J/ApJS/91/659 Ultracompact HII regions radio images (Kurtz+ 1994)
Ultracompact HII regions II. New high-resolution radio images.
Kurtz S., Churchwell E., Wood D.O.S.
<Astrophys. J. Suppl. Ser. 91, 659 (1994)>
=1994ApJS...91..659K 1994ApJS...91..659K (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Radio sources
Keywords: H II regions - ISM: structure - radio continuum: ISM
Abstract:
Radio continuum observations were made of 59 IRAS sources that have
100µm flux densities ≥1000Jy and far-infrared colors identified
with ultracompact (UC) HII regions. Eighty percent were found to have
associated compact radio sources. Seventy-five sources were detected
at ≲1" resolution at 3.6 and 2cm wavelengths, for which we provide
contour plots and flux density distributions ranging from the radio to
the near-infrared. Over half are unresolved and their morphologies
undetermined. The remaining sources can be described by only five
morphological classes, whose frequency of occurrence is consistent
with that of the Wood and Churchwell survey (1989ApJS...69..831W 1989ApJS...69..831W). We
calculate physical properties of the nebulae and show that they are
consistent with UC photoionized regions. Alternative explanations are
explored and found to be unlikely. The correlation of UC HII region
positions with proposed spiral arms is examined and found to be well
correlated only for the local spiral arm or "spur". No obvious
enhancement of UC HII regions is apparent along the proposed
Sagittarius and Scutum arms, probably because of inaccuracies in the
kinematic distances. We find the latitude distribution of UC HII
regions to lie in the range 0.5deg<[bFWHM]≤0.8deg. No correlation
between size and density of cometary and core-halo UC HII regions is
found, consistent with the bow shock interpretation of these
morphologies. Spherical and unresolved UC HII regions, however, appear
to show a trend toward lower densities with increasing size, as
expected for expanding HII regions. The observed ratios of
far-infrared to radio flux densities of UC HII regions lie in the
range 103 to ≥105. By applying the results of model atmospheres,
it is shown that this ratio depends on spectral type, ranging from
∼103 for an O4 star to ≥105 for a B3 star. We find that many of
the UC HII regions in our sample must be excited by a cluster of
stars, and most probably contain significant amounts of dust.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 111 135 Observed Source Parameters
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See also:
1989ApJS...69..831W 1989ApJS...69..831W : Wood and Churchwell, Paper I
Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Radiosource designation
17- 18 A2 --- Mtype Morphological type (1)
21- 23 F3.1 cm lambda Observations wavelength (2 or 3.6)
25- 26 I2 h RAh Source right ascension (1950) (2)
28- 29 I2 min RAm Source right ascension (1950)
31- 36 F6.3 s RAs Source right ascension (1950)
38 A1 --- DE- Declination sign
39- 40 I2 deg DEd Source declination (1950) (2)
42- 43 I2 arcmin DEm Source declination (1950)
45- 49 F5.2 arcsec DEs Source declination (1950)
51- 55 F5.1 mJy SPeak ? Peak flux density (in mJy/beam)
57- 62 F6.1 mJy SInt ? Integrated flux density
64- 67 F4.1 arcsec RAbox ? Integrated box right ascension
69- 72 F4.1 arcsec DEbox ? Integrated box declination
74- 77 F4.1 arcsec Dmax ? Maximum diameter (3)
78 A1 --- n_Dmax [P] P: Ponctual source
80- 83 F4.1 arcsec Dmin ? Minimum diameter (3)
84 A1 --- n_Dmin [P] P: Ponctual source
86- 89 F4.2 arcsec Maj Half-power beam width (HPBW) major axis
91- 94 F4.2 arcsec Min Half-power beam width (HPBW) minor axis
96- 99 F4.2 mJy Map Map RMS (in mJy/beam)
100-105 A6 --- Note Notes (4)
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Note (1): We use the following abbreviations for the morphological types:
C = cometary
CH = core-halo
G = Gaussian
U = unresolved
SH = shell
MP = multiply peaked
I = irregular
Note (2): Source positions are accurate to approximately 0.1". We report
positions to 0.01" only to aid in the identification of closely
spaced components.
Note (3): Source dimensions are accurate to within approximately 15%.
Note (4): 1: Examination of the 3.6cm map indicates that this source is too
large to be imaged at 2cm in the B array. Although the source
was detected, no fluxes can be reliably reported.
2: Source is marginally detected at 2cm, observed parameters should
be considered approximate.
3: Source has an extended tail to the east. The source sizes reported
are for the core region of emission, but the integration boxes for
the flux densities include the tail.
4: At 3.6cm this appears as a multiply peaked source. At 2cm it is
resolved into two sources, G32.796+0.191 and a cometary source to
the north, G32.797+0.191. The 3.6cm flux density is for both
sources, but the 2cm flux is for G32.796 only.
5: At 3.6cm this is not resolved from G32.797; a separate 3.6cm flux
density cannot be measured. The peak position at 3.6cm is the
position quoted for the two sources combined (see note 6).
6: At 3.6cm this is not resolved from G32.796; the peak position and
flux at 3.6cm are reported, but a separate integrated flux
density cannot be determined.
7: A central core with an extended tail to the north; the flux density
and size given here are for the core only.
8: The total flux density of the complex-including the three
individual sources and the extended tails-is 2.55 Jy at 3.6cm
(10.3"x12.2" integration box) and 2.52 Jy at 2cm (9.1"x12.7"
integration box).
9: Field contains both as compact Gaussian component (G43.237-0.046)
and an extended irregular source (G43.239 0.049). The integrated
flux density for the irregular source was calculated by measuring
the total for both, then subtracting the flux density from a
Gaussian fit of G43.237-0.046.
10: Sizes and flux densities given are for the central core only. A
broad extension to the south of size 7"x4" gives a total
integrated flux density of 78.2mJy at 3.6cm and 61.5mJy at 2cm.
11: Due to the large primary-beam correction factor, the 2cm flux
density cannot be reliably reported.
12: G28.198-0.150 and G28.200-0.049 are ∼7" apart but are plotted
separately to emphasize the structure of G28.198-0.150, which is
10-20 times weaker than G28.200-0.049. The structure of
G28.198-0.150 varies significantly between 3.6 and 2cm.
13: The 3.6 and 2cm images strongly suggest that more than one
ionization source is present.
14: A second source, G35.025+0.350, is detected ∼2" to the east, so
this field is designated as a complex. The second source is
marginally detected, and no flux densities are reported.
15: The wide-field images suggest that this is a compact source
embedded in a larger field of emission.
16: This field is designated a complex, since 2 separate sources
appear to be present; the angular separation is very small,
however.
17: This source is in the Cep A East field. There are numerous weak
components in the field which we do not image well with our
snapshot observations. For more extensive observational results
see Hughes (1988ApJ...333..788H 1988ApJ...333..788H).
18: This is the S 140 complex. Coincidence of radio and IR peaks is not
strong: IR peaks are seen without significant radio emission and
vice versa. See the references indicated in the flux density
distribution (Fig.137) for additional information.
19: This is the DR 21 complex. Large-scale structures have been
suppressed by removal of the shortest baselines. We detect a third
component in the field at delta 42deg09'03" (see Fig.73) but do
not report it as a source. Roelfsema, Goss & Geballe
(1989A&A...222..247R 1989A&A...222..247R) report it as component B.
20: G70.330+1.589 and its eastern companion G70.333+1.586 are both
shown in the 3.6cm map (Fig.55); only the former is detected at
2cm (Fig.56). Both of these components are more than 2' from the
IRAS position, which is coincident with the K3-50 nebula. G70.330
is component C1, and G70.333 is C2 in both Golley & Scott
(1977MNRAS.181..703C 1977MNRAS.181..703C) and Harris (1975MNRAS.170..139H 1975MNRAS.170..139H).
21: Turner & Matthews (1984ApJ...277..164T 1984ApJ...277..164T) report ∼0.1" resolution
observations and classify both K3-50 (G70.293+1.600) and component
C1 (G70.330+ 1.589) as shell structures.
22: Literature values for the distance to ON1 range from 0.4 to 6.6kpc.
A value of 1.4 kpc seems the most popular, but we consider the
distance too uncertain to derive parameters. Turner & Matthews
(1984ApJ...277..164T 1984ApJ...277..164T) report ∼0.1" resolution observations and
classify it as a shell morphology. Zheng et al.
(1985ApJ...293..522Z 1985ApJ...293..522Z) provide a useful map showing the radio
continuum overlaid with infrared and H2O and OH maser
positions from the literature.
23: The 3.6cm map (Fig.19) suggests a cometary morphology, but the 2cm
map (Fig.20) is ambiguous.
24: This source lies on the eastern edge of S252, component C, as
reported by Felli, Habing, & Israel (1977A&A....59...43F 1977A&A....59...43F).
25: Marti, Rodriguez, & Reipurth (1993ApJ...416..208M 1993ApJ...416..208M) have made deep
continuum images of this source at 20, 6, 3.6, and 2cm. In their
maps the object appears highly elongated and is the central
exciting source of a very highly collimated double jet with a
total projected extent of 5pc.
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History: Prepared via OCR at CDS.
* 25-Aug-1997: errata to table3 forwarded by H. Andernach
A, from a comparison with a TeX file
from Stan Kurtz
(End) James Marcout, Patricia Bauer [CDS] 17-Mar-1997