Stars in Diffuse Nebulae.

Abstract

view Abstract Citations (32) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stars in Diffuse Nebulae. Greenstein, Jesse L. Abstract Slit spectrograms of a group of stars in bright and dark nebulosity have been obtained; taken with a wide slit, they are suitable for spectrophotometric comparison of the nebulous objects with B stars of known color. In a field near o Per, nine stars of-types B6-A8, magnitudes 10-12.5, were observed; no trace of emission was found. Two B5 stars, heavily involved in NGC 2068, also showed normal spectra. Spectra of -6°1253, R Mon, and NGC 2261 were measured to obtain relative gradients and the intensi- ties of the Balmer emission and absorption lines. From the space reddening and from distances deter- mined by other means, both -6°1253 and R Mon seem too bright to be normal T Tauri objects; it is possible that there is an extra-stellar source of luminosity in R Mon. The line H7 is stronger in absorp- tion in NGC 2261 than it is in R Mon; line absorption may occur in the nebula. The Balmer emission decrement, after correction for space reddening, is steeper than in planetary nebulae (recombination spectrum); it more nearly resembles that in the chromosphere or Be stars. Theoretical decrements under conditions approaching thermodynamic equilibrium fit moderately well; this suggests a higher space density and less dilution than in planetary nebulae. Possible sources of continuous emission are dis- cussed, and it is shown that the normally expected Paschen continuum is negligible Publication: The Astrophysical Journal Pub Date: May 1948 DOI: 10.1086/145020 Bibcode: 1948ApJ...107..375G full text sources ADS |