Diff for "TelescopeSystemStatus"

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• This page provides information on the current status of the 30m telescope. It is intended for visiting astromers at the telescope and for astronomers preparing 30m observations. The IRAM staff tries to keep this page up to date as much as possible, however, some information may still be outdated. Please contact the Astronomer of Duty (AoD) or Operator in case of doubt. For an overview of the entire system and its performance, see the [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary Telescope System Summary]. (CK, 30.8.08)

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System - General

• Observations less than 5 degree from the Sun are not yet supported. There is no specific alarm, but integrations don't start and tracking errors remain high.

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Antenna and wobbling secondary

• Observations with high wind speeds are degraded for several reasons. At velocities of more than about 15m/s tracking errors become larger than usual. In addition, the wind load may lead to deformations of the primary dish, depending on direction and orientation of the telescope (Morris et al. 2006). In this case, consider changing to a different source at a different antenna position. If the wind becomes too strong and puts the antenna in danger, the operator may have to decide to stop the observations and put the antenna in the safe stow position. (CK&JP 1.9.08)

• The upper elevation limit of the telescope has been set to 83 degrees, when tracking problems are known to set in. In addition, the point source sensitivity is degraded at high elevations and especially for high observing frequencies (see the gain-elevation curves e.g. in the 30m manual). (CK 11.9.08)

• Bolometer observations with "rotated" wobbler are now possible. The permitted rotation range is +- 65 deg., in a fixed rotation, without tracking on the sky (the limitation for the tracking comes from the observing program). After finishing with rotated Wobbler, make sure that the operator puts the rotation back to exactly 0 degrees. (JP&CK 1.9.08)

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Frontends

SIS Receivers A, B, C, D

• If you plan to use the 3mm receivers at low frequencies, please send your frequencies to the receiver group at least two weeks in advance. (23-8-2008 CK)

• Image/Signal gain-ratio calibration using the continuum backends(!) is supported by NCS, processing in MIRA. It is highly recommended to use this feature!

• A standard table of T_cold calibration temperatures for A, B, C, D receivers is implemented in the NCS. This built-in table covers most frequencies. Outside this range, T_cold has to be set manually, ask the RX engineers or operators! [http://gra-lx1/mainWiki/ReceiverGroupColdLoadPlotsCurrent Tables and plots (internal link)] (2007-10-11 dj)

• CHECK Receiver C150 shows low continuum signal at the higher frequencies (>168 GHz). It has to be fully checked. Use D150 instead. (2005-11-16)

• In the receiver cabin, Martin-Puplett interferometers MPI are used to seperate frequencies to be send to two different receivers. An overview of the receiver cabin optics is given [http://www.iram.es/IRAMES/telescope/telescopeSummary/receiver6.html here]. The MPIs have high losses at certain frequency ratios, especially at a ratio of 3. Simultaneous observations of e.g. HCN(1-0) and HCN(3-2) or HCO+ are therefore difficult and may lead to increased receiver noise temperatures, depending on how the MPI is optimized.

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HERA

HERA is a HEterodyne REceiver Array, a 3x3 dual polarisation array in the 1.2mm band. For details on HERA see the [http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html Telescope Summary page] or the [http://www.iram.es/IRAMES/mainWiki/HeraWebPage HERA page].

• SSB (Single side band) tuning tables for standard frequencies.
• Only few frequencies can be tuned automatically. Observers should send observing frequencies to the IRAM Granada receiver group at least three weeks in advance.
• Sideband rejections not determined (2004-12-01 AW). Use standard value of 0.1!
• For HERA calibration, measured values of the load temperatures are automatically used!

• Watch the computer control of the derotator closely (2002-12-22). Make sure the derotator tracking is stopped after observations, i.e., set to zero degrees in "frame". Do this also if you continue to observe a source at a large angular distance. In MIRA, after loading a HERA scan, you can visualize the evolution of the derotator angle with time by using command "VIEW /DEROTATOR" (2008-09-12).

• The automatic tuning of both HERA1 and 2 can be improved by manually changing the mixer current according to DJ; HERA Pool managers should be aware of this, and operators will receive training (2007-09-19 RM)
• HERA 2 is more noisy than HERA 1, limiting HERA2's useful frequency range to below about 242 GHz (2006-09-27 HU according to info from SN)
• Tests have shown that the pixels of HERA-2 (second polarisation) have relatively strong variations of noise over the IF band (LSB Tuning). While the consequences are not too dramatic for wide band operation (WILMA) unfortunately the narrow band mode as used mostly with VESPA picks up the end of the IF band with the highest noise. The problem will be further investigated and eventual improvements indicated asap. To be confirmed at the beginning of the HERA pool (2008-09-30).

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Bolometers

Details about the bolometers are given on the [http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html Telescope Summary page] and on a dedicated [http://www.iram.es/IRAMES/mainWiki/MamboWebPage MAMBO page.]

• MAMBO1 is OFFLINE
• MAMBO2 is operational (ck 19.9.08)

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Backends

• VESPA platforming is often caused by total power offsets between different phases, e.g. ON and OFF. VESPA spectra occasionally show spikes at band edges. Check with the AoD to run vespamon.py to check where the problem stems from. The local expert of VESPA is Gabriel Paubert. (30.8.08 ck)

• ABBA2 has been reinstalled by Giorgio Siringo (MPIfR) mid September 08.

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Computer/Software

• The New Control System (NCS) supports source coordinates in Equatorial J2000.0 system. More coordinate systems, i.e. B1950, Galactic Coordinates, etc., will soon be available. You may want to try NASA's [http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/convcoord/convcoord.pl HEASARC tool].

• Midnight bug: Online data processing may still occasionally have problems with scans extending over midnight. Please check data and report problems to the AoD and Albrecht Sievers. Avoid starting scans directly before UT-midnight. (AS & CK 7.9.08)

• It is recommended to run the observations, i.e. to run Pako, on mrt-lx1. On mrt-lx3, mrt-lx2, switch to a different GILDAS version and type gag_aug06, before starting pako (2008-01-15 AS).

• Data processing using MIRA or CLASS on mrt-lx3 occasionally slows down the observing system on mrt-lx1 as both system currently access the same disk, /vis, which is at present connected to mrt-lx3. This may mean that the work on mrt-lx3 has to be stopped as observations have priority. Please contact the AoD in case of such problems; for work with CLASS/GREG it helps to copy the 30m file over onto the local disk of mrt-lx2 and to continue working there. For MIRA processing of raw data, this would not help. We are working on a better solution. (2008-08-29 wb, ck). On mrt-lx2, please create a directory /aux/<project> and copy the spectraOdp.30m file to that directory. Use this file only for reading as it is not included in the standard visitor cd/dvd !

• Automatic calibration and processing of heterodyne data using the MIRA software is in operation for all observing modes. MIRA can also be used manually and offline.

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Pointing

Heterodyne Pointing Model and Focus

The Pointing Model is maintained with respect to the 3mm receiver B100. The misalignment and focus error (D-focus) of the other receivers with respect to B100 is the following:

  Rx       misal.(")       date            D_focus(mm)       date
 A100     0.16 ±0.06     27-Feb-07,        +0.09 ±0.03     13-Mar-07
 A230     1.34 ±0.18     27-Feb-07,        +0.43 ±0.02     13-Mar-07
 B100     0.00                              0.00
 B230     1.74 ±0.16     27-Feb-07,        +0.40 ±0.10     17-Apr-07
 C150     1.26 ±0.24      5-Feb-07,        +0.64 ±0.13     17-Apr-07
 C270     0.78 ±0.18      5-Feb-07,        +0.36 ±0.15     17-Apr-07
 D150     1.03 ±0.13     12-Mar-07,        +0.26 ±0.02     12-Mar-07
 D270     1.40 ±0.19     12-Mar-07,        +0.18 ±0.05     12-Mar-07
 HERA    ~5              04-Aug-08 (for central pixel, staff meeting, JP)               

• Pointing on spectral line sources like SiO masers is not yet supported by the data processing.

• heterodyne pointing model: last update: 2008-06-25, 29 points, previous rms = 2.58", new rms = 1.97". The coverage and scatter of the pointing session were: attachment:coverage.jpg attachment:scatter.jpg

Bolometer Pointing model

• bolometer pointing model: last update: 2007-12-19, 46 points, previous rms = 2.33", new rms = 1.75"

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Pointing with SIS receivers

• Continuum instability ("ripple") can occur with all receivers, making pointing and focusing difficult.
• In general some receivers are better than others in this respect as summarized here:
  • A100 generally OK for pointing. (2003-11-12)

  • B100 OK, is best for pointing. B100 is the standard reference for the heterodyne pointing model

  • C150 often bad for pointing, ripple. (2002-07-16)

  • D150 generally good performance for pointing.(2002-07-16)

  • A230 often unstable, bad for pointing and flux monitoring. (2003-11-12)

  • B230 OK

  • C270 can be unstable and difficult for pointing. (2007-04-30)

  • D270 can be unstable and difficult for pointing. (2002-07-16)

  • With HERA pointing may be difficult using beam switch mode - total power mode may give better results but requires excellent weather

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Updates/History/Legend

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