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CAUP Researchers: M. S. Nanda Kumar, Jorge M. C. Grave
Team at CAUP: Origin and Evolution of Stars and Planets
Other Researchers: Saurabh Sharma (CL/IN), Christopher J. Davis (US)

H2 flows in the Corona Australis cloud and their driving sources,
Astronomy and Astrophysics, Volume 533, pp. A137 (2011)

In order to uncover the H2 flows in the Corona Australis molecular cloud and in particular identify the flows from the Coronet cluster, a deep, near-infrared H2 v=1–0 S(1), 2.122 µm line narrow band imaging survey of the R CrA cloud core was carried out. The nature of all candidate driving sources in the region was evaluated using data available from literature and also by fitting the spectral energy distributions (SED) of each source either with an extincted photosphere or YSO model. Archival Spitzer-IRAC and MIPS data was used to obtain photometry, which was combined with USNO, 2MASS catalogs and millimeter photometry from literature, to build the SEDs. We identify the best candidate driving source for each outflow by comparing the flow properties, available proper motions, and the known/estimated properties of the driving sources. We also adopted the thumbrule of outflow power being proportional to source luminosity and inversely proportional to the source age to reach a consensus. Continuum-subtracted narrow-band images reveal several new Molecular Hydrogen emission-line Objects (MHOs). Together with previously known MHOs and Herbig-Haro objects we catalogue at least 14 individual flow components of which 11 appear to be driven by the R CrA aggregate members. The flows originating from the Coronet cluster have lengths of ~0.1-0.2 pc. Eight out of nine submillimeter cores mapped in the Coronet cluster region display embedded stars driving an outflow component. Roughly 80% of the youngest objects in the Coronet are associated with outflows. The MHO flows to the west of the Coronet display lobes moving to the west and vice-versa, resulting in non-detections of the counter-lobe in our deep-imaging. We speculate that these counter-flows may be experiencing a stunting effect in penetrating the dense central core. Although this work has reduced the ambiguities for many flows in the Coronet region, one of the brightest H2 feature (MHO2014) and a few fainter features in the region remain unassociated with a clear driving source. The flows from Coronet, therefore, continue to be interesting targets for future studies.

Figure 1 | A coloured image of the region studied in this work. The colour image was obtained by coding Spitzer IRAC 4.5 μm image as red, H2 narrowband image as green and SII image[1] as blue. The SII data do not cover the lower portion of the image.

Being one of the nearest known molecular clouds, Corona Australis has been observed multiple times, at several different wavelengths, from X-rays to submillimeter. Nevertheless, for most of its numerous H2 outflows and jets, no association with a given driving source was yet possible; this is particularly the case for the densest core of Corona Australis, the so-called Coronet region, which surrounds the Herbig Ae/Be star R Corona Austrinae and its associated Coronet cluster.

In order to disentangle the complex structure of these outflows and associate them with their driving sources, this team explored the fact that an outflow power is expected to be directly proportional to the luminosity and inversely to the evolutionary stage of the star. The luminosity and age of many candidate driving sources was not previously available, therefore, these parameters had to be obtained by the team.

For this, deep narrow-band H2 imaging with the Vitor Blanco Telescope at the Cerro-Tololo Inter-American Observatory, at 2.12 and 2.2 µm were conducted; archival Spitzer Space telescope data was also used to obtain infrared photometry of the sources. With these measurements, spectral energy distribution fittings were performed for all relevant sources, yielding the most likely age and mass for each object.

This allowed the association of most outflows with a single star and showed that about 80% of stars in the Coronet cluster have associated outflows. It was also realized that, with a single exception, only one of the H2 outflow lobes of each source could be detected. Furthermore, all the outflows detected are directed away from the densest core of the Coronet region. This suggests that the outflows which encounter a dense medium don’t have enough energy to penetrate it and don’t produce enough H2 emission in order for them to be detectable. On the other hand, this also suggests that the density of the interstellar medium plays an important role in the visibility of H2 outflows, hinting that the outflowing gas is considerably less dense than the core on which they originate.

This project was planned by CAUP researcher Nanda Kumar, who also performed the data reduction and analysis and wrote the paper. Jorge Grave, also a CAUP researcher, conducted the spectral energy modeling and derived the physical parameters of the candidate driving sources.

[1] Wang, H., Mundt, R., Henning, T., & Apai, D. 2004, ApJ, 617, 1191

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