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Decoupled nuclei and nuclear polar rings in regular spiral galaxies
NGC 7217 *
Received 21 July 2000 / Accepted 26 September 2000
The regular isolated Sab galaxy NGC 7217 has been studied with the Multi-Pupil Fiber Spectrograph of the 6m telescope of the Special Astrophysical Observatory RAS (Nizhnij Arkhyz, Russia) in two spectral ranges, the blue one including the strong absorption lines MgI and FeI and the red one including the emission lines H and [NII ]6583. We confirm the existence of a circumnuclear gaseous polar disk with a radius of 3" which we reported earlier. The same area, with a radius of 3" -4", elongated orthogonally to the line of nodes, is distinguished by high values of the Lick index and shows a Mg/Fe ratio lower than solar. This implies that there were at least two discrete star formation bursts in the circumnuclear region with a temporal separation of a few Gyrs. We relate this pair of bursts to the complex structure of the global brightness profile of the galaxy, which may be decomposed into three exponential segments with different scalelengths.
Key words: galaxies: kinematics and dynamics galaxies: structure galaxies: spiral galaxies: evolution galaxies: nuclei galaxies: photometry galaxies: individual: NGC 7217
* Partly based on observations collected with the 6m telescope of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS) which is operated under the financial support of Science Department of Russia (registration number 01-43) and on data from the ING Archive and the HST Archive.
Send offprint requests to: O.K. Sil'chenko (firstname.lastname@example.org)
Online publication: January 29, 2001