The Lower Main Sequence UV Ceti Stars –M dwarf flare stars –About half of M dwarfs are flare stars (and a few K dwarfs, too) –A flare star brightens by a few tenths up to a magnitude in V (more in the UV) in a few seconds, returning to its normal luminosity within a few hours –Flare temperatures may be a million degrees or more –Some are spotted (BY Dra variables) –Emission line spectra, chromospheres and coronae; x-ray sources –Younger=more active –Activity related to magnetic fields (dynamos) –But, even stars later than M3 (fully convective) are active – where does the magnetic field come from in a fully convective star? –These fully convective stars have higher rotation rates (no magnetic braking?)

Solar Type Stars Pulsators –The delta Scuti stars –SX Phe stars Binaries –FK Comae Berenices Stars –RS CVn stars –W UMa stars –Blue Stragglers

Chemically Peculiar Stars of the Upper Main Sequence Ap stars –SrCrEu stars –Silicon Stars –Magnetic fields –Oblique rotators –Slow rotators Am-Fm stars –Ca, Sc deficient –Fe group, heavies enhanced –diffusion HgMn stars The  Boo stars Binaries?

The Upper Main Sequence 100 (or so) solar masses, T~20,000 – 50,000 K Luminosities of 10 6 L Sun Generally cluster in groups (Trapezium, galactic center, eta Carinae, LMC’s R136 cluster) (Some of) The Brightest Stars in the Galaxy StarmVmV MVMV M bol Sp. T.Dist. Pistol Star…… kpc HD 93129A O3If 3.4 kpc Eta Carina B kpc Cyg OB2# B5 Ia + e1.7 kpc Zeta-1 Sco B1.5 Ia kpc

Types of Massive Stars Luminous Blue Variables (LBVs) –Large variations in brightness (9-10 magnitudes) –Mass loss rates ~10 -3 M sun per year, transient rates of M sun per year –Episodes of extreme mass loss with century-length periods of “quiescence” –Stars’ brightness relatively constant but circumstellar material absorbs and blocks starlight –UV absorbed and reradiated in the optical may make the star look brighter –Or dimmer if light reradiated in the IR –Hubble-Sandage variables are also LBVs, more frequent events –Possibly double stars? –Radiation pressure driven mass loss? –Near Eddington Limit?

Wolf-Rayet Stars Luminous, hot supergiants Spectra with emission lines Little or no hydrogen L sun Maybe 1000 in the Milky Way Losing mass at high rates, to M sun per year T from 50,000 to 100,000 K WN stars (nitrogen rich) Some hydrogen (1/3 to 1/10 HE) No carbon or oxygen WC stars (carbon rich) NO hydrogen C/He = 100 x solar or more Also high oxygen Outer hydrogen envelopes stripped by mass loss WN stars show results of the CNO cycle WC stars show results of helium burning Do WN stars turn into WC stars?

Red Giants Miras (long period variables) –Periods of a few x 100 to 1000 days –Amplitudes of several magnitudes in V (less in K near flux maximum) –Periods variable –“diameter” depends greatly on wavelength –Optical max precedes IR max by up to 2 months –Fundamental or first overtone oscillators –Stars not round – image of Mira –Pulsations produce shock waves, heating photosphere, emission lines –Mass loss rates ~ M sun per year, km/sec –Dust, gas cocoons (IRC ) some 10,000 AU in diameter Semi-regular and irregular variables (SRa, SRb, SRc) –Smaller amplitudes –Less regular periods, or no periods

Amplitude of Mira Light Curve

More Red Giants Normal red giants are oxygen rich – TiO dominates the spectrum When carbon dominates, we get carbon stars (old R and N spectral types) Instead of TiO: CN, CH, C 2, CO, CO2 Also s-process elements enhanced (technicium) Double-shell AGB stars

Weirder Red Giants Weirder Red Giants S, SC, CS stars –C/O near unity – drives molecular equilibrium to weird oxides Ba II stars –G, K giants –Carbon rich –S-process elements enhanced –No technicium –All binaries! R stars are warm carbon stars – origin still a mystery –Carbon rich K giants –No s-process enhancements –NOT binaries –Not luminous for AGB double-shell burning RV Tauri Stars

Mass Transfer Binaries The more massive star in a binary evolves to the AGB, becomes a peculiar red giant, and dumps its envelope onto the lower mass companion Ba II stars (strong, mild, dwarf) CH stars (Pop II giant and subgiant) Dwarf carbon stars Nitrogen-rich halo dwarfs Li-depleted Pop II turn-off stars

After the AGB Superwind at the end of the AGB phase strips most of the remaining hydrogen envelope Degenerate carbon-oxygen core, He- and H-burning shells, thin H layer, shrouded in dust from superwind (proto-planetary nebula) Mass loss rate decreases but wind speed increases Hydrogen layer thins further from mass loss and He burning shell Star evolves at constant luminosity (~10 4 L Sun ), shrinking and heating up, until nuclear burning ceases Masses between 0.55 and 1+ solar masses (more massive are brighter) Outflowing winds seen in “P Cygni” profiles Hydrogen abundance low, carbon abundance high (WC stars) If the stars reach T>25,000 before the gas/dust shell from the superwind dissipates, it will light up a planetary nebulae Temperatures from 25,000 K on up (to 300,000 K or even higher) Zanstra temperature - Measure brightness of star compared to brightness of nebula in optical hydrogen emission lines to estimate the uv/optical flux ratio to get temperature