Volume 448, Number 3, March IV 2006
|Page(s)||1095 - 1100|
|Section||Interstellar and circumstellar matter|
|Published online||03 March 2006|
Detection of an optical filament in the Monogem Ring
Institut für Astrophysik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria e-mail: [ronald.weinberger;giovanna.temporin]@uibk.ac.at
2 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: firstname.lastname@example.org
Accepted: 17 November 2005
The Monogem Ring is a huge bright soft X-ray enhancement with a diameter of ~25°. This 0.3 kpc distant structure is a peculiar Galactic supernova remnant in that it is obviously visible only in X-rays, due to its expansion into a region of extremely low ambient density: hence, practically no optical emission or a neutral shell was expected to be detectable. Here we report on the discovery of a very faint arc-like nebula on a POSS II R film copy, at the south-eastern borders of the MR. Spectroscopy revealed this filament to have a very large λ 6716+6731/Hα ratio of up to ~1.8, indicating shock excitation, and a low density of Ne < 100 cm-3. There is no hint of  emission in the spectra. On deep wide-field direct images in Hα and in  the nebula appears as a ~20´ long, thin (~1´), structured filament, stretching N-S. We believe that this filament belongs to the MR and became visible due to the interaction of the expanding remnant with a mild density increase in the interstellar medium. Only one other possible optical filament of the MR has been reported in the literature, but no spectrum was provided.
Key words: ISM: supernova remnants / ISM: individual objects: Monogem Ring
© ESO, 2006
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.