J/AJ/165/139 The celestial reference frame at K-band; imaging.I (de Witt+, 2023)
The Celestial Reference Frame at K-Band; Imaging.
I. The First 28 Epochs
de Witt A., Jacobs C.S., Gordon D., Bietenholz M., Nickola M.,
Bertarini A., K-band Celestial Reference Frame Collaboration
<Astron. J., 165, 139 (2023)>
=2023AJ....165..139D 2023AJ....165..139D
ADC_Keywords: Radio sources; Photometry, millimetric/submm
Keywords: Very long baseline interferometry ; Radio astrometry ;
Extragalactic radio sources ; Observational astronomy ; Radio
continuum emission ; Radio source catalogs ; Astronomical
coordinate systems ; High angular resolution
Abstract:
We present K-band (24GHz) images of 731 compact extragalactic radio
sources with submilliarcsecond resolution, based on radio
interferometric observations made with the Very Long Baseline Array of
10 telescopes during 29day long sessions spanning from 2015 to 2018
and recorded at 2048Mbps. Many of these sources are imaged with
submilliarcsecond resolution for the first time at frequencies above
X-band (8GHz). From each of the K-band images, we derive the following
source properties: peak brightness, core and total flux density, the
ratio of peak and core to total flux (compactness measure), radial
source extent, structure index, source size, and jet direction. The
vast majority of sources are imaged at multiple epochs, providing
insights into their temporal behavior. The use of K-band was motivated
by the fact that the sources are generally intrinsically more compact
at higher frequencies, as well as by the factor of 3 improvement in
interferometer resolution relative to the historically standard S/X
band (2.3/8.4GHz) used for a large amount of reference frame and
calibrator work. Lastly, as most of the sources imaged here are in the
K-band component of the third International Celestial Reference Frame,
these images serve to characterize the objects used in that
International Astronomical Union standard.
Description:
The imaging observations were taken with the Very Long Baseline Array
(VLBA), which consists of ten 25m Cassegrain antennas, using the 1.2cm
feed.
The BJ083 series consisted of five sessions between 2015 July and 2016
June at a center frequency of 24.568GHz for sessions BJ083A and B, and
23.968GHz for BJ083A1, C and D. The UD001 series consists of 24
sessions (UD001A to X), observed between 2017 August and 2018 July, at
a central frequency of 23.568GHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 101 732 *Summary of the 732 sources observed in the BJ083
and UD001 sessions
table5.dat 104 5879 Image parameters and image quality measures
table8.dat 79 5879 Results from the image quality and source
structure analysis
table9.dat 166 731 Variability in the source peak brightness, flux
densities and structure measures
table10.dat 68 5879 Modelfitting results
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Note on table3.dat: Coordinates from the ICRF-3 K-band astrometric
catalog, rounded to the nearest mas. For state-of-the-art positions
see Charlot+, 2020, J/A+A/644/A159. The coordinates for SgrA are taken
from Gordon+, 2023AJ....165...49G 2023AJ....165...49G.
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
J/ApJS/141/13 : VLBA calibrator survey: VCS1 catalog (Beasley+, 2002)
J/ApJ/614/607 : 8.4GHz obs. of scintillating sources (Ojha+, 2004)
J/ApJ/658/203 : VLBA imaging and polarimetry survey at 5GHz (Helmboldt+, 2007)
J/AJ/136/159 : Global 86GHz VLBI survey of compact radio sources (Lee+, 2008)
J/AJ/139/1713 : Celestial Reference Frame at 24 and 43GHz. II (Charlot+, 2010)
J/AJ/139/1695 : Celestial Reference Frame at 24 and 43 GHz (Lanyi+, 2010)
J/AJ/142/35 : The VLBA Galactic Plane Survey (VGaPS) (Petrov+, 2011)
J/AJ/151/154 : Second epoch VLBA Calibrator Survey (VCS-II) (Gordon+, 2016)
J/A+A/618/L10 : SgrA* orbital motions GRAVITY (GRAVITY Collaboration, 2018)
J/MNRAS/485/88 : Southern compact extragalactic radio sources (Petrov+, 2019)
J/ApJ/885/131 : ∼200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/A+A/644/A159 : The third realization of the ICRF, ICRF3 (Charlot+, 2020)
J/A+A/641/L2 : ALMA third image of lensed quasar PKS 1830-211 (Muller+, 2020)
J/AJ/162/121 : 3627 International Celestial Reference Frame (Hunt+, 2021)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000 source name
11 A1 --- f_Name [*] *: Core set of 40 sources
13- 20 A8 --- IVS IVS source name
22 A1 --- D [D] Indicates an ICRF-3 defining source
24- 25 I2 h RAh [0/23]? Hour of Right Ascension (J2000)
27- 28 I2 min RAm ? Minute of Right Ascension (J2000)
30- 36 F7.4 s RAs ? Second of Right Ascension (J2000)
38 A1 --- DE- ? Sign of the Declination (J2000)
39- 40 I2 deg DEd ? Degree of Declination (J2000)
42- 43 I2 arcmin DEm ? Arcminute of Declination (J2000)
45- 50 F6.3 arcsec DEs ? Arcsecond of Declination (J2000)
52- 65 A14 --- Type Object type
67- 73 F7.4 --- z [0/5.47]? Redshift (1)
75- 78 F4.1 mag Vmag [10.8/23]? V magnitude (1)
80- 83 F4.1 mag Gmag [13.2/21.4]? G magnitude (1)
85- 89 I5 --- MJD1 [0/58321] MJD for first observation of
source; MJD-2400000.5
91- 95 I5 --- MJD2 [0/58322] MJD for last observation of
source; MJD-2400000.5
97- 98 I2 --- Nsch [1/29] Number of times source was scheduled
100-101 I2 --- Nimh [0/28] Number of successful images produced
for each source
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Note (1): From the Optical Characteristics of Astrometric Radio
Sources (OCARS; Malkin, 2018ApJS..239...20M 2018ApJS..239...20M) catalog files. The 2021
February 05 update of the OCARS main catalogue file and the optical
and NIR magnitudes catalogue file were used.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000 source name
12- 18 A7 --- Session Session Name
20- 21 I2 --- Nantennas [4/10] Number of antennas
23- 23 I1 --- Nscans [1/6] Number of scans
25- 30 I6 --- Nvis [9810/288672] Number of visibilities
32- 37 F6.3 Jy/beam Speak [0.05/12] Image peak flux density
39- 44 F6.3 Jy Scln [0.06/18.1] CLEAN total flux density
46- 51 F6.3 Jy Sshort [-1/17.7] Correlated flux density on short
baselines (1)
53- 58 F6.3 Jy Slong [-1/9.621] Correlated flux density on long
baselines (2)
60- 65 F6.2 mJy/beam rms [0.16/127] Image background rms brightness
level
67- 70 I4 --- SNR [20/2892] Image Signal-to-Noise ratio
72- 75 F4.2 --- chi2 [0.78/7.54] Square root of reduced chi
squared (3)
77- 82 F6.2 mJy/beam Sr [0.7/493] Absolute maximum brightness value
in residual image
84- 87 F4.2 mas Beam-min [0.21/2.3] Minor axis FWHM of the restoring
beam
89- 92 F4.2 mas Beam-maj [0.38/7.46] Major axis FWHM of the
restoring beam
94- 98 F5.1 deg bpa [-89.9/89.8] Beam position angle
100-104 F5.3 rad EPhase [0.004/0.84] Estimated residual rms phase
calibration error
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Note (1): on baselines<900km (70Mλ).
Note (2): on baselines>5000km (400Mλ).
Note (3): The rms of the squared differences between the observed and
model visibilities (after self-calibration) divided by the variances
implied by the visibility weights.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000 source name
12- 18 A7 --- Session Session name
20- 23 F4.2 --- Q [0.33/0.97] Image quality fraction
25- 29 F5.2 Jy Core [0.06/12.5] Core flux density
31- 34 F4.2 --- C1 [0.28/1.21] Peak fraction
36- 39 F4.2 --- C2 [0.11/1.21] Core fraction
41- 45 F5.2 --- C3 [-1/1.66] Correlated flux fraction
47- 51 F5.2 mas R [0/51.86] Radial extent
53- 56 F4.2 mas R4.0 [0/3.93] Radial extent within 4mas
58- 62 F5.2 mas E [0/10.9] Flux-density-weighted radial extent
64- 67 F4.2 mas E4.0 [0/1.56] Flux-density-weighted radial extent
within 4mas
69- 74 F6.2 ps mDelay [0/138] Median value of the structure delay
corrections
76- 79 F4.2 --- SI [0/5.28] Structure Index
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Byte-by-byte Description of file: table9.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000 source name
12- 16 F5.2 --- Mean-Sp [-1/8.01] Peak brightness mean value
18- 22 F5.2 --- Var-Sp [-1/0.58] Peak brightness variability index
24- 28 F5.2 --- Mean-Sc [-1/8.81] Core flux density mean value
30- 34 F5.2 --- Var-Sc [-1/0.71] Core flux density variability index
36- 40 F5.2 --- Mean-Scln [-1/13.61] CLEAN flux density mean value
42- 46 F5.2 --- Var-Scln [-1/0.59] CLEAN fluxdensity variability index
48- 52 F5.2 --- Mean-Ss [-1/13.1] Correlated flux density on short
baselines mean value (1)
54- 58 F5.2 --- Var-Ss [-1/0.59] Correlated flux density on short
baselines variability index (1)
60- 64 F5.2 --- Mean-Sl [-1/6.4] Correlated flux density on long
baselines mean value (2)
66- 70 F5.2 --- Var-Sl [-1/0.91] Correlated flux density on long
baselines variability index (2)
72- 76 F5.2 --- Mean-C1 [-1/1.04] Peak fraction mean value
78- 82 F5.2 --- Std-C1 [-1/0.19] Peak fraction standard deviation
84- 88 F5.2 --- Mean-C2 [-1/1.04] Core fraction mean value
90- 94 F5.2 --- Std-C2 [-1/0.55] Core fraction standard deviation
96-100 F5.2 --- Mean-C3 [-1/1.02] Correlated flux fraction mean value
102-106 F5.2 --- Std-C3 [-1/0.33] Correlated flux fraction standard
deviation
108-112 F5.2 mas Mean-R [-1/18.55] Radial extent mean value
114-118 F5.2 mas Std-R [-1/25.76] Radial extent standard deviation
120-124 F5.2 mas Mean-R4.0 [-1/3.43] Radial extent within 4mas meanvalue
126-130 F5.2 mas Std-R4.0 [-1/1.61] Radial extent within 4mas standard
deviation
132-136 F5.2 mas Mean-E [-1/3.53] Flux weighted radial extent mean
value
138-142 F5.2 mas Std-E [-1/3.56] Flux weighted radial extent
standard deviation
144-148 F5.2 mas Mean-E4.0 [-1/1.26] Flux-density-weighted radial extent
within 4mas mean value
150-154 F5.2 mas Std-E4.0 [-1/0.33] Flux-density-weighted radial extent
within 4mas standard deviation
156-160 F5.2 --- Mean-SI [-1/4.14] Structure index mean value
162-166 F5.2 --- Std-SI [-1/1.98] Structure index standard deviation
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Note (1): on baselines<900km (70Mλ).
Note (2): on baselines>5000km (400Mλ).
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Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000 source name
12- 18 A7 --- Session Session name
20- 25 F6.2 --- Chi2 [0.61/329] Reduced chi squared from
the two-component modelfit
27- 34 F8.2 mJy FC1 [35/13400] Flux density of the core component
36 A1 --- l_FWHM-C1 Limit flag on FWHMSize-C1
37- 40 F4.2 mas FWHM-C1 [0.01/2.14] FWHM angular size of core component
42- 48 F7.2 mJy FJ1 [1.48/7538]? Flux density of the 2nd component
50 A1 --- l_FWHM-J1 Limit flag on FWHMSize-J1
51- 55 F5.2 mas FWHM-J1 [0.01/12.8]? FWHM angular size of 2nd component
57- 61 F5.2 mas Rad-J1 [0.15/16]? Radius of the 2nd component from
map centre
63- 68 F6.1 deg Ang-J1 [-180/180]? Position Angle of the 2nd component
measured north through east
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 05-Jul-2023