J/AJ/170/315 Titan ESPRESSO and UVES spectra (Sithajan+, 2025)
Identification of Likely Methane Absorption Features in the Optical Spectra of
Titan.
Sithajan S., Kaewbiang L., Jones H.R.A., Rittipruk P., Meethong S.
<Astron. J. 170, 315 (2025)>
=2025AJ....170..315S 2025AJ....170..315S (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Planets ; Spectra, optical
Keywords: Exoplanet atmospheres - Planetary atmospheres - Titan - Methane -
High resolution spectroscopy - Molecular spectroscopy -
Spectral line identification - Habitable planets
Abstract:
The optical spectra of Titan reveal a rich set of absorption features,
most of which are likely associated with methane (CH4). Methane is a
key molecule in planetary and exoplanetary atmospheres, yet a
comprehensive high-resolution linelist at optical wavelengths remains
incomplete. This study identified and characterized potential CH4
absorption features in high-resolution optical spectra of Titan,
providing essential data for linelist development and improving CH4
detection and characterization. We analyzed Titan spectra from the
ESPRESSO spectrograph (R∼190000), identifying intrinsic features and
measuring their relative strengths. A conservative detection approach
was employed, slightly overestimating solar and telluric contributions
to distinguish them from Titan's intrinsic features. To assess the
impact of spectral resolution, we compared the ESPRESSO data with
Titan UVES data (R∼110000). We identified 6195 absorption features in
the ESPRESSO spectra potentially associated with CH4, of which 5436
are newly reported. ESPRESSO detected twice as many features as UVES
in overlapping regions, highlighting the advantage of
higher-resolution data. Most detected lines remained unresolved, so
our reported features are primarily blended absorption structures. We
estimated the detection limit for feature identification to correspond
to a CH4 absorption coefficient of approximately 0.02km/am.
Comparison of our results with a previous analysis of Titan UVES
spectra and with experimental CH4 data at a similar temperature
showed good agreement, while some discrepancies were observed when
compared with data acquired at a different temperature. We provide a
comprehensive list of Titan absorption features with key reliability
metrics, along with Titan's intrinsic spectra, to support future
studies.
Description:
We analyze three spectra of Titan obtained from the European Southern
Observatory (ESO) Science Archive, processed using standard ESO
pipelines. The spectra were recorded on July 21, 2021, in the Ultra
High Resolution (UHR) mode of ESPRESSO (R∼190000;
{DELTA}λ=3772-7900Å), installed on the VLT at Paranal
Observatory, Chile. Each spectrum was acquired with an exposure time
of 16 minutes. These observations were conducted under program ID
106.218L.001 (PI: Turbet, M.).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 54 6195 Identified CH4 absorption features from the
ESPRESSO data, with wavelengths provided in vacuum
tablea1.dat 28 225847 ESPRESSO Titan spectrum
tablea2.dat 20 52801 UVES Titan spectrum
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambdaE ESPRESSO Wavelength
10- 14 F5.3 0.1nm e_lambdaE ESPRESSO Wavelength error
16- 20 F5.3 --- rdepthE ESPRESSO relative strength
22- 26 F5.3 --- e_rdepthE ESPRESSO relative strength error
28- 29 I2 --- SNRE ESPRESSO SNR
31- 38 F8.3 0.1nm lambdaU ? UVES Wavelength
40- 44 F5.3 --- rdepthU ? UVES relative strength
46 A1 --- RS24 [N/Y] Matches with Rianco-Silva et al. (2024,
Planetary and Space Science, 240, 105836)
data
48 A1 --- SO95 [N/Y] Matches with Singh & O'Brien (1995,
Journal of Quantitative Spectroscopy and
Radiative Transfer, 54, 6071996 and
1996, Ap&SS, 236, 97) data
50 A1 --- CP23-KP [N/Y] Matches with Campargue et al. (2023,
Phys Chem Chem Phys, 25, 32778) Kitt Peak
(KP) data
52 A1 --- CP23-CRDS [N/Y] Matches with Campargue et al. (2023,
Phys Chem Chem Phys, 25, 32778) CRDS data
54 A1 --- STmask [N/Y] Proximity to strong stellar or
telluric lines
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda Wavelength in vacuum
10- 20 F11.3 --- RFlux Relative flux (normalized Titan spectrum with
the best-fit background removed)
22- 26 F5.3 --- e_RFlux Relative flux error
28 I1 --- Mask [0/1] Binary mask indicating whether the
corresponding wavelength is in the vicinity
of strong solar or telluric lines
(0 = yes, 1 = no)
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Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda Vacuum wavelength
10- 14 F5.3 --- RFlux Relative flux (normalized Titan spectrum with
the best-fit background removed)
16- 20 F5.3 --- e_RFlux Relative flux error
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Acknowledgements:
Sirinrat Sithajan, sirinrat(at)narit.or.th
(End) Patricia Vannier [CDS] 02-Oct-2025