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Author Blasberger, Avi ♦ Behar, Ehud ♦ Perets, Hagai B. ♦ Brosch, Noah ♦ Tielens, Alexander G. G. M.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ ABSORPTION ♦ CORRELATIONS ♦ CRITICAL TEMPERATURE ♦ EMISSION ♦ INTERSTELLAR SPACE ♦ MOLECULAR STRUCTURE ♦ MOLECULES ♦ POLYCYCLIC AROMATIC HYDROCARBONS ♦ RED SHIFT ♦ STARS ♦ ULTRAVIOLET RADIATION ♦ WAVELENGTHS
Abstract The 2175 Å UV extinction feature was discovered in the mid-1960s, yet its physical origin remains poorly understood. One suggestion is absorption by polycyclic aromatic hydrocarbon (PAH) molecules, which is supported by theoretical molecular structure computations and by laboratory experiments. PAHs are positively detected by their 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 μ m IR emission bands, which are specified by their modes of vibration. A definitive empirical link between the 2175 Å UV extinction and the IR PAH emission bands, however, is still missing. We present a new sample of hot stars that have both 2175 Å absorption and IR PAH emission. We find significant shifts of the central wavelength of the UV absorption feature, up to 2350 Å, but predominantly in stars that also have IR PAH emission. These UV shifts depend on stellar temperature in a fashion that is similar to the shifts of the 6.2 and 7.7 μ m IR PAH bands, that is, the features are increasingly more redshifted as the stellar temperature decreases, but only below ∼15 kK. Above 15 kK both UV and IR features retain their nominal values. Moreover, we find a suggestive correlation between the UV and IR shifts. We hypothesize that these similar dependences of both the UV and IR features on stellar temperature hint at a common origin of the two in PAH molecules and may establish the missing link between the UV and IR observations. We further suggest that the shifts depend on molecular size, and that the critical temperature of ∼15 kK above which no shifts are observed is related to the onset of UV-driven hot-star winds and their associated shocks.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-02-20
Publisher Place United States
Journal Astrophysical Journal
Volume Number 836
Issue Number 2


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