HubbleSite: 'Shadow Play' Caused by Possible Planet

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bystander
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HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by bystander » Sat Jan 07, 2017 7:16 pm

Hubble Captures 'Shadow Play' Caused by Possible Planet
NASA | STScI | HubbleSite | 2017 Jan 07
STScI-H-p1703a-m2000x2000.jpg
Shadow on TW Hydrae's Disk - Credit: NASA, ESA, and J. Debes (STScI)
Searching for planets around other stars is a tricky business. They're so small and faint that it's hard to spot them. But a possible planet in a nearby stellar system may be betraying its presence in a unique way: by a shadow that is sweeping across the face of a vast pancake-shaped gas-and-dust disk surrounding a young star.

The planet itself is not casting the shadow. But it is doing some heavy lifting by gravitationally pulling on material near the star and warping the inner part of the disk. The twisted, misaligned inner disk is casting its shadow across the surface of the outer disk.

A team of astronomers led by John Debes of the Space Telescope Science Institute in Baltimore, Maryland, say this scenario is the most plausible explanation for the shadow they spotted in the stellar system TW Hydrae, located 192 light-years away in the constellation Hydra, also known as the Female Water Snake. The star is roughly 8 million years old and slightly less massive than our sun. The researchers uncovered the phenomenon while analyzing 18 years' worth of archival observations taken by NASA's Hubble Space Telescope. ...

Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk - John H. Debes et al

http://asterisk.apod.com/viewtopic.php?t=35785
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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by geckzilla » Sun Jan 08, 2017 12:19 am

So how do you get a Jupiter-sized planet to orbit a star .8 times the mass of the Sun at ~1AU in 16 years? Wouldn't it be a lot faster than that?
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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by geckzilla » Sun Jan 08, 2017 1:13 am

I think I managed to confuse myself with the press release text. Trying to understand the paper... All sorts of gaps and talk of asymmetry and disk inclinations and this and that.
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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by neufer » Sun Jan 08, 2017 1:54 am


geckzilla wrote:
I think I managed to confuse myself with the press release text. Trying to understand the paper... All sorts of gaps and talk of asymmetry and disk inclinations and this and that.
Art Neuendorffer

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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by Ann » Sun Jan 08, 2017 4:33 am

Nice illustration, Art! :D

TW Hydrae is not terribly red, but quite faint. Its B-V is 0.721 ± 0.134. Admittedly, that's a huge margin of error. Guide doesn't even provide a spectral class for this star! And its luminosity is 0.103 ± 0.024 solar. From the Earth, TW Hydrae is an 11th magnitude star, just like a much more famous star, Proxima Centauri!

Ann

EDIT: No! TW Hydrae is a little brighter than Hipparcos gives it credit for. Gaia has determined that it is 10% farther away than Hipparcos made it out to be, 59.5 parsec versus 53.7 ± 6.2 parsec as measured by Hipparcos. So TW Hya's luminosity is going to be a little more than 0.1 solar. (I think.)

I can't resist comparing TW Hydrae with another component of Alpha Centauri, Alpha Centauri B, the K1-type lesser component of the central bright binary. According to Jim Kaler, Alpha Cen-B has a mass of 0.92 solar, and a luminosity of 0.5 times solar. Just a little change in mass makes for a huge change in luminosity, and if TW Hydrae holds only 0.8 times the mass of the Sun, it might never get much brighter than, at best, 0.2 solar. Maybe not even that.

Yes, but the B-V index of Alpha Cen B is 0.900 ± 0.020. TW Hydrae seems anomalously non-red compared with Alpha Cen-B, because TW Hya should be redder than Alpha Cen-B, not the other way round. Of course, we see TW Hya pole on, and if the star is a fast rotator it might be distinctly flattened, and then we might see comparatively deep inside its relatively hot interior. That might make it appear anomalously non-red.
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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by Ann » Sun Jan 08, 2017 5:18 am

geckzilla wrote:So how do you get a Jupiter-sized planet to orbit a star .8 times the mass of the Sun at ~1AU in 16 years? Wouldn't it be a lot faster than that?
Geck, where did you find the information that TW Hydrae is 0.8 times the mass of the Sun, and its planet is Jupiter-sized? I couldn't find that information, but I might well have got lost in the text.

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Re: HubbleSite: 'Shadow Play' Caused by Possible Planet

Post by geckzilla » Sun Jan 08, 2017 2:43 pm

Just call me "geck" because "zilla" is like a last name.