Diff for "TelescopeSystemSummary"

Anchor(beginOfPage)

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 at the 30m observatory. BR The current status is described on another [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemStatus page].

TableOfContents(4)

Frontends

Heterodyne Receivers

• Eight single pixel, dual-sideband 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.

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 ]

Bolometers

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

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.

Table

1. 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).

Backends

Spectrometers

Table

Bolometer backends

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.