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Boër, M. 2000, in ASP Conf. Ser., Vol. 216, Astronomical Data Analysis Software and Systems IX, eds. N. Manset, C. Veillet, D. Crabtree (San Francisco: ASP), 327

The TAROT-2 Project

M. Boër
Centre d'Etude Spatiale des Rayonnements (CESR/CNRS),
BP 4346, F 31028 Toulouse Cedex 4, France


This paper presents the TAROT-2 project an automatic, autonomous observatory. Its main objectives are the study of cosmic Gamma-Ray bursts and the detection of extrasolar planets. The telescope will feature a 1.5m SiC mirror, and will have the ability to slew to any position at a speed of up to 60 deg/s. TAROT-2 will be completely autonomous from the request for observation management and scheduling, to the processing of observational data.

1. Introduction

Automated telescopes have seen much development in recent years. Many of them were built to respond to specific requirements of a particular scientific project: this is the case of the Télescope à Action Rapide pour les Objets Transitoires (TAROT, Boër et al. 1999; Boër et al. 2000), an automated telescope mainly devoted to the observation of cosmic gamma-ray bursts. This telescope has achieved a high degree of autonomy, being able to process the requests, establish its own schedule, and process the observations to produce a source list matched with several catalogs.

However, prompted by the need to reach a better sensitivity level, we decided to begin the study of a new, larger instrument. In this paper we present the scientific objectives, the materials and techniques we plan to use, as well as the foreseen characteristics of this project, named TAROT-2.

2. Scientific Objectives

2.1. Cosmic Gamma-Ray Bursts

Cosmic gamma-ray burst are probably the most violent explosions in the universe, other than the big-bang itself. These objects are located at cosmological distances with redshifts on the order of unity. For an isotropic expansion about $10^{53}$ ergs are released in few seconds. Their origin remains largely unknown, with models invoking the coalescence of a binary neutron star, or neutron star - black hole system, the core collapse of a super-massive star, and a variety of other combinations. This energy is released mainly at gamma-ray wavelengths, where GRBs were discovered, and are still mainly observed in this domain. However, quite recently they have been detected as multi-wavelength sources, i.e. they have been shown to emit at all wavelengths, including, radio, optical and infrared. Their emission may be separated in two phases. In the burst phase, most of the energy is released, mainly at gamma-ray and X-ray wavelengths. A bursting optical counterpart has been observed in only one case (Akerlof et al. 1999) out of approximately 20 contemporaneous optical burst observations. The bursting phase is followed by the afterglow phase, where the luminosity of the source decreases exponentially with an index on the order of 1. This phase has been observed at optical wavelength in approximately one third of the observed sources, and may last several months until the luminosity is too faint to be detected.

The TAROT-2 goals for the observation of GRBs are the following:

  1. Detection, and localization of the optical burst associated with the GRB, i.e. during the gamma-ray emission, upon reception of a position from a satellite, e.g. CGRO/BATSE, HETE-II, SWIFT, GLAST, INTEGRAL or BALLERINA;

  2. Study of the transition between the burst and the afterglow regimes;

  3. Detection and study of ``orphan'' optical transient or afterglow events, possibly associated with undetected GRBs.

Objective 1 implies a fast moving telescope, objective 2 a good sensitivity, and objective 3, in addition, the monitoring of large areas over the sky.

2.2. Extraterrestrial Planets

About 20 extra-solar planets have been discovered to date. These systems are frequent, and appear to be quite different from our solar system. These discoveries have all been made by measuring the radial velocity of selected stars, which introduces an important selection bias. The goal of TAROT-2 is to detect extra-solar planets using the transit method. In this method the light curves of a large number of stars are monitored for the variation caused by the partial occultation of the light by the planet transiting the star. It has the advantage of being able to derive directly the planet size, and may potentially lead to a larger number of detections. The main difficulty is to reach a photometric precision better than $10^{-3}$ for a Jupiter like planet. This accuracy is easily reachable by the current generation of CCD detectors. The other difficulty is the continuous monitoring of a large number of stars, implying a large field of view and a high duty cycle. This last feature implies an automatic telescope de facto. Short CCD readout times, and fast telescope slews between fields are required.

2.3. Other Objectives

The two examples given above show the diversity of objectives an automatic telescope can achieve. We have plans to observe active galactic nuclei in conjunction with very high energy detectors, detection of supernovae and monitoring of X-ray transient sources. Several objectives are connected to the solar system, as is the case with the detection and study of Kuiper objects. TAROT-2 will also be able to eventually detect Earth-grazing asteroids and to follow space debris.

3. Technical Design

These objectives lead to a telescope of 1.5m in size. In order to achieve the high slewing speed (60 deg/s) we require that the telescope be as light as possible. We need to accommodate to the large size of the GRB error boxes which may be provided by several spacecraft, hence the field of view will be 2 degrees. We plan to have a companion telescope, or time on another automated telescope, in order to be able to perform spectroscopy on selected sources.

TAROT-2 will be a prototype telescope in three ways:

  1. We plan to make use of a SiC ceramic for the mirror, the secondary mirrors, and the connecting structure (the tube). The advantages of this material are the following:

Since the structure and the optical parts are made of the same material, the design, as well as the realization of the various parts are greatly simplified. Because of the stiffness of the SiC we will be able to avoid several parts, like the barrel, actuators, enabling a further reduction of the weight and complexity. The telescope structure will weigh a total of 100kg, and will be quite compact to reduce the different moments of inertia. This will result in increased reliability because of the simplicity of the design.

The second major feature of TAROT-2 will be its high level of autonomy, and the introduction of an imaging and spectrographic instrument under the same functional observatory, while the instruments can actually be separated by thousands of kilometers. TAROT-2 will be able to process the observations from the request level sent by an astronomer, sitting anywhere around the globe, to the pre-processing of frames, including source extraction and separation, light curve analysis, etc. This last point implies that we will need to develop specific methods in order to maintain a high level of accuracy and reliability, with no human intervention, and in a very constrained timeframe(1 frame/minute).

Finally the huge amount of data, the complexity of the system, and its networked aspects imply that TAROT-2 will have to be accessible from the WWW in a flexible and comprehensive way, and that high level tools to navigate on the data have to be developed.

4. Discussion and Conclusions

TAROT-2 will need a large number of developments beyond the use of SiC. It will be the first networked observatory, linking an imaging/photometric telescope, a spectroscopic telescope, and the already working TAROT-1 telescope. In addition, other automatic observatories may be added, e.g. to perform continuous observation of a given object without interruption. Also, the efficient use of the instrument network, the scheduling algorithm being responsible of sending the right program to the right telescope (e.g. bright sources to TAROT-1 and fainter sources to TAROT-2), and to schedule eventually follow-up observations of interesting objects using the spectroscopic telescope.

The TAROT-2 project is at present under study and review by several institutions in France, and we hope to begin the development in 2000.


TAROT-2 is at present supported for a study by the Ministère de l'Education, de la Recherche et de la Technologie and the Université Paul Sabatier, Toulouse.


Akerlof, C., et al. 1999, Nature, 398, 400

Boër, M., et al. 1999, A&AS, 138, 579

Boër, M., et al. 2000, this volume, 115

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