J/ApJ/813/12 Empirical methane (CH4) line list (Hargreaves+, 2015)
Empirical line lists and absorption cross sections for methane at high
temperatures.
Hargreaves R.J., Bernath P.F., Bailey J., Dulick M.
<Astrophys. J., 813, 12 (2015)>
=2015ApJ...813...12H 2015ApJ...813...12H (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Line Profiles ; Spectra, infrared
Keywords: brown dwarfs; infrared: stars; methods: laboratory: molecular;
planets and satellites: atmospheres;
planets and satellites: composition; stars: atmospheres
Abstract:
Hot methane is found in many "cool" sub-stellar astronomical sources
including brown dwarfs and exoplanets, as well as in combustion
environments on Earth. We report on the first high-resolution
laboratory absorption spectra of hot methane at temperatures up to
1200K. Our observations are compared to the latest theoretical
spectral predictions and recent brown dwarf spectra. The expectation
that millions of weak absorption lines combine to form a continuum,
not seen at room temperature, is confirmed. Our high-resolution
transmittance spectra account for both the emission and absorption of
methane at elevated temperatures. From these spectra, we obtain an
empirical line list and continuum that is able to account for the
absorption of methane in high temperature environments at both high
and low resolution. Great advances have recently been made in the
theoretical prediction of hot methane, and our experimental
measurements highlight the progress made and the problems that still
remain.
Description:
Nine CH4 transmittance spectra have been acquired between room
temperature (i.e., 23°C) and 200°C-900°C in 100°C
intervals. For each transmittance spectrum, four individual spectra
are required to correct for the emission of CH4 and the cell. A
total of 36 spectra were acquired and the four resultant spectra at
700°C are illustrated in Figure 1. The 2600-5000/cm (2.0-3.8um)
spectral range has been covered and includes pentad and octad regions
of the CH4 infrared spectrum.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 40 194110 CH4 line list
apj520612.tar 883 192056 Empirical cross sections in HITRAN format
--------------------------------------------------------------------------------
Description of file: apj520612.tar.gz
The empirical cross sections are provided in the standard HITRAN cross section
format (Rothman et al. 2013JQSRT.130....4R 2013JQSRT.130....4R) and are available as a tar.gz
file.
The directory contains 8 files "CH4HBBD2015_T***.xsc" containing the cross
section files covering the same range as the CH4 line list (Table 3). The
"T***" gives temperature in degrees Celcius. See the ReadMe file in this
directory for more explanations.
See also:
J/MNRAS/440/1649 : ExoMol line lists for CH4 (Yurchenko+, 2014)
J/ApJ/757/46 : Hot methane (CH4) line list (Hargreaves+, 2012)
J/ApJ/735/111 : NH3 line lists at high temperatures (Hargreaves+, 2011)
J/ApJ/708/1452 : Quadratic Fij force field in l-CH4- (Senent+, 2010)
J/ApJ/637/1067 : NIR spectral classification of T dwarfs (Burgasser+, 2006)
J/other/ARA+A/43.195 : L and T dwarf stars (Kirkpatrick, 2005)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 degC T [200/900] Temperature in °C
5- 15 F11.6 cm-1 nu [2600/4884.1] Wavenumber (line position {bar}ν)
17- 25 E9.3 --- S' Line intensity in units of cm/molecule
27- 38 E12.6 cm-1 E [0/17440]? Lower state energy E" (1)
40 A1 --- QC Quality code (1=E" is the most accurate) (2)
--------------------------------------------------------------------------------
Note (1): A blank indicates a NAN value.
Note (2): A quality code (QC) is provided for each empirical lower state energy
E". Each QC is determined from F=(nR2)/9 (equation 5) where n
refers to the number of temperature spectra that the line appears
(nmax=9) and R2 is the coefficient of determination of the
empirical E" calculation. QC as follows:
1 = the lower state energies are considered the most accurate (F≥0.8),
2 = 0.8>F≥0.5
3 = the least accurate (0.5>F>0.0).
H = the line intensity and lower state energy are taken from HITRAN
(at the appropriate temperature).
See section 3 for more detail.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Feb-2016