Galactic H$\alpha $ emission line studies using DEFPOS at the TÜBİTAK National Observatory

Authors: MUHİTTİN ŞAHAN

Abstract: H$\alpha $ spectral line (6563 Å) profiles of eight northern H II regions in our galaxy (Sh2-25, Sh2-131, Sh2-237, IC 434, IC 1318, NGC 1982, NGC 6543, and NGC 6611) have been obtained using the Dual Etalon Fabry-Pérot Optical spectrometer (DEFPOS) with a 4' field of view, located at the coudé focus of the 150 cm RTT150 telescope at the TÜBİTAK National Observatory (TUG, Antalya, Turkey). Observations were carried out during the nights of 25-27 December 2015 and 6-7 June 2017 with different long exposure times ranging from 900 s to 3600 s. These spectra provide information about the local standard of rest (LSR) velocities, the full width at half maximum (FWHM), and densities of the sources. The LSR velocities and the FWHM of the H$\alpha $ emission lines were found to be in the range of -50.31 km/s to 27.57 km/s and 34.88 km/s to 44.54 km/s (mean FWHM: 37.19 km/s), respectively. The NGC 6543 (Cat's Eye Nebula) is the faintest one (75.06 R), while the NGC 1982 H II region is brightest source (38,477.3 R). The LSR velocity and the FWHM results of the DEFPOS/RTT150 system were compared with the data by several authors given in the literature and the results of DEFPOS data were found to be in good agreement with data given in the literature. Since there is not enough information on LSR velocities and intensities of such galactic sources with low angular size in the literature, we believe that this spectrometer will provide a powerful tool for the study of diffuse ionized gas and these new results may have significant contributions to the literature. In the future, we are planning to prepare H$\alpha $ maps with the 4' field of view of some diffuse ionized emission sources selected from VTSS and WHAM H$\alpha $ maps with large fields of view.

Keywords: ISM: H II regions, emission nebulae, planetary nebulae, open clusters, techniques: spectroscopic, Fabry-Pérot, radial velocities, line widths

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