Comparative Spectra of Oxygen-Rich vs. Carbon-Rich Circumstellar Shells:
  VY Canis Majoris and IRC+10216 at 215-285 GHz
  A sensitive (1{\sigma} rms at 1 MHz resolution ~3 mK) 1 mm spectral line
survey (214.5-285.5 GHz) of VY Canis Majoris (VY CMa) and IRC+10216 has been
conducted to compare the chemistries of oxygen and carbon-rich circumstellar
envelopes. This study was carried out using the Submillimeter Telescope (SMT)
of the Arizona Radio Observatory (ARO) with a new ALMA-type receiver. This
survey is the first to chemically characterize an O-rich circumstellar shell at
millimeter wavelengths. In VY CMa, 128 emission features were detected arising
from 18 different molecules, and in IRC+10216, 720 lines were observed,
assigned to 32 different species. The 1 mm spectrum of VY CMa is dominated by
SO2 and SiS; in IRC +10216, C4H and SiC2 are the most recurrent species. Ten
molecules were common to both sources: CO, SiS, SiO, CS, CN, HCN, HNC, NaCl,
PN, and HCO+. Sulfur plays an important role in VY CMa, but
saturated/unsaturated carbon dominates the molecular content of IRC+10216,
producing CH2NH, for example. Although the molecular complexity of IRC+10216 is
greater, VY CMa supports a unique "inorganic" chemistry leading to the oxides
PO, AlO, and AlOH. Only diatomic and triatomic compounds were observed in VY
CMa, while species with 4 or more atoms are common in IRC+10216, reflecting
carbon's ability to form strong multiple bonds, unlike oxygen. In VY CMa, a new
water maser (v_2=2) has been found, as well as vibrationally-excited NaCl.
Toward IRC+10216, vibrationally-excited CCH was detected for the first time.
