Call for Observing Proposals on the 30m Telescope

Summary

The next deadline for the submission of observing proposals for the IRAM 30m telescope is September 5th, 2001 16:00h (MET). The scheduling period extends from Nov 15, 2001 to May 15, 2002, covering roughly the winter period at Pico Veleta. Proposals for three types of receivers will be considered for the coming winter semester:

1.

the new 9 pixel heterodyne receiver array, HERA, operating at 1.3 mm wavelength,

2.

a 1.2mm bolometer array with at least 37 pixels,

3.

the observatory's set of eight heterodyne receivers at wavelengths of 3, 2, 1.3, and 1.1 mm.

Roughly 2800 hours of observing time will be available, which should allow scheduling of a few longer programmes (of the order of 100 hours). Emphasis is on observations in the 1mm window.

What is new ?

The new 1.3mm HEterodyne Receiver Array, HERA, built by IRAM, is being commissioned in its intermediate configuration (only one polarization) during this summer. The results are so far very encouraging. The instrument has 9 pixels separated by 24'' and arranged in a center-filled square. Each pixel has a diffraction-limited (11'' at 230 GHz) and linearly polarized beam. HERA will be available for the coming winter semester with some restrictions (see below) in tuning, backend coverage, and observing modes.

Updates on the progress with HERA will be posted on the Grenoble 30m web page at URL http://iram.fr/PV/veleta.html. The time estimator available on the Granada web page at URL http://www.iram.es will be updated to include the basic observing modes of HERA.

The 37-pixel bolometer array MAMBO which was used during the two previous winter semesters with excellent sensitivity is made available again by the MPIfR. A new array consisting of 117 pixels will be tested in autumn. If its sensitivity is found to be comparable to MAMBO, the new array may be used throughout this winter. Time estimates should be based on the 37-pixel system (MAMBO-37). If the 117-pixel array (MAMBO-117) should become available, the time allocation for approved proposals may be revised.

Experimentation with new flexible observing schedules will continue this winter. A suitable mix of proposals with high and moderate demands on atmospheric quality may be scheduled in several pools of a few weeks duration. Although priority will be given to high frequency proposals in general terms, lower frequency weather tolerant proposals are encouraged, since these programmes have good chances to be scheduled as backups in such pools. IRAM will contact the principal investigators of accepted proposals which could be scheduled in this way.

Applications

Valid proposals consist of the official cover page, up to two pages of text describing the scientific aims, and up to two more pages of figures, tables, and references. The official cover page, in postscript or in LaTeX format, may be obtained by anonymous ftp from iram.fr in directory dist/proposal, as well as a Latex style file proposal.sty; or through the IRAM 30m web page at URL http://iram.fr/PV/veleta.html. In case of problems, contact the secretary, Cathy Berjaud (e-mail: berjaud@iram.fr). Do not use characters smaller than 11pt. This could render your proposal illegible when copied or faxed.

Proposals may be submitted in one of the three following ways:

• by the web-based electronic submission facility. Please consult the detailed instructions on the web. The facility will be opened three weeks before the deadline.
• by fax to number: (33/0) 476 42 54 69.
• by ordinary or express mail addressed to:
  IRAM Scientific Secretariat,
  300, rue de la Piscine,
  F-38406 St. Martin d'Hères, France (tel. +33-(0)476-824900)

We strongly encourage submission through the web-based facility. More than 75% of the proposals were sent in this way for the last deadline. Submission through fax will be discontinued in the future. Proposals sent in by E-mail are not accepted.

All proposals must reach the Secretariat before September 5th, 2001 16:00h (MET). The Principal Investigator will receive by return mail an acknowledgement of reception and a proposal number. To avoid the allocation of several numbers per proposal, send only one copy of your proposal.

Proposals containing grey scale plots should be submitted electronically to avoid deterioration of image quality in the copying. Color plots will be printed/copied in grey scale. If the proposers want their color plots to be passed on to the program committee, the entire proposal must be sent in by ordinary mail in 12 copies.

On the title page, you must fill in the line `special requirements' if you request either polarimetric observations, service or remote observing, or specific dates for time dependent observations. If there are periods when you cannot observe for personal reasons, please specify them here; beware, however, that such additional restrictions could make your observations difficult or impossible to schedule.

We insist upon receiving, with proposals for heterodyne receivers, a complete list of frequencies corrected for source redshift (to 0.1 GHz). Also specify on the cover sheet which receivers you plan to use.

In order to avoid useless duplication of observations and to protect already accepted proposals, we keep up a computerized list of targets. We ask you to fill out carefully your source list. This list must contain all the sources (and only those sources) for which you request observing time. To allow electronic scanning of your source parameters, your list must be typed or printed following the format indicated on the proposal form (no hand writing, please). If your source list is long (e.g. more than 15 sources) you may print it on a separate page keeping the same format.

The scientific aims of the proposed programme should be explained in 2 pages of text maximum, plus up to two pages of figures, tables, and references. Proposals should be self-explanatory, clearly state these aims, and explain the need of the 30m telescope. The amount of time requested should be carefully estimated and justified. It should include all overheads (see below).

A scientific project should not be artificially cut into several small projects, but should rather be submitted as one bigger project, even if this means 100-150 hours.

If time has already been given to a project but turned out to be insufficient, explain the reasons, e.g. indicate the amount of time lost due to bad weather or equipment failure; if the fraction of time lost is close to 100%, don't rewrite the proposal, except for an introductory paragraph. For continuation of proposals having led to publications, please give references to the latter.

In all cases, indicate on the first page whether your proposal is (or is not) the resubmission of a previously rejected proposal or the continuation of a previously accepted 30m telescope proposal. We strongly recommend to state very briefly in the introduction why the proposal is being resubmitted (e.g. improved scientific justification) or is proposed to be continued (e.g. last observations wiped out by bad weather).

Reminders

A handbook (``The 30m Manual'') collecting most of the information necessary to plan 30m telescope observations is available [10]. It has been updated recently, including now a description of the refurbished receiver cabin. The report entitled ``Calibration of spectral line data at the IRAM 30m telescope'' explains in detail the applied calibration procedure. Both documents can be retrieved through the IRAM web pages in Granada (http://www.iram.es) and Grenoble (http://iram.fr/PV/veleta.html). A catalog of well calibrated spectra for a range of sources and transitions (Mauersberger et al. [13]) is very useful for monitoring spectral line calibration.

The On-the-Fly observing mode (OTF) is available for heterodyne observations since more than two years. Considerable progress was achieved in making the control of the observations and the data reduction user friendly. Documentation is available on the Granada web page. Due to the complexity of the OTF observing mode we advise proposers without a demonstrated experience of this technique on the 30m telescope to contact, or involve in their proposal, an astronomer with such experience. Ute Lisenfeld of the Granada staff (ute@iram.es) serves as the principal contact in OTF matters.

Frequency switching is available for both HERA and the observatory's standard SIS receivers. This observing mode is interesting for projects not demanding very flat baselines. Certain limitations exist with respect to maximum frequency throw ($\le 45$ km/s), backends, phase times etc.; for details see [8]. Little experience exists however with HERA, but more tests are planned. Please check our web pages for news on this topic.

Finally, to help us keeping up a computerized source list, we ask you to fill in your `list of objects' as explained before.

Observing time estimates

This matter needs special attention as a serious time underestimate may be considered as a sure sign of sloppy proposal preparation. Observing time estimates must take into account:

• integration time on source and comparison field(s), including overheads for ON/OFF telescope motions, deadtime for device switching and data transfer.
• pointing, focus, continuum and/or line calibrations
• telescope slew motions
• receiver tunings (for heterodyne observations),

A technical report explaining how to estimate the telescope time needed to reach a given sensitivity level in various modes of observation was published in the January 1995 issue² of the IRAM Newsletter [9]. It has been included in the 30m telescope Manual [10].

In order to facilitate the rather complex calculation of observing time we strongly recommend the easy-to-use Time Estimator on our web pages. The tool gives sufficiently accurate estimates of the total observing time and handles the vast majority of both heterodyne and bolometer observing modes. Now in its version 2.4, it includes the new HERA receiver array. Extensive on-line help is provided. Questions can be addressed to P. Hily-Blant (hilyblan@iram.es) or to his successor, F. Damour (damour@iram.es). Proposers are asked to use this tool whenever applicable.

If very special observing modes are proposed which are not covered by the Time Estimator proposers must give sufficient technical details so their time estimate can be reproduced. In particular, the proposal must give values for $T_{\rm sys}$, spectral resolution, antenna temperature of the signal, the signal/noise ratio which is aimed for, all overheads and dead times, and the resulting observing time).

Proposers should base their time request on normal winter conditions, corresponding to 4mm of precipitable water vapor. Sometimes, conditions may be degraded due to anomalous refraction. Observing efficiency is then reduced and temperature calibration is more uncertain than the typical 10 percent. If exceptionally good transmission or stability of the atmosphere is requested which may be reachable only in near perfect winter conditions, the proposers must clearly say so in their time estimate paragraph. Such proposals will however be particularly scrutinized.

Service observing

To facilitate the execution of short ($\leq$8 h) programmes, we propose ``service observing'' for some easy to observe programmes with only one set of tunings. Observations are made by the local staff using precisely laid-out instructions by the principal investigator. For this type of observation, we request an acknowledgement of the IRAM staff member's help in the forthcoming publication. If you are interested by this mode of observing, specify it as a ``special requirement'' in the proposal form. IRAM will decide which proposals can actually go to that mode.

Remote observing

This observing mode where the remote observer actually controls the telescope very much like on Pico Veleta, is available from the downtown Granada office, from MPIfR in Bonn, from ENS in Paris (often restricted to nighttime hours), and from IRAM in Grenoble. This observing mode is available to projects without any particular technical demands and to experienced 30m users. The prospective remote observer should note ``remote observing'' as a special requirement in the proposal cover sheet.

After time has been awarded to a remote proposal, the P.I. is requested to give sufficient detail to the Station Manager (mauers@iram.es) on how the remote observer can be contacted. Please note that IRAM is not responsible for the remote stations in Paris or Bonn.

Remote observers affiliated with the MPIfR or other institutes near Bonn should contact F. Bertoldi (bertoldi@mpifr-bonn.mpg.de) or D. Muders (dmuders@mpifr-bonn.mpg.de) at MPIfR for a short introduction into the remote observing station. Remote observers in the Paris area may contact D. Teyssier (teyssier@lra.ens.fr) for arrangements. Remote observers in or near Grenoble contact C. Thum (thum@iram.fr) or H. Wiesemeyer (wiesemey@iram.fr) at IRAM. Observers visiting the 30m might opt to do some of their observing from Granada if it eases their travel constraints. In this case, a Granada astronomer should be contacted as soon as possible, arrangements on very short notice may not always be possible.

Technical Information about the 30m Telescope

This section gives all the technical details of observations with the 30m telescope that the average user will have to know. See also the concise summary of telescope characteristics published on the IRAM web pages.

HERA

The new HEterodyne Receiver Array is now available for the first time. The 9 pixels are arranged in the form of a center-filled square, and are separated by 24''. A derotator optical assembly keeps the 9 pixel pattern stationary on the sky. Each pixel has a diffraction limited (11'' at 230 GHz) and linearly polarized beam. Receiver characteristics are listed in Tab. 1.

Frequency tuning of HERA, although fully under remote control and automatic, is substantially more complicated than for the observatory's other SIS receivers. So far, only the following frequencies can be tuned:

$\rhd$

CO isotopes at 230.5, 220.4, and 219.6 GHz

$\rhd$

CS( $5\rightarrow 4$) at 244.9 GHz

$\rhd$

HCN( $3\rightarrow 2$) at 265.9 GHz

$\rhd$

HCO⁺( $3\rightarrow 2$) at 267.6 GHz

Proposals for HERA at other frequencies within its nominal tuning range of 210 - 276 GHz are nevertheless invited, but we cannot guarantee at this moment that these proposals can actually be done. Uninterrupted coverage of the nominal tuning range depends on additional hardware which is expected to become available sometime in the winter semester.

Owing to ongoing work on a significant expansion of the autocorrelator, we expect that the HERA user will have the following backend options next winter, all with the new extended autocorrelator: two independent subbands connectable to each pixel, where the subbands have channel spacings between 40 kHz and 1.25 MHz and corresponding bandwidths between 20 and 160 MHz. Thus a maximum nominal bandwidth of 320 MHz is available per pixel, but note that platformimg cannot be excluded in this configuration. Software for the extended correlator may still be somewhat experimental early in the winter semester.

In case we run into severe problems with the upgrading of the correlator, the following two well tested sets of backends can always be used with HERA: (i) 8 autocorrelator sections of 80 kHz channel spacing and 40 MHz bandwidth combined with the narrow filterbank (128 channels of 100 kHz resolution), and (ii) 8 AC sections of 1.25 MHz channel spacing and 160 MHz bandwidth combined with one section of the wide filter bank (256 channels of 1 MHz resolution).

HERA is now operational in two basic spectroscopic observing modes: (i) raster maps of areas typically not smaller than 1', in position, wobbler, or frequency switching modes, and (ii) simple on-the-fly maps of moderate size (typically 2' - 10'). Other observing modes are conceivable and/or under tests, but they may not be ready this winter. For details, please contact the project scientist, Karl Schuster (schuster@iram.fr), Helmut Wiesemeyer (wiesemey@iram.fr), or Pierre Hily-Blant (hilyblan@iram.es).

HERA proposers are invited to check the IRAM web page at Grenoble at URL http://iram.fr/PV/veleta.html for updated information on the progress of the commissioning work. In particular, HERA proposers should use the web-based time estimator (Granada web page at URL http://www.iram.es.

The Observatory Heterodyne Receivers

Eight SIS receivers are available at the telescope for the upcoming observing season. They are designated according to the dewar in which they are housed (A, B, C, or D), followed by the center frequency (in GHz) of their tuning range. Their main characteristics are summarised in Tab. 1. All receivers are linearly polarized with the E-vectors, before rotation in the Martin-Puplett interferometers, being either horizontal or vertical in the Nasmyth cabin. Up to four of the receivers can be combined for simultaneous observations in the four ways depicted in Tab. 1. Note that they cannot be combined with HERA. Also listed are typical system temperatures which apply to normal winter weather (4mm of water) at the center of the tuning range and at 45 elevation. All receivers are tuned by the operators from the control room. Experience shows that it normally takes about 15 min to tune four such receivers.

 

 

Table: Heterodyne receivers available for the winter 2001/02 observing season. Performance figures are based on recent measurements at the telescope. $T^{\ast }_{sys}$ is the SSB system temperature in the T$^\ast _A$ scale at the nominal center of the tuning range, assuming average winter conditions and 45 elevation. g_i is the rejection factor of the image side band. $\nu _{IF}$ and $\Delta \nu _{IF}$ are the IF center frequency and width. Note that the 8 standard receivers can be combined in 4 different ways, but HERA cannot be combined with any one of them.

receiver	polar-	combinations					tuning range	TRx(SSB)	gi	$\nu _{IF}$	$\Delta \nu _{IF}$	$T^{\ast }_{sys}$	remark
	ization	1	2	3	4	5	GHz	K	dB	GHz	GHz	K
A100	V	1		3			80 - 115.5	45 - 65	>20	1.5	0.5	120
B100	H	1			4		81 - 115.5	60 - 85	>20	1.5	0.5	130
C150	V		2		4		129 - 183	70 - 115	15 - 25	4.0	1.0	200
D150	H		2	3			129 - 183	60 - 150	8 - 17	4.0	1.0	200
A230	V	1		3			197 - 266	85 - 185	12 - 17	4.0	1.0	420	1
B230	H	1			4		197 - 266	95 - 160	12 - 17	4.0	1.0	420	1
C270	V		2		4		241 - 281	125 - 290	10 - 20	4.0	1.0	900	2
D270	H		2	3			241 - 281	130 - 300	9 - 13	4.0	1.0	900	2
HERA	H					5	210 - 276	110 - 380	$\sim 10$	4.0	1.0	400	1, 3

1: noise increasing with frequency.
2: performance at $\nu<275$ GHz; noisier above 275 GHz.
3: so far only 10 frequencies available, see text.

General point about receiver operations

As receiver tuning is now considerably faster and more reproducible than before, we do not normally require anymore that observers send a list of frequencies to Granada before their observations. Only in case that a frequency is close to a limit of the tuning range or is otherwise peculiar, we still recommend to check with a Granada receiver engineer at least two weeks before the observations.

Polarimeter

An IF polarimeter is available for observations of compact sources. The instrument is designed for narrowband (40 MHz) line and continuum polarimetry. It takes the IF signals from two orthogonally polarized receivers as input and it generates 4 signals from which spectra of all four Stokes parameters can be derived. The tests made so far at 3 and 1.3 mm have demonstrated that the drift of the relative phase between the two receivers is often very small and always calibratable. Data reduction software using CLASS enhanced with a graphical user interface is now available. Please contact H. Wiesemeyer (wiesemey@iram.fr). A preliminary description of the instrument is available sec1.html">on the web at URL http://iram.fr/$\tilde{}$thum.html. Polarimetry proposals are invited with the restriction that the target sources be not larger than the main beam.

The RF polarimeter based on switching a quarter wave plate is still available. Interested observers please contact IRAM (preferentially B. Lazareff or C. Thum) to discuss what might actually be possible this winter.

MPIfR Bolometer arrays

The 37-pixel MAMBO array consists of 3 concentric hexagonal rings of horns centered on the central horn. The spacing between horns is $\simeq 20''$. Each pixel has a HPBW of 11'' and a sensitivity of $\simeq 30$ mJys^1/2. This figure applies for ``normal bolometric conditions'' (pwv 4mm and a stable atmosphere, i.e. no clouds, little turbulence, high elevation, application of skynoise reduction alogrithms). Often, such bolometric conditions are only found between sunset and noon.

The 37-pixel array was used extensively at the telescope last winter with good success. A second 37 pixel array of comparable performance or a new 117 pixel array will be available as backup. Further tests of the 117-pixel array are planned this autumn. If successful, the new big array may be used throughout this winter, making mapping observations of large areas more efficient. Proposers should however base their time request on MAMBO-37. If MAMBO-117 should indeed become available, the program committee may suggest to adjust accordingly the time allocation of mapping proposals.

The arrays are mostly used in two basic observing modes, ON/OFF and mapping.³ Experience of last winter shows that the ON/OFF reaches typically an rms noise of $\sim1.5$ mJy in 10 min of total observing time (about 200 sec of on-source integration time) under normal bolometric conditions. Up to 30 percent lower noise may be obtained in perfect weather. In this observing mode, the noise integrates down with time as $t^{\frac{1}{2}}$ to rms noise levels below 0.3 mJy.

In the mapping mode the telescope is scanned in azimuth, the direction of the wobbler throw, in such a way that all pixels cover the source. A typical single map covering $4\times3$ arcmin with a scan speed of 4''/sec and a raster step of 4'' in elevation takes about 60 min of telescope time. Under normal bolometric conditions and assuming effective skynoise suppression, an rms of 2 - 4 mJy is thus reached in the inner $2'\times 1'$. Maps may be co-added to reach lower noise levels. Mosaicing is also possible to map larger areas. Attempts to reach map noise levels below 1 mJy are still fraught with poorly understood problems and require sophisticated data reduction. If such observations are proposed, the proposers must indicate how they plan to reach this demanding goal.

Another note of caution: mapping of extended sources cannot rely on the sky-noise reduction algorithm (simple subtraction of correlated sky-noise) presently available, and the noise level reached may be at least twice as high as that quoted above.

Bolometer time requests should be based on normal winter conditions, like requests using SIS receivers. If exceptionally low noise levels are requested which may be reachable only in a perfectly stable winter atmosphere, the proposers must clearly say so in their time estimate paragraph. Such proposals will however be particularly scrutinized.

The bolometers are used with the wobbling (typically at a rate of 2 Hz in azimuth) secondary mirror. The orientation of the beams on the sky changes with hour angle due to parallactic and Nasmyth rotation, as the array is fixed in Nasmyth coordinates. Special software is made available at the telescope for data reduction (NIC [11] and MOPSI). Time estimators for planning ON/OFF or mapping observations are also available [11,17].

Efficiencies and error beam

Extensive work during the last years in measuring and setting the telescope surface has resulted in significantly improved aperture and beam efficiencies which have increased by nearly a factor of 2 at the highest frequencies accessible to the telescope. The current numbers are shown in Table 2.

At 1.3 mm (and a fortiori at shorter wavelengths) a large fraction of the power pattern is distributed in an error beam which can be approximated by two Gaussians of FWHP $\simeq 170''$and 800'' (see [16,1] for details). Astronomers should take into account this error beam when converting antenna temperatures into brightness temperatures.

The aperture efficiency depends somewhat on the elevation, particularly at shorter wavelengths. This gain/elevation effect is evaluated in [15].

 

Table: Forward and main beam efficiencies, $\eta_F$ and $\eta_{mb}$, and beam width at half-power, $\theta_b$.

frequency [GHz]	$\theta_b$ ['']$\,^1)$	$\eta_F$	$\eta_{mb}\,^2)$
86	29	0.95	0.80
110	22	0.95	0.80
145	17	0.93	0.65
170	14.5	0.91	0.66
210	12	0.90	0.54
235	10.5	0.91	0.50
260	9.5	0.88	0.51
279	9	0.86	0.46

¹) fit to all data: $\theta_b$ [''] = 2460 / frequency [GHz]
²) measured with receivers B and C. Values from receivers A are less than 3 percent different, values from receivers D not available
 

Backends

The observatory provides 4 types of spectral line backends which can be individually connected to any receiver.

• The 1 MHz filterbank, consisting of 4 units with 256 MHz each. The units can be connected to different or the same receivers giving bandwidths between 256 MHz and 1024 MHz. The maximum bandwidth of 1 GHz is available for only one receiver, naturally one having a 1 GHz wide IF bandwidth. Connection of the filterbank in 1 GHz mode presently excludes the use of any other backend with the same receiver.

  Other configurations of the 1 MHz filterbank include a setup in 2 units of 512 MHz connected to two different receivers, or 4 units of 256 MHz width connected to up to four (not necessarily) different receivers. Each unit can be shifted in steps of 32 MHz relative to the center frequency of the connected receiver.

• The 100 kHz filterbank, consisting of 256 channels of 100 kHz. It can be split into two halves, each movable inside the 500 MHz IF bandwidth, and connectable to two different receivers.

• The autocorrelator backend with up to 2048 channels. Available nominal resolutions are 10, 20, 40, 80, 320 and 1250 kHz. Nominal bandwidths range from 20 MHz to $2\times 512$ MHz, depending on resolution. The correlator can be split into 8 independent subbands, each of which can be configured individually, shifted inside a 500 MHz IF band, and connected to the same or different receivers. For the larger bandwidths (i.e. more than one subband of 80 MHz) there is often a problem of platforming, i.e. baselines from the different subbands have slightly different power levels.

• The new 4 MHz filterbank built by IRAM Granada is now available with a few restrictions. The new spectrometer consists two units, each with 256 channels (spacing of 4 MHz, spectral resolution 6.2 MHz) covering a total bandwidth of 1 GHz. Each unit can be connected to any spectral line receiver with a bandwidth of 1 GHz (i.e. to all but the A100 and B100 receivers). At the present time, a 4 MHz filterbank cannot be used with the autocorrelator or the 100 kHz filterbank on the same receiver.

  There is still no automatic online data reduction for the 4MHz filterbanks. The raw data from these backends are written to a HP workstation and have to be calibrated off-line. For the basic observing modes (PSWITCH, WSWITCH, RASTER) we have prepared macros in the CAL program to do this job. Frequency switching and On-The-Fly are not possible with these low resolution backends.

Pointing / Focusing

Pointing sessions are normally scheduled twice per week; at present, the fitted pointing parameters yield an absolute rms pointing accuracy of better than 3'' [14]. Receivers are closely aligned (within <2''. Checking the pointing, focus, and receiver alignment is the responsibility of the observers (use a planet for alignment checks). Systematic (up to 0.4 mm) differences between the foci of various receivers were noted in the past and may well persist, even with the new generation receivers. In such a case the foci should be carefully monitored and a compromise value be chosen. Not doing so may result in broadened and distorted beams ([1]).

Wobbling Secondary

• Beam-throw is $\le 240\hbox{$^{\prime\prime}$ }$ depending on wobbling frequency. At 2 Hz, the maximum throw is $90\hbox{$^{\prime\prime}$ }$.
• Standard phase duration: 2 sec for spectral line observations, 0.25 sec for continuum observations.