superbubbles, wolf-rayet stars, and the origin of galactic cosmic rays w.r. binns, m.h. israel, l.m....
TRANSCRIPT
![Page 1: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/1.jpg)
Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays
W.R. Binns, M.H. Israel, L.M. Scott: Washington University
M.E. Wiedenbeck: Jet Propulsion Laboratory
A.C. Cummings, J.S. George, R.A. Leske, R.A. Mewaldt, E.C. Stone: Caltech
T.T. von Rosenvinge: Goddard Space Flight Center
M. Arnould, S. Goriely: Institut d’Astronomie et d’Astrophysique, Bruxelles
![Page 2: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/2.jpg)
Outline
• Introduction—Cosmic Ray Source models» Superbubbles formed from OB associations as possible source of galactic
cosmic rays
» Wolf-Rayet (WR) Stars • as source of enhancement of certain isotopic ratios: e.g. 22Ne/20Ne, 58Fe/56Fe
• The CRIS experiment» Instrument
» Isotopic measurements
• WR component as tracer of galactic cosmic ray source» Comparison of data with WR model calculations
• Suggested scenario for cosmic ray origin• Conclusions
![Page 3: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/3.jpg)
Cosmic Ray Source?
• Stellar atmosphere injection (e.g. Meyer, Shapiro)» Low-FIP elements enhanced (as in the solar corona).
• Interstellar grain source (Most recently Meyer et al.)» Refractory elements enhanced
» Mass dependence for volatile elements
• Acceleration of material in superbubbles by SN shocks
• Higdon et al. ApJ To be pub., Aug. 2005; ApJ 590 (2003) 822; ApJ 509 (1998) L33; Lingenfelter et al. ApJL 500 (1998) L153.
• Streitmatter et al. A&A 143 (1985) 249.
» Supernova material
» Wind material from massive stars
![Page 4: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/4.jpg)
Superbubbles & Supernovae• Superbubbles blown by stellar winds & SN in OB associations• Superbubble size: ~100-1000 pc• The majority of core-collapse SN (80-90%) in our galaxy occur in superbubbles (Higdon & Lingenfelter).
• Mean time between SN within OB assoc.~106y• SN shocks accelerate ambient superbubble material
Superbubble in Perseus ArmSuperbubble (N 70) in the Large Magellanic Cloud (ESO-VLT image)
~100 pcdiameter
![Page 5: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/5.jpg)
Wolf-Rayet Stars
• Evolutionary phase of massive O & B type stars exist primarily in OB associations
• WR Mass—15-45 M⊙ • High velocity surface winds (~1,000-
4,000 km/s) eject material into the ISM
• Often are dusty and ~>60% are binaries—puzzle how dust can exist in such a hot environment
• Two phases—WN and WC» WN--CNO processed material is
ejected with production of high 13C/12C and 14N/16O ratios
» WC--Wind enrichment of He-burning products: esp. C, O, and 22Ne through reaction 14N(,)18F(e+)18O(,)22Ne
WR-124 in Sagittarius—Hubble Image
WR-104 in Sagittarius—Keck Telescope Image
Diam~0.2pc
Diam~200au
![Page 6: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/6.jpg)
• Evolution of surface abundances (mass fraction) with stellar mass for 60M⊙ star
(Meynet & Maeder, 2003)
Time evolution of WR abundancesNon-rotatingstar
RotatingStar300 km/sat equator •Top curve—total mass; Bottom
curve—convective core mass
•2D models—van Marle
Time evolution of mass
Non-rotatingStar
Rotating star
![Page 7: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/7.jpg)
Cosmic Ray Isotope Spectrometer (CRIS)
• Large geometrical factor of CRIS (~50 x previous instruments)
• Excellent mass resolution enables precise identification of abundances.
• Statistical sample is large enough so that the energy spectra of the Neon isotopic ratios (important ratios as will be seen later) have been obtained
![Page 8: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/8.jpg)
CRIS GCR Isotopic Measurements
![Page 9: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/9.jpg)
Source Abundances & Tracer Isotopes
• To obtain source abundances from measured abundances, use “tracer” method (Wiedenbeck & Stone)
• Use secondary isotopes to “subtract” the secondary component of isotopes that are predominantly primary
![Page 10: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/10.jpg)
•Two component models•Wolf-Rayet winds from stars with various initial masses, with and without rotation.•Adjust the WR fraction mixed with ISM to match CR 22Ne/20Ne.(Goriely, Arnould & MeynetModeling)
“Combined” data points (red) are mean values of ratios from Ulysses, Voyager, ISEE-3 and HEAO-3-C2
![Page 11: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/11.jpg)
Model WR Fraction
M60-no rot 0.20
M85-no rot 0.12
M120-no rot 0.16
M40-rot 0.22
M60-rot 0.16
M85-rot 0.41
M120-rot 0.35
Fraction of WR materialmixed with ISM with solarsystem composition tonormalize to 22Ne/20Ne ratio
300 km/s
But what about the 14N/16O and N/Ne ratios???
![Page 12: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/12.jpg)
Volatility & mass fractionated GCR source abundances
• Meyer et al., 1997 model—Refractory elements are enriched in GCRs since they sputter off accelerated dust grains preferential acceleration (~factor of 13 enhancement)» Additionally, even for volatile elements, there appears to be a mass bias for which
they estimate a mass dependency of A0.80.2
• Ratios need to be corrected for these effects.• Oxygen
» Volatile in elemental or molecular form» But 23% is estimated to reside in refractory compounds in the ISM (e.g. silicates)
(K. Lodders, 2003)
• Nitrogen» Exists primarily as a gas in space
• Carbon» Refractory in elemental form» But a poorly known fraction exists in volatile molecules (e.g. CO) in space.
• Neon» Entirely volatile
![Page 13: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/13.jpg)
GCR source abundances compared with WR model corrected for volatility and mass fractionation (open symbols)
![Page 14: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/14.jpg)
Suggested Scenario
• WR star ejecta, enriched in 22Ne and other neutron-rich isotopes, mixes within the superbubble (Higdon & Lingenfelter) with» Ejecta from core-collapse SN» Average ISM (represented by solar-system abundances)
• Refractory elements must exist mostly as grains and volatile elements mostly as gas.
• SN shocks accelerate mix of material in SB to cosmic ray energies» Grains are preferentially accelerated (Ellison et al.)
• Mean time between SN events in SB is ~3-35 x 105 y (Schaller et al. 1992)» Sufficient time for 59Ni to decay to 59Co
![Page 15: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/15.jpg)
Summary
• CRIS measurements have led to an improved value 22Ne/20Ne, 58Fe/56Fe, and other isotope ratios useful for identifying a WR component in GCRs.
• Comparison of CRIS and other data show » the three isotope ratios predicted to be most enhanced in WR
models, 12C/16O, 22Ne/20Ne, and 58Fe/56Fe, are indeed enhanced in the cosmic rays.
» Those for which enhancement is not predicted are consistent with solar system abundances, provided volatility and mass fractionation corrections are applied
![Page 16: Superbubbles, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays W.R. Binns, M.H. Israel, L.M. Scott: Washington University M.E. Wiedenbeck: Jet](https://reader033.vdocument.in/reader033/viewer/2022051516/56649e565503460f94b4d83a/html5/thumbnails/16.jpg)
Summary (cont)
• We take agreement as evidence that WR star ejecta is likely an important component of cosmic-ray source material.
• Since most WR stars & core-collapse SN reside in SBs, then SBs must be the predominant site of injection of WR material and SN ejecta into the GCR source material.
• Picture that emerges is that SBs appear to be the site of origin and acceleration of at least a substantial fraction of GCRs.