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Abstract The red hypergiant VY CMa is famous for its very visible record of high-mass-loss events. Recent CO observations with the Atacama Large Millimeter/submillimeter Array (ALMA) revealed three previously unknown large-scale outflows (Singh et al). In this paper, we use the CO maps to investigate the motions of a cluster of four clumps close to the star, not visible in the optical or infrared images. We present their proper motions measured from two epochs of ALMA images and determine the line-of-sight velocities of the gas in emission at the clumps. We estimate their masses and ages, or time since ejection, and conclude that all four were ejected during VY CMa’s active period in the early 20th century. Together with two additional knots observed with the Hubble Space Telescope, VY CMa experienced at least six massive outflows during a 30 yr period, with a total mass lost ≥0.07M⊙. The position–velocity map of the12CO emission reveals previously unnoticed attributes of the older outer ejecta. In a very narrow range of Doppler velocities,12CO absorption and emission causes some of this outer material to be quite opaque. At those frequencies the inner structure is hidden and we see only emission from an extended outer region. This fact produces a conspicuous but illusory dark spot if one attempts to subtract the continuum in a normal way.
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The Arizona Radio Observatory 1 mm Spectral Survey of the Hypergiant Star NML Cygni (215–285 GHz)
Abstract A sensitive (1σrms ≤ 3 mK; 2 MHz resolution) 1 mm spectral survey (214.5–285.5 GHz) of the envelope of the oxygen-rich supergiant star NML Cygni (NML Cyg) has been conducted using the 10 m Submillimeter Telescope of the Arizona Radio Observatory. These data represent the first spectral line survey of NML Cyg and are complementary to a previous 1 mm survey of the envelope of a similar hypergiant, VY Canis Majoris (VY CMa). The complete NML Cyg data set is presented here. In the survey, 104 emission lines were observed, arising from 17 different molecules and 4 unidentified features. Many of the observed features have complex line profiles, arising from asymmetric outflows characteristic of hypergiant stars. While most of the lines in the survey arise from SiO, SO, SO2, and SiS, CO had the strongest emission. Five other C-bearing species are identified in the survey (HCN, CN, HCO+, CS, and HNC), demonstrating an active carbon chemistry despite the O-rich environment. Moreover, NS was observed, but not NO, although favorable transitions of both molecules lie in the surveyed region. Sulfur chemistry appears to be prominent in NML Cyg and plays an important role in the collimated outflows. The refractory species observed, NaCl and AlO, have narrow emission lines, indicating that these molecules do not reach the terminal expansion velocity. NaCl and AlO likely condense into dust grains at r < 50R*. From NaCl, the chlorine isotope ratio was determined to be35Cl/37Cl = 3.85 ± 0.30.
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- Award ID(s):
- 1907910
- PAR ID:
- 10378363
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 164
- Issue:
- 6
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 230
- Size(s):
- Article No. 230
- Sponsoring Org:
- National Science Foundation
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