1 / 117

radius

100 M . mass. 400 R . 10 -6 g/cm 3. density. radius. 0.01R . 0.07M . 10 6 g/cm 3. Location depend on: Mass Age Composition. uses ~20,000 stars. Mass - Luminosity Relation. Stellar Evolution. Models Observations. Radius Mass L T Pressure Density Composition.

niran
Download Presentation

radius

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 100 M mass 400 R 10-6 g/cm3 density radius 0.01R 0.07M 106 g/cm3

  2. Location depend on: Mass Age Composition

  3. uses ~20,000 stars

  4. Mass - Luminosity Relation

  5. Stellar Evolution Models Observations Radius Mass L T Pressure Density Composition H-R Diagram [B-V, Mv] Stars pile up where times are long Evolution always faster for larger mass

  6. 0.5R T=3x106 =1 R T=6000K =3x10-8 g/cm3 0.1R T=15x106 =100g/cm3 Basic Stellar Structure Equations: Eqtn of State: PT P1/V~ PT so P=(k/H)T where 1/ = 2X + (3/4)Y + (1/2)Z with radiative P: P = (k/H)T + (a/3)T4

  7. Basic Stellar Structure Equations: Eqtn of State: PT P1/V~ PT so P=(k/H)T where 1/ = 2X + (3/4)Y + (1/2)Z with radiative P: P = (k/H)T + (a/3)T4 Hydrostatic Equilibrium: P(r)/r = -GM(r)(r)/r2 0.5R T=3x106 =1 R T=6000K =3x10-8 g/cm3 0.1R T=15x106 =100g/cm3

  8. Basic Stellar Structure Equations: Eqtn of State: PT P1/V~ PT so P=(k/H)T where 1/ = 2X + (3/4)Y + (1/2)Z with radiative P: P = (k/H)T + (a/3)T4 Hydrostatic Equilibrium: P(r)/r = -GM(r)(r)/r2 Mass continuity: M(r)/r = 4r2(r) 0.5R T=3x106 =1 R T=6000K =3x10-8 g/cm3 0.1R T=15x106 =100g/cm3

  9. Basic Stellar Structure Equations: Eqtn of State: PT P1/V~ PT so P=(k/H)T where 1/ = 2X + (3/4)Y + (1/2)Z with radiative P: P = (k/H)T + (a/3)T4 Hydrostatic Equilibrium: P(r)/r = -GM(r)(r)/r2 Mass continuity: M(r)/r = 4r2(r) Luminosity gradient (in thermal equilibrium): L(r)/r = 4r2(r)(,T, comp) where T 0.5R T=3x106 =1 R T=6000K =3x10-8 g/cm3 0.1R T=15x106 =100g/cm3

  10. Basic Stellar Structure Equations: Eqtn of State: PT P1/V~ PT so P=(k/H)T where 1/ = 2X + (3/4)Y + (1/2)Z with radiative P: P = (k/H)T + (a/3)T4 Hydrostatic Equilibrium: P(r)/r = -GM(r)(r)/r2 Mass continuity: M(r)/r = 4r2(r) Luminosity gradient (in thermal equilibrium): L(r)/r = 4r2(r)(,T, comp) where T T gradient: T(r)/r = -3(r)L(r)/16acr2T(r)3 where  T-3.5 (opacity is bound-free, free-free, e- scattering) 0.5R T=3x106 =1 R T=6000K =3x10-8 g/cm3 0.1R T=15x106 =100g/cm3

  11. Observation Theory Giant Molecular Clouds 10-100pc, 100,000M T<100K Radio Collapse trigger: SN cloud-cloud collisions density wave • O and B stars form • winds • smaller mass stars IR Herbig-Haro, T Tauri

  12. Birth Sequence • trigger [SN, cloud-cloud, density wave] • star formation “eats” its way into the cloud

  13. Cone nebula HST Clusters dissolve into the field in ~ 10 Myr

  14. Star Cluster NGC 2264

  15. Birth Sequence • trigger [SN, cloud-cloud, density wave] • cloud fragments and collapses [Jeans mass and radius] • free-fall [~4000 yr] Jean’s instability: Ugas = -1/2 Ω (internal energy vs g potential E

  16. Minimum mass for collapse (Jean’s Mass) MJ ~ (5kT/GmH)3/2 (3/4o)1/2 or MJ ~ 3kTR/GmH Minimum radius: RJ ~ (15kT/4GmH o)1/2 or RJ ~ GmHM/3kT Cloud fragments & collapses if M>MJ, R>RJ Free-fall time = (3/32Go)1/2 for T~150K, n~108/cm3, ~2x10-16 g/cm3 tff ~ 4700 yr Dense, cold regions can support only small masses (so collapse), while warm, diffuse regions can support larger masses (stable)

  17. Star Formation The dark region has just developed a Jeans instability. The central gases are heating as they fall into the newly forming protostar.

  18. Matthew Bate simulation of collapse and fragmentation of 500 solar mass cloud to produce a cluster of 183 stars and bds including 40 multiple systems

  19. Unfortunately, no good quantitative theory to predict star formation rate or stellar mass distribution ! IMF = Initial Mass Function •  (log m) = dN/d log m  m- • N is number of stars in logarithmic mass range log m + d log m • = 1.35 Salpeter slope (logarithmic) in linear units (m)= dN/dm m-  where  =  + 1(= 2.35 Salpeter) Big question: Is it universal?

  20. Birth Sequence • trigger [SN, cloud-cloud, density wave] • cloud fragments and collapses [Jeans mass and radius] • early collapse isothermal - E radiated away • interior becomes adiabatic[no heat transfer] - E trapped so T rises • protostellar core forms [~ 5 AU] with free-falling gas above • dust vaporizes as T increases • convective period • radiative period • nuclear fusion begins [starts zero-age main sequence]

  21. Pre–Main-Sequence Evolutionary Tracks

  22. Hiyashi tracks 105 yrs 106 yrs radiative 107 yrs convective

  23. outflow gives P Cyg profiles

  24. XZ Tau binary HH-30 edge-on

  25. no magnetic field Disk accretes at ~10-7M /yr, disk ejects 1-10% in high velocity wind

  26. strong magnetic field

  27. Middle Age - stable stars Gravity balances pressure Main sequence [stage of hydrostatic equilibrium] • Mass >1.5 Msun [CNO cycle, convective core, radiative envelope] • Mass = 0. 4 - 1.5Msun[p-p cycle, radiative core, convective envelope] • Mass = 0. 08 - 0. 4Msun[p-p cycle, all convective interior] • Mass = 10 - 80 MJup [0. 01 - 0. 08Msun][brown dwarf] • Mass < 10MJup[< 0.01Msun][planets] Lifetime on Main Sequence = 1010 M/L

  28. Mass - Luminosity Relation M<0.7M;L/L=0.35(M/M)2.62 M> 0.7M;L/L=1.02 (M/M)3.92

  29. Energy in sun (stars) L = 4 x 1033 ergs/s solar constant Age = 4.6 billion yrs (1.4 x 1017 secs) Total E = 6 x 1050 ergs fusion is only source capable of this energy mass with T > 10 million E=1. 3 x 1051 ergs lifetime = E available = 1. 3 x 1051 ergs ~ 3 x 1017s ~ 10 billion yrs E loss rate 4 x 1033 ergs/s test with neutrinos 37Cl +  37Ar + e- for E > 0.81 MeV 71Ga +  71Ge + e- for E > 0.23 MeV

  30. p + p  np + e+ +  np + p  npp +  npp + npp  npnp + p + p 4H  1 He + energy 4.0132  4.0026 (m=0.05 x 10-24g) E = mc2 = 0.05 x 10-24g (9 x 1020cm2/s2) = 4 x 10-5 ergs

  31. 0.43 MeV 1.44 MeV 1H + 1H  2H + e+ +  1H + 1H  2H + e+ +  99.8% 0.25% 2H + 1H  3He +  91% ppI 3He + 3He 4He + 2 1H 9% 3He + 3He 7Be +  0.1% 7Be + e- 7Li +  7Be + 1H  8B +  7Li + 1H  4He + 4He 8B  8Be + e+ +  ppII 8Be  4He + 4He ppIII

  32. High vs Low mass stars have different fusion reactions and different physical structure M > 1.5 M CNO cycle; convective core and radiative envelope M < 1.5 Mp-p cycle; radiative core and convective envelope M < 0.4 M p-p cycle; entire star is convective M < 0.07 MH fusion never begins

  33. CNO cycle

  34. Mass - Luminosity Relation

  35. Giant-Supergiant Stage • H fusion stops - core contracts and heats up • H shell burning starts - outer layers expand • core T reaches 100 million K - He flash, He fusion starts • high mass - multiple shell and fusion stages • C to O, O to Ne, Ne to Si, Si to Fe • Fusion stops at Fe

  36. Post–Main-Sequence Evolution

  37. He-C fusion : Triple Alpha 4He + 4He  8Be +  8Be + 4He  12C +  3He  1C energy = 1.17 x 10-5 ergs

  38. He flash

More Related