J/ApJS/149/123 WSRT survey of Cygnus OB2 (Setia Gunawan+, 2003)
A Westerbork Synthesis Radio Telescope 1400 and 350 MHz continuum survey of the
Cygnus OB2 association, in search of hot massive stars.
Setia Gunawan D.Y.A., de Bruyn A.G., van der Hucht K.A., Williams P.M.
<Astrophys. J. Suppl. Ser. 149, 123 (2003)>
=2003ApJS..149..123S 2003ApJS..149..123S
ADC_Keywords: Associations, stellar ; Radio sources
Keywords: binaries: general -
open clusters and associations: individual (Cygnus OB2) -
radio continuum: stars - stars: winds, outflows - surveys
Abstract:
We present a radio continuum survey at 1400 and 350 MHz of a region of
2°x2° centered on the Cygnus OB2 association (d=1.7kpc),
using the Westerbork Synthesis Radio Telescope (WSRT) with angular
resolutions of, respectively, 13" and 55". The resulting 5σ
flux-density limits of, respectively, ∼2mJy and ∼10-15mJy are a
significant improvement over previous surveys. We detected 210
discrete sources with sizes less than 1.9θbeam (beam size),
98 of which at both frequencies. We also detected 28 resolved sources
(sizes>1.9θbeam) still having well-defined peak intensities.
The observed spectral index α1400350 distribution and source
count strongly suggest an excess of sources of Galactic origin in the
direction of Cyg OB2.
Description:
The Cygnus region is too large to be imaged with a single pointing of
the 25m dishes of the WSRT. The half-power beamwidths (HPBW) of the
WSRT at 350 and 1400MHz are about 2.4° and 0.6°, respectively.
Therefore, we used a mosaicking technique at both frequencies. The
350MHz observations were taken in 1994 as part of a larger survey of
the Galactic plane in the Cygnus area (Vashist & de Bruyn,
unpublished); only a small part of it is used in this study.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 78 238 Discrete 1400-MHz and 350-MHz sources in Cyg OB2
table7.dat 135 247 *Sources identification.
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Note on table7.dat: Most sources fall within the 1400-MHz beam, except IRAS and
low-frequency objects, where larger angular separation is used. Refer to
Section 5 for sources with low LR (likelihood ratio).
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See also:
II/241 : 2MASS second incremental release
V/114 : MSX6C Infrared Point Source Catalog (Egan+ 2003)
VIII/42 : Texas Survey of radio sources at 365MHz (Douglas+ 1996)
J/ApJS/74/181 : Small-diameter radiosources catalogue (Zoonematkermani+, 1990)
J/AJ/101/1408 : Massive stars in Cyg OB2. (Massey+ 1991)
J/A+A/241/551 : Radio continuum in Cygnus X region (Wendker+ 1991)
J/A+AS/111/407 : VI Cygni red + reddened stars (Parthasarathy+, 1995)
J/ApJS/107/239 : 327 MHz survey of the galactic plane (Taylor+ 1996)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- SBHW The source sequence number (1)
6- 10 F5.1 mJy S1400MHz ? Flux density at 1400MHz
12- 14 F3.1 mJy e_S1400MHz The 1σ error in S1400MHz (2)
16- 19 I4 mJy SC1400MHz ? Convolved flux density at 1400MHz
21- 23 I3 mJy e_SC1400MHz The 1σ error in SC1400MHz (2)
25- 27 I3 mJy S350MHz ? Flux density at 350MHz
29- 30 I2 mJy e_S350MHz The 1σ error in S350MHz (2)
32 A1 --- l_Sp+Index [:<>] Limit flag on Sp+Index
33- 37 F5.2 --- Sp+Index ? Spectral index (3)
39 I1 --- f_Sp+Index [1/4] Flag on Sp+index (4)
41- 42 I2 h RAh Hour of Right Ascension (J2000) (5)
44- 45 I2 min RAm Minute of Right Ascension (J2000) (5)
47- 51 F5.2 s RAs Second of Right Ascension (J2000) (5)
53- 56 F4.2 s e_RAs Error in RAs (5)
58 A1 --- DE- Sign of the Declination (J2000) (5)
59- 60 I2 deg DEd Degree of Declination (J2000) (5)
62- 63 I2 arcmin DEm Arcminute of Declination (J2000) (5)
65- 69 F5.2 arcsec DEs Arcsecond of Declination (J2000) (5)
71- 75 F5.2 arcsec e_DEs Error in DEs (5)
77 I1 --- Size [1/4] Source size flag (6)
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Note (1): SBHW 001 - 211 are compact sources; SBHW 212 - 238 are extended
sources with sizes >1.9θbeam.
Note (2): A combination of the formal error from the fitting result and a
systematic error of 2% of the flux density.
Note (3): Derived from the flux densities in the convolved 1400 and 350-MHz
images.
Note (4): Denotes whether the spectral index was derived from a detection or
using the local rms noise in one or both of the images.
1 = SC1400MHz / S350MHz
2 = SC1400MHz / (3*e_S350MHz)
3 = (3*e_SC1400MHz) / S350MHz
4 = (3*e_SC1400MHz) / (3*e_S350MHz)
Note (5): When a source is detected in all images then the position listed
is only from the high-resolution 1400-MHz image, otherwise it is from
the 350-MHz image.
Note (6): Source size flags are numbered as follows:
1 = Ss<1.3θbeam
2 = 1.3θbeam<Ss<1.6θbeam
3 = 1.6θbeam<Ss<1.9θbeam
4 = Ss>1.9θbeam
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- SBHW The source sequence number
6- 9 F4.1 arcsec Sep ? Source and identification angular separation
11- 18 E8.3 --- lambda ? Normalized source number density
20- 22 F3.1 --- nSep ? Normalized separation
24 A1 --- l_LR Limit flag on LR
25- 33 E9.2 --- LR ? Likelihood ratio (1)
35- 59 A25 --- ID Identification designation (2)
61- 66 A6 --- Type Source type
68-135 A68 --- n_ID Flux density or magnitude of ID (3)
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Note (1): Larger LR implies a higher likelihood of the sources being related.
Note (2): The first letters in the identification denote the survey of origin:
18P, 19P, ECX = Wendker et al., 1991, Cat. J/A+A/241/551
(408, 1400, and 4800MHz)
2MASS = 2MASS (Cat. II/241) second incremental release (2µm)
GPSR = Zoonematkermani et al., 19990, Cat. J/ApJS/74/181 (20cm/1400MHz)
MT = Massey & Thompson, 1991, Cat. J/AJ/101/1408 (optical, B and V)
HWL94 = Higgs et al., 1994A&A...291..295H 1994A&A...291..295H
MSX = MSX PSC, Cat. V/114 (8.3, 4.3, 4.4, 12.1, 14.7, and 21.3µm)
POSSII = POSS-II I-band
TXS = Douglas et al., 1996, Cat. VIII/42 (365MHz)
WSRTGP = Taylor et al., 1996, Cat. J/ApJS/107/239 (327MHz)
Note (3): B and V associated with 2MASS are from the Tycho catalogue.
Radio flux densities are in mJy, IRAS and MSX flux densities are
in Jy, and BVIJHK are in magnitude.
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History:
* 17-Nov-2003: From electronic version of the journal
* 06-Jun-2005: Star#144 was added in table2.
(mail exchange with Karel A. van der Hucht)
(End) Greg Schwarz [AAS], Patricia Bauer, Francois Ochsenbein [CDS] 17-Nov-2003