Elsevier

New Astronomy

Volume 16, Issue 8, December 2011, Pages 485-491
New Astronomy

DEFPOS Hα observations of Hii regions

https://doi.org/10.1016/j.newast.2011.04.005Get rights and content

Abstract

We present Hα emission line measurements of northern bright Hii regions selected from the Sharpless (1959) catalog near the Galactic plane (b  ± 6°). A total of 10 Hii regions were observed with DEFPOS (Dual Etalon Fabry–Perot Optical Spectrometer) system at the f/48 Coude focus of 150 cm RTT150 telescope located at TUBITAK National Observatory (TUG) in Antalya/Turkey. The intensities, the local standard of rest (LSR) velocities (VLSR), and the linewidths (Full Width Half Maximum: FWHM) of the Hα emission line from our observations were in the range of 84 to 745 Rayleigh (R [one Rayleigh (R) is 106/4π photons cm−2 sr−1 s−1 =  2.4110−7 erg cm−2 sr−1 s−1 at Hα and corresponds to an emission measure (EM=ne2dl) of 2.3 pc cm−6 for a gas temperature of 8000 K, where ne is the averaged electron density within an emitting region in the interstellar medium; dl is distance element to the source region (Haffner et al., 2003, Reynolds et al., 2005), 3 to −43 km s−1 and 30 to 73 km s−1, respectively. The LSR velocities and the linewidths from the data were obtained and compared with early results. We found that our results are in close agreement with them. Moreover, associated stars of some of the Hii regions were updated by analyzing their location, velocities, and brightness.

Introduction

Hii regions are very important for Hα (6563 Å) sources within our Galaxy. They provide information about the early stages of stellar formation and they are also considered as a unique tool to investigate the spiral structure of the Galaxy. Moreover, using their radio emissions, distant parts of the Galactic plane can be probed. Diffuse Ionized Gas (DIG), also referred to as “Warm Ionized Medium WIM”, is a major component of the ISM – Interstellar Medium (Reynolds, 1991, Reynolds, 1993). The properties of WIMs are reviewed by Reynolds et al. (2000).

Investigation of Hα emission lines from Hii regions is very important for several reasons. Firstly, using Hα observations, the kinematics of the Hii regions can be mapped out, interactions with the surrounding molecular clouds can be seen, and the kinematics of the disk of the Galaxy can be modeled by combining radial velocities with distance (Fich et al., 1990). The other reason is to understand the physical state, its structure and the source of warm ionized gas in the Galaxy. Studying Hii regions helps us to determine the sources of ionization and how these regions are related to the ISM (Reynolds et al., 1998, Hausen et al., 2002). Therefore, it is important to observe Hii regions in visual band (especially at Hα) by using Hα emission line. Since Hii regions are relatively large in size, it might be difficult to study them with traditional long slit spectroscopy. Instead, high resolution spectral analysis of these faint, spatially extended sources requires high sensitivity, wide field of view spectrometers such as “Wisconsin H-Alpha Mapper – WHAM” (Tufte, 1997, Haffner et al., 2003) and DEFPOS (Sahan et al., 2005, Sahan et al., 2009).

DEFPOS spectrometer was designed and built to measure Hα emission line covering a 200 km s−1 (4.4 Å) spectral window with ∼30 km s−1 spectral resolution within a field of view of 4′ in diameter on the sky for observations by TUBITAK National Observatory (TUG) of Turkey (Aksaker et al., 2009, Sahan et al., 2009). Hα emission line of 10 bright Hii regions selected from the Sharpless’s Catalogue (Sharpless, 1959) were observed with DEFPOS. In the first part of present study, observations (Section 2.1), data reduction (Section 2.2) and intensity calibration of DEFPOS data (Section 2.3) are given. Then, a literature survey of ionization source(s) of these Hii regions is conducted in Section 2.4. After the analysis of our observations (see Section 3) we evaluated and compared our results with previous works, such as Fich et al., 1990, Lockman, 1989, Blitz et al., 1982. We conclude our work with some suggestions for future works.

Section snippets

Observations

To achieve a high signal-to-noise ratio (SNR), we selected 10 Hii regions, which are the brightest ones in the Galaxy. All of these regions were located near Galactic plane (b  ± 6°) and were observed by DEFPOS on 25–26 November, 2007 and 27 September, 2009 at TUG, Antalya. The journal of observations given in Table 1 contains the catalogue names of Hii regions, coordinates, observation dates and exposure times. DEFPOS was redesigned to observe Hii regions and the targets were located at Coude

Results and discussion

The intensity, the VLSR and the linewidth of Hα emission line analysis of these Hii regions were determined and their comparison with the literature is given in Table 3. The name of these Hii regions were given in the first column in Table 3. Errors due to scatter in the spectral data point was determined by the standard deviation calculation carried out by the least-squares Gaussian fitting program. The Hii regions are further described in subsections, below.

Conclusions

The DEFPOS instrument is a Fabry–Perot spectrometer was reconfigured to carry out Hii observations from Diffuse Ionized Gas in the PNe, Hii regions, and supernova remnants, having low angular resolution. Observations were carried out in year of 2007 using RTT150 Telescope of TUG at Antalya, Turkey. The spectrometer was able to observe Hα emission line within 200 km s−1 (4.4 Å) spectral window with a field of view of 4′ and with a spectral resolution of ∼30 km s−1. Further details on design of the

Acknowledgements

All observations were performed from the RTT150 so we thank to TUBITAK for a partial support in using RTT150 (Russian-Turkish 1.5-m telescope in Antalya) with project number 09ARTT150–436-1. We also thank to TUBITAK National Observatory (TUG) and TUG stuff. The authors also would like to thank R. J. Reynolds from the University of Wisconsin for his valuable help in the optical design of the DEFPOS as well as to start this study. We are grateful to S.K. Yerli and M.E. Ozel for reading and

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