Call for Observing Proposals on the 30m Telescope

Summary

The next deadline for the submission of observing proposals for the IRAM 30m telescope is March 2nd, 2000 18:00h (MET). The scheduling period extends from May 15, 2000 to Nov 15, 2000, covering roughly the summer period at Pico Veleta. Proposals will be considered for the observatory's standard heterodyne receivers at wavelengths of 3, 2 and 1.3 mm. Emphasis will be put on proposals for 3 and 2 mm. Proposals for bolometers or other special receivers will only be accepted in a few well justified cases.

Roughly 3000 hours of observing time will be available, which should allow scheduling of a few longer programmes (up to $\sim 150$ hours).

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

What is new ?

The telescope is now fully equipped with 8 new generation receivers which are housed in 4 dewars designated A, B, C, and D. Each of them contains a ``low frequency'' and a ``high frequency'' receiver, and together they cover nearly all of the 2, 3 and 1.3 mm atmospheric windows. At each frequency two orthogonally linearly polarized receivers are available. Up to 4 receivers can be used simultaneously. The 4 different ways of combining them are listed in Tab. 1 together with their technical characteristics.

A new filter spectrometer built by IRAM Granada is approaching completion. The new spectrometer has 512 filters of 4 MHz width. They are configured as $2\times1$ GHz for use with a pair of receivers of 1 GHz instantaneous bandwidth each. The new spectrometer is expected to be available for the summer scheduling period. It will make low spectral resolution observations more efficient, since 4 receivers can then be connected simultaneously to four broadband filter spectrometers.

For the last deadline, more than two thirds of the 30m proposals were submitted electronically. We strongly encourage proposers to use this medium (except for proposals with color plots; see below) rather than ordinary mail or fax which we tend to discontinue in the future.

The proposers for the last deadline made even heavier use (>90 percent of the proposals) of the web based observing time estimator. This tool is now available in its version 2.1 which now contains realistic parameters for all receivers as they were measured recently at the telescope. In view of the good quality of the time estimates obtained with this tool, we strongly recommend its use whenever possible.

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 L^ATEXformat, 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, which could make 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 (preferred). 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

Please note that proposals submitted electronically by means other than our web-based facility (e.g. ordinary E-mail) will not be accepted.

All proposals must reach the Secretariat before March 2nd, 2000 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 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 programme committee, the entire proposal must be sent in by ordinary mail in 12 copies.

On the title page, you must fill out 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 the 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 designing the control of the observations and the data reduction more 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.

Observing time estimates

This matter needs special attention as a serious time underestimate may be considered as a 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 issue¹ 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. Now in its version 2.1, the tool gives sufficiently accurate estimates of the total observing time required. The tool handles the vast majority of both heterodyne and bolometer observing modes. 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, expected antenna temperature of the source 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 summer conditions, corresponding to 7mm of precipitable water vapor. Conditions during summer afternoons may be degraded due to anomalous refraction. The observing efficiency is then reduced and the 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 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 (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

 

Table: Heterodyne receivers expected to be available for the summer 2000 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 summer 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	1		3		80 - 115.5	45 - 65	>20	1.5	0.5	150
B100	H	1			4	81 - 115.5	60 - 85	>20	1.5	0.5	160
C150	V		2		4	129 - 183	60 - 150	12 - 24	4.0	1.0	370
D150	H		2	3		129 - 183	75 - 180	8 - 17	4.0	1.0	370
A230	V	1		3		197 - 266	100 - 200	12 - 17	4.0	1.0	700	1
B230	H	1			4	197 - 266	100 - 250	12 - 17	4.0	1.0	700	1
C270	V		2		4	241 - 281	180 - 400	10 - 15	4.0	1.0	1000	2
D270	H		2	3		241 - 281	140 - 260	9 - 13	4.0	1.0	1000	2

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

Eight new generation 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. Also listed are typical system temperatures which apply to normal summer weather (7mm of water) at the center of the tuning range and 45 elevation. All new generation receivers are tuned entirely from the control room. Experience shows that it normally takes about 15 min to tune four such receivers.

General point about receiver operations

We recommend that observers send a list of their frequencies to Granada in time, in particular if frequencies near the edges of the tuning range are requested. 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 which had started tests last summer is now available on a restricted basis. The instrument is designed for narrow-band (40 MHz) line and continuum polarimetry. It needs 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 have demonstrated the viability of the concept for 3mm point sources. In particular, drift of the relative phase between the two receivers was found to be sufficiently slow so that it can be calibrated. A preliminary description of the instrument is available on the web at URL http://iram.fr/$\tilde{}$thum.html.

Polarimetry proposals are invited with the following restrictions: (i) the target sources should not be larger than the main beam and (ii) the observing frequency should be in the 3mm tuning range. A few higher frequency proposals may also be accepted on a shared risk basis. They may be observed if the 2 and 1.3mm tests planned this summer are successful.

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 summer.

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 nearly by a factor 2 at the highest frequencies accessible to the telescope (see report by D. Morris elsewhere in this Newsletter). 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 $\theta_b$.

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

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 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.

• Should the new 4 MHz filterbank become available during the coming summer semester it could be used, but observing time estimates should not be done on this assumption.

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 $\le 240''$ 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.