Diff for "TelescopeSystemStatus"

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 The IRAM staff tries to keep this page up to date as much as possible, however, some information may still be outdated.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 Telescope System Summary. (CK, 30.8.08)

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 positional deviations 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 10m/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 85 degrees, above which tracking is lost. 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). At 87deg the vertex is closed to protect the receivers against the CLOUDSAT satellite. (CK 31.12.08)

• 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

• We recommend sending observing frequencies at least two weeks in advance of an observing run by FAX to the receiver group. This holds in particular for frequencies near the receiver band edges, for HERA2 tunings, and for frequencies below 81 GHz. (to be CHECKEed) (23-8-2008 CK)

SIS Receivers A, B, C, D

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

  • A standard table of Tcold calibration temperatures for A, B, C, D receivers is implemented in the NCS. This built-in table covers most frequencies. (Use: pako>receiver /temp L)

  • Outside this range, Tcold has to be set manually (use pako>receiver /temp "Tcold"), ask the RX engineers or operators! 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 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

• 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. (to be CHECKEed)
• Sideband rejections not determined (2004-12-01 AW). Use standard value of 0.1!
• For HERA calibration, measured values of the load temperatures (Tcold, Thot) 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 Telescope Summary page and on a dedicated MAMBO page.

• MAMBO1 is OFFLINE
• MAMBO2 is online (24.2.09)

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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)

• Software on ABBA2 occasionally freezes and needs to be restarted. Check with the AoD. (24.2.09 ck)

• The 4MHz filterbank occasionally shows platforming and ripples. The local contact is Salvador Sanchez. (Assunming that ripples are caused by standing waves between reflecting surfaces or connectors, the ripple period P and the path length L are related via: 2L=Clight/P, i.e. L/(m)=150/(P/(MHz)). In coax cables, Clight is reduced to about 70%.) (2.11.08 ck)

• 13CO and C18O 2-1 can be observed simultaneously with WILMA but not with VESPA. The 2 lines are 839MHz apart.
  • With WILMA and 2MHz (2.6km/s@230GHz) resolution, both lines can be observed simultaneously. The WILMA bandwidth is 930MHz.

  • VESPA cannot be used to observe both lines simultaneously as the maximum bandwidth of one unit of VESPA is 512MHz. Two high resolution units cannot be moved sufficiently, to cover both lines, as the maximum offset is 250MHz.

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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 HEASARC tool.

• Midnight bug: Online data processing still has occasionally 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. (CK 28.9.08)

• 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. Exceptions (note added by H.W., 2009-01-12): (1) The processing of total-power on-the-fly maps without reference subscans (using MIRA's option /mask for command /calibrate needs user input). (2) XPOL observations (VESPA in polarimetry mode) when another spectrometer in non-polarimetry mode (e.g. 1MHz filterbank) is connected in parallel. To be reduced by hand, separating XPOL and filterbank data by e.g. "find /backend vespa" respectively "find /backend 1mhz".

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Pointing

Heterodyne Pointing Model and Focus

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

• Heterodyne pointing with wobbler switching is operational again in the default version of GILDAS (gag_mar08). Reliable results for the beam separation can only be obtained if the pointing scan is long enough to show the source in both wobbler phases (MIRA).

• swWobbler (wobbler switching) Pointing with the heterodyne receivers and rotated Wobbler is not yet supported by the data processing (MIRA).

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     <1 (JP&CT)     07-Jan-09,      +0.09 ±0.03     13-Mar-07
 A230     1.34 ±0.18     27-Feb-07,        +0.43 ±0.02     13-Mar-07
 A100     0.76 (from SN&JP, 19-Nov-08)
 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)               

• "normal" values for the aditional pointing corrections determined by the observer are close to 0, or +/- a few arc sec.
  • a larger value of the pointing correction does not affect the quality of the pointing if
    • it is well determined
    • has no strong variation with azimuth and elevation
    • does not change quickly with time
  • please inform the staff (AOD) about good quality pointing corrections that vary by more than 3 arc sec

• "normal" values for the optimized focus determined by the observer are close to -2.5mm for the B100 receiver.

  • depending on temperature changes (e.g. during sun set or sun rise) and the time of day, this may vary by +/-0.5mm, in extreme cases +/-1mm
  • please inform the staff (AOD) about good quality focus results that are not consistent with this
  • for good focus results one needs good weather and a strong source that is smaller than the beam, e.g., Mars, only when it is smaller than the beam, or one of the strongest quasars

Old Bolometer Pointing models

• Most recent MAMBO2 pointing model: update on 2008-11-09 by AS, RZ, 68 points, previous rms = 6.7", new rms = 1.7" (see internal wiki)

• 2007-12-19, 46 points, previous rms = 2.33", new rms = 1.75"

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Pointing with SIS receivers and continuum backends

• 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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Observers weekly pointing results

• Heterodyne and MAMBO Pointings from the AoD reports: PointingModelFits

Updates/History/Legend

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