Abstract
We present detailed observations of the Treasure Chest, a compact nebula at the head of a dust pillar in the southern Carina Nebula. This object is of interest because it is an example of a dense young cluster containing at least one massive star, the formation of which may have been triggered by feedback from the very massive stars in the Carina Nebula, and possibly η Carinae itself. Our observations include narrowband images of Hα, [S II], [O III], Paβ, [Fe II], and H2, broadband JHK images, and a visual wavelength spectrum of the nebula. We use these data to investigate both the nebular and stellar content of the object. The near-infrared emission-line images reveal a cavity inside the head of the dust pillar, which contains a dense cluster of young stars, whereas the observed spectrum of the nebula is consistent with an H II region ionized by the O9.5 V star CPD -59°2661. The embedded infrared cluster was discovered in Two Micron All Sky Survey data, but our new JHK images have improved spatial resolution and sensitivity, allowing an analysis of the stellar content of the newborn cluster. After subtracting contamination of field stars within the Carina Nebula itself, we compare the cluster's color-magnitude diagram with pre–main-sequence isochrones to derive a likely cluster age of less than about 0.1 Myr. This is in reasonable agreement with the dynamical age of a few times 104 yr for the expanding nebular cavity, indicating extreme youth. Stars in the Treasure Chest cluster are highly reddened, with extinction values as large as AV ~ 50. Two-thirds of cluster members show strong infrared excess colors indicative of circumstellar disks, which may prove to be among the highest fraction yet seen for a young cluster once L-band photometry is considered. All evidence suggests that the Treasure Chest is an extremely young cluster that is just now breaking out of its natal cloud into the surrounding massive star-forming region and is a good target for more detailed study.
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