Tangential velocity is the component of the Star’s velocity perpendicular to our line of
V = 4t74 x 10 U d
Where V is intm/s.
d is in pc.
U is in arcsec per year (“/year).
Space Velocity (V ) is tse actual velocity of the star in space.
Earth--------------V ----s-d--------V t
Star V r
2 2 1/2
V = (s + v r t
Distance/Velocity Problem: SIMILAR PROBLEMS ON TEST
Question: A nearby White Dwarf has a parallax angle of 0.232 arcsec ( =0.232”). Its proper
motion is 2.95 arcsec/year (=2.95”/year) and its radial velocity is 54 km/s. What is the objects
actual speed in space (in km/s)?
V = (s + v r , wetneed V t
V = 4t74 x 10 Ud, we need d
d = 1 = 1 = 4.31 pc
V = 4.74 x 10 Ud 3
V = 4t74 x 10 (2.95) (4.31) = 60.3 x 10 m/s = 60.3 km/s.
2 2 1/2
V = (s + V )r t
V = (s4 + 60.3 ) 2 1/2
V = 8s.9 km/s ~ 81 km/s.
Death of Stars:
Stars die in several different ways.
The manner of death is determined by the star’s mass.
Death of Lightweight Stars: REMEMBER FOR THE TEST WE NEED 10 MILLION K
IN THE CORE
These are < ~ 4 M o. These are normal stars…95% of stars are in this category.
1) Core runs low on Hydrogen fuel.
Star’s leaves Main Sequence (=Hydrogen fusion) phase.
2) Core contracts and at 100 x 10 k, Star fuses Helium (3 (Alpha) = C) in core.
3) Star runs low on Helium fuel in core which now consists of …
4) Mainly Carbon and some Oxygen.
5) Gravity causes outer layers to collapse onto carbon core, squashing it and raising the
6) Core temperature never becomes high enough to initiate carob-based nuclear fusion
7) Computer simulations = energy is released by gently blowing off the star’s outer
layers at ~25 km/s.
Planetary Nebula: REMEMBER FOR TEST
No more nuclear reactions in the core of star.
Stars dies with a compressed Carbon (Some Oxygen) Core.
Planetary Nebula = dying/dead star remnant surround by a shell of ejected gases.
The central remnant core= White Dwarf…small, very hot, plots on the lower left of the
Typical White Dwarf:
Mass ~0.8 M = 1o o.
Mass limit is 1.4 M ; the Chandrasekhar Limit.
Size~same size as Earth.
Density ~ 10 kg/cm . 3
Magnitude = M ~ + 11 (very dim).
Temperature ~15000 k on surface.
No longer has a central energy source.
We can detect ~500 White Dwarfs = our MW (Milky Way) galaxy must contain billions
Death of Middleweight Stars:
These are ~8 M = ~o20M o.
< ~ 5% of stars are > ~4M
1) Star undergoes several Red Giant phases, producing ever-heavier elements in the core.
Evolutionary Stages of a massive Star (~25 M ): o