# TW Hydrae

Observation data Constellation Epoch J2000.0      Equinox J2000.0 Inner region of TW Hydrae protoplanetary disc Credit: S. Andrews, B. Saxton, ALMA (see description) Hydra 11h 01m 52s[1] −34° 42′ 17″[1] 11.27 ± 0.09[1] Pre-main-sequence K6V:e[1] -0.33[2] 0.67[1] 0.659[1] 0.92[1] T Tauri Radial velocity (Rv) 13.40 ± 0.8[1] km/s Proper motion (μ) RA: -66.19 ± 1.85[1] mas/yr Dec.: -13.90 ± 1.47[1] mas/yr Parallax (π) 18.62 ± 2.14[1] mas Distance approx. 180 ly (approx. 54 pc) Mass 0.8[3] M☉ Radius 1.11[4] R☉ Luminosity (bolometric) 0.28[note 1] L☉ Temperature 4,000[4] K Age 8[4] Myr SIMBAD data

TW Hydrae is an orange dwarf star approximately 176 light-years away in the constellation of Hydra (the Sea Serpent). The star is the closest T Tauri star to the Solar System. TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. The star appears to be accreting from a face-on protoplanetary disk of dust and gas, which has been resolved in images from the Hubble Space Telescope. TW Hydrae is accompanied by about twenty other low-mass stars with similar ages and spatial motions, comprising the "TW Hydrae association" or TWA, one of the closest regions of recent "fossil" star-formation to the Sun.

## Protoplanetary disk

### Disproven protoplanet

In December 2007, a team led by Johny Setiawan of the Max Planck Institute for Astronomy in Heidelberg, Germany announced discovery of a planet orbiting TW Hydrae, dubbed "TW Hydrae b" with a minimum mass around 1.2 Jupiter masses, a period of 3.56 days, and an orbital radius of 0.04 astronomical units (inside the inner rim of the protoplanetary disk). Assuming it orbits in the same plane as the outer part of the dust disk (inclination 7±1°[5]), it has a true mass of 9.8±3.3 Jupiter masses.[5][6] However, if the inclination is similar to the inner part of the dust disk (4.3±1.0°[7]), the mass would be 16+5
−3
Jupiter masses, making it a brown dwarf.[7] Since the star itself is so young, it was presumed this is the youngest extrasolar planet yet discovered, and essentially still in formation.[8]

In 2008 a team of Spanish researchers concluded that the planet does not exist: the radial velocity variations were not consistent when observed at different wavelengths, which would not occur if the origin of the radial velocity variations was caused by an orbiting planet. Instead, the data was better modelled by starspots on TW Hydrae's surface passing in and out of view as the star rotates. "Results support the spot scenario rather than the presence of a hot Jupiter around TW Hya".[9] Similar wavelength-dependent radial velocity variations, also caused by starspots, have been detected on other T Tauri stars.[10]

### Detection of methanol

In 2016, methanol, one of the building blocks for life, was detected in the star's protoplanetary disk.[11]

## Gallery

 Simulation based on Hubble observations.
 TW Hydrae protoplanetary disc.
 This artist’s impression video shows the protoplanetary disc around TW Hydrae. The organic molecule methyl alcohol (methanol) has been found in this disc.

## Notes

1. ^ From ${\displaystyle {\begin{smallmatrix}L=4\pi R^{2}\sigma T_{\rm {eff}}^{4}\end{smallmatrix}}}$, where ${\displaystyle {\begin{smallmatrix}L\end{smallmatrix}}}$ is the luminosity, ${\displaystyle {\begin{smallmatrix}R\end{smallmatrix}}}$ is the radius, ${\displaystyle {\begin{smallmatrix}T_{\rm {eff}}\end{smallmatrix}}}$ is the effective surface temperature and ${\displaystyle {\begin{smallmatrix}\sigma \end{smallmatrix}}}$ is the Stefan–Boltzmann constant.

## References

1. "V* TW Hya -- T Tau-type Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2014-01-02.
2. ^ Mermilliod, J.C. (1991), Homogeneous Means in the UBV System, Institut d'Astronomie, Universite de Lausanne, Bibcode:2006yCat.2168....0M.Vizier catalog entry
3. ^ Chunhua, Qi; et al. (August 2013). "Imaging of the CO Snow Line in a Solar Nebula Analog". Science 341 (6146): 630–632. arXiv:1307.7439. Bibcode:2013Sci...341..630Q. doi:10.1126/science.1239560.
4. ^ a b c Rhee, J.H.; et al. (May 2007), "Characterization of dusty debris disks: the IRAS and Hipparcos catalogs", The Astrophysical Journal 660 (2): 1556–1571, arXiv:astro-ph/0609555, Bibcode:2007ApJ...660.1556R, doi:10.1086/509912.Vizier catalog entry
5. ^ a b Setiawan, J.; Henning, Th.; Launhardt, R.; Müller, A.; Weise, P.; Kürster, M. (3 January 2008). "A young massive planet in a star–disk system". Nature 451 (7174): 38–41. Bibcode:2008Natur.451...38S. doi:10.1038/nature06426. PMID 18172492.
6. ^ McKee, Maggie (2 January 2008). "First planet discovered around a youthful star". NewScientist.com news service. Retrieved 2008-01-02.
7. ^ a b Pontoppidan, Klaus M.; et al. (2008). "Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps". The Astrophysical Journal 684 (2): 1323–1329. arXiv:0805.3314. Bibcode:2008ApJ...684.1323P. doi:10.1086/590400.
8. ^
9. ^ Huelamo, N.; et al. (2008). "TW Hydrae: evidence of stellar spots instead of a Hot Jupiter". Astronomy and Astrophysics 489 (2): L9–L13. arXiv:0808.2386. Bibcode:2008A&A...489L...9H. doi:10.1051/0004-6361:200810596.
10. ^ Prato, L.; et al. (2008). "A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau". The Astrophysical Journal 687 (2): L103–L106. arXiv:0809.3599. Bibcode:2008ApJ...687L.103P. doi:10.1086/593201.
11. ^ http://www.space.com/33193-organic-molecule-planet-forming-disk.html