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Showing 1-20 of about 97 results.
A Pluto-Charon Concerto: An Impact on Charon as the Origin of the Small SatellitesBromley, Benjamin C.Kenyon, Scott J.DOI: info:10.3847/1538-3881/ab9e6cv. 16085
Bromley, Benjamin C. and Kenyon, Scott J. 2020. "A Pluto-Charon Concerto: An Impact on Charon as the Origin of the Small Satellites." The Astronomical Journal 160:85. https://doi.org/10.3847/1538-3881/ab9e6c
ID: 157652
Type: article
Authors: Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: We consider a scenario where the small satellites of Pluto and Charon grew within a disk of debris from an impact between Charon and a trans-Neptunian object (TNO). After Charon's orbital motion boosts the debris into a disk-like structure, rapid orbital damping of meter-sized or smaller objects is essential to prevent the subsequent reaccretion or dynamical ejection by the binary. From analytical estimates and simulations of disk evolution, we estimate an impactor radius of 30-100 km; smaller (larger) radii apply to an oblique (direct) impact. Although collisions between large TNOs and Charon are unlikely today, they were relatively common within the first 0.1-1 Gyr of the solar system. Compared to models where the small satellites agglomerate in the debris left over by the giant impact that produced the Pluto-Charon binary planet, satellite formation from a later impact on Charon avoids the destabilizing resonances that sweep past the satellites during the early orbital expansion of the binary.
The ELM Survey. VIII. Ninety-eight Double White Dwarf BinariesBrown, Warren R.Kilic, MukreminKosakowski, AlekzanderAndrews, Jeff J.Heinke, Craig O.Agüeros, Marcel A.Camilo, FernandoGianninas, A.Hermes, J. J.Kenyon, Scott J.DOI: info:10.3847/1538-4357/ab63cdv. 88949
Brown, Warren R., Kilic, Mukremin, Kosakowski, Alekzander, Andrews, Jeff J., Heinke, Craig O., Agüeros, Marcel A., Camilo, Fernando, Gianninas, A., Hermes, J. J., and Kenyon, Scott J. 2020. "The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries." The Astrophysical Journal 889:49. https://doi.org/10.3847/1538-4357/ab63cd
ID: 155706
Type: article
Authors: Brown, Warren R.; Kilic, Mukremin; Kosakowski, Alekzander; Andrews, Jeff J.; Heinke, Craig O.; Agüeros, Marcel A.; Camilo, Fernando; Gianninas, A.; Hermes, J. J.; Kenyon, Scott J.
Abstract: We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low-mass WD candidates like GD 278, which we show is a P = 0.19 day double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too high to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15 He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low-mass WD candidates like GD 278, which we show is a P = 0.19 day double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too high to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15 0 < 20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 day double WD binaries, 35% of which belong to the Galactic halo. We infer that these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass-transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The systems with the shortest periods, such as J0651+2844, are signature LISA verification binaries that can be studied with gravitational waves and light.
Craters on Charon: Impactors from a Collisional Cascade Among Trans-Neptunian ObjectsKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/PSJ/aba8a9v. 140
Kenyon, Scott J. and Bromley, Benjamin C. 2020. "Craters on Charon: Impactors from a Collisional Cascade Among Trans-Neptunian Objects." The Planetary Science Journal 1:40. https://doi.org/10.3847/PSJ/aba8a9
ID: 157651
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: We consider whether equilibrium size distributions from collisional cascades match the frequency of impactors derived from New Horizons crater counts on Charon. Using an analytic model and a suite of numerical simulations, we demonstrate that collisional cascades generate wavy size distributions; the morphology of the waves depends on the binding energy of solids ${Q}_{D}^{\star }$ and the collision velocity vc. For an adopted minimum size of solids, ${r}_{\min }$ = 1 μm, and collision velocity vc = 1-3 km s-1, the waves are rather insensitive to the gravitational component of ${Q}_{D}^{\star }$ . If the bulk strength component of ${Q}_{D}^{\star }$ is ${Q}_{s}{r}^{{e}_{s}}$ for particles with radius r, size distributions with small Qs are much wavier than those with large Qs; systems with es ≍ -0.4 have stronger waves than systems with es ≍ 0. Detailed comparisons with the New Horizons data suggest that a collisional cascade among solids with a bulk strength intermediate between weak ice and normal ice produces size distributions fairly similar to that of impactors on Charon. If the surface density Σ of the protosolar nebula varies with semimajor axis a as Σ ≍ 30 g cm-2 (a/1 au)-3/2, the timescale for a cascade to generate an approximate equilibrium is 100-300 Myr at 45 au and 10-30 Myr at 25 au. Although it is necessary to perform more complete evolutionary calculations of the Kuiper Belt, collisional cascades are a viable model for producing the size distribution of solids that impacted Charon throughout its history.
Ohmic Heating of Asteroids around Magnetic StarsBromley, Benjamin C.Kenyon, Scott J.DOI: info:10.3847/1538-4357/ab12e9v. 87617
Bromley, Benjamin C. and Kenyon, Scott J. 2019. "Ohmic Heating of Asteroids around Magnetic Stars." The Astrophysical Journal 876:17. https://doi.org/10.3847/1538-4357/ab12e9
ID: 151836
Type: article
Authors: Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: We consider the impact of electromagnetic induction and ohmic heating on a conducting planetary object that orbits a magnetic star. Power dissipated as heat saps orbital energy. If this heat is trapped by an insulating crust or mantle, interior temperatures increase substantially. We provide a quantitative description of this behavior and discuss the astrophysical scenarios in which it might occur. Magnetic fields around some main-sequence stars and white dwarfs are strong enough to cause the decay of close-in orbits of asteroids and dwarf planets, drawing them through the Roche limit on megayear timescales. We confirm that ohmic heating around neutron stars is driven by the rotation of the stellar magnetic dipole, not orbital dynamics. In any case, heating can raise interior temperatures of asteroids or dwarf planets on close-in orbits to well above liquidus. Hot material escaping to the surface may lead to volcanic ejections that can obscure the host star (as in the light curve of KIC 8462852) and pollute its atmosphere (as observed with metal-rich white dwarfs). We speculate that mixing of a volatile-rich mantle or crust with material from an induction-heated core may lead to an explosion that could destroy the asteroid prior to tidal breakup.
A Pluto–Charon Sonata: The Dynamical Architecture of the Circumbinary Satellite SystemKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-3881/aafa72v. 15779
Kenyon, Scott J. and Bromley, Benjamin C. 2019. "A Pluto–Charon Sonata: The Dynamical Architecture of the Circumbinary Satellite System." The Astronomical Journal 157:79. https://doi.org/10.3847/1538-3881/aafa72
ID: 150503
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: Using a large suite of n-body simulations, we explore the discovery space for new satellites in the Pluto–Charon system. For the adopted masses and orbits of the known satellites, there are few stable prograde or polar orbits with semimajor axes a≲ 1.1 {a}H, where a H is the semimajor axis of the outermost moon Hydra. Small moons with radii r ≲ 2 km and a ≲ 1.1 a H are ejected on timescales ranging from several years to more than 100 Myr. Orbits with a ≳ 1.1 a H are stable on timescales exceeding 150–300 Myr. Near-infrared (IR) and mid-IR imaging with several instruments on James Webb Space Telescope and ground-based occultation campaigns with 2–3 m class telescopes can detect 1–2 km satellites outside the orbit of Hydra. Searches for these moons enable new constraints on the masses of the known satellites and on theories for circumbinary satellite formation.
A Pluto-Charon Sonata. III. Growth of Charon from a Circum-Pluto Ring of DebrisKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-3881/ab38b7v. 158142
Kenyon, Scott J. and Bromley, Benjamin C. 2019. "A Pluto-Charon Sonata. III. Growth of Charon from a Circum-Pluto Ring of Debris." The Astronomical Journal 158:142. https://doi.org/10.3847/1538-3881/ab38b7
ID: 154624
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: Current theory considers two options for the formation of the Pluto-Charon binary. In the hit-and-run model, a lower mass projectile barely hits the more massive Pluto, kicks up some debris, and remains bound to Pluto. In a graze-and-merge scenario, the projectile ejects substantial debris as it merges with Pluto. To investigate the graze-and-merge idea in more detail, we consider the growth of Charon-mass objects within a circum-Pluto ring of solids. Numerical calculations demonstrate that Charon analogs form rapidly within a swarm of planetesimals with initial radii r 0 ≈ 145-230 km. On timescales of ̃30-100 days, newly formed Charon analogs have semimajor axes, a ≈ 5-6 r P , and orbital eccentricities, e ≈ 0.1-0.3, similar to Charon analogs that remain bound after hit-and-run collisions with Pluto. Although the early growth of Charon analogs generates rings of small particles at a ≈ 50-275 r P , ejection of several 145-230 km leftovers by the central Pluto-Charon binary removes these small solids in 10-100 yr. Simple estimates suggest that small particles might survive the passage of 10-20 km objects ejected by the central binary. Our results indicate that the Pluto-Charon circumbinary satellite system was not formed by a graze-and-merge impact when the formation of Charon within a circum- Pluto disk leads to the ejection of several 100-200 km particles through the orbital plane of the Pluto-Charon binary. If a growing Charon ejects only much smaller particles, however, graze-and-merge impacts are a plausible formation channel for the Pluto-Charon binary and an ensemble of small, circumbinary satellites.
A Pluto-Charon Sonata: Dynamical Limits on the Masses of the Small SatellitesKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-3881/ab2890v. 15869
Kenyon, Scott J. and Bromley, Benjamin C. 2019. "A Pluto-Charon Sonata: Dynamical Limits on the Masses of the Small Satellites." The Astronomical Journal 158:69. https://doi.org/10.3847/1538-3881/ab2890
ID: 154250
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: During 2005-2012, images from Hubble Space Telescope (HST) revealed four moons orbiting Pluto-Charon. Although their orbits and geometric shapes are well-known, the 2σ uncertainties in the masses of the two largest satellites-Nix and Hydra-are comparable to their HST masses. Remarkably, gravitational n-body computer calculations of the long-term system stability on 0.1-1 Gyr timescales place much tighter constraints on the masses of Nix and Hydra, with upper limits ̃10% larger than the HST mass. Constraints on the mass density using size measurements from New Horizons suggest Nix and Hydra formed in icier material than Pluto and Charon.
Gaia and the Galactic Center Origin of Hypervelocity StarsBrown, Warren R.Lattanzi, Mario G.Kenyon, Scott J.Geller, Margaret J.DOI: info:10.3847/1538-4357/aadb8ev. 86639
Brown, Warren R., Lattanzi, Mario G., Kenyon, Scott J., and Geller, Margaret J. 2018. "Gaia and the Galactic Center Origin of Hypervelocity Stars." The Astrophysical Journal 866:39. https://doi.org/10.3847/1538-4357/aadb8e
ID: 149385
Type: article
Authors: Brown, Warren R.; Lattanzi, Mario G.; Kenyon, Scott J.; Geller, Margaret J.
Abstract: We use new Gaia measurements to explore the origin of the highest velocity stars in the hypervelocity star (HVS) survey. The measurements reveal a clear pattern in B-type stars. Halo stars dominate the sample at speeds of ≃100 km s‑1 below Galactic escape velocity. Disk runaway stars have speeds up to ≃100 km s‑1 above Galactic escape velocity, but most disk runaways are bound. Stars with speeds ≳100 km s‑1 above Galactic escape velocity originate from the Galactic center. Two bound stars may also originate from the Galactic center. Future Gaia measurements will enable a large, clean sample of Galactic center ejections for measuring the massive black hole ejection rate of HVSs, and for constraining the mass distribution of the Milky Way dark matter halo.
An illumination effect and an eccentric orbit for the symbiotic binary PU Vul revealed by 32 yr of optical spectroscopyCúneo, Virginia A.Kenyon, Scott J.Gómez, Mercedes N.Chochol, DrahomirShugarov, Sergey Y.Kolotilov, Eugeni A.DOI: info:10.1093/mnras/sty1686v. 4792728–2742
Cúneo, Virginia A., Kenyon, Scott J., Gómez, Mercedes N., Chochol, Drahomir, Shugarov, Sergey Y., and Kolotilov, Eugeni A. 2018. "An illumination effect and an eccentric orbit for the symbiotic binary PU Vul revealed by 32 yr of optical spectroscopy." Monthly Notices of the Royal Astronomical Society 479:2728– 2742. https://doi.org/10.1093/mnras/sty1686
ID: 149153
Type: article
Authors: Cúneo, Virginia A.; Kenyon, Scott J.; Gómez, Mercedes N.; Chochol, Drahomir; Shugarov, Sergey Y.; Kolotilov, Eugeni A.
Abstract: We analyse ˜32 yr of optical spectra and photometry for the symbiotic binary PU Vul. Light curves for the He I λ4471, He II λ4686, and H β λ4861 emission lines reveal an illumination effect, where the hot white dwarf ionizes the outflowing wind of the red giant, and evidence for an eccentric orbit with e ≥ 0.16. Along with the gradual appearance of high ionization emission from [Fe VII] and O VI, the relative fluxes of these lines suggest an increase in the effective temperature of the hot component, from roughly 105 K on JD 244 8000 (1990) to roughly 2 × 105 K on JD 245 5000 (2009). During this period, the luminosity of the hot component dropped by a factor of 4-6 to a current value of roughly 1000 L.
Dust production and depletion in evolved planetary systemsFarihi, J.van Lieshout, R.Cauley, P. W.Dennihy, E.Su, K. Y. L.Kenyon, Scott J.Wilson, T. G.Toloza, O.Gänsicke, B. T.von Hippel, T.Redfield, S.Debes, J. H.Xu, S.Rogers, L.Bonsor, A.Swan, A.Pala, A. F.Reach, W. T.DOI: info:10.1093/mnras/sty2331v. 4812601–2611
Farihi, J., van Lieshout, R., Cauley, P. W., Dennihy, E., Su, K. Y. L., Kenyon, Scott J., Wilson, T. G., Toloza, O., Gänsicke, B. T., von Hippel, T., Redfield, S., Debes, J. H., Xu, S., Rogers, L., Bonsor, A., Swan, A., Pala, A. F., and Reach, W. T. 2018. "Dust production and depletion in evolved planetary systems." Monthly Notices of the Royal Astronomical Society 481:2601– 2611. https://doi.org/10.1093/mnras/sty2331
ID: 150190
Type: article
Authors: Farihi, J.; van Lieshout, R.; Cauley, P. W.; Dennihy, E.; Su, K. Y. L.; Kenyon, Scott J.; Wilson, T. G.; Toloza, O.; Gänsicke, B. T.; von Hippel, T.; Redfield, S.; Debes, J. H.; Xu, S.; Rogers, L.; Bonsor, A.; Swan, A.; Pala, A. F.; Reach, W. T.
Abstract: The infrared dust emission from the white dwarf GD 56 is found to rise and fall by 20 per cent peak-to-peak over 11.2 yr, and is consistent with ongoing dust production and depletion. It is hypothesized that the dust is produced via collisions associated with an evolving dust disc, temporarily increasing the emitting surface of warm debris, and is subsequently destroyed or assimilated within a few years. The variations are consistent with debris that does not change temperature, indicating that dust is produced and depleted within a fixed range of orbital radii. Gas produced in collisions may rapidly re-condense onto grains, or may accrete onto the white dwarf surface on viscous timescales that are considerably longer than Poynting-Robertson drag for micron-sized dust. This potential delay in mass accretion rate change is consistent with multi-epoch spectra of the unchanging Ca II and Mg II absorption features in GD 56 over 15 yr, although the sampling is sparse. Overall, these results indicate that collisions are likely to be the source of dust and gas, either inferred or observed, orbiting most or all polluted white dwarfs.
Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic CenterKenyon, Scott J.Bromley, Benjamin C.Brown, Warren R.Geller, Margaret J.DOI: info:10.3847/1538-4357/aada04v. 864130
Kenyon, Scott J., Bromley, Benjamin C., Brown, Warren R., and Geller, Margaret J. 2018. "Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center." The Astrophysical Journal 864:130. https://doi.org/10.3847/1538-4357/aada04
ID: 149170
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.; Brown, Warren R.; Geller, Margaret J.
Abstract: We consider how the gravity of the Galactic disk and the Large Magellanic Cloud (LMC) modifies the radial motions of hypervelocity stars (HVSs) ejected from the Galactic center (GC). For typical HVSs ejected toward low (high) Galactic latitudes, the disk bends trajectories by up to 30° (3°–10°). For many lines of sight through the Galaxy, the LMC produces similar and sometimes larger deflections. Bound HVSs suffer larger deflections than unbound HVSs. Gravitational focusing by the LMC also generates an overdensity of a factor of two along the line of sight toward the LMC. With large enough samples, observations can detect the non-radial orbits and the overdensity of HVSs toward the LMC. For any Galactic potential model, the tangential velocity in the Galactic rest frame provides an excellent way to detect unbound and nearly bound HVSs within 10 kpc of the Sun. Similarly, the radial velocity in the rest frame isolates unbound HVSs beyond 10–15 kpc from the Sun. Among samples of unbound HVSs, measurements of the radial and tangential velocities serve to distinguish GC ejections from other types of high-velocity stars.
A Framework for Planet Detection with Faint Light-curve EchoesMann, ChrisTellesbo, Christopher A.Bromley, Benjamin C.Kenyon, Scott J.DOI: info:10.3847/1538-3881/aadc5ev. 156200
Mann, Chris, Tellesbo, Christopher A., Bromley, Benjamin C., and Kenyon, Scott J. 2018. "A Framework for Planet Detection with Faint Light-curve Echoes." The Astronomical Journal 156:200. https://doi.org/10.3847/1538-3881/aadc5e
ID: 150048
Type: article
Authors: Mann, Chris; Tellesbo, Christopher A.; Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: A stellar flare can brighten a planet in orbit around its host star, producing a light curve with a faint echo. This echo, and others from subsequent flares, can lead to the planet’s discovery, revealing its orbital configuration and physical characteristics. A challenge is that an echo is faint relative to the flare and measurement noise. Here we use a method, based on autocorrelation function estimation, to extract faint planetary echoes from stellar flare light curves. A key component of our approach is that we compensate for planetary motion; measures of echo strength are then co-added into a strong signal. Using simple flare models in simulations, we explore the feasibility of this method with current technology for detecting planets around nearby M dwarfs. We also illustrate how our method can tightly constrain a planet’s orbital elements and the mass of its host star. This technique is most sensitive to giant planets within 0.1 au of active flare stars and offers new opportunities for planet discovery in orientations and configurations that are inaccessible with other planet search methods.
Terrestrial Planet Formation: Dynamical Shake-up and the Low Mass of MarsBromley, Benjamin C.Kenyon, Scott J.DOI: info:10.3847/1538-3881/aa6aaav. 153216
Bromley, Benjamin C. and Kenyon, Scott J. 2017. "Terrestrial Planet Formation: Dynamical Shake-up and the Low Mass of Mars." The Astronomical Journal 153:216. https://doi.org/10.3847/1538-3881/aa6aaa
ID: 143335
Type: article
Authors: Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: We consider a dynamical shake-up model to explain the low mass of Mars and the lack of planets in the asteroid belt. In our scenario, a secular resonance with Jupiter sweeps through the inner solar system as the solar nebula depletes, pitting resonant excitation against collisional damping in the Sun's protoplanetary disk. We report the outcome of extensive numerical calculations of planet formation from planetesimals in the terrestrial zone, with and without dynamical shake-up. If the Sun's gas disk within the terrestrial zone depletes in roughly a million years, then the sweeping resonance inhibits planet formation in the asteroid belt and substantially limits the size of Mars. This phenomenon likely occurs around other stars with long-period massive planets, suggesting that asteroid belt analogs are common.
Mapping the composition of chondritic meteorite Northwest Africa 3118 with micro-Raman spectroscopyDall'Asén, Analía G.Dimas, Sophia I.Tyler, SarahJohnston, Jessica F.Anderton, Timothy R.Ivans, Inese I.Gerton, Jordan M.Bromley, Benjamin C.Kenyon, Scott J.DOI: info:10.1080/00387010.2017.1346689v. 50417–425
Dall'Asén, Analía G., Dimas, Sophia I., Tyler, Sarah, Johnston, Jessica F., Anderton, Timothy R., Ivans, Inese I., Gerton, Jordan M., Bromley, Benjamin C., and Kenyon, Scott J. 2017. "Mapping the composition of chondritic meteorite Northwest Africa 3118 with micro-Raman spectroscopy." Spectroscopy Letters 50:417– 425. https://doi.org/10.1080/00387010.2017.1346689
ID: 144690
Type: article
Authors: Dall'Asén, Analía G.; Dimas, Sophia I.; Tyler, Sarah; Johnston, Jessica F.; Anderton, Timothy R.; Ivans, Inese I.; Gerton, Jordan M.; Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: Not Available
Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf StarsKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-4357/aa9570v. 85050
Kenyon, Scott J. and Bromley, Benjamin C. 2017. "Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf Stars." The Astrophysical Journal 850:50. https://doi.org/10.3847/1538-4357/aa9570
ID: 144805
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: We consider the long-term evolution of gaseous disks fed by the vaporization of small particles produced in a collisional cascade inside the Roche limit of a 0.6 {M} white dwarf. Adding solids with radius {r}0 at a constant rate {\dot{M}}0 into a narrow annulus leads to two distinct types of evolution. When {\dot{M}}0≳ {\dot{M}}0,{crit}≈ 3× {10}4 {({r}0/1{km})}3.92 {{g}} {{{s}}}-1, the cascade generates a fairly steady accretion disk where the mass transfer rate of gas onto the white dwarf is roughly {\dot{M}}0 and the mass in gas is {M}g≈ 2.3× {10}22 ({\dot{M}}0/{10}10 {{g}} {{{s}}}-1) (1500 {{K}}/{T}0) ({10}-3/α ) g, where T 0 is the temperature of the gas near the Roche limit and α is the dimensionless viscosity parameter. If {\dot{M}}0≲ {\dot{M}}0,{crit}, the system alternates between high states with large mass transfer rates and low states with negligible accretion. Although either mode of evolution adds significant amounts of metals to the white dwarf photosphere, none of our calculations yield a vertically thin ensemble of solids inside the Roche limit. X-ray observations can place limits on the mass transfer rate and test this model for metallic line white dwarfs.
Variations on Debris Disks. IV. An Improved Analytical Model for Collisional CascadesKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-4357/aa6982v. 83938
Kenyon, Scott J. and Bromley, Benjamin C. 2017. "Variations on Debris Disks. IV. An Improved Analytical Model for Collisional Cascades." The Astrophysical Journal 839:38. https://doi.org/10.3847/1538-4357/aa6982
ID: 143280
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: We derive a new analytical model for the evolution of a collisional cascade in a thin annulus around a single central star. In this model, r max the size of the largest object changes with time, {r}\max \propto {t}-? , with ? ? 0.1-0.2. Compared to standard models where r max is constant in time, this evolution results in a more rapid decline of M d , the total mass of solids in the annulus, and L d , the luminosity of small particles in the annulus: {M}d\propto {t}-(? +1) and {L}d\propto {t}-(? /2+1). We demonstrate that the analytical model provides an excellent match to a comprehensive suite of numerical coagulation simulations for annuli at 1 au and at 25 au. If the evolution of real debris disks follows the predictions of the analytical or numerical models, the observed luminosities for evolved stars require up to a factor of two more mass than predicted by previous analytical models.
Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf StarsKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-4357/aa7b85v. 844116
Kenyon, Scott J. and Bromley, Benjamin C. 2017. "Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf Stars." The Astrophysical Journal 844:116. https://doi.org/10.3847/1538-4357/aa7b85
ID: 143866
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: We consider the long-term collisional and dynamical evolution of solid material orbiting in a narrow annulus near the Roche limit of a white dwarf. With orbital velocities of 300 {km} {{{s}}}-1, systems of solids with initial eccentricity e≳ {10}-3 generate a collisional cascade where objects with radii r ≲ 100{--}300 {km} are ground to dust. This process converts 1-100 km asteroids into 1 μm particles in 102-106 yr. Throughout this evolution, the swarm maintains an initially large vertical scale height H. Adding solids at a rate \dot{M} enables the system to find an equilibrium where the mass in solids is roughly constant. This equilibrium depends on \dot{M} and {r}0, the radius of the largest solid added to the swarm. When {r}0 ≲ 10 km, this equilibrium is stable. For larger {r}0, the mass oscillates between high and low states; the fraction of time spent in high states ranges from 100% for large \dot{M} to much less than 1% for small \dot{M}. During high states, the stellar luminosity reprocessed by the solids is comparable to the excess infrared emission observed in many metallic line white dwarfs.
H-atmospheres of Icy Super-Earths Formed In Situ in the Outer Solar System: An Application to a Possible Planet NineLevi, AmitKenyon, Scott J.Podolak, M.Prialnik, D.DOI: info:10.3847/1538-4357/aa6ba6v. 839111
Levi, Amit, Kenyon, Scott J., Podolak, M., and Prialnik, D. 2017. "H-atmospheres of Icy Super-Earths Formed In Situ in the Outer Solar System: An Application to a Possible Planet Nine." The Astrophysical Journal 839:111. https://doi.org/10.3847/1538-4357/aa6ba6
ID: 143274
Type: article
Authors: Levi, Amit; Kenyon, Scott J.; Podolak, M.; Prialnik, D.
Abstract: We examine the possibility that icy super-Earth mass planets, formed over long timescales (0.1–1 Gyr) at large distances (∼200–1000 au) from their host stars, will develop massive H-rich atmospheres. Within the interior of these planets, high pressure converts CH4 into ethane, butane, or diamond and releases H2. Using simplified models that capture the basic physics of the internal structure, we show that the physical properties of the atmosphere depend on the outflux of H2 from the mantle. When this outflux is ≲ {10}10 molec cm‑2 s‑1, the outgassed atmosphere has a base pressure of ≲1 bar. Larger outflows result in a substantial atmosphere where the base pressure may approach 103–104 bar. For any pressure, the mean density of these planets, 2.4–3 g cm‑3, is much larger than the mean density of Uranus and Neptune, 1.3–1.6 g cm‑3. Thus, observations can distinguish between a Planet Nine with a primordial H/He-rich atmosphere accreted from the protosolar nebula and one with an atmosphere outgassed from the core.
Searching for Planet Nine with Coadded WISE and NEOWISE-Reactivation ImagesMeisner, Aaron M.Bromley, Benjamin C.Nugent, Peter E.Schlegel, David J.Kenyon, Scott J.Schlafly, Edward F.Dawson, Kyle S.DOI: info:10.3847/1538-3881/153/2/65v. 15365
Meisner, Aaron M., Bromley, Benjamin C., Nugent, Peter E., Schlegel, David J., Kenyon, Scott J., Schlafly, Edward F., and Dawson, Kyle S. 2017. "Searching for Planet Nine with Coadded WISE and NEOWISE-Reactivation Images." The Astronomical Journal 153:65. https://doi.org/10.3847/1538-3881/153/2/65
ID: 142823
Type: article
Authors: Meisner, Aaron M.; Bromley, Benjamin C.; Nugent, Peter E.; Schlegel, David J.; Kenyon, Scott J.; Schlafly, Edward F.; Dawson, Kyle S.
Abstract: A distant, as yet unseen ninth planet has been invoked to explain various observations of the outer solar system. While such a "Planet Nine," if it exists, is most likely to be discovered via reflected light in the optical, it may emit much more strongly at 3-5 ?m than simple blackbody predictions would suggest, depending on its atmospheric properties. As a result, Planet Nine may be detectable at 3.4 ?m with the Wide-field Infrared Survey Explorer, but single exposures are too shallow except at relatively small distances ({d}9? 430 au). We develop a method to search for Planet Nine far beyond the W1 single-exposure sensitivity, to distances as large as 800 au, using inertial coadds of W1 exposures binned into ~1 day intervals. We apply our methodology to a ~2000 square degree testbed sky region which overlaps a southern segment of Planet Nine's anticipated orbital path. We do not detect a plausible Planet Nine candidate, but are able to derive a detailed completeness curve, ruling out its presence within the parameter space searched at W1 < 16.66 (90% completeness). Our method uses all publicly available W1 imaging, spanning 2010 January to 2015 December, and will become more sensitive with future NEOWISE-Reactivation releases of additional W1 exposures. We anticipate that our method will be applicable to the entire high Galactic latitude sky, and we will extend our search to that full footprint in the near future.
Making Planet Nine: A Scattered Giant in the Outer Solar SystemBromley, Benjamin C.Kenyon, Scott J.DOI: info:10.3847/0004-637X/826/1/64v. 82664
Bromley, Benjamin C. and Kenyon, Scott J. 2016. "Making Planet Nine: A Scattered Giant in the Outer Solar System." The Astrophysical Journal 826:64. https://doi.org/10.3847/0004-637X/826/1/64
ID: 140225
Type: article
Authors: Bromley, Benjamin C.; Kenyon, Scott J.
Abstract: Correlations in the orbits of several minor planets in the outer solar system suggest the presence of a remote, massive Planet Nine. With at least 10 times the mass of the Earth and a perihelion well beyond 100 au, Planet Nine poses a challenge to planet formation theory. Here we expand on a scenario in which the planet formed closer to the Sun and was gravitationally scattered by Jupiter or Saturn onto a very eccentric orbit in an extended gaseous disk. Dynamical friction with the gas then allowed the planet to settle in the outer solar system. We explore this possibility with a set of numerical simulations. Depending on how the gas disk evolves, scattered super-Earths or small gas giants settle on a range of orbits, with perihelion distances as large as 300 au. Massive disks that clear from the inside out on million-year timescales yield orbits that allow a super-Earth or gas giant to shepherd the minor planets as observed. A massive planet can achieve a similar orbit in a persistent, low-mass disk over the lifetime of the solar system.