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- Krivov, A. V., et al.
(författare)
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Can gas in young debris disks be constrained by their radial brightness profiles?
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 507:3, s. 1503-1516
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Tidskriftsartikel (refereegranskat)abstract
- Disks around young stars are known to evolve from optically thick, gas-dominated protoplanetary disks to optically thin, almost gas-free debris disks. It is thought that the primordial gas is largely removed at ages of ~10 Myr and indeed, only little amounts of gas have been deduced from observations for debris disks at ages of ⪆10 Myr. However, gas detections are difficult and often indirect, not allowing one to discern the true gas densities. This suggests using dynamical arguments: it has been argued that gas, if present with higher densities, would lead to flatter radial profiles of the dust density and brightness than those actually observed. In this paper, we systematically study the influence of gas on the radial profiles of brightness. We assume that dust is replenished by planetesimals orbiting in a “birth ring” and model the dust distribution and scattered-light brightness profile in the outer part of the disk exterior to the birth ring, under different assumptions about the gas component. Our numerical simulations, supported with an analytic model, show that the radial profile of dust density and the surface brightness are surprisingly insensitive to variation of the parameters of a central star, location of the dust-producing planetesimal belt, dustiness of the disk and - most importantly - the parameters of the ambient gas. The radial brightness slopes in the outer disks are all typically in the range -3...-4. This result holds for a wide range of gas densities (three orders of magnitude), for different radial profiles of the gas temperature, both for gas of solar composition and gas of strongly non-solar composition. The slopes of -3...-4 we find are the same that were theoretically found for gas-free debris disks, and they are the same as actually retrieved from observations of many debris disks. Our specific results for three young (10-30 Myr old), spatially resolved, edge-on debris disks (β Pic, HD 32297, and AU Mic) show that the observed radial profiles of the surface brightness do not pose any stringent constraints on the gas component of the disk. We cannot exclude that outer parts of the systems may have retained substantial amounts of primordial gas which is not evident in the gas observations (e.g. as much as 50 Earth masses for β Pic). However, the possibility that gas, most likely secondary, is only present in little to moderate amounts, as deduced from gas detections (e.g. ~0.05 Earth masses in the β Pic disk or even less), remains open, too.
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| 2. |
- Liseau, René, 1949, et al.
(författare)
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q1 Eridani: a solar-type star with a planet and a dust belt
- 2008
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Ingår i: Astronomy & Astrophysics. ; 480, s. L47-L50
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Tidskriftsartikel (refereegranskat)abstract
- Context: Far-infrared excess emission from main-sequence stars is due to dust produced by orbiting minor bodies. In these disks, larger bodies, such as planets, may also be present and the understanding of their incidence and influence currently presents a challenge. Aims: Only very few solar-type stars exhibiting an infrared excess and harbouring planets are known to date. Indeed, merely a single case of a star-planet-disk system has previously been detected at submillimeter (submm) wavelengths. Consequently, one of our aims is to understand the reasons for these poor statistics, i.e., whether these results reflected the composition and/or the physics of the planetary disks or were simply due to observational bias and selection effects. Finding more examples would be very significant. Methods: The selected target, q1 Eri, is a solar-type star, which was known to possess a planet, q1 Eri b, and to exhibit excess emission at IRAS wavelengths, but had remained undetected in the millimeter regime. Therefore, submm flux densities would be needed to better constrain the physical characteristics of the planetary disk. Consequently, we performed submm imaging observations of q1 Eri. Results: The detected dust toward q1 Eri at 870 μm exhibits the remarkable fact that the entire SED, from the IR to mm-wavelengths, is fit by a single-temperature blackbody function (60 K). This would imply that the emitting regions are confined to a narrow region (ring) at radial distances much larger than the orbital distance of q1 Eri b, and that the emitting particles are considerably larger than some hundred micron. However, the 870 μm source is extended, with a full-width-half-maximum of roughly 600 AU. Therefore, a physically more compelling model also invokes a belt of cold dust (17 K), located at 300 AU from the star and about 60 AU wide. Conclusions: The minimum mass of 0.04 M⊕ (3 M_Moon) of 1 mm-size icy ring-particles is considerable, given the stellar age of ⪆ 1 Gyr. These big grains form an inner edge at about 25 AU, which may suggest the presence of an unseen outer planet (q1 Eri c).Based on observations with APEX, Llano Chajnantor, Chile.
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