Call for Observing Proposals for the 30m Telescope

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

What is new ?

Two wide band filter spectrometers built by IRAM-Granada are now available for observations with a few restrictions. Each of these spectrometers has 256 channels (channel spacing: 4 MHz; noise equivalent bandwidth: 6.2 MHz) and can be connected to any spectral line receiver that allows a bandwidth of 1GHz (i.e. to all but the A100 and B100 receivers). These two new 1 GHz banks together with our old $1024 \times 1$ MHz filterbank make observations of broad lines much more time efficient. The new banks are included in the web-based time estimator (version 2.2). Note that at the time we are writing these lines there is no automatic online data reduction for the 4MHz filterbanks: the raw data are written to a HP workstation and have to be calibrated off-line. For the basic observing modes (PSWITCH, WSWITCH, RASTER), this is done using macros in the CAL program. Note also that the new filterbanks cannot currently be used with on-the-fly observations.

The 37 channel bolometer array which was used last winter on the telescope with unprecedented sensitivity will be available again. Two bolometer sessions are planned, one before the end of this year and a second one early next year. Proposers are asked to clearly indicate on the proposal cover sheet which of the two sessions they prefer.

Since October 1999, the telescope is fully equipped with 8 new generation receivers which cover nearly all of the 2, 3 and 1.3 mm atmospheric windows. At each frequency two orthogonally linearly polarized receivers are available, and up to 4 receivers can be used simultaneously. The new receivers turned out to work well, with only a few qualifications. At the time of writing, dewar C is being exchanged with a laboratory spare. Although the installation is not yet complete, first tests have shown that the noise temperatures of the new receivers C150 and C270 are improved, and their optics fit well with the other receivers.

The new scheme of priority scheduling introduced last winter turned out to be largely successful. It will be continued this winter. The scheme applies to the highest rated proposals, up to a total of about 250 hours of telescope time. These proposals will be given a further chance if, because of weather or technical problems, their scientific goals were not obtained when scheduled first. Bolometer proposals which require excellent 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, heterodyne proposals at lower frequency or less demanding bolometer proposals will be observed whenever possible. Three remote observing stations which are operational now, support this more complex scheduling scheme.

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.

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

All proposals must reach the Secretariat before September 11th, 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.

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. 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

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 2.2, it includes the new 4 MHz filterbanks. Extensive on-line help is provided. Questions can be addressed to P. Hily-Blant (hilyblan@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 the MPIfR in Bonn, and from Grenoble. This observing mode is restricted to projects without particular technical demands and to experienced 30m users. The prospective remote observer should note ``remote observing from Grenoble or Granada or Bonn'' 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 (dmuders@mpifr-bonn.mpg.de) at MPIfR for a short introduction into the remote observing station. Remote observers in or near Grenoble should 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

Heterodyne Receivers

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 winter weather (4mm of water) at the center of the tuning range and at 45$^$ elevation. All new generation receivers are tuned 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 2000/01 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.
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
B100	H	1			4	81 - 115.5	60 - 85	>20	1.5	0.5	120
C150	V		2		4	129 - 183	80 - 100	15 - 25	4.0	1.0	200	3
D150	H		2	3		129 - 183	60 - 180	8 - 17	4.0	1.0	200
A230	V	1		3		197 - 266	100 - 200	12 - 17	4.0	1.0	450	1
B230	H	1			4	197 - 266	100 - 250	12 - 17	4.0	1.0	450	1
C270	V		2		4	241 - 281	130 - 300	10 - 20	4.0	1.0	1000	2,3
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.
3: noise temperatures are preliminary

General point about receiver operations

As receiver tuning is now considerably faster (typically 15 min for four receivers) 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 before the observations.

Polarimeter

A prototypal IF polarimeter is now available on a restricted basis. The instrument is designed for narrowband (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 sec1.html">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 later 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 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 a HPBW of 11'' and a sensitivity of $\simeq 30$ mJys^1/2. This figure applies under ``normal bolometric conditions'' (pwv 4mm and a stable atmosphere, i.e. no clouds, no turbulence). Often, such bolometric conditions are available only at night. The 37-pixel array was used extensively at the telescope last winter with good success. A second 37 channel array of comparable performance is 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 $\sim1.5$ 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 properly, even on times of several hours, and rms noise levels of under 0.3 mJy have been reached in particular cases.

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 map covers $4\times3$ arcmin and takes about 60 min of telescope time. Under normal bolometric conditions, an rms of $\sim3$ mJy is thus reached near the map center. Again somewhat better values may be obtained depending on weather and the effectiveness of skynoise suppression. 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 <1 mJy (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 (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 nearly a factor 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.

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). Ther are systematic differences between the foci of the various receivers: typically 0.1 mm, but reaching 0.3 mm in the worst case. The foci should be carefully monitored and, in the latter case, a compromise value be chosen. Not doing so may result in broadened and distorted beams ([1]).