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Calculating Escape Velocities: Analysis of Double Star Systems with Gaia Data Released 2

This study explores calculating escape velocities on 75,000 double star systems using Gaia Data Release 2. Examining the Washington Double Star catalogue, the research confirms orbits, finds mass, and distinguishes binaries from optical doubles. Utilizing parallax, proper motion, and radial velocity data, the study determines relative motion and escape velocities. By comparing results with Richard Harshaw’s data, the analysis reveals a nuanced range of Z-factors identifying binary and optical double stars. The study discusses implications for future research, including potential evolution of binaries and refining stellar mass formulas.

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Calculating Escape Velocities: Analysis of Double Star Systems with Gaia Data Released 2

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  1. Calculating Escape Velocities on 75,000 Double Star Systems Using Gaia Data Release 2 By Tol Wassman, Zachary Haarz, Morgan Watts, Jake North, and Kalée Tock

  2. Double Stars • Close together • Confirm orbits & find mass • Washington Double Star catalogue (WDS) tracks these stars • Gaia improves our ability to tell binaries from optical doubles

  3. Binary Stars • Same distance from Earth: parallax (Plx) • Moving together in space: Proper Motion (PM), radial velocity (RV) • Relative motion less than escape velocity (vesc)

  4. Richard Harshaw’s Data • Previous paper, also using Gaia data • Used parallax data, relative radial velocity, fit to R^2, and proper motion • Many stars did not have Gaia data • Created a spreadsheet with the scores

  5. Matching WDS and Gaia • Query Gaia around WDS coordinates • Guess and check: • Magnitude within 2 • PA within 3o • Sep within 1’’ • Algorithm: • Closer to WDS, better • Also PM, Dist to precise search coordinates wherever possible • Ideally obtain PMs, RVs, Lum/Mag, and Plxs

  6. Separation

  7. Velocities • Escape velocity needs mass, which needs luminosity, sometimes needs mag and plx • R is pythagorean theorem with tangential and radial separation • Relative velocity needs speeds which need Plx, PM, and RV

  8. Z factor • Z = Escape velocity/relative velocity • Z > 1.5 will be binary, Z < 0.5 will be optical • Simple range of 1.5 to 0.5 is nuanced range - looks best as Z - 0.5

  9. Results • Harshaw sorts stars without parallax, Z-Factor ignores them • 68.5% optical doubles using Z-factor, and 16% using Harshaw’s method • Large difference in stars considered physical, considering omissions

  10. Notes For Future Research • Small percent in between, binaries grow harsher over time? • Use orbital state vectors to determine theoretical orbits for binaries • Identify a more general stellar mass formula or refine the current one

  11. Categories

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