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Non-Uniform Outflow Observed around Infrared Object NML Cygni | | J. D. Monnier
; M. Bester
; W. C. Danchi
; M. A. Johnson
; E. A. Lipman
; C. H. Townes
; P. G. Tuthill
; T. R. Geballe
; D. Nishimoto
; P. W. Kervin
; | | Date: |
12 Feb 1997 | | Subject: | astro-ph | | Affiliation: | 1,2), E. A. Lipman , C. H. Townes , P. G. Tuthill , T. R. Geballe , D. Nishimoto , P. W. Kervin ( Space Sciences Laboratory, University of California, Lawrence Livermore National Laboratory, Joint Astronomy Centre, Rockwell Power Systems, USAF Phi | | Abstract: | Measurements by the U.C. Berkeley Infrared Spatial Interferometer at 11.15 micron have yielded strong evidence for multiple dust shells and/or significant asymmetric dust emission around NML Cyg. New observations reported also include multiple 8-13 micron spectra taken from 1994-1995 and N band (10.2 micron) photometry from 1980-1992. These and past measurements are analyzed and fitted to a model of the dust distribution around NML Cyg. No spherically symmetric single dust shell model is found consistent with both near- and mid-infrared observations. However, a circularly symmetric maximum entropy reconstruction of the 11 micron brightness distribution suggests a double shell model for the dust distribution. Such a model, consisting of a geometrically thin shell of intermediate optical depth ($ au_{11 micron} sim 1.9$) plus an outer shell ($ au_{11 micron} sim 0.33$), is consistent not only with the 11 micron visibility data, but also with near-infrared speckle measurements, the broadband spectrum, and the 9.7 micron silicate feature. The outer shell, or large scale structure, is revealed only by long-baseline interferometry at 11 micron, being too cold ($sim$ 400 K) to contribute in the near-infrared and having no unambiguous spectral signature in the mid-infrared. The optical constants of Ossenkopf, Henning, & Mathis (1992) proved superior to the Draine & Lee (1984) constants in fitting the detailed shape of the silicate feature and broadband spectrum for this object. Recent observations of H$_2$O maser emission around NML Cyg by Richards, Yates, & Cohen (1996) are consistent with the location of the two dust shells and provide further evidence for the two-shell model. | | Source: | arXiv, astro-ph/9702103 | | Services: | Forum | Review | PDF | Favorites | |
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