New Atomic Data for Astrophysics by High Resolution Fourier Transform Spectrometryl

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

1) Calibrating VUV FTS spectra from hollow cathode lamps (HCLs)

• Existing standards – Ar II lines from Learner & Thorne (1988).• Improved standards – wavelengths from laser frequency combs.

Example: High-precision wavelengths for -variation studies.

2) 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.

Outline

M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

Hollow-cathode Light Source (HCL)

To vacuumpump

High voltage~600 V at

50-1000 mA

Water cooled

Ne and/or Argas at 1-3 mbar

Glass GlassAnode Cathod

eAnode

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

Calibration Standards

Author Studying

Accuracy

Pickering et al. (2000)

Cr II, Zn II, and Ni II

0.002cm-1 at 2000Å 0.004cm-1 at 1700Å

Aldenius et al. (2006)

Zn II 0.001 to 0.002cm-1

at 2500Å

Ar II standard linesMg I and II standard linesWavenumbers 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 can sometimes change with lamp running conditions.

1obscal

[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

High-precision wavelengths for -variation studies

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.

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4

2

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2

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Newer analyses using many high-precision lab standards suggest a small reduction in as a function of time. (M. T. Murphy, 2007)

M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

New wavenumbers for two important Ti II lines

Calibrated by Ar IICalibrated by Mg I, II

Calibrated by Ar IICalibrated by Mg I, II

Uncertainty in each is a factor of 2 to 3 times smaller with the Mg I, II standards than with the Ar II standards.

M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

Experimentally measured oscillator strengths:

J. C. Pickering et al. Can J Phys 89 pp. 387 (2011)

Astrophysical spectroscopy in the IR

Spitzer Space Telescope

Apache Point Observatory

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

Sc Ti V Cr Mn Fe Co Ni Cu Zn

– 45 7 – 26 51 – 4 – 1

M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

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

2 micron sky survey (2MASS)

Sc Ti V Cr Mn Fe Co Ni Cu Zn

– 45 7 – 26 51 – 4 – 1

Theory suggests there are 13,000 strong Fe-group transitions between 1.0 and 5.0 mm wavelength (Kurucz, 1995).

FTS Branching Fraction Measurements

Wavenumber / cm-1

6000 7000 8000 9000 10000

Wavenumber / cm-1

5000 15000 20000 25000 30000

No lines in overlap region.

Intensity calibration cannot be carried through

All lines seen in a single spectrum

Most lines seen in 1st spectrum 2 lines in different region1 line in different region

Ideally, all lines from an upper level are measured in one spectrum and intensity calibrated.

More frequently, lines are spaced over 2 or more regions. Lines in overlap region(s) link intensity calibration.

42%

29%26%

3%

M. P. Ruffoni - 4th July 2011 – SPAT Seminar Series

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

/ Å log(gf) Jlower Configlower Jupper Configupper Br. Frac.

1616.5032 0.467 6.0 s (6D) 4d e7G 7.0 s (6D) 7/4f[6] 0.914

1508.0223 -0.907 6.0 s (6D) 4d e5G 7.0 s (6D) 7/4f[6] 0.044

1467.9833 -0.965 6.0 s (6D) 4d e7F 7.0 s (6D) 7/4f[6] 0.041

/ Å log(gf) Jlower Configlower Jupper Configupper Br. Frac.

1689.2364 -0.476 5.0 s 6D 4d e7G 6.0 s 6D 7/4f[5] 0.047

1617.9585 -0.269 6.0 s 6D 4d e7G 6.0 s 6D 7/4f[5] 0.083

1583.5167 0.250 5.0 s 6D 4d e7F 6.0 s 6D 7/4f[5] 0.285

199.1298 -1.252 5.0 4F 4s a5F 6.0 s 6D 7/4f[5] 0.568

M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto

Closing Remarks

Our thanks to:

G. Nave et al. (NIST) for collaboration on IR measurementsJ. Lawler et al. (U. Wisconsin) for collaboration on lifetime measurementsUK 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/FTSE-mail: m.ruffoni@imperial.ac.uk

M. P. Ruffoni - 14th July 2011 - OSA FTS Conference, Toronto