ABSTRACT
We report the discovery of TOI-2119b, a transiting brown dwarf (BD) that orbits and is completely eclipsed by an active M-dwarf star. Using light-curve data from the Transiting Exoplanet ...Survey Satellite mission and follow-up high-resolution Doppler spectroscopic observations, we find the BD has a radius of Rb = 1.08 ± 0.03RJ, a mass of Mb = 64.4 ± 2.3MJ, an orbital period of P = 7.200865 ± 0.00002 d, and an eccentricity of e = 0.337 ± 0.002. The host star has a mass of M⋆ = 0.53 ± 0.02M⊙, a radius of R⋆ = 0.50 ± 0.01R⊙, an effective temperature of Teff = 3621 ± 48K, and a metallicity of $\rm Fe/H=+0.06\pm 0.08$. TOI-2119b joins an emerging population of transiting BDs around M-dwarf host stars, with TOI-2119 being the ninth such system. These M-dwarf–brown dwarf systems typically occupy mass ratios near q = Mb/M⋆ ≈ 0.1−0.2, which separates them from the typical mass ratios for systems with transiting substellar objects and giant exoplanets that orbit more massive stars. The nature of the secondary eclipse of the BD by the star enables us to estimate the effective temperature of the substellar object to be 2030 ± 84K, which is consistent with predictions by substellar evolutionary models.
Abstract
We present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely ...astrometric brown dwarf orbiting a bright (
V
J
= 12.5,
K
s
= 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04
R
⊕
and 0.98 ± 0.06
R
⊕
in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35
M
⊕
and 1.4
M
⊕
for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1
R
⊕
in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung–Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.
Abstract
Populating the exoplanet mass–radius diagram in order to identify the underlying relationship that governs planet composition is driving an interdisciplinary effort within the exoplanet ...community. The discovery of hot super-Earths—a high-temperature, short-period subset of the super-Earth planet population—has presented many unresolved questions concerning the formation, evolution, and composition of rocky planets. We report the discovery of a transiting, ultra-short-period hot super-Earth orbiting
TOI-1075
(TIC
351601843)
, a nearby (
d
= 61.4 pc) late-K/early-M-dwarf star, using data from the Transiting Exoplanet Survey Satellite. The newly discovered planet has a radius of 1.791
−
0.081
+
0.116
R
⊕
and an orbital period of 0.605 day (14.5 hr). We precisely measure the planet mass to be 9.95
−
1.30
+
1.36
M
⊕
using radial velocity measurements obtained with the Planet Finder Spectrograph mounted on the Magellan II telescope. Our radial velocity data also show a long-term trend, suggesting an additional planet in the system. While TOI-1075 b is expected to have a substantial H/He atmosphere given its size relative to the radius gap, its high density (
9.32
−
1.85
+
2.05
g cm
−3
) is likely inconsistent with this possibility. We explore TOI-1075 b’s location relative to the M-dwarf radius valley, evaluate the planet’s prospects for atmospheric characterization, and discuss potential planet formation mechanisms. Studying the TOI-1075 system in the broader context of ultra-short-period planetary systems is necessary for testing planet formation and evolution theories and density-enhancing mechanisms and for future atmospheric and surface characterization studies via emission spectroscopy with the JWST.
We have begun a large-scale photometric survey of nearby open clusters and star-forming regions, the Monitor project, aiming to measure time-series photometry for >10 000 cluster members over >10 ...deg2 of sky, to find low-mass eclipsing binary and planet systems. We describe the software pipeline we have developed for this project, showing that we can achieve peak rms accuracy over the entire data set of better than ∼2 mmag using aperture photometry, with rms <1 per cent over ∼4 mag, in data from 2- and 4-m class telescopes with wide-field mosaic cameras. We investigate the noise properties of our data, finding correlated ‘red’ noise at the ∼1–1.5 mmag level in bright stars, over transit-like time-scales of 2.5 h. An important source of correlated noise in aperture photometry is image blending, which produces variations correlated with the seeing. We present a simple blend index based on fitting polynomials to these variations, and find that subtracting the fit from the data provides a method to reduce their amplitude, in lieu of using techniques, such as point spread function fitting photometry, which tackle their cause. Finally, we use the sysrem algorithm to search for any further systematic effects.
ABSTRACT We report evidence for excess blue light from the Type Ia supernova (Sn Ia) SN 2012cg at 15 and 16 days before maximum B-band brightness. The emission is consistent with predictions for the ...impact of the supernova on a non-degenerate binary companion. This is the first evidence for emission from a companion to a normal SN Ia. Sixteen days before maximum light, the color of SN 2012cg is 0.2 mag bluer than for other normal SN Ia. At later times, this supernova has a typical SN Ia light curve, with extinction-corrected mag and . Our data set is extensive, with photometry in seven filters from five independent sources. Early spectra also show the effects of blue light, and high-velocity features are observed at early times. Near maximum, the spectra are normal with a silicon velocity vSi = −10,500 km s−1. Comparing the early data with models by Kasen favors a main-sequence companion of about six solar masses. It is possible that many other SN Ia have main-sequence companions that have eluded detection because the emission from the impact is fleeting and faint.
The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report ...precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate ω over this period by dω/dt = 2.0 (±0.2) x 10⁻⁴ degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of ~20 seconds toward the end of its expected lifetime.
We report on the results of an i-band time-series photometric survey of NGC 2516 using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and 8k Mosaic-II detector, achieving ...better than 1 per cent photometric precision per data point over 15 ≲i≲ 19. Candidate cluster members were selected from a V versus V−I colour–magnitude diagram over 16 < V < 26 (covering masses from 0.7 M⊙ down to below the brown dwarf limit), finding 1685 candidates, of which we expect ∼1000 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 362 detections over the mass range 0.15 ≲M/M⊙≲ 0.7. The rotation period distributions were found to show a remarkable morphology as a function of mass, with the fastest rotators bounded by P > 0.25 d, and the slowest rotators for M≲ 0.5 M⊙ bounded by a line of P∝M3, with those for M≳ 0.5 M⊙ following a flatter relation closer to P∼ constant. Models of the rotational evolution were investigated, finding that the evolution of the fastest rotators was well reproduced by a conventional solid body model with a mass-dependent saturation velocity, whereas core–envelope decoupling was needed to reproduce the evolution of the slowest rotators. None of our models were able to simultaneously reproduce the behaviour of both populations.
We report on the results of an I-band time-series photometric survey of NGC 2547 using the MPG/ESO 2.2-m telescope with Wide Field Imager, achieving better than 1 per cent photometric precision per ...data point over 14 ≲I≲ 18. Candidate cluster members were selected from a V versus V−I colour–magnitude diagram over 12.5 < V < 24 (covering masses from 0.9 M⊙ down to below the brown dwarf limit), finding 800 candidates, of which we expect ∼330 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 176 detections over the mass range 0.1 ≲M/M⊙≲ 0.9. The rotation period distributions were found to show a clear mass-dependent morphology, qualitatively intermediate between the distributions obtained from similar surveys in NGC 2362 and 2516, as would be expected from the age of this cluster. Models of the rotational evolution were investigated, finding that the evolution from NGC 2362 to 2547 was qualitatively reproduced (given the uncertainty in the age of NGC 2547) by solid body and core-envelope decoupled models from our earlier NGC 2516 study without need for significant modification.
Abstract
We present the discovery of TOI-3235 b, a short-period Jupiter orbiting an M dwarf with a stellar mass close to the critical mass at which stars transition from partially to fully ...convective. TOI-3235 b was first identified as a candidate from TESS photometry and confirmed with radial velocities from ESPRESSO and ground-based photometry from HATSouth, MEarth-South, TRAPPIST-South, LCOGT, and ExTrA. We find that the planet has a mass of 0.665 ± 0.025
M
J
and a radius of 1.017 ± 0.044
R
J
. It orbits close to its host star, with an orbital period of 2.5926 days but has an equilibrium temperature of ≈ 604 K, well below the expected threshold for radius inflation of hot Jupiters. The host star has a mass of 0.3939 ± 0.0030
M
☉
, a radius of 0.3697 ± 0.0018
R
☉
, an effective temperature of 3389 K, and a
J
-band magnitude of 11.706 ± 0.025. Current planet formation models do not predict the existence of gas giants such as TOI-3235 b around such low-mass stars. With a high transmission spectroscopy metric, TOI-3235 b is one of the best-suited giants orbiting M dwarfs for atmospheric characterization.
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