Improvements on the fundamental parameters of the open cluster Tombaugh 1 through Washington system photometry

¹ Instituto de Astronomía y Física del Espacio, CC 67, Suc. 28, 1428, Buenos Aires, Argentina
² Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina e-mail: [claria;andrea]@mail.oac.uncor.edu

Corresponding author: A. E. Piatti, andres@iafe.uba.ar

Received: 8 January 2004
Accepted: 31 March 2004

Abstract

We present CCD photometry in the Washington system C and T₁ passbands down to  mag in the field of Tombaugh 1, a little studied open cluster located in the third Galactic quadrant. We measured T₁ magnitudes and colours for a total of 1351 stars distributed throughout an area of . A cluster radius of was estimated from star counts in 100-pixel a side boxes distributed throughout the entire observed field. Based on the best fits of isochrones computed by the Geneva group for Z = 0.008 to the T₁ vs.  colour–magnitude diagram, we derive a colour excess = , equivalent to , a distance of () kpc from the Sun and an age of 1.3  Gyr. The latter value is in good agreement with that derived from the independent metallicity δT₁ index defined in Geisler et al. (1997, AJ, 114, 1920). An independent metallicity estimation using the [ , ] plane with the standard giant branches of Geisler & Sarajedini (1999, AJ, 117, 308) yields  dex, a value which lends support to the one obtained from the isochrone fit. Tombaugh 1 is then found to be a relatively metal-poor intermediate-age open cluster.