EMIR Users Guide

News (last update: 11-Jul-2016, CK)

see also historic news

Upgrades

Dec-2015: New 2SB mixers for E0 and E1

EMIR bands E090 and E150 have been upgraded end of November 2015. Mixers have been replaced by NOEMA-type mixers. For E090, an ortho-mode transducer with one horn only, splits both polarisations. The frequency range of E090 has been extended down to almost 70GHz (see details below). Commissioning has shown that in general the upgrade went well. See further comments in the news section.

Sep-2013: 2SB mixers 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 mixers 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

EMIR

Fsky

mixer

polar-

IF width

Trx

Gim

combinations

Trx

Status

Remark

band

GHz

type

isation

GHz

K

dB

E0/2

E1/3

E0/1

K

E0

73-117

2SB

H/V

8

50

>10

X

X

65

haken.gif

(1.1)

LSB: 73-97 (105)

(1.2)

USB: 89-117

E1

125-184

2SB

H/V

8

50

>10

X

X

65

haken.gif

(2)

LSB: 125-168

USB: 141-184

E2

202-274

2SB

H/V

8

80

>10

X

95

haken.gif

(4, 5)

LSB: 202 (LO) - 268 (LI)

USB: 217 (UI) - 274 (UO)

E3

277-350 (375)

2SB

H/V

8

80

>10

X

95

haken.gif

(3, 4, 5, 6)

LSB: 277-335

USB: 293-350 (375)

Table 1: EMIR Frontend. Sky frequencies Fsky are given for the centers of the outer, respectively inner, 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).

General comment: Observers who intend to observe beyond the frequency ranges offered on the EMIR homepage should contact the Granada receiver group at least a week before the start of observations, even if these frequencies had previously been observed. This is to allow for time to check again if needed and inform the operators.
(1.1) After the upgrade of E090 in November 2015, its frequency range has been extended down to 73 GHz. (The lower frequency limit of the local oscillator is 82.5GHz.) Note that the atmospheric transmission slowly degrades when going from 81 to 71GHz due to an atmospheric oxygen line at 60GHz. Thanks to the dominance of this line, the transmission over this frequency range hardly varies with water vapour and is therefore robust against changing weather conditions. The DCN 1-0 line at 72.41GHz and the DCO+ 1-0 line at 72.04 GHz are not officially covered by VESPA. However, both lines can be observed with the FTS at 50kHz or 200kHz resolution, and with WILMA.
(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 atmospheric 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) In brackets is the frequency limit with the YIG local oscillator (LO), which extends beyond the nominal range offered by the Gunn LO.

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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Atmospheric transmission
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

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) haken.gif

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

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

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

    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) haken.gif

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

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

    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, 12-Jan-2012)
      4. E0LOH, E0LOV, E0UIH, E2LIV (HCN/HCO+ in dual-pol, 13CO 1-0 & 2-1 in single-pol; seems possible but has not been tested)

  3. E1/E3:

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

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

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

    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) haken.gif

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

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

    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)

emir.png 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):

E0/E2

E0/E1

E1/E3

E0

E0

E2

E2

E0

E0

E1

E1

E1

E1

E3

E3

GHz

%

GHz

%

GHz

%

GHz

%

GHz

%

GHz

%

84-108

2.5

202

10

84

4

129

5

129-138

2.5

261-357

<2.5

116

<2

213

5

92

3.2

138-156

1

147

4.5

369

7

225

3

100-110

5

168

2

156

3.5

231

2

110-115

~10

171

2

174

2.5

243

5

174

2

180

~5

255

5

258

10

267

50(!)

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:

Example plot
Figure 3: Frequency coverages of the various backends.

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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.

All 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

Telescope efficiencies

Alignment

Observatory status

Reports and publications

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Historic news

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

www.iram.es mainWiki: EmirforAstronomers (last edited 2016-07-14 08:27:05 by CarstenKramer)