Astronomers Discovered Super Neptune Around M-dwarf Star (Planetary Science)

Using precision radial velocity (RVs) from the near infrared (NIR) Habitable-zone Planet Finder spectrograph (HPF), a team of international astronomers reported the discovery and confirmation of a super Neptune, TOI-532b, orbiting an M-dwarf star TOI-532 in a ∼ 2.3 day circular orbit. Their findings recently appeared in Arxiv.

TOI-532 is an early type metal-rich M dwarf star located in the constellation of Orion. It was observed by TESS in Sector 6 in Camera 1 from 11 December 2018 to 7th January 2019 at two minute cadence.

Figure 1. Short cadence (2 minute) time series TESS PDCSAP photometry (without detrending) from Sector 6, with the binned data (in 1 hour bins), along with the TOI-532b transits overlaid in blue. © Shubham Kanodia et al.

Now, a team of international astronomers led by Shubham Kanodia reported the discovery of a super neptune orbiting TOI-532. They performed a comprehensive characterization of the stellar and planetary properties using space-based photometric observations from TESS, additional ground-based transit observations, adaptive optics imaging, and high-contrast speckle imaging.

Table 1: Derived Parameters for the TOI-532 System © Shubham Kanodia et al.

They showed that, TOI-532 is a metal-rich M dwarf with an effective temperature of 3957 K and [Fe/H] = 0.38; it hosts a transiting gaseous planet with a period of ∼ 2.3 days. Joint fitting of the radial velocities with the TESS and ground-based transits revealed a planet with radius of 5.82 R, and a mass of 61.5 M (more parameters are shown in Table 1 above).

“TOI-532b is the largest and most massive super Neptune detected around an M dwarf with both mass and radius measurements, and it bridges the gap between the Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs.”

— they said.

Additionally, it has been shown that the planet is situated at the edge of the Neptune desert in the Radius–Insolation plane, which will help place constraints on the mechanisms responsible for sculpting this region of planetary parameter space.

Figure 2. They showed TOI-532b (circled) in different planet parameter space along with other M dwarf planets with mass measurements at > 3σ © Shubham Kanodia et al.

Finally, they suggested that, TOI-532 is relatively faint (J = 11.46), but is still accessible from 10-m class telescopes, as a potential target for detecting atmospheric escape using the He 10830 Å triplet.

“The discovery and mass measurement of gas giants such as TOI-532b adds to the small sample of such planets around M dwarf host stars, and can help inform theories of planetary formation and evolution. Therefore, we encourage future observations to place limits on atmospheric escape using the He 10830 Å transition.”

— they concluded.

Featured image: Neptune Illustration © Getty images

Reference: Shubham Kanodia, Gudmundur Stefansson, Caleb I. Canas, Marissa Maney, Andrea S. Lin, Joe P. Ninan, Sinclaire Jones, Andrew J. Monson, Brock A. Parker, Henry A. Kobulnicky, Jason Rothenberg, Corey Beard, Jack Lubin, Paul Robertson, Arvind F. Gupta, Suvrath Mahadevan, William D. Cochran, Chad F. Bender, Scott A. Diddams, Connor Fredrick, Samuel P. Halverson, Suzanne L. Hawley, Fred R. Hearty, Leslie Hebb, Ravi K. Kopparapu, Andrew J. Metcalf, Lawrence W. Ramsey, Arpita Roy, Christian Schwab, Maria Schutte, Ryan C. Terrien, John P. Wisniewski, Jason T. Wright, “TOI-532b: The Habitable-zone Planet Finder confirms a Large Super Neptune in the Neptune Desert orbiting a metal-rich M dwarf host”, Arxiv, 2021.

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