Optical and Mid-IR Interstellar Dust Extinction Observations

Optical and Mid-IR Interstellar Dust Extinction Observations

New measurements at spectroscopic resolution of the optical and mid-IR diffuse ISM dust extinction.

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Karl Gordon

March 04, 2019
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  1. Optical and Mid-IR Interstellar Dust Extinction Observations Near-IR for Near

    Future Karl D. Gordon STScI, Baltimore, MD USA Dusting the Universe Tucson, AZ 4 Mar 2019 ISM@ST member kgordon@stsci.edu @karllark2000 karllark@github “Have Dust – Will Study”
  2. Summary • Spectroscopic diffuse ISM extinction measurements – Mid-IR and

    optical (joining UV) • Silicate features 10 & 18 micron – Do not correlate w/ 2175 A or R(V) • New optical features (4370, 4870, & 6300 A) – Two blue correlate w/ 2175 A • NIR spectroscopic next – IRTF SpeX data in hand
  3. Why Extinction? • Pillar in constraining dust grain properties Weingartner

    & Draine (2003)
  4. Why Extinction? Jones et al. (2013)

  5. Extinction vs Attenuation Github: karllark/dust_attenuation Github: karllark/dust_extinction

  6. Extinction HowTo Github: karllark/measure_extinction

  7. Mid-Infrared Extinction

  8. Past MIR measurements • Selection (but representative) • Usually high

    A(V) sightlines
  9. Spitzer program • Two programs (PIs: Gordon & Misselt) –

    IRS spectra (5-40 um) – IRAC/IRS Blue/MIPS photometry (pesky slit losses) • Classical pair method • Stars with measured UV extinction curves – Compare with UV properties • Spectral reduction challenging – Multiple techniques used → convergence! Gordon, Misselt et al. 2019, goal submission
  10. IR Spectra (standards)

  11. IR Spectra

  12. E(λ – V) Curves

  13. E(lambda-V) → A(lambda)/A(V) • Usually done via ~1.1 E(K-V) •

    More accuracy needed • Fit Pei (1992) functional form
  14. None
  15. None
  16. None
  17. None
  18. No Correlations(!)

  19. Optical Extinction

  20. Optical Extinction • Spectroscopic! • Hubble/STIS • R(V) dependence •

    Very Broad Structure Fitzpatrick, Massa, Gordon, et al. 2019, almost submitted
  21. Comparison to Previous (all from photometry)

  22. 3 Drudes + polynomial Massa, Fitzpatrick, Gordon, et al. 2019,

    almost submitted Centers: 4370, 4870, & 6300 A Widths: ~10% Two blue correlate w/ 2175 A
  23. Near-Infrared Extinction

  24. NIR Extinction • Spectroscopic! • NASA IRTF – SpeX instrument

    • Spectra taken, analysis soon – Publish before JWST launch
  25. Summary • Spectroscopic diffuse ISM extinction measurements – Mid-IR and

    optical (joining UV) • Silicate features 10 & 18 micron – Do not correlate w/ 2175 A or R(V) • New optical features (4370, 4870, & 6300 A) – Two blue correlate w/ 2175 A • NIR spectroscopic next – IRTF SpeX data in hand
  26. Thanks

  27. Extinction (not Attenuation) • Extinction – Absorption and scattering out

    of the line-of-sight – Specific to a point source behind a screen of dust • (not too near the point source) • Attenuation includes information not present in extinction – scattering into the line-of-sight – Star/dust geometry – Applies to galaxies, regions of galaxies, stars with circumstellar dust
  28. Simple Attenuation Example