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J/A+A/268/419 HII Regions in NGC 4258 (Courtes+ 1993)
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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
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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
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.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 53 137 The catalogue
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Table 1: Observational parameters for NGC 4258
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Telescope Aperture FWHM EqF* Source
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1 OHP 193cm F/l Halpha 50A 1.93m 1
2 OHP 193cm F/2 Halpha 10A 3.86m 2
3 OHP 193cm F/l Halpha 6A* 1.93m 3
4 Meg 160cm F/3.5 Halpha 10A* 5.60m 4
5 OHP 120cm F/6 Halpha 48A 7.20m 5
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* EqF = Equivalent focal length. Filters centred at peak wavelength
corresponding to (3): 310 km/s and (4): 463 km/s with a
resolution of 1.1" per pixel.
References:
1) Courtes & Cruvellier 1961, A&A 200, 58
2) Deharveng & Pellet 1970, A&A 9, 181
3) Courtes et al. 1965, "Quasi Stellar Sources and Gravitational
Collapse", Univ. Chicago Press, 307
4) Martin et al. 1989, ApJ 345, 707
5) This paper with 0.83" per pixel.
In 1 and 5, the [NII] line contribution is not negligible (~30%)
due to the 48-50A bandwidths.
Table 2: Observed Fields in NGC 4258 (Centres of the fields)
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Area alpha (1950) delta
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N 19h 16m 01s +47d39'01"
C 12h 16m 29s +47d34'53" Field Centre
S 12h 16m 48s +47d28'59"
Sa 12h 16m 43s +47d32'45"
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Reference Star Positions (1950) (see Fig.1)
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12h 15m 59.022s +47d40'45"02
12h 16m 02.921s +47d35'48"79
12h 16m 22.033s +47d30'52"06
12h 16m 32.994s +47d25'57"11
12h 16m 41.500s +47d29'49"20
12h 16m 43.324s +47d27'48"08
12h 17m 02.810s +47d36'06"24
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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2- 5 A4 --- Name HII region name as shown in the charts (1)
7- 13 F7.2 arcsec Xpos Position of photometric centre (East)
15- 21 F7.2 arcsec Ypos Position of photometric centre (North)
23- 26 I4 10-19W/m2 F(Ha) Total H-alpha flux uncorrected for extinction
(10-16 erg/cm2/s)
28- 33 F6.2 10+30W Lum Luminosity based on a distance of 5.5Mpc
35- 39 F5.2 10-7W log(Lum) Logarithm of luminosity (in erg/s)
42- 45 F4.1 arcsec Deff ? Half-flux effective diameter (2)
49- 52 F4.1 arcsec Dgeom Geometrical diameter
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Note (1): the designation is made of a running number in one of the
four fields S, Sa, C and N (see Table 2)
Note (2): see definition in Milliard & Marcellin 1981, A&A 95, 59.
For bubbles the limit geometrical diameters are provided.
The value is blank if the region is not resolved
Historical Notes: Keypunched at CDS
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(End) James Marcout, Francois Ochsenbein [CDS] 13-Jul-1995