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![Page 1: Wavelength Standards for IR Spectrographs at ESO Supporting high resolution spectroscopy Florian Kerber, ESO.](https://reader030.fdocuments.us/reader030/viewer/2022032707/56649e205503460f94b0c547/html5/thumbnails/1.jpg)
Wavelength Standards for IR Wavelength Standards for IR Spectrographs at ESOSpectrographs at ESO
Supporting high resolution spectroscopy
Florian Kerber, ESO
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F. Kerber (ESO) ESAC, March 22nd, 2007 2
Wavelength Calibration - Near IRWavelength Calibration - Near IR
Night Sky OH Meinel Bands (Abrams et al., 1994; Rousselot et al. 2000)– Present on science exposure
– Number of lines at given wavelength and resolution
– Variability
– Stability at high resolution ? (< 25 m s-1)
Lack of good sources – Lamps - Ne, Kr– Gas cells
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F. Kerber (ESO) ESAC, March 22nd, 2007 3
Th-Ar hollow cathode lampTh-Ar hollow cathode lamp
Anode
Cathode
Kerber et al. 2007, ASP Conf. Series. 364, p.461
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F. Kerber (ESO) ESAC, March 22nd, 2007 4
Hollow cathode lampHollow cathode lamp
Introduced by Paschen (1916) – Study of hyperfine structure
Atomic Absorption (AA) Spectroscopy (Walsh 1950s)– Lifetime - Getter– Quantitative chemical analysis– Great variety of materials– Mass production for commercial market
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F. Kerber (ESO) ESAC, March 22nd, 2007 5
Th-Ar lamp:Visible and Near IRTh-Ar lamp:Visible and Near IR
Why Thorium ?– Nature: 232Th - no isotope splitting – zero nuclear spin - no hyperfine structure
Established standard source in Visual– Palmer & Engleman (1983) 278 - 1000 nm– FEROS, FLAMES, HARPS, UVES, X-shooter
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F. Kerber (ESO) ESAC, March 22nd, 2007 6
CRIRESCRIRES
Cryogenic High Resolution InfraRed Echelle Spectrometer (CRIRES) at VLT– 950 - 5000 nm, – Resolution / 100,000– Project to establish
wavelength standards (NIST)
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F. Kerber (ESO) ESAC, March 22nd, 2007 7
Th-Ar Lamp ProjectTh-Ar Lamp Project
Physical Modelling Group (ESO INS)– F. Kerber, P. Bristow
NIST Atomic Spectroscopy Group– J. Reader, G. Nave, C.J. Sansonetti
Space Telescope European Coordinating Facility (ST-ECF)– M.R. Rosa
ESO La Silla-Paranal Observatory– G. Lo Curto
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F. Kerber (ESO) ESAC, March 22nd, 2007 8
Th-Ar lamp:Visible and Near IRTh-Ar lamp:Visible and Near IR
Th-Ar is work in progress for near-IR – Hinkle et al. (2001), 1000 - 2500 nm, 500 lines
• Gaps in wavelength coverage• FTS and grating spectrometer data
– Engleman et al. (2003), 1000 - 5000 nm, > 5000 lines
• High current source, rich Th spectrum• Differences in spectrum but …
![Page 9: Wavelength Standards for IR Spectrographs at ESO Supporting high resolution spectroscopy Florian Kerber, ESO.](https://reader030.fdocuments.us/reader030/viewer/2022032707/56649e205503460f94b0c547/html5/thumbnails/9.jpg)
F. Kerber (ESO) ESAC, March 22nd, 2007 9
Visible/IR FTS at NISTVisible/IR FTS at NIST
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F. Kerber (ESO) ESAC, March 22nd, 2007 10
NIST Experimental WorkNIST Experimental Work
2-m UV/Visible/IR FTS – CaF2 beamsplitter, silver coated mirrors, InSb detectors
Two different settings optimized for wavelength– 800 - 2000 nm, resolution 0.01 cm-1
– > 2000 nm, resolution 0.005 cm-1
Data acquisition times: up to 20 hours Radiometric standard lamp
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F. Kerber (ESO) ESAC, March 22nd, 2007 11
Th-Ar
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F. Kerber (ESO) ESAC, March 22nd, 2007 12
CRIRES
FTS
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F. Kerber (ESO) ESAC, March 22nd, 2007 13
Th-Ar at NIST: ResultsTh-Ar at NIST: Results
Total ~2500 lines between 750 nm and 4800 nm – accuracy ~ 0.001 cm-1 for strong lines
Absolute accuracy in wavelength: ~1.4 x 10-8 – calibration using laser measurements of Th lines
(DeGraffenreid & Sansonetti 2002) – 5 x 10-8 1/100 of a pixel in CRIRES
Engleman et al. (2003) and our work agree:– Th: (6 ± 2) x 10-9 (weighted mean)– Ar: (-2 ± 0.2) x 10-8
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F. Kerber (ESO) ESAC, March 22nd, 2007 14
ResultsResults
The absolute accuracy in wavelength is about 1.4 10-8 – calibration using laser measurements of Th lines (DeGraffenreid &
Sansonetti 2002, JOSA, B19, 1715) Engleman et al (2003) and our work agree:
– Th: 6 x 10-9 (weighted mean)
– Ar: 2 x 10-8
CRIRES wavelength calibration: 5 x 10-8 corresponds to ~1/100 of a pixel
Th-Ar lamp is able to support CRIRES science
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F. Kerber (ESO) ESAC, March 22nd, 2007 15
Additional MeasurementsAdditional Measurements
Parabolic Mirror
Integrating Sphere
FTS
Elliptical Mirror
Sample Compartment
At ESO
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F. Kerber (ESO) ESAC, March 22nd, 2007 16
Spectrum - Operating CurrentSpectrum - Operating Current
0
1
2
3
4
5
6
7
8
2 6 10 14 18 22
Lamp operating current [mA]
Intensity [normalised to 10 mA]
ArgonThorium
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F. Kerber (ESO) ESAC, March 22nd, 2007 17
Gas Cells - Status and next StepsGas Cells - Status and next Steps
CRIRES commissioning: efficient use of the N2O gas cells (l=18 cm) as calibration source: ~2200 - 4100 nm
primary calibration molecule from Heterodyne frequency measurements at NIST (Maki & Wells)– Fundamental mode: 523 – 2845 cm -1 (1912 – 3515 nm)
Characterize spectrum of the CRIRES gas cell (P,T) Q2 2007– optimal choice of fill gas pressure - measurements using ESO’s FTS
Wavelength Standards for first overtone transitions of N2O Possible use of OCS (carbonyl sulfide) as calibrator (Q2 07)
– separate gas cell or in a mixture with N2O Long-term Stability of spectrum (Q4 2007)
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F. Kerber (ESO) ESAC, March 22nd, 2007 18
Gas Cells - NGas Cells - N22O O
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F. Kerber (ESO) ESAC, March 22nd, 2007 19
Summary: CRIRES Calibration Summary: CRIRES Calibration
• Calibration Reference Data– Established Wavelength Standards
Th-Ar: 950 - 2200 nm, ~5000 lines; N2O: 2200 - 4100 nm– Laboratory “ground truth” Accuracy few
parts in 10-8; ≤ 1/100 pixel
• Properties of Sources– Optimize use: Th-Ar - current; N2O - gas pressure
• Paradigma for wavelength calibration in near IR– very similar to the UV-visible region
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F. Kerber (ESO) ESAC, March 22nd, 2007 20
OutlookOutlook
• CRIRES Science Verification: – Nissen et al. astro-ph/0702689: Sulphur abundances
• CRIRES operational: April 1st, 2007– ESO archive
• Spectral Data Model - Simple Line Access Protocol• Publish IR data set for Th: VOTable - metadata
– Q2/Q3 2007– linking astronomical and atomic physics communities