1. Binary and variable stars

2. Students learn to: describe binary stars in terms of means of detection: visual,eclipsing, spectroscopic and astrometric

3. visual binaries Both stars are visible through a telescope. The orbital positions can be seen and measured through powerful telescopes

4. Astrometric Binaries Only the brightest star of the pair can be seen.. Measurement of the star’s changing position reveals the centre of mass of the system and the presence of the other star.

5. Spectroscopic Binaries Two sets of spectral lines representing two different spectral classes can be seen, but the stars cannot be distinguished through a telescope. During the orbit, one set of spectral lines is red shifted during recession while at the same time the other set is blue shifted because it is approaching

6. Eclipsing Binaries The stars appear as a single star through a telescope. The light curve reveals a periodic variation in the brightness.....

7. Binary and variable stars Students: perform an investigation to model the light curves of eclipsing binaries using computer simulation

8. Binary and variable stars explain the importance of binary stars in determining stellar masses

9. Binary and variable stars solve problems and analyse information by applying: m + m = 4 π r 23 G T 12 2 Units for each term above: masses of stars - kg, radius of orbit - m, period of orbit - years.

10. Binary and variable stars classify variable stars as either intrinsic or extrinsic and periodic or non-periodic Stars with regular variations in brightness are periodic variables Stars with irregular variations in brightness (e.g flickering, rapid flaring) are non- periodic variables VARIATIONS WHICH ARE DUE TO INTERNAL CAUSES AND ASSOCIATED WITH THE SURFACE ARE INTRINSIC VARIABLES VARIATIONS WHICH ARE DUE TO EXTERNAL CAUSES SUCH AS A BINARY PARTNER POURING MATERIAL ONTO IT ARE EXTRINSIC VARIABLES

11. Binary and variable stars explain the importance of the period-luminosity relationship for distance determination for cepheids Absolute Magnitude Period (Days) If we know the period of variation of a Cepheid and the apparent magnitude (m), we can use the graph and M = m - 5 log (d/10) to work out the distance to the star