1. Wavelength Standards for IR Spectrographs at ESO Supporting high resolution spectroscopy Florian Kerber, ESO

2. F. Kerber (ESO)ESAC, March 22nd, 20072 Wavelength 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

3. F. Kerber (ESO)ESAC, March 22nd, 20073 Th-Ar hollow cathode lamp Anode Cathode Kerber et al. 2007, ASP Conf. Series. 364, p.461

4. F. Kerber (ESO)ESAC, March 22nd, 20074 Hollow 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

5. F. Kerber (ESO)ESAC, March 22nd, 20075 Th-Ar lamp:Visible and Near IR  Why Thorium ? –Nature: 232 Th - 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

6. F. Kerber (ESO)ESAC, March 22nd, 20076 CRIRES  Cryogenic High Resolution InfraRed Echelle Spectrometer (CRIRES) at VLT –950 - 5000 nm, –Resolution /  100,000 –Project to establish wavelength standards (NIST)

7. F. Kerber (ESO)ESAC, March 22nd, 20077 Th-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

8. F. Kerber (ESO)ESAC, March 22nd, 20078 Th-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 …

9. F. Kerber (ESO)ESAC, March 22nd, 20079 Visible/IR FTS at NIST

10. F. Kerber (ESO)ESAC, March 22nd, 200710 NIST Experimental Work  2-m UV/Visible/IR FTS –CaF 2 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

11. F. Kerber (ESO)ESAC, March 22nd, 200711 Th-Ar

12. F. Kerber (ESO)ESAC, March 22nd, 200712 CRIRES FTS

13. F. Kerber (ESO)ESAC, March 22nd, 200713 Th-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

14. F. Kerber (ESO)ESAC, March 22nd, 200714 Results  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

15. F. Kerber (ESO)ESAC, March 22nd, 200715 Additional Measurements Parabolic Mirror Integrating Sphere FTS Elliptical Mirror Sample Compartment At ESO

16. F. Kerber (ESO)ESAC, March 22nd, 200716 Spectrum - Operating Current

17. F. Kerber (ESO)ESAC, March 22nd, 200717 Gas Cells - Status and next Steps  CRIRES commissioning: efficient use of the N 2 O 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 N 2 O  Possible use of OCS (carbonyl sulfide) as calibrator (Q2 07) – separate gas cell or in a mixture with N 2 O  Long-term Stability of spectrum (Q4 2007)

18. F. Kerber (ESO)ESAC, March 22nd, 200718 Gas Cells - N 2 O

19. F. Kerber (ESO)ESAC, March 22nd, 200719 Summary: CRIRES Calibration Calibration Reference Data –Established Wavelength Standards Th-Ar: 950 - 2200 nm, ~5000 lines; N 2 O: 2200 - 4100 nm –Laboratory “ground truth” Accuracy few parts in 10 -8 ; ≤ 1/100 pixel Properties of Sources – Optimize use: Th-Ar - current; N 2 O - gas pressure Paradigma for wavelength calibration in near IR –very similar to the UV-visible region

20. F. Kerber (ESO)ESAC, March 22nd, 200720 Outlook 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