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تسجيل مستخدم جديدA Census of the Carina Nebula -- II. Energy Budget and Global Properties of the Nebulosity
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The first paper in this series took a direct census of energy input from the known OB stars in the Carina Nebula, and in this paper we study the global properties of the surrounding nebulosity. We find that the total IR luminosity of Carina is about 1.2E7 Lsun, accounting for only about 50-60% of the known stellar luminosity from Paper I. Similarly, the ionizing photon luminosity -- (abridged; many important details omitted). Synchronized star formation around the periphery of Carina provides a strong case that star formation here was indeed triggered by stellar winds and UV radiation. This second generation appears to involve a cascade toward preferentially intermediate- and low-mass stars, but this may soon change when eta Car and its siblings explode. If the current reservoir of atomic and molecular gas can be tapped at that time, massive star formation may be rejuvinated around the periphery of Carina much as if it were a young version of Goulds Belt. Also, when these multiple SNe occur, the triggered second generation will be pelted repeatedly with SN ejecta bearing short-lived radioactive nuclides. Carina may therefore represent the most observable analog to the cradle of our own Solar System.
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We present the first extensive spectroscopic study of the global population in star clusters Trumpler~16, Trumpler~14 and Collinder~232 in the Carina Nebula, using data from the Gaia-ESO Survey, down to solar-mass stars. In addition to the standard h
omogeneous Survey data reduction, a special processing was applied here because of the bright nebulosity surrounding Carina stars. We find about four hundred good candidate members ranging from OB types down to slightly sub-solar masses. About one-hundred heavily-reddened early-type Carina members found here were previously unrecognized or poorly classified, including two candidate O stars and several candidate Herbig Ae/Be stars. Their large brightness makes them useful tracers of the obscured Carina population. The spectroscopically-derived temperatures for nearly 300 low-mass members allows the inference of individual extinction values, and the study of the relative placement of stars along the line of sight. We find a complex spatial structure, with definite clustering of low-mass members around the most massive stars, and spatially-variable extinction. By combining the new data with existing X-ray data we obtain a more complete picture of the three-dimensional spatial structure of the Carina clusters, and of their connection to bright and dark nebulosity, and UV sources. The identification of tens of background giants enables us also to determine the total optical depth of the Carina nebula along many sightlines. We are also able to put constraints on the star-formation history of the region, with Trumpler~14 stars found to be systematically younger than stars in other sub-clusters. We find a large percentage of fast-rotating stars among Carina solar-mass members, which provide new constraints on the rotational evolution of pre-main-sequence stars in this mass range.
The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of
those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the Lx/Lbol ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(Lx/Lbol) is -7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the Lx/Lbol ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the Lx/Lbol ratio in the medium (1.0--2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared to normal O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest amongst these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.
We present a Spitzer based census of the IC 348 nebula and embedded star cluster. Our Spitzer census supplemented by ground based spectra has added 42 class II T-Tauri sources to the cluster membership and identified ~20 class 0/I protostars. The pop
ulation of IC 348 likely exceeds 400 sources after accounting statistically for unidentified diskless members. Our Spitzer census of IC 348 reveals a population of protostars that is anti-correlated spatially with the T-Tauri members, which comprise the centrally condensed cluster around a B star. The protostars are instead found mostly at the cluster periphery about 1 pc from the B star and spread out along a filamentary ridge. We find that the star formation rate in this protostellar ridge is consistent with that rate which built the exposed cluster while the presence of fifteen cold, starless, millimeter cores intermingled with this protostellar population indicates that the IC 348 nebula has yet to finish forming stars. We show that the IC 348 cluster is of order 3-5 crossing times old, and, as evidenced by its smooth radial profile and confirmed mass segregation, is likely relaxed. While it seems apparent that the current cluster configuration is the result of dynamical evolution and its primordial structure has been erased, our findings support a model where embedded clusters are built up from numerous smaller sub-clusters. Finally, the results of our Spitzer census indicate that the supposition that star formation must progress rapidly in a dark cloud should not preclude these observations that show it can be relatively long lived.
We have carried out near-infrared (NIR) imaging observations of the Carina Nebula for an area of ~400 sq. arcmin. including the star clusters Trumpler 14 (Tr 14) and Trumpler 16 (Tr 16). With 10 sigma limiting magnitudes of J ~ 18.5, H ~ 17.5 and K_s
~ 16.5, we identified 544 Class II and 11 Class I young star candidates. We find some 40 previously unknown very red sources with H-K_s > 2, most of which remain undetected at the J band. The red NIR sources are found to be concentrated to the south-east of Tr 16, along the `V shaped dust lane, where the next generation of stars seems to be forming. In addition, we find indications of ongoing star formation near the three MSX point sources, G287.51-0.49, G287.47-0.54, and G287.63-0.72. A handful of red NIR sources are seen to populate around each of these MSX sources. Apart from this, we identified two hard Chandra X-ray sources near G287.47-0.54, one of which does not have an NIR counterpart and may be associated with a Class I/Class 0 object. The majority of the Class II candidates, on the other hand, are seen to be distributed in the directions of the clusters, demarcating different evolutionary stages in this massive star-forming region. A comparison of the color-magnitude diagrams of the clusters with pre-main sequence model tracks shows that the stellar population of these clusters is very young (< 3 Myr). The K_s band luminosity function (KLF) of Tr 14 shows structure at the faint end, including a sharp peak due to the onset of deuterium burning, implying an age of 1-2 Myr for the cluster. The KLF of Tr 16, in contrast, is found to rise smoothly until it turns over. The slopes of the mass functions derived for the clusters are found to be in agreement with the canonical value of the field star initial mass function derived by Salpeter.
Linear polarization maps of the Carina Nebula were obtained at 250, 350, and 500 $mu$m during the 2012 flight of the BLASTPol balloon-borne telescope. These measurements are combined with Planck 850 $mu$m data in order to produce a submillimeter spec
trum of the polarization fraction of the dust emission, averaged over the cloud. This spectrum is flat to within $pm$15% (relative to the 350 $mu$m polarization fraction). In particular, there is no evidence for a pronounced minimum of the spectrum near 350 $mu$m, as suggested by previous ground-based measurements of other molecular clouds. This result of a flat polarization spectrum in Carina is consistent with recently-published BLASTPol measurements of the Vela C molecular cloud, and also agrees with a published model for an externally-illuminated, dense molecular cloud by Bethell and collaborators. The shape of the spectrum in Carina does not show any dependence on the radiative environment of the dust, as quantified by the Planck-derived dust temperature or dust optical depth at 353 GHz.
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