In some cases even when a parameter cannot be fully determined, a probability distribution of its values can be, which has value in studies of entire populations. For example, if the the viewing angle of a binary system's orbit is undetermined, the distribution of viewing angles is known so data from a population of such binary systems still reveals information about the distribution of parameters that the viewing angle would have revealed. The most direct methods: - Parallax - triangulation to measure the distance to nearby stars.
- Astrometry - to measure the radius of nearby giants.
- Spectroscopy - Effective Temperature (T
_{eff}) (Black-Body Radiation) curve and qualitative indication of their makeup.
Less direct methods: - Luminosity (L) is Apparent Magnitude (m) "times" distance (with any two, you have the third).
- luminosity, radius and temperature are related (with any two, you have the third).
- H-R Diagram (HRD) and spectrum shows temperature, and approximate radius, mass, and luminosity.
- Photometry gives an approximate temperature, which relates radius to luminosity.
Binary Stars observed over time reveal much: - Visual Binary - allows the orbital period to be determined.
- Visual Binary and astrometry give the orbit size if the distance is known.
- Spectroscopic Binary - shows the orbital period and ratio of masses.
- Double-Line Spectroscopic Binary - reveals the ratio of orbital velocities.
- Eclipsing Binary reveals viewing angle.
- Orbital velocity over time reveals the orbit size.
- Ratio of orbital velocities reveals ratio of masses.
- Ratio of orbital velocities and viewing angle reveals actual orbital velocities.
- Orbital size and period determine sum of masses (with any two, you have the third).
- Period and distance determine orbital size (with any two, you have the third).
- Eclipsing binary reveals individual spectra.
See Stellar Distance Determination, Stellar Mass Determination, Stellar Radius Determination, Stellar Luminosity Determination, Stellar Temperature Determination, Stellar Age Determination, Stellar Rotation, and Gyrochronology. stars,astrophysics)Referenced by:
ATLAS Stellar Model Binary Star Mass-Radius Relation |