A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau

TL;DR

This study presents evidence for a massive planet orbiting the young star CI Tau, based on extensive infrared and optical radial velocity measurements, suggesting a ~9-day period planet with a mass around 11 Jupiter masses.

Contribution

First detection of a candidate massive planet around a young T Tauri star using combined infrared and optical RV data, demonstrating the effectiveness of multi-wavelength RV analysis.

Findings

Infrared RV data reveal a ~9-day periodicity.

Optical and IR RV data phase coherently, supporting planetary origin.

Estimated planet mass is approximately 11.3 Jupiter masses.

Abstract

The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in its radial velocity (RV) variations measured at infrared (IR) and optical wavelengths. We find that these observations are consistent with a massive planet in a ~9-day period orbit. These results are based on 71 IR RV measurements of this system obtained over 5 years, and on 26 optical RV measurements obtained over 9 years. CI Tau was also observed photometrically in the optical on 34 nights over ~one month in 2012. The optical RV data alone are inadequate to identify an orbital period, likely the result of star spot and activity induced noise for this relatively small dataset. The infrared RV measurements reveal significant periodicity at ~9 days. In addition, the full set of optical and IR RV measurements taken together phase coherently and with equal amplitudes to the ~9 day period. Periodic radial velocity signals can in principle be produced by cool spots, hot spots, and reflection of the stellar spectrum off the inner disk, in addition to resulting from a planetary companion. We have considered each of these and find the planet hypothesis most consistent with the data. The radial velocity amplitude yields an Msin(i) of ~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the circumstellar disk inclination from the literature, we find a planet mass of ~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.