Astronomers Discover Circumbinary Planet TIC 172900988b (Planetary Science)

A team of international astronomers reported on the discovery of the first TESS circumbinary planet (CBP), “TIC 172900988 b”, using the multiple-transits-in-one-conjunction technique. Their study recently appeared in Arxiv.

A circumbinary planet is a planet that orbits two stars instead of one. Finding transiting planets around binary stars is much more difficult than around single stars. The transits are shallower (due to the constant ‘third-light’ dilution from the binary companion), noisier (due to starspots and stellar activity from two stars), and can be blended with the stellar eclipses.

In the current study, astronomers detected planet, “TIC 172900988 b” from a single sector of TESS data. They found that, during Sector 21, the planet TIC 172900988b transited the primary star and then 5 days later it transited the secondary star i.e. it produced just two transits.

They also revealed, a prominent apsidal motion of the binary orbit, caused by the dynamical interactions between the binary and the planet, from an extensive archival data from multiple surveys like ASAS-SN, Evryscope, KELT, and SuperWASP.

In addition, they found, binary star is itself eclipsing, with an orbital period of 19.7 days and an eccentricity of 0.45. Moreover, stellar masses of 1.24 and 1.2 M respectively, and stellar radii of 1.38 and 1.31 R have been found for the primary and secondary stars respectively.

Upper panels, from left to right: the TESS data for the primary eclipse, the secondary eclipse, the planet transit of the primary, and the planet transit of the secondary. Lower panels: Configuration of the system at the times of the two transits. © Veselin Kostov

For a circumbinary planet, the radius is found to be 11.07 R (1.009 RJup). However, they couldn’t able to determine the planet’s mass and orbital properties uniquely—there are six solutions with nearly equal likelihood. Specifically, they found that the planet’s mass is in the range of 820-980 M, its orbital period could be in between 190-205 days, and the eccentricity is in between 0.02 and 0.09.

“Follow-up observations from other instruments are key for strongly constraining the orbit and mass of the CBP. In particular, observing the predicted 2022 February-March conjunction of the CBP is critical for solving the currently-ambiguous orbit of the planet.”

Finally, they concluded that, as a relative bright target (V=10.141 mag), the system is accessible for high resolution spectroscopy, e.g. Rossiter-McLaughlin effect, transit spectroscopy.

Featured image: The inset image is of the primary target to within 300 of the target, with an arrow marking the position of the detected companion. © Veselin Kostov

Reference: Veselin B. Kostov, Brian P. Powell, Jerome A. Orosz, William F. Welsh, William Cochran, Karen A. Collins, Michael Endl, Coel Hellier, David W. Latham, Phillip MacQueen, Joshua Pepper, Billy Quarles, Lalitha Sairam, Guillermo Torres, Robert F. Wilson, Serge Bergeron, Pat Boyce, Robert Buchheim, Caleb Ben Christiansen, David R. Ciardi, Kevin I. Collins, Dennis M. Conti, Scott Dixon, Pere Guerra, Nader Haghighipour, Jeffrey Herman, Eric G. Hintz, Ward S. Howard, Eric L. N. Jensen, Ethan Kruse, Nicholas M. Law, David Martin, Pierre F. L. Maxted, Benjamin T. Montet, Felipe Murgas, Matt Nelson, Greg Olmschenk, Sebastian Otero, Robert Quimby, Michael Richmond, Richard P. Schwarz, Avi Shporer, Keivan G. Stassun, Denise C. Stephens, Amaury H. M. J. Triaud, Joe Ulowetz, Bradley S. Walter, Edward Wiley, David Wood, Mitchell Yenawine, Eric Agol, Thomas Barclay, Thomas G. Beatty, Isabelle Boisse, Douglas A. Caldwell, Jessie Christiansen, Knicole D. Colon, Magali Deleuil, Laurance Doyle, Daniel Fabrycky, Michael Fausnaugh, Gabor Furesz, Emily A. Gilbert, Guillaume Hebrard, David J. James, Jon Jenkins, Stephen R. Kane, Richard C. Kidwell Jr., Ravi Kopparapu, Gongjie Li, Jack J. Lissauer, Michael B. Lund, Steve Majewski, Tsevi Mazeh, Samuel N. Quinn, George Ricker, Joseph E. Rodriguez, Jason Rowe, Alexander Santerne, Joshua Schlieder, Sara Seager, Matthew R. Standing, Daniel J. Stevens, Eric B. Ting, Roland Vanderspek, Joshua N. Winn, “TIC 172900988: A Transiting Circumbinary Planet Detected in One Sector of TESS Data”, Arxiv, pp. 1-64, 2021.

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