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Millimeter and sub-millimeter molecular-line observations of planetary nebula (PN) NGC 6537 (Red Spider) have been carried out using the Sub-Millimeter Telescope and the 12 m antenna of the Arizona Radio Observatory in the frequency range 86-692 GHz. CN, HCN, HNC, CCH, CS, SO, H 2 CO, HCO + and N 2 H + , along with the J = 3 → 2 and 6 → 5 lines of CO and those of several isotopologues, were detected toward the Red Spider, estimated to be ∼1600 yr old. This extremely high excitation PN evidently fosters a rich molecular environment. The presence of CS and SO suggest that sulfur may be sequestered in molecular form in such nebulae. A radiative transfer analysis of the CO and CS spectra indicate a kinetic temperature of T K ∼ 60-80 K and gas densities of n(H 2 ) ∼ 1-8 × 10 5 cm −3 in NGC 6537. Column densities of the molecules in the nebula and their fractional abundances relative to H 2 ranged from N tot ∼ 10 16 cm −2 and f ∼ 10 −4 for CO, to ∼7 × 10 11 cm −2 and f ∼ 8 × 10 −9 for the least abundant species, N 2 H + . For SO and CS, N tot ∼ 2 × 10 12 cm −2 and 10 13 cm −2 , respectively, with f ∼ 10 −7 and 2 × 10 −8 . It was also found that HCN/HNC ≈ 2. A low 12 C/ 13 C ratio of ∼4 was measured, indicative of hot-bottom burning. These results, coupled with past observations, suggest that molecular abundances in PNe are governed principally by the physical and chemical properties of the individual object and its progenitor star, rather than nebular age.

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A sensitive (1σ rms ≤ 3 mK) 1 mm spectral survey (214.5–285.5 GHz) of the oxygen-rich circumstellar envelope of the red hypergiant NML Cygni (NML Cyg) has been conducted using the Sub-millimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). Over 100 spectral lines were detected, arising from 17 different molecules, including the carbon-bearing species CO, HCN, HCO+, CN, and HNC; sulfur- and silicon-containing compounds H2S, SO, SO2, SiO, and SiS; and more exotic NaCl and AlO. The 1 mm spectrum of NML Cyg closely resembles that of VY Canis Majoris (VY CMa) suggesting that the chemistries of hypergiant stars are similar. The line profiles in NML Cyg consist of multiple velocity features, particularly evident in SO2 and SO. In addition to a spherical wind at the star’s systemic velocity, the spectra suggest an asymmetric, blueshifted component near V LSR = −21 ± 3 km s−1 and a collimated, redshifted component near 15 ± 3 km s−1, positioned ∼34° and ∼12°, respectively, from the line of sight. The red- and blueshifted flows appear to be randomly oriented, and likely trace sporadic mass loss events. Their LSR velocities align closely with those of 22 GHz water masers, suggesting an NE–SE orientation. The winds may also be associated with the asymmetric nebula in F555W HST images but extending to 5″ (∼600R *). NML Cyg appears to be another example of rare, massive stars with collimated, episodic ejections, analogous to Betelgeuse and VY CMa, lending support for an important new mass loss mechanism—surface activity.