A revision of the fundamental parameters of the open cluster Hogg 15 and the projected star WR 47

¹ Instituto de Astronomía y Física del Espacio, CC 67, Suc. 28, 1428, Buenos Aires, Argentina
² Instituto de Fisica-UFRGS, CP 15051, CEP 91501-970 POA – RS, Brazil
³ Departamento de Fisica, ICEx, UFMG, CP 702, 30123-970 BH – MG, Brazil
⁴ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina

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

Received: 11 December 2001
Accepted: 1 March 2002

Abstract

We revise the fundamental parameters of the faint open cluster Hogg 15, for which two recent colour-magnitude diagram (CMD) studies have obtained significantly different ages. In the present study, we combine a series of methods trying to constrain age, together with other fundamental parameters. We employ spatial extractions to construct the CMDs, and the cluster integrated spectrum to compare it with those of templates of known age. We derive fundamental parameters, in particular, distance, of the closely projected Wolf-Rayet star HDE 311884 (WR 47) – often proposed to be physically related to Hogg 15. Based on the WR 47 spectrum and available photometry, we conclude that the short distance implied by the Hipparcos parallax (216 pc) is affected by binary motion. From the WR 47 spectrum we estimate a reddening and a distance of 1.10 ± 0.05 and 5.2 ± 0.9 kpc, respectively. For Hogg 15 we derive an age of 20 ± 10 Myr, a reddening of 1.10 ± 0.05, and a distance of 3.1 ± 0.5 kpc. We conclude that Hogg 15 is not related to WR 47 from the point of view of origin, since the cluster and the star do not belong to the same formation event.