An unusual high-ionization nebula in NGC 55
Abstract
We report on the detection of a previously unknown extended low-density nebula of very high temperature and excitation, TR 001507.7-391206, located above the midplane of NGC 55. The nebular emission line spectrum, in which He II is present, is consistent with photoionization by about 3 very hot massive O3 or WR-type stars. There are no indications for shock ionization. The faint blue optical continuum and XMM-Newton EPIC-pn and OM-data also support our assumption that this nebula is not a supernova remnant. Galactic nebulae harboring massive Wolf-Rayet (WR) stars may be appropriate examples, in particular the highly ionized nebula G2.4+1.4 around WR 102 (aka Sk 4 or LSS 4368). The relatively large diameter of the inhomogeneously expanding nebula in NGC 55 of about 58 pc, compared to 11 pc of G2.4+1.4, would also be consistent with the number of ionizing stars.
Based on observations collected at the European Southern Observatory, La Silla & Cerro Paranal (Chile); Proposal No.: 64.N-0399(A,B), 66.B-0551(A). Based upon data obtained from the ESA XMM-Newton data archive.- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 2004
- DOI:
- 10.1051/0004-6361:20031712
- arXiv:
- arXiv:astro-ph/0312085
- Bibcode:
- 2004A&A...416..243T
- Keywords:
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- stars: Wolf-Rayet;
- ISM: abundances;
- ISM: individual: TR 001507.7-391206;
- galaxies: individual: NGC 55;
- X-rays: ISM;
- Astrophysics
- E-Print:
- 8 pages, 6 figures, 3 tables, A&