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Astron. Astrophys. 355, 138-144 (2000)


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CCD photometry in the region of NGC 6994: The remains of an old open cluster *

L.P. Bassino ** , S. Waldhausen *** and R.E. Martínez ***

Facultad de Ciencias Astronómicas y Geofísicas de la Universidad Nacional de La Plata and CONICET, Argentina
Observatorio Astronómico de la UNLP, Paseo del Bosque s/n, 1900-La Plata, Argentina (lbassino@fcaglp.fcaglp.unlp.edu.ar)

Received 22 July 1999 / Accepted 11 January 2000

Abstract

We present the results of [FORMULA] CCD photometry down to [FORMULA] mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it.

We obtain a color excess [FORMULA] mag by means of the [FORMULA] technique. Based on the theoretical isochrones from VandenBerg (1985) that are in better agreement with our data, we estimate for this cluster a distance from the Sun of 620 pc ([FORMULA] mag) and an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus, the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at about 350 pc below the Galactic plane. According to these results, NGC 6994 belongs to the old open cluster population located in the outer disk and at large distances from the Galactic plane, and must have suffered significant individual dynamical evolution, resulting in mass segregation and evaporation of low mass stars.

Key words: open clusters and associations: general – open clusters and associations: individual: NGC 6994 – techniques: photometric

* Table 1 is only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/355/138 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/355/138
** Member of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
*** Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the CONICET (Argentina) and the National Universities of La Plata, Córdoba and San Juan

Send offprint requests to: L.P. Bassino

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000

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