Call for proposals on the 30-m telescope

Summary

The next deadline for the submission of observing proposals for the IRAM 30m telescope is Sept 10 th, 1999 18:00h (MET). The scheduling period extends from Nov. 15th, 1999 to May 15, 2000, covering roughly the winter period at Pico Veleta. Two types of proposals will be considered:

1.

proposals using the observatory's heterodyne receivers at wavelengths of 3, 2 and 1.3 mm.

2.

proposals using a 1.3mm bolometer array with 37 channels.

Roughly 2800 hours of observing time will be available, which should allow scheduling of a few longer programmes (of the order of 100 hours), with emphasis on 1.3 mm observations.

The main news, proposal formalities, details of the various receivers, and observing modes are described below.

What is new ?

Following the successful refurbishment of the receiver cabin last autumn (new optics; four new generation SIS receivers in dewars A and B) two more such dual frequency dewars will be installed this October. Each of these dewars, C and D, contains two mixers: one covering the 2mm window and one for the higher frequency part of the 1.3mm window (246 to 293 GHz). The 4 new receivers, designated C150, C270, D150, and D270 can be used together simultaneously, or either C or D can be combined with the A or B receivers. Tab. 1 describes the four possible combinations. Note that the new generation C270 and D270 receivers are expected to make the 30m telescope the most sensitive instrument operating in the high frequency part of the 1.3mm atmospheric window.

The 37 channel bolometer array which was used last winter on the telescope with unprecedented sensitivity will be available again. Two 37 ch. bolometer sessions are planned, one before the end of this year (Session I) and a second one early next year (Session II). Proposers are asked to clearly indicate on the cover page (section ``Special Requirements'') which of the two sessions they prefer.

In an effort to improve the chances to successfully observe the scientifically most interesting proposals we plan to introduce a new scheme of priority scheduling. The highest rated proposals, up to a total of about 250 hours of telescope time, will be included in this scheme. These proposals will be given a further chance, if their scientific goals were not obtained when scheduled first. Bolometer proposals which require perfect weather may also profit from the priority scheme if they are rated sufficiently high. If the weather is not good enough when the priority proposals are scheduled, backup proposals depending less critically on weather will be observed whenever possible. We strongly encourage investigators whose programs require very good weather conditions to submit their own backup programs. Those must be presented on separate forms as independant proposals and will be rated as such by the Program Committee.

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, please contact the secretary, Cathy Berjaud (e-mail: berjaud@iram.fr). Do not use characters smaller than 11pt, which could make your proposal illegible when copied or faxed.

Proposals may be submitted in one of the 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 mail addressed to:
  IRAM Scientific Secretariat,
  300, rue de la piscine,
  F-38406 St. Martin d'Hères, France

All proposals must reach the Secretariat before Sept 10 th, 1999 18:00h (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, either electronically, by ordinary mail, or by fax. Proposals sent in by E-mail are not accepted.

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 send in by ordinary mail in 12 copies.

On the title page, you must fill out the line ``special requirements'' if you request either spectral line on-the-fly observations, or the polarimeter, 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 the scientific 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 one 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. In case of a resubmission, state very briefly in the introduction why the proposal is being resubmitted (e.g. improved scientific justification).

Reminders

A handbook (``The 30m Manual'') collecting most of the information necessary to plan 30-m 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. [12]) 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 made 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. It used to yield satisfactory baselines within certain limitations (maximum frequency throw of 45 km/s, backends, phase times etc.; for details see [8]). Little experience exists however with the new generation receivers, but more tests are planned.

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

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 issue¹ of the IRAM Newsletter [9]. It has been included in the 30-m telescope Manual [10].

Many proposals still underestimate the time needed to carry out their programme, even under excellent weather conditions. We ask you to pay special attention to this matter as a serious time underestimate may be considered as a sure sign of sloppy proposal preparation.

To circumvent such problems we strongly recommend the easy-to-use Time Estimator on our web pages. Now in its version 2, the tool gives sufficiently accurate estimates of the total observing time required. The tool now handles the vast majority of both heterodyne and bolometer observing modes (see the description by D. Teyssier in this Newsletter). 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 $T_{\rm sys}, \Delta T_{MB}, B,$ total integration time, overheads and dead times.

Proposers should base their time request on normal winter conditions, corresponding to 4mm of precipitable water vapor. If exceptionally good transmission or stability of the atmosphere is requested which may be reachable only in perfect winter weather, the proposers must clearly say so in their time estimate paragraph. Such proposals will however be particularly scrutinized, as they may have to be scheduled in our new priority scheme (see above), for which only a small fraction of winter time will be reserved.

Service observing

To facilitate the execution of short ($\leq$8 h) programmes, we propose ``service observing'' for some easy to observe (e.g. short, single source) 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 and from Grenoble. The prospective remote observer receives a quick introduction into the peculiarities of this observing mode, but full time support like on the telescope is not available. Therefore this observing mode is restricted to projects without particular technical demands and to experienced 30m users.

Observers visiting the 30m might opt to do some of their observing from Granada if it eases their travel. In this case, a Granada astronomer should be contacted as soon as possible. If remote observing is planned from Grenoble the proposers are asked to check the corresponding entry in the proposal cover sheet.

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.

Heterodyne Receivers

Eight new generation receivers are expected to be 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. Also listed are typical system temperatures which apply to normal winter weather (4mm of water) at the center of the tuning rangeand 45 elevation. All new generation receivers are tuned entirely from the control room. Experience with the receivers A and B suggests that it takes about 15 min to tune four such receivers. Note however that no experience in operating receivers C and D exists at the time of writing.

 

 

Table: Heterodyne receivers expected to be available for the winter 1999/2000 observing season. Performance figures for dewars C and D are based on laboratory measurements. $T^{\ast }_{sys}$ 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.

receiver	polar-	combinations				tuning range	TRx(SSB)	gi	$\nu _{IF}$	$\Delta \nu _{IF}$	$T^{\ast }_{sys}$	remark
	ization	1	2	3	4	GHz	K	dB	GHz	GHz	K
A100	V	$\ast$		$\ast$		83.5 - 115.5	45 - 55	>20	1.5	0.5	120
B100	H	$\ast$			$\ast$	83.5 - 115.5	45 - 55	>20	1.5	0.5	120
C150	V		$\ast$		$\ast$	129 - 179	75	14	4.0	1.0	290
D150	H		$\ast$	$\ast$		139 - 184	75	14	4.0	1.0	290
A230	V	$\ast$		$\ast$		200 - 255	90 - 240	>10	4.0	1.0	330	1
B230	H	$\ast$			$\ast$	200 - 255	80 - 240	>10	4.0	1.0	330	1
C270	V		$\ast$		$\ast$	246 - 293	80 - 130	$\sim12$	4.0	1.0	570	2
D270	H		$\ast$	$\ast$		246 - 293	80 - 130	$\sim12$	4.0	1.0	570	2

1: noise increasing with frequency
2: performance at $\nu<275$ GHz; noisier above 275 GHz.

General point about receiver operations

In view of the little experience accumulated with the many new receivers, we recommend that observers restrict their list of frequencies as much as possible and that they send it early to Granada. For late arrivals (less than 2 weeks in advance), or a large number of frequencies, there is no guarantee for a prior test of the requested tunings.

Polarimeter

A new prototype IF polarimeter has started tests this summer. The instrument is designed for narrowband (40 MHz) line and continuum polarimetry of all Stokes parameters. First tests have demonstrated the viability of the concept for 3mm point sources. Further tests are scheduled.

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

MPIfR Bolometer array

The 37-pixel array consists of 3 concentric hexagonal rings of horns centered on the central horn. Spacing between horns is $\simeq 20''$. Each channel has a sensitivity of $\simeq 40$ mJys^1/2 under normal winter conditions (corresponding to 4mm pwv) and a HPBW of 11''. The 37-pixel array was used extensively at the telescope last winter with good success. A few improvements are planned, like the repair of a few bad channels and a better rejection of interference. A second 37 channel array of comparable performance or one 19 channel array are available as backup.

The arrays are mostly used in two basic observing modes, ON/OFF and mapping.² Experience of last winter shows that the ON/OFF reaches typically an rms noise of $\sim3$ mJy in 10 min of total observing time (about 200 sec of on source integration time) under normal winter conditions. Up to 30 percent lower noise may be obtained in perfect weather. In this observing mode, the noise integrates down properly, even over several hours.

In the mapping mode the telescope is scanned in azimuth in such a way that all pixels cover the source and fully sample the beam. A typical such map covers $4\times3$ arcmin and takes about 60 min of telescope time. In normal winter conditions, a rms of $\sim4$ mJy is thus reached. Again somewhat better values may be obtained in perfect weather. However, attempts to reach significantly lower noise by averaging several maps are fraught with poorly understood problems. Proposers who aim for a rms noise of 2 mJy or less (in mapping mode) are therefore asked to indicate how they plan to reach their demanding goal.

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, as they may have to be scheduled in our new priority scheme (see above), for which only a small fraction of winter time will be reserved.

The bolometers are used with the wobbling secondary mirror (typically at a rate of 2 Hz in azimuth) . 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 [11,16].

Efficiencies and error beam

The telescope efficiencies (main beam and aperture efficiency) are given in Appendix A of ``The 30m Manual''. A one-page summary of the telescope system is on the web (http://www.iram.es/Telescope/systsumm.ps).

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 [15,1] 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 [14].

Backends

There are 3 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 connected to up to four 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.

Pointing / Focusing

Pointing sessions are made every one to two weeks; at present, the fitted pointing parameters yield an absolute rms pointing accuracy of better than 3'' [13]. We also try to keep the receivers as closely aligned as possible (to about 2'', however, alignment can be lost occasionally). 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 $\le 240''$ depending on wobbling frequency. At 2 Hz, the maximum throw is 90''
• Standard phase duration: 2 sec for spectral line observations, 0.25 sec for continuum observations.