Detection of PAH Absorption and Determination of the Mid-Infrared Diffuse Interstellar Extinction Curve from the Sightline Toward Cyg OB2-12

Abstract

The sightline toward the luminous blue hypergiant Cyg OB2-12 is widely used in studying interstellar dust on account of its large extinction ($A_V\simeq 10$ mag) 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 ISO-SWS and Spitzer IRS observations of Cyg OB2-12 using a model of the emission from the star and its stellar wind to determine the total extinction $A_{\lambda }$ from 2.4--37 $\mu$m. In addition to the prominent 9.7 and 18 $\mu$m silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons (PAHs), including the first identification of the 7.7 $\mu$m feature in absorption. The 3.3 $\mu$m aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 $\mu$m aliphatic hydrocarbon features are observed with relative strengths consistent with observation of these features on sightlines toward the Galactic Center. We identify and characterize more than sixty 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 $A_{\lambda }/A_{2.2\mu m}$ 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.

Submitted to ApJ, comments welcome

References in corpus (14)

• The NumPy array: a structure for efficient numerical computation
• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
• Planck intermediate results. XXII. Frequency dependence of thermal emission from Galactic dust in intensity and polarization
• The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds
• A new, large-scale map of interstellar reddening derived from HI emission
• CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II. High-resolution observations
• Silicate Composition of the Interstellar Medium
• Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2
• Graphite Revisited
• High resolution optical spectroscopy of an LBV-candidate inside the CygOB2 association
• e-MERLIN 21cm constraints on the mass-loss rates of OB stars in Cyg OB2
• On the binary nature of massive blue hypergiants: high-resolution X-ray spectroscopy suggests that Cyg OB2 12 is a colliding wind binary

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