Recombination line observations of a normal helium abundance in the galactic-center H II region Sagittarius B2

Journal Article · Mon Sep 15 04:00:00 EDT 1975 · Astrophys. J., Lett., v. 200, no. 3, pp. L155-L159

DOI:https://doi.org/10.1086/181920· OSTI ID:4124534

Brown, R L; Lockman, F J

We have detected both the H 76$alpha$ and He 76$alpha$ recombination lines in the Sgr B2 H II region; from a comparison of the integrated power in these lines we infer that the ratio of ionized helium to ionized hydrogen in Sgr B2 is =0.085 + or - 0.015. These observations require that the hydrogen and helium Stromgren spheres be spatially coextensive. Hence if processes intrinsic to the H II region, such as dust absorption of Lyman continuum photons, compete effectively with the gas for the stellar ionizing radiation, then the dust opacity at the helium ionization threshold cannot exceed the dust opacity at the Lyman limit, tau/subd/(504 A) < or = tau/subd/(912 A). The anomalously low He$sup +$/H$sup +$ ratio in Sgr B2 derived from recombination line observations at lower frequencies very likely results from preferential enhancement of the nebular hydrogen lines in the ionized component of the Sgr B2/ molecular cloud interface. (AIP)

• Research Organization: National Radio Astronomy Observatory, Charlottesville, VA
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-010164
• OSTI ID: 4124534
• Journal Information: Astrophys. J., Lett., v. 200, no. 3, pp. L155-L159, Journal Name: Astrophys. J., Lett., v. 200, no. 3, pp. L155-L159; ISSN AJLEA
• Country of Publication: United States
• Language: English

Related Subjects

*H2 REGIONS-- RADIOWAVE RADIATION
*HELIUM-- RECOMBINATION
640105* --Physics Research--Astrophysics &amp; Cosmology-- Galaxies
CHEMICAL COMPOSITION
COSMIC DUST
COSMOCHEMISTRY
HYDROGEN
N56500* --Physics (Astrophysics &amp; Cosmology)--Galaxies
NEBULAE
OPACITY