Astronomers Discovered A High Mass Transiting Brown Dwarf (Planetary Science)

A team of international astronomers using Next Generation Transit Survey (NGTS), reported on the discovery of NGTS-19b, a high mass brown dwarf in an eccentric 17-day orbit around a main sequence K-star, NGTS-19. Their study recently appeared in Arxiv.

Brown dwarfs are substellar mass objects which bridge the gap between planets and stars. These are the objects with radii similar to that of Jupiter, but with masses ranging between 13 MJup and ∼80 MJup. The lower mass limit corresponds to the minimum mass at which deuterium burning can occur, below which lie the planets. Whilst the upper mass limit is the classical hydrogen burning limit, above which objects are considered to be low mass stars.

In the current study, astronomers make use of follow up photometry from the South African Astronomical Observatory, as well as sector 11 TESS data, in combination with radial velocity measurements from the CORALIE spectrograph to precisely characterise the system.

(article continues below images)

Table 1: NGTS-19 stellar parameters derived using specmatch-emp and ariadne © J. Acton et al.
Table 2: Derived brown dwarf parameters © J. Acton et al.

They found that, NGTS-19b is a brown dwarf companion to a K-star, with a mass of 69.5 MJup (i.e. 69.5 times that of the mass of the jupiter) and radius of 1.034 RJup (i.e. 1.034 times that of the radius of the jupiter). They also found that, the system has a reasonably long period of 17.84 days, and a high degree of eccentricity of 0.3767.

In addition, it has been found that the mass and radius of the brown dwarf imply an age of 0.5 Gyr, however this is inconsistent with age measurements from their spectroscopic or SED analysis, suggesting that the brown dwarf may be inflated due to interactions with its host star.

“This is unusual given that its large mass and relatively low levels of irradiation would make it much harder to inflate.”

“NGTS-19b is the 29th transiting brown dwarf to be discovered, adding to the population of companions to main sequence stars known as the brown dwarf desert. With the continuing survey of the TESS mission it is quite possible that there will be many more additions to this once sparse region of parameter space in the years to come.

— concluded authors of the study

Featured image: Mass-Radius relation for known brown dwarfs around Main Sequence stars. NGTS-19b is plotted in red. © Jack Acton et al.

Reference: Jack S. Acton, Michael R. Goad, Matthew R. Burleigh, Sarah L. Casewell, Hannes Breytenbach, Louise D. Nielsen, Gareth Smith, David R. Anderson, Matthew P. Battley, Daniel Bayliss, François Bouchy, Edward M. Bryant, Szilárd Csizmadia, Phillip Eigmüller, Samuel Gill, Edward Gillen, Nolan Grieves, Maximilian N. Günther, Beth A. Henderson, Simon T. Hodgkin, James A. G. Jackman, James S. Jenkins, Monika Lendl, James McCormac, Maximiliano Moyano, Richard P. Nelson, Ramotholo R. Sefako, Alexis M. S. Smith, Manu Stalport, Jessymol K. Thomas, Rosanna H. Tilbrook, Stéphane Udry, Richard G. West, Peter J. Wheatley, Hannah L. Worters, Jose I. Vines, Douglas R. Alves, “NGTS-19b : A high mass transiting brown dwarf in a 17-day eccentric orbit”, Arxiv, pp. 1-12, 2021.

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