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

Context. The Carina Nebula harbors a large population of high-mass stars, including at least 75 O-type and Wolf-Rayet (WR) 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. Aims. 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 η Car. Methods. We used the integral-field spectrograph KMOS at the ESO VLT to obtain H- and K-band spectra with a resolution of R ≈ 4000 (Δλ ≈ 5 Å) for 45 out of the 47 possible OB candidate stars in Tr 16-SE, and we derived spectral types for these stars. Results. We find 15 stars in Tr 16-SE with spectral types between O5 and B2 (i.e., high-mass stars with M ≥ 8 M⊙), 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. Conclusions. Our study increases the number of spectroscopically identified high-mass stars (M ≥ 8 M⊙) 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.

On the compressive nature of turbulence driven by ionizing feedback in the pillars of the Carina Nebula

ABSTRACT The ionizing radiation of massive stars sculpts the surrounding neutral gas into pillar-like structures. Direct signatures of star formation through outflows and jets are observed in these structures, typically at their tips. Recent numerical simulations have suggested that this star formation could potentially be triggered by photoionizing radiation, driving compressive modes of turbulence in the pillars. In this study, we use recent high-resolution ALMA observations of 12CO, 13CO, and C18O, J = 2 − 1 emission to test this hypothesis for pillars in the Carina Nebula. We analyse column density and intensity-weighted velocity maps, and subtract any large-scale bulk motions in the plane of the sky to isolate the turbulent motions. We then reconstruct the dominant turbulence driving mode in the pillars, by computing the turbulence driving parameter b, characterized by the relation $\sigma _{\rho /\rho _0} = b \mathcal {M}$ between the standard deviation of the density contrast $\sigma _{\rho /\rho _0}$ (with gas density ρ and its average ρ0) and the turbulent Mach number $\mathcal {M}$. We find values of b ∼ 0.7–1.0 for most of the pillars, suggesting that predominantly compressive modes of turbulence are driven in the pillars by the ionizing radiation from nearby massive stars. We find that this range of b values can produce star formation rates in the pillars that are a factor ∼3 greater than with b ∼ 0.5, a typical average value of b for spiral-arm molecular clouds. Our results provide further evidence for the potential triggering of star formation in pillars through compressive turbulent motions.

Massive star formation in the Carina nebula complex and Gum 31. I. the Carina nebula complex

Herein, we present results from observations of the 12CO (J = 1–0), 13CO (J = 1–0), and 12CO (J = 2–1) emission lines toward the Carina nebula complex (CNC) obtained with the Mopra and NANTEN2 telescopes. We focused on massive-star-forming regions associated with the CNC including the three star clusters Tr 14, Tr 15, and Tr 16, and the isolated WR-star HD 92740. We found that the molecular clouds in the CNC are separated into mainly four clouds at velocities −27, −20, −14, and −8 km s−1. Their masses are 0.7 × 104 M⊙, 5.0 × 104 M⊙, 1.6 × 104 M⊙, and 0.7 × 104 M⊙, respectively. Most are likely associated with the star clusters, because of their high 12CO (J = 2–1)/12CO (J = 1–0) intensity ratios and their correspondence to the Spitzer 8 μm distributions. In addition, these clouds show the observational signatures of cloud–cloud collisions. In particular, there is a V-shaped structure in the position–velocity diagram and a complementary spatial distribution between the −20 km s−1 cloud and the −14 km s−1 cloud. Furthermore, we found that SiO emission, which is a tracer of a shocked molecular gas, is enhanced between the colliding clouds by using ALMA archive data. Based on these observational signatures, we propose a scenario wherein the formation of massive stars in the clusters was triggered by a collision between the two clouds. By using the path length of the collision and the assumed velocity separation, we estimate the timescale of the collision to be ∼1 Myr. This is comparable to the ages of the clusters estimated in previous studies.

Illuminating a tadpole’s metamorphosis III: quantifying past and present environmental impact

ABSTRACT We combine Multi-Unit Spectroscopic Explorer and Atacama Large Millimeter/sub-millimeter Array observations with theoretical models to evaluate how a tadpole-shaped globule located in the Carina Nebula has been influenced by its environment. This globule is now relatively small (radius ∼2500 au), hosts a protostellar jet+outflow (HH 900), and, with a blueshifted velocity of ∼10 km s−1, is travelling faster than it should be if its kinematics were set by the turbulent velocity dispersion of the precursor cloud. Its outer layers are currently still subject to heating, but comparing the internal and external pressures implies that the globule is in a post-collapse phase. Intriguingly the outflow is bent, implying that the Young Stellar Object (YSO) responsible for launching it is comoving with the globule, which requires that the star formed after the globule was up to speed since otherwise it would have been left behind. We conclude that the most likely scenario is one in which the cloud was much larger before being subject to radiatively driven implosion, which accelerated the globule to the high observed speeds under the photoevaporative rocket effect and triggered the formation of the star responsible for the outflow. The globule may now be in a quasi-steady state following collapse. Finally, the HH 900 YSO is likely ≳1 M⊙ and may be the only star forming in the globule. It may be that this process of triggered star formation has prevented the globule from fragmenting to form multiple stars (e.g. due to heating) and has produced a single higher mass star.

Illuminating a tadpole’s metamorphosis II: observing the ongoing transformation with ALMA

ABSTRACT We present new Atacama Large Millimeter/submillimeter Array observations of the tadpole, a small globule in the Carina Nebula that hosts the HH 900 jet+outflow system. Our data include 12CO, 13CO, C18O J=2–1, 13CO, C18O J=3–2, and serendipitous detections of DCN J=3–2 and CS J=7–6. With angular resolution comparable to the Hubble Space Telescope, our data reveal for the first time the bipolar molecular outflow in CO, seen only inside the globule, that is launched from the previously unseen jet-driving protostar (the HH 900 YSO). The biconical morphology joins smoothly with the externally irradiated outflow seen in ionized gas tracers outside the globule, tracing the overall morphology of a jet-driven molecular outflow. Continuum emission at the location of the HH 900 YSO appears to be slightly flattened perpendicular to outflow axis. Model fits to the continuum have a best-fitting spectral index of ∼2, suggesting cold dust and the onset of grain growth. In position–velocity space, 13CO and C18O gas kinematics trace a C-shaped morphology, similar to infall profiles seen in other sources, although the global dynamical behaviour of the gas remains unclear. Line profiles of the CO isotopologues display features consistent with externally heated gas. We estimate a globule mass of ∼1.9 M⊙, indicating a remaining lifetime of ∼4 Myr, assuming a constant photoevaporation rate. This long globule lifetime will shield the disc from external irradiation perhaps prolonging its life and enabling planet formation in regions where discs are typically rapidly destroyed.

Suzaku observation of diffuse X-ray emission from a southwest region of the Carina Nebula

A southwest region of the Carina Nebula was observed with the Suzaku observatory for $47\:$ks in 2010 December. This region shows distinctively soft X-ray emission in the Chandra campaign observations. Suzaku clearly detects the diffuse emission above known foreground and background components between 0.4–$5\:$keV at the surface brightness of $3.3\times 10^{-14}\:$erg$\:$s$^{-1}\:$arcmin$^{-2}$. The spectrum requires two plasma emission components with $kT \sim 0.2$ and $0.5\:$keV, which suffer interstellar absorption of $N_{\,\rm H} \sim 1.9 \times 10^{21}\:$cm$^{-2}$. Multiple absorption models assuming two-temperature plasmas at ionization equilibrium or non-equilibrium are tested but there is no significant difference in terms of $\chi ^{2}/$d.o.f. These plasma temperatures are similar to those of the central and eastern parts of the Carina Nebula measured in earlier Suzaku observations, but the surface brightness of the hot component is significantly lower than those of the other regions. This means that these two plasma components are physically separated and have different origins. The elemental abundances of O, Ne, and Mg with respect to Fe favor that the diffuse plasma originates from core-collapsed supernovae or massive stellar winds.