The Transiting Exoplanet Survey Satellite (TESS) recently observed 18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6 11.7 s earlier than had been predicted, based on data ...stretching back to 2007. This is unlikely to be the result of a clock error, because TESS observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with a constant period, ruling out an 81.6 s offset at the 6.4 level. The 1.3 day orbital period of WASP-4b appears to be decreasing at a rate of ms per year. The apparent period change might be caused by tidal orbital decay or apsidal precession, although both interpretations have shortcomings. The gravitational influence of a third body is another possibility, though at present there is minimal evidence for such a body. Further observations are needed to confirm and understand the timing variation.
We present multi-epoch simultaneous radio, optical, H alpha , UV, and X-ray observations of the active, young, low-mass binary NLTT 33370 AB (blended spectral type M7e). This system is remarkable for ...its extreme levels of magnetic activity: it is the most radio-luminous ultracool dwarf (UCD) known, and here we show that it is also one of the most X-ray luminous UCDs known. We detect the system in all bands and find a complex phenomenology of both flaring and periodic variability. Analysis of the optical light curve reveals the simultaneous presence of two periodicities, 3.7859 + or - 0.0001 and 3.7130 + or - 0.0002 hr. While these differ by only ~2%, studies of differential rotation in the UCD regime suggest that it cannot be responsible for the two signals. The system's radio emission consists of at least three components: rapid 100% polarized flares, bright emission modulating periodically in phase with the optical emission, and an additional periodic component that appears only in the 2013 observational campaign. We interpret the last of these as a gyrosynchrotron feature associated with large-scale magnetic fields and a cool, equatorial plasma torus. However, the persistent rapid flares at all rotational phases imply that small-scale magnetic loops are also present and reconnect nearly continuously. We present a spectral energy distribution of the blended system spanning more than 9 orders of magnitude in wavelength. The significant magnetism present in NLTT 33370 AB will affect its fundamental parameters, with the components' radii and temperatures potentially altered by ~+20% and 10%, respectively. Finally, we suggest spatially resolved observations that could clarify many aspects of this system's nature.
The source GJ1132 is a nearby red dwarf known to host a transiting Earth-size planet. After its initial detection, we pursued an intense follow-up with the HARPS velocimeter. We now confirm the ...detection of GJ1132b with radial velocities alone. We refined its orbital parameters, and in particular, its mass (
m
b
= 1.66 ± 0.23
M
⊕
), density (
ρ
b
= 6.3 ± 1.3 g cm
−3
), and eccentricity (
e
b
< 0.22; 95%). We also detected at least one more planet in the system. GJ1132c is a super-Earth with period
P
c
= 8.93 ± 0.01 days and minimum mass
m
c
sin
i
c
= 2.64 ± 0.44
M
⊕
. Receiving about 1.9 times more flux than Earth in our solar system, its equilibrium temperature is that of a temperate planet (
T
eq
= 230−300 K for albedos
A
= 0.75 − 0.00), which places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favorable orientation for the system,
Spitzer
observations reject most transit configurations, leaving a posterior probability <1% that GJ1132c transits. GJ1132(d) is a third signal with period
P
d
= 177 ± 5 days attributed to either a planet candidate with minimum mass
m
d
sin
i
d
= 8.4
−2.5
+1.7
M
⊕
or stellar activity. Its Doppler signal is the most powerful in our HARPS time series but appears on a timescale where either the stellar rotation or a magnetic cycle are viable alternatives to the planet hypothesis. On the one hand, the period is different than that measured for the stellar rotation (~125 days), and a Bayesian statistical analysis we performed with a Markov chain Monte Carlo and Gaussian processes demonstrates that the signal is better described by a Keplerian function than by correlated noise. On the other hand, periodograms of spectral indices sensitive to stellar activity show power excess at similar periods to that of this third signal, and radial velocity shifts induced by stellar activity can also match a Keplerian function. We, therefore, prefer to leave the status of GJ1132(d) undecided.
The high-energy radiative output, from the X-ray to the ultraviolet, of exoplanet host stars drives photochemical reactions and mass loss in the upper regions of planetary atmospheres. In order to ...place constraints on the atmospheric properties of the three closest terrestrial exoplanets transiting M dwarfs, we observe the high-energy spectra of the host stars and in the X-ray with XMM-Newton and Chandra and in the ultraviolet with HST/COS and STIS. We combine these observations with estimates of extreme-ultraviolet flux, reconstructions of the lines, and stellar models at optical and infrared wavelengths to produce panchromatic spectra from 1 to 20 mu m for each star. While and do not possess primordial hydrogen-dominated atmospheres, we calculate that they are able to retain pure atmospheres if starting with 10, 15, and 50<!PCT!> of Earth's total budget, respectively, in the presence of their host stars' stellar wind. We use age--activity relationships to place lower limits of 2.2 and 6.6 Gyr on the ages of the host stars and Despite both and appearing inactive at optical wavelengths, we detect flares at ultraviolet and X-ray wavelengths for both stars. In particular exhibits two far-ultraviolet flares with absolute energies of 10 and 10 erg (equivalent durations of $4357 and $19724 s) occurring three hours apart. Based on the timing of the observations, we suggest that these high-energy flares are related and indicative of heightened flaring activity that lasts for a period of days, but our interpretations are limited by sparse time-sampling. Consistent high-energy monitoring is needed to determine the duration and extent of high-energy activity on individual M dwarfs and the population as a whole.
Context.
Several planetary formation models have been proposed to explain the observed abundance and variety of compositions of super-Earths and mini-Neptunes. In this context, multitransiting ...systems orbiting low-mass stars whose planets are close to the radius valley are benchmark systems, which help to elucidate which formation model dominates.
Aims.
We report the discovery, validation, and initial characterization of one such system, TOI-2096 (TIC 142748283), a two-planet system composed of a super-Earth and a mini-Neptune hosted by a mid-type M dwarf located 48 pc away.
Methods.
We characterized the host star by combining optical spectra, analyzing its broadband spectral energy distribution, and using evolutionary models for low-mass stars. Then, we derived the planetary properties by modeling the photometric data from TESS and ground-based facilities. In addition, we used archival data, high-resolution imaging, and statistical validation to support our planetary interpretation.
Results.
We found that the stellar properties of TOI-2096 correspond to a dwarf star of spectral type M4±0.5. It harbors a super-Earth (
R
= 1.24 ± 0.07
R
⊕
) and a mini-Neptune (
R
= 1.90 ± 0.09
R
⊕
) in likely slightly eccentric orbits with orbital periods of 3.12 d and 6.39 d, respectively. These orbital periods are close to the first-order 2:1 mean-motion resonance (MMR), a configuration that may lead to measurable transit timing variations (TTVs). We computed the expected TTVs amplitude for each planet and found that they might be measurable with high-precision photometry delivering mid-transit times with accuracies of ≲2 min. Moreover, we conclude that measuring the planetary masses via radial velocities (RVs) could also be possible. Lastly, we found that these planets are among the best in their class to conduct atmospheric studies using the NIRSpec/Prism onboard the
James Webb
Space Telescope (JWST).
Conclusions.
The properties of this system make it a suitable candidate for further studies, particularly for mass determination using RVs and/or TTVs, decreasing the scarcity of systems that can be used to test planetary formation models around low-mass stars.
The planetary system around the naked-eye star
v
2
Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (
M
⊕
). The TESS and CHEOPS missions ...revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6
M
⊕
exoplanet
v
2
Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to
P
= 107.1361
−0.0022
+0.0019
days and
T
c
= 2459009.7759
−0.0096
+0.0101
BJD
TDB
, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet’s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet’s Hill sphere, which is as large as the Earth’s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of
v
2
Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet.
The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M⊕). The TESS and CHEOPS missions revealed ...that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M⊕ exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.1361−0.0022+0.0019 days and Tc = 2459009.7759−0.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet's Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet's Hill sphere, which is as large as the Earth's, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet. Undetrended and detrended light curves are only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/671/A154
The source GJ1132 is a nearby red dwarf known to host a transiting Earth-size planet. After its initial detection, we pursued an intense follow-up with the HARPS velocimeter. We now confirm the ...detection of GJ1132b with radial velocities alone. We refined its orbital parameters, and in particular, its mass (mb = 1.66 ± 0.23 M⊕), density (ρb = 6.3 ± 1.3 g cm−3), and eccentricity (eb < 0.22; 95%). We also detected at least one more planet in the system. GJ1132c is a super-Earth with period Pc = 8.93 ± 0.01 days and minimum mass mc sinic = 2.64 ± 0.44 M⊕. Receiving about 1.9 times more flux than Earth in our solar system, its equilibrium temperature is that of a temperate planet (Teq = 230−300 K for albedos A = 0.75 − 0.00), which places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favorable orientation for the system, Spitzer observations reject most transit configurations, leaving a posterior probability <1% that GJ1132c transits. GJ1132(d) is a third signal with period Pd = 177 ± 5 days attributed to either a planet candidate with minimum mass md sin id = 8.4−2.5+1.7 M⊕$m_d \sin i_d = 8.4^{+1.7}_{-2.5}~M_{\oplus}$mdsinid=8.4−2.5+1.7 M⊕ or stellar activity. Its Doppler signal is the most powerful in our HARPS time series but appears on a timescale where either the stellar rotation or a magnetic cycle are viable alternatives to the planet hypothesis. On the one hand, the period is different than that measured for the stellar rotation (~125 days), and a Bayesian statistical analysis we performed with a Markov chain Monte Carlo and Gaussian processes demonstrates that the signal is better described by a Keplerian function than by correlated noise. On the other hand, periodograms of spectral indices sensitive to stellar activity show power excess at similar periods to that of this third signal, and radial velocity shifts induced by stellar activity can also match a Keplerian function. We, therefore, prefer to leave the status of GJ1132(d) undecided.
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