binary and variable stars. students learn to: describe binary stars in terms of means of detection:...
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Binary and variable stars
Binary and variable starsStudents learn to:
• describe binary stars in terms of means of detection:
visual,eclipsing, spectroscopic and astrometric
visual binariesBoth stars are visible through a telescope.
The orbital positions can be seen and measured through powerful telescopes
Astrometric BinariesOnly 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.
Spectroscopic BinariesTwo 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
Eclipsing BinariesThe stars appear as a single star through a telescope.
The light curve reveals a periodic variation in the brightness.....
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Binary and variable starsStudents:
• perform an investigation to model the light curves
of eclipsing binaries using computer simulation
Binary and variable stars• explain the importance of binary
stars in determining stellar
masses
Binary and variable stars
• solve problems and analyse
information by applying:
m + m = 4 π r2 3
G T
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Units for each term above:
masses of stars - kg,
radius of orbit - m,
period of orbit - years.
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
Binary and variable stars• explain the importance of the
period-luminosity relationship for
distance determination for cepheids
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Line 1Absolute
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