Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II

Details Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II

Apr 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...388..495b&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 388, April 1, 1992, p. 495-512.

Astronomy and Astrophysics

Astrophysics

11

Atomic Excitations, Fine Structure, Ionized Gases, Molecular Clouds, Nitrogen Ions, Scorpius Constellation, Absorption Spectra, Ground State, Ion Charge, Line Spectra, Massive Stars, Star Formation

Scientific paper

The column density and the emission of the ionized gas along the line of sight toward the B1 V + B2 V binary star Pi Sco are measured on the basis of the fine-structure absorption lines of the ground state N II. It is found that the bulk of this ionized gas must be clumped on a length scale of 0.025 pc, which is far smaller than the observed size of the diffuse H II region surrounding Pi Sco of about 6 pc. The observed column density of S III toward Pi Sco yields an upper limit on the distance of the absorbing, clumped gas from the star of less than about 0.02 pc, assuming that both the N II and S III absorption arise from the same gas. The possibility that the ionized gas originates from a photoevaporating circumstellar disk directly surrounding Pi Sco is excluded, since such a disk would have an unusual size of order 0.025 pc and would have had to survive for the estimated age of Pi Sco of 5-8 Myr. The derived mean density of the clumped gas is of order 40/cu cm, so that the gas is at a pressure that far exceeds the mean pressure in the H II region. It is concluded that the ionized gas could originate from evaporation flows off a cluster of compact neutral objects that evaporate due to the ionizing radiation of Pi Sco.

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