The Magellan-TESS Survey. I. Survey Description and Midsurvey Results* †

Abstract

Kepler revealed that roughly one-third of Sunlike stars host planets orbiting within 100 days and between the size of Earth and Neptune. How do these planets form, what are they made of, and do they represent a continuous population or multiple populations? To help address these questions, we began the Magellan-TESS Survey (MTS), which uses Magellan II/PFS to obtain radial velocity (RV) masses of 30 TESS-detected exoplanets and develops an analysis framework that connects observed planet distributions to underlying populations. In the past, small-planet RV measurements have been challenging to obtain due to host star faintness and low RV semiamplitudes and challenging to interpret due to the potential biases in target selection and observation planning decisions. The MTS attempts to minimize these biases by focusing on bright TESS targets and employing a quantitative selection function and observing strategy. In this paper, we (1) describe our motivation and survey strategy, (2) present our first catalog of planet density constraints for 27 TESS Objects of Interest (TOIs; 22 in our population analysis sample, 12 that are members of the same systems), and (3) employ a hierarchical Bayesian model to produce preliminary constraints on the mass–radius (M-R) relation. We find that the biases causing previous M-R relations to predict fairly high masses at 1 R ⊕ have been reduced. This work can inform more detailed studies of individual systems and offer a framework that can be applied to future RV surveys with the goal of population inferences.

Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c*

“…However, when Otegi et al (2020a) curated a high-fidelity sample of exoplanet mass and radius measurements from the We only include planets with better than 15% fractional measurement precision in radius and 33% fractional precision in mass. We note that the sample of planets shown here may lack completeness for low-density sub-Neptunes due to our fractional precision requirements, but they should not impact completeness at high density (Burt et al 2018;Montet 2018;Teske et al 2021). Planets and their 1σ measurement uncertainties are colored by equilibrium temperature assuming zero Bond albedo.…”

“…While we found that our mass measurement for K2-182 b was consistent between RV models with and without a GP trained on the K2 photometry, we suggest that additional monitoring will better inform the influence of stellar activity on the spectroscopic observations. Furthermore, cases where starspots contribute to planet RV amplitude may be subject to publication bias because the inflated signal can more easily overcome standard fractional precision thresholds, like M p s  5 M p (Burt et al 2018;Montet 2018;Batalha et al 2019;Teske et al 2021).…”

The TESS-Keck Survey: * Science Goals and Target Selection

“…There are several ongoing, ground-based TESS RV surveys, e.g., MTS (Teske et al 2021), NCORES (Armstrong & consortium 2021), KESPRINT (Kabath et al 2021), etc., many of which have science interests that overlap with those of TKS. Our target selection procedure was strategically implemented to achieve the most optimal sample that simultaneously addressed the different science goals within the survey (see Section 5 for more details).…”

“…Therefore, a critical ingredient for the realization of these surveys is understanding the process by which targets were initially selected. Indeed, recent groundbased TESS follow-up programs such as the Magellan-TESS Survey (MTS; Teske et al 2021) have begun to describe target selection functions, providing a pathway to properly correct for survey biases or incompleteness.…”

A Close-in Puffy Neptune with Hidden Friends: The Enigma of TOI 620

“…Due to the relatively large TESS pixels spanning 22″ on the sky, fainter visual eclipsing binaries can blend with the nearby bright target stars and produce false positives (barring instrumental artifacts). This is an important consideration, particularly when only a single transiting planet is found in the TESS 27 day time baseline of sector observations, at lower ecliptic latitudes, and away from the ecliptic poles (Lissauer et al 2012;Vanderburg et al 2019;Rodríguez Martínez et al 2020;Hobson et al 2021;Addison et al 2021;Osborn et al 2021;Dreizler et al 2020;Brahm et al 2020;Nowak et al 2020;Teske et al 2020;Sha et al 2021;Gan et al 2021;Bluhm et al 2020).…”