Abstract
Several millimeter-wave transitions of HCO+ have been detected toward comet Hale-Bopp (C/1995 O1) using the Arizona Radio Observatory 12 m telescope. The J = 2 → 1 transition at 178 GHz was observed toward the comet nucleus near perihelion on 1997 March 10 and 20, as well as the J = 3 → 2 transition at 268 GHz on 1997 March 9, with angular resolutions of 36″ and 23″, respectively. These data all show a slight velocity shift (∼1.2 km s-1) from the nominal comet velocity, and the J = 3 → 2 profile is asymmetric with a redshifted wing. These differences likely arise from ion acceleration by the solar wind. A rotational diagram analysis of the data yielded a column density of 1.1 × 1012 cm-2 for HCO+ in Hale-Bopp, which corresponds to an average number density of 36 cm-3. The data taken on March 9 show a second velocity component redshifted by 7.0 ± 0.6 km s-1, which is considerably weaker than the main feature and appears to have a counterpart in the HNC, J = 3 → 2 data, observed within an hour of the HCO+ measurements. The velocity difference between the main and secondary emission lines deprojected onto the extended solar radius vector is ∼10 km s-1 for both HCO+ and HNC, and the weak-to-strong line intensity ratios (∼5%) are identical to within observational errors, suggesting a common high-velocity volatile secondary source. A plausible model that may account for the redshifted velocity components is a comoving, localized debris field of submicron refractory grains accelerated by solar radiation pressure located ∼105-10 6 km from the nucleus. The parent material of the weaker redshifted HNC and HCO+ lines may be predominately complex organic polymers. An examination of the production rates for HCO+ suggests that the reaction H2 + CO+ is likely to be an important route to this ion in the outer coma beyond the collisionopause, where it has its peak abundance.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1054-1062 |
| Number of pages | 9 |
| Journal | Astrophysical Journal |
| Volume | 615 |
| Issue number | 2 I |
| DOIs | |
| State | Published - Nov 10 2004 |
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Keywords
- Astrochemistry
- Comets: individual (Hale-Bopp (C/1995 O1))
- Line: profiles
- Molecular data
- Radio lines: solar system
- Solar wind
ASJC Scopus subject areas
- Space and Planetary Science
Cite this
HCO+ observations toward comet Hale-Bopp (C/1995 O1) : Ion-molecule chemistry and evidence for a volatile secondary source. / Milam, S. N.; Savage, C.; Ziurys, Lucy M; Wyckoff, S.
In: Astrophysical Journal, Vol. 615, No. 2 I, 10.11.2004, p. 1054-1062.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - HCO+ observations toward comet Hale-Bopp (C/1995 O1)
T2 - Ion-molecule chemistry and evidence for a volatile secondary source
AU - Milam, S. N.
AU - Savage, C.
AU - Ziurys, Lucy M
AU - Wyckoff, S.
PY - 2004/11/10
Y1 - 2004/11/10
N2 - Several millimeter-wave transitions of HCO+ have been detected toward comet Hale-Bopp (C/1995 O1) using the Arizona Radio Observatory 12 m telescope. The J = 2 → 1 transition at 178 GHz was observed toward the comet nucleus near perihelion on 1997 March 10 and 20, as well as the J = 3 → 2 transition at 268 GHz on 1997 March 9, with angular resolutions of 36″ and 23″, respectively. These data all show a slight velocity shift (∼1.2 km s-1) from the nominal comet velocity, and the J = 3 → 2 profile is asymmetric with a redshifted wing. These differences likely arise from ion acceleration by the solar wind. A rotational diagram analysis of the data yielded a column density of 1.1 × 1012 cm-2 for HCO+ in Hale-Bopp, which corresponds to an average number density of 36 cm-3. The data taken on March 9 show a second velocity component redshifted by 7.0 ± 0.6 km s-1, which is considerably weaker than the main feature and appears to have a counterpart in the HNC, J = 3 → 2 data, observed within an hour of the HCO+ measurements. The velocity difference between the main and secondary emission lines deprojected onto the extended solar radius vector is ∼10 km s-1 for both HCO+ and HNC, and the weak-to-strong line intensity ratios (∼5%) are identical to within observational errors, suggesting a common high-velocity volatile secondary source. A plausible model that may account for the redshifted velocity components is a comoving, localized debris field of submicron refractory grains accelerated by solar radiation pressure located ∼105-10 6 km from the nucleus. The parent material of the weaker redshifted HNC and HCO+ lines may be predominately complex organic polymers. An examination of the production rates for HCO+ suggests that the reaction H2 + CO+ is likely to be an important route to this ion in the outer coma beyond the collisionopause, where it has its peak abundance.
AB - Several millimeter-wave transitions of HCO+ have been detected toward comet Hale-Bopp (C/1995 O1) using the Arizona Radio Observatory 12 m telescope. The J = 2 → 1 transition at 178 GHz was observed toward the comet nucleus near perihelion on 1997 March 10 and 20, as well as the J = 3 → 2 transition at 268 GHz on 1997 March 9, with angular resolutions of 36″ and 23″, respectively. These data all show a slight velocity shift (∼1.2 km s-1) from the nominal comet velocity, and the J = 3 → 2 profile is asymmetric with a redshifted wing. These differences likely arise from ion acceleration by the solar wind. A rotational diagram analysis of the data yielded a column density of 1.1 × 1012 cm-2 for HCO+ in Hale-Bopp, which corresponds to an average number density of 36 cm-3. The data taken on March 9 show a second velocity component redshifted by 7.0 ± 0.6 km s-1, which is considerably weaker than the main feature and appears to have a counterpart in the HNC, J = 3 → 2 data, observed within an hour of the HCO+ measurements. The velocity difference between the main and secondary emission lines deprojected onto the extended solar radius vector is ∼10 km s-1 for both HCO+ and HNC, and the weak-to-strong line intensity ratios (∼5%) are identical to within observational errors, suggesting a common high-velocity volatile secondary source. A plausible model that may account for the redshifted velocity components is a comoving, localized debris field of submicron refractory grains accelerated by solar radiation pressure located ∼105-10 6 km from the nucleus. The parent material of the weaker redshifted HNC and HCO+ lines may be predominately complex organic polymers. An examination of the production rates for HCO+ suggests that the reaction H2 + CO+ is likely to be an important route to this ion in the outer coma beyond the collisionopause, where it has its peak abundance.
KW - Astrochemistry
KW - Comets: individual (Hale-Bopp (C/1995 O1))
KW - Line: profiles
KW - Molecular data
KW - Radio lines: solar system
KW - Solar wind
UR - http://www.scopus.com/inward/record.url?scp=11144276031&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=11144276031&partnerID=8YFLogxK
U2 - 10.1086/424701
DO - 10.1086/424701
M3 - Article
AN - SCOPUS:11144276031
VL - 615
SP - 1054
EP - 1062
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2 I
ER -