We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA Transiting Exoplanet Survey Satellite mission, the ESA Gaia mission, ...ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a T = 9.9 mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of and is slightly smaller than Jupiter ( ). From radial velocity monitoring, we limit to less than 1.20 MJup (3 ). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false-positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multicolor photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.
ABSTRACT
We report the detection of a new planetary system orbiting the nearby M2.5V star GJ 357, using precision radial velocities from three separate echelle spectrographs, High Accuracy Radial ...velocity Planet Searcher (HARPS), High Resolution Echelle Spectrograph (HiRES), and Ultraviolet and Visible Echelle Spectrograph (UVES). Three small planets have been confirmed in the system, with periods of 9.125 ± 0.001, 3.9306 ± 0.0003, and 55.70 ± 0.05 d, and minimum masses of 3.33 ± 0.48, 2.09 ± 0.32, and 6.72 ± 0.94 M⊕, respectively. The second planet in our system, GJ 357 c, was recently shown to transit by the Transiting Exoplanet Survey Satellite (TESS), but we could find no transit signatures for the other two planets. Dynamical analysis reveals the system is likely to be close to coplanar, is stable on Myr time-scales, and places strong upper limits on the masses of the two non-transiting planets GJ 357 b and GJ 357 d of 4.25 and 11.20 M⊕, respectively. Therefore, we confirm the system contains at least two super-Earths, and either a third super-Earth or mini-Neptune planet. GJ 357 b and GJ 357 c are found to be close to a 7:3 mean motion resonance, however no libration of the orbital parameters was found in our simulations. Analysis of the photometric light curve of the star from the TESS, when combined with our radial velocities, reveals GJ 357 c has an absolute mass, radius, and density of $2.248^{+0.117}_{-0.120}$ M⊕, $1.167^{+0.037}_{-0.036}$ R⊕, and $7.757^{+0.889}_{-0.789}$ g cm−3, respectively. Comparison to super-Earth structure models reveals the planet is likely an iron-dominated world. The GJ 357 system adds to the small sample of low-mass planetary systems with well constrained masses, and further observational and dynamical follow-up is warranted to better understand the overall population of small multiplanet systems in the solar neighbourhood.
Context.
The sub-Jovian, or Neptunian, desert is a previously identified region of parameter space where there is a relative dearth of intermediate-mass planets with short orbital periods.
Aims.
We ...present the discovery of a new transiting planetary system within the Neptunian desert, NGTS-14.
Methods.
Transits of NGTS-14Ab were discovered in photometry from the Next Generation Transit Survey (NGTS). Follow-up transit photometry was conducted from several ground-based facilities, as well as extracted from TESS full-frame images. We combine radial velocities from the HARPS spectrograph with the photometry in a global analysis to determine the system parameters.
Results.
NGTS-14Ab has a radius that is about 30 per cent larger than that of Neptune (0.444 ± 0.030
R
Jup
) and is around 70 per cent more massive than Neptune (0.092 ± 0.012
M
Jup
). It transits the main-sequence K1 star, NGTS-14A, with a period of 3.54 days, just far away enough to have maintained at least some of its primordial atmosphere. We have also identified a possible long-period stellar mass companion to the system, NGTS-14B, and we investigate the binarity of exoplanet host stars inside and outside the Neptunian desert using
Gaia
.
Abstract
Previous examinations of fully convective M-dwarf stars have highlighted enhanced rates of nanoflare activity on these distant stellar sources. However, the specific role the convective ...boundary, which is believed to be present for spectral types earlier than M2.5V, plays on the observed nanoflare rates is not yet known. Here, we utilize a combination of statistical and Fourier techniques to examine M-dwarf stellar lightcurves that lie on either side of the convective boundary. We find that fully convective M2.5V (and later subtypes) stars have greatly enhanced nanoflare rates compared with their pre-dynamo mode-transition counterparts. Specifically, we derive a flaring power-law index in the region of 3.00 ± 0.20, alongside a decay timescale of 200 ± 100 s for M2.5V and M3V stars, matching those seen in prior observations of similar stellar subtypes. Interestingly, M4V stars exhibit longer decay timescales of 450 ± 50 s, along with an increased power-law index of 3.10 ± 0.18, suggesting an interplay between the rate of nanoflare occurrence and the intrinsic plasma parameters, e.g., the underlying Lundquist number. In contrast, partially convective (i.e., earlier subtypes from M0V to M2V) M-dwarf stars exhibit very weak nanoflare activity, which is not easily identifiable using statistical or Fourier techniques. This suggests that fully convective stellar atmospheres favor small-scale magnetic reconnection, leading to implications for the flare-energy budgets of these stars. Understanding why small-scale reconnection is enhanced in fully convective atmospheres may help solve questions relating to the dynamo behavior of these stellar sources.
Understanding the energization processes and constituent composition of the plasma and energetic particles injected into the near‐Earth region from the tail is an important component of understanding ...magnetospheric dynamics. In this study, we present multiple case studies of the high‐energy (≳40 keV) suprathermal ion populations during energetic particle enhancement events observed by the Energetic Ion Spectrometer (EIS) on NASA's Magnetospheric Multiscale (MMS) mission in the magnetotail. We present results from correlation analysis of the flux response between different energy channels of different ion species (hydrogen, helium, and oxygen) for multiple cases. We demonstrate that this technique can be used to infer the dominant charge state of the heavy ions, despite the fact that charge is not directly measured by EIS. Using this technique, we find that the energization and dispersion of suprathermal ions during energetic particle enhancements concurrent with (or near) fast plasma flows are ordered by energy per charge state (E/q) throughout the magnetotail regions examined (~7 to 25 Earth radii). The ions with the highest energies (≳300 keV) are helium and oxygen of solar wind origin, which obtain their greater energization due to their higher charge states. Additionally, the case studies show that during these injections the flux ratio of enhancement is also well ordered by E/q. These results expand on previous results which showed that high‐energy total ion measurements in the magnetosphere are dominated by high‐charge‐state heavy ions and that protons are often not the dominant species above ~300 keV.
Key Points
In the magnetotail during injections, the charge states of suprathermal He and O ions can be inferred with a correlation analysis
Energization of ionospheric and solar wind ions during injections in the magnetotail is remarkably coherent and ordered by charge state
The highest energy ions (≳300 keV) observed are heavies of solar wind origin and reach higher energies due to their higher charge states
The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was ...made in achieving the mission’s primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS’s observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star TOI-125, a V = 11.0 K0 dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TOI-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4.65 d, a radius of 2.726 ± 0.075 R(E), a mass of 9.50 ± 0.88 M(E), and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2.759 ± 0.10 R(E) and a mass of 6.63 ± 0.99 M(E), being the puffiest of the three planets. TOI-125d has an orbital period of 19.98 d and a radius of 2.93 ± 0.17 R(E) and mass 13.6 ± 1.2 M(E). For TOI-125b and d, we find unusual high eccentricities of 0.19 ± 0.04 and 0.17(sup +0.08, sub −0.06), respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for TOI-125.04 (R(P) = 1.36 R(E), P = 0.53 d), we find a 2σ upper mass limit of 1.6 M(E), whereas TOI-125.05 (R(P) = 4.2(sup +2.4, sub −1.4 R(E), P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 M(E). We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.
On December 08, 2018 the Twin Rocket Investigation of Cusp Electrodynamics 2 (TRICE 2) mission was successfully launched. The mission consisted of two sounding rockets, each carrying a payload ...capable of measuring electron and ion distributions, electric and magnetic fields, and plasma waves occurring in the northern magnetospheric cusp. This study highlights the ion and wave observations obtained by TRICE 2 in the cusp and observations from the magnetospheric multiscale (MMS) spacecraft at the low‐latitude magnetopause two hours prior to the TRICE 2 traversal of the cusp. Within the cusp, typical ion cusp features were observed, that is, energy‐latitude dispersion of injected magnetosheath plasma. However, a lower energy population was also measured near the equatorward edge of the cusp on open field lines. Pitch‐angle distributions of the low‐energy ions suggest that this population was magnetospheric in origin, and not from ionospheric upflows. Data from MMS show that counterstreaming ions were present in the outer magnetosphere and low‐latitude boundary layer at similar energies to those observed by TRICE 2 in the cusp. Correlations between the low‐energy ions within the cusp and broadband extremely low frequency waves suggest that the low‐energy magnetospheric ions that filled the flux tube may have undergone wave‐particle interactions. These interactions may cause pitch‐angle scattering of low‐energy magnetospheric ions closer to the loss cone, thereby allowing them to precipitate into the cusp and be measured by the TRICE 2 sounding rockets.
Key Points
Low‐energy ions measured near the equatorward edge of the cusp by TRICE 2 are locally mirroring and propagating toward the ionosphere
A similar counter‐streaming ion population is observed at the magnetopause by MMS two hours prior to the TRICE 2 cusp traversal
Ion and wave data in the cusp suggest wave‐particle interactions are pitch angle scattering low‐energy magnetospheric ions
Foreshock bubbles (FBs) occur when interplanetary magnetic field discontinuities encounter the Earth's foreshock. These transient (∼1 to 5 min) features exhibit depressed densities and magnetic field ...strengths, enhanced temperatures, and deflected plasma flows trailed by a region of enhanced plasma density and magnetic field strength. Ions can be accelerated inside the FBs through the Fermi acceleration process. Hybrid simulations and test particle calculations predict that the maximum energies of ions accelerated by FBs reach 5.6 times the solar wind ram energy (Esw). We identify 23 FBs from September 2015 to January 2020 Magnetospheric Multiscale spacecraft observations. Most FBs (17 of 23) occurred upstream of the dusk‐side bow shock and above the ecliptic. The FBs occurred for Alfvé $\acute{e}$n Mach numbers ranging from 5 to 15, with 11 FBs having an Alfvé $\acute{e}$n Mach number near 10. To investigate ion energization inside the cores of the FBs we compare the proton spectra observed by the Hot Plasma Composition Analyzer and Energetic Ion Spectrometer before (upstream), during (core), and after (downstream) the FBs. The proton intensities at energies from Esw (the solar wind ram energy, 0.5×m×Vsw2 $0.5\times m\times {V}_{sw}^{2}$) up to about 5.6Esw are greater inside than outside 19 of 23 FBs, confirming that FBs can accelerate particles to these energies. The proton flux intensities at energies between Esw and 5.6Esw in the core of the FBs are consistent with results from global hybrid simulations for ion energization from FBs through second‐order Fermi acceleration.
Key Points
Hybrid simulations and test particle calculations predict that foreshock bubbles (FBs) can accelerate ions up to 5.6 times solar wind ram energy
We identified 23 FBs during 5 Magnetospheric Multiscale dayside seasons from September 2015 to January 2020
Proton intensities at energies between Esw and 5.6Esw during the FB events exceed those before and after for 19 out of 23 FB events
We present a continuing investigation of mass‐/charge‐dependent interactions between energetic ions (greater than tens of kiloelectron volts) and planetary magnetopauses and of the escape of the ions ...across the boundary. Previous studies at Earth using Magnetospheric Multiscale mission data are refined and advanced showing profound behavior differences between light (H, He) and singly charged heavy ions (O+). We highlight a distinctive feature of oxygen ions: an angular distribution bifurcation providing clear indication of entrainment along the magnetopause in Speiser‐like orbits during relatively stable magnetic conditions. This signature, interpreted using a simple kinetic model, suggests that these ions tend to be carried substantial distances along the boundary (even with boundary‐normal magnetic fields) in a fashion that impedes their full dayside escape. While large fluctuations and waves can likely sometimes disrupt the observed ordering, the following picture emerges. Energetic particles with gyroradii much smaller than the magnetopause thickness (e.g., electrons and absent boundary‐normal magnetic fields) and ions with gyroradii much larger than the thickness (e.g., O+) are impeded from fully escaping across the boundary. However, energetic ions with intermediate‐sized gyroradii commensurate with the thickness (e.g., H+, He++, and O6+) can be effectively scattered within the boundary causing them to escape much more readily, with and without boundary‐normal fields. This picture is supported by observations from the Juno spacecraft at the near‐dawn meridian side of Jupiter's magnetopause. There it is observed that energetic electrons and heavy ions are more strongly contained by the magnetopause than are the energetic protons and helium ions.
Plain Language Summary
Strongly magnetized planets, like Earth, Jupiter, Saturn, Uranus, and Neptune, have space environments, called magnetospheres, that energize charge particles, like electrons and ions (charged atoms), to very high energies (thousands to millions of electron volts). Some of these energetic charge particles can leak across the “magnetopause” boundary that separates the magnetosphere from the interplanetary environment and become a part of that vast region of the sun‐generated solar wind. Charge particles in a magnetic field gyrate around in circular “gyro‐orbits.” The heavier the charged particle, the larger is its gyro‐orbit. We find in this paper that the ability of the ions to leak across the magnetopause boundary depends on the sizes of the gyro‐orbits in a counterintuitive fashion. Traditionally, it has been thought that the larger the gyroradii, the easier it is for the particle to escape. Here we find that ions (and electrons) with the smaller gyroradii and ions with the larger gyroradii (heavy ions like those of oxygen) are both impeded in their abilities to leak across the magnetopause boundary. It is the ions with intermediate‐sized gyroradii (like protons), with gyroradii sizes close the thickness of the magnetopause that find it easiest to escape across the boundary.
Key Points
Earth's >100‐keV‐injected magnetospheric O+ ions encountering the magnetopause tend to stay with it and are impeded from fully escaping
Energetic protons, with gyroradii similar to magnetopause thicknesses, are more likely to scatter within the boundary and escape
Observations at Jupiter's dawn magnetopause also show that large gyroradii ions appear less likely to escape than intermediate ones
We report the discovery of planetary companions orbiting four low-luminosity giant stars with
M
⋆
between 1.04 and 1.39
M
⊙
. All four host stars have been independently observed by the EXoPlanets ...aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between ~1.2 and 7.1 yr, minimum masses of
m
p
sin
i
~ 1.8–3.7
M
J
, and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (
m
p
≳ 1– 2
M
J
) orbiting within 5 AU from their parent star of
f
= 33.3
−7.1
+9.0
%. This fraction is slightly higher than but consistent at the 1
σ
level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.
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