CO, Water, and Tentative Methanol in η Carinae Approaching Periastron

April 2020 • 2020ApJ...892L..23M

Authors • Morris, Patrick W. • Charnley, Steven B. • Corcoran, Michael • Cordiner, Martin • Damineli, Augusto • Groh, Jose H. • Gull, Theodore R. • Loinard, Laurent • Madura, Thomas • Mehner, Andrea • Moffat, Anthony • Palmer, Maureen Y. • Rau, Gioia • Richardson, Noel D. • Weigelt, Gerd

Abstract • The complex circumstellar environment around the massive binary and luminous blue variable η Carinae is known to harbor numerous light molecules, emitting most strongly in rotational states with upper level energies to ∼300 K. In circumstellar gas, the complex organic molecule methanol (CH₃OH) has been found almost exclusively around young stellar objects, and thus regarded as a signpost of recent star formation. Here we report the first potential detection of methanol around a highly evolved high-mass star, while using the Atacama Large Millimeter Array to investigate molecular cloud conditions traced by CO (2-1) in an orbit phase preceding the 2020 periastron. The methanol emission originates from hot (T_gas ≃ 700 K) material, ∼2″ (0.02 pc) across, centered on the dust-obscured binary, and is accompanied by prominent absorption of continuum radiation in a cooler (T_gas ≃ 110 K) layer of gas. We also report a first detection of water in Herschel observations at 557 and 988 GHz. The methanol abundance is several to 50 times higher than observed toward several lower-mass stars, while water abundances are similar to those observed in cool, dense molecular clouds. The very high methanol:water abundance ratio in the core of η Car may suggest methanol formation processes similar to Fischer-Tropsch-type catalytic reactions on dust grains. These observations prove that complex molecule formation can occur in a chemically evolved massive stellar environment, given sufficient gas densities and shielding conditions as may occur in material around massive interacting companions and merger remnants.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020ApJ...892L..23M
• PDF https://iopscience.iop.org/article/10.3847/2041-8213/ab784a/pdf
• PDF https://stacks.iop.org/2041-8205/892/L23/pdf
• PREPRINT http://arxiv.org/abs/2002.11053
• DATA http://archives.esac.esa.int/hsa/whsa/?ACTION=PUBLICATION&ID=2020ApJ...892L..23M
• DATA https://telbib.eso.org/detail.php?bibcode=2020ApJ...892L..23M
• ELECTR https://doi.org/10.3847%2F2041-8213%2Fab784a