Spectropolarimetric Constraints on the Nature of the 3.4 Micron Absorber in the Interstellar Medium

Spectropolarimetry of the 3.4 μm aliphatic C-H stretch feature, generally attributed to carbonaceous dust in the diffuse interstellar medium, has been carried out in the line of sight from the Galactic center source Sagittarius A IRS 7. The feature is unpolarized (Δp/Δτ<0.2): the upper limit for polarization is well below that expected on the basis of a model in which the carrier molecules are associated with the aligned silicate component of interstellar dust, for example, as an organic or carbonaceous mantle on a silicate core. The simplest explanation is that the 3.4 μm carrier resides in a population of small, nonpolarizing carbonaceous grains, physically separate from the silicates and sharing many characteristics with the carriers of the 217.5 nm extinction bump.

[1]  A. Tielens,et al.  Near-Infrared Spectroscopy of the Proto-Planetary Nebula CRL 618 and the Origin of the Hydrocarbon Dust Component in the Interstellar Medium , 1998, The Astrophysical journal.

[2]  J. Bowey,et al.  The 10-μm profile of molecular-cloud and diffuse ISM silicate dust , 1998 .

[3]  T. Henning,et al.  Matrix-isolated Nano-sized Carbon Grains as an Analog for the 217.5 Nanometer Feature Carrier , 1998 .

[4]  J. Mathis The Near-Infrared Interstellar Silicate Bands and Grain Theories , 1998 .

[5]  T. Prusti,et al.  Infrared Spectroscopy of Dust in the Diffuse Interstellar Medium toward Cygnus OB2 No. 12 , 1997 .

[6]  J. Mathis,et al.  Dust Grain Size Distributions and the Abundance of Refractory Elements in the Diffuse Interstellar Medium , 1997 .

[7]  M. Wolff,et al.  Ultraviolet Interstellar Linear Polarization. III. Features , 1997 .

[8]  A. Adamson,et al.  Three Micron Hydrocarbon and Methanol Absorption in Taurus , 1996 .

[9]  J. J. Johnson,et al.  Ultraviolet Interstellar Polarization of Galactic Starlight.I.Observations by the Wisconsin Ultraviolet Photo Polarimeter Experiment , 1996 .

[10]  A. Lazarian,et al.  Interstellar Polarization from CO and XCN Mantled Grains: A Severe Test for Grain Alignment Mechanisms , 1996 .

[11]  A. Tielens,et al.  The infrared spectrum of the Galactic center and the composition of interstellar dust. , 1996, The Astrophysical journal.

[12]  J. Hough,et al.  Spectropolarimetry of the 3 Micron Ice Feature toward the Becklin-Neugebauer Object , 1996 .

[13]  J. Mayo Greenberg,et al.  Approaching the Interstellar Grain Organic Refractory Component , 1995 .

[14]  S. M. Scarrott,et al.  Molecular Diffuse Interstellar Band Carriers in the Red Rectangle , 1995, Science.

[15]  A. Adamson,et al.  A Search for Polarization in Diffuse Interstellar Bands toward HD 197770 , 1995 .

[16]  S. Sandford,et al.  The galactic distribution of aliphatic hydrocarbons in the diffuse interstellar medium. , 1995, The Astrophysical journal.

[17]  Alexander G. G. M. Tielens,et al.  Near-infrared absorption spectroscopy of interstellar hydrocarbon grains , 1994 .

[18]  K. Sellgren,et al.  The 3.2-3.6 micron spectra of monoceros R2/IRS-3 and Elias 16 , 1994 .

[19]  T. Nagata,et al.  Spectropolarimetry of Five Objects toward the Galactic Center from 1.4 to 4.2 Microns , 1994 .

[20]  P. Martin,et al.  The Size Distribution of Interstellar Dust Particles as Determined from Extinction , 1993 .

[21]  S. Sandford,et al.  Diamonds in dense molecular clouds: a challenge to the standard interstellar medium paradigm. , 1993, Science.

[22]  M. Wolff,et al.  Ultraviolet interstellar linear polarization. I - Applicability of current dust grain models , 1993 .

[23]  Motohide Tamura,et al.  Interstellar polarization from 3 to 5 microns in reddened stars , 1992 .

[24]  S. Fossey Red Rectangle emission , 1991, Nature.

[25]  K. Sellgren,et al.  The interstellar C-H stretching band near 3.4 microns: constraints on the composition of organic material in the diffuse interstellar medium. , 1991, The Astrophysical journal.

[26]  W. Duley,et al.  The 3.4-mu.m interstellar absorption feature in CYG OB2 No 12. , 1990 .

[27]  M. Bode,et al.  Infrared studies of dust and gas towards the Galactic Centre: 3–5 µm spectroscopy , 1989 .

[28]  J. Hough,et al.  Spectropolarimetry of the 3-µm ice feature in molecular clouds – II. GL 2591, GL 2136, W33A and Elias 29 (ρ Ophiuchi dark cloud) , 1989 .

[29]  J. Mathis,et al.  Composite interstellar grains , 1989 .

[30]  Scott A. Sandford,et al.  Photochemical and thermal evolution of interstellar/precometary ice analogs , 1988 .

[31]  S. D. James,et al.  Infrared spectropolarimetry of AFGL 2591: evidence for an annealed grain component , 1988 .

[32]  M. Tamura,et al.  Spectropolarimetry of the 3-μm ice band in Elias 16 (Taurus Dark Cloud) , 1988 .

[33]  J. Mathis The alignment of interstellar grains , 1986 .

[34]  P. Roche,et al.  Infrared spectropolarimetry of the Galactic Centre: magnetic alignment in the discrete sources , 1986 .

[35]  P. Roche,et al.  An investigation of the interstellar extinction – II. Towards the mid-infrared sources in the Galactic centre , 1985 .

[36]  D. Depoy,et al.  The location of infrared sources in the galactic center from a deep 1 micron CCD image , 1984 .

[37]  H. M. Lee,et al.  Optical properties of interstellar graphite and silicate grains , 1984 .

[38]  J. Hough,et al.  Imaging and polarimetry of the Galactic Centre in the near-infrared , 1984 .

[39]  K. Nordsieck,et al.  The Size distribution of interstellar grains , 1977 .

[40]  R. Knacke,et al.  Infrared polarization of the galactic center. II. , 1977 .

[41]  A. S. Wexler Integrated Intensities of Absorption Bands in Infrared Spectroscopy , 1967 .

[42]  L. Gribov,et al.  INTENSITIES IN THE INFRA-RED ABSORPTION SPECTRA OF POLYATOMIC MOLECULES , 1962 .