The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better ...understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between and M* spanning 0.075 M < M* < 0.70 M . The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of Keck/NIRC2 imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved KS magnitudes and system parallaxes, to calibrate the -M* relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%-3%, which we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond measured M* uncertainties, perhaps driven by intrinsic variation in the -M* relation or underestimated uncertainties in the input parallaxes. We find that the effect of Fe/H on the -M* relation is likely negligible for metallicities in the solar neighborhood (0.0% 2.2% change in mass per dex change in Fe/H). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from MESA Isochrones and Stellar Tracks (at 5 ). A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic halo or thick disk).
We present the discovery of a transiting hot Jupiter orbiting HIP 67522 (Teff ∼ 5650 K; M* ∼ 1.2M ) in the 10-20 Myr old Sco-Cen OB association. We identified the transits in the TESS data using our ...custom notch filter planet search pipeline and characterize the system with additional photometry from Spitzer; spectroscopy from SOAR/Goodman, SALT/HRS, LCOGT/NRES, and SMARTS/CHIRON; and speckle imaging from SOAR/HRCam. We model the photometry as a periodic Gaussian process with transits to account for stellar variability and find an orbital period of days and radius of R⊕. We also identify a single transit of an additional candidate planet with radius R⊕ that has an orbital period of 23 days. The validated planet HIP 67522b is currently the youngest transiting hot Jupiter discovered and is an ideal candidate for transmission spectroscopy and radial velocity follow-up studies, while also demonstrating that some young giant planets either form in situ at small orbital radii or else migrate promptly from formation sites farther out in the disk.
Abstract
Young exoplanets are attractive targets for atmospheric characterization to explore the early phase of planetary evolution and the surrounding environment. Recent observations of the 10 Myr ...young Neptune-sized exoplanet K2-33b revealed that the planet’s transit depth drastically decreases from the optical to near-infrared wavelengths. Thao et al. suggested that a thick planetary haze and/or stellar spots may be the cause; however, even the best-fit model only barely explains the data. Here, we propose that the peculiar transmission spectrum may indicate that K2-33b possesses a circumplanetary dust ring; an analog of Jupiter’s dust ring. We demonstrate that the ring could produce a steep slope in the transmission spectrum even if its optical depth is as low as ∼10
−2
. We then apply a novel joint atmosphere-ring retrieval to K2-33b and find that the ring scenario could well explain the observed spectrum for various possible ring compositions. Importantly, the dust ring also exhibits prominent ring particle absorption features of ring particles around ∼10
μ
m, whose shape and strength depend on the composition of the ring. Thus, future observations by JWST-MIRI would be able to test not only the ring hypothesis but also, if it indeed exists, to constrain the composition of the ring—providing a unique opportunity to explore the origins of the dust ring around its parent planet, soon after the planetary system’s formation.
Abstract
Young planets provide a window into the early stages and evolution of planetary systems. Ideal planets for such research are in coeval associations, where the parent population can precisely ...determine their ages. We describe a young association (MELANGE-3) in the Kepler field, which harbors two transiting planetary systems (KOI-3876 and Kepler-970). We identify MELANGE-3 by searching for kinematic and spatial overdensities around Kepler planet hosts with high levels of lithium. To determine the age and membership of MELANGE-3, we combine new high-resolution spectra with archival light curves, velocities, and astrometry of stars near KOI-3876 spatially and kinematically. We use the resulting rotation sequence, lithium levels, and color–magnitude diagram of candidate members to confirm the presence of a coeval 105 ± 10 Myr population. MELANGE-3 may be part of the recently identified Theia 316 stream. For the two exoplanet systems, we revise the stellar and planetary parameters, taking into account the newly determined age. Fitting the 4.5 yr Kepler light curves, we find that KOI-3876b is a 2.0 ± 0.1
R
⊕
planet on a 19.58 day orbit, while Kepler-970 b is a 2.8 ± 0.2
R
⊕
planet on a 16.73 day orbit. KOI-3876 was previously flagged as an eclipsing binary, which we rule out using radial velocities from APOGEE and statistically validate the signal as planetary in origin. Given its overlap with the Kepler field, MELANGE-3 is valuable for studies of spot evolution on year timescales, and both planets contribute to the growing work on transiting planets in young stellar associations.
Abstract
The dispersed remnants of stellar nurseries, stellar associations, provide unparalleled samples of coeval stars critical for studies of stellar and planetary formation and evolution. The ...Carina Stellar Association is one of the closest stellar associations to Earth, and yet measurements of its age have varied from 13 to 45 Myr. We aim to update the age of Carina using the lithium depletion boundary (LDB) method. We obtain new measurements of the Li 6708 Å absorption feature in likely members using optical spectra from the Goodman High Throughput Spectrograph on SOAR and NRES on LCO. We detect the depletion boundary at
M
K
≃ 6.8 (M5). This age is consistent within uncertainties across six different models, including those that account for magnetic fields and spots. We also estimate the age through analysis of the group’s overall variability, and by comparing the association members’ color–magnitude diagram to stellar evolutionary models using a Gaussian Mixture Model, recovering ages consistent with the LDB. Combining these age measures we obtain an age for the Carina association of
41
−
5
+
3
Myr. The resulting age agrees with the older end of previous age measurements and is consistent with the lithium depletion age for the neighboring Tucana-Horologium moving group.
Abstract
The evolution of magnetism in late-type dwarfs remains murky, as we can only weakly predict levels of activity for M dwarfs of a given mass and age. We report results from our spectroscopic ...survey of M dwarfs in the Southern Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite (TESS). As the TESS CVZs overlap with those of the James Webb Space Telescope, our targets constitute a legacy sample for studies of nearby M dwarfs. For 122 stars, we obtained at least one
R
≈ 2000 optical spectrum with which we measure chromospheric H
α
emission, a proxy for magnetic field strength. The fraction of active stars is consistent with what is expected for field M dwarfs; as in previous studies, we find that late-type M dwarfs remain active for longer than their early-type counterparts. While the TESS light curves for ≈20% of our targets show modulations consistent with rotation, TESS systematics are not well enough understood for confident measurements of rotation periods (
P
rot
) longer than half the length of an observing sector. We report periods for 12 stars for which we measure
P
rot
≲ 15 days or find confirmation for the TESS-derived
P
rot
in the literature. Our sample of 21
P
rot
, which includes periods from the literature, is consistent with our targets being spun-down field stars. Finally, we examine the H
α
-to-bolometric luminosity distribution for our sample. Two stars are rotating fast enough to be magnetically saturated, but are not, hinting at the possibility that fast rotators may appear inactive in H
α
.
Abstract
Although all-sky surveys have led to the discovery of dozens of young planets, little is known about their atmospheres. Here, we present multiwavelength transit data for the super-Neptune ...sized exoplanet, K2-33b—the youngest (∼10 Myr) transiting exoplanet to date. We combined photometric observations of K2-33 covering a total of 33 transits spanning >2 yr, taken from K2, MEarth, the Hubble Space Telescope (HST), and Spitzer. The transit photometry spanned from the optical to the near-infrared (0.6–4.5
μ
m), enabling us to construct a transmission spectrum of the planet. We find that the optical transit depths are nearly a factor of 2 deeper than those from the near-infrared. This difference holds across multiple data sets taken over years, ruling out issues of data analysis and unconstrained systematics. Surface inhomogeneities on the young star can reproduce some of the difference, but required spot coverage fractions (>60%) are ruled out by the observed stellar spectrum (<20%). We find a better fit to the transmission spectrum using photochemical hazes, which were predicted to be strong in young, moderate-temperature, and large-radius planets like K2-33b. A tholin haze with CO as the dominant gaseous carbon carrier in the atmosphere can reasonably reproduce the data with small or no stellar surface inhomogeneities, consistent with the stellar spectrum. The HST data quality is insufficient for the detection of any molecular features. More observations would be required to fully characterize the hazes and spot properties and confirm the presence of CO suggested by current data.
Abstract
We report the discovery and characterization of a nearby (∼85 pc), older (27 ± 3 Myr), distributed stellar population near Lower Centaurus Crux (LCC), initially identified by searching for ...stars comoving with a candidate transiting planet from TESS (HD 109833; TOI 1097). We determine the association membership using Gaia kinematics, color–magnitude information, and rotation periods of candidate members. We measure its age using isochrones, gyrochronology, and Li depletion. While the association is near known populations of LCC, we find that it is older than any previously found LCC subgroup (10–16 Myr), and distinct in both position and velocity. In addition to the candidate planets around HD 109833, the association contains four directly imaged planetary-mass companions around three stars, YSES-1, YSES-2, and HD 95086, all of which were previously assigned membership in the younger LCC. Using the Notch pipeline, we identify a second candidate transiting planet around HD 109833. We use a suite of ground-based follow-up observations to validate the two transit signals as planetary in nature. HD 109833 b and c join the small but growing population of <100 Myr transiting planets from TESS. HD 109833 has a rotation period and Li abundance indicative of a young age (≲100 Myr), but a position and velocity on the outskirts of the new population, lower Li levels than similar members, and a color–magnitude diagram position below model predictions for 27 Myr. So, we cannot reject the possibility that HD 109833 is a young field star coincidentally nearby the population.
Transiting planets in nearby young clusters offer the opportunity to study the atmospheres and dynamics of planets during their formative years. To this end, we focused on K2-25b-a close-in (P = 3.48 ...days), Neptune-sized exoplanet orbiting a M4.5 dwarf in the 650 Myr Hyades cluster. We combined photometric observations of K2-25 covering a total of 44 transits and spanning >2 yr, drawn from a mix of space-based telescopes (Spitzer Space Telescope and K2) and ground-based facilities (Las Cumbres Observatory Global Telescope network and MEarth). The transit photometry spanned 0.6-4.5 m, which enabled our study of K2-25b's transmission spectrum. We combined and fit each data set at a common wavelength within a Markov Chain Monte Carlo framework, yielding consistent planet parameters. The resulting transit depths ruled out a solar-composition atmosphere for K2-25b for the range of expected planetary masses and equilibrium temperature at a >4 confidence level, and are consistent with a flat transmission spectrum. Mass constraints and transit observations at a finer grid of wavelengths (e.g., from the Hubble Space Telescope) are needed to make more definitive statements about the presence of clouds or an atmosphere of high mean molecular weight. Our precise measurements of K2-25b's transit duration also enabled new constraints on the eccentricity of K2-25's orbit. We find K2-25b's orbit to be eccentric (e > 0.20) for all reasonable stellar densities and independent of the observation wavelength or instrument. The high eccentricity is suggestive of a complex dynamical history and motivates future searches for additional planets or stellar companions.
Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets (<1 Gyr) offer an opportunity to probe the ...critical early stages of this evolution, where planets evolve the fastest. However, most of the known young planets orbit prohibitively faint stars. We present the discovery of two planets transiting HD 63433 (TOI 1726, TIC 130181866), a young Sun-like ( ) star. Through kinematics, lithium abundance, and rotation, we confirm that HD 63433 is a member of the Ursa Major moving group (τ = 414 23 Myr). Based on the TESS light curve and updated stellar parameters, we estimate that the planet radii are 2.15 0.10 R⊕ and 2.67 0.12 R⊕, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. Using High Accuracy Radial velocity Planet Searcher for the Northern hemisphere velocities, we measure the Rossiter-McLaughlin signal of the inner planet, demonstrating that the orbit is prograde. Since the host star is bright (V = 6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. This system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.
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