J/ApJ/895/38 MIR extinction toward Cyg OB2-12 ISM (Hensley+, 2020)
Detection of PAH Absorption and Determination of the Mid-infrared Diffuse
Interstellar Extinction Curve from the Sight Line toward Cyg OB2-12.
Hensley B.S., Draine B.T.
<Astrophys. J., 895, 38 (2020)>
=2020ApJ...895...38H 2020ApJ...895...38H
ADC_Keywords: Stars, supergiant; Stars, blue; Interstellar medium;
Spectra, infrared; Extinction
Keywords: Interstellar dust ; Carbonaceous grains ;
Polycyclic aromatic hydrocarbons ; Silicate grains ; Stellar winds ;
Interstellar dust extinction
Abstract:
The sight line toward the luminous blue hypergiant CygOB2-12 is widely
used to study interstellar dust on account of its large extinction
(AV∼10mag) and the fact that this extinction appears to be dominated
by dust typical of the diffuse interstellar medium. We present a new
analysis of archival Infrared Space Observatory Short Wavelength
Spectrometer and Spitzer IRS observations of CygOB2-12 using a model
of the emission from the star and its stellar wind to determine the
total extinction Aλ from 2.4 to 37µm. In addition to the
prominent 9.7 and 18µm silicate features, we robustly detect
absorption features associated with polycyclic aromatic hydrocarbons,
including the first identification of the 7.7µm feature in
absorption. The 3.3µm aromatic feature is found to be much broader
in absorption than is typically seen in emission. The 3.4 and
6.85µm aliphatic hydrocarbon features are observed with relative
strengths that are consistent with observations of these features on
sight lines toward the Galactic center. We identify and characterize
more than 60 spectral lines in this wavelength range, which may be
useful in constraining models of the star and its stellar wind. Based
on this analysis, we present an extinction curve
Aλ/A2.2µm that extrapolates smoothly to determinations
of the mean Galactic extinction curve at shorter wavelengths and to
dust opacities inferred from emission at longer wavelengths, providing
a new constraint on models of interstellar dust in the mid-infrared.
Description:
CygOB2-12 is one of 159 stars that compose the Spitzer Atlas of
Stellar Spectra (SASS), a set of prototype stellar spectra taken by
the Spitzer Infrared Spectrograph (IRS) that have been reduced in a
homogeneous way. The SASS CygOB2-12 spectrum is a synthesis of two
observations, one in 2004 October (AOR9834496) and the other in 2008
August (AOR27570176), that include data from both the Short-Low and
Long-Low modules. Together, these provide full spectral coverage from
5.2 to 35µm.
With its high signal-to-noise ratio and spectral resolution, the
Spitzer IRS spectrum of Cyg OB2-12 provides perhaps the most detailed
characterization of MIR extinction from the diffuse interstellar
medium (ISM) of any current data. We therefore propose using these
data to extend determinations of the mean Galactic extinction curve
into the MIR and even FIR.
Objects:
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RA (2000) DE Designation(s)
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20 32 40.96 +41 14 29.3 Cyg OB2-12 = Schulte 12
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig5.dat 23 10000 Mid-IR extinction curve of the diffuse ISM based
on the sightline toward Cyg OB2-12
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/333/231 : O-M stars model atmospheres (Bessell+ 1998)
J/A+A/400/903 : The ISOGAL field FC-01863+00035 (Jiang+, 2003)
J/AZh/81/1104 : Optical spectrum of Cyg OB2 No. 12 (Klochkova+, 2004)
J/ApJ/656/770 : Mid-IR spectrum of star-forming galaxies (Smith+, 2007)
J/ApJ/693/L81 : Extinction in star-forming regions (McClure, 2009)
J/ApJ/707/89 : Variation of mid-IR extinction (Gao+, 2009)
J/ApJS/191/301 : Spitzer Atlas of Stellar Spectra (SASS) (Ardila+, 2010)
J/A+A/536/A31 : Cyg OB2 XMM observations (Rauw, 2011)
J/MNRAS/484/1838 : Spatial substructure of Cygnus OB2 (Berlanas+, 2019)
Byte-by-byte Description of file: fig5.dat
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Bytes Format Units Label Explanations
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1- 11 E11.5 um lambda Wavelength
13- 23 E11.5 --- Ratio Aλ/A2.2um (1)
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Note (1): Cyg OB2-12 has A(2.2um)=0.96mag (see Table 1 in article)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 20-Sep-2021