When do aging brown dwarfs sweep the clouds away?

February 27, 2018, Carnegie Institution for Science
Artist's conception of a different brown dwarf to the one studied by Jonathan Gagné and his team. The brown dwarf depicted here is also part of a moving group, although a different one than AB Doradus. Credit: NASA/JPL, slightly modified by Jonathan Gagné

Brown dwarfs, the larger cousins of giant planets, undergo atmospheric changes from cloudy to cloudless as they age and cool. A team of astronomers led by Carnegie's Jonathan Gagné measured for the first time the temperature at which this shift happens in young brown dwarfs. Their findings, published by the Astrophysical Journal Letters, may help them better understand how gas giant planets like our own Solar System's Jupiter evolved.

Brown dwarfs are too small to sustain the hydrogen fusion process that fuels stars and allows them to remain hot and bright for a long time. After formation, slowly cool down and contract over time—at some point shifting from heavily cloud covered to having completely clear skies.

Because they are freely floating in space, the atmospheric properties of brown dwarfs are much easier to study than the atmospheres of exoplanets, where the light of a central star can be completely overwhelming.

In this paper, Gagné and his colleagues—Katelyn Allers of Bucknell University; Christopher Theissen of University of California San Diego; Jacqueline Faherty and Daniella Bardalez Gagliuffi of the American Museum of Natural History, and Etienne Artigau of Institute for Research on Exoplanets, Université de Montréal—focused on an unusually red brown dwarf called 2MASS J13243553+6358281, which they were able to determine is one of the nearest known objects to our Solar System.

The redness of this object had previously been suggested to indicate that it was actually a binary system, but the research team's findings indicate that it is a single free floating planetary mass object.

Why study brown dwarfs? What are they and what can they teach us? Credit: Carnegie Institution for Science.

They confirmed that it is part of a group of roughly 80 stars of similar ages and compositions drifting together through space, called the AB Doradus moving group, which revealed that it is about 150 million years old.

By knowing the object's age and measuring its luminosity and distance, the team could determine its likely radius, mass, and, most-importantly its temperature.

They could then compare its temperature to that of another previously studied brown dwarf in the same moving group—one that was still cloudy while 2MASS J1324+6358 was already cloudless. This allowed them to figure out the temperature at which the cloudy to cloudless transition happens.

"We were able to constrain the point in the cool-down process at which brown dwarfs like J1324transition from cloudy to cloud-free," explained Gagné

The shift occurs about 1,150 degrees kelvin, or 1,600 degrees Fahrenheit, for planetary- objects that are 150 million years old like 2MASS J1324+6358 and other members of the AB Doradus moving group.

"Because brown dwarfs like this one are so analogous to , this information could help us understand some of the evolutionary processes that occurred right here in our own Solar System's history," Gagné added.

Explore further: Surprise! When a brown dwarf is actually a planetary mass object

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1 / 5 (1) Feb 27, 2018
"Brown dwarfs are too small to sustain the hydrogen fusion process that fuels stars and allows them to remain hot and bright for a long time." From article
Mass up to 15 MJ/(vs) Mass above 15 MJ
Brown dwarf (& planets)......Mass of Jupiter....Temperature °K....Planets orbit AU
ROXs 42Bb .................................. 9…………… 1.950 ± 100…………157
54 Piscium B ……………………50……………...810±50

DH Tauri b ……………………...12…………….2.750………………..330
ULAS J133553.45+113005.2 …..15 _31………….500 -550

Mass vs Mass
B Tauri FU…………………….. 15……………..2.375…………………700
DENIS J081730.0-615520… .15……………….950 etc.
From http://www.svemir...ncorrect
3 / 5 (2) Feb 27, 2018
#wd, what's your point ?
1 / 5 (2) Feb 28, 2018

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