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Variable Stars
clues: timescale,
amplitude, light curve shape, spectrum
Eclipsing: Algol
B8-M
ß Lyr
W UMa
(hrs-days) B8-G3
Eruptive: single
binary
SNII 15-20 mag (yrs)
flare 1-6 mag (<hr) K-M
Pulsating: short P
Cepheids:F-K, 1-50d, 1.5mag
RR Lyr: A-F, 0.5 day, 1 mag
 Scuti: A-F, hrs, 0.02 mag
F0-K0 (hrs)
WD: SNI -20mag (yrs)
N -10mag (1000s yrs)
DN - 2-7 mag (weeks)
NL - erratic
Symbiotic: 3mag (erratic)
XRB: HMXRB, LMXRB
-ray Bursters
RS CVn: F,G+KIV, spots
long P
Mira:M, yrs, 1-5mag
S-R: K, M
odd
ß Ceph: B, 0.5d
ZZ Ceti: WD, min
Binary Evolution: Roche equipotential surfaces
rc /A = 0.38 + 0.2 log q [0.3 < q < 2]
rc /A = 0.46 (M1/M2 + M1)1/3 [0<q<0.3]
Massive X-ray Binaries (MXRBs)
Name
P (days)
Vela X-1
9
Cen X-3
2.1
Cyg X-1
5.6
Sp
q
B0Ia 12
O7III 17
O9.7I 3
Mx
1.9
1
6
Low Mass X-ray Binaries (LMXRBs)
Name
1626-67
P(hrs)
0.7
Sec
Mx
WD
Cyg X-3 4.8
IR
Her X-1 40.8
B-F
1
long
E >1051ergs
short
20M + 8M P=5 days
t = 1 million yrs
transfers 15M in 30,000yrs
5M + 23M P=11 days
P= 13 days t=10 million yrs
X-ray binary for 10,000 yrs
P = 4 hrs
Cataclysmic Variables
white dwarf primary with a low mass (G-M) secondary,
orbital periods of 67 min-2 days
Nova: TNR, high mass WD, outbursts
8-15 mag every few thousand yrs
Dwarf nova: disk instability, outbursts
2-7 mag every week-30 yrs
Novalike: high, low states on
timescales of months, high accretion
AM CVn: 2 white dwarfs, orbital
periods of 10-45 min
Asteroseismology
• Pulsations 
Only systematic
way to study
the stellar
interior
• Pulsations are
observed in stars
all over the HR
diagram
ZZ Ceti stars
Pulsations in a star
Pulsation period and amplitude depend on
the average density. P  -1/2
Low density
long P, high amplitude
High density
short P, low amplitude
Density profile decides how deep the pulsations penetrate in the star.
(Deeper the penetration
more we learn about the interior)
Centrally condensed stars like our Sun have shallow pulsations
Uniform density stars like white dwarfs have deep pulsations
Cepheids and RR Lyrae
RR Lyrae: A giants, Mv = 0.5, P<1 day
Cepheids: F-G SG, P-L relation, HeII
ionization zone pulsation mechanism
P-L relation
1) measure mv with CCD
2) find P from light curve
3) use P-L to get Mv
4) m-M
d
Two flavors of ZZ Ceti stars (DAVs)
cool
Teff = 11000K
P ~ 1000s
Larger amp,
more modes,
unstable amps
hot
Teff = 12000K
P ~ 200s
Less modes,
more stability
Flare Stars
Flare <15s to 1 hr, repeats hrs - days
Amplitude up to 4 mag
Opt is thermal brem at T ~ 107K, radio is non-thermal
Between flares, spectrum is K-M with CaII, H emission