cranmer cs14talk web

Winds of Main-Sequence Stars:: 

Winds of Main-Sequence Stars: Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics Observational Limits & a path to Theoretical Prediction

Winds of Main-Sequence Stars:: 

Winds of Main-Sequence Stars: Steven R. Cranmer Harvard-Smithsonian Center for Astrophysics Outline: Background: the solar wind (M ~ 10–14 M /yr) Cool-star winds: observational M methods & results How can theory be folded in? Should it be?

Slide3: 

Mariner 2 (1962): first direct confirmation of continuous supersonic solar wind. Helios probed in to 0.3 AU, Voyager continues past 100+ AU. Ulysses (1990s) left the ecliptic; provided 3D view of the wind’s magnetic geometry. Brief history: solar wind

Slide4: 

Mariner 2 (1962): first direct confirmation of continuous supersonic solar wind. Helios probed in to 0.3 AU, Voyager continues past 100+ AU. Ulysses (1990s) left the ecliptic; provided 3D view of the wind’s magnetic geometry. Brief history: solar wind SOHO gave us new views of “source regions” of solar wind.

The solar wind mass los rate: 

The solar wind mass los rate The sphere-averaged “M” isn’t usually considered by solar physicists! Wang (1998, CS10) used empirical relationships between B-field, wind speed, and density to reconstruct M over two solar cycles. ACE (in ecliptic)

Mass loss over the Sun’s lifetime: 

Mass loss over the Sun’s lifetime T Tauri phase: Does accretion drive wind? (Matt & Pudritz 2005) ZAMS: Was there a “bright young Sun?” HB/AGB: Is mass loss the “2nd parameter?” Do winds clear out “missing ISM” in clusters? Close binaries: SN Ia properties!

Cool-star winds: “traditional” diagnostics: 

Cool-star winds: “traditional” diagnostics (Bernat 1976) Optical/UV spectroscopy: simple blueshifts or full “P Cygni” profiles IR continuum: circumstellar dust causes SED excess Molecular lines (mm, sub-mm): CO, OH maser (van den Oord & Doyle 1997) wind star Radio: free-free emission from (partially ionized?) components of the wind Continuum methods need V from another diagnostic to get mass loss rate. Clumping?

Cool-star mass loss rates: 

Cool-star mass loss rates de Jager et al. (1988)

Multi-line spectroscopy: 

Multi-line spectroscopy 1990s: more self-consistent treatments of radiative transfer AND better data (GHRS, FUSE, high-spectral-res ground-based) led to better stellar wind diagnostic techniques! A nice example: He I 10830 Å for TW Hya (pole-on T Tauri star) . . . Dupree et al. (2006)

Cool-star mass loss rates: 

Cool-star mass loss rates de Jager et al. (1988)

New ideas (1): astrosphere absorption: 

New ideas (1): astrosphere absorption Wood et al. (2001, 2002, 2005) distinguished cool ISM H I Lyα absorption from hotter “piled up” H0 in stellar astrospheres. Derived M depends on models . . .

New ideas (2): accretion in pre-CVs: 

New ideas (2): accretion in pre-CVs Some H-rich & He-rich white dwarfs show metal lines in their atmospheres (classes DAZ, DZ). Accretion from ISM and/or “comets” is problematic. Debes (2006) suggested that M-dwarf companions deposit metal-rich gas via stellar winds onto the WD surfaces. Observed abundances (usually from Ca H, K lines) modeled as steady-state balance between accretion & downward diffusion; this provides Macc ; Bondi-Hoyle accretion rate provides the density; Mass conservation (spherical geometry) provides Mwind . Largest uncertainty: wind velocity (v4).

Cool-star mass loss rates: 

Cool-star mass loss rates

New ideas (3): charge exchange X-rays: 

New ideas (3): charge exchange X-rays ISM neutrals flow into an “astrosphere” and CX with wind ions. Ions left in excited state emit X-rays. Wargelin & Drake (2001, 2002) suggest using this to probe stellar wind properties. So far, upper limits only (M dwarfs). Better spatial & spectral res. needed. With good enough spectra, one can also obtain wind speed, composition, and ionization state.

Theory: 

Theory

Theory: dimensional analysis . . .: 

Theory: dimensional analysis . . . Stellar wind power: Reimers (1975, 1977) proposed a semi-empirical scaling:

Theory: dimensional analysis . . .: 

Theory: dimensional analysis . . . Stellar wind power: Schröder & Cuntz (2005) investigated an explanation via convective turbulence generating atmospheric waves . . . Funny things happen during rapid evolutionary stages! (e.g., Willson 2000, Ann. Rev.) Reimers (1975, 1977) proposed a semi-empirical scaling:

Cool-star mass loss rates: 

Cool-star mass loss rates

What sets solar mass loss?: 

What sets solar mass loss? Coronal heating must be ultimately responsible! Hammer (1982) & Withbroe (1988) suggested a steady-state energy balance: Only a fraction of total coronal heat flux conducts down, but in general, we expect something close to . . . along open flux tubes!

Stellar coronal heating: 

Stellar coronal heating The well-known “rotation-age-activity” relationship shows how coronal heating weakens as young (solar-type) stars spin down. Heating rates also scale with mean magnetic field. Saar (2001, CS11) Judge, Güdel, Kürster, Garcia-Alvarez, Preibisch, Feigelson, Jeffries

Solar X-rays & magnetic flux: 

Solar X-rays & magnetic flux Empirically, does solar mass loss really scale with FX ~ Φ ? It depends on which field lines are considered! Schwadron et al. (2006) Quiet regions Active regions Coronal hole (open)

Solar X-rays & magnetic flux: 

Solar X-rays & magnetic flux Empirically, does solar mass loss really scale with FX ~ Φ ? It depends on which field lines are considered! Quiet regions Active regions Schwadron et al. (2006) M ~ ΦAR0.06 M ~ ΦQR0.41

Sun’s mass loss history: 

Sun’s mass loss history Did liquid water exist on Earth 4 Gyr ago? If “standard” solar models are correct, a strong greenhouse effect was needed. Sackmann & Boothroyd (2003) argued that a more massive (~1.07 M) young Sun could have been luminous enough to solve this problem, but it would have needed strong early mass loss . . . Sackmann & Boothroyd (2003) M ~ LX0.4 M ~ LX1.3 M ~ LX0.1 M ~ LX1.0

Heating & wind acceleration: 

Heating & wind acceleration Models of how coronal heating (FX) scales with magnetic flux (Φ) are growing more sophisticated . . . Open field lines: MHD turbulence! T (K) reflection coefficient Closed loops: Magnetic reconnection e.g., Longcope & Kankelborg 1999 Cranmer & van Ballegooijen (2005, 2007) T. Suzuki (CS14, Poster II)

Conclusions: 

Theory: Conclusions Combined multi-ion spectroscopy & atmosphere modeling still has unexplored potential. Magnetic field measurements are also key to constraining stellar wind properties. ZDI! Coming soon: X-ray charge exchange M’s ? Understanding mass loss depends on modeling coronal heating on open & closed field lines. Coming soon: 3D convection simulations for rapid rotators, with implications for how the photospheric waves affect coronal heating . . . Here now: turbulence-driven wind models with “real” coronal heating! Observations: B. Brown et al. (2004)