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
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were taken in 1994 as part of a larger survey of the Galactic plane in the Cygnus area (Vashist & de Bruyn, unpublished); only a small part of it is used in this study.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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 78 238 Discrete 1400-MHz and 350-MHz sources in Cyg OB2 table7.dat 135 247 *Sources identification.
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).
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
Bytes Format Units Label Explanations
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)
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
Byte-by-byte Description of file: table7.dat
Bytes Format Units Label Explanations
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)
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 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.
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
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