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Astron. Astrophys. 353, 371-379 (2000)

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Optical CCD imaging of the supernova remnant CTA 1

F. Mavromatakis 1, J. Papamastorakis 1,2, E.V. Paleologou 2 and J. Ventura 1,2

1 University of Crete, Physics Department, P.O. Box 2208, 710 03 Heraklion, Crete, Greece
2 Foundation for Research and Technology-Hellas, P.O. Box 1527, 711 10 Heraklion, Crete, Greece

Received 2 June 1999 / Accepted 26 October 1999

Abstract

Deep H[FORMULA]+[NII], [NII] , [SII] and [OIII] CCD images have been obtained from the high galactic latitude supernova remnant CTA 1. The filamentary morphology in the light of the [OIII] emission is now clearly seen in the full field of the remnant. Contrary to the [OIII] morphology, the remnant appears less sharply defined in the light of the H[FORMULA]+[NII], [NII] and [SII] . The morphological differences between the [OIII] and H[FORMULA]+[NII] emission lines and the presence of a number of filaments with projected lengths ranging from 0.5 to several pc suggest an inhomogeneous insterstellar medium. The presence of incomplete recombination zones is supported by the variations seen in the [OIII] /[FORMULA] ratio which ranges from 5-20. A low dispersion spectrum taken in the south of CTA 1 indicates surface brightness values of H[FORMULA] , [NII] and [SII] of [FORMULA] 13, 14 and 18 in units of [FORMULA] erg s-1 cm-2 arcsec-2 respectively, while the sulfur line ratio suggests an electron density of [FORMULA] 200 cm-3. Rough upper limits to the preshock cloud density are of the order of [FORMULA] 1 nuclei cm-3. The strong [OIII] emission is indicative of shock velocities higher than 100 km s-1 while in certain areas of the remnant where the H[FORMULA] emission dominates lower velocities are possible. It is the first time that significant optical emission is detected in the northwest area of the remnant, where diffuse radio emission is mainly seen. The small scale filaments detected there and their flux suggest that we observe shocked material, most likely associated to CTA 1. Three more distinct filamentary structures are detected in the south-west area, outside of the main emission shell. Their lengths range from [FORMULA] to [FORMULA]. The spatial locations of the newly detected emission features suggest an angular shock radius of 59´.

Key words: book reviews – ISM: supernova remnants – ISM: individual objects: CTA 1

Send offprint requests to: F. Mavromatakis (fotis@physics.uch.gr)

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© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999
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