TY - JOUR
T1 - Carbon chemistry in the envelope of VY Canis Majoris
T2 - Implications for oxygen-rich evolved stars
AU - Ziurys, L. M.
AU - Tenenbaum, E. D.
AU - Pulliam, R. L.
AU - Woolf, N. J.
AU - Milam, S. N.
N1 - Funding Information:
This research is supported by NSF Grant AST-06-07803 and the NASA Astrobiology Institute under cooperative agreement CAN-02-0SS02 issued through the Office of Space Science. E.D.T. thanks the NSF for her graduate fellowship. The authors also thank the staff of the ARO for their assistance, and Eugene Lauria for his efforts in providing the new ARO 0.4 mm receiver.
Publisher Copyright:
© 2009 The American Astronomical Society. All rights reserved. Printed in the U.S.A.
PY - 2009/4/20
Y1 - 2009/4/20
N2 - Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO+ have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6→5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO+ in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H2 and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f ∼ 0.4-5 × 10-4, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f ∼ 0.9-9 × 10-6), with no obvious dependence on the mass-loss rate. In VY CMa, HCO+ is present in all three outflows with f ∼ 0.4-1.6 × 10-8 and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with [HCN]/[HNC] ∼ 150-190, while [CN]/[HCN] ∼ 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f ∼ 2-6 × 10-7. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.
AB - Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO+ have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6→5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO+ in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H2 and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f ∼ 0.4-5 × 10-4, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f ∼ 0.9-9 × 10-6), with no obvious dependence on the mass-loss rate. In VY CMa, HCO+ is present in all three outflows with f ∼ 0.4-1.6 × 10-8 and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with [HCN]/[HNC] ∼ 150-190, while [CN]/[HCN] ∼ 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f ∼ 2-6 × 10-7. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.
KW - Astrochemistry
KW - Circumstellar matter
KW - Radio lines: stars
KW - Stars: AGB and post-AGB
KW - Supergiants
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U2 - 10.1088/0004-637X/695/2/1604
DO - 10.1088/0004-637X/695/2/1604
M3 - Article
AN - SCOPUS:85007306545
SN - 0004-637X
VL - 695
SP - 1604
EP - 1613
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -