TOI-942b: A Prograde Neptune in a ∼ 60 Myr Old Multi-transiting System*
Christopher P. Wirth, George Zhou, Samuel N. Quinn, Andrew W. Mann, Luke G. Bouma, David W. Latham, Johanna K. Teske, Sharon X. Wang, Stephen A. Shectman, R. P. Butler, Jeffrey D. Crane
Abstract
Abstract Mapping the orbital obliquity distribution of young planets is one avenue toward understanding mechanisms that sculpt the architectures of planetary systems. TOI-942 is a young field star, with an age of ∼60 Myr, hosting a planetary system consisting of two transiting Neptune-sized planets in 4.3 and 10.1 day period orbits. We observed the spectroscopic transits of the inner Neptune TOI-942b to determine its projected orbital obliquity angle. Through two partial transits, we find the planet to be in a prograde orbit, with a projected obliquity angle of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">∣</mml:mo> <mml:mi>λ</mml:mi> <mml:mo stretchy="false">∣</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>41</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> deg. In addition, incorporating the light curve and the stellar rotation period, we find the true 3D obliquity to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>23</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>27</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> deg. We explored various sources of uncertainties specific to the spectroscopic transits of planets around young active stars, and showed that our reported obliquity uncertainty fully encompassed these effects. TOI-942b is one of the youngest planets to have its obliquity characterized, and one of even fewer residing in a multi-planet system. The prograde orbital geometry of TOI-942b is in line with systems of similar ages, none of which have yet been identified to be in strongly misaligned orbits.