We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of sub-micron dust repelled by the host star's wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few AU across -- the "avalanche zone" -- located on AU Mic's primary "birth" ring, at a true distance of $\sim$35 AU from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the sub-micron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind's magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass-loss rate or, more speculatively, by some self-regulating limit cycle.
A collisional avalanche is set off by the breakup of a large planetesimal, releasing small unbound grains that enter a debris disc located further away from the star, triggering there a collisional chain reaction that can potentially create detectable transient structures. We explore this mechanism, using for the first time a code coupling dynamical and collisional evolutions, and investigate if avalanches could explain the short-term luminosity variations observed in some extremely bright discs. We consider two set-ups: a cold disc case, with a dust release at 10au and an outer disc extending…
Understanding the motion of debris cloud produced by the anti-satellite test can help us to know the danger of these tests. This study presents the orbit status of 57 fragments observed by the CelesTrak and presented in the NORAD Two-Line Element Sets of India Anti-Satellite Test. There are 10 of these observed fragments have altitudes of the apogee larger than 1000.0km, the maximum one is 1725.7km. We also numerical calculated the number of debris, the results show that the number of debris with the diameter larger than 0.2m is 14, the number of debris with the diameter larger than 0.01m is 6…
We explore whether assumptions about dust grain shape affect resulting estimates of the composition and grain size distribution of the AU Microscopii (AU Mic) debris disk from scattered light data collected by Lomax et al. (2018). The near edge-on orientation of the AU Mic debris disk makes it ideal for studying the effect of the scattering phase function (SPF) on the measured flux ratios as a function of wavelength and projected distance. Previous efforts to model the AU Mic debris disk have invoked a variety of dust grain compositions and explored the effect of porosity, but did not undertak…
We present new ALMA Band 7 observations of the edge-on debris disc around the M1V star GSC 07396-00759. At ~20 Myr old and in the beta Pictoris Moving Group along with AU Mic, GSC 07396-00759 joins it in the handful of low mass M-dwarf discs to be resolved in the sub-mm. With previous VLT/SPHERE scattered light observations we present a multi-wavelength view of the dust distribution within the system under the effects of stellar wind forces. We find the mm dust grains to be well described by a Gaussian torus at 70 au with a FWHM of 48 au and we do not detect the presence of CO in the system. O…
Context. Little is known about the properties of the warm (Tdust >~ 150 K) debris disk material located close to the central star, which has a more direct link to the formation of terrestrial planets than the low temperature debris dust that has been detected to date. Aims. To discover new warm debris disk candidates that show large 18 micron excess and estimate the fraction of stars with excess based on the AKARI/IRC Mid-Infrared All-Sky Survey data. Methods. We have searched for point sources detected in the AKARI/IRC All-Sky Survey, which show a positional match with A-M dwarf stars in the …
We investigate whether varying the dust composition (described by the optical constants) can solve a persistent problem in debris disk modeling--the inability to fit the thermal emission without over-predicting the scattered light. We model five images of the beta Pictoris disk: two in scattered light from HST/STIS at 0.58 microns and HST/WFC3 at 1.16 microns, and three in thermal emission from Spitzer/MIPS at 24 microns, Herschel/PACS at 70 microns, and ALMA at 870 microns. The WFC3 and MIPS data are published here for the first time. We focus our modeling on the outer part of this disk, cons…
We present multi-wavelength photometric monitoring of WD 1145+017, a white dwarf exhibiting periodic dimming events interpreted to be the transits of orbiting, disintegrating planetesimals. Our observations include the first set of near-infrared light curves for the object, obtained on multiple nights over the span of one month, and recorded multiple transit events with depths varying between ~20 to 50 per cent. Simultaneous near-infrared and optical observations of the deepest and longest duration transit event were obtained on two epochs with the Anglo-Australian Telescope and three optical …
We report an intriguing debris disk towards the F3V star HD 15407A, in which an extremely large amount of warm fine dust (~ 10^(-7) M_Earth) is detected. The dust temperature is derived as ~ 500-600 K and the location of the debris dust is estimated as 0.6-1.0 AU from the central star, a terrestrial planet region. The fractional luminosity of the debris disk is ~ 0.005, which is much larger than those predicted by steady-state models of the debris disk produced by planetesimal collisions. The mid-infrared spectrum obtained by Spitzer indicates the presence of abundant micron-sized silica dust,…
We present imaging observations at 1.3 millimeters of the debris disk surrounding the nearby M-type flare star AU Mic with beam size 3 arcsec (30 AU) from the Submillimeter Array. These data reveal a belt of thermal dust emission surrounding the star with the same edge-on geometry as the more extended scattered light disk detected at optical wavelengths. Simple modeling indicates a central radius of ~35 AU for the emission belt. This location is consistent with the reservoir of planetesimals previously invoked to explain the shape of the scattered light surface brightness profile through size-…
Gas has been detected in a number of debris disk systems. This gas may have arisen from grain sublimation or grain photodesorption. It interacts with the surrounding dust grains through a number of charge and heat exchanges. Studying the chemical composition and physical state of this gas can therefore reveal much about the dust component in these debris disks. We have produced a new code, ontario, to address gas emission from dusty gas-poor disks around A--F stars. This code computes the gas ionization and thermal balance self-consistently, with particular care taken of heating/cooling mechan…
We report Herschel and AKARI photometric observations at far-infrared (FIR) wavelengths of the debris disk around the F3V star HD 15407A, in which the presence of an extremely large amount of warm dust (~500-600 K) has been suggested by mid-infrared (MIR) photometry and spectroscopy. The observed flux densities of the debris disk at 60-160 micron are clearly above the photospheric level of the star, suggesting excess emission at FIR as well as at MIR wavelengths previously reported. The observed FIR excess emission is consistent with the continuum level extrapolated from the MIR excess, sugges…
The spatially resolved AU Mic debris disc is among the most famous and best-studied debris discs. We aim at a comprehensive understanding of the dust production and the dynamics of the disc objects with in depth collisional modelling including stellar radiative and corpuscular forces. Our models are compared to a suite of observational data for thermal and scattered light emission, ranging from the ALMA radial surface brightness profile at 1.3mm to polarisation measurements in the visible. Most of the data can be reproduced with a planetesimal belt having an outer edge at around 40au and subse…
Herschel images in six photometric bands show the thermal emission of the debris disk surrounding beta Pic. In the three PACS bands at 70 micron, 100 micron and 160 micron and in the 250 micron SPIRE band, the disk is well-resolved, and additional photometry is available in the SPIRE bands at 350 micron and 500 micron, where the disk is only marginally resolved. The SPIRE maps reveal a blob to the southwest of beta Pic, coinciding with submillimetre detection of excess emission in the disk. We investigated the nature of this blob. Our comparison of the colours, spectral energy distribution and…
Observations of debris disks allow for the study of planetary systems, even where planets have not been detected. However, debris disks are often only characterized by unresolved infrared excesses that resemble featureless blackbodies, and the location of the emitting dust is uncertain due to a degeneracy with the dust grain properties. Here we characterize the Spitzer IRS spectra of 22 debris disks exhibiting 10 micron silicate emission features. Such features arise from small warm dust grains, and their presence can significantly constrain the orbital location of the emitting debris. We find…
An Inclined, Eccentric Planet and an Inner Debris Disk Could Reproduce AU Mic Structure
University of Exeter（埃克塞特大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）；John Hopkins University（约翰斯·霍普金斯大学）；University of Colorado Boulder（科罗拉多大学博尔德分校）
Debris disks are scaled-up analogs of the Kuiper Belt in which dust is generated by collisions between planetesimals. In the "collisional cascade" model of debris disks, dust lost to radiation pressure and winds is constantly replenished by grinding collisions between planetesimals. The model assumes that collisions are destructive and involve large velocities; this assumption has not been tested beyond our Solar System. We present 0"25 ($\approx$2.4 au) resolution observations of the $λ$ = 450 $μ$m dust continuum emission from the debris disk around the nearby M dwarf AU Microscopii with the …
Context. The formation of planetary systems is a common, yet complex mechanism. Numerous stars have been identified to possess a debris disk, a proto-planetary disk or a planetary system. The understanding of such formation process requires the study of debris disks. These targets are substantial and particularly suitable for optical and infrared observations. Sparse Aperture masking (SAM) is a high angular resolution technique strongly contributing to probe the region from 30 to 200 mas around the stars. This area is usually unreachable with classical imaging, and the technique also remains h…
We present 24 micron photometry of the intermediate-age open cluster Praesepe. We assemble a catalog of 193 probable cluster members that are detected in optical databases, the Two Micron All Sky Survey (2MASS), and at 24 micron, within an area of ~ 2.47 square degrees. Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. Corrections for sampling statistics yield a 24 micron excess fraction (debris disk fraction) of 6.5 +- 4.1% for luminous and 1.9 +- 1.2% for solar-type stars. The incidence of excesses is in agreement with the decay trend of deb…
We investigate the chance of detecting proto-planetary or debris disks in stars that induce microlensing events (lenses). The modification of the light curves shapes due to occultation and extinction by the disks as well as the additional gravitational deflection caused by the additional mass is considered. The magnification of gravitational microlensing events is calculated using the ray shooting method. The occultation is taken into account by neglecting or weighting the images on the lens plane according to a transmission map of the corresponding disk for a point source point lens (PSPL) mo…
We present 5 to 15 micron Spitzer Infrared Spectrograph (IRS) low resolution spectral data of a candidate debris disk around an M4.5 star identified as a likely member of the ~40 Myr old cluster NGC2547. The IRS spectrum shows a silicate emission feature, indicating the presence of warm, small, (sub)micron-sized dust grains in the disk. Of the fifteen previously known candidate debris disks around M-type stars, the one we discuss in this paper is the first to have an observed mid-infrared spectrum and is also the first to have measured silicate emission. We combined the IRS data with ancillary…
The connection between the nature of a protoplanetary disk and that of a debris disk is not well understood. Dust evolution, planet formation, and disk dissipation likely play a role in the processes involved. We aim to reconcile both manifestations of dusty circumstellar disks through a study of optically thin Class III disks and how they correlate to younger and older disks. In this work, we collect literature and ALMA archival millimeter fluxes for 85 disks (8%) of all Class III disks across nearby star-forming regions. We derive millimeter-dust masses $M_{\text{dust}}$ and compare these wi…
Photometry of the A0 V main-sequence star HD 106797 with AKARI and Gemini/T-ReCS is used to detect excess emission over the expected stellar photospheric emission between 10 and 20 micron, which is best attributed to hot circumstellar debris dust surrounding the star. The temperature of the debris dust is derived as Td ~ 190 K by assuming that the excess emission is approximated by a single temperature blackbody. The derived temperature suggests that the inner radius of the debris disk is ~ 14 AU. The fractional luminosity of the debris disk is 1000 times brighter than that of our own zodiacal…
The vertical distribution of dust in debris disks is sensitive to the number and size of large planetesimals dynamically stirring the disk, and is therefore well-suited for constraining the prevalence of otherwise unobservable Uranus and Neptune analogs. Information regarding stirring bodies has previously been inferred from infrared and optical observations of debris disk vertical structure, but theoretical works predict that the small particles traced by short-wavelength observations will be `puffed up' by radiation pressure, yielding only upper limits. The large grains that dominate the dis…
Spectro-photometry of debris disks in total intensity and polarimetry can provide new insight into the properties of the dust grains therein (size distribution and optical properties). We aim to constrain the morphology of the highly inclined debris disk HD 32297. We also intend to obtain spectroscopic and polarimetric measurements to retrieve information on the particle size distribution within the disk for certain grain compositions. We observed HD 32297 with SPHERE in Y, J, and H bands in total intensity and in J band in polarimetry. The observations are compared to synthetic models of debr…
We present observations of the debris disk around gamma Doradus, an F1V star, from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The disk is well-resolved at 70, 100 and 160 micron, resolved along its major axis at 250 micron, detected but not resolved at 350 micron, and confused with a background source at 500 micron. It is one of our best resolved targets and we find it to have a radially broad dust distribution. The modelling of the resolved images cannot distinguish between two configurations: an arrangement of a warm inner ri…
We present new high fidelity optical coronagraphic imagery of the inner $\sim$50 au of AU Mic's edge-on debris disk using the BAR5 occulter of the Hubble Space Telescope Imaging Spectrograph (HST/STIS) obtained on 26-27 July 2018. This new imagery reveals that "feature A", residing at a projected stellocentric separation of 14.2 au on SE-side of the disk, exhibits an apparent "loop-like" morphology at the time of our observations. The loop has a projected width of 1.5 au and rises 2.3 au above the disk midplane. We also explored TESS photometric observations of AU Mic that are consistent with …
AU Microscopii (AU Mic) is the second closest pre main sequence star, at a distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses a relatively rare and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star, and with clumps exhibiting non-Keplerian motion. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic activity on the star. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbit…
We present 1.3 millimeter ALMA Cycle 0 observations of the edge-on debris disk around the nearby, ~10 Myr-old, M-type star AU Mic. These observations obtain 0.6 arcsec (6 AU) resolution and reveal two distinct emission components: (1) the previously known dust belt that extends to a radius of 40 AU, and (2) a newly recognized central peak that remains unresolved. The cold dust belt of mass about 1 lunar mass is resolved in the radial direction with a rising emission profile that peaks sharply at the location of the outer edge of the "birth ring" of planetesimals hypothesized to explain the mid…
Analyzing Spitzer and Herschel archival measurements we identified a debris disk around the young K7/M0 star CP-72 2713. The system belongs to the 24Myr old $β$ Pic moving group. Our new 1.33mm continuum observation, obtained with the ALMA 7-m array, revealed an extended dust disk with a peak radius of 140au, probably tracing the location of the planetesimal belt in the system. The disk is outstandingly large compared to known spatially resolved debris disks and also to protoplanetary disks around stars of comparable masses. The dynamical excitation of the belt at this radius is found to be re…
Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE photometry, were obtained. The 123 objects observed by the…
Mid-infrared (5 micron to 25 micron) transmission/absorption spectra of differentiated meteorites (achondrites) were measured to permit comparison with astronomical observations of dust in different stages of evolution of young stellar objects. In contrast to primitive chondrites, achondrites underwent heavy metamorphism and/or extensive melting and represent more advanced stages of planetesimal evolution. Spectra were obtained from primitive achondrites (acapulcoite, winonaite, ureilite, and brachinite) and differentiated achondrites (eucrite, diogenite, aubrite, and mesosiderite silicates). …
We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple unstable gas giants. We previously showed that the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and debris disks. Here we present new simulations that show that this connection is qualitatively robust to changes in: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk. We discuss how variations in these …
A Recurrent Infrared Modulation in the Warm Post-impact Debris Disk NGC 2547 ID8
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Beijing Normal University（北京师范大学）；University of Chinese Academy of Sciences（中国科学院大学）；Beihang University（北京航空航天大学）
(abridged) We present 24 and 70 micron MIPS observations of 70 A through M-type dwarfs with estimated ages from 8 Myr to 1.1 Gyr, as part of a Spitzer guaranteed time program. Our sample is selected from stars with common youth indicators such as lithium abundance, X-ray activity, chromospheric activity, and rapid rotation. We compare our MIPS observations to empirically derived K-[24] colors as a function of the stellar effective temperature to identify 24 and 70 micron excesses. We confirm the previously published 70 micron excesses for HD 92945, HD 112429, and AU Mic. We present the discove…
We observed the edge-on, planet-bearing disk of β Pictoris using T-ReCS at Gemini to clarify and extend previous observations and conclusions about this unique system. Our spectroscopy and spectral modeling of the 10-micron silicate feature constrain the spatial distributions of three representative dust components (0.1-micron/2.0-micron glassy olivine and crystalline forsterite) across the inner 20-AU of the disk. We confirm that the 2.0-micron glassy olivine is strongly peaked in the disk center and that the 0.1-micron glassy olivine does not show this concentration, but rather is double pea…
We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J=8-7 rotational transition from the vibrational ground state, carried out with the APEX sub-millimeter telescope and heterodyne receiver at 863 microns, and (2) a search at 8.3 microns for the P(17) ro-vibrational transition of gas phase SiO, carried out with VLT/VISIR with a resolution, $λ/Δλ$, of 30000. The APEX measurement resulted in a 3 $σ$ non-detection of an interstellar feature, but only an upper limit to emission at the radial velocity and line…
The Spitzer Space Telescope has advanced debris disk science tremendously with a wealth of information on debris disks around nearby A, F, G, K and M stars at 24 and 70 microns with the MIPS photometer and at 8-34 microns with IRS. Here we present 160 micron observations of a small sub-set of these stars. At this wavelength, the stellar photospheric emission is negligible and any detected emission corresponds to cold dust in extended Kuiper belt analogs. However, the Spitzer 160 micron observations are limited in sensitivity by the large beam size which results in significant ''noise'' due to …
The formation channel of the tens of compact debris discs which orbit white dwarfs (WDs) at a distance of one Solar radius remains unknown. Asteroids that survive the giant branch stellar phases beyond a few au are assumed to be dynamically thrust towards the WD and tidally disrupted within its Roche radius, generating extremely eccentric (e>0.98) rings. Here, we establish that WD radiation compresses and circularizes the orbits of super-micron to cm-sized ring constituents to entirely within the WD's Roche radius. We derive a closed algebraic formula which well-approximates the shrinking time…
[abridged] We present resolved images of the HR 4796A debris disk using the Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the disk at 0.77 \microns, 0.91 \microns, 0.99 \microns, 2.15 \microns, 3.1 \microns, 3.3 \microns, and 3.8 \microns. We find that the deprojected center of the ring is offset from the star by 4.76$\pm$1.6 AU and that the deprojected eccentricity is 0.06$\pm$0.02, in general agreement with previous studies. We find that the average width of the ring is 14$^{+3}_{-2}%$, also comparable to previous measurements. Such a narrow ring precludes the exist…
We present an analysis of debris disk data around Solar-type stars (spectral types F0-K5) using the steady-state analytical model of Wyatt et al. (2007). Models are fitted to published data from the FEPS (Meyer et al. 2006) project and various GTO programs obtained with MIPS on the Spitzer Space Telescope at 24 micron and 70 micron, and compared to a previously published analysis of debris disks around A stars using the same evolutionary model. We find that the model reproduces most features found in the data sets, noting that the model disk parameters for solar-type stars are different to tho…
