J/A+A/637/A64 Cygnus OB2 e-MERLIN 21cm survey (COBRaS) (Morford+, 2020)
COBRaS: The e-MERLIN 21 cm Legacy survey of Cygnus OB2.
Morford J.C., Fenech D.M., Prinja R.K., Blomme R., Yates J.A., Drake J.J.,
Eyres S.P.S., Richards A.M.S., Stevens I.R., Wright N.J., Clark J.S.,
Dougherty S., Pittard J.M., Smith H.A., Vink J.S.
<Astron. Astrophys., 637, A64 (2020)>
=2020A&A...637A..64M 2020A&A...637A..64M (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Radio lines ; Interferometry
Keywords: open clusters and associations: individual: Cygnus OB2 -
radio continuum: stars - techniques: interferometric -
stars: massive - stars: winds, outflows
Abstract:
The role of massive stars is central to an understanding of galactic
ecology. It is important to establish the details of how massive stars
provide radiative, chemical, and mechanical feedback in galaxies.
Central to these issues is an understanding of the evolution of
massive stars, and the critical role of mass loss via strongly
structured winds and stellar binarity. Ultimately, and acting
collectively, massive stellar clusters shape the structure and
energetics of galaxies.
We aim to conduct high-resolution, deep field mapping at 21cm of the
core of the massive Cygnus OB2 association and to characterise the
properties of the massive stars and colliding winds at this waveband.
We used seven stations of the e-MERLIN radio facility, with its
upgraded bandwidth and enhanced sensitivity to conduct a 21cm census
of Cygnus OB2. Based on 42 hours of observations, seven overlapping
pointings were employed over multiple epochs during 2014 resulting in
1σ sensitivities down to ∼21µJy and a resolution of ∼180mas.
A total of 61 sources are detected at 21cm over a ∼0.48°x0.48°
region centred on the heart of the Cyg OB2 association. Of these 61
sources, 33 are detected for the first time. We detect a number of
previously identified sources including four massive stellar binary
systems, two YSOs, and several known X-ray and radio sources. We also
detect the LBV candidate (possible binary system) and blue hypergiant
star of Cyg OB2 #12.
The 21cm observations secured in the COBRaS Legacy project provide
data to constrain conditions in the outer wind regions of massive
stars; determine the non-thermal properties of massive interacting
binaries; examine evidence for transient sources, including those
associated with young stellar objects; and provide unidentified
sources that merit follow-up observations. The 21cm data are of
lasting value and will serve in combination with other key surveys of
Cyg OB2, including Chandra and Spitzer.
Description:
The L-band (21cm) observations presented here were obtained as part of
the COBRaS e-MERLIN Legacy project. The bulk of these observations
(∼75% of the total allocation) were completed over a three day period
from April 25 to 27, 2014 (from here after denoted as April 26),
whilst additional observations, contributing to the final quarter of
the total allocation at L-band were taken on April 11, 2014 (from here
after April 11).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 80 71 COBRaS L-band All Source Catalogue
tablea2.dat 111 66 Source identification information
tablea3.dat 112 71 Information regarding the spatial extent of each
of the 61 CLASC sources on the sky as measured
with the e-MERLIN interferometer
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJS/149/123 : WSRT survey of Cygnus OB2 (Setia Gunawan+, 2003)
J/A+A/472/557 : Cygnus OB2 region 610MHz sources (Marti+, 2007)
J/ApJS/184/84 : X-ray sources in Cyg OB2 region (Wright+, 2009)
J/A+A/536/A31 : Cyg OB2 XMM observations (Rauw, 2011)
J/ApJS/202/19 : riz photometry in Cyg OB2 (Guarcello+, 2012)
J/ApJ/773/135 : Disk-bearing stars in Cygnus OB2 (Guarcello+, 2013)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- CLASC Identification number given to the sources
from this work, sequentially increasing in
order of right ascension
3 A1 --- m_CLASC [abc] Multiplicity index on CLASC
5- 14 A10 --- OName Any other identifier the source may have from
a previous identification (G1)
16- 17 I2 h RAh Right ascension (J2000) (2)
19- 20 I2 min RAm Right ascension (J2000) (2)
22- 26 F5.2 s RAs Right ascension (J2000) (2)
28 A1 --- DE- Declination sign (J2000) (2)
29- 30 I2 deg DEd Declination (J2000) (2)
32- 33 I2 arcmin DEm Declination (J2000) (2)
35- 39 F5.2 arcsec DEs Declination (J2000) (2)
41- 45 I5 uJy F11th ? 21cm integrated flux density
from April 11 observations
47- 50 I4 uJy e_F11th ? 21cm Integrated flux density 1σ RMS
noise level
51 A1 --- n_F11th [+d] Note on F11th (4)
52- 54 I3 uJy/beam sigma11th σ within an 3" radius surrounding the
edge of the source for April 11 observations
56- 59 F4.1 --- S/N11th ? Signal-to-noise ratio
for April 11 observations (3)
61- 65 I5 uJy F26th ? 21cm integrated flux density
from April 26 observations
67- 70 I4 uJy e_F26th ? 21cm Integrated flux density 1σ RMS
noise level
71 A1 --- n_F26th [+d] Note on F26th (4)
73- 74 I2 uJy/beam sigma26th σ within an 3" radius surrounding the
edge of the source for April 26 observations
76- 80 F5.1 --- S/N26th ? Signal-to-noise ratio
for April 26 observations (3)
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Note (2): J2000 positional information of each source as measured from the
April 26 observations. Each position was calculated from SEAC by taking a
weighted mean of the detected pixel area (see Sect. 3.1.3).
The positions are all accurate to <0.032 arcsec in both RA and Dec.
Note (3): S/N (Fp/σ11th, where Fp is the peak flux density) of each of
the sources detected at 21 cm.
Note (4): Notes as follows:
+ = These sources are faint detections and their flux density has been measured
with SEAC using threshold values, σs=4.5 and σf=3
d = These sources are faint detections and their flux density has been measured
with SEAC using threshold values, σs=4.0 and σf=2.6
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- CLASC ID number of each source from CLASC
as given in TableA1
4- 13 A10 --- OName Any existing common identifier (G1)
17- 21 F5.3 arcsec Offset Offset between the position of the CLASC
source and that of the identification
23- 30 E8.3 --- lambda ? Calculated values lambda (see Eq. (3)) (1)
32- 34 F3.1 --- r ? Calculated values r (see Eq. (3)) (1)
36 A1 --- l_LR Limit flag on LR
37- 42 F6.1 --- LR Calculated values LR (see Eq. (3)) (1)
44- 51 A8 --- Ref Reference to the observations or survey from
which each identification is taken (2)
53-111 A59 --- Notes Any additional information regarding the flux
density, magnitude, or X-ray flux of each
identification
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Note (1): the least likelihood ratio, LR, is given as:
LR(r)=(1/2λ)exp{r2(2λ-1)/2}, Eq. (3),
where r is the normalised separation between a source, and
lambda is the number of sources within an area corresponding to the
size of the combined positional error in RA and in Dec.
Note (2): References as follows:
M07 = Marti et al. (2007, Cat. J/A+A/472/557)
S09 = Skiff (2009, Cat. B/mk)
R11 = Rauw (2011, Cat. J/A+A/536/A31)
S03 = Setia Gunawan et al. (2003, Cat. J/ApJS/149/123)
2MASS = Cutri et al. (2003, Cat. II/246)
M05 = Marti et al. (2005A&A...439..279M 2005A&A...439..279M)
W14 = Wright et al. (2014a, 1408.6579)
W09 = Wright & Drake (2009, Cat. J/ApJS/184/84)
G12 = Guarcello et al. (2012, Cat. J/ApJS/202/19)
G13 = Guarcello et al. (2013, Cat. J/ApJ/773/135)
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- CLASC Identification number of each source from
CLASC as given in TableA1
3 A1 ---- m_CLASC [abc] Multiplicity index on CLASC
5- 9 F5.2 --- A/sigma11th ? Source area (S: in pixels) divided by the
beam area (σbeam: in pixels), as
measured by SEAC for the sources detected
in the April 11 epoch
11- 13 A3 --- n_A/sigma11th Indication of whether each source is
resolved (Y) or not (N)
16- 19 F4.2 --- Sint/Sp11th ? Ratio of the integrated flux density
(Sint) to the peak pixel flux density
(Speak) of each of the CLASC sources
(as measured by SEAC), for the
April 11 epoch
21- 23 A3 --- n_Sint/Sp11th Indication of whether each source is
resolved (Y) or not (N)
26- 30 F5.2 --- Ratio11th ? Convolved angular area for the
April 11 epoch (1)
32- 34 A3 --- n_Ratio11th Indication of whether each source is
resolved (Y) or not (N)
36- 39 F4.2 --- Maj11th ? Major axis of the deconvolved angular
sizes across April 11 epochs (2)
41- 44 F4.2 --- e_Maj11th ? rms uncertainty on Maj11th
46- 49 F4.2 --- Min11th ? Minor axis of the deconvolved angular
sizes across April 11 epochs (2)
51- 54 F4.2 --- e_Min11th ? rms uncertainty on Min11th
55- 57 A3 --- n_Maj11th [LAS ] LAS when Maj11th is the
convolved largest angular size
59- 63 F5.2 --- A/sigma24th ? Source area (S: in pixels) divided by the
beam area (σbeam: in pixels), as
measured by SEAC for the sources detected
in the April 24 epoch
65- 67 A3 --- n_A/sigma24th Indication of whether each source is
resolved (Y) or not (N)
69- 73 F5.2 --- Sint/Sp24th ? Ratio of the integrated flux density
(Sint) to the peak pixel flux density
(Speak) of each of the CLASC sources
(as measured by SEAC), for the
April 24 epoch
75- 77 A3 --- n_Sint/Sp24th Indication of whether each source is
resolved (Y) or not (N)
79- 84 F6.2 --- Ratio24th ? Convolved angular area for the
April 24 epoch (1)
86- 88 A3 --- n_Ratio24th Indication of whether each source is
resolved (Y) or not (N)
90- 93 F4.2 --- Maj24th ? Major axis of the deconvolved angular
sizes across April 24 epochs (2)
95- 98 F4.2 --- e_Maj24th ? rms uncertainty on Maj24th
100-103 F4.2 --- Min24th ? Minor axis of the deconvolved angular
sizes across April 24 epochs (2)
105-108 F4.2 --- e_Min24th ? rms uncertainty on Min24th
110-112 A3 --- n_Maj24th [LAS ] LAS when Maj24th is the convolved
largest angular size
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Note (1): Convolved angular area of each CLASC source as measured from JMFIT,
i.e. θmaj and θmin, divided by the beam area,
i.e. bmaj and bmin
Note (2): major and minor axes of the deconvolved angular sizes of each of the
sources within the CLASC, across both the April 11 and April 26 epochs.
Size/θ_beam has been measured within SEAC (i.e. down to a level of
3σ) and gives a quantitative measure of the source size in pixels
compared to that of the beam size (θ_beam). Major and minor axis
measurements when given are deconvolved.
LAS is the convolved largest angular size.
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Global notes:
Note (G1): Other identifiers as follows:
Cyg = Schulte (1958ApJ...128...41S 1958ApJ...128...41S)
HSC N = Marti et al. (2005A&A...439..279M 2005A&A...439..279M), [MPG2005] HSC N in Simbad
A11 = Comeron et al. (2002A&A...389..874C 2002A&A...389..874C), [CPR2002] A11 in Simbad
SBHW = Setia Gunawan et al. (2003, Cat. J/ApJS/149/123)
W14 = Wright et al. (2014a, 1408.6579)
G13 = Guarcello et al. (2013, Cat. J/ApJ/773/135)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Jul-2020