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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
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, ~20/yr in MW
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
Disk
Intermediate Polar
Polar
MAGNETIC
ACCRETION
DISK ACCRETION
.
= 1/2GMM
For slowly rotating WD:
Ldisk = LBL
.
High M
wd/Rwd
.
Low M
108 K
X-rays
9000-40000 K
BL
Hard X-rays
Soft X-rays
Cyclotron
-WD accretes until thick degenerate envelope leads to TNR
-10-6 to 10-4 solar masses ejected (dust can form)
-Envelope returns to quasi-static equil (nuclear burning)
-Envelopoe gradually ejected by winds, phot recedes, T
increases and peak radiaiton in soft X-ray
-Constant bol phase lasts until envelope exhausted (1-100 yrs)
Typical DN
Outburst cycle
of the Dwarf
Nova SS Cyg
Cannizzo &
Mattei, 1998,
ApJ 505, 344
Outbursts
are DISK
instabilities
Typical CV
spectra in
DR1
CVs in EDR in
Szkody et al.
2002, AJ, 123,
430
Symbiotic stars
Late type RG +
WD +
high excitation
emission lines
Possible
progenitors of
Type Ia SN?
RS CVn star (convection +
high rotation gives spots)
K0III
Pulsating stars:
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 [P=(4π/3G)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
Radial pulsators
RR Lyrae: A giants, Mv = 0.5, P<1 day
Cepheids: F-G SG, P-L relation, P ~ 2-60 days,
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
•
White dwarfs show non-radial g-modes on account of their high gravity
Periods of 100s to 1000s
•
These modes are characterized by quantum numbers (k,l,m)
similar to atomic orbitals
Spherical gravitational potential  Spherical electrostatic potential
l determines the number of borders between hot and cool zones on the surface
m is the number of borders that pass through the pole of the rotation axis
k determines the number of times the pulsation wiggles from the center to the surface
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
Mira - pulsating RG
Period ~ 11 months
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
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
Supernovae
X-ray Binaries
CVs
Morford,
Ortez
Chadney/Fowler
Kong
Campion
Smith
Stevens
Markert
Slinker
Sheets
Green
Belleci
Vos
Timpe
Jennings
Filbrandt
Magnuson
Pulsators
Flares
Others
Mayorga
Hua
Evans
Draper
Jewell
Hansen