Astron. Astrophys. Suppl. Ser. 135, 103-109

Bright populations of the LMC cluster NGC 1978 from multicolor CCD photometry

G. Alcaíno¹ - W. Liller¹ - F. Alvarado ¹ - V. Kravtsov² - A. Ipatov³ - N. Samus³ - O. Smirnov³

Send offprint request: G. Alcaíno

1 - Isaac Newton Institute, Ministry of Education of Chile, Casilla 8-9, Correo 9, Santiago, Chile
e-mail: inewton@reuna.cl
2 - Sternberg Astronomical Institute and Isaac Newton Institute Moscow Branch, 13, University Ave., Moscow 119899, Russia
e-mail: scorpi@sai.msu.su
3 - Institute of Astronomy of Russian Acad. Sci. and Isaac Newton Institute Moscow Branch, 48, Pyatnitskaya Str., Moscow 109017, Russia
e-mail: ipatov@inasan.rssi.ru, samus@sai.msu.su, oms@inasan.rssi.ru

Received March 4; accepted October 6, 1998

Abstract:

We have carried out multicolor (BVRI) photometry for 3077 stars in the field of the populous cluster NGC 1978 in the Large Magellanic Cloud. We find a clear discrepancy in the zero point of our V magnitudes in NGC 1978 with earlier work (Bomans et al. 1995). A large sample of horizontal-branch stars (319 objects) has been isolated. Our study of color distributions of HB stars in different parts of the cluster reveals some variations of the shape of the distributions across the cluster face. We also find some difference in CMD positions of the lower giant branch dependent upon the position in the cluster. Thus, we do not exclude the presence of two subpopulations in NGC 1978; to explain the observations, a difference in [Fe/H] by $\sim0.1-0.2$between them would be sufficient.

Key words: galaxies: star clusters -- Magellanic Clouds -- clusters: globular: NGC 1978 (LMC) -- HR diagram