KELT-25b and KELT-26b: A Hot Jupiter and a Substellar Companion Transiting Young A-stars Observed by TESS

Abstract

We present the discoveries of KELT-25b (TIC 65412605, TOI-626.01) and KELT-26b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A-stars. The transit signals were initially detected by the KELT survey, and subsequently confirmed by \textit{TESS} photometry. KELT-25b is on a 4.40-day orbit around the V = 9.66 star CD-24 5016 ($T_{\mathrm{eff}}=8280_{-180}^{+440}$ K, $M_{\star }$ = $2.18_{-0.11}^{+0.12}$ $M_{\odot }$), while KELT-26b is on a 3.34-day orbit around the V = 9.95 star HD 134004 ($T_{\mathrm{eff}}$ =$8640_{-240}^{+500}$ K, $M_{\star }$ = $1.93_{-0.16}^{+0.14}$ $M_{\odot }$), which is likely an Am star. We have confirmed the sub-stellar nature of both companions through detailed characterization of each system using ground-based and \textit{TESS} photometry, radial velocity measurements, Doppler Tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of $R_{\mathrm{P}}$ = $1.64_{-0.043}^{+0.039}$ $R_{\mathrm{J}}$, and a 3-sigma upper limit on the companion's mass of $\sim 64M_{\mathrm{J}}$. For KELT-26b, we infer a planetary mass and radius of $M_{\mathrm{P}}$ = $1.41_{-0.51}^{+0.43}$ $M_{\mathrm{J}}$ and $R_{\mathrm{P}}$ = $1.940_{-0.058}^{+0.060}$ $R_{\mathrm{J}}$. From Doppler Tomographic observations, we find KELT-26b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the \textit{TESS} data. KELT-25b appears to be in a well-aligned, prograde orbit, and the system is likely a member of a cluster or moving group.

24 pages, 18 figures, 8 tables