arXiv subjects

Jonathan D. Slavin

Publications and source records attributed to Jonathan D. Slavin.

At least 19 recordsLinked to original sources

arXiv2026

Interstellar Dust Transport Through the Heliosphere Including the Sector Region

Interstellar dust has been detected in situ flowing through the heliosphere. However, our ability to derive the density and size distribution of the interstellar dust in the local interstellar medium from this directly detected dust requires modeling the transport of the grains as they interact with the solar wind magnetic field. The magnetic field in the sector region that contains the heliospheric current sheet has rapid polarity flips which can present an effectively very low averaged field strength to dust grains that have gyroradii tens of au in size. We present new calculations of dust transport through the heliosphere using models that include the sector region to assess the effects on dust transport. We show that the sector region can act as a window allowing even relatively small grains to penetrate deep into the heliosphere. We find the sector region reduces the variation in dust density with the solar cycle (as compared to models without the sector region), with very little concentration or dilution of the dust for grains larger than \sim 0.1$ $\mu$m for most of the solar cycle. We still find a substantial concentration of the dust in the ecliptic plane for a focusing overall polarity of the field at solar minimum. These models do not include the time dependence of the magnetic field during transport of grains through the heliosphere. Nevertheless, our results imply that observations of interstellar dust grains, even near Earth, could be fairly accurate in determining their size distribution in the surrounding interstellar medium.

astro-ph.GA↗

arXiv2025

Ionization Sources of the Local Interstellar Clouds: Two B-stars, Three White Dwarfs, and the Local Hot Bubble

The dominant sources of photoionizing radiation in the extreme ultraviolet (EUV) incident on the exterior of the local interstellar clouds include two nearby early B-type stars, $\epsilon$ CMa ($124\pm2$ pc) and $\beta$ CMa ($151\pm5$ pc), three hot dwarfs, and the local hot bubble (LHB). Line emission (170-912A) from highly ionized metals (Fe, Ne, Mg) in million-degree LHB plasma may be responsible for the elevated ionization fractions of helium ($n_{\rm HeII}/n_{\rm He} \approx 0.4$) compared to hydrogen ($n_{\rm HII} / n_{\rm H} \approx 0.2$) in the local clouds. We update the stellar parameters and ionizing flux for $\beta$ CMa, after correcting the EUV spectra for intervening HI column density, $N_{\rm HI} = 1.9\pm0.1\times10^{18}~{\rm cm}^{-2}$, and its hotter effective temperature, $T_{\rm eff} \approx 25,000$K vs. 21,000K for $\epsilon$ CMa. These two stars produce a combined H-ionizing photon flux $\Phi_{\rm H} \approx 6800\pm1400$ cm$^{-2}$ s$^{-1}$ at the external surface of the local clouds. The hot bubble could produce comparable fluxes, $\Phi_{\rm H} =$ 2000-9000 cm$^{-2}$ s$^{-1}$, depending on the amount of metal depletion into dust grains that survive sputtering. The radial velocities and proper motions of $\beta$ CMa and $\epsilon$ CMa indicate that both stars passed within $10\pm1$ pc of the Sun $4.4\pm0.1$ Myr ago, with 100-200 times higher local ionizing fluxes. At that time, the local clouds were likely farther from the Sun, owing to their transverse motion. Over the last few Myr, EUV radiation from these two stars left a wake of highly ionized gas in a hot, low-density cavity produced by past supernova explosions in the Sco-Cen OB association and connected with the LHB.

astro-ph.GA↗

arXiv2023

Infrared Ejecta and Cold Dust in the Young Supernova Remnant N132D

We present Spitzer, WISE, and Herschel observations of the young supernova remnant (SNR) N132D in the LMC, including 3-40 microns Spitzer IRS mapping, 12 microns WISE and 70, 100, 160, 250, 350, and 500 microns Herschel images. The high-velocity lines of [Ne II] at 12.8 microns, [Ne III] at 15.5 microns, and [O IV] 26 microns reveal infrared ejecta concentrated in a central ring and coincide the optical and X-ray ejecta. Herschel images reveal far-IR emission coinciding with the central ejecta, which suggests that the IR emission is freshly formed, cold dust in the SN-ejecta. The infrared spectra are remarkably similar to those of another young SNR of 1E0102 with Ne and O lines. Shock modeling of the Ne ejecta emission suggests a gas temperature of 300 - 600 K and densities in the range 1000-20,000 cm^{-3} in the post-shock photoionized region. The IR continuum from the ejecta shows an 18 microns-peak dust feature. We performed spectral fitting to the IRS dust continuum and Herschel photometry. The dust mass associated with the central ejecta is 1.25+-0.65 Msun, while the 18 microns dust feature requires forsterite grains. The dust mass of the central ejecta region in N132D is higher than those of other young SNRs, which is likely associated with its higher progenitor mass. We discuss the dust productivity in the ejecta of N132D and infer its plausible implications for the dust in the early Universe.

astro-ph.GA↗

arXiv2022

Near-Earth Supernovae in the Past 10 Myr: Implications for the Heliosphere

We summarize evidence that multiple supernovae exploded within 100 pc of Earth in the past few Myr. These events had dramatic effects on the heliosphere, compressing it to within ~20 au. We advocate for cross-disciplinary research of nearby supernovae, including on interstellar dust and cosmic rays. We urge for support of theory work, direct exploration, and study of extrasolar astrospheres.

astro-ph.IM↗

arXiv2020

Turbulence and Particle Acceleration in Radiative Shock Waves in the Cygnus Loop II: Development of Postshock Turbulence

Radiative shock waves in the Cygnus Loop and other supernova remnants show different morphologies in [O III] and Hα emission. We use HST spectra and narrowband images to study the development of turbulence in the cooling region behind a shock on the west limb of the Cygnus Loop. We refine our earlier estimates of shock parameters that were based upon ground-based spectra, including ram pressure, vorticity and magnetic field strength. We apply several techniques, including Fourier power spectra and the Rolling Hough Transform, to quantify the shape of the rippled shock front as viewed in different emission lines. We assess the relative importance of thermal instabilities, the thin shell instability, upstream density variations, and upstream magnetic field variations in producing the observed structure.

astro-ph.GA↗

arXiv2020

The Dynamics, Destruction, and Survival of Supernova-Formed Dust Grains

Observations have demonstrated that supernovae efficiently produce dust. This is consistent with the hypothesis that supernovae and asymptotic giant branch stars are the primary producers of dust in the Universe. However, there has been a longstanding question of how much of the dust detected in the interiors of young supernova remnants can escape into the interstellar medium. We present new hydrodynamical calculations of the evolution of dust grains that were formed in dense ejecta clumps within a Cas A-like remnant. We follow the dynamics of the grains as they decouple from the gas after their clump is hit by the reverse shock. They are subsequently subject to destruction by thermal and kinetic sputtering as they traverse the remnant. Grains that are large enough ($\sim 0.25\,μ$m for silicates and $\sim 0.1\,μ$m for carbonaceous grains) escape into the interstellar medium while smaller grains get trapped and destroyed. However, grains that reach the interstellar medium still have high velocities, and are subject to further destruction as they are slowed down. We find that for initial grain size distributions that include large ($\sim 0.25 - 0.5\,μ$m) grains, 10--20\% of silicate grains can survive, while 30--50\% of carbonaceous grains survive even when the initial size distribution cuts off at smaller ($0.25\,μ$m) sizes. For a 19 M$_{\odot}$ star similar to the progenitor of Cas A, up to 0.1 M$_{\odot}$ of dust can survive if the dust grains formed are large. Thus we show that supernovae under the right conditions can be significant sources of interstellar dust.

astro-ph.HE↗

arXiv2020

Interstellar Dust and Gas in the Heliosphere

Interstellar dust and gas that enter the heliosphere provide us with important clues about both the heliosphere and the local interstellar medium (LISM). The picture we have of the Local Interstellar Cloud (LIC) from both \emph{in situ} detections and absorption line data presents questions that have important implications for the origins and evolution of the cloud. New detections of $^{60}$Fe on Earth in deep sea crusts and Antarctic snow cores provide evidence for the role of supernovae in shaping the LISM. We discuss our models for the evolution of the LIC inside the Local Bubble and possible explanations for the source of the supernova produced dust.

astro-ph.GA↗

arXiv2020

Turbulence and Energetic Particles in Radiative Shock Waves in the Cygnus Loop I: Shock Properties

We have obtained a contiguous set of long-slit spectra of a shock wave in the Cygnus Loop to investigate its structure, which is far from the morphology predicted by 1D models. Proper motions from Hubble Space Telescope images combined with the known distance to the Cygnus Loop provide an accurate shock speed. Earlier analyses of shock spectra estimated the shock speed, postshock density, temperature, and elemental abundances. In this paper we determine several more shock parameters: a more accurate shock speed, ram pressure, density, compression ratio, dust destruction efficiency, magnetic field strength, and vorticity in the cooling region. From the derived shock properties we estimate the emissivities of synchrotron emission in the radio and pion decay emission in the gamma rays. Both are consistent with the observations if we assume simple adiabatic compression of ambient cosmic rays as in the van der Laan mechanism. We also find that, although the morphology is far from that predicted by 1D models and the line ratios vary dramatically from point to point, the average spectrum is matched reasonably well by 1D shock models with the shock speed derived from the measured proper motion. A subsequent paper will analyze the development of turbulence in the cooling zone behind the shock.

astro-ph.GA↗

arXiv2019

Non-equilibrium ionization in mixed-morphology supernova remnants

The mixed morphology class of supernova remnants (MMSNRs) comprises a substantial fraction of observed remnants and yet there is as yet no consensus on their origin. A clue to their nature is the presence of regions that show X-ray evidence of recombining plasmas. Recent calculations of remnant evolution in a cloudy interstellar medium (ISM) that included thermal conduction but not non-equilibrium ionization (NEI) showed promise in explaining observed surface brightness distributions but could not determine if recombining plasmas were present. In this paper, we present numerical hydrodynamical models of MMSNRs in 2D and 3D including explicit calculation of NEI effects. Both the spatial ionization distribution and temperature-density diagrams show that recombination occurs inside the simulated MMSNR, and that both adiabatic expansion and thermal conduction cause recombination, albeit in different regions. Features created by the adiabatic expansion stand out in the spatial and temperature-density diagrams, but thermal conduction also plays a role. Thus thermal conduction and adiabatic expansion both contribute significantly to the cooling of high-temperature gas. Realistic observational data are simulated with both spatial and spectral input from various regions. We also discuss the possibility of analyzing the sources of recombination and dominant hydrodynamical processes in observations using temperature-density diagrams and spatial maps.

astro-ph.HE↗

arXiv2017

Numerical Simulations of Supernova Remnant Evolution in a Cloudy Interstellar Medium

The mixed morphology class of supernova remnants has centrally peaked X-ray emission along with a shell-like morphology in radio emission. White & Long proposed that these remnants are evolving in a cloudy medium wherein the clouds are evaporated via thermal conduction once being overrun by the expanding shock. Their analytical model made detailed predictions regarding temperature, density and emission profiles as well as shock evolution. We present numerical hydrodynamical models in 2D and 3D including thermal conduction, testing the White & Long model and presenting results for the evolution and emission from remnants evolving in a cloudy medium. We find that, while certain general results of the White & Long model hold, such as the way the remnants expand and the flattening of the X-ray surface brightness distribution, in detail there are substantial differences. In particular we find that the X-ray luminosity is dominated by emission from shocked cloud gas early on, leading to a bright peak which then declines and flattens as evaporation becomes more important. In addition, the effects of thermal conduction on the intercloud gas, which is not included in the White & Long model, are important and lead to further flattening of the X-ray brightness profile as well as lower X-ray emission temperatures.

astro-ph.HE↗

arXiv2016

Dust Destruction by the Reverse Shock in the Cassiopeia A Supernova Remnant

Core collapse supernovae (CCSNe) are important sources of interstellar dust, potentially capable of producing one solar mass of dust in their explosively expelled ejecta. However, unlike other dust sources, the dust has to survive the passage of the reverse shock, generated by the interaction of the supernova blast wave with its surrounding medium. Knowledge of the net amount of dust produced by CCSNe is crucial for understanding the origin and evolution of dust in the local and high-redshift universe. Our aim is to identify the dust destruction mechanisms in the ejecta, and derive the net amount of dust that survives the passage of the reverse shock. We use analytical models for the evolution of a supernova blast wave and of the reverse shock, with special application to the clumpy ejecta of the remnant of Cassiopeia A. We assume that the dust resides in cool oxygen-rich clumps that are uniformly distributed within the remnant and surrounded by a hot X-ray emitting plasma, and that the dust consists of silicates (MgSiO3) and amorphous carbon grains. The passage of the reverse shock through the clumps gives rise to a relative gas-grain motion and also destroys the clumps. Inside the ejecta clouds, dust is processed via kinetic sputtering, which is terminated either when the grains escape the clumps, or when the clumps are destroyed by the reverse shock. In either case, grain destruction proceeds thereafter by thermal sputtering in the hot ambient gas. We find that 11.8% and 15.9% of, respectively, the silicate and carbon dust survives the passage of the reverse shock by the time the shock has reached the center of the remnant. These fractions depend on the morphology of the ejecta and the medium into which the remnant is expanding, as well as the composition and size distribution of the grains that formed in the ejecta. Results will therefore differ for different types of supernovae.

astro-ph.GA↗

arXiv2015

Destruction of Interstellar Dust in Evolving Supernova Remnant Shock Waves

Supernova generated shock waves are responsible for most of the destruction of dust grains in the interstellar medium (ISM). Calculations of the dust destruction timescale have so far been carried out using plane parallel steady shocks, however that approximation breaks down when the destruction timescale becomes longer than that for the evolution of the supernova remnant (SNR) shock. In this paper we present new calculations of grain destruction in evolving, radiative SNRs. To facilitate comparison with the previous study by Jones et al. (1996), we adopt the same dust properties as in that paper. We find that the efficiencies of grain destruction are most divergent from those for a steady shock when the thermal history of a shocked gas parcel in the SNR differs significantly from that behind a steady shock. This occurs in shocks with velocities >~ 200 km/s for which the remnant is just beginning to go radiative. Assuming SNRs evolve in a warm phase dominated ISM, we find dust destruction timescales are increased by a factor of ~2 compared to those of Jones et al. (1996), who assumed a hot gas dominated ISM. Recent estimates of supernova rates and ISM mass lead to another factor of ~3 increase in the destruction timescales, resulting in a silicate grain destruction timescale of ~2-3 Gyr. These increases, while not able resolve the problem of the discrepant timescales for silicate grain destruction and creation, are an important step towards understanding the origin, and evolution of dust in the ISM.

astro-ph.GA↗

arXiv2013

IBEX, SWCX and a Consistent Model for the Local ISM

The Local Interstellar Medium (LISM) makes its presence felt in the heliosphere in a number of ways including inflowing neutral atoms and dust and shaping of the heliosphere via its ram pressure and magnetic field. Modelers of the heliosphere need to know the ISM density and magnetic field as boundary conditions while ISM modelers would like to use the data and models of the heliosphere to constrain the nature of the LISM. An important data set on the LISM is the diffuse soft X-ray background (SXRB), which is thought to originate in hot gas that surrounds the local interstellar cloud (LIC) in which the heliosphere resides. However, in the past decade or so it has become clear that there is a significant X-ray foreground due to emission within the heliosphere generated when solar wind ions charge exchange with inflowing neutrals. The existence of this SWCX emission complicates the interpretation of the SXRB. We discuss how data from IBEX and models for the Ribbon in particular provide the possibility of tying together heliosphere models with models for the LISM, providing a consistent picture for the pressure in the LISM, the ionization in the LIC and the size and shape of the heliosphere.

astro-ph.GA↗

arXiv2012

Trajectories and Distribution of Interstellar Dust Grains in the Heliosphere

The solar wind carves a bubble in the surrounding interstellar medium (ISM), known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full 3-D magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done separately for each polarity. Small grains a_gr ~ 0.01 micron are completely excluded from the inner heliosphere. Large grains, a_gr ~ 1.0 micron pass into the inner solar system and are concentrated near the Sun by its gravity. Trajectories of intermediate size grains depend strongly on the SWMF polarity. When the field has magnetic north pointing to ecliptic north, the field de-focuses the grains resulting in low densities in the inner heliosphere, while for the opposite polarity the dust is focused near the Sun. The ISDG density outside the heliosphere inferred from applying the model results to in situ dust measurements is inconsistent with local ISM depletion data for both SWMF polarities, but is bracketed by them. This result points to the need to include the time variation in the SWMF polarity during grain propagation. Our results provide valuable insights for interpretation of the in situ dust observations from Ulysses.

astro-ph.SR↗

arXiv2012

Interstellar Dust Close to the Sun

The low density interstellar medium (ISM) close to the Sun and inside of the heliosphere provides a unique laboratory for studying interstellar dust grains. Grain characteristics in the nearby ISM are obtained from observations of interstellar gas and dust inside of the heliosphere and the interstellar gas towards nearby stars. Comparison between the gas composition and solar abundances suggests that grains are dominated by olivines and possibly some form of iron oxide. Measurements of the interstellar Ne/O ratio by the Interstellar Boundary Explorer spacecraft indicate that a high fraction of interstellar oxygen in the ISM must be depleted onto dust grains. Local interstellar abundances are consistent with grain destruction in ~150 km/s interstellar shocks, provided that the carbonaceous component is hydrogenated amorphous carbon and carbon abundances are correct. Variations in relative abundances of refractories in gas suggest variations in the history of grain destruction in nearby ISM. The large observed grains, > 1 micron, may indicate a nearby reservoir of denser ISM. Theoretical three-dimensional models of the interaction between interstellar dust grains and the solar wind predict that plumes of about 0.18 micron dust grains form around the heliosphere.

astro-ph.GA↗

arXiv2010

Comparisons of the Interstellar Magnetic Field Directions obtained from the IBEX Ribbon and Interstellar Polarizations

Variations in the spatial configuration of the interstellar magnetic field (ISMF) near the Sun can be constrained by comparing the ISMF direction at the heliosphere found from the Interstellar Boundary Explorer spacecraft (IBEX) observations of a 'Ribbon' of energetic neutral atoms (ENAs), with the ISMF direction derived from optical polarization data for stars within ~40 pc. Using interstellar polarization observations towards ~30 nearby stars within 90 deg of the heliosphere nose, we find that the best fits to the polarization position angles are obtained for a magnetic pole directed towards ecliptic coordinates of lambda, beta 263 deg, 37 deg (or galactic coordinates of L,B 38 deg, 23deg), with uncertainties of +/- 35 deg, based on the broad minimum of the best fits and the range of data quality. This magnetic pole is 33 deg from the magnetic pole that is defined by the center of the arc of the ENA Ribbon. The IBEX ENA ribbon is seen in sightlines that are perpendicular to the ISMF as it drapes over the heliosphere. The similarity of the polarization and Ribbon directions for the local ISMF suggest that the local field is coherent over scale sizes of tens of parsecs. The ISMF vector direction is nearly perpendicular to the flow of local ISM through the local standard of rest, supporting a possible local ISM origin related to an evolved expanding magnetized shell. The local ISMF direction is found to have a curious geometry with respect to the cosmic microwave background dipole moment.

astro-ph.GA↗

arXiv2010

Five Years of Mid-Infrared Evolution of the Remnant of SN 1987A: The Encounter Between the Blast Wave and the Dusty Equatorial Ring

We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from ~180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of ~5x10^6 K and 3x10^4 cm-3, respectively. The mass of the radiating dust is ~1.2x10^(-6) Msun on day 7554, and scales linearly with IR flux. The infrared to soft-X-ray flux ratio is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of of this ratio suggests that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased with a time dependence of t^(0.87), t being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER.

astro-ph.CO↗

arXiv2008

The Origins and Physical Properties of the Complex of Local Interstellar Clouds

The Complex of Local Interstellar Clouds (CLIC) is a relatively tight grouping of low density, warm, partially ionized clouds within about 15 pc of the Solar System. The Local Interstellar Cloud (LIC) is the cloud observed on most lines of sight and may be the cloud that immediately surrounds our Solar System, the properties of which set the outer boundary conditions of the heliosphere. Using absorption line data toward nearby stars, in situ observations of inflowing interstellar gas from spacecraft in the Solar System, and theoretical modeling of the interstellar radiation field and radiative transfer, we can deduce many characteristics of the LIC. We find that the LIC is partially ionized with modest electron density, n(e) ~ 0.07 cm^-3. The combination of its temperature and ionization favor photoionization/thermal equilibrium over a non-equilibrium cooling cloud picture. The abundances in the LIC suggest moderate dust destruction for silicate dust but complete destruction of carbonaceous grains. An origin for the LIC as a density enhancement in the ambient medium that has been overrun by a shock seems likely, while its velocity away from the Sco-Cen association points to a possible connection to that region and the Loop I bubble.

astro-ph↗