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C. Yuan, D.C.C. Yen, I.H. Li (Institute of Astronomy & Astrophysics, Academia Sinica, Taiwan, ROC)
Most of the nearby galaxies are found to have a central gas-dust disk. Their structures, however, are often obscured by the background luminous star lights. These hidden structures, however, can be extracted from the observations by using wavelet methods. The atrous wavelet method proves to be extremely useful for such a purpose. We have analyzed the NICMOS and WFPC (WFPC2) data from HST for more than 30 nearby disk galaxies. For most of them, the central regions are characterized by spiral or/and bar structures. We shall present our results for the following four groups: galaxies with a major bar, and galaxies without a major bar, then subdivided with or without starburst-Seyfert acvtivities. For galaxies with a major bar, there are two possible scenarios: one is that the two-arm spirals can be traced all the way to the center,e.g., NGC1097 and NGC5383; the other is that a nucler bar exists (bar within a bar), e.g., NGC4314 and NGC6951. For galaxies without a major bar, most of them have a central or nuclear bar coupled with two-arm spirals, e.g., NGC1068 and NGC4321. Among our sample of Seyfert galaxies, all have central bar-spiral or oval distortion structure. This implies that the mechanism of fueling Seyfert (or AGN) activities in the center by means of a central bar cannot be readily ruled out. We compare our results with CO observations, whenever they are available. CO spirals always coincide with the NICMOS spirals and they lie between V-band spirals, as expected. The work is supported by NSC Grant 90-2112-M-001-052, for which we acknowlege.