We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the st... more We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the stable burning regime of accretion rates as modeled by time-dependent calculations done with Modules for Experiments in Stellar Astrophysics (MESA). We report the stability boundary for WDs of masses between 0.51 M and 1.34 M as found via time-dependent calculations. We also examine recurrent novae that are accreting at rates close to, but below, the stable burning limit and report their recurrence times. Our dense grid in accretion rates finds the expected minimum possible recurrence times as a function of the WD mass. This enables inferences to be made about the minimum WD mass possible to reach a specific recurrence time. We compare our computational models of post-outburst novae to the stably burning WDs and explicitly calculate the duration and effective temperature (Teff) of the post-novae WD in the supersoft phase. We agree with the measured turnoff time- Teff relation in M31 by Hen...
We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the st... more We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the stable burning regime of accretion rates as modeled by time-dependent calculations done with Modules for Experiments in Stellar Astrophysics (MESA). We report the stability boundary for WDs of masses between 0.51 solar masses and 1.34 solar masses as found via time-dependent calculations. We also examine recurrent novae that are accreting at rates close to, but below, the stable burning limit and report their recurrence times and ignition masses. Our dense grid in accretion rates finds the expected minimum possible recurrence times as a function of the WD mass. This enables inferences to be made about the minimum WD mass possible to reach a specific recurrence time. We compare our computational models of post-outburst novae to the stably burning WDs and explicitly calculate the duration and effective temperature (Teff) of the post-novae WD in the supersoft phase. We agree with the measured...
Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandra... more Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandrasekhar mass (M_ Ch), reaching central densities that trigger electron captures in the core. Using Modules for Experiments in Stellar Astrophysics (MESA), we present the first true binary simulations of He star + O/Ne WD binaries, focusing on a 1.5 M_ He star in a 3 hour orbital period with 1.1-1.3 M_ O/Ne WDs. The helium star fills its Roche lobe after core helium burning is completed and donates helium on its thermal timescale to the WD, Ṁ≈3×10^-6 M_/yr, a rate high enough that the accreting helium burns stably on the WD. The accumulated carbon/oxygen ashes from the helium burning undergo an unstable shell flash that initiates an inwardly moving carbon burning flame. This flame is only quenched when it runs out of carbon at the surface of the original O/Ne core. Subsequent accumulation of fresh carbon/oxygen layers also undergo thermal instabilities, but no mass loss is triggered, allow...
The creation of "hybrid" white dwarfs, made of a C-O core within a O-Ne shell has been ... more The creation of "hybrid" white dwarfs, made of a C-O core within a O-Ne shell has been proposed, and studies indicate that ignition in the C-rich central region makes these viable progenitors for thermonuclear (type Ia) supernovae. Recent work found that the C-O core is mixed with the surrounding O-Ne as the white dwarf cools prior to accretion, which results in lower central C fractions in the massive progenitor than previously assumed. To further investigate the efficacy of hybrid white dwarfs as progenitors of thermonuclear supernovae, we performed simulations of thermonuclear supernovae from a new series of hybrid progenitors that include the effects of mixing during cooling. The progenitor white dwarf model was constructed with the one-dimensional stellar evolution code MESA and represented a star evolved through the phase of unstable interior mixing followed by accretion until it reached conditions for the ignition of carbon burning. This MESA model was then mapped t...
MESA inlists and run_star_extras associated with Brooks et al. (2017). MESA version 5118. Publica... more MESA inlists and run_star_extras associated with Brooks et al. (2017). MESA version 5118. Publication DOI: 10.3847/2041-8213/834/2/L9
Author(s): Brooks, Jared | Advisor(s): Bildsten, Lars | Abstract: Accretion of helium onto white ... more Author(s): Brooks, Jared | Advisor(s): Bildsten, Lars | Abstract: Accretion of helium onto white dwarfs at various rates can lead to several different types of explosive outcomes. Slow accretion from low mass He stars or He WDs in binaries with orbital periods less than an hour can build up helium shells of ${\approx}0.1 M_\odot$ that ignite and detonate, generating faint and fast transients.In this dissertation, I explore this well known channel for generating transients from He accretion onto WDs, as well as with less explored channels that accrete He onto WD at rates that allow for steady helium shell burning.Stable helium burning significantly grows the degenerate core, which can result in several different outcomes, including type Ia supernovae and accretion induced collapse.I also explore deep convection in C/O/Ne hybrid WDs and found effective mixing to a level that will strongly affect their later explosions.Some binaries are unstable to mass transfer and merge the component...
We explore the outcome of mass transfer via Roche lobe overflow (RLOF) of M_ He≲0.51 M_ pure heli... more We explore the outcome of mass transfer via Roche lobe overflow (RLOF) of M_ He≲0.51 M_ pure helium burning stars in close binaries with white dwarfs (WDs). The evolution is driven by the loss of angular momentum through gravitational wave radiation (GWR), and both stars are modeled using Modules for Experiments in Stellar Astrophysics (MESA). The donors have masses of M_ He=0.35, 0.4, & 0.51M_ and accrete onto WDs of mass M_ WD from 0.6M_ to 1.26M_. The initial orbital periods (P_orb) span 20 to 80 minutes. For all cases, the accretion rate onto the WD is below the stable helium burning range, leading to accumulation of helium followed by unstable ignition. The mass of the convective core in the donors is small enough so that the WD accretes enough helium-rich matter to undergo a thermonuclear runaway in the helium shell before any carbon-oxygen enriched matter is transferred. The mass of the accumulated helium shell depends on M_ WD and the accretion rate. We show that for M_ He≳0...
We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the st... more We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the stable burning regime of accretion rates as modeled by time-dependent calculations done with Modules for Experiments in Stellar Astrophysics (MESA). We report the stability boundary for WDs of masses between 0.51 M and 1.34 M as found via time-dependent calculations. We also examine recurrent novae that are accreting at rates close to, but below, the stable burning limit and report their recurrence times. Our dense grid in accretion rates finds the expected minimum possible recurrence times as a function of the WD mass. This enables inferences to be made about the minimum WD mass possible to reach a specific recurrence time. We compare our computational models of post-outburst novae to the stably burning WDs and explicitly calculate the duration and effective temperature (Teff) of the post-novae WD in the supersoft phase. We agree with the measured turnoff time- Teff relation in M31 by Hen...
We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the st... more We examine the properties of white dwarfs (WDs) accreting hydrogen-rich matter in and near the stable burning regime of accretion rates as modeled by time-dependent calculations done with Modules for Experiments in Stellar Astrophysics (MESA). We report the stability boundary for WDs of masses between 0.51 solar masses and 1.34 solar masses as found via time-dependent calculations. We also examine recurrent novae that are accreting at rates close to, but below, the stable burning limit and report their recurrence times and ignition masses. Our dense grid in accretion rates finds the expected minimum possible recurrence times as a function of the WD mass. This enables inferences to be made about the minimum WD mass possible to reach a specific recurrence time. We compare our computational models of post-outburst novae to the stably burning WDs and explicitly calculate the duration and effective temperature (Teff) of the post-novae WD in the supersoft phase. We agree with the measured...
Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandra... more Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandrasekhar mass (M_ Ch), reaching central densities that trigger electron captures in the core. Using Modules for Experiments in Stellar Astrophysics (MESA), we present the first true binary simulations of He star + O/Ne WD binaries, focusing on a 1.5 M_ He star in a 3 hour orbital period with 1.1-1.3 M_ O/Ne WDs. The helium star fills its Roche lobe after core helium burning is completed and donates helium on its thermal timescale to the WD, Ṁ≈3×10^-6 M_/yr, a rate high enough that the accreting helium burns stably on the WD. The accumulated carbon/oxygen ashes from the helium burning undergo an unstable shell flash that initiates an inwardly moving carbon burning flame. This flame is only quenched when it runs out of carbon at the surface of the original O/Ne core. Subsequent accumulation of fresh carbon/oxygen layers also undergo thermal instabilities, but no mass loss is triggered, allow...
The creation of "hybrid" white dwarfs, made of a C-O core within a O-Ne shell has been ... more The creation of "hybrid" white dwarfs, made of a C-O core within a O-Ne shell has been proposed, and studies indicate that ignition in the C-rich central region makes these viable progenitors for thermonuclear (type Ia) supernovae. Recent work found that the C-O core is mixed with the surrounding O-Ne as the white dwarf cools prior to accretion, which results in lower central C fractions in the massive progenitor than previously assumed. To further investigate the efficacy of hybrid white dwarfs as progenitors of thermonuclear supernovae, we performed simulations of thermonuclear supernovae from a new series of hybrid progenitors that include the effects of mixing during cooling. The progenitor white dwarf model was constructed with the one-dimensional stellar evolution code MESA and represented a star evolved through the phase of unstable interior mixing followed by accretion until it reached conditions for the ignition of carbon burning. This MESA model was then mapped t...
MESA inlists and run_star_extras associated with Brooks et al. (2017). MESA version 5118. Publica... more MESA inlists and run_star_extras associated with Brooks et al. (2017). MESA version 5118. Publication DOI: 10.3847/2041-8213/834/2/L9
Author(s): Brooks, Jared | Advisor(s): Bildsten, Lars | Abstract: Accretion of helium onto white ... more Author(s): Brooks, Jared | Advisor(s): Bildsten, Lars | Abstract: Accretion of helium onto white dwarfs at various rates can lead to several different types of explosive outcomes. Slow accretion from low mass He stars or He WDs in binaries with orbital periods less than an hour can build up helium shells of ${\approx}0.1 M_\odot$ that ignite and detonate, generating faint and fast transients.In this dissertation, I explore this well known channel for generating transients from He accretion onto WDs, as well as with less explored channels that accrete He onto WD at rates that allow for steady helium shell burning.Stable helium burning significantly grows the degenerate core, which can result in several different outcomes, including type Ia supernovae and accretion induced collapse.I also explore deep convection in C/O/Ne hybrid WDs and found effective mixing to a level that will strongly affect their later explosions.Some binaries are unstable to mass transfer and merge the component...
We explore the outcome of mass transfer via Roche lobe overflow (RLOF) of M_ He≲0.51 M_ pure heli... more We explore the outcome of mass transfer via Roche lobe overflow (RLOF) of M_ He≲0.51 M_ pure helium burning stars in close binaries with white dwarfs (WDs). The evolution is driven by the loss of angular momentum through gravitational wave radiation (GWR), and both stars are modeled using Modules for Experiments in Stellar Astrophysics (MESA). The donors have masses of M_ He=0.35, 0.4, & 0.51M_ and accrete onto WDs of mass M_ WD from 0.6M_ to 1.26M_. The initial orbital periods (P_orb) span 20 to 80 minutes. For all cases, the accretion rate onto the WD is below the stable helium burning range, leading to accumulation of helium followed by unstable ignition. The mass of the convective core in the donors is small enough so that the WD accretes enough helium-rich matter to undergo a thermonuclear runaway in the helium shell before any carbon-oxygen enriched matter is transferred. The mass of the accumulated helium shell depends on M_ WD and the accretion rate. We show that for M_ He≳0...
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