SAURON: The Wallace Observatory Small AUtonomous Robotic Optical Nightwatcher

The optics system is currently a repurposed 11-inch Celestron NexStar GPS optical tube⁴ , mounted with a dovetail to a SoftwareBisque Paramount ME II⁵ (optical tube and mount specifications located in Tables 3 and 4). This preliminary optical tube was used to test the autonomous abilities of the other components. Once the system has been fully tested, the optics will be upgraded to an 17-inch tube so that fainter targets can be observed. The mount was chosen because it is capable of robotically pointing to target locations and has instrument capacity for 109 kg (Bisque), which is compatible with both the preliminary 11-inch telescope and the final 17-inch telescope.

The Paramount is mounted on a custom-made steel pier designed by T. Brothers and fabricated by machinists at the MIT Haystack Observatory. The pier is located in the center of the dome and is bolted to a 18'' wide, 6'' tall, concrete cylinder with an internal steel pipe, decoupled from the concrete pad. This concrete pier is resting on underlying bedrock and stabilized by the surrounding concrete so that surface vibrations do not affect the telescope. More information about the optics and mount specifications can be found in Appendix A.

The dome used for this project is a Technical Innovations 10-foot ProDome. This dome was chosen because it can operate during all four seasons in Massachusetts and can take conditional commands from the weather monitoring systems and location commands from TheSkyX via ASCOM. The dome is mounted 24 inches above the ground on top of two support rings; the telescope mounted inside matches the shutter height and can observe in all directions. The minimum observable altitude due to the treeline is 30 degrees in the North, 10 degrees in the South, and 20 degrees in the East and West.

Three different charge-coupled devices (CCDs) were used while testing: Portable Instrument for Capturing Occultations (PICO) (Lockhart et al. 2010), Quantum Scientific Imaging (QSI) 683s CCD (Q. S. Imaging)⁶ , and Santa Barbara Instrument Group (SBIG) ST-7XME Detector (S. A. Instruments)⁷ (detector specifications located in Table 5). The SBIG ST-7XME is currently mounted onto SAURON; we plan on upgrading this camera to a Finger Lakes Instrumentation CCD Camera in the future.

Other necessary instruments include the Starlight Xpress USB filter wheel, Custom Scientific Johnson/Cousins Photometric BVRIC filters, the Integrated-Control Temperature Compensating Focuser (TCF-Si), and Orion 80 mm refractor finderscope (Appendix B, Figure 2). The filter wheel is a five-position, 2-inch plate and has T adapters on both sides. Other necessary components include a computer, monitor, keyboard, mouse, security camera, programmable power outlets, uninterrupted power supply (UPS), fan, industrial USB hub, and weather monitoring system. We selected a Shuttle DS81 computer to operate the equipment in the dome. This computer is designed to perform well outdoors in a large temperature and humidity range due to its LED billboard, solid state drive, industrial capacitors, heat pipe cooling, and efficient power consumption.

The essential software for a remote telescope includes TheSkyX Professional Edition (equipment control), MasterSync (GPS time base), Digital Dome Works (dome setup) and various equipment drivers. CCDWare's CCDAutoPilot is required for automation.

It is essential to have accurate pointing and tracking for an autonomous telescope. MasterSync supplies the time from a GPS-based Network Time Protocol server to result in precise time recordings for each image and precise telescope pointing. TheSkyX uses a TPoint Add On to initially polar align the telescope and to subsequently point the telescope. TheSkyX performs a periodic error correction to improve the tracking of the telescope by taking into account the locations of the mount motor wheels. TheSkyX also combines all of this information in ProTrack to further improve tracking.

The site was first prepared by clearing unused telephone poles and nearby trees, digging a drainage trench, and running ethernet cables to the concrete pier. Removal of an original damaged concrete pier was done by Legace of Westford, MA. Electrical work was done by L. Pothier, J. Byford and T. Brothers. Next, the steel pier was attached to the existing concrete pier to raise the optical tube up to match the 36-inch dome base.

To construct the dome, the pieces were first loosely bolted together, placed on the concrete pad, and circularized. The dome is 119.5 inches in diameter and level to 0.3 degrees. The dome ring was then attached to the pad with 24 half-inch lag screws and lag shield anchors. Next, two pairs of dome roof quarters were bolted together. Then, those two halves were attached to the dome support ring with the three shutter pieces in between (Appendix B, Figure 3). A metal bar was machined and installed vertically from the concrete pad to the dome wall next to the door in order to reduce deformation when the door is opened.

To automate the shutter, cables were strung along the edge of the shutter, attached to the motor in the back, and tensioned with shutter clamps. The shutter is a three-piece interlocking system that opens from one side, resulting in a 2-foot window from the southern horizon to 70 degrees above the northern horizon. Shutter testing was performed with the hand paddle that is wired directly to the control board in the dome and with the homing switch on the outside of the dome. Afterwards, the dome was paired with the telescope mount through TheSkyX Professional Edition to match the shutter opening with the telescope pointing location.

Once the dome was operational and fully sealed off from the weather, the telescope components were installed. First, the Paramount ME II was bolted to the steel pier and leveled using the microlevelers at the base of the mount. The mount is level to within 0.1 degrees. Afterward, all of the other instrumentation (listed in Section 2.2) were installed in the dome. Finally, a wooden platform was built around the base of the telescope mount, power cables were threaded through the mount, and exterior cables were bundled together.

Afterward, data were collected to test and calibrate the system as a robotic telescope. At the same time, dome movement and telescope pairing troubleshooting were performed. Finally, CCDAutoPilot was installed to communicate between the weather system and telescope system; to control dome and telescope movement; and to automate the observations.

2.4.1. Weatherproofing the Dome

2.4.2. Dome Rotation

2.4.3. Dome Home Sensor

To demonstrate the scientific capabilities of SAURON, eight nights of data were collected on T-And0-15785, an eclipsing binary star, from 2015 January to March. T-And0-15785 has a baseline R magnitude of 13.380, a period of 0.7311466 days, and is located at 01 03 13.82 RA and +47 59 46.6 DEC in the constellation Andromeda (Devor et al. 2008). The Simbad identifier for T-And0-15785 is UCAC2 47685084 (S. A. D. Center). Additional measurements of T-And0-15785 were taken using a robotic 14-inch telescope at WAO over 2014 September and October. A summary of all observations can be found in Table 1.

To produce astronomical light curves, the data were first reduced using AstroImageJ, with flat, dark, and bias images. Then photometry was performed on the reduced data to find the apparent magnitude of T-And0-15785 using field stars from the USNO-A2.0 Catalogue et al. (Monet 1998).

The data were folded over the rotational period of 0.7311466 (Devor et al. 2008) to result in a light curve (Figure 1). Data from January 7 and 10 were not included in the plot due to the repeated breaks in the data collection  to troubleshoot problems with the camera shutter and the dome movement. The baseline was found to be 13.3258 ± 0.0015 R mag by finding the average value of the data taken on 2014 September 19, September 26, and October 8. These data were used because they contained baseline data, had the lowest scatter, and were all observed using the R filter. The unfiltered data were then shifted to fit the baseline. Shifts are summarized in Table 2.

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The Lorentzian fit was found for the primary eclipse using the data from 2015 February 3 and 2015 March 19. The complete fit assumed a symmetric eclipse. The delta magnitude for the primary eclipse is 0.7145 ± 0.0515 R mag over 0.25 ± 0.01 days. The Lorentzian fit was found for the secondary eclipse using the data for 2015 January 19 and 22, and 2014 October 8. The delta magnitude for the secondary eclipse is 0.6085 ± 0.0165 R mag over 0.254 ± 0.005 days. These values are consistent with Devor et al. (2008), who reports the delta magnitude for the primary and secondary eclipses as 0.703 and 0.632 mag respectively (Devor et al. 2008). Finally, we find the epoch for the primary and secondary eclipses to be 2457101.5296 ± 0.0053 and 2457042.6366 ± 0.0009 days, respectively.