Detection of new O-type stars in the obscured stellar cluster Tr 16-SE in the Carina Nebula with KMOS

TL;DR

This study used infrared spectroscopy with KMOS at the ESO VLT to identify 15 high-mass stars, including 9 new O- and early B-type stars, in the obscured cluster Tr 16-SE within the Carina Nebula, expanding the known stellar census.

Contribution

First infrared spectroscopic survey of stars in Tr 16-SE, revealing new high-mass stars and increasing the known population in this obscured cluster.

Findings

Identified 15 high-mass stars, including 9 new O- and early B-type stars.

Increased the number of spectroscopically confirmed high-mass stars in Tr 16-SE from 2 to 9.

Discovered that Tr 16-SE is one of the larger clusters in the Carina Nebula.

Abstract

The Carina Nebula harbors a large population of high-mass stars, including at least 75 O-type and Wolf-Rayet stars, but the current census is not complete since further high-mass stars may be hidden in or behind the dense dark clouds that pervade the association. With the aim of identifying optically obscured O- and early B-type stars in the Carina Nebula, we performed the first infrared spectroscopic study of stars in the optically obscured stellar cluster Tr 16-SE, located behind a dark dust lane south of eta Car. We used the integral-field spectrograph KMOS at the ESO VLT to obtain H- and K-band spectra with a resolution of R sim 4000 (Delta lambda sim 5 A) for 45 out of the 47 possible OB candidate stars in Tr 16-SE, and we derived spectral types for these stars. We find 15 stars in Tr 16-SE with spectral types between O5 and B2 (i.e., high-mass stars with M >= 8 Msun, only two of which were known before. An additional nine stars are classified as (Ae)Be stars (i.e., intermediate-mass pre-main-sequence stars), and most of the remaining targets show clear signatures of being late-type stars and are thus most likely foreground stars or background giants unrelated to the Carina Nebula. Our estimates of the stellar luminosities suggest that nine of the 15 O- and early B-type stars are members of Tr 16-SE, whereas the other six seem to be background objects. Our study increases the number of spectroscopically identified high-mass stars (M >= 8 Msun) in Tr 16-SE from two to nine and shows that Tr 16-SE is one of the larger clusters in the Carina Nebula. Our identification of three new stars with spectral types between O5 and O7 and four new stars with spectral types O9 to B1 significantly increases the number of spectroscopically identified O-type stars in the Carina Nebula.