Are polar rings indeed polar?

We have considered polar ring galaxy candidates, the images of which can be found in the SDSS. The sample of 78 galaxies includes the most reliable candidates from the SPRC and PRC catalogs, some of which already have kinematic confirmations. We analyze the distributions of studied objects by the angle between the polar ring and the central disk, and by the optical diameter of the outer ring structures. In the vast majority of cases, the outer structures lie in the plane close to polar (within 10-20 deg) which indicates the stability of the corresponding orbits in the gravitational potential of the halo. Moderately inclined outer structures are observed only in about 6% of objects which probably indicates their short lifetime. In such an unstable configuration, the polar ring would often cross the disk of the galaxy, being smaller than it in the diameter. We show that the inner polar structures and outer large-scale polar rings form a single family in the distribution of diameters normalized to the optical size of the galaxy. At the same time, this distribution is bimodal, as the number of objects with d_ring= (0.4-0.7)*d_disk is negligible. Such a shape of size distribution is most likely due to the fact that the stability of polar orbits in the inner regions of galaxies is maintained by the bulge or the bar, while in the outer regions it is provided by the spheroidal (or triaxial) halo.Comment: Corrected version accepted in Astrophysical Bulletin, 8 pages, 5 EPS figure

Nature of nuclear rings in unbarred galaxies: NGC 7742 and NGC 7217

We have studied the unbarred Sb galaxy with a nuclear star-forming ring, NGC 7742, by means of 2D spectroscopy, long-slit spectroscopy, and imaging, and have compared the results with the properties of another galaxy of this type, NGC 7217, which is studied by us earlier. Both galaxies have many peculiar features in common: each has two global exponential stellar disks with different scalelengths, each possesses a circumnuclear inclined gaseous disk with a radius of 300 pc, and each has a global counterrotating subsystem, gaseous one in NGC 7742 and stellar one in NGC 7217. We suggest that past minor merger is the probable cause of all these peculiarities, including appearance of the nuclear star-forming rings without global bars; the rings might be produced as resonance features by tidally induced oval distortions of the global stellar disks.Comment: Accepted to AJ, 11 PS/EPS figures (5 figures were added in color

Time- and frequency-domain polariton interference

We present experimental observations of interference between an atomic spin coherence and an optical field in a {\Lambda}-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple {\Lambda} transitions driving a single spin coherence. In principle, the interference in each scheme can yield a near unity visibility.Comment: 11 pages, 5 figure