Two Directly Imaged, Wide-orbit Giant Planets around the Young, Solar Analog TYC 8998-760-1

Abstract: Even though tens of directly imaged companions have been discovered in the past decades, the number of directly confirmed multiplanet systems is still small. Dynamical analysis of these systems imposes important constraints on formation mechanisms of these wide-orbit companions. As part of the Young Suns Exoplanet Survey (YSES) we report the detection of a second planetary-mass companion around the 17 Myr-old, solar-type star TYC 8998-760-1 that is located in the Lower Centaurus Crux subgroup of the Scorpius-Centaurus association. The companion has a projected physical separation of 320 au and several individual photometric measurements from 1.1 to 3.8 microns constrain a companion mass of $6\pm1\,M_\mathrm{Jup}$, which is equivalent to a mass ratio of $q=0.57\pm0.10\%$ with respect to the primary. With the previously detected $14\pm3\,M_\mathrm{Jup}$ companion that is orbiting the primary at 160 au, TYC 8998-760-1 is the first directly imaged multiplanet system that is detected around a young, solar analog. We show that circular orbits are stable, but that mildly eccentric orbits for either/both components ($e > 0.1$) are chaotic on Gyr timescales, implying in-situ formation or a very specific ejection by an unseen third companion. Due to the wide separations of the companions TYC 8998-760-1 is an excellent system for spectroscopic and photometric follow-up with space-based observatories such as the James Webb Space Telescope.

• The paper reports the discovery of two directly imaged giant exoplanets orbiting TYC 8998-760-1, marking the first multiplanet system observed around a solar analog.
• Researchers employed high-contrast imaging instruments like SPHERE/IRDIS and NACO alongside custom Python-based pipelines to obtain precise photometric and astrometric measurements.
• Numerical simulations demonstrated that near-circular orbits could remain stable over long timescales, offering new insights into planetary formation and migration in young stellar systems.

Direct Imaging of Two Wide-Orbit Giants around TYC 8998-760-1

In the paper titled "Two Directly Imaged, Wide-orbit Giant Planets around the Young, Solar Analog TYC 8998-760-1" by Bohn et al., the researchers disclose the discovery of two giant planetary companions orbiting TYC 8998-760-1, a 17 million-year-old solar-type star situated in the Lower Centaurus-Crux subgroup of the Scorpius–Centaurus association. This astrophysical study is conducted as part of the Young Suns Exoplanet Survey (YSES) and involves observations from facilities such as the European Southern Observatory (ESO).

Discoveries and Observations

The two planets identified are among the few known directly imaged exoplanets, making this discovery noteworthy in planetary science. The outer companion, TYC 8998-760-1 c, manifests a projected separation of 320 AU from its host star. Photometric data spanning wavelengths from 1.1 to 3.8 microns suggest a mass of $6\pm1\,M_\mathrm{Jup}$, calculated using a combination of atmospheric and evolutionary models. For the inner companion, TYC 8998-760-1 b, earlier observations indicated a mass of $14\pm3\,M_\mathrm{Jup}$ at a separation of 160 AU. This constitutes the first identified directly imaged multiplanet system manifesting around a solar analog.

Methodology and Data Reduction

Data was collected utilizing instruments like SPHERE/IRDIS and NACO, harnessing high-contrast imaging and extreme adaptive optics that facilitate precise photometric and astrometric measurements. The data are processed through a custom pipeline employing Python-based tools such as PynPoint, with steps including background subtraction, flat-fielding, and astrometric calibration. The statistical techniques employed for data analysis prioritize minimizing observational and instrumental biases, ensuring the reliability of detected signals.

Astrometric and Photometric Analysis

Astrometric analysis reinforced the gravitational binding of the companions by examining their motion across epochs to confirm common proper motion with the primary star. Photometric analysis, utilizing spectral energy distributions (SEDs), allowed for effective temperature estimations and informed constraints on surface gravity and luminosity. TYC 8998-760-1 c is characterized by an effective temperature of $1240^{+160}_{-170}$ K and a luminosity of $\log\left(L/L_\sun\right)=-4.65^{+0.05}_{-0.08}$.

Dynamical Stability Analysis

Stability studies conducted via numerical simulations indicated that circular orbits might be stable over considerable timescales, whereas mildly eccentric configurations might lead to chaos. This highlights the system's potential dynamical intricacies and poses intriguing questions regarding planetary formation and migration mechanisms in wide-orbit systems. These findings imply possibilities of in-situ formation or historical dynamical interactions with unseen companions.

Implications and Future Perspectives

The implications of this discovery extend both practical and theoretical domains. From a theoretical perspective, the results contribute to our understanding of planetary formation, particularly in circumstellar environments analogous to young solar systems. Practically, this system stands as a prime candidate for further studies using high-resolution spectroscopy and coronagraphy to investigate atmospheric compositions and dynamics.

Future high-resolution observations, potentially facilitated by the James Webb Space Telescope (JWST), could provide insights into atmospheric traits, including molecular abundances and cloud structures. Additionally, the system's architecture can inform the theoretical modeling of planet formation and evolution.

Conclusively, the study of TYC 8998-760-1 enriches the field of exoplanetary science by exploring the dynamics of a multiplanet system at an early evolutionary stage, thereby enhancing the conceptual frameworks addressing planetary systems' formation and evolution pathways.