Stellar Phenomenology and Stellar Properties•Stellar spectral classification•Hertzsprung-Russel and color-magnitude diagrams•Fundamental stellar properties, observables•Stellar population properties2Spectral Classification: Temperatureinfrared spectravisible spectraSpectral Classification: TemperatureT1,400–2,500 K noneMolecules: H2O, hydridesreddest star-like objects~ 0.1 10–5–10–3>100 Gyr400–1,400 KnoneMolecules: H2O, CH4~ 0.1 10–6–10–5N/A<0.08Weak Ca+Y<400 KnoneMolecules: H2O, CH4, NH3~ 0.1 <10–6N/A<0.084Stellar Classification: TemperatureSunM dwarf T dwarfL dwarf Jupiterbrown dwarfs planetsstars5700 K ~3500 K~2000 K ~1000 K 160 K(G dwarf)Spectral Classification: Luminosity• luminosity, radius, surface gravity, and surface pressure are mutually related–L = 4πR2σTeff4, g = GM/R2, P = ρgl (l is photon m.f.p.)• define “luminosity spectral class”V: dwarfs, log g ~ 4.5 [cgs units]IV: subgiants, log g ~ 3 (approximately as on Earth)III: giants, log g ~ 1.5II: (bright) giants, log g ~ 0.5I: supergiants, log g ~ –0.5• Sun: G2 V star (Teff = 5777K, log g = 4.43)(figure from D. Gray)Hertzsprung-Russell (H-R) Diagram•log L vs. log Teff• main sequence:– locus of most stars– bulk of stellar lifetimes–L ∝ M3.8–τMS ≈ 1010 yr (M/MSun)–2.88Color-Magnitude Diagram (CMD)•proxy for the (Teff-L) Hertzsprung-Russell diagram•e.g., B–V vs. MV, J–K vs. MK, etc.Stellar Abundances•derived from spectral lines•compared to the Sun or to abundance of hydrogen (H) in star–or both•a.k.a., “metallicity”•“metal-poor” stars, a.k.a. “subdwarfs” are hotter than dwarfs of same luminosity[Fe/H] = log [n(Fe) / n(H)]* – log [n(Fe) / n(H)]SunStellar Populations•Population I: •low galatic scale heights, rotate with galactic disk, similar composition to Sun•Population II:•large scale heights, high space velocities, low mass: old starsStar Clusters•globular clusters (e.g., M80: Pop II stars, gravitationally bound, dense•open clusters (e.g., Pleiades): Pop I stars, gravitationally bound, < 2 Gyr•“O-B” associations: loose, not gravitationally bound, < 20 MyrMessier 80PleiadesStellar Phenomenology and Properties•Stellar spectral classification•Hertzsprung-Russel and color-magnitude diagrams•Fundamental stellar properties, observables•Stellar population properties13Spectroscopic Binary• double-lined (SB2)– spectra of both stars visible• single-lined (SB1)– only spectrum of brighter star visible(a)(b)(c)(d)(a)(d)(b)(c)Radial Velocity vs. Time for Double-lined SB in a Circular OrbitTotally Eclipsing Binariesta – start of secondary ingresstb – end of secondary ingresstc – start of secondary egresstd – end of secondary egressLuminosity-mass relation for binary stars with well-determined orbitsData fromPopper(1980; ARA&A 18, 115)Mass vs. TeffTaking the Stellar Temperature•(Fe II λ5317 / Fe I λ5328) line ratio decreases with decreasing TeffTeffEnergy Generation: p-p Chain•ξL ≡ dN / (dlog M/MSun) ∝ ∝ (M/MSun)–Γ•ξ ≡ dN / (d M/MSun) ∝ (M/MSun)–α • slope Γ ≡ α + 1Initial Mass FunctionKroupa (2002)log M/MSunSingle Star Fraction• lower mass stars are more commonly singleLada