The KELT-South Telescope1 Joshua Pepper1, Rudolf B. Kuhn2,3, Robert Siverd1, David James4, Keivan Stassun1,5 ABSTRACT The Kilodegree Extremely Little Telescope (KELT) project is a survey for new transiting planets around bright stars. KELT-South is a small-aperture, wide-field automated telescope located at Sutherland, South Africa. The telescope surveys a set of 26◦ × 26◦ fields around the southern sky, and targets stars in the range of 8 < V < 10 mag, searching for transits by Hot Jupiters. This paper describes the KELT- South system hardware and software and discusses the quality of the observations. We show that KELT-South is able to achieve the necessary photometric precision to detect transits of Hot Jupiters around solar-type main-sequence stars. 1. Introduction Ground-based surveys for transiting exoplanets have become increasingly successful, identifying nearly 130 transiting planets7. These surveys, notably HATNet (?), SuperWASP (?), and XO (?), utilize small-aperture, wide-field robotic telescopes to obtain high-precision photometric lightcurves of relatively bright stars. The Kilodegree Extremely Little Telescope (KELT) project follows a similar methodology, originally based on the model derived in ?, with the KELT-North telescope (?) operating for several years at Winer Observatory8 in Arizona. While KELT-North has been gathering data, we have constructed a duplicate telescope for Southern hemisphere observations: KELT-South. The KELT-South telescope was deployed to the Sutherland observing station of the South African As- tronomical Observatory (SAAO) in 2009, and is now operating regularly, accumulating data for arXiv:1202.1826v2 [astro-ph.IM] 26 Mar 2012 1Department of Physics & Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 2South African Astronomical Observatory, P.O. Box 9, Observatory 7935, Cape Town, South Africa 3Astrophysics, Cosmology and Gravity Centre, Department of Astronomy, University of Cape Town, South Africa 4Cerro Tololo InterAmerican Observatory, Colina El Pino, S/N, La Serena, Chile 5Department of Physics, Fisk University, 1000 17th Ave. N., Nashville, TN 37208 1The KELT-South Telescope is funded and operated by Vanderbilt University and Fisk University in cooperation with the South African Astronomical Observatory. 7http://exoplanet.eu/ 8http://www.winer.org/ – 2 – transit detection and other science. In this paper, we describe our hardware and facilities (§2) and observing operations and data handling procedures (§3). We then characterize the telescope per- formance (§4) and image quality (§5), and conclude with sample lightcurves of interesting variable objects (§6). 2. Hardware and Facilities KELT-South consists of an optical assembly (CCD Detector, camera lens, and filter) mounted on a robotic telescope mount (see Figure 1). The mount is housed inside an enclosure with a roll-off roof that was specifically built for the telescope. Inside the enclosure there is a climate-controlled cabinet that houses the control computer and hard drives. The control computer is responsible for controlling the robotic mount, CCD camera, observing operations, preliminary image processing and local data archiving. KELT-South was assembled using as many off-the-shelf components as possible to speed up the development process, as well as to ensure that replacing any part of the telescope would be relatively easy and quick. 2.1. Enclosure and PLC The KELT-South telescope is located in a custom-built building to protect it from the elements as well as hold the various system components. The building is a brick construction with a steel roll-off roof, equipped with power and network connections. Cowlings on either side of the building allow air to flow through the building and keep components inside near the ambient temperature. A flat field screen is bolted to the underside of the roll-off roof and interior lights can be turned on remotely to check on the condition of the telescope via an IP camera attached to the inside of the building. Control of the building mechanisms is mediated by a custom-built programmable logic con- troller (PLC) located in a box on the interior wall of the building, remotely accessible through the control computer. The PLC is connected to an uninterruptible power supply (UPS) that is responsible for closing the roof in the case of a power failure (see Section 2.4). The PLC has a hard-coded trigger that will close the roof and switch off any lights when no commands have been received from the control computer for a set amount of time. This is known as the “watchdog” and is currently set to 900 seconds. This ensures that the enclosure is closed and set to an “off” state in the event that the control computer fails or crashes during an observing run when the roof is open. The control computer monitors the weather via three local weather station feeds provided – 3 – Fig. 1.— The KELT-South telescope installed at Sutherland. – 4 – by the SALT (Southern African Large Telescope)9 weather station10, the SuperWASP11 weather station 12, and the GFZ13 weather station. An external rain sensor is attached to the KELT-South building and serves as an extra safety feature. This rain sensor is connected directly to the PLC and will close the roof in the case of rain detection while the roof is open. Should the weather information collected by the control computer be wrong or the control computer not respond fast enough to incoming precipitation, the rain sensor will trigger and close the roof to prevent damage to the telescope and other systems. The rain sensor is located on the side of the building that faces west, the direction from which storms typically approach the Sutherland observing site. 2.2. Control Computer and Cabinet The computer that controls all aspects of the telescope operation is a Dell Optiplex 755 small- form-factor PC running the Windows XP operating system. Software packages (TheSky6 Profes- sional14 [Version 6.0.0.60] and CCDSoft15 [Version 5.00.188]) provided by Software Bisque16, enable the control computer to operate the CCD and mount via a script-accessible interface. The com- puter clock is synchronized using the free software package Dimension 417 to keep the clock time accurate. Two external hard drives are connected to the control computer via USB cables and are used to store the data. The control computer is housed in a Rittal computer cabinet (type 8845.500) with a Rittal Top Therm Plus Cooling Unit. The cabinet also contains a transformer (§2.4) to convert the local South African power (220V, 50Hz) to American standards (120V, 60Hz), required for the the American- manufactured components (i.e. camera, mount, and computer). The cooling unit is set up to keep the interior temperature below 20◦C to protect the electronic components. 9http://www.salt.ac.za/ 10http://www.salt.ac.za/html/weather.php 11http://www.superwasp.org/waspsouth.htm 12http://wasp.astro.keele.ac.uk/live/ 13http://www.gfz-potsdam.de/ 14http://www.bisque.com/sc/pages/thesky6family.aspx 15http://www.bisque.com/sc/shops/store/CCDSoftWin2.aspx 16http://www.bisque.com/sc/ 17http://www.thinkman.com/dimension4/ – 5 – 2.3. Temperature Probes Two temperature probes record the temperatures inside and outside the computer cabinet. These probes are connected to the control computer through a USB interface, and software on the computer logs the temperatures at one minute intervals. The probes were manufactured by Qti (Quality Thermistor, inc)18 and provide absolute accuracy of up to ±0.1◦C. At present the temperatures are simply recorded and no actions are taken if the temperatures are outside the control limits. In the future, the control computer will alert the technical staff in Sutherland if this situation should happen. 2.4. UPS and Transformer The telescope operates with two UPS units and a transformer. The first UPS is an Eaton Pow- erware 9125 UPS. Attached to this UPS is an Eaton PowerPass Distribution Module transformer. Together the two systems are responsible for providing surge protection to the telescope as well as stepping down the power from 220V (South African standard) to 120V (American standard). The 120V output power is required to operate the mount, camera and control computer (all these components were bought in the USA). The second UPS is an Eaton Powerware 9120 UPS that provides backup power to the enclosure only. The roof motor, interior lights (including flat field lights) and internal IP camera are connected to this UPS. The PLC is plugged into this UPS as well as a standard power outlet. If the normal power should fail, the PLC will sense the failure and will close the roof of the enclosure within 120 seconds if normal power is not restored. This action cannot be stopped and is hardwired into the circuitry of the PLC. This prevents the roof from staying open during a power failure and limits the possibility of damage to the telescope. If this action should occur, the PLC trips an electronic flag that needs to be reset remotely by a user to open the roof again. 2.5. Camera, Lens, and Filter The KELT-South detector is an Apogee Instruments Alta U16M thermoelectrically cooled CCD camera. The camera uses the Kodak KAF-16803 front illuminated CCD with 4096 × 4096 9µm pixels (36.88 × 36.88 mm2 detector area) and has a peak quantum efficiency of ∼60% at 550nm19 (See Figure 2). The interface between the camera and the computer is a 5m long USB 2.0 standard cable. The camera has a three-stage thermoelectric Peltier cooler (with the D09F Apogee camera housing) that is capable of maintaining a temperature of 65 – 70◦C below ambient 18http://www.thermistor.com/productsDirecTemp.html 19http://www.kodak.com/global/en/business/ISS/Products/Fullframe/index.jhtml?pq-path=11937/11938/14425 – 6 – temperature. For the purpose of KELT-South the CCD is maintained at -20◦C year-round to reduce thermal noise.