Diff for "TelescopeSystemSummary"

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This page summarizes the present instrumentation installed at the 30m observatory. BR The current system status is described [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemStatus on a second page].

TableOfContents(4)

Frontends

Heterodyne Receivers

• Eight single pixel receivers A,B,C,D, and the 3x3 dual-polarisation HERA receiver are installed in the [http://www.iram.es/IRAMES/telescope/telescopeSummary/receiver6.html receiver cabin].

• Four of the 8 A,B,C,D receivers can be used simultaneously. HERA cannot be combined with other receivers.

• [http://www.iram.es/IRAMES/groups/receiver/receiver.html More information on the heterodyne receivers.]

Remarks:

1. Using a special external LO, frequencies down to 77 GHz can be measured with good sideband rejection. For frequencies below 77 GHz, the sideband recection becomes weaker, and the sideband ratio reaches unity at 72 GHz. [http://www.iram.fr/IRAMFR/PV/lowfreqs/report.ps.gz Test report of 2004], [http://www.iram.fr/IRAMFR/PV/lowfreqs/spectra.html Test spectra]

2. Noise increasing with frequency
3. HERA is a heterodyne receiver array consisting of two arrays of 3x3 pixels with 24" spacing. The two arrays have orthogonal polarization (V, H) the two polarizations pointing at identical locations on the sky. HERA is equipped with a derotator allowing to follow a source in the sky maintaining the same "footprint". The tunable range is between 215 and 272 GHz. In this range the beamwidth varies between 12" and 9".

   • [http://www.iram.es/IRAMES/otherDocuments/manuals/HERA_manual_v20.pdf HERA manual, version 2.0] by Schuster et al. 2006

   • [http://esoads.eso.org/abs/2004A%26A...423.1171S Schuster et al. 2004, A&A, 423, 1171] A 230 GHz Heterodyne Receiver Array for the IRAM 30m telescope ([http://www.iram.es/IRAMES/otherDocuments/manuals/0179hera.pdf local copy])

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Bolometers

Two large field bolometer cameras are installed: MAMBO1 with 37 pixels, and MAMBO2 with 117 pixels ([http://www.mpifr-bonn.mpg.de/div/bolometer/#mamgo MAx-Planck Millimeter BOlometer Array]). Usually MAMBO2 is in use. Both cameras work at 1.2mm wavelength, the HPBW is 11", pixel spacing is 20", and the sensitivity is 1.5mJy. This is the rms after 10 minutes integration (normal bolometric conditions) with skynoise removal. See [http://www.iram.es/IRAMES/mainWiki/MamboWebPage the MAMBO page for details.]

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Telescope efficiencies and beam widths

• 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 ).

  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

• The half power beam width, HPBW, can be well fitted by: HPBW/arcsec = 2460/freq/GHz.

• 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.

• Aperture efficiency, Aeff The aperture efficiency of the 30-m telescope can be obtained using Aeff=Beff*0.79

• Point source sensitivity S/T_A*. For a Gaussian source and beam size, and a source which is much smaller than the beam, S(Jy)/T_mb(K)=8.18E-7*theta(")**2*nu(GHz)**2 (Rohlfs & Wilson, Tools of Radioastronomy (2. ed., Eq. 8.20). Using the approximation in 1) yields for the 30m telescope S/T_mb=4.95 Jy/K. S/T_A* is obtained by multiplying 4.95 J/K with Feff/Beff. CHECK

• Gain-elevation curves. The most recent curves are given in the IRAM Annual Report 2007 attachment:IRAM_2007.pdf

• 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.

• 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.

• 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].

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Backends

In general, several backends can be attached to one receiver. Exceptions are listed below. The [http://www.iram.es/IRAMES/documents/ncs30mPako/Current/PDF/pako.pdf pako manual] describes in detail how to configure the backends.

1. 1MHz Filterbank: max. 4 parts; series, parallel, or mixed mode possible; using the 1MHz filterbank with 1GHz bandwidth excludes the use of VESPA with the same receiver. The filterbank can be shifted in multiples of 32MHz from the center frequency of the connected receiver.

2. 4MHz Filterbank: max. 9 parts; use of the 4MHz filterbank excludes the use of VESPA on the same receiver. Frequency switching not available. While the channel spacing is 4MHz, the 3dB width is 5.4MHz and the noise equivalent width is 6.5 MHz

3. WILMA: [http://www.iram.fr/IRAMFR/TA/backend/veleta/wilma/index.htm The Wideband Line Multiple Autocorrelator] for HERA

4. VESPA: [http://www.iram.fr/IRAMFR/TA/backend/veleta/vespa/index.htm The Versatile SPectrometer Array]. Up to 18000 channels. In connection with HERA (9 pixels) the following combinations of resolution (kHz) and bandwidth (MHz) are possible: (20/40), (40,80), (80, 160), (320,320), (1250, 640); [http://www.iram.es/IRAMES/otherDocuments/manuals/vespa_ug.ps VESPA User Guide (2002)], [http://www.iram.es/IRAMFR/ARN/dec02/node6.html Summary in IRAM Newsletter No. 54 (Dec 2002)], local contact: G. Paubert

5. XPOL: Line and continuum polarimetry is possible at the 30m using a new type of IF polarimeter designated XPOL. The central feature of XPOL is the correlator VESPA where the IF signals from two orthogonally polarized receivers are cross correlated to determine the four Stokes parameters. A manual is in preparation, contact: C. Thum

6. ABBA1 and ABBA2 (Adc Bolometer Backend) are the bolometer backends, i.e. dedicated PCs connected to the bolometers.

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Control System

The 30-m telescope runs under the New Control System (NCS), see:

• [http://www.iram.es/IRAMES/ncs30m/ NCS documentation] [http://mrt-lx1/mainWiki/ Wiki with up-to-date Notes on NCS]

Observing modes and source offsets in:

• Projection "Radio" (same offsets as in old CS) in Equatorial J2000.0
• "true angle" horizontal
• Nasmyth (receiver offsets)

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Observing Modes and Switching Modes

• for more details on observing and switching modes, see the section "NCS explained" in the [http://www.iram.es/IRAMES/documents/ncs30mPako/Current/PDF/pako.pdf pako cookbook]

• swTotal stands for total power observations without switching, while still using the internal synchronization signals.

• swBeam beam switched observations using the chopper wheel on mirror M4.

• swWobbler switching the wobbling secondary (M2). The maximum allowed throw is +/-2'.

• swFrequency switching the local oscillator frequency

• Pointing: Using nearby (within 10 degree) pointing sources, <1" accuracy can be obtained; with absolute ("blind") pointing, the accuracy is about 2" rms, the receivers are aligned within 1.7" (see the [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemStatus Telescope Status page] for current values). Checking the pointing and alignment (using e.g. a planet) is the responsibility of the observer.

• Focus: residual errors of <1mm may need correction. There are systematic differences of upto 0.6mm in the focus of the different receivers (cf. [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemStatus Telescope Status page]). The focus is subject to change especially during sunrise and sunset.

• Position switching (psw): the combination of ONOFF with swTotal is called "Position Switching". Only relative off-source reference positions are possible.

• Wobbler switching (wsw): often called double beam switching mode: max. 240" throw at 0.25 Hz, standard phase duration 0.5 Hz.

• Frequency switching (fsw): max. 45 km/s throw up to about 10 Hz.

• On the fly mapping (Heterodyne): Works with all receivers and backends, typical dump rate 0.5 to 10 Hz. OTF can be observed without reference position, e.g. for galaxies, and MIRA is able to use emission-free OTF data as reference!

• Raster mapping is at present not offered. The observer may want to use eigher psw or otf instead.

• Polarimetry: using VESPA as an IF polarimeter

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Weather station and Taumeter

• [http://mrt-lx3.iram.es/tau/meteo-main.php Weather station]

  • Wind velocity and direction measured on hill behind the telescope
  • Outside temperature and relative humidity measured at base of telescope. In case the sensors are frozen, the operator will use a mobile weather station and enter values by hand into the drive program.
  • Pressure measured at entrance to control building

• [http://mrt-lx3.iram.es/tau/taumeter-main-db.php Taumeter] does regular skydips to inform the observer about the sky transmission near 225 GHz. The local oscillator works at 225GHz. The IF is 1.5GHz and the bandwidth is 0.5GHz. It is a double-sideband Schottky receiver.

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Old [http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html Telescope System Summary page of September 07]

This is page http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary moderated by Carsten Kramer