Call for Observing Proposals on the 30m Telescope

Emphasis will be put on observations at the longer wavelengths (3 amd 2 mm). In total, about 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 correlator upgrade project, VESPA (VErsatile SPectrometer Assembly), is rapidly approaching completion. VESPA is expected to replace the present autocorrelator well before the beginning of the summer scheduling period. VESPA integrates into a new design components of the old 30m and interferometer correlators with the result that the number of available correlator channels is at least tripled. When connected to the backend distribution box VESPA provides up to 12000 spectral channels (typically 3000 per receiver). When connected to HERA, 18000 channels can be used (nominally 2000 per pixel). Spectral resolutions range from currently 10 kHz to 1.25 MHz. Bandwidths are in the range from 20 to 512 MHz.

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, which could make your proposal illegible when copied or faxed.

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 in 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]. 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. 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 a staff astronomer, e.g. Hans Ungerechts (ungerechts@iram.es) or Albrecht Sievers (siever@iram.es).

Frequency switching is available. It yields acceptable baselines only for sources with very narrow lines (2 km/s or less) within certain limitations (maximum frequency throw of 45 km/s, backends, phase times etc.; for details see [8]).

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:

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. 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 4 MHz filterbanks and the multibeam array HERA. Extensive on-line help is provided. Questions can be addressed to Frederic 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 summer conditions, corresponding to 7mm of precipitable water vapor. Conditions during summer afternoons 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 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. This observing mode is well suited for projects without strong demand on weather quality (backup projects). 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 IRAM Grenoble and, with restrictions, from the Radioastronomy Lab at the ENS in Paris. This observing mode is limited to projects without particular technical demands and to experienced 30m users. The prospective remote observer should note ``remote observing from Grenoble, Granada, Bonn or Paris '' as a special requirement in the proposal cover sheet.

Remote observers affiliated with the MPIfR or other institutes near Bonn should contact F. Bertoldi (bertoldi@mpifr-bonn.mpg.de) or D. Muders (muders@mpifr-bonn.mpg.de) at MPIfR for a short introduction into the remote observing station. Remote observers from Paris should contact David Teyssier (teyssier@lra.ens.fr). The Bonn and Paris stations are not maintained by IRAM. It is therefore the responsibility of the observer to ensure with their local contact that the stations are tested sufficiently in advance, and they have access to the respective offices.

We recommend that remote observers leave their private and/or mobile phone numbers to the operator at Pico Veleta and prepare the catalogs in advance so that in the unlikely case of a failure, the observations can be performed by the astronomer on duty or the operator.

Remote observers in or near Grenoble contact C. Thum or H. Wiesemeyer 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.

Technical Information about the 30m Telescope

HERA

A so far limited list of popular frequencies is available under automatic tuning. With the recent advent of a new LO injection and SSB measurement unit any frequency within HERA's nominal tuning range of 210 - 276 GHz can now be tuned and SSB calibrated.

A significant expansion of the autocorrelator is in progress (see the paragraph on VESPA in the backend section below) which is expected to vastly improve the backend options available with HERA, for both extragalactic and galactic applications. VESPA provides 18000 spectral channels when connected to HERA, i.e. nominally 2000 channels per pixel. Spectral resolutions of 20, 40, 80, 320, and 1250 kHz are available.

HERA is now operational in two basic spectroscopic observing modes: (i) raster maps, typically fully sampled, of areas not smaller than 1' in position, wobbler, or frequency switching modes, and (ii) simple on-the-fly maps of moderate size (typically 3' - 30'). Other observing modes are conceivable and/or under tests, but they may not yet be ready. For details, please contact the project scientist, Karl Schuster (schuster@iram.fr), or Helmut Wiesemeyer (wiesemey@iram.fr).

As HERA commissioning is not yet completed, proposers are invited to check the 30m 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.

Heterodyne Receivers

Eight SIS receivers are available, covering virtually all of the frequency range from 80 to 281 GHz accessible with the 30m telescope. These single-beam receivers 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 heterodyne receivers are tuned entirely from the control room. Experience shows that it normally takes about 15 min to tune four such receivers.

**Table:** Heterodyne receivers available for the summer 2002 observing semester. 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 (pwv = 7mm) 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	T_Rx(SSB)	g_i	$\nu _{IF}$	$\Delta \nu _{IF}$	$T^{\ast }_{sys}$	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	120	4
B100	H	1			4	81 - 115.5	60 - 85	>20	1.5	0.5	120
C150	V		2		4	129 - 183	70 - 115	15 - 25	4.0	1.0	200	3
D150	H		2	3		129 - 183	65 - 150	8 - 17	4.0	1.0	200
A230	V	1		3		197 - 266	85 - 185	12 - 17	4.0	1.0	450	1, 4
B230	H	1			4	197 - 266	95 - 160	12 - 17	4.0	1.0	450	1
C270	V		2		4	241 - 281	125 - 290	10 - 20	4.0	1.0	1000	2, 3
D270	H		2	3		241 - 281	130 - 300	9 - 13	4.0	1.0	1000	2

1: noise increasing with frequency
2: performance at $\nu<275$ GHz; noisier above 275 GHz.
3: noise temperatures are preliminary
4: these receivers will be replaced in March 2002 by new modules of very similar performance.

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

The IF polarimeter is available. The instrument is designed for narrowband (40 MHz) line and continuum polarimetry in the 3, 2 and 1.3 mm atmospheric windows. It needs two orthogonally polarized receivers as input and it generates 4 signals from which spectra of all four Stokes parameters can be derived. A preliminary description of the instrument which includes a sensitivity estimate, is available on the web at URL http://iram.fr/~thum.html.

Polarimetry observations of extended sources need to take into account the polarization of the beam pattern which is presently known only at 3mm. Interested observers are invited to contact Helmut Wiesemeyer or Clemens Thum.

The RF polarimeter based on switching a quarter wave plate is still available. Interested observers please contact B. Lazareff) to discuss what might actually be possible this summer.

MPIfR Bolometer array

Two bolometers arrays were used and tested last winter, the ``old'' 37 pixel array MAMBO and the new 117 pixel array MAMBO-2. Both arrays have nearly equivalent point source sensitivity and beam sizes (HPBW of 11''). One of these arrays, possibly MAMBO, will be made available again for some period during the summer semester. During some additional time, the bolometer may be kept on standby for target-of-opportunity and other urgent projects.

In view of the less transparent and often considerably less stable atmosphere during summer, bolometer proposals should concentrate on observations requiring an rms noise not below 1 mJy. We also recommend to avoid sources which are visible only during daytime during the bolometer session, currently planned in October.

The arrays are mostly used in two basic observing modes, ON/OFF and mapping ². We expect that the ON/OFF typically reaches an rms noise of $\sim 3$ mJy in 10 min of total observing time (about 200 sec of on source integration time) under ``normal summer conditions'' (pwv 7mm and a stable atmosphere, i.e. no clouds, no turbulence). This corresponds to a nominal sensitivity of $\simeq 45\rm mJy/\sqrt{Hz}$ . It requires that skynoise can be subtracted, which is efficiently possible only for compact (<20'') sources. For mapping more extended sources, where skynoise cannot be easily removed, the noise is twice as high, and, hence, the integration time must be quadrupled to reach the same signal-to-noise ratio. Please consult the Time Estimator on the Observatory's web page.

The minimum useful integration time per position should be 10 minutes plus an overhead of 10 minutes.

If noise levels below 1mJy are requested which may be reachable only in exceptionally stable weather, 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[12]). 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 nearly a factor 2 at the highest frequencies accessible to the telescope (see note by U. Lisenfeld and A. Sievers, Newsletter No. 47, Feb. 2001). 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].

Backends

The following four spectral line backends are available which can be individually connected to any receiver.

The 1 MHz filterbank consists of 4 units. Each unit has 256 channels with 1 MHz spacing and can be connected to different or the same receivers giving bandwidths between 256 MHz and 1024 MHz. The maximum bandwidth 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 consists of 256 channels of 100 kHz spacing. It can be split into two halves, each movable inside the 500 MHz if bandwidth, and connectable to two different receivers.

The 4 MHz filterbank currently consists of 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 simultaneously with the autocorrelator or the 100 kHz filterbank on the same receiver.

The raw data from these filterbanks are written to a Linux workstation. An off-line calibration macro is available for the basic observing modes (PSWITCH, WSWITCH, RASTER), but automatic calibration is being prepared. Frequency switching is not possible with these low resolution backends.

The upgraded correlator VESPA, the new (VErsatile SPectrometer Assembly) is rapidly approaching completion. It is expected to replace the present autocorrelator well before the beginning of the summer scheduling period. Connected to a set of 4 receivers it provides up to 12000 spectral channels. Nominal spectral resolutions range from currently 10 kHz to 1.25 MHz. Nominal bandwidths are in the range 20 -- 512 MHz. When VESPA is connected to HERA, up to 18000 spectral channels can be used. The many configurations available in both connection modes are best visualised on a demonstration program which can be downloaded from the 30m web page at Grenoble at URL http://iram.fr/PV/veleta.html.

**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	0.78
110	22	0.95	0.75
145	17	0.93	0.69
170	14.5	0.93	0.65
210	12	0.91	0.57
235	10.5	0.91	0.51
260	9.5	0.88	0.46
279	9	0.88	0.42

¹) fit to all data: $\theta_b$ [''] = 2460 / frequency [GHz]
²) based on a fit of recently measured data to the Ruze formula: $\eta_{\rm F}=1.2\epsilon \exp(-(4\pi R \sigma /\lambda)^2)$
with $\epsilon=0.69$ and $R\sigma=0.07$

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 sometimes 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]).