Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems

Farihi, Jay; Fossati, L.; Wheatley, P. J.; Metzger, Brian D.; Mauerhan, Jon C.; Bachman, Stephanie; Gänsicke, B. T.; Redfield, Seth; Cauley, P. Wilson; Kochukhov, O.; Achilleos, N.; Stone, Nicholas C.

doi:10.1093/mnras/stx2664

Cited by 63 publications

(56 citation statements)

References 90 publications

(139 reference statements)

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“…As we discussed in section 4.5 of the Method, such hot WDs will have its sublimation radius larger than the Roche radius, thus the disk is likely to be dominated by gas. The gas accretion could be affected by stellar magnetic field, and could be highly unstable and result in variable accretion flux [65]. This may explain the large range of accretion rates of those very young WDs as shown in Fig.8 of Koester et al (2014).…”

Section: Other Mechanisms For Mass Accretionmentioning

confidence: 99%

A power-law decay evolution scenario for polluted single white dwarfs

et al. 2018

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Planetary systems can survive the stellar evolution, as evidenced by the atmospheric metal pollution and circumstellar dusty disks of single white dwarfs [1,2]. Recent observations show that 1% − 4% of single white dwarfs are accompanied by dusty disks [3,4,5,6], while the occurrence rate of metal pollution is about 25%−50% [1,7,8]. The dusty disks and metal pollution have been associated with accretion of remanent planetary systems around white dwarfs [1,9], yet the relation between these two phenomena is still unclear. Here we suggest an evolutionary scenario to link the two observational phenomena. By analyzing a sample of metal polluted white dwarfs, we find that the mass accretion rate onto the white dwarf generally follows a broken power law decay, which matches well with the theoretical prediction, if assuming dust accretion is primarily driven by Poynting-Robertson drag [10] and the dust source is primarily delivered via dynamically falling asteroids perturbed by a Jovian planet [11]. The presence of disks is mainly at the early stage (t cool ∼ 0.1 − 0.7 Gyr) of the whole process of metal pollution, which is detectable until ∼ 8 Gyr, naturally explaining the fraction (∼ 2% -16%) of metal-polluted white dwarfs having dusty disks. The success of this scenario also implies that the configuration of an asteroid belt with an outer gas giant might be common around stars of several solar masses.

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Section: Other Mechanisms For Mass Accretionmentioning

confidence: 99%

A power-law decay evolution scenario for polluted single white dwarfs

et al. 2018

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“…Our MESA models indicate that inferred accretion rates in polluted WDs with hydrogen dominated atmospheres of T eff 10, 000 K require systematic increases due to thermohaline mixing, often by several orders of magnitude. These higher rates can be tested, especially via X-ray observations (Farihi et al 2018). Very thin hydrogen envelopes (M H 10 −8 M ) are not considered in the models presented here, but are often poorly constrained.…”

Section: Discussionmentioning

confidence: 99%

Increases to Inferred Rates of Planetesimal Accretion due to Thermohaline Mixing in Metal-accreting White Dwarfs

Bauer

Bildsten

2018

ApJL

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Many isolated, old white dwarfs (WDs) show surprising evidence of metals in their photospheres. Given that the timescale for gravitational sedimentation is astronomically short, this is taken as evidence for ongoing accretion, likely of tidally disrupted planetesimals. The rate of such accretion,Ṁ acc , is important to constrain, and most modeling of this process relies on assuming an equilibrium between diffusive sedimentation and metal accretion supplied to the WD's surface convective envelope. Building on earlier work of Deal and collaborators, we show that highṀ acc models with only diffusive sedimentation are unstable to thermohaline mixing and that models which account for the enhanced mixing from the active thermohaline instability require larger accretion rates, sometimes reachingṀ acc ≈ 10 13 g s −1 to explain observed Calcium abundances. We present results from a grid of MESA models that include both diffusion and thermohaline mixing. These results demonstrate that both mechanisms are essential for understanding metal pollution across the range of polluted WDs with hydrogen atmospheres. Another consequence of active thermohaline mixing is that the observed metal abundance ratios are identical to accreted material.

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“…Another intriguing interpretation is broadening due to Zeeman-splitting from a magnetic field at the white dwarf surface. Given the proximity of the circumstellar debris to the white dwarf star, weak magnetic fields can have a strong effect on circumstellar material, as the Alfvén radius for the magnetic capture of infalling material strongly overlaps with the debris disk region (see Figure 5 of Farihi et al 2018a). For a rough estimate of the magnetic field strength (B * ), we compared the measured FWHM of the Ca K absorption feature to simulated spectra of varying magnetic field strengths assuming the stellar parameters listed in Table 1 and a fixed calcium abundance.…”

Section: White Dwarf Atmospheric Properties and Signs Of Accretionmentioning

confidence: 99%

Five New Post-main-sequence Debris Disks with Gaseous Emission

Dennihy

Lai

et al. 2020

ApJ

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Observations of debris disks, the products of the collisional evolution of rocky planetesimals, can be used to trace planetary activity across a wide range of stellar types. The most common end points of stellar evolution are no exception, as debris disks have been observed around several dozen white dwarf stars. But instead of planetary formation, post-main-sequence debris disks are a signpost of planetary destruction, resulting in compact debris disks from the tidal disruption of remnant planetesimals. In this work, we present the discovery of five new debris disks around white dwarf stars with gaseous debris in emission. All five systems exhibit excess infrared radiation from dusty debris, emission lines from gaseous debris, and atmospheric absorption features indicating ongoing accretion of metal-rich debris. In four of the systems, we detect multiple metal species in emission, some of which occur at strengths and transitions previously unseen in debris disks around white dwarf stars. Our first year of spectroscopic follow-up hints at strong variability in the emission lines that can be studied in the future, expanding the range of phenomena these post-main-sequence debris disks exhibit.

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Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems

Cited by 63 publications

References 90 publications

A power-law decay evolution scenario for polluted single white dwarfs

A power-law decay evolution scenario for polluted single white dwarfs

Increases to Inferred Rates of Planetesimal Accretion due to Thermohaline Mixing in Metal-accreting White Dwarfs

Five New Post-main-sequence Debris Disks with Gaseous Emission

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