| 24th of June 2020 |
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| The Circumstellar Environment and Disk of the Forming O-star AFGL 4176 |
| by Katharine Johnston et al. |
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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. |