Call for Observing Proposals on the 30m Telescope

Emphasis will be put on observations at the longer wavelengths (3 and 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 full complement of low resolution (4 MHz) filterbanks, 9 units in total, is now at the telescope. Each of these units covers 1 GHz with 256 spectral channels. The nine units can be connected to HERA. A subset of 4 units can be connected to single pixel SIS receivers. The new filterbanks undergo extensive testing during January/February. Equipped with this spectrometer HERA will make 1.3mm mapping of broadband line sources very efficient.

HERA will be upgraded into a dual polarization array later this year. This probably means that the instrument will not be available in the second half of the summer semester. Accepted proposals will therefore likely be scheduled during spring.

VESPA is now nearly fully operational in its many modes and configurations. The basic, parallel, multi-beam, and high resolution modes have already been heavily used. Only the polarimetry mode needs some more work, but it is expected to be also available in summer.

After the upgrades last summer MAMBO-2, the 117 pixel bolometer array, is now as sensitive as the older 37 pixel MAMBO-1. Both bolometers are provided by the MPIfR for the summer semester, although successful bolometer proposals will be scheduled in only one or two sessions.

Applications

On the official cover page, please fill in the line `special requirements' if you request either polarimetric observations, service or remote observing. If the observations need or have to avoid specific dates, enter them here. If there are periods when you cannot observe for personal reasons, please specify them here.

We insist upon receiving, with proposals for heterodyne receivers, a complete list of frequencies corrected for source redshift (to 0.1 GHz) and precise positions. If in very special cases the proposers do not feel to be in a position to give this information, they should take up contact with the scheduler. The proposers should also specify on the cover sheet which receivers they 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 in J2000 coordinates.

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.

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 proposal cover page whether your proposal is (or is not) a resubmission of a previously rejected proposal or a continuation of a previously accepted 30m telescope proposal. In both cases we request that you describe very briefly in the introductory paragraph (automatically generated header ``Proposal history:'') 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 [6]. 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 from (http://www.iram.es/IRAMES/otherDocuments/manuals). A catalog of well calibrated spectra for a range of sources and transitions (Mauersberger et al. [9]) is very useful for monitoring spectral line calibration. A copy of the 30m file with the calibrated spectra can be downloaded from here

The astronomer on duty (whose schedule can be found at URL http://www.iram.es/IRAMES/groups/astronomy/aodsched.html) should be contacted well in advance of an observing run for any special questions concerning the preparation of an observing run (e.g. setup of on-the-fly maps etc).

Frequency switching is available for both HERA and the observatory's standard SIS receivers. This observing mode is interesting for observations of narrow lines where flat baselines are not essential, although the spectral baselines with HERA are among the best known in frequency switching. Certain limitations exist with respect to maximum frequency throw ( $\le 45$ km/s), backends, phase times etc.; for a detailed report see [4].

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. We strongly recommend to use the web-based Time Estimator (URL: http://www.iram.es/IRAMES/obstime/time_estimator.html), whenever applicable. A new version 2.5 handles heterodyne (single pixel and HERA) as well as bolometer observations with updated instrumental parameters. Suggestions and questions can be addressed to Axel Weiß (aweiss@iram.es).

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 $T_{\rm sys}$ , the spectral resolution, the expected antenna temperature of the signal, the signal/noise ratio which is aimed for, all overheads and dead times, and the resulting observing time. 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 [5]. It has been included in the 30m telescope Manual [6].

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 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 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 then decide which proposals can actually be accepted for this 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, from OAN in Madrid (near Parque de Retiro), 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 proposal, the P.I. is requested to give sufficient detail to the secretary, Cathy Berjaud (berjaud@iram.fr) on how the remote observer can be contacted. Please note that IRAM is not responsible for the remote stations in Paris, Madrid, or Bonn.

Remote observers affiliated with the MPIfR or other institutes near Bonn should contact F. Bertoldi (bertoldi@mpifr-bonn.mpg.de) or Dirk Muders (dmuders@mpifr-bonn.mpg.de) at MPIfR for a short introduction to the remote observing station. Remote observers in the Paris area may contact D. Teyssier (teyssier@lra.ens.fr) for arrangements. Astronomers who want to use the Madrid station contact Javier Alcolea (j.alcolea@oan.es). Remote observers in or near Grenoble contact C. Thum 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

HERA

Frequency tuning of HERA, although fully under remote control and automatic, is substantially more complicated than for the observatory's other SIS receivers. Although the tuning is still known for only a few frequencies, (the 3 CO isotopes at 230.5, 220.4, and 219.6 GHz; CS at 244.9 GHz; HCN at 265.9 GHz; HCO⁺ at 267.6 GHz; DCN and HC¹⁵N at 217.2 and 259 GHz; H₂CO at 225.7 GHz), HERA proposals for any frequency within the nominal tuning range of 210 - 276 GHz are invited, but we cannot guarantee at this moment that these proposals can actually be done. In any case, HERA observers should send the list of their frequencies to Granada as early as possible.

HERA is 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) on-the-fly maps of moderate size (typically 2' - 10'). Other observing modes are conceivable and/or under test, but they may not be ready for this semester. HERA proposers should use the web-based Time Estimator. For details about observing with HERA, contact Karl Schuster (schuster@iram.fr), the HERA project scientist, or Albrecht Sievers, the astronomer in charge of HERA (sievers@iram.es).

The single pixel heterodyne receivers

Four dual polarization 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, either horizontal or vertical in the Nasmyth cabin. Up to four of these eight receivers can be combined for simultaneous observations in the four ways depicted in Tab. 1. Note that they cannot be combined with HERA nor with the bolometers. Also listed are typical system temperatures which apply to normal summer weather (7mm of precipitable 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 not more than 15 min to tune four such receivers.

**Table:** Heterodyne receivers available for the summer 2003 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	60 - 80	>20	1.5	0.5	120
B100	H	1			4	81 - 115.5	60 - 80	>20	1.5	0.5	120
C150	V		2		4	129 - 183	70 - 125	15 - 25	4.0	1.0	200
D150	H		2	3		129 - 183	80 - 125	8 - 17	4.0	1.0	200
A230	V	1		3		197 - 266	85 - 150	12 - 17	4.0	1.0	450	1
B230	H	1			4	197 - 266	95 - 160	12 - 17	4.0	1.0	450	1
C270	V		2		4	241 - 281	125 - 250	10 - 20	4.0	1.0	1000	2
D270	H		2	3		241 - 281	150 - 250	9 - 13	4.0	1.0	1000	2
HERA	H					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: tuning parameters are not yet complete

General point about receiver operations

Tuning of the single pixel/dual polarization receivers is now considerably faster and more reproducible than before. Particular frequencies, like those near a limit of the tuning range, may still be problematic, and we recommend in such cases to check with a Granada receiver engineer at least two weeks before the observations. HERA observers, however, are requested to send their frequencies as soon as their project gets scheduled.

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 generates 4 signals from which spectra of all four Stokes parameters can be derived. Data reduction software using CLASS enhanced with a graphical user interface is available (H. Wiesemeyer). Polarimetry proposals are invited with the restriction that the target sources be not larger than the main beam.

Broader bandwidths, up to 500 MHz, are now available with a variant of IF polarimetry where the IF signals from the orthogonal receivers are correlated digitally in VESPA. A few issues of calibration still need to be worked out. Contact C. Thum for the current status.

MPIfR Bolometer arrays

The bolometer arrays consist of concentric hexagonal rings of horns centered on the central horn. Spacing between horns is $\simeq 20''$ . Each pixel has a HPBW of 11''. Two arrays may be used this summer: MAMBO-1 with 37 pixels and MAMBO-2 with 117 pixels. The effective sensitivity of MAMBO-1 for onoff and mapping observations is 39 mJys $^\frac{1}{2}$ . For MAMBO-2 effective sensitivities of 46 mJys $^\frac{1}{2}$ (ON/OFF mode) and 52 mJys $^\frac{1}{2}$ (mapping mode) were measured. Since in the mapping mode all beams cover the inner region of the map area, MAMBO-2 turns out to be more sensitive if areas of 2' and larger are to be mapped (see the Time Estimator). The sensitivities apply to bolometric summer conditions ( $\tau(250 {\rm GHz}\sim 0.4$ , elevation 45 deg, and application of skynoise reduction algorithms). In cases where skynoise reduction algorithms (simply the subtraction of correlated sky-noise) can not be applied (e.g. extended source structure), the effective sensitivity is typically about a factor of 2 worse. For those projects, only atmospheric conditions with low skynoise (i.e. stable atmosphere, no clouds, little turbulence) are recommened unless the expected signal is about 1 Jy/beam or stronger.

There is the possibility that MAMBO-2 will not be available throughout the entire summer semester for technical reasons. Proposals which cannot be done efficiently with MAMBO-1 (e.g. large mapping projects) should clearly say so in order to allow correct scheduling.

The arrays are mostly used in two basic observing modes, ON/OFF and mapping. Previous experience with MAMBO-2 shows that the ON/OFF reaches typically an rms noise of $\sim3.3$ mJy in 10 min of total observing time (about 200 sec of ON source integration time) under bolometric conditions in summer. Up to 30 percent lower noise may be obtained in perfect weather. In this observing mode, the noise integrates down with time t as $\sqrt{t}$ to rms noise levels below 0.5 mJy.

In the mapping mode, the telescope is scanned in azimuth (also the direction of the wobbler throw) in such a way that all pixels see the source once. A typical single map² with MAMBO-2 covering a fully and homogeneously sampled area of $150''\times150''$ (scanning speed: 5''per sec, raster step: 8'') reaches an rms of 2.8 mJy/beam in 1.3 hours. The area actually scanned ( $7.3'\times6.5'$ ) is larger than this by the wobbler throw and the array size. 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 ambitious goal.

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 [7] and MOPSI[8]). Time estimators for planning ON/OFF or mapping observations are also available [7,13].

Bolometer proposals will probably be pooled together like in previous semesters. Their time requests should be based on ``bolometric conditions'', and the web-based time estimator is again strongly recommended. If exceptionally low noise levels are requested which may be reachable only in a perfectly stable (quasi winter) atmosphere, the proposers must clearly say so in their time estimate paragraph. Such proposals will however be particularly scrutinized.

The Telescope

Beam and Efficiencies

Table 2 lists the size of the telescope beam for the range of frequencies of interest. Forward and main beam efficiencies are also shown (see also the note by U. Lisenfeld and A. Sievers, IRAM Newsletter No. 47, Feb. 2001). The variation of the coupling efficiency to sources of different sizes can be estimated from plots in Greve et al. [12].

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 [12] for details). Astronomers should take into account this error beam when converting antenna temperatures into brightness temperatures. A variable and sometimes large contribution to the error beam was known to come from telescope astigmatism[3]. Extensive work during the last years had shown that the astigmatism resulted from temperature differences between the telescope backup structure and the yoke. The recent installation of heaters in the yoke by J. Peñalver has nearly completely removed the astigmatism[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	0.78
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 and Focusing

Since the systematic use of inclinometers the telescope pointing became much more stable. Pointing sessions are now scheduled only once every 2 weeks. The fitted pointing parameters typically yield an absolute rms pointing accuracy of better than 3'' [10]. Receivers are closely aligned (within $\leq 2''$ ). 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 can occasionally occur. 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

Backends

The following four spectral line backends are available which can be individually connected to any single pixel receiver and, if indicated, also to HERA.

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.

VESPA, the versatile spectrometric and polarimetric array, can be connected either to HERA or to a subset of 4 single pixel receivers, or to a pair of single pixel receivers for polarimetry. The many VESPA configurations and user modes are summarized in a Newsletter contribution [14] and in a user guide, but are best visualised on a demonstration program which can be downloaded from our web page at URL http://www.iram.fr/IRAMFR/PV/veleta.html. Connected to a set of 4 single pixel receivers VESPA typically provides up to 12000 spectral channels (on average 3000 per receiver). Up to 18000 channels are possible in special configurations. Nominal spectral resolutions range from 3.3 KHz to 1.25 MHz. Nominal bandwidths are in the range 10 -- 512 MHz. When VESPA is connected to HERA, up to 18000 spectral channels can be used with the following typical combinations of nominal resolution (KHz) and maximum bandwidth (MHz): 20/40, 40/80, 80/160, 320/320, 1250/640.

The 4 MHz filterbank consists of nine units. Each unit has 256 channels (spacing of 4 MHz, spectral resolution at 3 dB is 6.2 MHz) and thus covers a total bandwidth of 1 GHz. The 9 units are designed for connection to HERA, but a subset of 4 units can also be connected to the backend distribution box which feeds the single pixel spectral line receivers. All these receivers have a 1 GHz RF bandwidth except for A100 and B100 (500 MHz only). At the present time, a 4 MHz filterbank cannot be used simultaneously with the autocorrelator or the 100 KHz filterbank on the same receiver.

An on-line calibration routine automatically writes calibrated spectrometer data, including the 4 MHz filterbanks, to the linux machines. The routine, although still experimental, works for all observing modes. A logical link named ``data.30m'' pointing to this file of calibrated spectra is made available in all newly created project accounts.