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
[email protected]
@karllark2000
karllark@github
“Have Dust – Will Study”
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Summary
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Spectroscopic diffuse ISM extinction measurements
– Mid-IR and optical (joining UV)
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Silicate features 10 & 18 micron
– Do not correlate w/ 2175 A or R(V)
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New optical features (4370, 4870, & 6300 A)
– Two blue correlate w/ 2175 A
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NIR spectroscopic next
– IRTF SpeX data in hand
Past MIR measurements
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Selection (but representative)
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Usually high A(V) sightlines
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Spitzer program
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Two programs (PIs: Gordon & Misselt)
– IRS spectra (5-40 um)
– IRAC/IRS Blue/MIPS photometry (pesky slit losses)
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Classical pair method
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Stars with measured UV extinction curves
– Compare with UV properties
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Spectral reduction challenging
– Multiple techniques used → convergence!
Gordon, Misselt et al. 2019, goal submission
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IR
Spectra
(standards)
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IR
Spectra
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E(λ – V)
Curves
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E(lambda-V) → A(lambda)/A(V)
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Usually done via ~1.1 E(K-V)
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More accuracy needed
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Fit Pei (1992) functional form
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No Correlations(!)
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Optical Extinction
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Optical
Extinction
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Spectroscopic!
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Hubble/STIS
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R(V) dependence
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Very Broad Structure
Fitzpatrick, Massa, Gordon, et al. 2019, almost submitted
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Comparison
to Previous
(all from
photometry)
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3 Drudes + polynomial
Massa, Fitzpatrick, Gordon, et al. 2019, almost submitted
Centers: 4370, 4870, & 6300 A
Widths: ~10%
Two blue correlate w/ 2175 A
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Near-Infrared Extinction
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NIR Extinction
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Spectroscopic!
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NASA IRTF – SpeX instrument
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Spectra taken, analysis soon
– Publish before JWST launch
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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
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Thanks
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Extinction (not Attenuation)
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Extinction
– Absorption and scattering out of the line-of-sight
– Specific to a point source behind a screen of dust
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(not too near the point source)
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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