Ammonia observations around Herbig stars - The adjacent zone to the photodissociation region in NGC 7023

Details Ammonia observations around Herbig stars - The adjacent zone to the photodissociation region in NGC 7023 Ammonia observations around Herbig stars - The adjacent zone to the photodissociation region in NGC 7023

Oct 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...237..471f&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 237, no. 2, Oct. 1990, p. 471-478. Research supported by CICYT.

Astronomy and Astrophysics

Astrophysics

32

A Stars, Ammonia, B Stars, Interstellar Matter, Photodissociation, Stellar Evolution, Abundance, Emission Spectra, Gas Temperature, Interstellar Gas, Spatial Distribution

Scientific paper

High-angular-resolution observations of the (1,1) and (2,2) ammonia lines toward the Be Herbig stars BD+404124, LKH alpha 198, and HD 200775 are reported. Integrated intensity maps of the main hyperfine component of the (1,1) and (2,2) lines of NH3 toward BD+404124 and HD 200775 are presented, and physical conditions of the molecular gas including kinetic temperatures, H2 densities and masses, NH3 column densities, and ammonia abundance are discussed. Combining all the data available for NGC 7023, the ammonia emission is interpreted as arising from an adjacent zone to the photodissociation region produced by the UV radiation of this star. With this interpretation, the kinetic temperature gradient is seen as arising from a region with a visual extinction from the star between 4.8 and 6.8 mag; while a smaller differential extinction (1.2 mag) is required to explain the NH3 abundance gradient.

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