Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-12-03
Astron.Astrophys. 416 (2004) 243-250
Astronomy and Astrophysics
Astrophysics
8 pages, 6 figures, 3 tables, A&A in press
Scientific paper
10.1051/0004-6361:20031712
We report on the detection of a previously unknown extended low-density nebula of very high temperature and excitation, TR001507.7-391206, located above the midplane of NGC55. The nebular emission line spectrum, in which HeII 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 Sk4 or LSS4368). The relatively large diameter of the inhomogeneously expanding nebula in NGC55 of about 58pc, compared to 11pc of G2.4+1.4, would also be consistent with the number of ionizing stars.
Rosa Michael R.
Tuellmann Ralph
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