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.

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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 binary SNII mag (yrs) flare 1-6 mag (<hr) K-M WD: SNI -20mag (yrs) N -10mag (1000s yrs)‏ DN mag (weeks)‏ NL - erratic Symbiotic: 3mag (erratic)‏ XRB: HMXRB, LMXRB  -ray Bursters RS CVn: F,G+KIV, spots Pulsating: short P long P odd Cepheids: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, 1-5mag S-R: K, M ß Ceph: B, 0.5d ZZ Ceti: WD, min

Binary Evolution: Roche equipotential surfaces r c /A = log q [0.3 < q < 2] r c /A = 0.46 (M 1 /M 2 + M 1 ) 1/3 [0<q<0.3]

Massive X-ray Binaries (MXRBs)‏ Name P (days) Sp q M x Vela X-1 9 B0Ia Cen X O7III 17 1 Cyg X O9.7I 3 6 Low Mass X-ray Binaries (LMXRBs)‏ Name P(hrs) Sec M x WD Cyg X IR Her X B-F 1

E >10 51 ergs 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 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 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 Cepheids: F-G SG, P-L relation, HeII ionization zone pulsation mechanism RR Lyrae: A giants, M v = 0.5, P<1 day

P-L relation 1) measure m v with CCD 2) find P from light curve 3) use P-L to get M v 4) m-M d

Two flavors of ZZ Ceti stars (DAVs)‏ T eff = 11000K P ~ 1000s T eff = 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 ~ 10 7 K, radio is non-thermal Between flares, spectrum is K-M with CaII, H emission