1 / 10

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.

zonta
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related