Astron. Astrophys. Suppl. Ser. 136, 461-470

Deep multicolor CCD photometry of the globular cluster NGC 6723

G. Alcaíno¹ - W. Liller¹ - F. Alvarado ¹ - A. Mironov² - A. Ipatov³ - A. Piskunov³ - 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: almir@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, piskunov@inasan.rssi.ru, samus@sai.msu.su, oms@inasan.rssi.ru

Received November 17, 1998; accepted March 23, 1999

Abstract:

We have obtained CCD UBVRI photometry of 3620 stars in the globular cluster NGC 6723, one of the few globular clusters with a horizontal branch well-populated on both sides of the instability strip. This is the first deep five-color study of NGC 6723. We have determined several important parameters for this cluster. Its color excess is $E(B-V) =0.11\pm{}0.01$. The most plausible value of metallicity is $\rm [Fe/H]=-1.22\pm{}0.15$;even lower values are possible. The apparent distance modulus of the cluster is (m-M)_V,6723=14.76. From isochrone analysis, we prefer the NGC 6723 age in the range between 15 and 16 Gyr, in the scale of Bergbusch & VandenBerg (1992). We find a close similarity of the shape and slope of the red giant branch in NGC 6723 and M 3 and of the magnitude difference between the main-sequence turnoff and the horizontal branch in NGC 6723, M 3, and M 5.

Key words: globular clusters: individual (NGC 6723)