MESA Tutorial Day 2: Novae Bill Wolf ASU → U of Wisconsin — Eau Claire
Outline Outcomes • Background • Greater familiarity with MESA • Modeling a simple nova • Learn capabili6es for novae • Adding 6me resolu6on when we • Gain awareness of pi@alls (and how want it to overcome them) • Changing mass loss prescrip6ons • Basic customiza6on of code • Adding your own physics • Adding your own physics to MESA
What are Novae? ” • Classical vs Recurrent Novae are • Not Dwarf Novae thermonuclear flashes • Environments resulting from the accretion • Cataclysmic Variables of hydrogen-rich material • Symbio6c Stars onto a white dwarf. ”
A Typical Nova Cycle 10 5 260 days Accretion 10 4 Luminosity [ L � ] Runaway 12 years 10 3 Mass Loss 10 days 10 2 SSS 10 1 46000 years 10 0 M WD = 1 . 0 M � 10 � 1 M = 10 � 9 M � yr � 1 ˙ 10 � 2 H Envelope Mass [ M � ] 10 � 4 ∆ M ign 10 � 5 ∆ M crit ∆ M stable 10 � 6 10 6 10 5 10 4 E ff ective Temperature [K]
Novae Have Stability Regimes, Too Stable H Burning
Goal: Determine Ṁ for Stable Burning on a 1.3 M ⊙ White Dwarf Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Part 1: Starting from a Test Case Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Create Work Directory Step 1: Copy the starting work directory and cd into it $ cp -r $MESA_DIR/star/test_suite/nova nova_tutorial $ cd nova_tutorial Step 2: Fix makefile (or else it ignores your MESA_DIR ) • Open make/makefile • Delete or comment out the line that sets MESA_DIR Step 3: Confirm that it compiles $ ./mk Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Edit Stopping Condition 1 Open src/run_star_extras.f Notice near the top: And later, the subroutine extras_check_model Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Edit Stopping Condition 2 We want to get the time between two bursts, so this stopping condition occurs too quickly. Challenge 1: Edit extras_check_model to stop after two bursts instead of one. We’re going to accrete matter so rapidly that after a burst, the luminosity may not ever go below 10 3 L ⊙ (so the condition would never be met) Challenge 2: Edit extras_check_model to define the end of a burst as when luminosity drops below 5 ⨉ 10 3 L ⊙ (instead of 1 ⨉ 10 3 L ⊙ ) Confirm your solution compiles with ./mk Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Edit Stopping Condition Solutions Challenge 1: Edit extras_check_model to stop after two bursts instead of one. Challenge 2: Edit extras_check_model to define the end of a burst as when luminosity drops below 5 ⨉ 10 3 L ⊙ (instead of 1 ⨉ 10 3 L ⊙ ) Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Replace inlists Grab tarball from tutorial website: billwolf.space/projects/leiden_2019/#part3b Navigate to the “Download Files” button, click it, and extract it in your work directory. Replaces/adds: • inlist : now points to inlist_pgstar for plots • inlist_nova : streamlined, faster (and wronger) • inlist_pgstar : custom dashboard; saves pngs every timestep • history_columns.list : additional data for pgstar dashboard Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Part 2: Finding the Stability Boundary Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Select an Accretion Rate Pick a random accretion rate between 3.1 ⨉ 10 -7 M ⊙ and 3.7 ⨉ 10 -7 M ⊙ Challenge 3: Edit inlist_nova to accrete at this new rate. Challenge 4: Run your model ./rn and determine if it is stable (one flash and then constant luminosity) or unstable (two full flashes). If unstable, determine • recurrence time (time between runaways) • duration of SSS phase (from minimum in T eff to end of last flash) Report values on google sheet (see tutorial website for link) Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Part 3: Resolving the SSS Phase Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Two Ways to Control Timesteps varcontrol_target Sets the desired value of an unweighted average of the change in logarithms of many basic variables (density, temperature, velocity, mass fractions, etc.). Smaller → shorter time steps *_limit & *_hard_limit Sets desired limits on changes in specific quantities. Regular limit adjusts next timestep if limit is exceeded. Hard limits will require a retry (redo this timestep with a shorter timestep) if exceeded. Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Catching the SSS Phase As Ṁ→Ṁ stable , we expect two things: 1. Time between end of a flash to beginning of next flash decreases because ignition mass is obtained more quickly (and ignition mass decreased) 2. Supersoft duration (t SSS ) increases because accretion replenishes fuel at nearly the rate it is burned away At the absolute limit, the recurrence time should increase as the supersoft begins to dominate the cycle lifetime, but we don’t see this… maybe we need better time resolution of the SSS phase! Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
<latexit sha1_base64="8PklifW7Ql3pnwOtPTqNq6jEik=">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</latexit> Sledgehammer or Scalpel? Reducing varcontrol_target ? Too broad, and will slow everything. Just care about motion through HR diagram during supersoft source (SSS) phase delta_HR_limit delta_HR_hard_limit Limit how much changes in one timestep, but we q [log( L/L � )] 2 + [log( T e ff / K)] 2 only want this during the SSS phase. Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Selective Timestep Control Let’s define the situation where we want tighter timestep controls to be when all of the following are true simultaneously: • the luminosity exceeds L burst (10 4 L ⊙ ) • the effective temperature exceeds 8 ⨉ 10 5 K, • and when the total energy generated by hydrogen burning is less than 110% of the photospheric luminosity Challenge 5: Edit extras_check_model to adjust the values of the delta_HR_limit and delta_HR_hard_limit to 5e-3 and 1e-2, respectively during the SSS phase, and to -1 otherwise. Compile and run your solution, reporting if it is stable or not, as well as the recurrence time and SSS duration to the second tab of the Google sheet. Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Selective Timestep Control Solution run_star_extras.f
Part 4: A New Wind Scheme Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
<latexit sha1_base64="+zwdQlC+DYFryTyOrPA83mDK6Q=">ACJHicdVDJSgNBEO2JW4xb1KOXxiB4McxEcUEUQPChHMAkMPT09SWPQndPIDT9MV78FS8eXPDgxW+xJ4m4Pyh4vFdFVT03ZlRI2361MmPjE5NT2enczOzc/EJ+cakqoRjUsERi3jdRYIwGpKpJKReswJClxGau71cerXeoQLGoWXsh+TVoA6IfUpRtJI7fx+0+cIK0erkm56kVTnutdWzQDJLg8UEVjrqxI8gGdwA59Giep3U7X7CLe7azt+3A38Qp2gMUwAjldv7JrMBJQEKJGRKi4dixbCnEJcWM6FwzESRG+Bp1SMPQEAVEtNTgSQ3XjOJBP+KmQgkH6tcJhQIh+oFrOtMjxU8vFf/yGon0d1uKhnEiSYiHi/yEQRnBNDHoU6wZH1DEObU3ApxF5nUpMk1Z0L4+BT+T6qlorNZLF1sFQ6PRnFkwQpYBevATvgEJyCMqgADG7AHXgAj9atdW89Wy/D1ow1mlkG32C9vQMbaqW2</latexit> The Super Eddington Wind Scheme In our current model, mass loss is determined by the following equation: 1 ˙ Mv 2 esc = L − L Edd 2 Essentially, the “extra” energy in excess of the Eddington luminosity drives a mass flux traveling at the escape velocity. While physically motivated, this prevents novae from expanding much (contrary to observations), and it is quite sensitive to our choice of boundary condition. Are our results sensitive to the mass loss mechanism? Follow along with tutor ial at billwolf.spac e /proj e c ts/le ide n_2019
Recommend
More recommend
