Article

# Debris Disk Evolution around A Stars

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(Impact Factor: 5.99). 12/2008; 653(1):675. DOI: 10.1086/508649
Source: arXiv

ABSTRACT

We report 24 and/or 70 μm measurements of ~160 A-type main-sequence stars using the Multiband Imaging Photometer for Spitzer (MIPS). Their ages range from 5 to 850 Myr, based on estimates from the literature (cluster or moving group associations) or from the H-R diagram and isochrones. The thermal infrared excess is identified by comparing the deviation (~3% and ~15% at the 1 σ level at 24 and 70 μm, respectively) between the measurements and the synthetic Kurucz photospheric predictions. Stars showing excess infrared emission due to strong emission lines or extended nebulosity seen at 24 μm are excluded from our sample; therefore, the remaining infrared excesses are likely to arise from circumstellar debris disks. At the 3 σ confidence level, the excess rate at 24 and 70 μm is 32% and ≥33% (with an uncertainty of 5%), considerably higher than what has been found for old solar analogs and M dwarfs. Our measurements place constraints on the fractional dust luminosities and temperatures in the disks. We find that older stars tend to have lower fractional dust luminosity than younger ones. While the fractional luminosity from the excess infrared emission follows a general 1/t relationship, the values at a given stellar age vary by at least 2 orders of magnitude. We also find that (1) older stars possess a narrow range of temperature distribution peaking at colder temperatures, and (2) the disk emission at 70 μm persists longer than that at 24 μm. Both results suggest that the debris disk clearing process is more effective in the inner regions.

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Available from: James Muzerolle, Jun 10, 2014
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• "The debris disc around Vega was the first debris disc discovered in this way (Aumann et al. 1984) and after that more than 100 discs have been subsequently discovered. Observations from recent surveys indicate that at least 15 per cent of FGK stars and 32 per cent of A stars have a detectable amount of circumstellar debris (Bonsor et al. (2014), Bryden et al. (2006), Moro-Martín et al. (2007), Hillenbrand et al. (2008),Greaves et al. (2009) and Su et al. (2006)). "
##### Article: Feasibility of transit photometry of nearby debris discs
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ABSTRACT: Dust in debris discs is constantly replenished by collisions between larger objects. In this paper, we investigate a method to detect these collisions. We generate models based on recent results on the Fomalhaut debris disc, where we simulate a background star transiting behind the disc, due to the proper motion of Fomalhaut. By simulating the expanding dust clouds caused by the collisions in the debris disc, we investigate whether it is possible to observe changes in the brightness of the background star. We conclude that in the case of the Fomalhaut debris disc, changes in the optical depth can be observed, with values of the optical depth ranging from $10^{-0.5}$ for the densest dust clouds to $10^{-8}$ for the most diffuse clouds with respect to the background optical depth of $\sim1.2\times10^{-3}$.
Monthly Notices of the Royal Astronomical Society 02/2014; 439(1). DOI:10.1093/mnras/stt2471 · 5.11 Impact Factor
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##### Article: Extrasolar Kuiper Belt Dust Disks
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ABSTRACT: The dust disks observed around mature stars are evidence that plantesimals are present in these systems on spatial scales that are similar to that of the asteroids and the Kuiper belt objects (KBOs) in the solar system. These dust disks (a.k.a. "debris disks") present a wide range of sizes, morphologies, and properties. It is inferred that their dust mass declines with time as the dust-producing planetesimals get depleted, and that this decline can be punctuated by large spikes that are produced as a result of individual collisional events. The lack of solid-state features indicate that, generally, the dust in these disks have sizes >~10 æm, but exceptionally, strong silicate features in some disks suggest the presence of large quantities of small grains, thought to be the result of recent collisions. Spatially resolved observations of debris disks show a diversity of structural features, such as inner cavities, warps, offsets, brightness asymmetries, spirals, rings, and clumps. There is growing evidence that, in some cases, these structures are the result of the dynamical perturbations of a massive planet. Our solar system also harbors a debris disk and some of its properties resemble those of extrasolar debris disks. From the cratering record, we can infer that its dust mass has decayed with time, and that there was at least one major "spike" in the past during the late heavy bombardment. This offers a unique opportunity to use extrasolar debris disks to shed some light in how the solar system might have looked in the past. Similarly, our knowledge of the solar system is influencing our understanding of the types of processes that might be at play in the extrasolar debris disks.
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##### Article: Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer . I. The Stellar Calibrator Sample and the 24 μm Calibration
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ABSTRACT: We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 µm channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54 × 10 −2 MJy sr −1 (DN/s) −1 , with a nominal uncertainty of 2%. We discuss the data-reduction procedures required to attain this accuracy; without these procdures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6%±0.6% lower. We extend this work to predict 24 µm flux densities for a sample of 238 stars which covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 µm. This sample covers a factor of ∼ 460 in 24 µm flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3-second exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10-and 30-second exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a root-mean-square scatter of only 0.4%. Finally, we show that the point spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.
Publications of the Astronomical Society of the Pacific 05/2007; 119(859). DOI:10.1086/521881 · 3.50 Impact Factor