Probable detection of an eruptive filament from a superflare on a solar-type star

Solar flares are often accompanied by filament/prominence eruptions (~104 K and ~1010−11 cm−3), sometimes leading to coronal mass ejections that directly affect the Earth’s environment1,2. ‘Superflares’ are found on some active solar-type (G-type main-sequence) stars3–5, but the filament eruption–coronal mass ejection association has not been established. Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of 2.0 × 1033 erg, and a blueshifted hydrogen absorption component with a high velocity of −510 km s−1 was observed shortly afterwards. The temporal changes in the spectra strongly resemble those of solar filament eruptions. Comparing this eruption with solar filament eruptions in terms of the length scale and velocity strongly suggests that a stellar coronal mass ejection occurred. The erupted filament mass of 1.1 × 1018 g is ten times larger than those of the largest solar coronal mass ejections. The massive filament eruption and an associated coronal mass ejection provide the opportunity to evaluate how they affect the environment of young exoplanets/the young Earth6 and stellar mass/angular momentum evolution7.

The Galactic cosmic ray intensity at the evolving Earth and young exoplanets

ABSTRACT Cosmic rays may have contributed to the start of life on the Earth. Here, we investigate the evolution of the Galactic cosmic ray spectrum at the Earth from ages t = 0.6−6.0 Gyr. We use a 1D cosmic ray transport model and a 1.5D stellar wind model to derive the evolving wind properties of a solar-type star. At $t=1\,$ Gyr, approximately when life is thought to have begun on the Earth, we find that the intensity of ∼GeV Galactic cosmic rays would have been ∼10 times smaller than the present-day value. At lower kinetic energies, Galactic cosmic ray modulation would have been even more severe. More generally, we find that the differential intensity of low-energy Galactic cosmic rays decreases at younger ages and is well described by a broken power law in solar rotation rate. We provide an analytic formula of our Galactic cosmic ray spectra at the Earth’s orbit for different ages. Our model is also applicable to other solar-type stars with exoplanets orbiting at different radii. Specifically, we use our Galactic cosmic ray spectrum at 20 au for $t=600\,$ Myr to estimate the penetration of cosmic rays in the atmosphere of HR 2562b, a directly imaged exoplanet orbiting a young solar-type star. We find that the majority of particles <0.1 GeV are attenuated at pressures ≳10−5 bar and thus do not reach altitudes below ∼100 km. Observationally constraining the Galactic cosmic ray spectrum in the atmosphere of a warm Jupiter would in turn help constrain the flux of cosmic rays reaching young Earth-like exoplanets.

Possible evidence of induced repetitive magnetic reconnection in a superflare from a young solar-type star

We report the detection of multiple quasi-periodic pulsations (QPPs) observed during the flaring activity of KIC 8414845, a young, active solar-type star observed by the Kepler mission launched by NASA. We analyzed the QQP signal using a data-driven, nonparametric method called singular spectrum analysis (SSA), which has never been utilized previously for analyzing solar or stellar QPPs. Because it is not based on a prescribed choice of basis functions, SSA is particularly suitable for analyzing nonstationary, nonlinear signals such as those observed in QPPs during major flares. The analysis has revealed that the apparent anharmonic shape of the QPP in this superflare results from a superposition of two intrinsic modes of periods of 49 min and 86 min, which display quasi-harmonic behaviors and different modulation patterns. The two reconstructed signals are consistent with slow-mode transverse and/or longitudinal magnetohydrodynamic oscillations excited in a coronal loop inducing periodic releases of flaring energy in a nearby loop through a mechanism of repetitive reconnection. The peculiar amplitude modulation of the two modes evinced by SSA favors the interpretation of the observed QPP pattern as due to the excitation in a coronal loop of the second harmonic of a standing slow-mode magnetoacoustic oscillation and a global kink oscillation periodically triggering magnetic reconnection in a nearby loop. Concurrent interpretations cannot however be ruled out on the basis of the available data.

Breakthrough Discoveries vs Incremental Science

Professor Didier Queloz talks about his challenging journey from the discovery of the first exoplanet orbiting a solar-type star in 1995 to the acknowledgement of his discovery by the scientific community. He explores his experience in reporting a paradigm-changing finding and how this triggered hard scepticism from the publishing industry and fellow scientists, which lasted about 3 years. He and Michel Mayor were eventually acknowledged as the founders of the new field of exoplanets and were awarded the Nobel Prize for Physics in 2019.

The Discovery of the First Exoplanet Orbiting a Solar-Type Star

Didier Queloz is Professor of Physics at the Cavendish Laboratory (University of Cambridge) and Geneva University. He was jointly awarded the 2019 Nobel Prize in Physics for “the discovery of an exoplanet orbiting a solar-type star”. In the first part of his conversation with Mejd Alsari he discusses the impact of his 1995 discovery on the theory of planetary systems formation.

Spectrum variability of the active solar-type star ξ Bootis A

An extensive spectroscopic study on ξ Boo A (a chromospherically active solar-type star) was conducted based on the spectra obtained from 2008 December through to 2010 May, with the aim of detecting any spectrum variability and understanding its physical origin. For each spectrum, the atmospheric parameters were spectroscopically determined based on Fe lines, and the equivalent widths (along with the line-broadening parameters) of 99 selected lines were measured. We could detect meaningful small fluctuations in the equivalent widths of medium-strength lines. This variation was found to correlate with the effective temperature ($T_{\rm eff}$) consistently with the T-sensitivity of each line, which indicates that the difference in the mean temperature averaged over the disk of inhomogeneous condition is mainly responsible for this variability. It was also found that the macrobroadening widths of medium-strength lines and the equivalent widths’ dispersion of saturated lines tend to increase with the effective Landé factor, suggesting the influence of a magnetic field. Our power spectrum analysis applied to the time-sequence data of the V i$/$Fe ii line-strength ratio and $T_{\rm eff}$ could not confirm the 6.4 d period reported by previous studies. We suspect that surface inhomogeneities of ξ Boo A at the time of our observations were not so much simple (such as a single star patch) as rather complex (e.g., intricate aggregate of spots and faculae).

Seeds of Life in Space (SOLIS)

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6–82.6 GHz and 96.65–97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (H2CCO), propyne (CH3CCH), formamide (NH2CHO), methoxy (CH3O), methanol (CH3OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3). Results. Only two transitions of methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E1) in a very compact emission blob (~7′′ corresponding to ~1000 au) toward the northeast of the L1521F protostar. The CS 2–1 transition is also detected within the WideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ~1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H2 gas density (estimated from the detected CS 2–1 emission and previous CS 5–4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H2) ≥ 107 cm−3). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system.

A dusty benchmark brown dwarf near the ice line of HD 72946

Context. HD 72946 is a bright and nearby solar-type star hosting a low-mass companion at long period (P ∼ 16 yr) detected with the radial velocity (RV) method. The companion has a minimum mass of 60.4 ± 2.2 MJ and might be a brown dwarf. Its expected semi-major axis of ∼243 mas makes it a suitable target for further characterization with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus definitely establish its substellar nature. Aims. We aim to further characterize the orbit, atmosphere, and physical nature of HD 72946B. Methods. We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. We also use proper motion measurements of the star from HIPPARCOS and Gaia. Results. The SPHERE data reveal a point source with a contrast of ∼9 mag at a projected separation of ∼235 mas. No other point sources are detected in the field of view. By jointly fitting the RV, imaging, and proper motion data, we constrain all the orbital parameters of HD 72946B and assess a dynamical mass of 72.4 ± 1.6 MJ and a semi-major axis of 6.456.45+0.08−0.07 au. Empirical comparison of its SPHERE spectrum to template dwarfs indicates a spectral type of L5.0 ± 1.5. The J–H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmosphere. Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of ∼1700 K. The bolometric luminosity (log(L/L⊙) = −4.11 ± 0.10 dex) and dynamical mass of HD 72946B are more compatible with evolutionary models for an age range of ∼0.9−3 Gyr. The formation mechanism of the companion is currently unclear as the object appears slightly away from the bulk of model predictions. HD 72946B is currently the closest benchmark brown dwarf companion to a solar-type star with imaging, RV, and proper motion measurements.