Diff for "TelescopeSystemSummary"

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THIS PAGE IS STILL UNDER CONSTRUCTION For the moment, please use the old [http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html Telescope System Summary page] BR

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 here].

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Frontends

Heterodyne Receivers

• Eight single pixel receivers A,B,C,D, and the 3x3 dual-polarisation HERA receiver are installed.
• 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/telescope/telescopeSummary/receiver3.html Plots of the receiver characteristics (taken 2000)]

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
2. Noise increasing with frequency

3. [http://www.iram.es/IRAMES/mainWiki/HeraWebPage More information on HERA ]

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Bolometers

• Two wide field bolometer cameras are installed:

1. rms after 10 minutes (normal bolometric conditions) with skynoise removal.

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Efficiencies and Half-power beam width

• Below you find the most recent values for the forward and beam efficiencies. We have also compiled the [http://www.iram.es/IRAMES/telescope/telescopeSummary/effi_history.html value of the efficiencies in the past].

• Here you can find the [http://www.iram.es/IRAMES/telescope/telescopeSummary/beam_effis.html plot of efficiencies measured in 2000]. A more recent compilation can be found in the Annual Report 2007.

1. The half power beam width, HPBW, can be well fitted by: HPBW/arcsec = 2460/freq/GHz.
2. Main beam efficiency Beff. The data can be well fit by a Ruze function Beff = 1.2 epsilon exp[-(4pi R sigma/ lambda)^2] with sigma being the rms value of the telescope optics deformations, R the reduction factor for a steep main reflector, epsilon the aperture efficieny of the perfect telescope and lambda the wavelength in mm. The data can be fit by R*sigma = 0.07 and epsilon = 0.69. The aperture efficiency of the 30-m telescope can be obtained using eta_a=B_eff*0.79

3. 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 30-m telescope S/T_mb=4.95 Jy/K. S/T_A* is obtained by multiplying 4.95 J/K with F_eff/B_eff.

4. The values for F_eff are valid after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. The moon efficiencies are equal to forward efficiencies (Kramer et al. 1997).

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Backends

Spectrometers

1. max 4 parts; series parallel or mixed mode possible; using the filterbanks with 1GHz bandwidth excludes the use of the AC or the 100 MHz FB with the same rx. The FB can be shifted in multiples of 32 MHz from the center frequency of the connected rx.
2. max 9 parts; use of the 4 MHz FBs excludes the use of the AC or the 100kHz FB on the same receiver. Frequency switching not available. While the channel spacing is 4MHz, the 3dB width is 5.4 MHz and the noise equivalent width is 6.5 MHz

3. 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)], local contact: G. Paubert

4. 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

Bolometer backends

• ABBA1
• ABBA2

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Spectral Line Observing Modes

• Position switching: only relative OFF positions possible (radio projection offsets).

• Wobbling secondary: max. 240" throw at 0.25 Hz, standard phase duration 0.5 Hz.

• Frequency switching: max. 45 km/s throw at max. 0.5 Hz., with 100 kHz filters and autocorrelator only

• On the fly mapping: Works with all receiver and backends, typical dump rate 0.5-1 Hz

• Polarimetry: using VESPA as an IF polarimeter

• Pointing: Using nearby (within 10 degree) pointing sources, <1" accuracy can be obtained; with absolute ("blind") pointing, the accuracy is <4", the receivers are usually aligned within 2". 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 may be systematic differences (<0.4") in the focus of the different receivers. Check focus at least at after sunrise and sunset.

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Moderator: Carsten Kramer, Created by Rainer Mauersberger (1999)