Stars science questions

1. Stars science questions • Origin of the Elements • Mass Loss, Enrichment • High Mass Stars • Binary Stars

2. Origin of the Elements • Key questions • What is the composition of the earliest generation of stars? • What do abundance patterns tell us about nucleosynthesis? • What causes mass loss, and how does it enrich the ISM? • What is the current abundance distribution of high mass stars?

3. Origin of the Elements • Earliest generation of stars • Measure elemental abundances at very low metallicity • [Fe/H] = -5.3 (VLT spectrum) • [R=50-100K; NUV, optical, NIR; high S/N] Christlieb et al. 2002

4. Origin of the Elements • Nucleosynthesis • Need alpha elements, rare elements, isotopic abundances • [R=50-100K; NUV, optical, NIR; high S/N] NIR spectrum of a Bulge M giant (IRTF/CSHELL) showing Fe, Mg, Ca Figure from S. Balachandran

5. Origin of the Elements Isotopic 16O/17O measurement in a metal poor giant (Keck/NIRSPEC) Implications for stellar structure, mixing, galactic chemical evolution Figure from S. Balachandran

6. Mass loss and enrichment • Old stars -- RGB, AGB • Massive stars -- Wolf-Rayet • Young stars -- TTs, Herbig AeBe • Image outflows in H2, H3+ [2-4 mu, 1e-6 contrast] • Image scattered light from dust [1-2.5 mu, 1e-6 contrast, dual polarization] • Spectroscopy of outflows [R=150K, optical/NIR] • mid-IR spectroscopy of dust emission features • Complements ALMA

7. Mass Loss from Evolved Stars - 1 • Broad Scientific Goals & Key Objectives • Measure outflow characteristics for evolved stars • Temperature, density, velocity, and composition • Radial dependence for resolved sources • Understand molecular and dust chemistry in outflows • Nonequilibrium gas chemistry • Dust formation mechanisms and rates • Understand dynamical mechanisms driving outflows • Radiative acceleration beyond a few stellar radii • Adams & MacCormack (1935), Spitzer (1938) • Predictive model of mass loss from evolved stars • Function of stellar age and initial stellar mass • Feedback on interstellar structure and composition • Test stellar evolution models for evolved stars • Nuclear reaction pathways • Internal mixing mechanisms

8. Mass Loss from Evolved Stars - 2 • Key Measurements • Molecular lines at infrared and millimeter wavelengths • Over 50 species detected in IRC+10216 • Line ratios constrain temperature and density • Line shifts and widths constrain velocity fields • Isotopic abundance ratios constrain stellar models • Infrared dust features • A few dust families (silicates, graphites, ices, etc.) • Band strengths constrain dust chemistry • Angular resolution (10 mas) • Resolves radial dependence of outflow characteristics • Directly image clumps and general asymmetry • Measure proper motion of clumps in nearest sources • Spectral energy distribution constrains unresolved sources

9. High mass stars • Abundances of high mass stars in the Galaxy • Measure abundance patterns vs. location, age, understand recent enrichment history [1-5 mu, R=20-50K] • Measure terminal velocity of outflows, constrain mass and luminosity [He 10830, 1-2.5 mu, R=50K] • Complements SIRTF/GLIMPSE survey • IR is important because sources are usually highly embedded

10. Fundamental Stellar Physics • Binary stars - 1 • Measure masses of low mass PMS stars and young brown dwarfs in binaries, calibrate mass-luminosity relations (also for field main sequence low mass stars!) • In open clusters (age)  constrain evolutionary models. • [velocities -- R=10-50K, 1-2.5 mu needed]

11. Measure: Distance Mass, Radius B.C. Treatment of convection Molecules SpT-Teff Interiors Atmospheres Surface gravities of PMS stars? Initial conditions Rotation, Accretion? Birthline (t=0) Masses of PMS binaries • Determining Mass and Age of a Young Star Measure: V, SpT L, Teff PMS tracks Mass, age Figure from K. Stassun

12. Masses of PMS binaries • Need velocities and light curves (opt/NIR) Stassun et al. (2003) M1 = 1.01 +/- 0.015 Msun M2 = 0.72 +/- 0.008 Msun

13. Masses of PMS binaries • Constrain PMS evolutionary models M1 = 1.01 MsunM2 = 0.73 Msun Stassun et al. (2003)

14. Masses of PMS binaries • Current status – 4 systems in progress Each point represents the primary star in an eclipsing binary Figure from K. Stassun

15. Fundamental Stellar Physics • Binary stars - 2 • Understand evolution of secondary stars in cataclysmic variables, origin of period gap • Origin of type I SN population • Extreme case - mass loss turns the secondary star effectively into a brown dwarf. • Measure velocities, abundances • [need NIR spectra for sensitivity, contrast] • [R=10-50K]

16. IR spectrum of SS Cyg SS Cyg secondary • C, Mg depleted Figure from T. Harrison

17. IR spectrum of U Gem U Gem secondary • again C depleted • lower mass, very faint and red Figure from T. Harrison

18. IR spectrum of EF Eri Secondary is an irradiated “brown dwarf’’? Harrison et al. (2003)

19. Instrumentation Summary • High resolution [R=10-20-50-100-150K] spectroscopy • NUV, optical, NIR, MIR • High sensitivity (faint sources) • Good wavelength coverage • High contrast imaging [1.e-6] • 1-5 mu, polarization capability

20. Chick – 1

21. Chick - 2