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

Abstract

Abstract. We present CCD photometry in the Washington system C and T 1 passbands down to T 1 ∼ 18.5 mag in the field of Tombaugh 1, a little studied open cluster located in the third Galactic quadrant. We measured T 1 magnitudes and C − T 1 colours for a total of 1351 stars distributed throughout an area of 13. 6 × 13. 6. A cluster radius of 4. 3 ± 0. 3 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 T 1 vs. C − T 1 colour-magnitude diagram, we derive a colour excess E(C − T 1 ) = 0.55 ± 0.10, equivalent to E(B − V) = 0.30 ± 0.05, a distance of (2.2 ± 0.5) kpc from the Sun and an age of 1.3The latter value is in good agreement with that derived from the independent metallicity δT 1 index defined in Geisler et al. (1997( , AJ, 114, 1920). An independent metallicity estimation using the [M T 1 , (C − T 1 ) 0 ] plane with the standard giant branches of Geisler & Sarajedini (1999, AJ, 117, 308)

PROPERTIES OF THE OPEN CLUSTER TOMBAUGH 1 FROM HIGH-RESOLUTION SPECTROSCOPY AND uvbyCaHβ PHOTOMETRY*

“…In particular, they determined for Tombaugh 1 an age of 1.16 Gyr, a reddening -E B V ( )=0.281, and a distance of 2642 pc ( -m M ( )=12.98), values similar to those obtained by Piatti et al (2004). Kharchenko et al (2013) also estimated the average proper motion in R.A. (−0.99 mas yr −1 ) and in decl.…”

“…While this study dealt with only two filters and field star contamination makes it difficult to clearly identify the cluster turnoff, the parameter differences are not unexpected given the sparse sample of the earlier study. Piatti et al (2004) presented a more extensive CCD study using Washington photometry, covering a large area around the cluster. The cluster was found to be 1.3 Gyr old from a combination of CMD morphology and isochrone fits, assuming [Fe/H]=−0.40, with distance and reddening estimates intermediate between the Turner (1983) and Carraro & Patat (1995) values.…”

“…With a Galactic latitude of −7°.32 and an assumed a distance of 2-3 kpc (Carraro & Patat 1995;Piatti et al 2004), Tombaugh 1 is situated ∼300-400 pc below the Galactic plane, a location rare among open clusters of the presumed age of Tombaugh1 (10 9 years). The direction to Tombaugh1 intersects the Perseus and Orion arms in the third Galactic quadrant, and the cluster was for some time associated with the putative Canis Major dwarf galaxy (Bellazzini et al 2004).…”

“…Improved cluster distance and metallicity estimates would be of paramount importance in probing this picture of the chemical properties of the outer Galactic disk. Metallicity, in particular, has never been measured reliably, only inferred either from photometric indices or by comparison with isochrones (Piatti et al 2004).…”

Old open clusters as key tracers of Galactic chemical evolution

“…The former OC was recently investigated by Piatti et al (2004) who provided photometry in the JohnsonCousins VI c filters and the Washington system C and T 1 passbands; for NGC 2324 they derived E(B − V) = 0.25, distance 3.8 kpc and [Fe/H] = −0.31 from their best-fit isochrone. Kyeong et al (2001) presented UBVIc CCD photometry finding E(B − V) = 0.17, (m − M) 0 = 13.1, [Fe/H] ∼ −0.3, and an age of ∼600−700 Myr from a comparison with isochrones.…”