We present the result of a year-long effort to think, design, build, realize, and manage the robotic, autonomous REM observatory, placed since June 2003 on the cerro La Silla, ESO Chile. The various aspects of the management and control are here surveyed, with the nice ideas and the wrong dead ends we encountered under way. Now REM is offered to the international astronomical community, a real, schedulable telescope, automatic for the People.
REM (Rapid Eye Mount) was thought and realized in order to catch fast optical and infrared transient phenomena, correlated with high-energy events signaled by orbiting observatories, mainly GRB discovered by then recently launched Swift satellite. Its realization resulted in a workbench for various other existing and wish-list telescopes [
The statistics of pre-Swift bright GRB optical transient led to a 60 cm diameter telescope, equipped with VIS/IR cameras, fast enough to follow Swift acrobatics and to acquire images, process them fast, and detect the transient with good accuracy to alert larger telescopes’ spectrographs. We decided, in order to put it far from existing or proposed robotic telescopes, half a world apart in the southern hemisphere, on the Chilean Andes in the ESO site of La Silla.
In order to fulfill the requirements the telescope should have had the capabilities to react immediately to alerts, see the afterglow of the GRBs, and classify it to estimate the redshift by photometry. To this extent the mechanics of the telescope should have been robust and fast enough, the size of the mirror should have been large enough, and the photometry was needed in both visible and infrared. On the software side we should be able to control the telescope, command both cameras and analyze the images, and at the end also alert the rest of the world. Were we good at this? Unfortunately the belief that GRB afterglows were bright enough for our chosen size of 60 cm as primary mirror revealed false, and the mean, dim luminosity of the transients de facto prevented REM, as most of the other robotic telescopes of the same class, to observe a large fraction of the afterglows following Swift satellite alerts. In those early times, before we could enhance the REM pointing capabilities to observe down to 5 degrees above horizon, only 5% of the GRB alerts could be reached by REM pointing. Our lack of ability to detect precise coordinates in due time also led to abandon the finalization of the transient detection and alert software, which remained at the still remarkable level of producing automatic astrophotometry for good quality images.
The robotic nature also revealed to be somewhat tricky and we had to add to our system a full self-telemetry of vital signal of the various subsystems which was also able to send SMS and e-mail to real people. A team of trained real people on-site was also required and we received the help and collaboration from ESO-La Silla technical staff, which is now able to intervene in case of need or emergency.
After we added the funded possibility to use REM as a laboratory for new technologies and finally offered the nonalert time to the astronomical community via the classical systems of call for proposals, we finally completed the REM Observatory, working regularly and autonomously every night since 4 semesters (a full photo in Figure
The REM Observatory:
The companies and developers involved in the REM realization were both from the private industry and from public research institutions. Halfmann Teleskoptechnik designed together with our group the telescope body and main reflecting Zeiss optics, coated by Sagem with protected silver to enhance the performances in the infrared. The main near infrared REMIR camera [
NGC3606 imaged by the REM cameras. (a) The color composite of the REMIR J, H, and K filters. (b) Photo the composition of the ROSS V, R, and I images.
The REM dome is positioned in the ESO La Silla premises and can profit of all the (still, at date of writing) existing infrastructures and facilities. ESO provides power, UPS, and network connections, as well as liquid nitrogen refilling every 4 days. In every assembling phase the availability of a mechanical workshop and a clean room for the infrared detector assistance proved to be essential and both time sparing and mission proved to be critical.
The dome realization was performed by ESO general services and has two sliding roof which leave completely clear the sky without the need to have any movement during the observations (see a CAD rendering in Figure
The way REM acts is badly an imitation of autonomous machine. It needs a daily check from Italy in order to catch in with its many unforeseen situations and also, although now rare, unrecoverable stops in its sequences of jobs. In fact, we experienced some dome blockings, few main computer crashes and network halts, as well as some CCD driver timeouts. Many of these we recovered by remote commands but in some cases we had to wait for human help in La Silla.
Nevertheless its main sign of activity is the reaction to inputs. The main information flux starts from the Observing Block Scheduler which enters in the REM Observing Software (REM-OS, cfr. Stefanon et al. in this volume [
A series of (mainly) python programs run autonomously in the various machines in the dome to get the status of the sensors, encoders, and so forth, and fill the proper SQL tables in the REM-OS machine.
The control python program is the tREM-o-meter which runs every 2 minutes. The tREMometer collects the relevant data from archive, fills in the missing values, produces a public web page with the status of the telescope and all subsystems and performed observations, and, finally, checks for malfunctions and sends e-mail and SMS alerts. In case the conditions become dangerous in the infrared Dewar (the most delicate area), it is able to autonomously interrupt all IR data acquisitions. We in fact allow a small range in IR chip temperature as safe operational range: should the sensor get heated more than 105 K, the IR camera is turned off, returning to normal operations only after its temperature is lower than 100 K.
The information you can see in the tREMometer well summarizes the observatory life cycle. In Figures
(a) The status of every dome in La Silla is monitored and is used as one of the safety parameters we include in our opening decision algorithm. Also an automatic statistics is computed after each night in order to keep track of real night length (useful for meteo
Figure
The monitoring of the dome opening together with shutter-open time of every acquired image is the content of Figure
La Silla good nights of year 2008. (a) The percentage of nights with more than 6 hours of opening for REM dome: it may be considered very close to good weather nights in La Silla. (b) The shutter-open time percentage for REM cameras: red portions are the Observing Blocks ending with some error status which are to be repeated. No overheads have been included in this plot. The month of August included a two-week maintenance mission which makes those data inconsistent.
Other plots in the tREMometer include the status of the cryostat, temperatures, and meteo data from REM meteo station. Also, the program offers a Gannt graph of the past night, allowing the REM team to check for inconsistencies in the programmed observations. The degraded, small image previews are then posted on the web site for PI and public access.
During the following morning, every PI whose observations were continued in the previous night receives a detailed e-mail directly from the database in Bologna.
Furthermore, the Remos machine produces weekly reports which are sent to a restricted set of people: first, a report on a 4-month timeline of the pressure in the REMIR Dewar and the daily consumption of the liquid nitrogen supply. These are very useful to program mid term maintenance, such as repumping the vacuum in the cryostat and in the nitrogen lines.
The last information sent by the Remos system is the status of the observing programs accepted by the Italian Time Allocation Committee, allowing to follow the completion of the requested observations. In the last completed call (AOT18) all programs were well above 80%, not counting the ToO which did not use all their time.
The final repository for all the REM images is the REM Archive in Bologna. After an image is written on disk in Chile by the cameras, it is processed for quick astrophotometry and then sent to the database together with other data. In May 2009 the number of entries in the archive overcame 1 000 000. The archive web browser allows identified users to use a password layer to access their private data as well as all the public calibration frames.
Various preset types of query can be used to select and then retrieve the wanted images, and as well a custom SQL WHERE clause may be entered by the user.
It is also possible to perform basic on-line analysis on the observations, grouping by date or type, and showing the object position on the sky as shown in Figure
The REM archive browser allows PI and general public to select and retrieve observed targets. A limited statistical analysis can be performed on the fly: on the upper part of (a) all the flat field frames in the month of May 09, in the lower part of (a) the GRB observations during April 09. The sky chart on (b) the position in the southern hemisphere of all GRBs in the year 2008.
Among the 1 million images many have found their place in high ranked scientific papers, both in GRB science [
Even the most exciting project comes to a regime cycle that can hurt the creativity of a research group. REM Team to avoid becoming a managing and maintenance unit for yet another telescope turned the REM observatory into a working laboratory for experimenting new devices.
The first was the change in cooling system for the REMIR camera. The on-board Stirling cryocooler by Leibold Vacuum presented a series of problems ending in a serious instability of the system. The main problem was the underdimensioned power for our heat removal needs, but the Leibold company itself admitted that the maintenance of such cryocooler was so difficult that at the end they dismissed the production. Thus we adopted an ad hoc modified Continuous Flow Cryostat, a cryogenics system developed by ESO and extensively used in ESO instrumentation, whose main characteristic is that the LN2 vessel is separated from the cryostat, allowing a greater LN2 tank, then really improving the hold time [
A completely new experiment was also conceived in collaboration with IASF-Bologna, University of Bologna and SAO (Russia). TORTORA [
(a) A subframe of the wide field image centered on the optical transient 50 seconds after Swift trigger. The light curve (b) of GRB080319B measured by the TORTORA camera.
The future step of the REM lab will be the complete replacement of the optical camera ROSS. ROSS2 will have better optical quality which revealed not being optimized in the present camera and will produce 4 simultaneous images in the Sloan passbands
(a) ROSS2 visible camera optical layout: 4 separated images in four passbands will be recorded on a single 2 K
The experience of this project will not be lost. Our team is now deeply involved in the conceptual design of a 4-meter class telescope which will have a simultaneous camera like ROSS2 which extends into the infrared up to
The authors acknowledge the effort from all people which made REM possible; in particular the four ESO musqueteers in La Silla which helped and collaborated with them since the beginning and without their skill the project could have been in serious troubles. Also, they thank the American rock band R.E.M. for their prophetic song titles which have been used in this article.