Volume 464, Number 3, March IV 2007
|Page(s)||995 - 1002|
|Section||Interstellar and circumstellar matter|
|Published online||11 January 2007|
Helium abundance and ionization structure in the Orion nebula: radio recombination lines observations*
INAF – Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Str. 54, 09012 Capoterra (CA), Italy e-mail: email@example.com
2 P.N Lebedev Physical Institute, Academy of Sciences of Russia, Moscow, Russia
3 Isaac Newton Institute of Chile, Pushchino Branch, Pushchino, 142290 Russia
4 INAF – IASF Sezione di Bologna, via P. Gobetti 101, 40129 Bologna, Italy
5 Università degli Studi, Dipartimento di Astronomia, 40129 Bologna, Italy
Accepted: 27 November 2006
Results of the Ori A HII region mapping based on hydrogen (H), helium (He) and carbon (C) Radio Recombination lines (RRL) are presented. Observations were made with the same angular resolution () using the 32 m VLBI dish of Medicina (Italy, 22.4 GHz) and the Pushchino RT-22 dish (Russia, 36.5 GHz). The behaviour of the ionized helium abundance, y+, with distance from the center shows that the He+ zone size is smaller than that of H+. Such a behaviour is different for the core and for the envelope, as well as for different directions from the center. The helium abundance, %, is measured. Derived line radial velocities, their widths and y+ data support the well-known “blister-type” structure of this HII region. LTE electron temperatures ( K) are also measured.
Key words: ISM: abundances / ISM: HII regions / radio lines: ISM / ISM: individual objects: Orion Nebula
© ESO, 2007
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