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تسجيل مستخدم جديدA new sample of warm extreme debris disks from the ALLWISE catalog
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Extreme debris disks (EDDs) are rare systems with peculiarly large amounts of warm dust that may stem from recent giant impacts between planetary embryos during the final phases of terrestrial planet growth. Here we report on the identification and characterization of six new EDDs. These disks surround F5-G9 type main-sequence stars with ages >100 Myr, have dust temperatures higher than 300K and fractional luminosities between 0.01 and 0.07. Using time-domain photometric data at 3.4 and 4.6$mu$m from the WISE all sky surveys, we conclude that four of these disks exhibited variable mid-infrared emission between 2010 and 2019. Analyzing the sample of all known EDDs, now expanded to 17 objects, we find that 14 of them showed changes at 3-5$mu$m over the past decade suggesting that mid-infrared variability is an inherent characteristic of EDDs. We also report that wide-orbit pairs are significantly more common in EDD systems than in the normal stellar population. While current models of rocky planet formation predict that the majority of giant collisions occur in the first 100 Myr, we find that the sample of EDDs is dominated by systems older than this age. This raises the possibility that the era of giant impacts may be longer than we think, or that some other mechanism(s) can also produce EDDs. We examine a scenario where the observed warm dust stems from the disruption and/or collisions of comets delivered from an outer reservoir into the inner regions, and explore what role the wide companions could play in this process.
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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 Tycho-2 Spectral Type Catalogue and exhibit excess emission at 18 micron compared to that expected from the Ks magnitude in the 2MASS catalogue. Results. We find 24 warm debris candidates including 8 new candidates among A-K stars. The apparent debris disk frequency is estimated to be 2.8 +/- 0.6%. We also find that A stars and solar-type FGK stars have different characteristics of the inner component of the identified debris disk candidates --- while debris disks around A stars are cooler and consistent with steady-state evolutionary model of debris disks, those around FGK stars tend to be warmer and cannot be explained by the steady-state model.
The presence of dusty debris around main sequence stars denotes the existence of planetary systems. Such debris disks are often identified by the presence of excess continuum emission at infrared and (sub-)millimetre wavelengths, with measurements at
longer wavelengths tracing larger and cooler dust grains. The exponent of the slope of the disk emission at sub-millimetre wavelengths, `q, defines the size distribution of dust grains in the disk. This size distribution is a function of the rigid strength of the dust producing parent planetesimals. As part of the survey `PLAnetesimals around TYpical Pre-main seqUence Stars (PLATYPUS) we observed six debris disks at 9-mm using the Australian Telescope Compact Array. We obtain marginal (~3-sigma) detections of three targets: HD 105, HD 61005, and HD 131835. Upper limits for the three remaining disks, HD20807, HD109573, and HD109085, provide further constraint of the (sub-)millimetre slope of their spectral energy distributions. The values of q (or their limits) derived from our observations are all smaller than the oft-assumed steady state collisional cascade model (q = 3.5), but lie well within the theoretically expected range for debris disks q ~ 3 to 4. The measured q values for our targets are all < 3.3, consistent with both collisional modelling results and theoretical predictions for parent planetesimal bodies being `rubble piles held together loosely by their self-gravity.
The architectures of debris disks encode the history of planet formation in these systems. Studies of debris disks via their spectral energy distributions (SEDs) have found infrared excesses arising from cold dust, warm dust, or a combination of the
two. The cold outer belts of many systems have been imaged, facilitating their study in great detail. Far less is known about the warm components, including the origin of the dust. The regularity of the disk temperatures indicates an underlying structure that may be linked to the water snow line. If the dust is generated from collisions in an exo-asteroid belt, the dust will likely trace the location of the water snow line in the primordial protoplanetary disk where planetesimal growth was enhanced. If instead the warm dust arises from the inward transport from a reservoir of icy material farther out in the system, the dust location is expected to be set by the current snow line. We analyze the SEDs of a large sample of debris disks with warm components. We find that warm components in single-component systems (those without detectable cold components) follow the primordial snow line rather than the current snow line, so they likely arise from exo-asteroid belts. While the locations of many warm components in two-component systems are also consistent with the primordial snow line, there is more diversity among these systems, suggesting additional effects play a role.
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 d
isks 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 on-going 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.
We have bandmerged candidate transiting planetary systems (from the Kepler satellite) and confirmed transiting planetary systems (from the literature) with the recent Wide-field Infrared Survey Explorer (WISE) preliminary release catalog. We have fou
nd 13 stars showing infrared excesses at either 12 and/or 22 microns. Without longer wavelength observations it is not possible to conclusively determine the nature of the excesses, although we argue that they are likely due to debris disks around the stars. If confirmed, our sample ~ doubles the number of currently known warm excess disks around old main sequence stars. The ratios between the measured fluxes and the stellar photospheres are generally larger than expected for Gyr-old stars, such as these planetary hosts. Assuming temperature limits for the dust and emission from large dust particles, we derive estimates for the disk radii. These values are comparable to the planets semi-major axis, suggesting that the planets may be stirring the planetesimals in the system.
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