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M. P. Ruffoni , J. C. Pickering, A. P. Thorne, C. Holmes, R. Blackwell-Whitehead

New Atomic Data for Astrophysics by High Resolution Fourier Transform Spectrometry l Some technical developments and future challenges. M. P. Ruffoni , J. C. Pickering, A. P. Thorne, C. Holmes, R. Blackwell-Whitehead. M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto. Outline.

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M. P. Ruffoni , J. C. Pickering, A. P. Thorne, C. Holmes, R. Blackwell-Whitehead

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  1. New Atomic Data for Astrophysics by High Resolution Fourier Transform SpectrometrylSome technical developments and future challenges M. P. Ruffoni, J. C. Pickering, A. P. Thorne, C. Holmes, R. Blackwell-Whitehead M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  2. Outline • Calibrating VUV FTS spectra from hollow cathode lamps (HCLs) • Existing standards – ArII lines from Learner & Thorne (1988). • Improved standards – wavelengths from laser frequency combs. • Example: High-precision wavelengths for -variation studies. • Challenges in measuring IR log(gf)s and branching fractions • Such numbers are in high demand by astronomers. • Intensity of all transitions from an upper level must be known. • However, large gaps between lines hinder intensity calibration. • Example: log(gf) values needed for the APOGEE project. M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  3. Hollow-cathode Light Source (HCL) High voltage ~600 V at 50-1000 mA Water cooled To vacuum pump Ne and/or Ar gas at 1-3 mbar Glass Glass Anode Cathode Anode Designed and manufactured at Imperial College based on a similar lamp in use at Lund Observatory, Sweden. M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  4. Calibration Standards • Wavenumbers calibrated through a simple linear correction. • Ar II standards recommended by Learner & Thorne (1988) are typically used. However • Recommended lines are in the visible. Overlapping spectra needed to carry calibration to the UV and VUV. • Gas line s can sometimes change with lamp running conditions. Ar II standard lines Mg I and II standard lines [a] Salumbides et al., MNRAS 373 pp. L41 (2006) [b] Batteiger et al., Phys Rev A 80 pp. 022503 (2009) [c] Hannemann et al., Phys Rev A 74 pp. 012505 (2006) M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  5. High-precision wavelengths for a-variation studies Quasars Astronomers searching for possible variations in the fine-structure constant need high-precision absorption line wavenumbers. Many studies have produced null results due to large experimental uncertainties. Dust Clouds Earth Baselines up to 10 Gyr Newer analyses using many high-precision lab standards suggest a small reduction in aas a function of time. (M. T. Murphy, 2007) M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

  6. New wavenumbers for two important Ti II lines Calibrated by Ar II Calibrated by Mg I, II Uncertainty in each s is a factor of 2 to 3 times smaller with the Mg I, II standards than with the Ar II standards. Calibrated by Ar II Calibrated by Mg I, II M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  7. Astrophysical spectroscopy in the IR • Many new IR observatories have appeared in the last decade, with more to follow. • NASA’s Spitzer space telescope • ESA’s upcoming GAIA mission • CRIRES on the Very Large Telescope • APOGEE spectrometer in the SDSS III project • APOGEE is part of the 3rd Sloane Digital Sky Survey (www.sdss3.org) • It will improve our knowledge of galactic evolution • Dust obscures visible light. Use IR wavelengths • Will measure chemical abundances of 105 stars • Needs accurate transition probabilities / log(gf)s Spitzer Space Telescope 2 micron sky survey (2MASS) Theory suggests there are 13,000 strong Fe-group transitions between 1.0 and 5.0 mm wavelength (Kurucz, 1995). Experimentally measured oscillator strengths: J. C. Pickering et al. Can J Phys 89 pp. 387 (2011) Apache Point Observatory M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

  8. FTS Branching Fraction Measurements All lines seen in a single spectrum 42% Ideally, all lines from an upper level are measured in one spectrum and intensity calibrated. S/N Ratio 29% 26% 3% 6000 7000 8000 9000 10000 Wavenumber / cm-1 Most lines seen in 1st spectrum 2 lines in different region 1 line in different region More frequently, lines are spaced over 2 or more regions. Lines in overlap region(s) link intensity calibration. S/N Ratio No lines in overlap region. Intensity calibration cannot be carried through 5000 15000 20000 25000 30000 Wavenumber / cm-1 M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

  9. H-Band lines for the APOGEE project Branches from two Fe I upper levels taken from Kurucz. Upper level: 7.0 s6D7/4f[6] Upper level: 6.0 s6D7/4f[5] Cannot use overlapping FTS spectra to span gap between IR and UV M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

  10. Closing Remarks • Our thanks to: • G. Nave et al. (NIST) for collaboration on IR measurements • J. Lawler et al. (U. Wisconsin) for collaboration on lifetime measurements • UK Science and Technology Facilities Council for funding this research • For more information: • Calibration standards: M. P. Ruffoni et al. ApJ 725 pp. 424 (2010) • Oscillator strengths: J. C. Pickering et al. Can J Phys 89 pp. 387 (2011) • Atomic spectroscopy at IC: M. P. Ruffoni et al. Proc. NASA LAW (2011) • Website: www.sp.ph.ic.ac.uk/~jpickering/FTS • E-mail: m.ruffoni@imperial.ac.uk M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

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