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| * Below you find the forward and beam efficiencies upto 280 GHz measured in March 2005 ([http://www.iram.fr/IRAMFR/ARN/aug05/node6.html IRAM Newsletter 8/05]). Values above 300 GHz are predictions based on the observations compiled in the IRAM Annual Report 2007 attachment:IRAM_2007.pdf ). | |
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| || '''freq''' || '''HPBW''' || '''Beff''' || '''Aeff''' || '''S/TA*''' || '''Feff''' || '''Comments''' || || '''(GHz)''' || '''(arcsec)''' || '''(%)''' || '''(%)''' || '''(Jy/K)''' || '''(%)''' || || || || (1) || (2) || (3) || (4) || (5) || (6) || ||72 (extrapolated) || 34 || 79 || || 6.0 || 95 || || ||77 (extrapolated) || 32 || 79 || || 6.0 || 95 || || ||86 || 29 || 78 || || 6.0 || 95 || || ||110 || 22 || 75 || || 6.3 || 95 || || ||145 || 17 || 69 || || 6.7 || 93 || || ||170 || 14.5 || 65 || || 7.1 || 93 || || ||210 || 12 || 57 || || 7.9 || 91 || || ||235 || 10.5 || 52 || || 8.7 || 91 || || ||260 || 9.5 || 46 || || 9.5 || 88 || || ||279 || 9 || 42 || ||10.4 || 88 || || ||310 || 7.9 || || 37 || || || predicted || ||345 || 7.1 || || 32 || || || predicted || ||360 || 6.8 || || 30 || || || predicted || |
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| 1. The '''half power beam width, HPBW''', can be well fitted by: HPBW/arcsec = 2460/freq/GHz. | === Update on telescope efficiencies and errorbeam parameters === |
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| 1. '''Main beam efficiency Beff.''' The data can be well fit by a Ruze function Beff = 1.2 Aeff' exp[-(4pi R sigma/ lambda)^2] with sigma being the rms value of the surface errors of the main dish, R the reduction factor for a steep main reflector, Aeff' is the aperture efficieny of the perfect telescope and lambda the wavelength in mm. The data can be fitted by R*sigma = 0.07 and epsilon = 0.69. | The following table is taken from the report on "Improvement of the IRAM 30m telescope pattern" of 26-August 2013 which is available [[http://www.iram.es/IRAMES/mainWiki/CalibrationPapers|here]]. It gives the strengths (in percent) of the main beam, the three errorbeams, and the forward efficiency, as a function of observing frequency. |
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| 1. '''Aperture efficiency, Aeff.''' The aperture efficiency of the 30m telescope can be obtained via pointings on point-like celestial calibrators like Uranus or Mars. In the approximation that the beam is Gaussian and the edge taper is -14dB, it can also be derived from the beam efficiency using Aeff=Beff*0.80 (attachment:spatial_response_framework_v1.8.pdf) | || '''Freq''' || '''Beff''' || P1' || P2' || P3' || SumP || '''Feff''' || '''eta_fss''' || || 86 || 81 || 0 || 7 || 6 || 12 || 95 || 2 || || 115 || 78 || 1 || 8 || 6 || 14 || 94 || 2 || || 145 || 73 || 2 || 9 || 6 || 17 || 93 || 2 || || 210 || 63 || 4 || 11 || 9 || 24 || 94 || 6 || || 230 || 59 || 4 || 11 || 11 || 25 || 92 || 8 || || 280 || 49 || 3 || 11 || 15 || 29 || 87 || 9 || || 340 || 35 || 2 || 11 || 14 || 28 || 81 || 19 || || 345 || 34 || 2 || 11 || 14 || 28 || 80 || 18 || |
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| 1. '''Point source sensitivity S/TA*.''' S/TA* is 3.906*Feff/Aeff Jy/K for the 30m (see attachment:cali_rep.pdf). | See the report for explanations on the errorbeam parameters P1', P2', P3', SumP. The half power beamwidths (HPBW) of the main beam are described to a good accuracy by HPBW(arcsec) = 2460/Freq(GHz). For the aperture efficiencies and point source sensitivities see previous observations listed below. A fit of the Ruze formula to these main beam efficiencies results in a beam efficiency in the low frequency limit of Beff0 = 0.863 and a total surface rms of 66 micrometer: [[attachment:beff-jp-02nov2016.png]]. This includes the contribution of all mirrors between primary and the EMIR horns, but the main contribution comes from the primary with about 60 micrometer surface rms. |
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| 1. '''Gain-elevation curves.''' The most recent curves are given in the IRAM Annual Report 2007 | Lower frequencies have been made available in December 2015, with the upgrade of the E090 band. Beam properties are described in the commissioning report [[http://www.iram.es/IRAMES/mainWiki/EmirforAstronomers?action=AttachFile&do=get&target=report-e0e1upgrades-15dec2015-v1.1.pdf|here]]. |
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| 1. '''Forward efficiency Feff.''' The values for Feff are valid after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. Forward efficiencies are derived from skydips. | === Parameters describing the beam of the 30m telescope: HPBW, Feff, Beff, Aeff, point source sensitivity, Errorbeams === |
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| 1. '''Error beams.''' A part of the power pattern is distributed in three error beams (see the analysis of attachment:greve_1998.pdf). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved in the meanwhile, lowering the strengths of the error beams. A new paper is in preparation. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources. | 1. '''Half power beam width HPBW.''' The observed HPBWs can be well fitted by '''HPBW/arcsec=2460/Freq/GHz''' or HPBW/rad=1.166 Lambda/D, with the wavelength Lambda and the telescope diameter D. |
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| 1. Historic values: [http://www.iram.es/IRAMES/telescope/telescopeSummary/beam_effis.html Plot of efficiencies against frequency, measured in 2000], [http://www.iram.es/IRAMES/telescope/telescopeSummary/effi_history.html Compilation of efficiencies obtained in the past till 2001]. | 1. '''Forward efficiency Feff.''' The values for Feff were updated after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. Forward efficiencies are derived from skydips. |
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| [#beginOfPage Back to top] | 1. '''Main beam efficiency Beff.''' Beff is the ratio of main beam solid angle over the entire antenna pattern solid angle. It is best derived from a source which has a diameter comparable to the size of the main beam. It can be calculated from the peak antenna temperature TA*, the HPBW, the source diameter, and source brightness temperature Tb (see Eq. 18 of [[attachment:cali_rep.pdf]]). For a source which fills the main beam, Beff=TA* Feff/Jnu(Tb), where Jnu(Tb) is the Rayleigh Jeans brightness temperature at frequency nu. When using p.59, Eq.4.13, Eq.5.33 of Baars (2007, The Paraboloidal Reflector Antenna in Radio Astronomy and Communication), we find that the observed relation, HPBW=2460/nu with HPBW in arcsec and nu in GHz, is consistent with an edge taper of -16.2dB, HPBW=1.19 lambda/D in radian, and Beff=1.27Aeff (cf. te.greg, CK, 8-May-2015). Previously, we had sometimes assumed, HPBW=1.17Lambda/D, corresponding to HPBW=2405/nu, and to an canonical edge taper of -13dB, leading to Beff=1.21 Aeff. |
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| [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary Back to the IRAM 30m System Summary] | 1. '''Aperture Efficiency Aeff.''' Aeff can be obtained via pointings on point-like celestial calibrators with a well known flux, like Uranus or Mars, when it is small. Aeff can be computed from '''3.906 K TA* Feff / Ssou''', where K is the correction factor that considers the coupling of the disk size of the planet to the HPBW, TA* is the peak antenna temperature, and Ssou is the intrinsic flux density of the planet. (see Eq.16 in [[attachment:cali_rep.pdf]] or [[attachment:spatial_response_framework_v1.8.pdf]]) 1. '''Point source sensitivity S/TA*.''' S/TA* is expressed as '''3.906 Feff/Aeff''' in Jy/K (see Eq.17 in [[attachment:cali_rep.pdf]]) 1. '''Error beams.''' A part of the power pattern is distributed in three error beams (see the analysis of [[attachment:greve_1998.pdf]]). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved since 1998, lowering the strengths of the error beams. [[http://www.iram.es/IRAMES/mainWiki/CalibrationPapers|A new report by Kramer, Penalver, Greve of August 2013 is available online here]]. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources. === Gain elevation curves === The point source sensitivity or aperture efficiency drops for large and for low elevations above/below the optimum of about ~50deg. This effect becomes more pronounced with increasing frequency. At 210GHz, the aperture efficiency drops to 80% of its optimum value at an elevation of 20deg or 80deg (cf. [[http://www.iram.es/IRAMES/mainWiki/AstronomerOfDutyChecklist#Gain_elevation_correction|Report of April-2012 by J.Penalver where we also offer a CLASS script]] to observers to correct for the gain elevation curve). === Gain variation with wobbler throw === The point source sensitivity or aperture efficiency also drops with increasing wobbler throw. This effect becomes more pronounced with increasing frequency. At about 230GHz, the point source sensitivity drops to 80% of its optimum value for a wobbler throw of +-2' (cf. Figure 6 in [[http://www.iram.es/IRAMES/mainWiki/CalibrationPapers?action=AttachFile&do=view&target=greve_penalver_1996_near_focus.pdf|Greve et al. 1996]]). === Past efficiencies === ==== Efficiencies measured with EMIR in 2009 ==== || '''Freq''' || '''HPBW''' || '''Feff''' || '''Beff''' || '''Aeff''' || '''S/TA*''' || '''Date''' || '''Comments''' || '''Beff/Aeff''' || '''Beff''' with Beff=1.28Aeff || || GHz || arcsec || % || % || % || Jy/K || || || || || || 86 || 29 || 95 || 81 || 63 || 5.9 || 4.4.2009 || || 1.29 || 80.6 || || 115 || || || 78 || || || predicted || (1) || || || || 145 || 16 || 93 || 74 || 57 || 6.4 || 4.4.2009 || || 1.30 || 73.0 || || 210 || 11 || 94 || 63 || 49 || 7.5 || 29.3.2009 || || 1.29 || 62.7 || || 230 || 10.7 || 92 || 58 || 46 || || 14.11.2012 || (2) || 1.26 || 58.9 || || 260 || 9 || 88 || 53 || 41 || 8.4 || 29.3.2009 || || 1.29 || 52.5 || || 330 || || || || || || || || || || || 340 || 7.5 || 81 || 35 || 29 || 10.9 || 24.11.2009 || || 1.21 || 37.1 || Comments: (1) The beam efficiency at 115GHz is predicted from the measured beam efficiency at adjacent frequencies, using the Ruze formula. <CK, 15-Jan-2013> See also the [[http://www.iram.es/IRAMES/mainWiki/EmirforAstronomers|EMIR Users Manual and the EMIR Commissioning Report]]. (2) See report by JP. ==== Efficiencies measured with ABCD receivers in 8/07 (and 6/08) ==== || '''Freq''' || '''HPBW''' || '''Feff''' || '''Beff''' || '''Aeff''' || '''S/TA*''' || '''Comments''' || || '''GHz''' || '''arcsec''' || '''%''' || '''%''' || '''%''' || '''Jy/K''' || || || 72 || 33.4 || 98 || 79 || 65 || 5.9 || estimated || || 86 || 28.5 || 98 || 78 || 64 || 5.9 || || || 145 || 16.9 || 95 || 64 || 53 || 6.9 || || || 210 || 11.3 || 94 || 62 || 51 || 7.2 || || || 260 || 9.0 || 90 || 53 || 44 || 8.0 || || || 345 || 7.0 || 87 || 39 || 32 || 10.6 || estimated || * Measurements were conducted during night time when effects of anomalous refraction and any panel buckling are strongly reduced. In addition, the panel backstructure is heated in a random fashion since 8/05, improving on its thermal balance. (JP, CT, CK 2/09). ABCD receivers were used to observe Uranus and Mars, while small. Receivers were tuned to single sideband. Planetary brightness temperatures Tb from ASTRO/GILDAS: * Mars: 215K constant with frequency * Uranus: 139K at 86GHz, 116K at 145GHz, 102K at 210GHz, 94.5K at 260GHz, 85.6K at 345GHz following Griffin & Orton 1993 ==== Efficiencies before 2007 ==== * [[http://www.iram-institute.org/medias/uploads/file/PDFs/Annual_reports/IRAM_2007.pdf|Efficiencies measured on August, 31, 2007, Annual Report 2007,page 15ff]] * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html|Efficiencies of 3/2005]], see also the [[http://www.iram.fr/IRAMFR/ARN/aug05/node6.html|IRAM Newsletter 8/05]]. * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/beam_effis.html|Plot of efficiencies against frequency, measured in 2000]], * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/effi_history.html|Compilation of efficiencies obtained in the past till 2001]]. ---- [[#beginOfPage|Back to top]] [[http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary|Back to the IRAM 30m System Summary]] |
Contents
Telescope efficiencies and beam widths
Update on telescope efficiencies and errorbeam parameters
The following table is taken from the report on "Improvement of the IRAM 30m telescope pattern" of 26-August 2013 which is available here. It gives the strengths (in percent) of the main beam, the three errorbeams, and the forward efficiency, as a function of observing frequency.
Freq
Beff
P1'
P2'
P3'
SumP
Feff
eta_fss
86
81
0
7
6
12
95
2
115
78
1
8
6
14
94
2
145
73
2
9
6
17
93
2
210
63
4
11
9
24
94
6
230
59
4
11
11
25
92
8
280
49
3
11
15
29
87
9
340
35
2
11
14
28
81
19
345
34
2
11
14
28
80
18
See the report for explanations on the errorbeam parameters P1', P2', P3', SumP. The half power beamwidths (HPBW) of the main beam are described to a good accuracy by HPBW(arcsec) = 2460/Freq(GHz). For the aperture efficiencies and point source sensitivities see previous observations listed below. A fit of the Ruze formula to these main beam efficiencies results in a beam efficiency in the low frequency limit of Beff0 = 0.863 and a total surface rms of 66 micrometer: beff-jp-02nov2016.png. This includes the contribution of all mirrors between primary and the EMIR horns, but the main contribution comes from the primary with about 60 micrometer surface rms.
Lower frequencies have been made available in December 2015, with the upgrade of the E090 band. Beam properties are described in the commissioning report here.
Parameters describing the beam of the 30m telescope: HPBW, Feff, Beff, Aeff, point source sensitivity, Errorbeams
Half power beam width HPBW. The observed HPBWs can be well fitted by HPBW/arcsec=2460/Freq/GHz or HPBW/rad=1.166 Lambda/D, with the wavelength Lambda and the telescope diameter D.
Forward efficiency Feff. The values for Feff were updated after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. Forward efficiencies are derived from skydips.
Main beam efficiency Beff. Beff is the ratio of main beam solid angle over the entire antenna pattern solid angle. It is best derived from a source which has a diameter comparable to the size of the main beam. It can be calculated from the peak antenna temperature TA*, the HPBW, the source diameter, and source brightness temperature Tb (see Eq. 18 of cali_rep.pdf). For a source which fills the main beam, Beff=TA* Feff/Jnu(Tb), where Jnu(Tb) is the Rayleigh Jeans brightness temperature at frequency nu. When using p.59, Eq.4.13, Eq.5.33 of Baars (2007, The Paraboloidal Reflector Antenna in Radio Astronomy and Communication), we find that the observed relation, HPBW=2460/nu with HPBW in arcsec and nu in GHz, is consistent with an edge taper of -16.2dB, HPBW=1.19 lambda/D in radian, and Beff=1.27Aeff (cf. te.greg, CK, 8-May-2015). Previously, we had sometimes assumed, HPBW=1.17Lambda/D, corresponding to HPBW=2405/nu, and to an canonical edge taper of -13dB, leading to Beff=1.21 Aeff.
Aperture Efficiency Aeff. Aeff can be obtained via pointings on point-like celestial calibrators with a well known flux, like Uranus or Mars, when it is small. Aeff can be computed from 3.906 K TA* Feff / Ssou, where K is the correction factor that considers the coupling of the disk size of the planet to the HPBW, TA* is the peak antenna temperature, and Ssou is the intrinsic flux density of the planet. (see Eq.16 in cali_rep.pdf or spatial_response_framework_v1.8.pdf)
Point source sensitivity S/TA*. S/TA* is expressed as 3.906 Feff/Aeff in Jy/K (see Eq.17 in cali_rep.pdf)
Error beams. A part of the power pattern is distributed in three error beams (see the analysis of greve_1998.pdf). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved since 1998, lowering the strengths of the error beams. A new report by Kramer, Penalver, Greve of August 2013 is available online here. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources.
Gain elevation curves
The point source sensitivity or aperture efficiency drops for large and for low elevations above/below the optimum of about ~50deg. This effect becomes more pronounced with increasing frequency. At 210GHz, the aperture efficiency drops to 80% of its optimum value at an elevation of 20deg or 80deg (cf. Report of April-2012 by J.Penalver where we also offer a CLASS script to observers to correct for the gain elevation curve).
Gain variation with wobbler throw
The point source sensitivity or aperture efficiency also drops with increasing wobbler throw. This effect becomes more pronounced with increasing frequency. At about 230GHz, the point source sensitivity drops to 80% of its optimum value for a wobbler throw of +-2' (cf. Figure 6 in Greve et al. 1996).
Past efficiencies
Efficiencies measured with EMIR in 2009
Freq
HPBW
Feff
Beff
Aeff
S/TA*
Date
Comments
Beff/Aeff
Beff with Beff=1.28Aeff
GHz
arcsec
%
%
%
Jy/K
86
29
95
81
63
5.9
4.4.2009
1.29
80.6
115
78
predicted
(1)
145
16
93
74
57
6.4
4.4.2009
1.30
73.0
210
11
94
63
49
7.5
29.3.2009
1.29
62.7
230
10.7
92
58
46
14.11.2012
(2)
1.26
58.9
260
9
88
53
41
8.4
29.3.2009
1.29
52.5
330
340
7.5
81
35
29
10.9
24.11.2009
1.21
37.1
Comments: (1) The beam efficiency at 115GHz is predicted from the measured beam efficiency at adjacent frequencies, using the Ruze formula. <CK, 15-Jan-2013> See also the EMIR Users Manual and the EMIR Commissioning Report. (2) See report by JP.
Efficiencies measured with ABCD receivers in 8/07 (and 6/08)
Freq
HPBW
Feff
Beff
Aeff
S/TA*
Comments
GHz
arcsec
%
%
%
Jy/K
72
33.4
98
79
65
5.9
estimated
86
28.5
98
78
64
5.9
145
16.9
95
64
53
6.9
210
11.3
94
62
51
7.2
260
9.0
90
53
44
8.0
345
7.0
87
39
32
10.6
estimated
- Measurements were conducted during night time when effects of anomalous refraction and any panel buckling are strongly reduced. In addition, the panel backstructure is heated in a random fashion since 8/05, improving on its thermal balance. (JP, CT, CK 2/09). ABCD receivers were used to observe Uranus and Mars, while small. Receivers were tuned to single sideband. Planetary brightness temperatures Tb from ASTRO/GILDAS:
- Mars: 215K constant with frequency
Uranus: 139K at 86GHz, 116K at 145GHz, 102K at 210GHz, 94.5K at 260GHz, 85.6K at 345GHz following Griffin & Orton 1993
Efficiencies before 2007
Efficiencies measured on August, 31, 2007, Annual Report 2007,page 15ff
Efficiencies of 3/2005, see also the IRAM Newsletter 8/05.