1154Ori to be constant in light. We confirm the variability of V 917Ori, but not the period given in GCVS. For the chemically peculiar A0 V Si star V 1356Ori we definitely establish the period of 1.565 d, thus settling the uncertainty persisting in the literature since the star was discovered to be variable. In addition, we find two other stars to be variable in light. Both show irregular variations.
For V 917Ori, one of the two GCVS beta Cep variables, we determine a period of 0.267 d (frequency 3.7477d^-1). However, prewhitening with this period leaves a significant amount of the star's light-variation unaccounted for. Since the star shows emission at Hα, we hypothesize that the unaccounted for variation is caused by an erratic, Be-type activity. As to the periodic term, we consider three hypotheses: (1) beta Cep-type pulsation, (2) rotational modulation of the lambda Eri type, and (3) ellipsoidal variation due to distorted primary component in a close binary system. After deriving the star's effective temperature from Stromgren indices and the luminosity from the distance modulus of the cluster, we show that while the third hypothesis is untenable, the first two should be retained. However, neither is entirely satisfactory.
For a number of stars we provide the V magnitudes. For 14 brightest stars in our field we also obtain the photometric alpha-index, a measure of the Hα equivalent width. From the alpha index, we detect mild emission at Hα in two stars, V 917Ori and NGC 2169-8.

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