Brown dwarf in a dynamical-tide regime detected by WASP survey

August 2, 2018 by Tomasz Nowakowski, report
The radial velocity motion of WASP-128 due to its brown dwarf companion, folded on the best-fit period. The blue points correspond to RV measurements taken with CORALIE (circles) and HARPS (triangles). The solid line is the best-fit model. The residuals of the fit are shown in the lower panel. Credit: Hodzic et al., 2018.

European astronomers have discovered a new transiting brown dwarf in a dynamical-tide regime as part of the Wide Angle Search for Planets (WASP) survey. The newly found object, designated WASP-128b, orbits its host on a close orbit—the measured stellar rotation rate places it in a regime where tidal interaction is dominated by dynamical tides. The finding is detailed in a paper published July 19 on

Brown dwarfs are intermediate objects between planets and . Astronomers generally agree that they are substellar objects occupying the mass range between 13 and 80 Jupiter masses. To date, most of discovered were found to be solitary. However, some brown dwarfs orbit sun-like stars, and notably, up to 16 percent of such stars have companions more massive than Jupiter, of which fewer than 1 percent are brown dwarfs.

Furthermore, only a handful of brown dwarfs were found to be orbiting G-type dwarfs. Such objects in G dwarf systems are thought to undergo rapid orbital decay due to runaway tidal dissipation. Expanding the list of known brown dwarfs in that kind of systems could be helpful in studying various substellar evolution models.

Recently, a team of astronomers led by Vedad Hodzic of the University of f Birmingham, U.K., has detected a new brown dwarf in a close orbit around a G dwarf under the WASP program. The transit signal in the light curve of the star WASP-128 was identified using the 0.6 m TRAPPIST robotic telescope and the 1.2 m Euler telescope, both located at ESO La Silla Observatory in Chile. Follow-up spectroscopic observations of this star confirmed that the signal was caused by a massive circumstellar companion orbiting the host.

"We report the discovery of WASP-128b, a new transiting brown dwarf discovered by the WASP survey, orbiting a G0V host on a close , where the measured stellar rotation rate places the system well-within the dynamical-tide regime, suggesting strong tidal coupling between the pair," the researchers wrote in the paper.

WASP-128b is about the size of Jupiter (0.94 Jupiter radii) but 37.5 times more massive than our solar system's biggest planet. It orbits its parent star at a distance of approximately 0.036 AU, every 2.2 days.

Moreover, the researchers found that WASP-128b is mildly inflated and also calculated that its remaining lifetime is about 267 million years.

"While in the dynamically stable state, the infall time of WASP-128b is given by the magnetic braking timescale, and we derive a remaining lifetime of 267 Myr," the paper reads.

The astronomers noted that this value is similar to that of some ultra-short period massive "hot Jupiter" exoplanets.

The host, located about 1,375 light years away from the Earth, is some 16 percent larger and more massive than the sun. It has effective temperature of 5,950 K, an estimated age of about 2.3 billion years and a rotation period of around 2.93 days. As noted in the paper, such rotation rate is indicative of a tidal spin-up due to its massive companion.

Explore further: Brown dwarf detected in the CoRoT-20 system

More information: WASP-128b: a transiting brown dwarf in the dynamical-tide regime, arXiv:1807.07557 [astro-ph.EP]

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a 2.2d orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor logQ′⋆=6.96±0.19. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, M⋆=1.16±0.04M⊙, R⋆=1.16±0.02R⊙, and for the companion, Mb=37.5±0.8MJup, Rb=0.94±0.02RJup, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters.

Related Stories

Brown dwarf detected in the CoRoT-20 system

July 16, 2018

An international group of astronomers has discovered a new substellar object in the planetary system CoRoT-20. The newly identified object was classified as a brown dwarf due to its mass, which is greater than that of the ...

Eight new 'hot Jupiters' discovered by astronomers

March 14, 2018

European astronomers have detected eight new "hot Jupiter" exoplanets as part of the WASP-South transit survey. The newly discovered gas giants have short orbital periods and masses ranging from 0.42 to 5.2 Jupiter masses. ...

Astronomers discover a giant planet orbiting a brown dwarf

March 26, 2018

Using microlensing technique, astronomers have found a new giant planet orbiting a brown dwarf located in the bulge of the Milky Way galaxy. The newly discovered exoplanet, designated OGLE-2017-BLG-1522Lb, is most likely ...

Astronomers discover a near-grazing transiting 'hot Jupiter'

February 12, 2018

An international group of astronomers has detected a new "hot Jupiter" exoplanet making a near-grazing transit of its host star. The newly found alien world, designated WASP-174b, is most likely similar in size and mass to ...

'Hot Jupiter' transiting a rapidly-rotating star discovered

May 4, 2017

(—A "hot Jupiter" exoplanet transiting a rapidly rotating star has been discovered jointly by WASP and KELT survey, a new study reveals. The newly found alien world, designated WASP-167b/KELT-13b, is several times ...

Recommended for you

A new neptune-size exoplanet

December 16, 2018

The remarkable exoplanet discoveries made by the Kepler and K2 missions have enabled astronomers to begin to piece together the history of the Earth and to understand how and why it differs from its diverse exoplanetary cousins. ...

Mars InSight lander seen in first images from space

December 14, 2018

On Nov. 26, NASA's InSight mission knew the spacecraft touched down within an 81-mile-long (130-kilometer-long) landing ellipse on Mars. Now, the team has pinpointed InSight's exact location using images from HiRISE, a powerful ...

Video: Enjoying the Geminids from above and below

December 14, 2018

On the night of December 13, into the morning of December 14, 2018, tune into the night sky for a dazzling display of fireballs. Thanks to the International Space Station, this sky show – the Geminids meteor shower—will ...

Hubble finds far-away planet vanishing at record speed

December 13, 2018

The speed and distance at which planets orbit their respective blazing stars can determine each planet's fate—whether the planet remains a longstanding part of its solar system or evaporates into the universe's dark graveyard ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Aug 02, 2018
And, in the blink of a cosmological eye, it will be gone. Presumably, progressive bake-off will erode it to a 'Hot Jupiter', then a 'metals' core, then 'metals' contamination of its host star. Do we have candidates for such ? A robust way to distinguish from 'primordial' cloud mix ?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.