Massive open star clusters using the VVV survey

Abstract

Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims. This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods. Following the methodology presented in the first paper of the series, wide-field, deep JHK s VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results. We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 10 3 M ) clusters. They are highly obscured (A V ∼ 5−24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ∼30-50 M for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters.

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

“…We note that < 5% of WR stars discovered since the year 2011 are brighter than KS= 8 mag (Mauerhan et al 2011;Shara et al 2012;Smith et al 2012;Chené et al 2013). Therefore, we adopt this as the current completeness limit in systemic magnitude.. Figure 11 presents predicted magnitude distributions for WR populations containing 450, 550 and 650 stars between RG = 3-15 kpc plus 250 central stars (RG < 3 kpc).…”

“…( (23) Chené et al (2013), (24) Rahman, Moon, & Matzner (2011), (25) Anderson et al (2011), (26) Marston et al (2013), (27) Kanarek et al (2014), (28) Davies et al (2012), (29) de La Fuente, Najarro, Davies, & Figer (2013), (30) Borissova et al (2012), (31) Mikles et al (2006), (32) Hyodo et al (2008), (33) Faherty et al (2014) (34) Smith et al (2012), (35) Corradi et al (2010), (36) Gvaramadze et al (2009), (37) Burgemeister et al (2013) He ii This paper has been typeset from a T E X/ L A T E X file prepared by the author.…”

The embedded clusters DBS 77, 78, 102, and 160−161, and their link with the interstellar medium

“…As a measure of atmospheric absorption, we observed bright stars of spectral type G. We used the standard procedures to reduce the data. For more details of our reduction procedures see Moorwood et al (1998) and Chené et al (2012Chené et al ( , 2013.…”

“…In particular, several embedded clusters include massive stars and present important pre-main-sequence (PMS) populations (Chené et al 2013). They enable us to study early-type stars, their impact on the surrounding environment, and help us to outline the path of the spiral arms.…”

“…Our goal is to obtain the characteristic parameters of a large sample of embedded clusters using homogeneous data and analysis methods. Results for four known clusters have been presented by Chené et al (2012) and for six of the new VVV cluster candidates with Wolf-Rayet (WR) stars in Chené et al (2013). In this paper we follow similar analytical methods to those papers, but we applied these methods to a sample of clusters of the DBS catalogue (Dutra et al 2003) and we complemented them with optical and radio data.…”