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Post Info TOPIC: TW Hydrae
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Title: Deep imaging search for planets forming in the TW Hya protoplanetary disk with the Keck/NIRC2 vortex coronagraph
Author: G. Ruane, D. Mawet, J. Kastner, T. Meshkat, M. Bottom, B. Femenía Castellá, O. Absil, C. Gomez Gonzalez, E. Huby, Z. Zhu, R. Jenson-Clem, E. Choquet, E. Serabyn

Distinct gap features in the nearest protoplanetary disk, TW Hya (distance of 59.5±0.9 pc), may be signposts of ongoing planet formation. We performed long-exposure thermal infrared coronagraphic imaging observations to search for accreting planets especially within dust gaps previously detected in scattered light and submm-wave thermal emission. Three nights of observations with the Keck/NIRC2 vortex coronagraph in L' (3.4-4.1µm) did not reveal any statistically significant point sources. We thereby set strict upper limits on the masses of non-accreting planets. In the four most prominent disk gaps at 24, 41, 47, and 88 au, we obtain upper mass limits of 1.6-2.3, 1.1-1.6, 1.1-1.5, and 1.0-1.2 Jupiter masses (M_J) assuming an age range of 7-10 Myr for TW Hya. These limits correspond to the contrast at 95% completeness (true positive fraction of 0.95) with a 1% chance of a false positive within 1" of the star. We also approximate an upper limit on the product of planet mass and planetary accretion rate of M_p\dot{M} \lesssim 10^-8 M_J^2/yr implying that any putative ~0.1MJ planet, which could be responsible for opening the 24 au gap, is presently accreting at rates insufficient to build up a Jupiter mass within TW Hya's pre-main sequence lifetime.

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Blobrana


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Hubble Captures 'Shadow Play' Caused by Possible Planet

Hubble has 18 years' worth of observations of the star, called TW Hydrae. Therefore, astronomers could assemble a time-lapse movie of the shadow's rotation. Explaining it is another story. Astronomers think that an unseen planet in the disk 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. TW Hydrae resides 192 light-years away and is roughly 8 million years old.
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Blobrana


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Star's dust cloud gives birth to giant planet

Astronomers have discovered signs of a baby planet developing around another star.
The team used an array of radio telescopes in Chile to close in on a nascent planetary system lying 176 light-years from Earth - distant to us, but nearby in astronomical terms.
The forming planet is thought to be an ice giant, similar to Uranus or Neptune in our Solar System. 
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Blobrana


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Discovery of Multiple Ring-Like Gaps in a Protoplanetary Disk

The Strategic Exploration of Exoplanets and Disks team of astronomers, led by the National Astronomical Observatory of Japan (NAOJ), has found a close-in ring-like gap in the protoplanetary disk of gas and dust around the nearby sun-like young star, TW Hydrae (TW Hya). New Subaru Telescope images of the gap, including an earlier ring-like gap found by Hubble Space Telescope, suggest that ongoing planet formation is occurring in the disk, and provides a good picture of how the early formation of our own solar system might have looked.
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Blobrana


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Title: Discovery of a Disk Gap Candidate at 20 AU in TW Hydrae
Author: E. Akiyama, T. Muto, N. Kusakabe, A. Kataoka, J. Hashimoto, T. Tuskagoshi, J. Kwon, T. Kudo, R. Kandori, C. A. Grady, M. Takami, M. Janson, M. Kuzuhara, T. Henning, M. L. Sitko, J. C. Carson S. Mayama, T. Currie, C. Thalmann, J. Wisniewski, M. Momose, N. Ohashi, L. Abe, W. Brandner, T. D. Brandt, S. Egner, M. Feldt, M. Goto, O. Guyon, Y. Hayano, M. Hayashi, S. Hayashi, K. W. Hodapp, M. Ishi, M. Iye, G. R. Knapp, T. Matsuo, M. W. McElwain, S. Miyama, J. -I. Morino, A. Moro-Martin, T. Nishimura, T. -S. Pyo, G. Serabyn, T. Suenaga, H. Suto, R. Suzuki, Y. H. Takahashi, N. Takato, H. Terada, D. Tomono, E. L. Turner, M. Watanabe, T. Yamada, H. Takami, T. Usuda, M. Tamura

We present a new Subaru/HiCIAO high-contrast H-band polarised intensity (PI) image of a nearby transitional disk associated with TW Hydrae. The scattered light from the disk was detected from 0.2" to 1.5" (11 - 81 AU) and the PI image shows a clear axisymmetric depression in polarised intensity at ~ 0.4" (~ 20 AU) from the central star, similar to the ~ 80 AU gap previously reported from HST images. Azimuthal polarised intensity profile also shows the disk beyond 0.2" is almost axisymmetric. We discuss two possible scenarios explaining the origin of the polarised intensity depression: 1) a gap structure may exist at ~ 20 AU from the central star because of shallow slope seen in the polarised intensity profile, and 2) grain growth may be occurring in the inner region of the disk. Multi-band observations at NIR and millimetre/sub-millimetre wavelengths play a complementary role in investigating dust opacity and may help reveal the origin of the gap more precisely.

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Blobrana


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Exoplanet Formation Surprise

A team of researchers has discovered evidence that an extrasolar planet may be forming quite far from its star - about twice the distance Pluto is from our Sun. The planet lies inside a dusty, gaseous disk around a small red dwarf TW Hydrae, which is only about 55% of the mass of the Sun. The discovery adds to the ever-increasing variety of planetary systems in the Milky Way. The research is published in the Astrophysical Journal.
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Blobrana


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Hubble Uncovers Evidence for Extrasolar Planet Under Construction

The keen vision of NASA's Hubble Space Telescope has detected a mysterious gap in a vast protoplanetary disk of gas and dust swirling around the nearby star TW Hydrae, located 176 light-years away in the constellation Hydra (the Sea Serpent). The gap's presence is best explained as due to the effects of a growing, unseen planet that is gravitationally sweeping up material and carving out a lane in the disk, like a snow plough.
Researchers, led by John Debes of the Space Telescope Science Institute in Baltimore, Md., found the gap about 7.5 billion miles from the red dwarf star. If the putative planet orbited in our solar system, it would be roughly twice Pluto's distance from the Sun.
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Title: An Old Disk That Can Still Form a Planetary System
Authors: Edwin A. Bergin, L. Ilsedore Cleeves, Uma Gorti, Ke Zhang, Geoffrey A. Blake, Joel D. Green, Sean M. Andrews, Neal J. Evans II, Thomas Henning, Karin Oberg, Klaus Pontoppidan, Chunhua Qi, Colette Salyk, Ewine F. van Dishoeck

From the masses of planets orbiting our Sun, and relative elemental abundances, it is estimated that at birth our Solar System required a minimum disk mass of ~0.01 solar masses within ~100 AU of the star. The main constituent, gaseous molecular hydrogen, does not emit from the disk mass reservoir, so the most common measure of the disk mass is dust thermal emission and lines of gaseous carbon monoxide. Carbon monoxide emission generally probes the disk surface, while the conversion from dust emission to gas mass requires knowledge of the grain properties and gas-to-dust mass ratio, which likely differ from their interstellar values. Thus, mass estimates vary by orders of magnitude, as exemplified by the relatively old (3--10 Myr) star TW Hya, with estimates ranging from 0.0005 to 0.06 solar masses. Here we report the detection the fundamental rotational transition of hydrogen deuteride, HD, toward TW Hya. HD is a good tracer of disk gas because it follows the distribution of molecular hydrogen and its emission is sensitive to the total mass. The HD detection, combined with existing observations and detailed models, implies a disk mass >0.05 solar masses, enough to form a planetary system like our own.

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Title: Evidence for a Snow Line Beyond the Transitional Radius in the TW Hya Protoplanetary Disk
Authors: K. Zhang, K. M. Pontoppidan, C. Salyk, G. A. Blake

We present an observational reconstruction of the radial water vapour content near the surface of the TW Hya transitional protoplanetary disk, and report the first localisation of the snow line during this phase of disk evolution. The observations are comprised of Spitzer-IRS, Herschel-PACS, and Herschel-HIFI archival spectra. The abundance structure is retrieved by fitting a two-dimensional disk model to the available star+disk photometry and all observed H2O lines, using a simple step-function parameterisation of the water vapour content near the disk surface. We find that water vapour is abundant (~10^{-4} per H2) in a narrow ring, located at the disk transition radius some 4AU from the central star, but drops rapidly by several orders of magnitude beyond 4.2 AU over a scale length of no more than 0.5AU. The inner disk (0.5-4AU) is also dry, with an upper limit on the vertically averaged water abundance of 10^{-6} per H2. The water vapour peak occurs at a radius significantly more distant than that expected for a passive continuous disk around a 0.6 solar mass star, representing a volatile distribution in the TW Hya disk that bears strong similarities to that of the solar system. This is observational evidence for a snow line that moves outward with time in passive disks, with a dry inner disk that results either from gas giant formation or gas dissipation and a significant ice reservoir at large radii. The amount of water present near the snow line is sufficient to potentially catalyse the (further) formation of planetesimals and planets at distances beyond a few AU.

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Blobrana


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Herschel Finds Past-Prime Star may be Making Planets

A star thought to have passed the age at which it can form planets may, in fact, be creating new worlds. The disk of material surrounding the surprising star called TW Hydrae may be massive enough to make even more planets than we have in our own solar system.
The findings were made using the European Space Agency's Herschel Space Telescope, a mission in which NASA is a participant.
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