Using K2 data, we identified 23 very-low-mass members of the Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical ...mechanisms such as star spots, eclipsing binaries, or pulsation. All of these unusual stars are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally <1 day. Often the unusual light-curve signature takes the form of narrow flux dips; when we also have rotation periods from star spots, the two periods agree, suggesting that the flux dips are due to material orbiting the star at the Keplerian co-rotation radius. We sometimes see "state-changes" in the phased light-curve morphologies where ∼25% of the waveform changes shape on timescales less than a day; often, the "state-change" takes place immediately after a strong flare. For the group of stars with these sudden light-curve morphology shifts, we attribute their flux dips as most probably arising from eclipses of warm coronal gas clouds, analagous to the slingshot prominences postulated to explain transient H absorption features in AB Doradus and other rapidly rotating late-type stars. For another group of stars with somewhat longer periods, we find the short-duration flux dips to be highly variable on both short and long timescales, with generally asymmetric flux-dip profiles. We believe that these flux dips are due to particulate clouds possibly associated with a close-in planet or resulting from a recent collisional event.
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.
We report the discovery of a repeating photometric signal from a low-mass member of the Praesepe open cluster that we interpret as a Neptune-sized transiting planet. The star is JS 183 (HSHJ 163, ...EPIC 211916756), with Teff = 3325 100 K, M* = 0.44 0.04 M , R* = 0.44 0.03 R , and . The planet has an orbital period of 10.134588 days and a radius of RP = 0.32 0.02 RJ. Since the star is faint at V = 16.5 and J = 13.3, we are unable to obtain a measured radial velocity orbit, but we can constrain the companion mass to below about 1.7 MJ, and thus well below the planetary boundary. JS 183b (since designated as K2-95b) is the second transiting planet found with K2 that resides in a several-hundred-megayear open cluster; both planets orbit mid-M dwarf stars and are approximately Neptune sized. With a well-determined stellar density from the planetary transit, and with an independently known metallicity from its cluster membership, JS 183 provides a particularly valuable test of stellar models at the fully convective boundary. We find that JS 183 is the lowest-density transit host known at the fully convective boundary, and that its very low density is consistent with current models of stars just above the fully convective boundary but in tension with the models just below the fully convective boundary.
We have analyzed K2 light curves for more than 3000 low-mass stars in the ∼8 Myr old Upper Sco association, the ∼125 Myr age Pleiades open cluster, and the ∼700 Myr old Hyades and Praesepe open ...clusters to determine stellar rotation rates. Many of these K2 targets show two distinct periods, and for the lowest-mass stars in these clusters, virtually all of these systems with two periods are photometric binaries. The most likely explanation is that we are detecting the rotation periods for both components of these binaries. We explore the evolution of the rotation rate in both components of photometric binaries relative to one another and to nonphotometric binary stars. In Upper Sco and the Pleiades, these low-mass binary stars have periods that are much shorter on average and much closer to each other than would be true if drawn at random from the M dwarf single stars. In Upper Sco, this difference correlates strongly with the presence or absence of infrared excesses due to primordial circumstellar disks-the single-star population includes many stars with disks, and their rotation periods are distinctively longer on average than their binary star cousins of the same mass. By Praesepe age, the significance of the difference in rotation rate between the single and binary low-mass M dwarf stars is much less, suggesting that angular momentum loss from winds for fully convective zero-age main-sequence stars erases memory of the rotation rate dichotomy for binary and single very low mass stars at later ages.
We report on Submillimeter Array observations of the 870 μm continuum and CO (3–2), 13CO (2–1), and C18O (2–1) line emission of a faint object, SMM2E, near the driving source of the HH 797 outflow in ...the IC 348 cluster. The continuum emission shows an unresolved source for which we estimate a mass of gas and dust of 30 M
Jup, and the CO (3–2) line reveals a compact bipolar outflow centred on SMM2E, and barely seen also in 13CO (2–1). In addition, C18O (2–1) emission reveals hints of a possible rotating envelope/disc perpendicular to the outflow, for which we infer a dynamical mass of ∼16 M
Jup. In order to further constrain the accreted mass of the object, we gathered data from Spitzer, Herschel, and new and archive submillimetre observations, and built the spectral energy distribution (SED). The SED can be fitted with one single-modified blackbody from 70 μm down to 2.1 cm, using a dust temperature of ∼24 K, a dust emissivity index of 0.8, and an envelope mass of ∼35 M
Jup. The bolometric luminosity is 0.10 L⊙, and the bolometric temperature is 35 K. Thus, SMM2E is comparable to the known Class 0 objects in the stellar domain. An estimate of the final mass indicates that SMM2E will most likely remain substellar, and the SMM2E outflow force matches the trend with luminosity known for young stellar objects. Thus, SMM2E constitutes an excellent example of a Class 0 proto-brown dwarf candidate which forms as a scaled-down version of low-mass stars. Finally, SMM2E seems to be part of a wide (∼2400 au) multiple system of Class 0 sources.
Abstract We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2 day orbit located interior to a previously known hot Jupiter, TOI-1408 b ( P = 4.42 days, M = 1.86 ± 0.02 ...M Jup , R = 2.4 ± 0.5 R Jup ) that exhibits grazing transits. The two planets are near 2:1 period commensurability, resulting in significant transit timing variations (TTVs) for both planets and transit duration variations for the inner planet. The TTV amplitude for TOI-1408 c is 15% of the planet’s orbital period, marking the largest TTV amplitude relative to the orbital period measured to date. Photodynamical modeling of ground-based radial velocity (RV) observations and transit light curves obtained with the Transiting Exoplanet Survey Satellite and ground-based facilities leads to an inner planet radius of 2.22 ± 0.06 R ⊕ and mass of 7.6 ± 0.2 M ⊕ that locates the planet into the sub-Neptune regime. The proximity to the 2:1 period commensurability leads to the libration of the resonant argument of the inner planet. The RV measurements support the existence of a third body with an orbital period of several thousand days. This discovery places the system among the rare systems featuring a hot Jupiter accompanied by an inner low-mass planet.
Abstract SY Cha is a T Tauri star surrounded by a protoplanetary disk with a large cavity seen in the millimeter continuum but has the spectral energy distribution of a full disk. Here we report the ...first results from JWST/Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) observations taken as part of the MIRI mid-INfrared Disk Survey (MINDS) GTO Program. The much improved resolution and sensitivity of MIRI-MRS compared to Spitzer enables a robust analysis of the previously detected H 2 O, CO, HCN, and CO 2 emission as well as a marginal detection of C 2 H 2 . We also report the first robust detection of mid-infrared OH and rovibrational CO emission in this source. The derived molecular column densities reveal the inner disk of SY Cha to be rich in both oxygen- and carbon-bearing molecules. This is in contrast to PDS 70, another protoplanetary disk with a large cavity observed with JWST, which displays much weaker line emission. In the SY Cha disk, the continuum, and potentially the line, flux varies substantially between the new JWST observations and archival Spitzer observations, indicative of a highly dynamic inner disk.
Abstract
The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from Kepler. Owing ...to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey’s (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data that has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached ≥5
σ
precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three-year survey. We took the opportunity to assess the performance of our survey and found that we achieved many of our goals, including measuring the mass of 38 small (<4
R
⊕
) planets, nearly achieving the TESS mission’s basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder as survey support and observed meaningful constraints on system parameters, due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass–radius relations and investigated evidence of systematic bias.
Aims. The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014, Campaign 1 data from the mission was released, providing high-precision photometry for ~22 000 ...objects over an 80-day timespan. We searched these data with the aim of detecting more important new objects. Methods. Our search through two separate pipelines led to the independent discovery of K2-19b and c, a two-planet system of Neptune-sized objects (4.2 and 7.2 R⊕), orbiting a K dwarf extremely close to the 3:2 mean motion resonance. The two planets each show transits, sometimes simultaneously owing to their proximity to resonance and the alignment of conjunctions. Results. We obtained further ground-based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs), and used the observed TTVs to place mass constraints on the transiting objects under the hypothesis that the objects are near but not in resonance. We then statistically validated the planets through the PASTIS tool, independently of the TTV analysis.
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