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Another star showing bizarre circumstellar activity
Mongo
post Dec 5 2016, 02:14 AM
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Any ideas? Perhaps the circumstellar dust coalesced into planetesimals?

TYC 8241 2652 1 and the case of the disappearing disk: no smoking gun yet

TYC 8241 2652 1 is a young star that showed a strong mid-infrared (mid-IR, 8-25 mu) excess in all observations before 2008 consistent with a dusty disk. Between 2008 and 2010 the mid-IR luminosity of this system dropped dramatically by at least a factor of 30 suggesting a loss of dust mass of an order of magnitude or more. We aim to constrain possible models including removal of disk material by stellar activity processes, the presence of a binary companion, or other explanations suggested in the literature. We present new X-ray observations, optical spectroscopy, near-IR interferometry, and mid-IR photometry of this system to constrain its parameters and further explore the cause of the dust mass loss. In X-rays TYC 8241 2652 1 has all properties expected from a young star: Its luminosity is in the saturation regime and the abundance pattern shows enhancement of O/Fe. The photospheric Ha line is filled with a weak emission feature, indicating chromospheric activity consistent with the observed level of coronal emission. Interferometry does not detect a companion and sets upper limits on the companion mass of 0.2, 0.35, 0.1 and 0.05 M_sun at projected physical separations of 0.1-4 AU,4-5 AU, 5-10 AU, and 10-30 AU, respectively (assuming a distance of 120.9 pc). Our mid-IR measurements, the first of the system since 2012, are consistent with the depleted dust level seen after 2009. The new data confirms that stellar activity is unlikely to destroy the dust in the disk and shows that scenarios where either TYC 8241 2652 1 heats the disk of a binary companion or a potential companion heats the disk of TYC 8241 2652 1 are unlikely.
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TheAnt
post Dec 5 2016, 06:50 PM
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QUOTE (Mongo @ Dec 5 2016, 03:14 AM) *
Any ideas? Perhaps the circumstellar dust coalesced into planetesimals?


With just a few years, that's way to fast for coalescence into.....pebbles or small rocks. Unless a very strong and unexpected phenomenon is at work there with very strong magnetic and and or electrical charge work together with lets say a major squirt of superglue (sorry! tongue.gif ) ....make all dusk lump together and that over vast distances.
They do mention 'stellar activity processes' and young stars is thought to often have quite irregular processes with outbursts perhaps even coronal mass ejections, so I find it more likely that events of that kind could have cleared out the disk.
Even so such a massive change in a very short timescale still makes this both intriguing and I guess, provide an opportunity to learn something new. smile.gif
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JRehling
post Dec 5 2016, 09:11 PM
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For something to happen on such a large scale, it implies that a cause is somehow distributed spatially. Broad possibilities that occur to me:

1) The gravitational field of a massive planet mopped up a large amount of material within a few orbital periods.
2) Dusty material scattered over a large volume cooled considerably within a few years.
2a) Almost all of the debris in an elliptical orbit moved, at about the same time, from periastron out to greater distances.
3) The material that was radiating IR physically dissipated into finer grains and/or a gas.

None of those seem to be very likely events, but to explain a strange phenomenon, the mechanisms seemingly have to be unusual.
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serpens
post Dec 9 2016, 07:49 AM
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I assume that the high mid IR feature was considered to be a thermal emission feature. Dissipation of dust is measured in MYr and it is the dramatic drop from what seems to be one steady state to another in a very short time span that is intriguing. Circumstellar disks can vary in density and as TheAnt implies, stellar activity could result in a reasonably clear sector of the disc. Then the mid IR variation would be influenced by disk rotation and by the orientation of the disk to the observer. A lesser possibility is a multiple disk system where a cooler outer disc is now obscuring and attenuating the mid IR emissions.
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