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Stellar Phenomenology and Stellar Properties

• Stellar spectral classification • Hertzsprung-Russel and color- diagrams • Fundamental stellar properties, observables • properties spectra visible spectra Spectral Classification:

2 Spectral Classification: Temperature

Weak Ca+

1,400–2,500 K none : H2O, ~ 0.1 10–5–10–3 >100 Gyr reddest -like objects

–6 –5 T 400–1,400 K none Molecules: H2O, CH4 <0.08 ~ 0.1 10 –10 N/A –6 Y <400 K none Molecules: H2O, CH4, NH3 <0.08 ~ 0.1 <10 N/A Stellar Classification: Temperature

Sun brown dwarfs

(G dwarf) M dwarf L dwarf T dwarf

5700 K ~3500 K ~2000 K ~1000 K 160 K 4 Spectral Classification:

• luminosity, radius, surface , and surface pressure are mutually related 2 4 2 – L = 4πR σTeff , g = GM/R , P = ρgl (l is photon m.f.p.) • define “luminosity spectral class” V: dwarfs, log g ~ 4.5 [cgs units] IV: , log g ~ 3 (approximately as on ) III: giants, log g ~ 1.5 II: (bright) giants, log g ~ 0.5 I: supergiants, log g ~ –0.5

: G2 V star (Teff = 5777K, log g = 4.43) (figure from D. Gray) Hertzsprung -Russell (H-R) Diagram

• log L vs. log Teff

: – locus of most stars – bulk of stellar lifetimes – L ∝ M3.8

– τMS ≈ 10 –2.8 10 yr (M/MSun) Color-Magnitude Diagram (CMD)

• proxy for the (Teff-L) Hertzsprung-Russell diagram

• e.g., B–V vs. MV, J–K vs. MK, etc.

8 Stellar Abundances • derived from spectral lines • compared to the Sun or to abundance of (H) in star–or both • a.k.a., “” • “-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)]Sun Stellar 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 stars Star Clusters

Messier 80

• 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 Myr Stellar Phenomenology and Properties

• Stellar spectral classification • Hertzsprung-Russel and color-magnitude diagrams • Fundamental stellar properties, observables • Stellar population properties Spectroscopic Binary (a) • double-lined (SB2) – spectra of both stars visible (b) (d) (b) (a) (c) (c)

(d) • single-lined (SB1) – only of brighter star visible

13 vs. Time for Double- lined SB in a Circular Orbit Totally Eclipsing Binaries

ta – start of secondary ingress tb – end of secondary ingress tc – start of secondary egress td – end of secondary egress Luminosity-mass relation for binary stars with well- determined orbits

Data from Popper (1980; ARA&A 18, 115)

Mass vs. Teff Taking the Stellar Temperature

Teff

• (Fe II λ5317 / Fe I λ5328) line ratio decreases with decreasing Teff Energy Generation: p-p Chain

• ξL ≡ dN / (dlog M/MSun) ∝ –Γ ∝ (M/MSun) • ξ ≡ dN / (d M/MSun) ∝ –α (M/MSun)

• slope Γ ≡ α + 1

log M/MSun Kroupa (2002) Single Star Fraction

• lower mass stars are more commonly single

Lada (2006)