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

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

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

2 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?

3 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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

4 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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.

5 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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)

6 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Mass loss over the Sun’s lifetime T Tauri phase: Does accretion drive wind? HB ZAMS AGB Pre-MS (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!

7 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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?

8 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Cool-star mass loss rates de Jager et al. (1988)

9 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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)

10 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Cool-star mass loss rates de Jager et al. (1988) Hartigan et al. (1995) Carpenter, Harper, Dupree, etc.

11 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 New ideas (1): astrosphere absorption Wood et al. (2001, 2002, 2005) distinguished cool ISM H I Lyα absorption from hotter “piled up” H 0 in stellar astrospheres. Derived M depends on models...

12 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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 M acc ; Bondi-Hoyle accretion rate provides the density; Mass conservation (spherical geometry) provides M wind. Largest uncertainty: wind velocity (v 4 ).

13 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Cool-star mass loss rates Wood et al. (2005) Debes (2006)

14 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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. 100x M 

15 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Theory As M goes down, reliance on modeling goes up...

16 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Theory: dimensional analysis... Stellar wind power: Reimers (1975, 1977) proposed a semi-empirical scaling:

17 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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:

18 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Cool-star mass loss rates Schröder & Cuntz (2005) scaling for I, III, V

19 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 What sets solar mass loss? Coronal heating must be ultimately responsible! Hammer (1982) & Withbroe (1988) suggested a steady-state energy balance: heat conduction radiation losses — ρvkT 5252 Only a fraction of total coronal heat flux conducts down, but in general, we expect something close to... along open flux tubes!

20 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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. K, M stars Sun Saar (2001, CS11) Judge, Güdel, Kürster, Garcia-Alvarez, Preibisch, Feigelson, Jeffries open or closed fields?

21 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Solar X-rays & magnetic flux Empirically, does solar mass loss really scale with F X ~ Φ ? It depends on which field lines are considered! Schwadron et al. (2006) Quiet regions Active regions Coronal hole (open)

22 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Solar X-rays & magnetic flux Empirically, does solar mass loss really scale with F X ~ Φ ? It depends on which field lines are considered! Quiet regions Active regions Schwadron et al. (2006) M ~ Φ AR 0.06 M ~ Φ QR 0.41

23 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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 ~ L X 0.4 M ~ L X 1.3 M ~ L X 0.1 M ~ L X 1.0

24 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 Heating & wind acceleration Models of how coronal heating (F X ) scales with magnetic flux (Φ) are growing more sophisticated... Open field lines: MHD turbulence! T (K) reflection coefficient Z+Z+ Z–Z– Z–Z– Closed loops: Magnetic reconnection e.g., Longcope & Kankelborg 1999 Cranmer & van Ballegooijen (2005, 2007) T. Suzuki (CS14, Poster II)

25 Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction S. R. Cranmer Cool Stars 14, November 10, 2006 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)

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