========================================================================== J/A+A/268/419 HII Regions in NGC 4258 (Courtes+ 1993) The following files can be converted to FITS (extension .fit .fit.Z .fgz) table3 ========================================================================== Query from: http://vizier.u-strasbg.fr/cgi-bin/VizieR?-source=J/A+A/268/419 ==========================================================================
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Beginning of ReadMe : J/A+A/268/419 HII Regions in NGC 4258 (Courtes+ 1993) ================================================================================ Structure of the spiral arms of NGC 4258 in Halpha and at 2000Angstroems. Courtes G., Petit H., Hua C.T., Martin P., Blecha A., Huguenin D., Golay M. <Astron. Astrophys. 268, 419 (1993)> =1993A&A...268..419C ================================================================================ ADC_Keywords: Galaxies, photometry; H II regions Keywords: HII regions in extragalactic nebulae - NGC 4258 - structure of the interstellar gas - spiral arms - Halpha and UV 2000A stellar continuum - sites of star formation, spiral arm evolution - density waves - non thermal phenomenon - radio SNR 1983 Description (Abstract): The distribution of ionized hydrogen in the spiral galaxy NGC 4258 is revisited using Halpha images with both the Mont Megantic 160cm telescope equipped with a F/3 focal reducer and the Observatoire de Haute-Provence 120cm telescope at its newtonian F/6 focus in the direct imaging mode. The HII region distribution shows several well defined spiral structures as well as the very extended and peculiar "anomalous arms". The deprojection of these features is compared to the UV 2000A stellar arms obtained with the LAS- Geneva Observatory balloon-borne survey programme. The pitch angle of the N inner arm permits to detect the drift of the Halpha spiral structures with respect to the evolved hot stellar population in the corresponding sector of the UV arm. This phenomenon seems to systematically appear in other galaxies. The conclusion should be that the origin of the drift is mainly kinematic and of evolutionary nature and provides perhaps the best method to evaluate the effect of the density waves. The anomalous arms have no apparent UV 2000A counterpart except perhaps in the inner region of the central stellar bulge. A comparison of the Halpha morphology is made with the CO distribution and their radial velocity profiles that could renew the ballistic interpretation. A catalogue of 137 HII regions was compiled from the two sets of new CCD images, providing the X and Y off-set positions, along with the absolute flux and angular diameters corrected for observing conditions. The 1950 equatorial coordinates are given in the maps of our Halpha observations. The derived power-law luminosity function is compared to those obtained for other galaxies. Comparing previous image-tube plates, taken between 1961 and 1969, to the recent CCD data for NGC 4258, we obtain flux estimates of the HII region hosting the supernova first discovered in radio frequencies on 1983. As a result, the integrated magnitude is in fair agreement with the report by Wild (IAU Circ 3803, 1983) of a 17th mag object in the same location.
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