J/AJ/156/68 Comet C/2017 E4 composition with iSHELL at NASA/IRTF (Faggi+, 2018)
The volatile composition of comet C/2017 E4 (Lovejoy) before its disruption, as
revealed by high-resolution infrared spectroscopy with iSHELL at the NASA/IRTF.
Faggi S., Villanueva G.L., Mumma M.J., Paganini L.
<Astron. J., 156, 68 (2018)>
=2018AJ....156...68F 2018AJ....156...68F (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Comets ; Molecular data ; Spectra, infrared
Keywords: astrobiology - comets: individual (C/2017 E4 (Lovejoy)) -
infrared: general - molecular data - planetary systems -
techniques: spectroscopic
Abstract:
In 2017 April, we acquired comprehensive high-resolution spectra of
newly discovered comet C/2017 E4 (Lovejoy) as it approached perihelion,
and before its disintegration. We detected many cometary emission lines
in the range (2.8-5.3) µm, in four customized instrument settings
(L1-c, L3, Lp1-c, and M1) of iSHELL - the new near-IR high-resolution
immersion echelle spectrograph at NASA/IRTF (Maunakea, Hawaii). We
identified 12 molecular species: nine primary volatiles (H2O, HCN,
NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO) and three product
species (CN, NH2, OH). We detected 85 H2O emission lines from 12 water
vibrational bands across L1-c and M1 settings. The many detected water
emission lines enabled retrieval of accurate measures for ortho- and
para-H2O independently, thereby reducing systematic uncertainty in the
derived ortho-para ratio and nuclear spin temperature. Excitation
analyses and emission profile analyses were performed for all species,
and molecular abundance ratios relative to water are compared with
values found for other Oort Cloud comets in our infrared database.
Abundance ratios are consistent for most species, with the exception
of underabundant methanol and overabundant ammonia in E4.
Description:
Comet C/2017 E4 (Lovejoy), hereafter E4 (Lovejoy), was discovered on
2017 March 9 by Terry Lovejoy (Queensland, Australia) when the comet was
at ∼1 au from the Sun and it had a magnitude Mv∼15. This comet reached
perihelion on 2017 April 23 at 0.49 au and its closest approach to Earth
was on March 30 at 0.508 au.
We observed comet E4 (Lovejoy) for about 2.5 hr with iSHELL, the new
long-slit near-infrared high-resolution immersion echelle spectrograph,
a few months after its commissioning. iSHELL covers the wavelength range
of (1.1-5.3) µm with a resolving power of about
λ/Δλ=70000 when using a slit width of 0.375 arcsec
(3 pixels wide, considering plate scale of the 0.125 arcsec/pixel).
The instrument offers six different cross-dispersing gratings that allow
the observer to select specific wavelength ranges within the full range.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 37 59 Mean flux calibration factors
table4.dat 131 214 Detected individual emission lines of volatile
species in C/2017 E4 (Lovejoy)
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See also:
B/comets : Database of the orbital elements of comets (Rocher, 2007)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Set Instrument setting (G1)
7- 9 I3 --- Order [18/184] Order number per each setting
11- 19 F9.4 cm-1 Freq [1933.8252/3534.9645] Mean frequency across
the orders
21- 31 E11.4 W/m2.cm/ct/s Gamma [1.1642e-17/2.7809e-17] Mean Γ
calibration factor per order (1)
33- 37 F5.2 % Through [4.38/10.63] Throughputs of individuals
orders
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Note (1): In units of W/m2/cm-1/ADU/s.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Mol Molecule name
18- 25 A8 --- ID Molecular identifier
27- 28 I2 K Trot [75/81] Rotational temperature
30- 31 I2 K e_Trot [3/11]? Uncertainty in Trot
33- 36 E4.1 --- Multi [1e-08/1e-05] g-factor multiplier;
e.g. g-fac*Multi
38- 40 A3 --- Set iSHELL/IRTF setting (G1)
42- 43 I2 --- f_Set [1/12] Flag on Set giving the orders (1)
45- 74 A30 --- Trans Transition quantum numbers; up-low
76- 84 F9.4 cm-1 Freq [1949.8073/3539.52]? Mean frequency
86- 93 F8.4 10-19W/m2 Flux [0.06/112.59]? Flux of the cometary line at
top of the Earth atmosphere
95-101 F7.5 10-19W/m2 e_Flux [0.28/8.2182]? Uncertainty in Flux
103-109 F7.3 ph/s/mol g-fac [0.361/207.5]? Molecular g-factor
(fluorescence efficiency)
111-117 F7.3 cm-1 Erot [0/607.61]? Rotational energy
119-131 F13.11 --- Transm [0.1111/0.9963]? Atmospheric transmittance at
the Doppler-shifted position of the cometary
line
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Note (1): Flag as follows:
1 = Orders 172, 173, 174, 175, 176, 177, 178, 181, 182, 183, 184;
2 = Orders 101, 102, 103, 104, 105, 108, 109, 111, 112, 113;
3 = Orders 147, 148, 154, 155;
4 = Order 155;
5 = Orders 170, 171, 172, 173;
6 = Orders 175, 176;
7 = Orders 143, 144, 145, 147;
8 = Orders 169, 170, 171;
9 = Orders 154, 155;
10 = Orders 154, 155;
11 = Orders 157, 158, 159;
12 = Orders 109, 110, 111, 112.
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Global notes:
Note (G1): We used four different iSHELL settings (Figure 2):
L1 = Covering 2.81-3.11 µm;
L1-c = Customized at upper wavelength 3.11 µm and covering
2.81-3.11 µm;
L3 = Covering 3.20-3.48 µm;
Lp1 = Covering 3.33-3.71 µm;
Lp1-c = Customized at upper wavelength 3.71 µm and covering
3.33-3.71 µm;
M1 = Covering 4.52-5.25 µm.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 05-Feb-2019