GEMINI near-infrared spectroscopic observations of young massive stars embedded in molecular clouds

Abstract

K-band spectra of young stellar candidates in four Southern hemisphere clusters have been obtained with the Gemini Near-Infrared Spectrograph in Gemini South. The clusters are associated with IRAS sources that have colours characteristic of ultracompact H II regions. Spectral types were obtained by comparison of the observed spectra with those of a nearinfrared (NIR) library; the results include the spectral classification of nine massive stars and seven objects confirmed as background late-type stars. Two of the studied sources have K-band spectra compatible with those characteristic of very hot stars, as inferred from the presence of C IV, N III and N V emission lines at 2.078, 2.116 and 2.100 μm, respectively. One of them, I16177 IRS1, has a K-band spectrum similar to that of Cyg OB2 7, an O3If * supergiant star. The nebular K-band spectrum of the associated Ultra-Compact (UC) H II region shows the s-process [Kr III] and [Se IV] high excitation emission lines, previously identified only in planetary nebula. One young stellar object was found in each cluster, associated with either the main IRAS source or a nearby resolved Midecourse Space eXperiment (MSX) component, confirming the results obtained from previous NIR photometric surveys. The distances to the stars were derived from their spectral types and previously determined JHK magnitudes; they agree well with the values obtained from the kinematic method, except in the case of IRAS 15408−5356, for which the spectroscopic distance is about a factor of 2 smaller than the kinematic value.

Deep near-infrared adaptive-optics observations of a young embedded cluster at the edge of the RCW 41 H II region

“…At the edge of the Hα emission, the Spitzer and SofI images show a dense NIR cluster, which is associated with the source IRAS09149−4743 (marked with a cross in both figures). This region has been studied in detail by Ortiz et al (2007), Roman-Lopes et al (2009), andSantos et al (2012). The cluster's region is composed of two distinct substructures, as highlighted in Figs.…”

“…A small subcluster region is located 1.1 arcmin toward the southeast of the main cluster's center, and hosts Obj2 (Fig. 1), identified as an O9 v star at a distance of 1.27 ± 0.13 kpc (Roman-Lopes et al 2009), which is presumably the most massive object in the field. Following the conclusions drawn in Fig.…”

“…The source Obj1a ( Fig. 1) has been classified as a B0 V star, and it is at a distance of 1.2 ± 0.12 kpc (Roman-Lopes et al 2009). Pirogov et al (2007) report the detection of CS, N 2 H + , and 1.2 mm dust continuum emissions toward IRAS09149−4743, with the dust emissions forming an almost spherical core superposed to the northwestern part of the stellar cluster direction.…”

“…In particular, this cluster has been chosen because it has been studied in depth before, however at seeing limited angular resolution, in the NIR (Ortiz et al 2007;Roman-Lopes et al 2009;Santos et al 2012), and it hosts massive young stars and multiple masers emission in its vicinity as signposts of high-mass star formation (e.g., Walsh et al 1998;Pestalozzi et al 2005;Caswell et al 2010;Breen et al 2011;Voronkov et al 2014). Combining high-angular resolution, and deep NIR images, we are able to study the complete populations of this young star cluster, well below the hydrogen-burning limit (0.08 M ).…”

Atomic data for neutron-capture elements

“…Indeed, n-capture element emission lines have been detected in a variety of other environments, including H II regions (Aspin 1994;Lumsden & Puxley 1996;Luhman et al 1998;Baldwin et al 2000;Puxley et al 2000;Okumura et al 2001;Blum & McGregor 2008;Roman-Lopes et al 2009) and starburst galaxies (Vanzi et al 2008). These detections demonstrate the promise of nebular spectroscopy as a tool to study n-capture nucleosynthesis in low-mass stars, the chemical evolution of trans-iron elements in A&A 533, A62 (2011) the Universe, and the heavy-element nucleosynthetic histories of other galaxies.…”