Transcript Unit 6

DEPARTMENT OF PHYSICS AND ASTRONOMY
LIFECYCLES OF STARS
Option 2601
M.A.Burleigh 2601/Unit 6
Stellar Physics
 Unit 1 - Observational properties of
stars
 Unit 2 - Stellar Spectra
 Unit 3 - The Sun
 Unit 4 - Stellar Structure
 Unit 5 - Stellar Evolution
 Unit 6 - Stars of particular interest
M.R. Burleigh 2601/Unit 6
DEPARTMENT OF PHYSICS AND ASTRONOMY
Unit 6
Particularly Interesting Stars
M.A.Burleigh 2601/Unit 6
Particularly Interesting Stars
 Binaries – visual, spectroscopic,
eclipsing
 Variable stars
 Active/interacting binaries (Novae)
 Stellar pulsations
 Cepheid variables and the distance
scale
M.R. Burleigh 2601/Unit 6
Types of binary system
Apparent
Visual
Astrometric
Spectroscopic
Stars not physically associated but lie
close together along the line of sight
Stars can be resolved
Only one star visible but its motion on
the sky reveals an unseen companion
Unresolved system, see periodic
shifts/broadening of spectral lines
Spectrum
No movement of spectral features but
two different spectral signatures
visible
Eclipsing
Brightness changes as one star
passes in front of the other
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Spectroscopic Binaries
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Eclipsing Binaries
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Eclipsing Binaries
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Information from Binary Systems
 Masses of components
 Dimensions of components (particularly
in eclipsing systems)
 Physical characteristics of systems
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(Other) Variable Stars
 Intrinsic variables… i.e. pulsating stars
 Geometric (extrinsic) variables… i.e.
eclipsing systems
 Naming variables… constellation &
letters beginning with R
– R…. To Z, then RR…. To ZZ (i.e. R CrB)
– Then Vijk constellation (i.e. V471 Tau)
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Accretion in Binaries
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Novae
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Novae
 Brightness increases by 10 magnitudes
during outburst
 Rise time 2-3 days
 Gradual decline over months (fast
novae) or years (slow novae)
 Material ejected with velocities up to
~2000km s-1
 Explosions can repeat (recurrent novae)
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Nova Cassiopeiae 1993 light curve (first 3 months)
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Nova Cassiopeiae 1993 light curve (first 2½ years)
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Nova Cassiopeiae
1995 light curve
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M.R. Burleigh 2601/Unit 6
Pulsating Stars
 Pulsating stars are not in hydrostatic
equilibrium
 Star is partially ionized at some critical
depth
 Degree of ionization sensitive to small
temperature changes
 Small perturbation can be “amplified”
M.R. Burleigh 2601/Unit 6
Cycle of a
pulsating star
C
O
M
P
R
E
S
S
I
O
N
Max.
compression
rate
Gravity
(restoring
force)
MAX. COMPRESSION
Max. opacity &
ionisation, min.
photon flux
Phase
Min. opacity &
ionisation, max.
photon flux
MAX. EXPANSION
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Pressure
driving
Max.
expansion
rate
E
X
P
A
N
S
I
O
N
Type
Prototype
MV
Spectral
class
Pulsation
period
range
Characteris
tic period
Population
Classical
Cepheids
 Cephei
-0.5 to –6
F6 to K2
1d to 50d
5d to 10d
I
Population
II Cepheids
(W Virginis)
W Virginis
0 to –3
F2 to G6
2d to 45d
12d to 28d
II
RR Lyrae
stars
RR Lyrae
0.5 to 1
A2 to F6
1.5h to 24h
0.5d
II
Long-period
variables
(Mira)
 Ceti
1 to –2
M1 to M6
130d to 500d
270d
Disk
RV Tauri
stars
RV Tauri
-3
G, K
20d to 150d
75d
II
Beta Canis
Majoris
stars
 Canis
Majoris
-3
B1, B2
4h to 6h
5h
I
Semiregular
red
variables
 Herculis
-1 to –3
K, M, R, N,
S
100d to 200d
100d
I and II
Dwarf
Cepheids
 Scuti
4 to 2
A to F
1h to 3h
2h
I
M.R. Burleigh 2601/Unit 6
H-R diagram for pulsating stars
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Cepheid Variables
Typical Cepheid light curve
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Cepheid Variables
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Cepheid Variables
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The periodluminosity
relation for
Cepheids
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Redshift
 Edwin Hubble discovers galaxies are
receding from us (c. 1930)
 Hubbles Law - speed increases with
distance
 Expansion of the Universe - Big Bang
theory
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Cepheids in M100
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Beyond M100
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DEPARTMENT OF PHYSICS AND ASTRONOMY
Unit 6
Particularly Interesting Stars
M.A.Burleigh 2601/Unit 6
Particularly Interesting Stars
 Binaries – visual, spectroscopic,
eclipsing
 Variable stars
 Active/interacting binaries
 Stellar pulsations
 Cepheid variables and the distance
scale
M.R. Burleigh 2601/Unit 6
Stellar Physics
 Unit 1 - Observational properties of
stars
 Unit 2 - Stellar Spectra
 Unit 3 - The Sun
 Unit 4 - Stellar Structure
 Unit 5 - Stellar Evolution
 Unit 6 - Stars of particular interest
M.R. Burleigh 2601/Unit 6
DEPARTMENT OF PHYSICS AND ASTRONOMY
LIFECYCLES OF STARS
Option 2601
M.A.Burleigh 2601/Unit 6