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Abstract The red hypergiant VY CMa is remarkable for its very visible record of high-mass-loss events observed over the range of wavelengths from the optical and infrared to the submillimeter region with Atacama Large Millimeter/submillimeter Array (ALMA). The SW Clump or SW knots are unique in the ejecta of VY CMa. Except for the central star, they are the brightest sources of dusty infrared emission in its complex ejecta. In this paper we combine the proper motions from the Hubble Space Telescope images, and infrared fluxes from 2 to 12μm with the¹²CO images from ALMA to determine their ages and mass estimates. The SW knots were ejected more than 200 yr ago with an active period lasting about 30 yr, and with a total mass in the Clump > 2 × 10⁻²M_⊙. 

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. 

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. 

Abstract The millimeter-wave spectrum of the SiP radical (X²Π_i) has been measured in the laboratory for the first time using direct-absorption methods. SiP was created by the reaction of phosphorus vapor and SiH₄in argon in an AC discharge. Fifteen rotational transitions (J+ 1 ←J) were measured for SiP in the Ω = 3/2 ladder in the frequency range 151–533 GHz, and rotational, lambda doubling, and phosphorus hyperfine constants determined. Based on the laboratory measurements, SiP was detected in the circumstellar shell of IRC+10216, using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1 mm and 2 mm, respectively. Eight transitions of SiP were searched: four were completely obscured by stronger features, two were uncontaminated (J= 13.5 → 12.5 and 16.5 → 15.5), and two were partially blended with other lines (J= 8.5 → 7.5 and 17.5 → 16.5). The SiP line profiles were broader than expected for IRC+10216, consistent with the hyperfine splitting. From non-LTE radiative transfer modeling, SiP was found to have a shell distribution with a radius ∼300R_*, and an abundance, relative to H₂, off∼ 2 × 10⁻⁹. From additional modeling, abundances of 7 × 10⁻⁹and 9 × 10⁻¹⁰were determined for CP and PN, respectively, both located in shells at 550–650R_*. SiP may be formed from grain destruction, which liberates both phosphorus and silicon into the gas phase, and then is channeled into other P-bearing molecules such as PN and CP.