PDS 110 Type: Eclipsing binary/T Tauri AAVSO lightcurve (2020 ) AAVSO lightcurve (index) Eclipsing binary systems are binary systems with orbital planes so close to the observer's line of sight (the inclination of the orbital plane to the plane orthogonal to the line of sight is close to 90 deg.) that the components periodically eclipse each other. Consequently, the observer finds changes of the apparent combined brightness of the system with the period coincident with that of the components' orbital motion. T Tauri Stars: when their properties are well- known, they are classified in two sub- groups, CTTS (Classical) and WTTS (Weak-lined). AAVSO Alert 584: 21 June 2017 Dr. Joey Rodriguez (Harvard-Smithsonian Center for Astrophysics), Dr. Hugh Osborn (University of Warwick), Dr. Matthew Kenworthy (Leiden Observatory), and colleagues have requested AAVSO assistance in monitoring PDS 110 (HD 290380), a very interesting young star that may have a large orbiting body with an extremely large ring system (on the order of 200 times wider than that of Saturn). An eclipse of PDS 110 is expected in mid-September 2017, and monitoring is requested through October. PDS 110, a member of the Ori OB1a association, was observed with the SuperWASP and KELT surveys. Photometric monitoring is requested beginning as soon as PDS 100 becomes visible this August and continuing through October 2017. One to two observations per night (and per band if multicolor) are sufficient until the eclipse begins. Time series observations should be obtained throughout the eclipse, which is expected to last about two weeks. After the eclipse, nightly observations should be resumed and continued for three to four weeks, until the end of October (or later if necessary). The eclipse has been predicted for mid-September, with an uncertainty of ~ seven to ten days, thus the long monitoring window. The depth of the eclipse is expected to be about 30%. BVRI (or SDSS u’,g’,r’,i’,z’) photometry is preferred, although all bandpasses are welcome. Visual observations are also welcome. Support spectroscopy is not requested at this time. If it is needed at a later date, observers will be notified. Observations should be reported to the AAVSO via WebObs as soon as practical. When the eclipse onset is detected, please inform the AAVSO immediately via email and/or a posting to the relevant discussion thread (see below), and submit your observations as soon as possible. This immediate reporting will allow the astronomers to trigger additional resources to observe PDS 110. Dr. Rodriguez writes: "The multi-band observations requested here will provide high- cadence precise photometric observations of the potential sub-stellar ringed companion. The observations will be crucial in our follow-up analysis since they will 1) allow us to re- model the system with 3 eclipses, improving our parameters and allowing us to look for changes in the occulting body’s size and opacity. 2) The multi-band observations provide information on the grain size and distribution in the surrounding ring system. 3) Continuous monitoring of PDS 110 by the AAVSO can trigger the community when PDS 110 begins to eclipse. This trigger will allow us to increase the cadence of additional observations to support the AAVSO data."