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 The IRAM staff tries to keep this page up to date as much as possible, however, some information may still be outdated. Check the button Recent Changes and 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, 7.10.09)

Antenna and wobbling secondary

• Sun avoidance: The sun avoidance radius is 1 degree (CB, 26.1.10). When trying to observe sources within this circle, there is no specific alarm, but integrations don't start and positional deviations remain high.

• The upper elevation limit of the telescope has been set to 84 degrees, above which tracking is known to detoriate depending on the observing conditions. (CK 25-Aug-2010) 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 an elevation of 87degrees, the vertex is closed to protect the receivers against the CLOUDSAT satellite. (CK 31.12.08)

• 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)

• Bolometer observations with "rotated" wobbler are 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)

• The wobbler is available again with its full throw of +/- 120 arcseconds (15-Sep-2010, CK)

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Frontends Status

EMIR

• Band 4 (E330) is available, using one of the synthesizers usually connected to other EMIR bands, or the HEMT 3mm test receiver. Please contact the operator in case of problems. (22-Oct-2010, CK)

• The new 4 band EMIR receiver replaced the ABCD receivers in March/April 2009. See the EMIR homepage

• Polarimetry with EMIR has been commissioned in August 2009. VESPA will be used in cross-correlation mode, as before. Phase calibrations will be done with a polarizer in front of an external cold load (hw, 10.3.2009). A commissioning report by H.Wiesemeyer & C.Thum is available on the EMIR homepage.

• For E1 (and for E2) the observer has to select the sideband to be used for both polarisations (of the same band). It is not possible to observe simultaneously e.g. the upper sideband of the H mixer and the lower sideband of the V mixer. (ck & sn, 27.3.2009)

• Simultaneous observations of HCN 1-0 and 3-2 using E0 and E2 are possible. Beware, however, of the large dichroic losses in band E2, resulting in strongly enhanced receiver temperatures. See "Performance of the Dichroics" in the EMIR Users Manual

• C2H(1-0) @ 87.4 and C2H (2-1) @ 174.7 GHz has been observed, though the 2mm line is nominally outside the allowed tuning range and receiver temperature is high (~110K). (RA, 20.7.10)
• The CDOOCH3 line at 198.825 GHz is outside the nominal tuning range, i.e. the lower end of E230. (CK, 12.9.2010)

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HERA

• HERA Status Overview

• HERA re-commissioning (after EMIR) done (2009 Aug 2), including VESPA (narrow mode), 4MHz and WILMA (i.e., wide mode). Released for observing.

• Instructions for HERA pool observations

• Use default value of 0.1 for sideband gain ratio Gim.
• For calibration, use the automatically measured values of the load temperatures (Tcold, Thot).

• 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).

• Tuning and receiver temperatures:

  • Observers should send observing frequencies to the IRAM Granada receiver group at least two weeks in advance.

  • Due to degradation of the LO of HERA 1, it can not be tuned above 240 GHz (2010-03-10)
  • HERA 2 is noisier than HERA 1, limiting HERA2's useful frequency range to below about 242 GHz.
  • Tests on 2009 Aug 2 have shown that the pixels of HERA2 (second polarisation) have higher receiver temperatures than those of HERA1, but it remains to be confirmed (by 2009 September 30) whether the tuning was manually optimized or not (see above). The high receiver temperatures of HERA2 (100 - 300 K, as compared to 100 - 150 K for HERA1) are present both in wide and narrow IF mode, i,e,., are not due to a noisier part of the IF reserved for HERA's narrow band mode.
  • 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)
  • when resuming HERA observations after a longer halt, wait for the Gunn oscillators to warm up, otherwise frequencies may be difficult to lock (2009-12-03 HW).

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MAMBO2

• Backend Status Overview

• 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)

• VESPA spikes are a known problem, in particular in conjunction with EMIR. They are under investigation. VESPA platforming is often caused by total power offsets between different phases, e.g. ON and OFF. Check with the AoD to run vespamon.py to check where the problem stems from. The local expert of VESPA is Gabriel Paubert. (22.7.09 ck)

• VESPA has at most 512MHz of bandwidth:

  • 13CO and C18O 2-1 can be observed simultaneously with WILMA but not with VESPA, as the two lines are 839MHz apart. Two high resolution units cannot be moved sufficiently, to cover both lines, as the maximum offset is 250MHz.
  • It is impossible to observe simultaneously e.g. SiO (86.8 GHZ), HCO+ (89.2 GHz), and N2H+ (93.2 GHz). (ck, 27.3.2009)
  • N2H+ and HCO+ 1-0 cannot be observed simultaneously with VESPA. These lines lie at 93.1733922 and 89.188523, with a difference of 3.98GHz. The centers of the outer and inner bands of E0 do *not* lie excactly at 10 and 6 GHz. Instead, they lie at 9.43 and 6.25 and are 3.18GHz apart. (ck, 28.3.09)
  • N2H+ 1-0 at 93.2GHz and C18O 1-0 at 112.5GHz can --probably-- be observed simultaneously with VESPA. These lines are 19.3GHz apart. The centers of the outer bands are 18.86GHz apart, i.e. 440MHz different. When observing both lines at the band edges of VESPA, there still remains upto 30MHz of baseline, depending on the line widths. (ck, 30.9.2010)

• Software on ABBA2 occasionally freezes and needs to be restarted. Check with the AoD or the MAMBO pool manager Guillermo Quintana-Lacaci. (22.7.09 ck)

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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.

• Please note:

  • To run the observations, i.e. to run Pako, log into mrt-lx1.

  • Observations can be prepared with Pako on mrt-lx3 but you have to switch to a different GILDAS version by typing gag_aug06, before starting pako (2008-01-15 AS).

  • Avoid running Pako under the same account more than once, even on different computers.

• 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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Observations

• When observing pointlike sources and when the intensity calibration is important, it is recommended not to use the beam switch (chopper) mode, but either use total power, or wobbler switched mode, with a small throw. This referes e.g. to observations of planets to derive the telescope efficiencies or to flux monitoring observations. The reason is that beam switching suffers from spikes. And large wobbler throws result in a reduced aperture efficiency.

Pointing and Alignment

• 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).

• "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 -2mm for E0.

  • 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

EMIR

• EMIR has two beams, which are separated by 90" on the sky. The Nasmyth offsets are:

  • left beam: +51.0"/+5.5" -- E1 or E3, E1+E3 (2mm or 0.9mm, 2mm & 0.9mm)

  • right beam: -39.0"/+5.5" -- E0 or E2, E0+E2, E0+E1 (3mm or 1mm, 3mm & 1mm, 3mm & 2mm) as determined during EMIR Commissioning in March/April 2009 by JP

• Switching between the two focal plane positions is now transparent to the user. The observer does not need to command the Nasmyth offsets when switching between left and right beam. The currently active Nasmyth offsets are displayed on one of the status monitors. Observations using both beams simultaneously are not possible.

• The alignment between E0 and E1 is about 2 arcsec (see Mars observations of JP from 16sep09 alignmentE0E1-16sep09.pdf and the pointing analysis by RZ).

• The alignment between E1 and E3 is 0.75 +- 0.25 arcsec (see Mars observations of JP from 29-Oct-2009: alignmentE3E1-29oct09.pdf). Observations done on 24-Nov-2009, indicate an even better alignment of 0.3 +- 0.2 arcsec (see EMIR E3 Commissioning report v2.0).

HERA

To see the changes between the actual and the last version, please see Show Changes in the Wiki Interface. If you want to see the Revision History of this page, please see Get Info in the Wiki Interface.

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