Variable Stars clues: timescale, amplitude, light curve shape, spectrum

Eclipsing: Algol ß Lyr W UMa B8-M (hrs-days) B8-G3 F0-K0 (hrs)

Eruptive: single binarySNII 15-20 mag (yrs) flare 1-6 mag (<hr) K-M

WD: SNI -20mag (yrs) N -10mag (1000s yrs) DN - 2-7 mag (weeks) NL - erraticSymbiotic: 3mag (erratic)XRB: HMXRB, LMXRB-ray BurstersRS CVn: F,G+KIV, spots

Pulsating: short P long P oddCepheids:F-K, 1-50d, 1.5mag

RR Lyr: A-F, 0.5 day, 1 mag

Scuti: A-F, hrs, 0.02 mag

Mira:M, yrs, 1-5magS-R: K, M

ß Ceph: B, 0.5dZZ Ceti: WD, min

Binary Evolution: Roche equipotential surfacesrc /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) Sp q Mx

Vela X-1 9 B0Ia 12 1.9

Cen X-3 2.1 O7III 17 1

Cyg X-1 5.6 O9.7I 3 6

Low Mass X-ray Binaries (LMXRBs)

Name P(hrs) Sec Mx

1626-67 0.7 WD

Cyg X-3 4.8 IR

Her X-1 40.8 B-F 1

E >1051ergs

long

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 Variableswhite 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 onthe average density. P -1/2

Low density long P, high amplitudeHigh 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

Cepheids: F-G SG, P-L relation, HeII ionization zone pulsation mechanism

RR Lyrae: A giants, Mv = 0.5, P<1 day

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)

Teff = 11000K P ~ 1000s

Teff = 12000K P ~ 200s

cool

Larger amp, more modes, unstable amps

hot

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