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

• Autorzy: Jerzykiewicz, M. , Kopacki, G. , Molenda-Żakowicz, J. , Kołaczkowski, Z.
• Języki publikacji: EN

Abstrakty

EN

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 β Cep stars, V 916 and V 917 Ori, an α² CVn variable, V 1356 Ori, and an RRc variable, V 1154 Ori. We find V 916 and V 1154 Ori to be constant in light. We confirm the variability of V 917 Ori, but not the period given in GCVS. For the chemically peculiar A0 V Si star V 1356 Ori 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 917 Ori, one of the two GCVS &beta Cep variables, we determine a period of 0.267 d (frequency 3.7477 d^-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) β Cep-type pulsation, (2) rotational modulation of the λ Eri type, and (3) ellipsoidal variation due to distorted primary component in a close binary system. After deriving the star's effective temperature from Strömgren 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 α-index, a measure of the Hα equivalent width. From the α index, we detect mild emission at Hα in two stars, V 917 Ori and NGC 2169-8.

Słowa kluczowe

EN

stars: early-type; stars: oscillations; open cluster: individual: NGC 2169; associations: individual: NGC 2169

• Czasopismo: Acta Astronomica
• Rocznik: 2003
• Tom: Vol. 56, No. 2
• Strony: 151--165
• Opis fizyczny: Bibliogr. 34 poz., rys., wykr.

Twórcy

autor

Jerzykiewicz, M.

• Wrocław University Observatory, Kopernika 11, 51-622 Wrocław, Poland ,

autor

Kopacki, G.

• Wrocław University Observatory, Kopernika 11, 51-622 Wrocław, Poland ,

autor

Molenda-Żakowicz, J.

• Wrocław University Observatory, Kopernika 11, 51-622 Wrocław, Poland ,

autor

Kołaczkowski, Z.

• Wrocław University Observatory, Kopernika 11, 51-622 Wrocław, Poland ,

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