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EMIR Users Guide

News (last update: 28-Jul-2014)

• A report on gain ratios and receiver temperatures from lab measurements of the installed EMIR mixers for all four bands has been prepared by D.Maier (IRAM/Grenoble). See also the comment 1.2. in Table 1 on the recommended LSB frequency range of E090.

• E150 frequency range: Information on the E150 frequency range has been updated (cf. Table 1). See also a report by A.L.Fontana (IRAM/Grenoble) on the system performance of E150 at its band edges.

• EMIR Ghost Lines: The EMIR local oscillators (LOs) do create harmonics of its Gunn oscillators, which are mixed in the sideband separating mixers, and then down converted into the IF (intermediate frequency) band. The LOs do, however, also create unwanted harmonics which may not be sufficiently suppressed, leak through, and pump the mixers. This may lead to detections of ghost lines stemming from much higher frequencies, far outside the nominal frequency range, polluting the observed spectra. Such lines have recently been identified in frequency surveys of IRC+10216: in one example, a ghost line showed-up at 129GHz in the E150 band, which does however stem from a line at 196GHz. With the large bandwidths provided by EMIR, and with deep frequency surveys on sources showing a large dynamic range of line temperatures, addressing these ghost lines becomes important. A report has been prepared to inform the observers of the current status of this issue, describe the origin of the harmonics, give observational examples showing also how to detect ghosts, and describe counter measures which are currently being prepared by the IRAM frontend groups. <28-Jul-2014 CK>

• The script to check the possibility to observe several lines with one of the EMIR receivers and the present set of backends, has been updated now providing more information on the frequency distance to the edges of the bands and on possible sky frequencies for pako. See below "Connection to Backends".

• The current beam pattern of the 30m telescope is described in a new report, based on EMIR observations covering the entire frequency range between 86 and 345GHz. The main beam efficiencies have considerably improved relative to the values compiled in Greve et al. (1998). See here or here.

Upgrades

Sep-2013: 2SB for E1

We exchanged the current SSB mixers of E1 by 2SB mixers of the type used already for the other three bands. The available frequency coverage may change slightly. In addition, we exchanged the local oscillator for the E330 band by a YIG LO to allow observations up to 370 GHz.

Nov-2011: 2SB for E2 and E3

In the first week of November 2011, we upgraded EMIR with dual sideband (2SB) mixers for bands E230 and E330. These mixers cov er 8 GHz of instantaneous bandwidth per sideband and per polarization, like E090. E150 is unchanged with single sideband (SSB) mixers and 4 GHz bandwidth per polarization. Below, comment (4) on Table 1, gives the new frequency ranges of E2 and E3. Figures below show the new bands, the new switch box scheme, and examples of band combinations which can be observed simultaneously. Commissioning has finished. First regular observations with EMIR have started again on 15-Nov.

Jul-2011: 32GHz IF-system, FTS backends

Since July 2011, we have made available a new 32GHz IF system which includes 24 fast fourier transform spectrometers (FTS). This upgrade has duplicated the amount of instantaneous bandwidth available at the 30m telescope. 16 GHz of bandwidth can now be used instantaneously, in both polarisations. Eight cables of 4GHz width now carry the intermediate frequencies through the telescope cable spiral to the backend room. The full 32GHz of bandwidth are covered by 24 FTS working at 200kHz resolution. This improves the available velocity resolution over large bandwidths by a factor of 10 compared to WILMA with its 2MHz resolution. It is now possible to observe at 0.6km/s resolution in the 3mm band allowing to resolve star forming clouds in the Milky Way and in nearby galaxies. The resolution of the 24 FTS can further be increased to 50 kHz, in which case only the inner 1.82GHz of the 4GHz EMIR bands are covered. The previous 4x4GHz system is still in use, and the additional 4x4GHz cables are connected to the outer 4GHz wide bands of EMIR 3mm channel, i.e. to E0UO and E0LO in both polarisations. All FTS units work either at 200 kHz or at 50 kHz. However it is not possible to set them individually to different resolutions. The new FTS can also be connected to the 2x9 HERA cables of 1GHz width, both at 200kHz or at 50kHz resolution. See also the call for proposals for the deadline in September 2011.

See a brief report further below, and an overview of available backends, including the new broad band continuum (bbc) backend and the new IF distribution.

Sky frequencies

Table 1: EMIR Frontend. Sky frequencies Fsky are given for the centers of the outermost 4GHz IF bands. Acronyms: 2SB - dual sideband mixers, SSB - single side band mixers, H/V -- horizontal and vertical polarizations, Trx is the SSB receiver temperature in single sideband observations, Gim is the image band rejection, LSB/USB are the lower and upper sidebands. Note that the receiver noise is somewhat increased when observing with two bands simultaneously due to the dichroic elements needed for these observations (see below for more details).

(1.1) At frequencies below 83GHz, the receiver gain ratio is known to vary strongly over the bandpass and between the two polarisations. In addition, the receiver noise temperatures increase.
(1.2) The LSB should be used for local oscillator frequencies of up to about 108GHz because at higher LO frequencies, the LSB shows rather poor image band rejections of upto -5dB. The USB should be used instead (cf. plots of the gain ratios observed in the lab by D.Maier)
(2) New 2SB E1 mixers have been installed in September 2013. The nominal RF frequency range of the E1 receiver is 127-179 GHz, which, referred to the centers of the outer 4 GHz bands, corresponds to 129-177 GHz. However, lab measurements done in the range 124-184GHz (centers of outer bands; LO frequencies 134-174GHz) show a good performance of receiver temperatures and sideband ratios over this range (cf. report by D.Maier (IRAM/Grenoble)), which we therefore offer to the astronomers. The receiver temperatures and gain ratios at the telescope will be roughly the same, but not exactly so, as the temperature environment and also some of the optics are different. The properties of the beam at the band edges are described in a report by A.L.Fontana (IRAM/Grenoble). Observations near the water line at 183.31GHz require special care to correct for low atmospheric transmission. Observers requesting observations beyond the offered frequency range, i.e. beyond 184GHz, should contact the Granada receiver group as such observations require a good calibration strategy to measure the gain ratios (cf. a recent detection of H2Cl+ at 189GHz by Gerin et al. 2013).
(3) As described in the commissioning report, the local oscillator of E3 shows instabilities at a few frequencies. If you as observer encounter such problems, please contact the operator and/or receiver engineer. Swapping the sideband may help.
(4) In November 2011, EMIR bands E2 and E3 have been upgraded to full dual-polarisation, dual-sideband 8GHz each mixers. The frequency ranges have changed, in particular the overlap region between E2 and E3. Above, we give the new frequency ranges of E2 and E3. These are the centers of the outer bands which are reachable by all backends including VESPA. The FTS at 200kHz can reach frequencies which lie 2GHz further out.
(5) E2 and E3 receiver temperatures have been measured at the telescope by SN in January 2012. For dual-band observations, we've added here 15K, as average number. However, observers should be aware that losses in the dichroics are frequency dependent as described further below.
(6) Oct-2013: The new YIG local oscillator allows to reach much higher frequencies than the Gunn LO used previously. In case the YIG fails, we'd need however to go back to the Gunn LO and to the previous upper frequency of 350GHz.

Overview

The Eight MIxer Receiver EMIR was installed and commissioned at the 30m telescope in March through April 2009. EMIR replaced the single pixel heterodyne receivers A/B100, C/D150, A/B230, and C/D270. HERA, the bolometers, and the backends are unchanged. Since 2009, EMIR was upgraded to now offer an instantaneous bandwidth of up to 16 GHz in each of the two orthogonal linear polarizations for the 3, 2, 1.3 and 0.9mm atmospheric windows. In addition to the vast increase in bandwidth, the receiver offers considerably improved noise performance, a stable alignment between bands, and other practical advantages.

The four EMIR bands are designated as E090, E150, E230, and E330 according to their approximate center frequencies in GHz. All bands are operated in dual-sideband, 2SB, mode with good imageband-rejections, where both sidebands are available for connection to backends. Furthermore, these bands are built in a technology that offers 8 GHz instantaneous bandwidth per sideband and polarization. Both polarizations of a given band will always be tuned to the same frequency as they share a single common local oscillator. The tuning ranges of the 4 bands, the typical receiver noise temperatures, and other parameters are listed in Tab.1.

EMIR provides for the first time in the history of the 30m telescope a permanently available high sensitivity E330 band, opening this atmospheric window for regular use under good weather conditions. See the commissioning report below.

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Figure 1: Atmospheric transmission between 60 and 400GHz for two precipitable water vapors, modeled with the ATM model. The EMIR bands are marked together with the frequencies of a few important molecular transitions.

EMIR bands

Figure 2: Overview of EMIR band combinations and frequencies which are available after the EMIR upgrade and commissioning in September/October-2013. Central frequencies of the (sub-)bands refer to VESPA, and the band edge frequencies are given for WILMA and the FTS backends in the two resolution presets. Frequency edges are taken from the list provided by G.Paubert on the backends page.

EMIR band combinations

EMIR has four different bands covering the four main atmospheric windows in the millimetre range: E090, E150, E230 and E330. Dual band observation is possible but only the E0/E1, E0/E2 and E1/E3 band combinations are allowed by the receiver optics. Each of the four bands (E0, E1, E2, and E3) have four IF outputs: 2 polarizations (H,V) and 2 sidebands (L,U), each of them is 8 GHz wide. The 8GHz wide IF outputs are split in two blocks, 4 GHz wide each, denoted by I and O (inner and outer) and sent to the spectrometers by the use of in total 8 coaxial cables. This means that a total of 32GHz of bandwidth are transferred to the spectrometers. In the future, we plan to upgrade the IF-system and backends to allow for 64GHz of total bandwidth, the maximum EMIR offers.

The FTS backends can be connected to all 8 cables, while the old backends VESPA and WILMA can only be connected to IF cables 1-4.

When designing the new switch box, we assumed that most will want to use both polarisations simultaneously. Aside from improving the signal-to-noise ratios, this observing mode allows for easy checks of the relative calibration.

Commissioned EMIR band combinations or setups:

1. One band only:

   1. E0 LI+LO, UI+UO (dual-pol, 16GHz bandwidth)

   2. E1 LI+LO, UI+UO (dual-pol, 16GHz bandwidth)

   3. E2 LI+LO, UI+UO (dual-pol, 16GHz bandwidth)

   4. E3 LI+LO, UI+UO (dual-pol, 16GHz bandwidth)

   5. E2 LO+UO (special setup to use only IF bands 1-4, allowing to connect VESPA e.g. for polarimetry)

2. E0/E2:

   1. E0: UI+UO, E2: UI+UO (dual-pol, 16GHz, e.g. 12CO, 13CO 1-0, 12CO 2-1)

   2. E0: LI+LO, E2: LI+LO (dual-pol, 16GHz, e.g. HCN, HCO+ 1-0, 13CO 2-1)

   3. E0H: LO+LI+UI+UO, E2V: LO+LI+UI+UO (single-pol, 32GHz, H<->V)

   4. Special setups (not tested after the upgrade in Sep-2013):

      1. E0VUO (12CO 1-0), E2VUI, E2HUI (12CO 2-1), E2HLI (13CO & C18O 2-1) [only 4 IF-cables used]

      2. E2HLI, E2HUI, E0VUI (or any other E0V band) (12CO & 13CO 2-1 + 3mm) [single-pol]

      3. E2UO, E2UI, E0UO, E0UI (using IF-cables 1-4, available since 12-Jan-2012)

3. E1/E3:

   1. E1: UI+UO, E3: UI+UO (dual-pol, 16GHz)

   2. E1: LI+LO, E3: LI+LO (dual-pol, 16GHz)

   3. E1H: LO+LI+UI+UO, E3V: LO+LI+UI+UO (single-pol, 32GHz)

   4. Obsolete setups after Sep-2013:
      1. E1V+E1H+E3VL+E3HL
      2. E1LI, E3LI, E3LO (dual-pol)
      3. E1UI, E3LI, E3VLO (dual-pol)
      4. E1UI, E3UI [after the switchbox upgrade in Oct-12]
      5. E1LI, E3UI [after the switchbox upgrade in Oct-12]

4. E0/E1:

   1. E0: UI+UO, E1: UI+UO (dual-pol, 16GHz)

   2. E0: LI+LO, E1: LI+LO (dual-pol, 16GHz)

   3. E0H: LO+LI+UI+UO, E1V: LO+LI+UI+UO (single-pol, 32GHz, H<->V)

   4. Obsolete setups after Sep-2013:
      1. Together with E1, only the lower bands of E0 can be observed in dual-pol. Inner and outer bands can be observed simultaneously for E0. Important application: CS 2-1, 3-2.
      2. EOLI, E0LO, E1LI (dual-pol)
      3. E0LI, E0LO, E1UI (dual-pol)
      4. E0UI, E1UI [after the switchbox upgrade in Oct-12]
      5. E0UI, E1LI [after the switchbox upgrade in Oct-12]
      6. E0LOH, E0LIV, E0UIH, E1LIV ! special setup, as only one polarisation is used. Allows to observe three transitions of NH2D simultaneously.

Setups which are not possible:

1. 3mm: UI+UO, 1mm: LI+UI (12CO, 13CO 1-0 & 2-1) ! Only a maximum of 4 inner cables can be selected.

2. E0 LI,UI + E2 LI,UI ! Only a maximum of 4 inner bands can be selected. In general, when connecting to E2 LI+UI with both polarisations, none of the inputs of E0 are accessible.
3. E0 LO UO + E2 LO LI
4. 50kHz FTS: C18O, 13CO, 12CO 1-0 simultaneously. These lines lie 5.49GHz apart, while the outer edges of the FTS 50kHz units in the inner and outer band of EMIR lie 5.42GHz apart. The inner edges lie 1.78GHz apart. However, it is no problem to observe these lines simultaneously with 200kHz resolution.
5. E0 alone with only two If cables attached, e.g. horizontal LI vertical LI, results in corrupted FTS raw data (imbfits files that mira can not read and result in a Segmentation fault). A Workaround is to attach 4 cables, e.g. horizontal UI+LI and vertical UI+LI.

More details on the selection rules and a sketch of the switch box, are given here: SwitchBoxDetails. See also the commissioning report below.

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Focal plane geometry

The four bands will be combined in only two possible beams (left and the right beams when looking to the cryostat front face). The left and right beams are offset by about 90" on the sky. See the telescope status page for the present Nasmyth offsets (cf. EMIR Commissioning report below). Observations are carried out with either of the two beams. Simultaneous observations with both beams are at present not supported.

Selection of EMIR bands (Dichroics)

Before reaching the Nasmyth mirrors, the four beams of the EMIR bands pass through warm optics that contains switchable mirrors and dichroic elements for redirection of the beams towards calibration loads and for combining beams. In its simplest mode, the warm optics unit selects one single EMIR band for observation. This mode avoids the use of the slightly lossy dichroic elements and therefore offers the best receiver noise temperatures.

Three dichroic mirrors are available for combining either the E090 and E150 beams, or the E090 and E230 beams, or the E150 and E330 beams (Table 1). The combination of bands is not polarization selective, i.e. the combined bands will stay dual polarization. The loss of these dichroics increases however the receiver temperatures by, in general, only 10 - 15 K. The losses of E2 (due to the use of the dichroic) are higher than 10% for frequencies above ~258GHz and below ~202GHz (cf. Table 2). The polarization angle of the dichroic was chosen to minimize the losses for 231GHz. The observer is therefore adviced to carefully evaluate whether an observation involving two different bands is more efficiently made in parallel or in series.

Note that simultaneous observations of e.g. HCO+ at 89.7 and 266.5GHz with E0 and E2, will suffer from much increased system temperatures in E2, due to the losses of the dichroics using this frequency combination.

The dichroics are needed for dual-band observations with EMIR. The following table shows the losses of the dichroics, based on a separate mixer and dichroic characterization done in the receiver lab by Anne-Laure Fontana in Feb 09. This table is subject to change with new measurements of the integrated receiver, and with new dichroics.

Table 2: Performance of dichroics (February 2009, Report of Anne Laure):

Each percent of losses, increases the receiver temperature by about 4K.

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IF Distribution

An overview of the current disbribution of intermediate frequencies (IF) is given here.

Connection to backends

Eight output channels are sent via the IF cables to the backends at the IRAM 30m telescope:

• the Fast Fourier Transform Spectrometers (FTS) handle input from all 4 cables.
• The other backends take as input the (old) IF cables 1-4 only: Three backend processors have been build to feed the new 4 GHz wide IF channels to the existing backends:

  • The WILMA processor rearranges the four incoming 4 GHz wide IF channels into 16 channels of 1 GHz width which can be processed by 16 WILMA autocorrelator units. Since each unit provides 512 spectral channels of 2 MHz, sufficient backend power is available at low spectral resolution for full coverage of the 4x4GHz bottleneck.

  • The narrow backend processor prepares the 4 incoming IF channels for input into VESPA. Only the central part of the 4 GHz IF channels is accessible to these backends. Inside this central part (1 GHz for the filterbank and 640 MHz for VESPA), these backends can be configured as before. The VLBI terminal is also fed from this processor.

• When planning to observe several interstellar lines simultaneously with EMIR, it is sometimes difficult to check whether this is possible with the FTS at 50kHz resolution and VESPA. A small greg script is available here, to help finding a local oscillator frequency to allow for simultaneous observations of several lines with both sidebands of one of the four EMIR receivers. The greg-script plots the frequency coverage of the FTS at 200 and 50kHz, and the 500MHz bandwidth of VESPA, together with a set of lines to be observed, using a given LO frequency:
  .

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Temperature calibration

EMIR comes with a new calibration system. The external warm optics provides ambient temperature loads and mirrors reflecting the beams back into the 15 K stage of the cryostat. This system is expected to be very reliable and constant over time. Absolute calibration accuracy will be better than 10% with EMIR when all details are well settled.

Band E150 has backshort tuned single-sideband mixers; DSB tuning is not possible, but sidebands (USB or LSB) may be selectable within limitations. The image rejection is better than 10 dB for all frequencies. On-site measurements of the rejection is not longer straightforward for these mixers, since the Martin--Puplett interferometers are not available anymore. As the optimum way of calibrating the image rejection is still under exploration, users who propose observations which rely on an enhanced accuracy of calibration of image gains should mention this request in the proposal.

The other bands have tunerless sideband separation mixers, allowing simultaneous observations of both sidebands in separate IF bands. These mixers have been characterized in the laboratory for their image rejection and are expected to have the same performance on site (>13dB).

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Correct frequency scales over upto 24 GHz of bandwidth

It is common practice at radio observatories to correct the frequency of an observation for the strongly time variable velocity of the Observatory with respect to the solar system barycenter. This guarantees that lines observed near the Doppler-tracked frequency, usually the band center, always have the correct barycentric velocity, independent of the time of observation. At the 30m, the local oscillator and its synthesizers are constantly adjusted during observations to track the changing Doppler factor for one spectral line with its rest frequency. This causes a slight shift of lines observed simultaneously at a diff erent frequency. This shift is proportional to the frequency diff erence and the Doppler factor. CLASS corrects for this shift by adapting the spectral resolution.

As the report below describes, these shifts correspond to time variable changes of the frequency resolution. Co-adding or averaging spectra taken at different times, may then lead to a broadening of the effective frequency resolution.

Accurate line center frequencies: Report of 03-Aug-2011 by Buchbender, Kramer et al.. Two bugs in mira and class caused frequency shifts and have been corrected for. The new versions of mira and class were installed at the 30m on 16-Aug-2011.

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PaKo user interface

The new default PaKo version supports the upgraded E2 and E3 mixers and the enhanced IF switch box. See the current PaKo manual.

Please contact your astronomer-of-duty to help you prepare scripts or in case of any questions.

EMIR Observations Time Estimator

• EMIR observing time estimator

Telescope efficiencies

• Telescope Efficiencies

Observatory status

• Telescope Status Page

Reports and publications

• Report on EMIR ghost lines (unwanted harmonics of the local oscillators, 28-July-2014 by Kramer, Navarrini, Navarro, John, Cernicharo

• Report on E1 optics in the 122 - 186 GHz range: performance at the band edges, July 2014 by Anne Laure Fontana (IRAM/Grenoble)

• Report on Lab measurements of EMIR receivers: receiver temperatures and image band rejections, June 2014 by Doris Maier (IRAM/Grenoble)

• The EMIR Multi-band mm-Wave Receiver for the IRAM 30m Telescope, Carter, Lazareff et al. 2012 (A&A, 538, 89)

• Commissioning Reports:

  • Bands 1-3: EmirCommissioningReportVers1.1.pdf (4/2009)

  • Band 4: emir-e3-com-report-05apr2010.pdf (4/2010)

  • Polarimetry (Bands 1&3) wiesemeyer-thum-xpol-report-10aug2010.pdf (8/2010)

  • Upgrade to 32GHz IF system kramer-aug2011-32ghz-newsletter.pdf (7/2011)

  • Upgrade of E2 and E3 mixers (Nov 2011)

    • emir-nov11-com-report-v1.0.pdf Report on spectral line commissioning observations by Kramer et al.

    • e2-09apr2012.pdf Report on E230 issues encountered till 23-February-2012.

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Historic news

• The local oscillator for EMIR band 4, E330, had to be sent to Grenoble for repair. We re-installed the Gunn LO with its upper frequency limit of 358 GHz. (12-February-2014)
• News on the upgrade of E150 and E330 in Sep-2013:
  • Installation of the new 2SB mixers for E150 and of the new YIG LO for E330, went well. New versions of pako and of the software controlling the IF switchbox have been tested and implemented. A commissioning report is in preparation.

    • E1 frequency survey between 125 and 186GHz went well. Same for tests of the basic setups of the IF switchbox. All successfully tested setups are marked with a in the listing of setups below.

    • E3 has been tested at local oscillator frequencies between 300 and 360 GHz.

• Antenna temperatures of E1 upper sideband (USB) observations at sky frequencies between 144 and 147 GHz have been found to be a factor ~2 lower than lower sideband (LSB) spectra due to a wrong tuning table leading to a poor image band rejection. The tuning table was wrong since the installation of EMIR in 4/2009, but has been corrected now. We have found no indications for such problems outside the above frequency range. <9-Jan-2013 CK>

• We have implemented a small upgrade of the IF switchbox which now allows simultaneous observations of E3 in USB together with E1, and of E0 USB together with E1. The former setup will be helpful for high frequency E3 observations together with pointings using E1. All previously possible IF setups stay available after this upgrade. See switch box details below. <28-Oct-2012 CK>

• The local oscillator for E330 has been refurbished such that EMIR can now reach sky frequencies up to 358 GHz, giving access to the 4-3 transitions of HCN and HCO+ under excellent weather conditions. <30-Jul-2012 CK>

• A dedicated paper on the working of EMIR and first results has been published by Carter, Lazareff et al. 2012 (A&A, 538, 89).

• Observers have been informed on 26-Apr-2012 on problems for some frequencies with E230 between 15-Nov-2011 and 23-Feb-2011 when this band showed excess noise, spurious signals, and calibration problems. Improving on the tuning parameters solved this.
• The E0/E1 alignment is better than 1", after repositioning the EMIR caroussel no. 2 on 29-Nov-2011, and later replacing its position sensor.
• The main EMIR band setups possible after the upgrade of E2 and E3, and of the IF switch-box, have been successfully commissioned in November 2011. Possible EMIR band combinations are detailed below.

This page is maintained by C.Kramer. Any comments are welcome.