2001/02/08 by Adolf N. Witt, Randall K. Smith, Eli Dwek · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Cosmic dust #Extinction (optical mineralogy) #Grain growth #Halo #Interplanetary dust cloud #Interstellar medium #Population #Power law #RADIUS #astro-ph
paper · pdf · doi:10.1086/319630
17 pages, incl. 1 figure, accepted for publ. by ApJ Letters
arxiv created 2001/02/08 · openalex publication_date 2001/04/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Recent observations with dust detectors on board the interplanetary spacecrafts Ulysses and Galileo have recorded a substantial flux of large interstellar grains with radii between 0.25 and 2.0 μm entering the solar system from the local interstellar cloud. The most commonly used interstellar grain size distribution is characterized by an a -3.5 power law in grain radii a and extends to a maximum grain radius of 0.25 μm. The extension of the interstellar grain size distribution to such large radii will have a major effect on the median grain size and on the amount of mass needed to be tied up in dust for a given visual optical depth. It is therefore important to investigate whether this population of larger dust particles prevails in the general interstellar medium or whether it is merely a local phenomenon. The presence of large interstellar grains can be inferred mainly from their effect on the intensity and radial profile of scattering halos around X-ray sources. In this Letter, we examine the grain size distribution that gives rise to the X-ray halo around Nova Cygni 1992. The results of our study confirm the need to extend the interstellar grain size distribution in the direction of this source to and possibly beyond 2 μm. The model that gives the best fit to the halo data is characterized by (1) a grain size distribution that follows an a -3.5 power law up to 0.50 μm, followed by an a -4.0 extension from 0.50 to 2.0 μm, and (2) silicate and graphite (carbon) dust-to-gas mass ratios of 0.0044 and 0.0022, respectively, consistent with solar abundance constraints. Additional observations of X-ray halos probing other spatial directions are badly needed to test the general validity of this result.