1. Variable stars and binaries
Mr.Sroka
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2. About Variable Stars
Variable stars are stars that vary in apparent brightness over a period of time.
There are 2 types of variable stars: intrinsic and extrinsic.
Intrinsic: lumunosity actually changes (ex: pulsating stars, big sun spots)
Extrinsic: lumonisity appears to change (ex: binaries)

3. (some) Categories of Variables
Cepheid
RR Lyrae
T Tauri
Explosive variables (supernova, novea)
Eclipsing binaries
Rotating stars

4. Cepheid Varibles
Cepheids – Cepheid variables pulsate with periods from 1 to 70 days,
with light variations from 0.1 to 2 magnitudes.
These massive stars have high luminosity and are of F spectral class at maximum, and G to K at minimum

5. RR Lyrae RR Lyrae stars – These are short-period (.05 to 1.2 days).
white giant stars, usually of spectral class A.
They are older and less massive than Cepheids

6. RV Tauri stars
RV Tauri stars – These are yellow supergiants having a characteristic light variation
Their periods, defined as the interval between two deep minima, range from 30 to 150 days

7. Explosive variable
Supernovae – These massive stars show sudden, dramatic, and final magnitude
increases of 20 magnitudes or more, as a result of a catastrophic stellar explosion.
There are also binary star systems when they start to combine together creating variations in energy.

8. Extrinsic variables Changes in brightness are apparent Two types
Eclipsing binaries (what we’ll deal with today)
Rotating stars
Eclipsing binary
Changes in brightness caused from eclipses of two stars as they orbit each other
We have been talking a lot about intrinsic variables.The other class of variable stars is extrinsic. This is where the brightness is only apparent. There are two types: eclipsing binaries and rotating stars. In this lab, we’ll be dealing with eclipsing binaries.
An eclipsing binary is a star whose brightness changes from eclipses of two stars as they orbit each other.

9. Primary eclipse happens when hottest star goes behind
This shows a diagram of an eclipsing binary.
You will have two eclipses, one when the higher mass star passes behind the lower mass star, and vice versa. The higher mass star is hotter and therefore brighter. So when do you lose the most light? When the high mass star is behind the low mass. We call this the primary eclipse.
It seems counterintuitive that the higher mass star is smaller, but : Low mass star is larger because less gravity to hold it together, high mass star is brighter
OK, so we can see that the change in brightness is from an eclipse. This going to be a sharp change in brightness.
So what will our light curve look like? - two sharp dips at different light levels.
Primary eclipse happens when hottest star goes behind
Note: a higher mass star is smaller in size

10. Extrinsic Pulsar
Pulsars are rotating neutron stars —that emit electromagnetic radiation that is only seen when the beam is pointing at Earth.
Pulsars produce precise, measurable intervals of light, and are often compared to lighthouses as they periodically sweep beams of energy while they orbit. 

11. Quasars