J/ApJ/803/97 Transitions of methyl formate toward Orion KL (Sakai+, 2015)
An ALMA imaging study of methyl formate (HCOOCH3) in torsionally excited
states toward Orion KL.
Sakai Y., Kobayashi K., Hirota T.
<Astrophys. J., 803, 97 (2015)>
=2015ApJ...803...97S 2015ApJ...803...97S (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Interstellar medium
Keywords: ISM: individual: Orion KL - ISM: molecules - line: identification -
radio lines: ISM
Abstract:
We recently reported the first identification of rotational
transitions of methyl formate (HCOOCH3) in the second torsionally
excited state toward Orion Kleinmann-Low (KL), observed with the
Nobeyama 45 m telescope. In combination with the identified
transitions of methyl formate in the ground state and the first
torsional excited state, it was found that there is a difference in
rotational temperature and vibrational temperature, where the latter
is higher. In this study, high spatial resolution analysis by using
Atacama Large Millimeter/Submillimeter Array (ALMA) science
verification data was carried out to verify and understand this
difference. Toward the Compact Ridge, two different velocity
components at 7.3 and 9.1 km/s were confirmed, while a single
component at 7.3 km/s was identified toward the Hot Core. The
intensity maps in the ground, first, and second torsional excited
states have quite similar distributions. Using extensive ALMA data, we
determined the rotational and vibrational temperatures for the Compact
Ridge and Hot Core by the conventional rotation diagram method. The
rotational temperature and vibrational temperatures agree for the Hot
Core and for one component of the Compact Ridge. At the 7.3 km/s
velocity component for the Compact Ridge, the rotational temperature
was found to be higher than the vibrational temperature. This is
different from what we obtained from the results by using the
single-dish observation. The difference might be explained by the beam
dilution effect of the single-dish data and/or the smaller number of
observed transitions within the limited range of energy levels (≤30 K)
of Eu in the previous study.
Description:
The public spectral line survey data, ALMA SV toward the Orion KL, was
used in this study. The band 6 (215-245 GHz) covers the 1 mm wavelength
region. The tracking center position of Orion KL was set to be
RA=05h35m14.35s and DE=-05°22'35.0" (J2000). The data consist of 20
spectral settings and the net on-source time for each setting was about
20 minutes. The baseline lengths ranged from 17 to 265 m and consisted of
16x12 m antennas. The primary beam size of each 12 m antenna is about
30" at band 6. The spectral resolution of the ALMA correlator was 488 kHz,
which corresponds to the velocity resolution of 0.60-0.65 km/s at the
observed frequency range. The data were analyzed by using the Common
Astronomy Software Applications package. The natural-weighted beam size
was 1.7"x1.4" with a position angle of 171°.
Objects:
-------------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------------
05 35 14.16 -05 22 21.5 Orion KL = NAME Orion-KL
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 117 226 Transition List for the Compact Ridge
table2.dat 117 226 Transition List for the Hot Core
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See also:
J/A+A/532/A32 : HCOOCH3 map of Orion-KL (Favre+, 2011)
J/ApJS/205/9 : Rotational transition frequencies of HCOOCH3
(Kobayashi+, 2013)
J/ApJS/215/25 : Methyl formate (HCOOCH3) observations (Favre+, 2014)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 10 F10.3 MHz Freq The rest frequency of methyl formate
12 I1 --- vt [0/2] Quantum number of the torsional state
14- 15 I2 --- J' [6/39] Rotational quantum number of the lower
state
17- 18 I2 --- Ka' [0/17] Lower Ka quantum number
20- 21 I2 --- Kc' [0/32] Lower Kc quantum number
23- 24 I2 --- J" [5/39] Rotational quantum number of the upper
state
26- 27 I2 --- Ka" [0/17] Upper Ka quantum number
29- 30 I2 --- Kc" [0/33] Upper Kc quantum number
32 A1 --- Sym [AE] Symmetry sublevel
34- 37 F4.1 D+2 Smu2 Line strength, Sµ2
39- 43 F5.1 K Eu Upper level energy
45- 49 F5.2 K T7.3 ? Temperature (1)
51- 54 F4.2 km/s FWHM7.3 ? FWHM (1)
56- 59 F4.2 km/s VLSR7.3 ? Local Standard of Rest velocity (1)
61- 66 F6.2 km/s W7.3 ? W component of the velocity (1)
68- 72 F5.2 K T9.1 ? Temperature (2)
74- 77 F4.2 km/s FWHM9.1 ? FWHM (2)
79- 82 F4.2 km/s VLSR9.1 ? Local Standard of Rest velocity (2)
84- 89 F6.2 km/s W9.1 ? W component of the velocity (2)
91- 95 F5.2 K T ? Temperature (3)
97-100 F4.2 km/s FWHM ? FWHM (3)
102-105 F4.2 km/s VLSR ? Local Standard of Rest velocity (3)
107-112 F6.2 km/s W ? W component of the velocity (3)
114-115 A2 --- Com Comment (4)
117 A1 --- Diag [*-] Diagram (5)
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Note (1): Compact Ridge 7.3 km/s component.
Note (2): Compact Ridge 9.1 km/s component.
Note (3): Hot Core component.
Note (4): Comment as follows:
B = Blend. Apparently, contamination by other species was acknowledged. In
the case of the Compact Ridge, two velocity components centered at
7.3 km/s and 9.1 km/s are identified. If either component is
contaminated, the transition was considered to be a blended line. Some of
the severely blended lines were excluded when extracting intensity
information;
NB = Not blended. When the intensity of the contaminated line is weaker than
about 10% of the methyl formate line, it was considered to be no blend;
ND = Not detected.
Note (5): An asterisk indicates that the optically thin line was used in the
rotation diagram analysis.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 13-Sep-2017