Abstract
The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau) - the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of 5 × 10-9 in VY CMa and ∞ × 10-9 in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where ∞ ∼ (0.2-2) × 10-9, although it appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T ∼ 1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells.
| Original language | English (US) |
|---|---|
| Journal | Astrophysical Journal |
| Volume | 668 |
| Issue number | 2 PART 2 |
| DOIs | |
| State | Published - 2007 |
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Keywords
- Astrochemistry
- IK Tauri
- Radio lines: stars
- Stars: chemically peculiar
- Stars: individual (VY Canis Majoris
ASJC Scopus subject areas
- Space and Planetary Science
- Astronomy and Astrophysics
Cite this
Oxygen-rich mass loss with a pinch of salt : Nacl in the circumstellar gas of ik tauri and vy canis majoris. / Milam, S. N.; Apponi, A. J.; Woolf, N. J.; Ziurys, Lucy M.
In: Astrophysical Journal, Vol. 668, No. 2 PART 2, 2007.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Oxygen-rich mass loss with a pinch of salt
T2 - Nacl in the circumstellar gas of ik tauri and vy canis majoris
AU - Milam, S. N.
AU - Apponi, A. J.
AU - Woolf, N. J.
AU - Ziurys, Lucy M
PY - 2007
Y1 - 2007
N2 - The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau) - the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of 5 × 10-9 in VY CMa and ∞ × 10-9 in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where ∞ ∼ (0.2-2) × 10-9, although it appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T ∼ 1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells.
AB - The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau) - the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of 5 × 10-9 in VY CMa and ∞ × 10-9 in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where ∞ ∼ (0.2-2) × 10-9, although it appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T ∼ 1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells.
KW - Astrochemistry
KW - IK Tauri
KW - Radio lines: stars
KW - Stars: chemically peculiar
KW - Stars: individual (VY Canis Majoris
UR - http://www.scopus.com/inward/record.url?scp=64849109625&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=64849109625&partnerID=8YFLogxK
U2 - 10.1086/522928
DO - 10.1086/522928
M3 - Article
AN - SCOPUS:64849109625
VL - 668
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2 PART 2
ER -