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Register a new userUnveiling the molecular environment of the ring nebula RCW 78
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C. E. Cappa
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We present a study of the ionized, neutral atomic, and molecular gas associated with the ring nebula RCW 78 around the WR star HD 117688 (= WR 55). We based our study on CO observations carried out with the SEST and NANTEN telescopes. We report the detection of molecular gas with velocities in the range -56 to -33 km/s. The CO emission is mainly connected to the western section, with a total molecular mass of 1.3 x 10^5 solar masses. The analysis of the HI gas distribution reveals the HI envelope of the molecular cloud, while the radio continuum emission shows a ring-like structure, which is the radio counterpart of the optical nebula. The gas distribution is compatible with the western section of RCW 78 having originated in the photodissociation and ionization of the molecular gas by HD 117688, and with the action of the stellar winds of the WR star. A number of infrared point sources classified as YSO candidates showed that stellar formation activity is present in the molecular gas linked to the nebula. The fact that the expansion of the bubble have triggered star formation in this region can not be discarded.
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Here we report observations of the two lowest inversion transitions of ammonia with the 70-m Tidbinbilla radio telescope. They were conducted to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate temperatures have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the timescales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SIMBA 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer GLIMPSE 8.0 $mu$m emission to separate the sample into IR-bright and IR-faint clumps, we use statistical tests to examine whether our classification shows different populations in terms of mass and temperature. We find that clump mass and column density show no significant population difference, and that kinetic temperature is the best parameter to distinguish between the gravitationally bound state of each clump. The kinetic temperature was the only parameter found to have a significantly low probability of being drawn from the same population. This suggests that clump radii does not have a large effect on the temperature of a clump, so clumps of similar radii may have different internal heating mechanisms. We also find that while the IR-bright clumps have a higher median virial mass, both samples have a similar range for both virial mass and FWHM. There are 87 per cent (40 of 46) of the clumps with masses larger than the virial mass, suggesting that they will form stars or are already undergoing star formation.
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