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24th of June 2020
The Circumstellar Environment and Disk of the Forming O-star AFGL 4176
by Katharine Johnston et al.
Johnston et al. present a detailed analysis of massive young stellar object (MYSO) AFGL 4176 (also known as G308.918+0.123 or IRAS 13395-6153). Using ALMA (the Atacama Large Millimeter/submillimeter Array) they detect seventeen 1.2 mm continuum sources within 5 arcseconds (21,000 Astronomical Units) of the forming O-type star AFGL 4176 mm1. They find that >87% of the 1.2 mm continuum emission from AFGL 4176 mm1 comes from dust. The nearby source mm2 may be a companion or a blueshifted knot in a jet. The ALMA spectra contain 203 lines from 25 molecules, showing that AFGL 4176 mm1 provides an example of a forming O-star with a large and chemically complex disk, which is mainly traced by nitrogen-bearing molecules. With the Australia Telescope Compact Array (ATCA), we detect a compact continuum source at 1.2 cm, associated with mm1, of which >96% is from ionized gas. The ATCA NH3(1,1) and (2,2) emission traces a large-scale rotating toroid with the disk source mm1 in the blueshifted part of this structure offset to the northwest.

The figure above shows the ATCA continuum emission toward AFGL 4176 at 24 GHz (a wavelength of 1.2 cm) shown in grayscale and black contours (with the lowest contour set at three times the image noise level of 0.2 mJy/beam). Orange contours show the ALMA 1.21 mm continuum emission. The ATCA and ALMA beams are shown in the bottom right and left corners, respectively. The inset panel shows a zoom-in of the area surrounding the forming O-star AFGL 4176 mm1. The paper has been published in the Astrophysical Journal.

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