J/AJ/150/147 Galactic HII regions. I. Stellar distances (Foster+, 2015)
A CGPS look at the spiral structure of the outer Milky Way.
I. Distances and velocities to star-forming regions.
Foster T., Brunt C.M.
<Astron. J., 150, 147 (2015)>
=2015AJ....150..147F 2015AJ....150..147F (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; H II regions ; Nebulae ; Stars, distances ;
Stars, nearby
Keywords: H II regions - ISM: kinematics and dynamics
Abstract:
We present a new catalog of spectrophotometric distances and line of
sight systemic velocities to 103 HII regions between
90°≤l≤195° (longitude quadrants II and part of III). Two
new velocities for each region are independently measured using 1
arcmin resolution 21cm HI and 2.6mm12CO line maps (from the Canadian
Galactic Plane Survey and Five College Radio Astronomy Observatory
Outer Galaxy Surveys) that show where gaseous shells are observed
around the periphery of the ionized gas. Known and neighboring O- and
B-type stars with published UBV photometry and MK classifications are
overlaid onto 21cm continuum maps, and those stars observed within the
boundary of the HII emission (and whose distance is not more than
three times the standard deviation of the others) are used to
calculate new mean stellar distances to each of the 103 nebulae. Using
this approach of excluding distance outliers from the mean distance to
a group of many stars in each HII region lessens the impact of
anomalous reddening for certain individuals. The standard deviation of
individual stellar distances in a cluster is typically 20% per stellar
distance, and the error in the mean distance to the cluster is
typically ±10%. Final mean distances of nine common objects with
very long baseline interferometry parallax distances show a 1:1
correspondence. Further, comparison with previous catalogs of HII
regions in these quadrants shows a 50% reduction in scatter for the
distance to Perseus spiral arm objects in the same region, and a
reduction by ∼1/20.5 in scatter around a common angular velocity
relative to the Sun Ω-Ω0(km/s/kpc). The purpose of the
catalog is to provide a foundation for more detailed large-scale
Galactic spiral structure and dynamics (rotation curve, density wave
streaming) studies in the 2nd and 3rd quadrants, which from the Sun's
location is the most favorably viewed section of the Galaxy.
Description:
The cornerstone of our catalog of HII regions is the new systemic
velocity measurements (with respect to the LSR), which come from
high-resolution (1arcmin) λ21cm HI data and λ2.6mm
12CO (J=1-0) data. The HI data are entirely from the Canadian
Galactic Plane Survey (CGPS; Taylor et al. 2003, cat. VI/128), whereas
CO data are from either CGPS or the Exeter Five College Radio
Astronomy Observatory (FCRAO) CO Galactic Plane Survey (described in
Mottram & Brunt, 2010ASPC..438...98M 2010ASPC..438...98M; C. M. Brunt et al. 2013, in
preparation), depending on longitude. Our catalog covers HII regions
in the outer Galaxy only (R>R0) in the longitude range
90°≤l≤193° and mainly within a latitude of
-3.5°≤b≤+5.5°. A high-latitude extension was also
observed as part of the CGPS (99.85°≤l≤116.96°) up to
b=+17.56°. The complete CGPS data set of 21cm line and continuum
from 50.2°≤l≤193.3° and -3.55°≤b≤+5.55°
are available at the Canadian Astronomy Data Centre (CADC;
http://cadc.hia.nrc.ca/).
21cm HI line observations used herein were carried out with the
seven-element interferometer and 26m radio telescopes at the Dominion
Radio Astrophysical Observatory for the CGPS (Taylor et al. 2033, cat.
VI/128).
To trace molecular material in the second quadrant, we make use of the
FCRAO Outer Galaxy Survey (OGS; Heyer et al., 1998ApJS..115..241H 1998ApJS..115..241H).
We present our full catalog of 355 stars found in and around Galactic
HII regions in Table1. Table2 in this paper gives the final
heliocentric stellar distance to each of 103 nebulae in the outer
Galaxy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 152 380 HII regions, HI and 12CO velocities, distances
with fractional uncertainties, and photometric and
spectroscopic information for stars identified as
candidates for association with the region
table2.dat 71 110 Final velocities, distances with uncertainties,
number of stars and mean total reddening
calculated for each HII region
notes.dat 433 380 Notes (comments on ionizing star(s))
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See also:
VI/128 : Log of CGPS exposures (Taylor+, 2003-)
VII/50 : CO Radial Velocities Toward Galactic H II Regions (Blitz+ 1982)
J/ApJ/672/930 : Distant CO clouds in third galactic quadrant (Vazquez+, 2008)
J/A+A/397/213 : Galactic HII regions (Paladini+, 2003)
J/A+A/397/133 : Star-forming complexes in the Galaxy (Russeil+, 2003)
http://cadc.hia.nrc.ca/ : Canadian Astronomy Data Centre
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- HII Identifier of the HII region
14- 23 A10 --- OName Other name (Sh2-208=Wat 1)
25- 30 F6.2 deg GLON [90.23/197.82]? Galactic Longitude
32- 36 F5.2 deg GLAT [-6.29/8]? Galactic Latitude
38- 44 F7.2 km/s vCO ? The 12CO velocity
46- 65 A20 --- n_vCO Note for grouped objects (1)
67- 74 F8.3 km/s vHI [-102.46/23.68]? The HI velocity
76- 83 A8 --- n_vHI Name of association (CAS OB4, CAS OB7, CEPOB4,
Cep OB2, NGC 1893)
85- 89 F5.1 km/s vHa [-98.9/24.2]? The Hα velocity (from Fich et
al., 1990AJ.....99..622F 1990AJ.....99..622F)
91- 95 F5.2 kpc [0.6/10.58]? Mean distance or location
97-100 A4 --- f_ [exc.] Excluded star (do not contribute to the
final distance calculation)
102-105 F4.2 --- dr/ [0.01/0.33]? Fractional distance uncertainty
ΔDr/
107-112 F6.4 mag E(B-V) [0.128/2.415]? The (B-V) color excess
114-118 F5.2 mag Vmag [5.06/17.53]? The V band magnitude
120-125 F6.3 mag B-V [-0.06/2.11]? The (B-V) color index
127-130 A4 --- SpT Spectral type
132-134 A3 --- LC Luminosity class (Ia, Iab, Ib, II, III, IV,
V, or (V)=assumed LCV)
136-142 F7.4 mag E(B-V)0 [-0.33/-0.13]? Reddening corrected (B-V) color
excess
144-148 F5.2 mag VMag [-6.9/-0.9]? Reed (2003AJ....125.2531R 2003AJ....125.2531R) absolute
V band magnitude
150-152 I3 --- N [1/380] Note identification number (2)
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Note (1): Some objects in Hou et al. (2009A&A...499..473H 2009A&A...499..473H) are "grouped"
together into two entries with duplicated distances and velocities. For
proper comparison to our data (which is not grouped) we remove one member
of the Sh2-148/149 from the comparison. See Section 5.1 for additional
details.
Note (2): This column was added at CDS.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1 A1 --- A [A] Additional HII region beyond Canadian
Galactic Plane Survey (CGPS; Taylor et al.
2033, cat. VI/128) (1)
3- 12 A10 --- HII Identifier of the HII region
14- 18 A5 --- OName Other name for Sh2-208 (Wat 1)
20- 26 F7.3 deg GLON [90.23/197.8] Galactic Longitude
28- 33 F6.3 deg GLAT [-6.29/8] Galactic Latitude
35- 41 F7.2 km/s vCO [-103.7/25.6]? Final systemic 12CO velocity
43- 49 F7.2 km/s vHI [-102.46/23.68]? Final systemic HI velocity
51- 55 F5.2 kpc r [0.6/10.58] Final heliocentric stellar distance
57- 60 F4.2 kpc dr [0.04/1.99] Uncertainty in the mean distance
to the HII region
(dr=σ*/(n*)0.5) (2)
62- 63 I2 --- Ns [1/13] Number of associated stars identified
65 I1 --- Ne [1/4]? Number of excluded stars
67- 71 F5.3 mag <E(B-V)> [0.27/2.415] Mean total reddening
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Note (1): We include mean stellar distances calculated to seven additional HII
regions (associated with 10 additional stars) just outside the CGPS
high-longitude border (Sh2-261 and Sh2-267 through 272). Although these
objects could not be scrutinized in the same way as regions observed in the
Canadian Galactic Plane Survey (CGPS; Taylor et al. 2003, cat. VI/128) 21cm
maps and (thus) are not part of our main catalog, Sh2-267-272 in particular
are an important cluster of six HII regions tracing the extension of the
Cygnus spiral arm into the 3rd quadrant (discussed in Paper II,
T. Foster & C. Brunt 2013, in prep.), so their distances are presented here
for use later on.
Note (2): Fifty-six of the nebulae have two or more associated stars identified,
so uncertainties in the mean distance to the HII region can be assessed
directly with the standard deviation of stellar distances in a cluster of
n* stars as σ*/(n*)0.5. Here σ* is the standard
deviation of the stars 'distances, or the average uncertainty in an
individual star's distance.
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Byte-by-byte Description of file: notes.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- HII Identifier of the HII region
14- 16 I3 --- N Note identification number
18 A1 --- f_Note [r] Flag - Spectral type of star in literature
probably wrong; Radio/IR ratio method
indicates significantly different spectral
type of ionizing source
20-433 A414 --- Note Additional comments on ionizing star(s)
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History:
From electronic version of the journal
References:
T. Foster & C. Brunt 2013, Paper II
Paper III
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 18-Apr-2016