J/A+A/674/A104 Automatic line selection (Kordopatis+, 2023)
Automatic line selection for abundance determination in large stellar
spectroscopic surveys.
Kordopatis G., Hill V., Lind K.
<Astron. Astrophys. 674, A104 (2023)>
=2023A&A...674A.104K 2023A&A...674A.104K (SIMBAD/NED BibCode)
ADC_Keywords: Spectroscopy
Keywords: line: identification - techniques: spectroscopic -
stars: abundances - Galaxy: abundances
Abstract:
Over the past few years, new multiplex spectrographs have emerged to
observe several millions of stars. The optimisation of these
instruments (w.r.t. their resolution or wavelength range), their
associated surveys (choice of instrumental set-up), and their
parameterisation pipelines require methods that estimate which
wavelengths (or pixels) contain useful information.
We propose a method that establishes the usefulness (purity &
detectability) of an atomic line. We show two applications: a)
optimising an instrument, by comparing the number of useful lines at a
given setup, and b) optimising the line-list for a given setup by
choosing the least blended lines detectable at different
signal-to-noise ratios.
The method compares pre-computed synthetic stellar spectra
containing all of the elements and molecules with spectra containing the
lines of specific elements alone. Then, the flux ratios between the full
spectrum and the element spectrum are computed to estimate the line
purities. The method identifies automatically
(i) the line's central wavelength,
(ii) its detectability based on its depth and a given S/N threshold and
(iii) its usefulness based on the purity ratio.
We compare the three WEAVE high-resolution setups (Blue: 404-465nm,
Green: 473-545nm, Red: 595-685nm),and find that the Green+Red setup
both allows one to measure more elements and contains more useful
lines. However, there is a disparity in terms of which elements are
detected, which we characterise. We also study the performances of
R∼20 000 and R∼6000 spectra covering the entire optical range.
Assuming a purity threshold of 60%, we find that the HR setup contains
a much wealthier selection of lines, for any of the considered
elements, whereas the LR has a "loss" of 50 to 90% of the lines even
for higher S/N.
The method provides a diagnostic of where to focus to get the most out
of a spectrograph, and is easy to implement for future instruments, or
for pipelines that require line masks.
Description:
Results obtained with the presented code for five different resolving
powers (R = 3000, 6000, 20000, 40000 and 80000) for lines that
have a purity greater than 0.4 in at least one of their wings, for the
entire wavelength range between 300nm and 1000nm. Results for other
resolving powers can be provided by contacting the first author of
this paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
r3000.dat 92 52490 Results for R=3000
r6000.dat 92 97566 Results for R=6000
r20000.dat 92 259171 Results for R=20000
r40000.dat 92 411154 Results for R=40000
r80000.dat 92 619825 Results for R=80000
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Byte-by-byte Description of file: *.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 nm ll Central wavelength of the detected line
9- 15 F7.3 nm ll-blue Detected blue-end of the line
17- 24 F8.3 nm ll-red Detected red-end of the line
26- 30 F5.3 --- max-purity Line's max purity (max of blue, red or all)
32- 36 F5.3 --- fmin Depth of the line in the elemental spectrum
38- 42 F5.3 --- fmin-sp Depth of the line in the full spectrum
44- 48 F5.3 --- purity-blue Purity of the blue wing of the line
50- 54 F5.3 --- purity-red Purity of the red wing of the line
56- 60 F5.3 --- purity Purity of the total line
62- 63 A2 --- Element Atomic element associated to the line
66 I1 --- Ion [1/2] Ionisation level of the element
68 I1 --- Channel [1/4] Nucleosynthetic channel of the
element (1)
70- 73 I4 K Teff Effective temperature of the template
75- 79 F5.3 [cm/s2] logg Surface gravity of the template
81- 86 F6.3 [-] [Fe/H] Metallicity of the template
88- 92 I5 --- R Resolving power of the template
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Note (1): Channel as follows:
1 = odd
2 = even
3 = Fe-peak
4 = n-capture
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Acknowledgements:
Georges Kordopatis, georges.kordopatis(at)oca.eu
(End) Georges Kordopatis [OCA, France], Patricia Vannier [CDS] 17-May-2023