Vol. 16 No. 2 April 1, 2020 Page 173 Journal of Double Star Observations Introduction Targets for this study were selected and imaged by the course TA, Ryan Caputo. The targets have compo- nent stars of similar brightness (delta magnitude < 3) and separations of approximately 10". These criteria ensure that the stars can be resolved easily and meas- ured unambiguously. Moreover, the targets all have similar parallax and proper motions (PMs). The simi- larity of the component PMs is assessed by taking the ratio of the magnitude of the proper motion difference vector to the magnitude of the longer proper motion vector between the two component stars. This ratio is called the rPM, and double star systems are considered to have common proper motion if its value is smaller than 0.2 (Harshaw, 2016). According to this criterion, all of the systems in Table 1 have common proper mo- tion. Two of them also have orbital solutions in the Washington Double Star Catalog. As is evident from Table 1, STF1050AB and STF1124AB have parallaxes below 5 milliarcseconds (mas), which causes the fractional parallax uncertainty for these systems to be relatively high. This leads to a large uncertainty in the distances of these systems, where distance is calculated by inverting the parallax. In general, parallax measurements below 5 mas must be treated with caution, as such low values approach the limits of the instrument’s sensitivity, and some of the systematic errors associated with Gaia DR2 instrumen- tation are not fully understood (Luri et. al., 2018). Instruments Used For 13 of the 14 systems, images were obtained using a 6-inch aperture classical Cassegrain telescope. The methodology is as described in Caputo 2019. There were no filters used. The camera and telescope combination yields a pixel scale of approximately 0.4“ per pixel, giving excellent sampling for seeing-limited measurements. Guiding was employed for longer expo- sures to improve tracking accuracy. The remaining system, STF1547AB, was imaged using the Las Cum- bres Observatory 0.4m robotic telescope. Measurements The position angle and separation of each system was measured using AstroImageJ. The measurements are shown in Table 2. Current measurements in the context of previous measurements Previous measurements for each system were re- quested from the US Naval Observatory. These data are plotted along with the measurements above for each system in Figure 1. Outlying data points more than 3 (Text continues on page 175) Observation and Investigation of 14 Wide Common Proper Motion Doubles in the Washington Double Star Catalog Ryan Caputo, Brandon Bonifacio, Sahana Datar, Sebastian Dehnadi, Lian E, Talia Green, Krithi Koodli, Elias Koubaa, Calla Marchetti, Sujay Nair, Greta Olson, Quinn Perian, Gurmehar Singh, Cindy Wang, Paige Yeung, Peyton Robertson, Elliott Chalcraft, Kalée Tock Stanford Online High School, Stanford, California Abstract: As a class-wide introduction to double star research, we investigated and meas- ured 14 physical systems with separations between 6" and 20" from the Washington Double Star Catalog. Between 8 and 12 images of each system were reduced using AstroImageJ to extract position angles and separations that are current for 2020.0. The resulting measure- ments are reported here and are plotted along with each system’s historical data. Along with these plots, each system’s measurements in Gaia Data Release 2 were analyzed to assess the probability that the two stars in the system might have a gravitational relationship.