DEFPOS H
a
observations of HII
regions
N. Aksaker
a,b,⇑, M. Sahan
c, I. Yegingil
d, N. Emrahoglu
e aTechnical Sciences Vocational College, Çukurova University, Adana, Turkey
b
Orta Dog˘u Teknik Üniversitesi, Physics Department, Ankara, Turkey
c
Department of Physics, Faculty of Science and Letter, University of Osmaniye Korkut Ata, 80000 Osmaniye, Turkey
d
Department of Physics, Çukurova University, 01330 Adana, Turkey
e
Faculty of Education, Çukurova University, 01330 Adana, Turkey
a r t i c l e
i n f o
Article history: Received 31 May 2010
Received in revised form 17 April 2011 Accepted 21 April 2011
Available online 4 May 2011 Communicated by M. Fukugita Keywords:
Instrumentation: interferometers ISM: HIIregions
Techniques: radial velocities Techniques: interferometric
a b s t r a c t
We present Haemission line measurements of northern bright HIIregions selected from theSharpless (1959)catalog near the Galactic plane (b 6 ± 6°). A total of 10 HIIregions were observed with DEFPOS (Dual Etalon Fabry–Perot Optical Spectrometer) system at the f/48 Coude focus of 150 cm RTT150 tele-scope located at TUBITAK National Observatory (TUG) in Antalya/Turkey. The intensities, the local stan-dard of rest (LSR) velocities (VLSR), and the linewidths (Full Width Half Maximum: FWHM) of the Ha
emission line from our observations were in the range of 84 to 745 Rayleigh (R [one Rayleigh (R) is 106/4pphotons cm2sr1s1= 2.41107erg cm2sr1s1at Haand corresponds to an emission
mea-sure ðEM ¼Rn2
edlÞ of 2.3 pc cm
6for a gas temperature of 8000 K, where n
eis the averaged electron
den-sity 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 s1and 30 to 73 km s1, 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 HIIregions
were updated by analyzing their location, velocities, and brightness.
Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction
HII regions are very important for H
a
(6563 Å) sources withinour 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 Med-ium WIM’’, is a major component of the ISM – Interstellar MedMed-ium (Reynolds, 1991, 1993). The properties of WIMs are reviewed by Reynolds et al. (2000).
Investigation of H
a
emission lines from HII regions is veryimportant for several reasons. Firstly, using H
a
observations, the kinematics of the HIIregions 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 HIIregions helps us todeter-mine 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 HIIregions in visual band (especially at
H
a
) by using Ha
emission line. Since HIIregions are relatively largein 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 H
a
emission line covering a 200 km s1 (4.4 Å) spectral window with 30 km s1 spectral resolution within a field of view of 40 in diameter on the sky for observations by TUBITAK National Observatory (TUG) of Turkey (Aksaker et al., 2009; Sahan et al., 2009). Ha
emission line of 10 bright HII regions selected fromthe 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 Sec-tion 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) and Blitz et al. (1982). We conclude our work with some suggestions for future works.
1384-1076/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.newast.2011.04.005
⇑ Corresponding author at: Orta Dog˘u Teknik Üniversitesi, Physics Department, Ankara, Turkey.
E-mail address:aknazim@yahoo.com(N. Aksaker).
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2. Observations and data analysis 2.1. 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 re-gions were located near Galactic plane (b 6 ± 6°) and were ob-served by DEFPOS on 25–26 November, 2007 and 27 September, 2009 at TUG, Antalya. The journal of observations given inTable 1contains the catalogue names of HIIregions, coordinates, obser-vation dates and exposure times. DEFPOS was redesigned to ob-serve HIIregions and the targets were located at Coude focus (f/
48) of 150 cm Russian-Turkish Telescope (RTT150) at TUG located at a height of 2500 m at Bakirlitepe/Antalya, Turkey. An aperture of 7.5 cm dual etalon Fabry–Perot spectrometer is set to observe the H
a
emission line with a spectral window of the 200 km s1from HII regions and Planetary Nebulae (PNe) with its 40field of view(FOV). Additional information about the instrument and the meth-ods of data analysis can be found inSahan et al. (2005), Sahan et al. (2009), Aksaker (2009)and its intensity calibration can be found in Aksaker et al. (2009).
2.2. Data reduction
A data reduction pipeline for DEFPOS spectra was written in IDL (Interactive Data Language) (Aksaker, 2009; Sahan et al., 2009). In the output, VLSR, intensity and other physical information of inves-tigated sources were produced. The spectra were recorded onto a 2048x2048 CCD cooled with liquid N2. The standard CCD data reduction techniques (dark, bias and flat field corrections; remov-ing cosmic rays and bad columns) were applied to the data. Then, Reflections due to DEFPOS’s optics (Sahan et al., 2009), arising from the uncoated glass surfaces, had to be subtracted from the data in
the pipeline. Hydrogen (H) and Hydrogen–Deuterium (H–D) emis-sion lamps were used in the wavelength calibration and determi-nation of ring centers.
Due to the nature of Fabry–Perot spectroscopy, the spectrum formed on the CCD is in a ring shape. After the data reduction pipe-line, the ring is converted to a one dimensional H
a
spectrum with 50 data points by the ring summing procedure (Coakley et al., 1996). The horizontal and vertical axes of the spectrum were given in the velocity scale [km s1] and in the intensity scale [R (km s1)1], respectively. The velocity resolution elements of 4 km s1 (0.087 Å) for the spectral resolution within the 200 km s1(4.4 Å) spectral window according to the optical design of the DEFPOS. By using a fitting program, the best Gaussian profile for each spectrum was obtained and the best-fitting intensity, the radial velocity and the line width of the each Ha
spectrum were then determined. A sample reduced CCD data and its spectrum is shown inFig. 1.After the above reduction and analysis, we then found the LSR velocity values from a special calculator1. The uncertainty of the LSR calculation is only a few ten meters per seconds as reported from this web site. The radial velocities were given with respect to the LSR (VLSR). In VLSRcalculation, a location of H
a
line from a Hydrogen lamp was used as a reference in the velocity axis in spec-tra because of the weakness of the geocoronal Ha
emission line. These calibrations were also checked against an empirical predic-tion based on the tuning parameters of the Fabry–Perot etalons. The line center of the geocoronal Ha
emission line is shifted by 2.33 km s1from the rest wavelength of the recombination line at 6562.82 Å(Haffner et al., 2003). Thus, the LSR velocity was cor-rected as VLSR= VLSR 2.33 km s1. The systematic uncertainty of this method is typically 2–3 km s1. The contribution to the uncertainty in the velocity calibration from random noise in the data is mainly less than 2 km s1 (see Table 3) (Aksaker et al., 2009; Aksaker, 2009).Instrumental line width of the DEFPOS is measured to be 29.5 km s1using a Thorium–Argon (Th–Ar) hollow cathode lamp. This value is very close to 30 km s1the instrumental resolution of DEFPOS over the spectral window near the H
a
. The line width val-ues were then convolved by using a line fitting program. The intrinsic line widths can be estimated by quadratic subtraction of the 30 km s1instrumental line width (Aksaker et al., 2009).2.3. Intensity calibration
An intensity calibration for the DEFPOS data has to be per-formed for the following reason: the absolute intensities need to be calculated and they have to be compared with the literature. For the intensity calibration, a standard nebular source, the North
Table 1
Journal of observations.
Data set number Region Coordinates Obs. date Exp. time (s)
a2000(h:m:s) d2000(d:m:s) 1 Sh2–106 20:27:28 +37:23:49 25 Nov. 2007 1200 2 Sh2–125 21:53:33 +47:16:18 26 Nov. 2007 2400 3 Sh2–140 22:19:08 +63:17:07 ’’ 2400 4 Sh2–142 22:47:36 +58:03:40 ’’ 2400 5 Sh2–162 23:20:42 +61:11:52 ’’ 1200 6 Sh2–168 23:53:04 +60:28:23 ’’ 2400 7 Sh2–171 00:04:40 +67:09:24 ’’ 2400 8 Sh2–184 00:52:50 +56:36:37 ’’ 1200 9 Sh2–212 04:40:38 +50:22:52 ’’ 1200 10 Sh2–252 06:09:42 +20:30:00 27 Sep. 2008 600
Fig. 1. (a) The CCD image taken from the center of Sh2–142 HIIregion on 26 November, 2007. b) Top panel shows the spectrum and the residuals of fit were plotted in the bottom panel. The spectrum consist of 50 spectral elements corresponding to a 4 km s1spectral window (+ symbol). The horizontal bar
defines the zero level (see the text for the detailed description of the panels). 1
American Nebula (NAN or NGC 7000), was observed. The absolute intensity of the emission from NGC 7000 was determined by Scherb (1981) using the planetary nebula NGC 7662 and some standard stars as reference objects.Scherb (1981)measured the intensity of the NGC 7000 to be 850 ± 50 R for a 490 FOV using Fabry–Perot spectrometer. This measurement was confirmed by Nossal (1994)by using a blackbody source. Therefore, the value found byScherb (1981)has been used in all 1° WHAM (Haffner et al., 2003) and 0.8° Wisconsin PBO (Pine Bluff Observatory) data sets (Mierkiewicz et al., 2006). We obtained the H
a
spectra from nine different points inside the central region of NGC 7000 with different exposure times (60 s to 1200 s) in different observing nights. These regions were selected within 1° WHAM FOV which is approximately the same area as 490 FOV used by Scherb (1981). The resultant absolute intensity values were then com-pared withIshida and Kawajiri (1968), Scherb (1981), VTSS by Dennison et al. (1998), Morgenthaler et al. (2001)and WHAM by Haffner et al. (2003). These values were all related to NGC 7000.Based on these comparisons and calculations for the 40DEFPOS FOV, the H
a
surface brightness of NGC 7000 (a
= 20h58m04s.0, d= +44°3504300.0, equinox = 2000.0) was taken to be 900 R which is similar value to given inMorgenthaler et al. (2001)for same coordinate. The intensity calibration factor was then found to be 2337.4 R for 1200 s exposure per 1 ADU.km.s1 (Aksaker et al., 2009).There was approximately 15% uncertainty in the absolute inten-sity calibration and 9% uncertainty emerging from the source of random photons of the data obtained from NGC 7000. One more error source need to be added to our intensity calibration; non-uni-form sensitivity of DEFPOS optics within its beam. Thus, we need to measure the beam sensitivity function but we could not do the ab-sence of observation time which is necessary to reduce such errors in the intensity calibration. Detailed intensity calibration of DEF-POS data can be found inAksaker et al. (2009) and Aksaker (2009).
2.4. Selected HIIregions and their stellar parameters
Since angular sizes of many HIIregions observed with DEFPOS
were larger than DEFPOS’s FOV, only the selected coordinates given inTable 1were observed. The ‘Region’ column shows the names of the HIIregions from the Sharpless’ catalog (Sharpless, 1959).Table
1was listed in ascending order of the Sharpless’ catalog numbers for HIIregions.Table 2to supplementTable 1giving the ionizing
stars of each HIIregions is also provided. The names and spectral
types of the central stars which ionize their surrounding gas to cre-ate the HIIregions are listed inTable 2in the second and third
col-umns, respectively. The distance (d) to the HIIregion and angular
diameter (h) of the HIIregion are given in the fourth and fifth col-umns, respectively. The radius of the HIIregions (R) were
calcu-lated from RHII= dsin (hHII/2) (Reynolds, 1988) and were given in
the sixth column.
The stars listed in the second column ofTable 2are young OB stars and they are the ionization sources of HIIregions. These stars
are selected according to the following method. The method relies on a H
a
map from Finkbeiner (2003). The target coordinates of DEFPOS and coordinates of OB stars from Cruz-González et al. (1974), Avedisova and Kondratenko (1984), Cruz-Gonzalez et al. (1995)2andFoster and MacWilliams (2006)were plotted on this map. Each HIIregion and star (s) that (possibly) ionizes thesere-gions were studied in turn. Finally the selection is achieved when the following three criteria are satisfied: (i) DEFPOS pointing should be the closest to the OB star (s); (ii) the radial velocity of the HIIregion found by DEFPOS should be close to the value of
ra-dial velocities of OB stars; (iii) the brightest OB star (s) were then selected, however O type stars were selected first if there is any. The selection method might not be sufficient in finding an exact match. Thus, literature search was also carried out and coordinate and brightness information were retrieved from the work of Cruz-González et al. (1974)using the VizieR service (Ochsenbein et al., 2000).
3. Results and discussion
The intensity, the VLSRand the linewidth of H
a
emission line analysis of these HIIregions were determined and their comparisonwith the literature is given inTable 3. The name of these HIIregions
were given in the first column inTable 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 pro-gram. The HIIregions are further described in subsections, below. Table 2
Adopted parameters for the HIIregions and their ionizing stars.
Region Ionizing star (s) de,f
(kpc) hHIIf(arcmin) RHII(pc)
Name Spectral typed
Sh2–106 NAME SH 2–106 IR O9.5 – 3 – Sh2–125 BD + 46 3474c B1 V 1.0 ± 0.16 9 1 IC5146c Sh2–140 BD + 62 2061b B0.5 V 0.9 ± 0.1 30 4 Sh2–142 HD 215835a O5 3.4 ± 0.3 30 15 Sh2–162 BD + 60 2522a,b,c O6.5III 3.5 ± 1.1 40 20 Sh2–168 ALS 13255 B0 V 3.8 ± 1.2 7 4 Sh2–171 BD + 66 1674a,c B0 0.84 ± 0.1 180 22 BD + 66 1675a,c O7 N 7822 29a,c O9 Sh2–184 HD 5005a,c O5.5 2.2 ± 0.7 40 13 Sh2–212 NGC 1624c – 6.0 ± 0.6 5 4 Sh2–252 HD 42088a,c O6.5 V 1.5 ± 0.15 40 9 a Cruz-González et al. (1974). b
Foster and MacWilliams (2006).
cAvedisova and Kondratenko (1984).
dSpectral type of star retrived from SIMBAD database.
eFich et al. (1989)
f
Blitz et al. (1982).
2
Available at http://viz er.u-strasbg.fr/viz bin/VizieR?-source=III/84Burlhttp://viz er.u-strasbg.fr/viz bin/VizieR?-source=III/84B
3.1. The Sh2–142 HIIregion
This is brightest HIIregion observed with DEFPOS, a large HII
re-gion (300) in Cepheus situated in the Perseus arm with a physical size of 3.4 kpc (Fich et al., 1989) in radius. The region is ionized by the massive eclipsing binary DH Cephei (HD 215835; spectral type of O5). The principal excitation sources are O and early B stars in the system (Chavarria-K. et al., 1994). A CCD image taken from this region and its spectrum are given in Fig. 1. The bright ring on the image represents the H
a
spectrum obtained from the re-gion. In addition to the ring, there are two bad columns and some CCD defects on the image and they were removed in the reduction process. In the top panel ofFig. 1b, real spectrum values are given by plus (+) symbols each of which represents a 4 km s1spectral resolution element and dotted line represents the best Gaussian fit to the spectrum. In the bottom panel ofFig. 1b, the residuals (data minus fit) are plotted. The dashed vertical line represents the difference between center of the spectrum and its fit position of the LSR. Due primarily to the orbital velocity of Earth and the pe-culiar velocity of the Sun with respect to the LSR, this separation depends on both, direction in the sky and time of the observation (Reynolds et al., 1990).The LSR for this spectrum was calculated as 0.17 km s1, the VLSR of the region was measured to be 35.8 ± 0.7 km s1, the FWHM of the line was measured to be 42.9 ± 0.7 km s1, and the intensity of the H
a
emission line was measured to be 349 ± 12 R. These values are consistent with the earlier values ofFich et al. (1990)who observed the linewidths and radial velocities of Ha
emission from many HII regions from the northern hemisphereusing a Fabry–Perot spectrometer at the 0.76 m telescope at the Leuschner Observatory of the University of California. They mea-sured the VLSR to be 36.1 ± 0.2 km s1 and the FWHM as 29.2 ± 0.4 km s1 of the Sh2–142. A study by Blitz et al. (1982) measured VLSRto be 41.0 ± 0.5 km s1line related to the HII re-gions using the 5 m telescope at Milimeter Wave Observatory,
Texas. In addition,Lockman (1989)using the radio recombination lines measured the VLSRand the FWHM of the H
a
emission line to be 36.0 ± 1.8 km s1and 33.0 ± 4.2 km s1, respectively. Finally, Chavarria-K. et al. (1994) measured the mean VLSR as 40.3 ± 0.2 km s1with a Fabry–Perot interferometer which is also consistent with our results. This indicates that present measure-ments of the radial velocity of the HIIregion are a good agreementwith early results in literature. 3.2. The Sh2–106 HIIregion
Sh2–106 HIIregion, also known as GRS 76.4–0.6 and CRL 2584,
is a bipolar nebula embedded in a giant molecular cloud in the con-stellation Cygnus. The star formation region is ionized by an O9.5 star NAME SH 2–106 IR (Gehrz et al., 1982) and is well known as the outflow sources. The optical diameter of the Sh2–106 (from the Sharpless Catalog) is approximately 30with a physical size of 0.5 kpc (Eiroa et al., 1979) in radius. The observations were made using the Fabry–Perot spectrometer on the night of 2007 Novem-ber 25. This HIIregion has the largest linewidth value among the
sources presently measured with our DEFPOS observations. The exposure time was 1200 s. The radial velocity and the linewidth ta-ken from the region were measured to be 2.4 ± 2.9 km s1and 73.0 ± 2.9 km s1, respectively. Its intensity was also measured to be 156.1 ± 12.7 R.Blitz et al. (1982)had also measured the CO ra-dial LSR velocity for same region to be 1.0 ± 1.5 km s1. Addition-ally,Lockman (1989)measured the VLSRand the linewidth to be 4.0 ± 0.6 km s1 and 42.4 ± 1.5 km s1, respectively. Finally, Fich et al. (1990)found the VLSRand the linewidth for same region to be 6.7 ± 0.3 km s1and 64.5 ± 0.6 km s1, respectively.
3.3. The Sh2–125 HIIregion
Sh2–125 HIIregion known as Cocoon Nebula is a very faint neb-ulosity in the constellation Cygnus and is ionized by the B1V class
Table 3
Haobservations from different HIIregions within our galaxy.
Region This work Literature
Intensity (R) FWHM (km s1 ) VLSR(km s1) FWHM (km s1) VLSR(km s1) Reference Sh2–106 156.1 ± 12.7 73.0 ± 2.9 2.4 ± 2.9 64.5 ± 0.6 6.7 ± 0.3 1 42.4 ± 1.5 4.0 ± 0.6 2 1.0 ± 1.5 3 Sh2–125 246.8 ± 11.2 48.4 ± 1.1 1.8 ± 1.1 24.3 ± 0.3 0.4 ± 0.2 1 23.7 ± 3.1 0.9 ± 2.3 2 8.0 ± 1.0 3 Sh2–140 182.5 ± 9.7 40.3 ± 1.1 12.4 ± 1.1 24.3 ± 0.2 8.7 ± 0.1 1 8.5 ± 1.0 3 Sh2–142 348.6 ± 11.7 42.9 ± 0.7 35.8 ± 0.7 29.2 ± 0.4 36.1 ± 0.2 1 33.0 ± 4.2 36.0 ± 1.8 2 41.0 ± 0.5 3 40.3 ± 0.2 4 Sh2–162 745.3 ± 16.1 42.3 ± 0.5 39.6 ± 0.5 35.0 ± 0.3 45.1 ± 0.1 1 23.4 ± 3.5 41.8 ± 1.5 2 44.7 ± 0.5 3 Sh2–168 83.7 ± 11.8 51.2 ± 3.5 35.1 ± 3.5 29.2 ± 0.4 45.5 ± 0.2 1 25.1 ± 3.5 40.8 ± 1.5 2 40.6 ± 1.4 3 Sh2–171 168.3 ± 11.9 42.5 ± 1.5 13.2 ± 1.5 29.8 ± 0.3 12.0 ± 0.2 1 19.8 ± 2.7 9.1 ± 1.1 2 Sh2–184 135.2 ± 14.9 45.3 ± 2.4 24.9 ± 2.4 27.2 ± 0.2 27.3 ± 0.1 1 20.4 ± 1.4 29.7 ± 0.6 2 – 30.4 ± 1.1 3 Sh2–212 162.2 ± 22.7 37.6 ± 2.6 43.2 ± 2.6 30.1 ± 0.2 43.9 ± 0.1 1 22.0 ± 2.4 40.1 ± 1.0 2 35.3 ± 0.3 3 Sh2–252 239.8 ± 14.6 50.0 ± 1.5 3.39 ± 1.4 36.1 ± 0.2 7.7 ± 0.1 1 7.5 ± 1.0 2
star (BD + 46 3474) and the star cluster IC 5146. HIIRegion has a
size of angular diameter of 90 with a physical size of 1 kpc (Fich et al., 1989) in radius. We obtained an H
a
spectrum for the HII re-gion using DEFPOS with an exposure time of 1200 s. The spectrum has a brightness of 246.8 ± 11.2 R. From this spectrum, we found that the VLSR and the linewidth were 1.8 ± 1.1 km s1 and 48.4 ± 1.1 km s1, respectively. In the literature, radial velocity of the HII region were given as + 8.0 ± 1.0 km s1 by Blitz et al.(1982), +0.9 ± 2.3 km s1byLockman (1989)and 0.4 ± 0.2 km s1 byFich et al. (1990). The linewidth values, on the other hand, were given as 24.3 ± 0.3 km s1 by Fich et al. (1990) and 23.7 ± 3.1 km s1byLockman (1989).
3.4. The Sh2–140 HIIregion
Sh2–140 HIIregion is a faint nebula (angular size of 300) and is a
part of the Cepheus Bubble with a physical size of 0.9 kpc in radius in the same constellation (Fich et al., 1989). The HII region was
created by the B0.5 V star BD + 62 2061 (Vmag = 7.75). The H
a
emission line spectrum was measured from the center of HIIregionwith an exposure of 2400 s. The measured VLSR was 12.4 ± 1.1 km s1. The FWHM and the intensity were also measured to be 40.3 ± 1.1 km s1 and 182.5 ± 9.7 R, respectively. Earlier mea-surements were as follows: the VLSRwas found 8.5 ± 1.0 km s1 byBlitz et al. (1982). The VLSRand the linewidth of H
a
emission line were measured as 8.7 ± 0.1 km s1and 24.3 ± 0.2 km s1byFich et al. (1990), respectively.3.5. The Sh2–162 HIIregion
Sh2–162 HIIregion, also known as NGC 7635, lying within the
Perseus arm of the Galaxy is an emission region associated with the O6.5III emission-line star BD + 60 2522 (Vmag = 8.7) located in the Cas OB2 association at distance estimates of 2.6 kpc (Humphreys, 1978) and 3.5 kpc (Fich et al., 1989). The region is characterized by a striking emission ring with a radius of nearly 1.660. We measured the H
a
emission line spectrum from the center of Sh2–162 with an exposure of 1200 s on the night of 2007 November 26. The VLSR velocity for this nebula is found to be 39.60 km s1. The linewidth and the intensity of the nebula are also measured to be 42.25 km s1 and 745.2 R, respectively, (Sahan et al., 2009). For the same region the radial velocity was found earlier to be 44.7 ± 0.5 km s1byBlitz et al. (1982). In addi-tion, the radial velocity and the linewidth were found to be 41.8 ± 1.5 km s1and 23.4 ± 3.5 km s1, respectively byLockman (1989). In the latest study byFich et al. (1990)the radial velocity and the linewidth were measured to be 45.1 ± 0.1 km s1 and 35.0 ± 0.3 km s1, respectively.3.6. The Sh2–168 HIIregion
Sh2–168 HIIregion is in the direction of Cas OB5 associated at Cassiopeia with a physical size of 3.8 kpc (Fich et al., 1989) in ra-dius with an angular size of 70and is ionized by the B0V star ALS 13255 (the nearest bright star). We obtained its H
a
spectrum in 2400 s exposure time and we found the VLSRand the linewidth to be 35.1 ± 3.5 km s1and 51.2 ± 3.5 km s1, respectively. We also found that the intensity value was to be 83.7 ± 11.8 R. Also, the VLSR was given byBlitz et al. (1982)to be 40.6 ± 1.4 km s1. Moreover, the radial velocity and the linewidth were found to be 40.8 ± 1.5 km s1and 25.1 ± 3.5 km s1, respectively, byLockman (1989) and 45.5 ± 0.2 km s1and 29.2 ± 0.4 km s1, respectively, byFich et al. (1990).3.7. The Sh2–171 HIIregion
Sh2–171 HIIregion is a very faint extensive nebula in the con-stellation Cepheus, created by the star cluster at the heart of Cep OB4 with an angular diameter of 1800 and with a physical size of 840 pc (Blitz et al., 1982) in radius. It is ionized by the young star cluster which have BD + 66 1674, BD + 66 1675 and N 7822 29 as ionizers. We measured its VLSR and the linewidth to be 13.2 ± 1.5 km s1 and to be 42.5 ± 1.5 km s1, respectively. We also measured intensity to be 168.3 ± 11.9 R. The exposure time for the observation was 2400 s.Lockman (1989)measured the VLSR and the linewidth of the H
a
emission line to be 9.1 ± 1.1 km s1 and 19.8 ± 2.7 km s1, respectively.Fich et al. (1990)also measured the VLSR and the linewidth to be 12.0 ± 0.2 km s1 and 29.8 ± 0.3 km s1.3.8. The Sh2–184 HIIregion
Sh2–184 HIIregion, often called NGC 281, is located far below
the galactic plane with a physical size of 2.2 kpc (Fich et al., 1989) in radius and is ionized by the double or multiple star in which the brightest is HD 5005 (O5.5). Sh2–184 has an angular size of 400. H
a
observation of the region was made using DEFPOS on the night of 2007 November 26 with 1200 s exposure times. We mea-sured the VLSRof the HII region to be 24.9 ± 2.4 km s1and thelinewidth and the intensity to be 45.3 ± 2.4 km s1 and to be 135.2 ± 14.9R, respectively. In the literature, Blitz et al. (1982) had earlier found that its VLSRwas to be 30.4 ± 1.1 km s1. Lock-man (1989)measured the VLSRand the linewidth of the Sh2–184 HII region to be 29.7 ± 0.6 km s1 and to be 20.4 ± 1.4 km s1,
respectively.Fich et al. (1990)also measured the VLSRand the line-width of the H
a
emission line to be 27.3 ± 0.1 km s1 and 27.2 ± 0.2 km s1, respectively.3.9. The Sh2–212 HIIregion
The Sh2–212 HIIregion is an optically bright intermediate size
( 250) HIIregion and contains the young star cluster NGC 1624 (Sharpless, 1959). It lies high above the Galactic plane with a phys-ical size of 6 kpc (Fich et al., 1989) in radius and far from the Galac-tic centre (14.7 kpc) with a diameter of 50. Its diameter is thus close to the DEFPOS’ FOV, it is important for us to observe. Average radial velocity and the FWHM of the DEFPOS data for the Sh2–212 HII
re-gion as 43.2 ± 2.6 km s1and 37.6 ± 2.6 km s1, respectively, and the intensity was 162.2 ± 22.7 R. The exposure length was 1200 s for this image. In the literature, the VLSRwas also reported to be 35.3 ± 0.3 km s1byBlitz et al. (1982).Henkel et al. (1986) dis-covered an H2O maser associated with the Sh2–212 at VLSR= 35 km s1. The radial velocity and the linewidth obtained from the same region were given as 40.1 ± 1.0 km s1 and 22.0 ± 2.4 km s1byLockman (1989)and 43.9 ± 0.1 km s1 and 30.1 ± 0.2 km s1byFich et al. (1990), respectively.
3.10. The Sh2–252 HIIregion
Sh2–252 HIIregion, also known as the Monkey’s Head Nebula,
surrounds the NGC 2175 star cluster in the depths of the Gemini giant molecular clouds (Sharpless, 1959). The main exciting star for the HIIregion, O6.5 V star HD 42088, is located near the center
of the nebula. H
a
observations of Sh2–252 was made on the night of 2009 September 27 with a 600 s exposure time. The FWHM and the VLSRof Sh2–252 HIIregion were found to be 50.0 ± 1.4 km s1 and 3.39 ± 1.4 km s1, respectively, and the intensity was approxi-mately 239.8 ± 14.6R. Blitz et al. (1982) gave a velocity of 7.5 ± 1.0 km s1for this source.Fich et al. (1990)also gave the VLSR as 7.7 ± 0.1 km s1and the linewidth as 36.1 ± 0.2 km s1.
3.11. Discussion
A total of 10 H
a
spectra obtained from different 10 HIIregions using a dual etalon Fabry–Perot spectrometer called DEFPOS have been compared with the data fromFich et al. (1990)and other re-searches given in literature. The results are given inTable 3 Fich et al. (1990)used a Fabry–Perot spectrometer with 15 km s1 spec-tral resolution and 2 arcmin FOV similar with DEFPOS. Since this Fabry–Perot spectrometer usedFich et al. (1990)has higher spec-tral resolution and narrower FOV than that of DEFPOS, it resolves smaller linewidths of sources than DEFPOS. However, the VLSR and their errors values are approximately similar for both spec-trometers. Since other researchers used completely different experimental setup, the results were not fully compatible with each other and therefore were analyzed in detail in Sections3.1– 3.10.As is known, VLSR of Galactic sources may change with ±100km s1and thus V
LSRof the target HIIregions were in between
3 and 43 km s1(seeTable 3). Many of the regions are receding from the LSR. As expected, their VLSRvalues were found close to the measured VLSRvalues from the Galactic rotation. If we compare our VLSRvalues withFich et al. (1990), the difference of the VLSR be-tween DEFPOS andFich et al. (1990)is smaller than 5 km s1. Thus, referring toTable 3, the VLSRvalues of the DEFPOS data are well cor-related with the VLSRof theFich et al. (1990). On the other hand, they can be easily seen that the VLSRvalues of other researchers have larger discrepancy with each other (e.g. Sh2–106, Sh2–168 etc.). In general, when the VLSRvalues of DEFPOS data when com-pared to the literature, it was found that the difference was approximately ± 3 km s1. This difference is acceptable error, be-cause, some data in literature are from instruments very different from each other.
Since the instrumental resolution of DEFPOS was approximately 30 km s1over the spectral window near H
a
(Sahan et al., 2009), linewidths less than 30 km s1 can not be resolved. Moreover, instrumental profile of the DEFPOS is larger than that of used by Fich et al. (1990) (15 km s1). From some literature values, we can easily see that, FWHM values have larger than ( 30km s1) discrepancy with respect to each other (e.g. Sh2–106, Sh2–162 etc.). The FWHM values of DEFPOS data are approximately 10 km s1larger than the literature values because of our poorer instrumental resolution (seeTable 3). Consequently, since the res-olution of our spectrometer is lower, we measure larger FWHM values than that of literature. Moreover, we did not apply any cor-rection for instrumental profile and we didn’t make any estimation for the instrumental effect, in order not to include further compli-cations to the evaluation processes. An estimation of intrinsic line widths was actually be made by the quadratic subtraction of the 30 km s1instrumental line width (Aksaker et al., 2009) which are in the range 30 to 73 km s1.Intensities of the H
a
emission line of HIIregions were found tobe in the range of 84-745 R (seeTable 3). As expected, our values are brighter than 25-45 R measured byReynolds et al. (1990)from the Diffuse Ionized Gas (DIG). For the intensity calibration,Fich et al. (1990)did not use a standard astronomical source. Instead, they assumed the peak height of H
a
profile was related to its inten-sity. Therefore, we didn’t compare the intensities with the other re-sults, because of different units and FOVs. Details of DEFPOS measurements (the intensity, the linewidth and the VLSR) with their error sources were also discussed earlier inAksaker et al. (2009). 4. ConclusionsThe DEFPOS instrument is a Fabry–Perot spectrometer was rec-onfigured to carry out HIIobservations from Diffuse Ionized Gas in the PNe, HIIregions, 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 H
a
emission line within 200 km s1 (4.4 Å) spectral window with a field of view of 40and with a spectral res-olution of 30km s1. Further details on design of the spectrome-ter can be found inSahan et al. (2009).Integrated H
a
emission line profiles of 10 HIIregions have beenobtained with a Fabry–Perot spectrometer with DEFPOS. The inten-sity, the radial velocity and the linewidths of the H
a
emission line are found to be in the range of 84 to 745 R, 30 to 73 km s1and 3 to 43 km s1, respectively (Table 3). All measurements have been done with relatively high signal to noise ratio. As can be seen in Table 3, the measured parameters (the linewidth and the VLSR) are consistent with the literature except for Sh2–106 and Sh2– 162 for which no explanation is seen except widely differing instrumentation and calibration processes. Further observations of these sources can resolve the dispute. The linewidths of DEFPOS data were found to be in general, about 10 km s1larger than that of literature. Also, comparing the DEFPOS data with literature we found that our VLSRvalues differ approximately by 3 km s1. Thus, in general, for most of the cases, we confirm already known prop-erties of these 10 HIIregions obtained with DEFPOS.In addition, we have also studied the central parts of the target HII regions. As an outcome of these studies, associated stars of
some of the HIIregions were updated by analyzing their location,
velocities and brightness (see Section2.4). Some of the associated stars were just confirmed with the present analysis. Thus, we pres-ent our study as a contribution and a reference to the study of Gal-axy dynamics and of HII region properties. Results show that DEFPOS is a reliable new instrument in the field and we will con-tinue H
a
observation of HIIregions and a complete catalog of suchsources will be constructed in the near future. 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 nu1.5-mber 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 correcting the manuscript and for their remarks. We special thank an anonymous referee for help-ful comments. This work is supported by the TUBITAK (The Scien-tific and Technical Research Council of Turkey) with Grant No. 104T252. NA gratefully acknowledges support through a Post-Doc Fellowship from the TUBITAK-BIDEB at Physics Department of Mid-dle East Technical University. This work also supported with Aca-demic Research Project unit of Cukurova University with Grant No. TBMYO2010BAP4.
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