Measuring stellar masses We measure mass using gravity. Direct mass - PowerPoint PPT Presentation

Measuring stellar masses

We measure mass using gravity. Direct mass measurements are possible only for stars in binary star systems. 4 π 2 P 2 = a 3 G ( M 1 + M 2 ) P = orbital period a = orbital semimajor axis

Need 2 out of 3 observables to measure mass: 1) Orbital Period ( T ) 2) Orbital Separation ( a or r = radius of circular orbit) v 3) Orbital Velocity ( v ) r M For circular orbits, v = 2 p r / T

Visual Binary We can directly observe the orbital motions of these stars. = r = a 2 = m 1 α 1 2 r a 1 m 2 α 2 1

Spectroscopic Binary We determine the orbit by measuring Doppler shifts.

Spectroscopic Binary: Circular Orbits

Spectroscopic Binary: Elliptical Orbits

Most massive stars: ~100 M Sun Least massive (hydrogen- burning) stars: 0.08 M Sun

First exoplanet detected around a Sun-like star, discovered independently in 1995 by Mayor & Queloz (Switzerland) and Marcy & Butler (San Francisco State U.)

Eclipsing Binary We can measure periodic eclipses.

Eclipsing Binaries— Light Curves Partial eclipses Total eclipses

Orbit Models Fit to Light Curves of Eclipsing Binaries Credit: P. Zasche, Astronomical Institute, Prague, Czech Republic

Exoplanet Detections as of December 2011 Wright & Gaudi (2012)

3,529 confirmed exoplanets as of October 5, 2017 https://exoplanetarchive.ipac.caltech.edu