Revisiting the area of the open cluster Stock 16

Free access article

This article has an erratum: [erratum]

Issue		A&A Volume 430, Number 2, February I 2005


Page(s)		471 - 480
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20041089

A&A 430, 471-480 (2005)
DOI: 10.1051/0004-6361:20041089

Revisiting the area of the open cluster Stock 16

R. A. Vázquez¹,

G. L. Baume^{1, 2}, C. Feinstein¹, J. A. Nuñez¹ and M. M. Vergne¹

¹ Facultad de Ciencias Astronómicas y Geofísicas UNLP, IALP-CONICET, Paseo del Bosque s/n, 1900, La Plata, Argentina
e-mail: rvazquez@fcaglp.fcaglp.unlp.edu.ar
² Dipartimento di Astronomía, Università di Padova, Vicolo Osservatorio 2, 35122 Padova, Italy

(Received 15 April 2004 /Accepted 10 August 2004 )

Abstract
Deep CCD $\it UBV(RI)_{\rm C}$ photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars. The first of them, the cluster Stock 16, suffers from slightly variable reddening with a mean color excess $\langle E_{B-V}\rangle = 0.51~$ . The second group, reddened by $\langle E_{B-V}\rangle = 0.84~$ , includes the Wolf-Rayet star WR 50 (a WC7+OB), and the third one, with a mean $\langle E_{B-V}\rangle = 1.18~$ , also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results confirm the distance and reddening already stated for Stock 16 but include new members. Concerning the other two highly reddened groups, we show that the first one - located at a distance of 3600 pc - is probably related to an anonymous OB association behind Cen OB1 also at 3600 pc already mentioned in the literature; the other seems to be a distant OB association - at more than 9000 pc - which may belong to the Scutum-Crux spiral arm. In these two groups we find evidence that the absorption law, A_V/E_B-V = R amounts to 4.0 approximately. The ages of the different star populations in the zone range from $5 \times 10^6$ yr to $6.4 \times 10^6$ yr for Stock 16, $8 \times 10^6$ for the second most reddened group and $5 \times 10^6$ for the probable association in Scutum-Crux. A determination of the IMF slope of Stock 16 was also carried out for stars in the mass range 1.8 < M < 14 $M_{\odot}$ , giving a normal value x = 1.3.

Key words: Galaxy: open clusters and associations: individual: WR 50 -- stars: luminosity function, mass function Galaxy: open clusters and associations: individual: WR 51 -- stars: imaging

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