J/AJ/162/191 2011-2021 calibrator observations of SCUBA-2 (Mairs+, 2021)
A decade of SCUBA-2: a comprehensive guide to calibrating 450µm and 850µm
continuum data at the JCMT.
Mairs S., Dempsey J.T., Bell G.S., Parsons H., Currie M.J., Friberg P.,
Jiang X.-J., Tetarenko A.J., Bintley D., Cookson J., Li S., Rawlings M.G.,
Wouterloot J., Berry D., Graves S., Mizuno I., Acohido A.A., Clark A.,
Cox J., Fuchs M., Hoge J., Kemp J., Lee E., Matulonis C., Montgomerie W.,
Silva K., Smith P.
<Astron. J., 162, 191-191 (2021)>
=2021AJ....162..191M 2021AJ....162..191M (SIMBAD/NED BibCode)
ADC_Keywords: Photometry, millimetric/submm
Keywords: Submillimeter astronomy; Calibration; Astronomical methods
Observational astronomy; Astronomical instrumentation
Ground-based astronomy; Astronomical techniques
Abstract:
The Submillimetre Common User Bolometer Array 2 (SCUBA-2) is the James
Clerk Maxwell Telescope's continuum imager, operating simultaneously
at 450 and 850µm. SCUBA-2 was commissioned in 2009-2011, and since
that time, regular observations of point-like standard sources have
been performed whenever the instrument is in use. Expanding the
calibrator observation sample by an order of magnitude compared to
previous work, in this paper we derive updated opacity relations at
each wavelength for a new atmospheric extinction correction, analyze
the Flux Conversion Factors used to convert instrumental units to
physical flux units as a function of date and observation time,
present information on the beam profiles for each wavelength, and
update secondary calibrator source fluxes. Between 07:00 and 17:00
UTC, the portion of the night that is most stable to temperature
gradients that cause dish deformation, the total flux uncertainty and
the peak flux uncertainty measured at 450µm are found to be 14% and
17%, respectively. Measured at 850µm, the total flux and peak flux
uncertainties are 6% and 7%, respectively. The analysis presented in
this work is applicable to all SCUBA-2 projects observed since 2011.
Description:
The Submillimetre Common User Bolometer Array 2 (SCUBA-2) is the James
Clerk Maxwell Telescope's continuum imager, operating simultaneously
at 450 and 850µm. SCUBA-2 obtains continuum data at 450 and
850µm simultaneously with beam sizes of 10.0" and 14.4",
respectively. All observations that are used in this work were
performed using the "CV Daisy" scan pattern, which yields a ∼12'
diameter map with a central 3' region exhibiting a highly uniform
sensitivity.
The first SCUBA-2 calibrator observations addressed by this study were
performed in 2011 May during the instrument's commissioning phase.
Dempsey+ 2013MNRAS.430.2534D 2013MNRAS.430.2534D analyzed the calibrator data taken over
one year beginning on 2011 May 1 to derive the initial Flux Conversion
Factors (FCFs; see Section 4 for details), beam profiles, and
secondary calibrator brightnesses. Now, we continue the analysis
through 2021 February 10.
Over the course of 10yr, more than 1200 reliable observations of the
primary calibrator, Uranus, alone have been obtained.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 83 4 Secondary calibrator fluxes
table3.dat 60 1201 Uranus-derived Flux Conversion Factor (FCF)
information
table8.dat 60 5495 Secondary-calibrator flux information
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See also:
J/MNRAS/401/1240 : Light curves of flat-spectrum radio sources (Jenness+, 2010)
J/MNRAS/469/492 : JCMT/SCUBA2 obs. in COSMOS & UDS fields (Michalowski+ 2017)
J/ApJ/880/43 : Bright SCUBA-2 submm sources in COSMOS (Simpson+, 2019)
J/ApJS/248/24 : MUSTANG-2 Galactic Plane survey at 3mm (Ginsburg+, 2020)
http://www.eaobservatory.org/jcmt/instrumentation/continuum/scuba-2/calibration : JCMT SCUBA-2 Calibration home page
Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Name of the secondary calibrator
9- 10 I2 h RAh Hour of right ascension (J2000)
12- 13 I2 min RAm Minute of right ascension (J2000)
15- 19 F5.2 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000)
22- 23 I2 deg DEd Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 32 F5.2 arcsec DEs Arcsecond of declination (J2000)
34- 38 F5.2 Jy/beam F450umpk [5/25] SCUBA-2 450um peak flux (1)
40- 43 F4.2 Jy/beam e_F450umpk [1/5] F450umpk uncertainty
45- 48 F4.2 Jy/beam F850umpk [0.8/5.5] SCUBA-2 850um peak flux (1)
50- 53 F4.2 Jy/beam e_F850umpk [0.06/0.31] F850umpk uncertainty
55- 59 F5.2 Jy F450um [6/30] SCUBA-2 450um total flux (1)
61- 64 F4.2 Jy e_F450um [1/5] F450um uncertainty
66- 69 F4.2 Jy F850um [0.8/6.1] SCUBA-2 850um total flux (1)
71- 74 F4.2 Jy e_F850um [0.09/0.3] F850um uncertainty
76- 78 I3 --- N450 [34/691] Number of 450um observations (2)
80- 83 I4 --- N850 [37/1482] Number of 850um observations (2)
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Note (1): Secondary calibrator fluxes derived by applying the FCFs presented
in Table 4 to the extinction-corrected raw flux measurements obtained
during the stable part of the night.
Table 4: recommended FCFs for observations obtained between 07:00 and
17:00 (UTC):
------------------------------------------------------------------------
Wavelength, Date range FCFpeak FCFarcsec
------------------------------------------------------------------------
450um, Pre 2018 Jun 30 531 +or- 93 4.61 +or- 0.60
450um, Post 2018 Jun 30 472 +or- 76 3.87 +or- 0.53
850um, Pre 2016 Nov 19 525 +or- 37 2.25 +or- 0.13
850um, 2016 Nov 19-2018 Jun 30 516 +or- 42 2.13 +or- 0.12
850um, Post 2018 Jun 30 495 +or- 32 2.07 +or- 0.12
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Note: These FCFs assume the opacity relations presented in Equation (6)
and Table 1 were applied during the extinction correction. The same
extinction correction must be used for a direct comparison with the FCF
values presented by Dempsey+ 2013MNRAS.430.2534D 2013MNRAS.430.2534D (D13). The atmospheric
transmission lower limits included in the FCF determination are 10% and
25% for 450 and 850um, respectively. The primary calibrator, Uranus, was
used to derive these FCFs.
Note (2): Fewer observations taken at 450um than at 850um are used, due to
the exclusion of low-transmission data that could not be used to fit a
reliable peak flux.
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Byte-by-byte Description of file: table[38].dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Calibrator identification
9- 18 F10.4 d MJD [55693.6/59254.6] Modified Julian Date
of observation (JD-2400000.5)
20- 24 F5.3 --- tau225 [0.017/0.32] Atmosphere opacity, τ,
at 225GHz at MJD
26- 30 F5.3 --- Airmass [1/3.5] Airmass at MJD
32- 38 F7.2 Jy/pW/beam F450umpk [-446/4132]? Peak FCF, 450um (1)
40- 46 F7.2 Jy/pW/arcsec2 F450um [-16/4401]? Arcsec FCF, 450um (2)
48- 54 F7.2 Jy/pW/beam F850umpk [0.3/2332]? Peak FCF, 850um (1)
56- 60 F5.2 Jy/pW/arcsec2 F850um [0.1/12]? Arcsec FCF, 850um (2)
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Note (1): Peak FCF calculated from fluxes measured by performing a Gaussian
fit to the source while the data was still in units of picowatts. These
measurements were then compared to the expected (model) peak flux of
Uranus at the time of observation.
Note (2): Arcsec FCF calculated from total fluxes that were measured using
aperture photometry while the data was still in units of picowatts. The
total flux was calculated within a 1 arcminute diameter aperture
centered on the source. The background level was determined using an
annulus with inner diameter 1.5 arcminutes and outer diameter 2
arcminutes. These measurements were then compared to the expected
(model) total flux of Uranus at the time of observation.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 22-Dec-2021