Astronomers discover a new 'warm Jupiter'

Astronomers from the Harvard–Smithsonian Center for Astrophysics (CfA) and elsewhere, report the discovery of a new 'warm Jupiter' exoplanet orbiting a rapidly rotating F-type star. The newfound alien world, designated TOI-4641 b could be nearly four times as massive as Jupiter. The finding was detailed in a paper published December 7 on the pre-print server arXiv.

In general, warm Jupiters are gas giant planets with orbital periods between 10 and 200 days. This makes them challenging targets for transit detection, and radial velocity follow-up studies, compared to their shorter-orbit counterparts known as hot Jupiters.

Now, a group of astronomers led by CfA's Allyson Bieryla has found a new exoplanet of this type. Using NASA's Transiting Exoplanet Survey Satellite (TESS), which is conducting an all-sky survey searching for transiting extrasolar worlds, they identified a transit signal in the light curve of TOI-4641—a bright and rapidly rotating F-star (with a projected rotational velocity of approximately 86.3 km/s). The planetary nature of this signal was confirmed by follow-up photometric and spectroscopic observations.

"A candidate exoplanet orbiting TOI-4641 with a period of 22.1d was identified in light curves including data through Sector 43 in both SPOC and QLP pipelines," the researchers wrote in the paper.

The newfound planet has a radius of about 0.73 Jupiter radii and its maximum mass was calculated to be 3.87 Jupiter masses. The observations indicate that TOI-4641 b orbits its host star every 22.09 days at a well-aligned orbit, at a distance of some 0.173 AU from it. TOI-4641 b is therefore among the longest period planets, to be thoroughly characterized, that orbits a hot rapidly rotating star.

The parent star TOI-4641 (also known as TIC 436873727), located some 286 light years away, has a radius of about 1.72 solar radii and is approximately 41% more massive than the sun. The star is estimated to be 2.69 billion years old, has a metallicity at a level of -0.09, and its effective temperature was found to be 6,560 K.

The authors of the paper underlined that long-period exoplanets like TOI-4641 b could be crucial for testing mechanisms that induce primordial misalignment in planetary systems, given that at such orbital distances, star-planet tidal interactions are assumed to be too weak to modify the orbital obliquity.

"Testing these predictions motivate full characterizations of planets in long-period orbits about early-type stars," the scientists concluded.

All in all, Bieryla's team proposes a few mechanisms behind such misalignment, including chaotic accretion, magnetic warping, or changes to the spin axes of early-type stars, as well as stellar or planetary companions during the primordial phase of formation.