Exotic metal molecules in oxygen-rich envelopes: Detection of ALOH (X 1Σ+) in VY Canis Majoris

E. D. Tenenbaum, L. M. Ziurys

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79 Scopus citations


A new interstellar molecule, AlOH, has been detected toward the envelope of VY Canis Majoris (VY CMa), an oxygen-rich red supergiant. Three rotational transitions of AlOH were observed using the facilities of the Arizona Radio Observatory (ARO). The J = 9 → 8 and J = 7 → 6 lines at 1mm were measured with the ARO Submillimeter Telescope, while the J = 5 → 4 transition at 2mm was observed with the ARO 12m antenna on Kitt Peak. The AlOH spectra exhibit quite narrow line widths of 16-23kms-1, as found for NaCl in this source, indicating that the emission arises from within the dust acceleration zone of the central circumstellar outflow. From a radiative transfer analysis, the abundance of AlOH relative to H2 was found to be 1 × 10-7 for a source size of 0.26″ or 22 R * . In contrast, AlCl was not detected with f ≤ 5 × 10-8. AlOH is likely formed just beyond the photosphere via thermodynamic equilibrium chemistry and then disappears due to dust condensation. The AlOH/AlO abundance ratio found in VY CMa is 17. Therefore, AlOH appears to be the dominant gas-phase molecular carrier of aluminum in this oxygen-rich shell. Local thermodynamic equilibrium calculations predict that the monohydroxides should be the major carriers of Al, Ca, and Mg in O-rich envelopes, as opposed to the oxides or halides. The apparent predominance of aluminum-bearing molecules in VY CMa may reflect proton addition processes in H-shell burning.

Original languageEnglish (US)
Pages (from-to)L93-L97
JournalAstrophysical Journal Letters
Issue number1 PART 2
StatePublished - 2010


  • Astrochemistry
  • Circumstellar matter
  • ISM: molecules
  • Radio lines: stars
  • Stars: individual (VY CMa)
  • Supergiants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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