Call for Observing Proposals on the 30m Telescope

Roughly 2800 hours of observing time will be available, which should allow scheduling of a few longer programmes (of the order of 100 hours). Emphasis is on observations in the 1mm window, but lower frequency observations may be scheduled as marginal weather backup.

What is new ?

The 1.3mm HEterodyne Receiver Array, HERA was successfully used in several projects during the past semester. In its present form, HERA has 9 pixels separated by 24'' and arranged in a center-filled square. HERA will be available again for the coming winter semester with extended backend capabilities (fully operational VESPA and probably (see below) a set of nine low resolution filterbanks of 1 GHz bandwidth each. HERA proposals for extragalactic (or other wide bandwidth) observations are therefore invited, in addition to the higher spectral resolution proposals using VESPA.

The correlator upgrade project, VESPA (VErsa- tile Spectral and Polarimetric Analyser), is fully completed. This powerful backend can now be used with HERA where up to nominally 2000 spectral channels per pixel are available, or with (a suitable subset of 4 of) the eight standard Observatory receivers where up to 12000 spectral channels (typically 3000 per receiver) can be connected. Spectral resolutions range from 3.3 KHz to 1.25 MHz. Bandwidths are in the range from 10 to 512 MHz.

We plan to have at least one of the bolometer arrays, MAMBO-1 (37 pixels) or MAMBO-2 (117 pixels), installed at the telescope. Several upgrades of MAMBO-2 are planned during the summer. Depending on the sensitivity improvements achieved, one or both arrays will be available this winter.

Experience with flexible scheduling during last winter was mostly positive. The success rate of the strongly weather-sensitive projects with a high scientific priority was clearly improved. This winter, we plan to continue this observing mode. A suitable mix of proposals with high and moderate demands on atmospheric quality will be pooled together and observed by a team of qualified observers in several sessions. The total duration of these sessions depends on the overall demand on pooled time, the recommendations of the program committee, and on the availability of qualified observers. Although priority will be given to high frequency proposals in general terms, lower frequency weather tolerant proposals are encouraged, since these programs have good chances to be scheduled as backups in such pools. Participation in these pooled observations is voluntary, and IRAM will contact the principal investigators of those accepted proposals which could be scheduled in this way. In order to speed up this process, candidate pool participants (either with a very weather-sensitive or as a weather-tolerant proposal) are invited to mention their preference in the proposal and to mark ``Pooled obs'' on the cover sheet.

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 from 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.

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.

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, J2000 coordinates are preferred.

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 carefully 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 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 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 [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). 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 powerful On-the-Fly observing mode (OTF) is available for heterodyne observations. 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 the astronomer on duty well in advance of the observations.

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 of strong concern, 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 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:

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. In its version 2.4, it includes HERA. Extensive on-line help is provided. Questions can be addressed to Axel Weiss (aweiss@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. 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 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 MPIfR in Bonn, from ENS in Paris (often restricted to nighttime hours), 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 remote proposal, the P.I. is requested to give sufficient detail to the Station Manager (mauers@iram.es) on how the remote observer can be contacted. Please note that IRAM is not responsible for the remote stations in Paris or Bonn.

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 to the remote observing station. Remote observers in the Paris area may contact D. Teyssier (teyssier@lra.ens.fr) for arrangements. Remote observers in or near Grenoble contact C. Thum ( thum@iram.fr) 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 currently known for only a few frequencies, HERA proposals for any frequency within the nominal tuning range of 210 - 276 GHz are nevertheless 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 this winter. HERA proposers should use the web-based time estimator on the Granada web page. For details about observing with HERA, contact Karl Schuster (schuster@iram.fr), the HERA project scientist, or Albrecht Sievers, the astronomer now in charge of HERA (sievers@iram.es).

The Observatory 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 two of these dual polarization receivers can be combined for simultaneous observations in the four ways depicted in Tab. 1. Note that they cannot be combined with HERA. 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 receivers are tuned by the operators 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 2002/03 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. Note that the 8 standard receivers can be combined in 4 different ways.
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	130
C150	V		2		4	129 - 183	70 - 115	15 - 25	4.0	1.0	200
D150	H		2	3		129 - 183	60 - 150	8 - 17	4.0	1.0	200
A230	V	1		3		197 - 266	85 - 185	12 - 17	4.0	1.0	420	1
B230	H	1			4	197 - 266	95 - 160	12 - 17	4.0	1.0	420	1
C270	V		2		4	241 - 281	125 - 290	10 - 20	4.0	1.0	900	2
D270	H		2	3		241 - 281	130 - 300	9 - 13	4.0	1.0	900	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: so far only few frequencies available, see text.

General point about receiver operations

As tuning of the single pixel/dual polarization receivers is now considerably faster 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 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 it 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 now available. Please contact H. Wiesemeyer (wiesemey@iram.fr). 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 restriction that the target sources be not larger than the main beam.

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.

A potentially promising variant of IF polarimetry where the cross correlation is made digitally in VESPA, is investigated. Contact C. Thum for the current status.

MPIfR Bolometer arrays

The 37-pixel MAMBO-1 array consists of 3 concentric hexagonal rings of horns centered on the central horn. Spacing between horns is $\simeq 20''$ . Each pixel has a HPBW of 11'' and a sensitivity of $\simeq 30$ mJys^1/2. This figure applies for ``normal bolometric conditions'' (pwv 4mm and a stable atmosphere, i.e. no clouds, little turbulence, high elevation, application of skynoise reduction alogrithms). Often, such bolometric conditions are only found after sunset and before noon.

The 37-pixel array (MAMBO-1) was used extensively at the telescope last winter with good success. The 117 pixel array (MAMBO-2) which undergoes a few upgrades this summer, may also be available. Depending on the relative sensitivity of the two arrays for observations of compact and extended sources, separate sessions may be scheduled for (mainly) ON/OFF and (mainly) mapping proposals. Proposers of mapping observations should base their time request conservatively on MAMBO-1. If MAMBO-2 should become available, the program committee may suggest to adjust appropriately the time allocation for these proposals.

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 with time as $t^{\frac{1}{2}}$ to rms noise levels below 0.3 mJy.

In the mapping mode the telescope is scanned in azimuth, the direction of the wobbler throw, in such a way that all pixels see the source once. A typical single map covering $4\times3$ arcmin with a scan speed of 4''/sec and a raster step of 4'' in elevation takes about 60 min of telescope time. Under normal bolometric conditions and assuming effective skynoise suppression, an rms of 2 - 4 mJy is thus reached in the inner $2'\times 1'$ . 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 demanding goal.

Another note of caution: mapping of extended sources cannot rely on the skynoise reduction algorithm (simple subtraction of correlated sky-noise) presently available, and the noise level reached may be at least twice as high as that quoted above.

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].

Bolometer time requests should be based on normal winter conditions, like requests using SIS receivers, 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 winter atmosphere, the proposers must clearly say so in their time estimate paragraph. Such proposals will however be particularly scrutinized.

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 of 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. The variation of the coupling efficiency to sources of different sizes can be estimated from plots in Greve et al. [16].

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] 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	0.78
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 $R\sigma=0.07$

Backends

The following four spectral line backends are available which can be individually connected to any single pixel receiver and/or 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.

The upgraded correlator VESPA, the new (VErsatile SPectrometer Assembly) 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 available in these connection modes are best visualised on a demonstration program which can be downloaded from the Grenoble web page at URL http://iram.fr/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 currently consists of two units. An extension to a total of 9 units is expected to be completed during the winter semester. Each unit has 256 channels (spacing of 4 MHz, spectral resolution 6.2 MHz) and thus covers a total bandwidth of 1 GHz. The 9 units are designed for connection to HERA, but they can also be used with the single pixel spectral line receivers which are equipped with a 1 GHz bandwidth (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.

A new 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, including On-the-Fly. A logical link named ``data.30m'' pointing to this file of calibrated spectra is made available in all newly created project accounts.

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]).