ATLAS-Teide: the next generation of ATLAS units for the Teide Observatory

Summary

In this work we present the design of the ATLAS (Asteroid Terrestrial-impact Last Alert System) unit that will be installed at Teide Observatory in Tenerife island (Spain). ATLAS-Teide will be built by the IAC and will operated as part of the ATLAS network in the framework of an operation and science exploitation agreement between the IAC and the ATLAS team at University of Hawaii.

ATLAS-Teide will be the first ATLAS unit based on COTS.  Its design is modular, each module (“building block”) consist of four Celestron RASA 11 telescopes that point to the same sky field, equipped with QHY600 CMOS cameras on a equatorial Direct Drive mount. Each module is equivalent to a 56cm effective diameter telescope and provides a 7.3 deg²  field of view and a 1.25 “/pix plate scale. ATLAS-Teide will consist of four ATLAS modules in a roll-off roof building. This configuration allows to cover the same sky area of the actual ATLAS telescopes.  This design is cheaper to build and maintain, and more flexible than the actual one.

The first ATLAS “building block” will be operational before the end of 2022 and we aim to complete the four modules of ATLAS-Teide by the end of 2023.

The ATLAS survey. 

ATLAS is an asteroid impact early warning system developed by the University of Hawaii and funded by NASA (see http://atlas.fallingstar.com). It consists of four 50cm telescopes (Hawaii ×2, Chile, South Africa). Each ATLAS unit maps 1/4 of the night sky, making 4 observations of each field at intervals of one hour, detecting objects of V=19.5-20 in 30s exposures. The software automatically detects moving targets, discovering hundreds of new objects every night. It also allows thousands of these bodies to be observed, taking very precise astronomical and photometric measurements, making ATLAS one of the most prolific asteroid database. ATLAS also processes the survey data to find stationary transient events, which are immediately reported to the IAU. These include supernovae, starbursts, and fast transients like GRB afterglows, etc. It also has an agreement with LIGO to search for electromagnetic counterparts of gravitational wave sources. ATLAS is among the 3 main projects of the world in reporting this type of event, with more than 300 supernova candidates found per year. 

ATLAS-Teide, the next generation of ATLAS units.
 
Late 2021, the IAC obtained funding from the Spanish “Subprograma Estatal de Infraestructuras de Investigación y Equipamiento Científico Técnico (Ref. EQC2021-007122-P)” to install an ATLAS unit at Teide Observatory. ATLAS-Teide will be the 5th ATLAS unit and will be operated together with the other four thanks to an agreement between the IAC and the Institute for Astronomy of the University of Hawaii (IfA-UH).
The design of the existing ATLAS is based on a telescope that is a variant of the Wright-Schmidt cameras that use a 50cm Schmidt correcting foil, a 65cm spherical primary mirror and a 3-element field correcting lens and a f/D=2.0. Each telescope is equipped with ACAM, a back-illuminated 110Mpix CCD camera providing a field of view of 5.4 x 5.4 deg and a plate scale of 1.88 “/pix. The design and construction of the telescope is of the company DFM Engineering Inc. After several interactions with DFM we have concluded that doing it with them is actually impossible and that it is necessary to opt for another design. 
After studying different options, we concluded that the best solution is to design a new ATLAS unit using a modular structure based on existing “commercial off-the-shelf” (COTS) equipment.  It should have capabilities similar to the telescopes that ATLAS currently has in terms of detection limit and sky area covered per night. The solution we found is cheaper to build and maintain, very efficient and more flexible than the current ATLAS. The new ATLAS design is based on optic telescope assemblies (OTAs) Celestron model RASA11, QHY600 CMOS cameras that use back-illuminated IMX-455 chip from SONY, with 9576*6388 pixels of 3.76 microns, and mounts of the L-series of the PlaneWave company. 

An ATLAS module or “building block” consists of four RASA 11 telescopes mounted together on a L-series PlaneWave equatorial mount (see Fig. 1), each one equipped with a QHY600 camera. All 4 telescopes point to the same field, so, combining the 4 images obtained simultaneously we have a system with an equivalent collecting area equivalent to that of a telescope with 56cm aperture (25.4% larger than that of the current ATLAS) with a field of view of 7,37 deg2 and a 1.25 “/pix plate scale. Considering the slightly lower sensitivity of the QHY cameras respect to ACAM the ATLAS module should detect objects of V=19.5-20 in 30s exposures.  

Figure 1- Schematic drawing of an ATLAS module.

To cover a similar sky area of the ATLAS units, ATLAS-Teide will consist of four ATLAS building blocks (16 OTAs RASA 11 in total) installed in a building with a roll-off roof structure. This design provides a similar sensitivity and sky coverage with a better plate scale. Moreover, it has several advantages: (i) its cost is a fraction of the cost of the old ones; (ii) it is much more flexible, allowing e.g. to point the four modules to the same field going 0.75 mag deeper; (iii) it is more efficient as in case some of its part fail the other modules can continue operating while the failed component is rapidly replaced, thus, if the COTS parts behave as promised, it is cheaper and easier to maintain and operate.

We are building the first ATLAS “building block” that will be operational before the end of 2022. It will be used to test its capabilities, develop all the needed software (control and image reduction) and the integration of the system into the ATLAS network.  The main aim is to complete the four modules of ATLAS-Teide by the end of 2023 and have it fully integrated in the ATLAS network early 2024. 

Acknowledgements. This project has received funding from the “Subprograma Estatal de Infraestructuras de Investigación y Equipamiento Científico Técnico (Ref. EQC2021-007122-P)”