dc.description.abstract | We carried out a multiwavelength study of the central ∼400 arcmin2 area of
the Carina Nebula that covers the star clusters, Trumpler 14 (Tr 14), and Trumpler
16 (Tr 16). Our approach to identify the pre-main sequence (PMS) population of
this massive star forming region is to combine the X-ray and near-infrared (NIR)
wavelength information. NIR wavelengths, as compared to optical wavelengths, suffer
much less problem due to extinctions which are typically high in a star-forming region
and NIR colors of young stars provide a very useful tool to classify PMS objects. On
the other hand, X-ray surveys provide clean samples of star forming regions as they
suffer little contamination due to field stars and are the most efficient in identifying
the weak-lined T Tauri population, which otherwise is difficult to be distinguished
from unrelated field stars for its lack of classic signatures of youth, i.e., NIR excess,
strong H emission, etc.
We have used three archival Chandra datasets to derive a sample of ∼800 X-ray
sources of this region, with a limiting X-ray flux of ∼ 10−14 ergs cm−2 s−1. With
10 limiting magnitudes of ∼18.5, 17.5, and 16.5 mag, in the J, H, and Ks bands,
respectively, our NIR imaging observations are deeper by 2–3 magnitudes than any
existing NIR observations of this large field in the Carina Nebula. We have identified
∼1000 T Tauri candidates (i.e. Class II and III candidates), and some dozen Class
I candidates using the X-ray and NIR properties of the sources, thus producing the
most comprehensive sample of the PMS candidates of this region.
X-ray emission is detected from all the O stars and 10% of early-B stars in our
field. We also detected X-ray emission from several mid- or late-B stars, with their X-ray luminosities being comparable to those typical of T Tauri candidates in our
sample, providing a circumstantial evidence that the X-ray emission could come from
a low/intermediate-mass PMS companion. Most O and early-B stars in our sample
satisfy the canonical relation, LX ∝ 10−7Lbol, and none of the O stars are found to
be variable in X-ray emission—both of these findings being consistent with the windshock
model as the X-ray emission mechanism in these massive stars. We identified
16 candidate OB stars which have likely escaped previous detections due to larger
extinctions they suffer in optical wavelengths.
The spatial distribution of the PMS candidates and very red NIR sources (H −
Ks > 2) suggests that we are apparently seeing star formation in different evolutionary
stages. The T Tauri candidates are seen to be distributed in the direction of Tr 14
and Tr 16, with Tr 14 containing a much larger population of Class II candidates than
Tr 16—implying a younger age for Tr 14. The Ks band luminosity function (KLF) of
Tr 14 shows a sharp peak, likely due to the deuterium burning PMS stars—implying
an age of 1–2 Myr for the cluster. In contrast, the KLF of Tr 16 is seen to rise smoothly
until it turns over at Ks ∼17 mag due to the sensitivity of our data. Most of the
red NIR sources, on the other hand, are seen to be concentrated to the south-east
of Tr 16, where few T Tauri candidates are found, representing a still younger and
probably the current generation of star birth. In particular, a compact, embedded
group of ten X-ray sources, Tr 16-SE group, where many of these sources are massive
star candidates, with one known O4 star, is discovered. The KLF of the Tr 16-SE
group shows that the group has a much higher number density of sources relative to
the field, indicating that it is indeed a bona fide young star group or cluster. We also
find strong indications of ongoing cluster formation near three mid-infrared sources,
where we see striking correlation of some very red NIR sources (H − Ks > 2) and
hard X-ray sources. | en_US |