1 / 7

H Exhaustion

H Exhaustion. After core H exhaustion core must contract and heat before He burning can begin Shell around contracting core heated to H burning T. H Exhaustion. Convective core - H depleted out to r = r convective core

orde
Download Presentation

H Exhaustion

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. H Exhaustion After core H exhaustion core must contract and heat before He burning can begin Shell around contracting core heated to H burning T

  2. H Exhaustion Convective core - H depleted out to r = rconvective core T much lower where H still present - must contract in order to heat to H ignition temperature

  3. H Exhaustion Convective core - H depleted out to r = rconvective core T much lower where H still present - must contract in order to heat to H ignition temperature Whole star contracts on Kelvin-Helmholz (thermal) timescale - star briefly increases in luminosity and moves blueward

  4. H Exhaustion No convective core - H depleted only at r = 0+ Smooth transition to shell burning - no K-H jag

  5. H shell burning • Shell must support envelope against gravity of inert core. All L from small r so burning takes place at higher temperatures in shells • Thermodynamic gradients outside shell very steep - excess L goes into expanding star to flatten gradients - star moves to red

  6. H shell burning • Shell must support envelope against gravity of inert core. All L from small r so burning takes place at higher temperatures in shells • Thermodynamic gradients outside shell very steep - excess L goes into expanding star to flatten gradients - star moves to red • Low mass stars (~2M) have degenerate cores & produce enough L in shell to support envelope - move to RGB on H burning timescales • Sun will spend ~4 Gyr moving from core H exhaustion to RGB - 40% of total H consumption and lifetime

  7. H shell burning • Shell must support envelope against gravity of inert core. All L from small r so burning takes place at higher temperatures in shells • Thermodynamic gradients outside shell very steep - excess L goes into expanding star to flatten gradients - star moves to red • Higher mass stars (~2M) have non-degenerate cores -don’t produce enough L in shell to support envelope - move to RGB on K-H timescale • Time for crossing can be as little as 103-104 yr - stars not observed in this part of HR diagram - Hertzsprung Gap

More Related