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

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?

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

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

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

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

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

Mass Loss from Evolved Stars - 2 Key Measurements Molecular lines at infrared and millimeter wavelengths Over 50 species detected in IRC 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

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, mu, R=50K]  Complements SIRTF/GLIMPSE survey  IR is important because sources are usually highly embedded

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, mu needed]

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

Masses of PMS binaries M 1 = / M sun M 2 = / M sun Stassun et al. (2003)  Need velocities and light curves (opt/NIR)

Masses of PMS binaries Stassun et al. (2003) M1 = 1.01 Msun M2 = 0.73 Msun  Constrain PMS evolutionary models

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

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]

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

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

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

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

Chick – 1

Chick - 2