Stars science questions

•Origin of the Elements•Mass Loss, Enrichment•High Mass Stars•Binary Stars

Origin of the Elements

Key questionsWhat 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 aBulge M giant(IRTF/CSHELL)showing Fe, Mg, Ca

Figure fromS. 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, AGBMassive stars -- Wolf-RayetYoung 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+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

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

Fundamental Stellar Physics

Binary stars - 1Measure 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]

Masses of PMS binaries

Measure:

V, SpT

Mass, age

L, Teff

PMS tracks

Mass, Radius

Measure:

InteriorsAtmospheres

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

M1 = 1.01 +/- 0.015 Msun

M2 = 0.72 +/- 0.008 Msun

Stassun et al. (2003)

Need velocities and light curves (opt/NIR)

Masses of PMS binaries

Stassun et al. (2003)

M1 = 1.01 MsunM2 = 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 - 2Understand evolution of secondary stars in cataclysmic variables, origin of period gap

Origin of type I SN populationExtreme 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 anirradiated “browndwarf’’?

Harrison et al.(2003)

Instrumentation Summary

High resolution [R=10-20-50-100-150K] spectroscopyNUV, optical, NIR, MIRHigh sensitivity (faint sources)Good wavelength coverage

High contrast imaging [1.e-6]1-5 mu, polarization capability

Chick – 1

Chick - 2