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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 (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 ------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 117 226 Transition List for the Compact Ridge table2.dat 117 226 Transition List for the Hot Core
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
Bytes Format Units Label Explanations
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)
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.
History: From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 13-Sep-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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