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 LTT1445A and GJ486 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 Ly-a lines, and stellar models at optical and infrared wavelengths to produce panchromatic spectra from 1A--20um for each star. While LTT1445Ab, LTT1445Ac, and GJ486b do not possess primordial hydrogen-dominated atmospheres, we calculate that they are able to retain pure CO2 atmospheres if starting with 10, 15, and 50% of Earth's total CO2 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 LTT1445A and GJ486. Despite both LTT1445A and GJ486 appearing inactive at optical wavelengths, we detect flares at ultraviolet and X-ray wavelengths for both stars. In particular, GJ486 exhibits two flares with absolute energies of 10^29.5 and 10^30.1 erg (equivalent durations of 4357+/-96 and 19724+/-169 s) occurring three hours apart, captured with HST/COS G130M. 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, as well as the population as a whole.
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. We report the discovery, validation, and initial characterization of one such system, TOI-2096, composed of a super-Earth and a mini-Neptune hosted by a mid-type M dwarf located 48 pc away. We first characterized the host star by combining different methods. Then, we derived the planetary properties by modeling the photometric data from TESS and ground-based facilities. We used archival data, high-resolution imaging, and statistical validation to support our planetary interpretation. We found that TOI-2096 corresponds to a dwarf star of spectral type M4. It harbors a super-Earth (R\(\sim1.2 R_{\oplus}\)) and a mini-Neptune (R\(\sim1.90 R_{\oplus}\)) 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), which 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 \(\lesssim\)2 min. Moreover, measuring the planetary masses via radial velocities (RVs) is also possible. Lastly, we found that these planets are among the best in their class to conduct atmospheric studies using the James Webb Space Telescope (JWST). 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.
Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble ...and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species\(-\)in particular the primary carbon-bearing molecules. Here we report a broad-wavelength 0.5-5.5 \(\mu\)m atmospheric transmission spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting Exoplanet Community Early Release Science Team program. We robustly detect multiple chemical species at high significance, including Na (19\(\sigma\)), H\(_2\)O (33\(\sigma\)), CO\(_2\) (28\(\sigma\)), and CO (7\(\sigma\)). The non-detection of CH\(_4\), combined with a strong CO\(_2\) feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4\(\mu\)m is best explained by SO\(_2\) (2.7\(\sigma\)), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes.
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 \(\pm\) 0.0001 and 3.7130 \(\pm\) 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 an SED 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.
A&A 671, A154 (2023) The planetary system around the naked-eye star $\nu^2$ Lupi (HD 136352;
TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6
Earth masses. 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
Earth-mass exoplanet $\nu^2$ 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
(+0.0019/-0.0022) days and Tc = 2,459,009.7759 (+0.0101/-0.0096) 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 $\nu^2$ Lup d transits will warrant a comprehensive search for a moon around
this outstanding exoplanet.
Abstract
We present the early-time light curves of Type Ia supernovae (SNe Ia) observed in the first six sectors of Transiting Exoplanet Survey Satellite (TESS) data. Ten of these SNe were discovered ...by ASAS-SN, seven by ATLAS, six by ZTF, and one by Gaia. For nine of these objects with sufficient dynamic range (>3.0 mag from detection to peak), we fit power-law models and searched for signatures of companion stars. We found a diversity of early-time light-curve shapes, although most of our sources are consistent with fireball models where the flux increases as ∝
t
2
. Three SNe displayed a flatter rise with flux ∝
t
. We did not find any obvious evidence for additional structures, such as multiple power-law components, in the early rising light curves. For assumptions about the SN properties and the observer viewing angle (ejecta mass of 1.4
M
⊙
, expansion velocity of 10
4
km s
−1
, opacity of 0.2 cm
2
g
−1
, and viewing angle of 45°) and a further assumption that any companion stars would be in Roche lobe overflow, it is possible to place upper limits on the radii of any companion stars. Six of the nine SNe had complete coverage of the early-time light curves, and we placed upper limits on the radii of companion stars of ≲32
R
⊙
for these SNe, ≲20
R
⊙
for five of the six, and ≲4
R
⊙
for two of the six. The small sample size did not allow us to put limits on the occurrence rate of companion stars in the progenitors of SNe Ia. However, we expect that TESS observed enough SNe in its two-year primary mission (26 sectors) to either detect the signature of a large companion (
R
> 20
R
⊙
) or constrain the occurrence rate of such systems, at least for the fiducial SN properties adopted here. We also show that TESS is capable of detecting emission from a 1
R
⊙
companion for an SN Ia within 50 Mpc and has a reasonable chance of doing so after about six years.
As part of the Mega MUSCLES Hubble Space Telescope (HST) Treasury program, we obtained time-series ultraviolet spectroscopy of the M2.5V star, GJ~674. During the FUV monitoring observations, the ...target exhibited several small flares and one large flare (E_FUV = 10^{30.75} ergs) that persisted over the entirety of a HST orbit and had an equivalent duration >30,000 sec, comparable to the highest relative amplitude event previously recorded in the FUV. The flare spectrum exhibited enhanced line emission from chromospheric, transition region, and coronal transitions and a blue FUV continuum with an unprecedented color temperature of T_c ~ 40,000+/-10,000 K. In this paper, we compare the flare FUV continuum emission with parameterizations of radiative hydrodynamic model atmospheres of M star flares. We find that the observed flare continuum can be reproduced using flare models but only with the ad hoc addition of hot, dense emitting component. This observation demonstrates that flares with hot FUV continuum temperatures and significant EUV/FUV energy deposition will continue to be of importance to exoplanet atmospheric chemistry and heating even as the host M dwarfs age beyond their most active evolutionary phases.
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 only. We refined its orbital parameters and, in particular, its mass (\(m_b = 1.66\pm0.23 M_\oplus\)), density (\(\rho_b = 6.3\pm1.3\) g.cm\(^{-3}\)) and eccentricity (\(e_b < 0.22 \); 95\%). We also detect at least one more planet in the system. GJ1132c is a super-Earth with period \(P_c = 8.93\pm0.01\) days and minimum mass \(m_c \sin i_c = 2.64\pm0.44~M_\oplus\). 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 \(A=0.75-0.00\)) and places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favourable 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 \(P_d = 177\pm5\) days attributed to either a planet candidate with minimum mass \(m_d \sin i_d = 8.4^{+1.7}_{-2.5}~M_\oplus\) or stellar activity. (abridged)
The Transiting Exoplanet Survey Satellite (TESS) recently observed 18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6 \(\pm\) 11.7 seconds 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-second offset at the 6.4\(\sigma\) level. The 1.3-day orbital period of WASP-4b appears to be decreasing at a rate of \(\dot{P} = -12.6 \pm 1.2\) milliseconds 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.
Over the past decade, a large number of jet substructure observables have been proposed in the literature, and explored at the LHC experiments. Such observables attempt to utilize the internal ...structure of jets in order to distinguish those initiated by quarks, gluons, or by boosted heavy objects, such as top quarks and
W
bosons. This report, originating from and motivated by the BOOST2013 workshop, presents original particle-level studies that aim to improve our understanding of the relationships between jet substructure observables, their complementarity, and their dependence on the underlying jet properties, particularly the jet radius and jet transverse momentum. This is explored in the context of quark/gluon discrimination, boosted
W
boson tagging and boosted top quark tagging.
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