Frequent Flaring in the TRAPPIST-1 System: Unsuited for Life?

Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

Authors:

Vida et al

Abstract:
We analyze the K2 light curve of the TRAPPIST-1 system. The Fourier analysis of the data suggests P rot = 3.295 ± 0.003 days. The light curve shows several flares, of which we analyzed 42 events with integrated flare energies of 1.26 × 1030–1.24 × 1033 erg. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, which makes these less favorable for hosting life.

L Class Brown Dwarf EPIC 220186653 had a Superflare

K2 Ultracool Dwarfs Survey I: Photometry of an L Dwarf Superflare

Authors:

Gizis et al

Abstract:

We report on K2 Campaign 8 measurements of a huge white light flare on the L1 dwarf SDSSp J005406.55-003101.8 (EPIC 220186653). The source is a typical L1 dwarf at a distance of ∼50 pc, probably an old hydrogen-burning star rather than a young brown dwarf. In the long (30-minute) cadence photometry, the flare peak is 21 times the flux of the stellar photosphere in the broad optical Kepler filter, which we estimate corresponds to ΔV≈−7.1. The total equivalent duration of the flare is 15.4 hr. We estimate the total bolometric energy of the flare was 4×1033 erg, more powerful that the previously reported Kepler white light flares for the L1 dwarf WISEP J190648.47+401106.8, but weaker than the ΔV=−11 L0 dwarf superflare ASASSN-16ae. The initial (impulsive) cooling phase is too rapid to resolve with our 30-minute cadence data, but after one hour the gradual cooling phase has an exponential time constant of 1.8 hours. We use template fitting to estimate that the full-time-width-at-half-amplitude of the light curve is

Looking for Radio Flares From Brown Dwarfs

The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs

Authors:

Route et al

Abstract:

We describe our second installment of the 4.75 GHz survey of ultracool dwarfs (UCDs) conducted with the Arecibo radio telescope, which has observed 27 such objects and resulted in the detection of sporadic flaring from the T6 dwarf, WISEPC J112254.73+255021.5. We also present follow up observations of the first radio-emitting T dwarf, 2MASS J10475385+2124234, a tentatively identified radio emitting L1 dwarf, 2MASS J1439284+192915, and the known radio-flaring source, 2MASS J13142039+132011 AB. Our new data indicate that 2MASS J1439284+192915 is not a radio flaring source. The overall detection rate of our unbiased survey for radio-flaring UCDs is ~5% for new sources, with a detection rate for each spectral class of ~5-10%. Evidently, radio luminosity of the UCDs does not appear to monotonically decline with spectral type from M7 dwarfs to giant planets, in contradiction to theories of the magnetic field generation and internal structure of these objects. Along with other, recently published results, our data exemplify the unique value of using radio surveys to reveal and study properties of substellar magnetic activity.

Biological fluorescence as a temporal biosignature for flare star worlds

Biofluorescent Worlds: Biological fluorescence as a temporal biosignature for flare star worlds

Authors:

O'Malley-James et al

Abstract:

Habitability for planets orbiting active stars has been questioned. Especially, planets in the Habitable Zone (HZ) of M-stars, like our closest star Proxima Centauri, experience temporal high-ultraviolet (UV) radiation. The high fraction of M-stars (75%) within the solar neighborhood, the high occurrence rate of rocky planets around M-stars, and the favorable contrast ratio between the star and a potentially habitable rocky planet, makes such planets interesting targets for upcoming observations. During M-star flares, the UV flux on a HZ planet can increase by up to two orders of magnitude. High UV radiation is harmful to life and can cause cell and DNA damage. Common UV protection methods (e.g. living underground, or underwater) would make a biosphere harder to detect. However, photoprotective biofluorescence, "up-shifting" UV to longer, safer wavelengths (a proposed UV protection mechanism for some corals), would increase the detectability of biota and even uncover normally hidden biospheres during a flare. Such biofluorescence could be observable as a "temporal biosignature" for planets around UV-active stars. We model temporal biofluorescence as a biosignature for an exoplanet biosphere exposed to such conditions, based on planets in M-star HZs. We use fluorescing coral proteins to model biofluorescence, comparing observable spectra, and colors, to vegetation and fluorescent minerals. Our planetary models assume a present-day Earth atmosphere and explore the effect of varying cloud coverage and land:ocean fractions. UV flare-induced biofluorescence could be remotely detectable, comparable in strength to vegetation on Earth. On planets in the HZ of M-stars, biofluorescence could be a temporary biosignature, distinguishable from fluorescing minerals and vegetation.

Flares From Proxima Centauri

MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri

Authors:

Davenport et al

Abstract:

We present a study of white light flares from the active M5.5 dwarf Proxima Centauri using the Canadian microsatellite MOST. Using 37.6 days of monitoring data from 2014 and 2015, we have detected 66 individual flare events, the largest number of white light flares observed to date on Proxima Cen. Flare energies in our sample range from 1029-1031.5 erg, with complex, multi-peaked structure found in 22% of these events. The flare rate is lower than that of other classic flare stars of similar spectral type, such as UV Ceti, which may indicate Proxima Cen had a higher flare rate in its youth. Proxima Cen does have an unusually high flare rate given the slow reported rotation period, however. Extending the observed power-law occurrence distribution down to 1028 erg, we show that flares with flux amplitudes of 0.5% occur 63 times per day, while superflares with energies of 1033 erg occur ~8 times per year. Small flares may therefore pose a great difficulty in searches for transits from the recently announced 1.27 M_earth Proxima b, while frequent large flares could have significant impact on the stellar atmosphere.

2MASS 0335+23: a 23 Million Year old Brown Dwarf has Flares Larger Than our sun

Although astronomers often refer to brown dwarfs as "failed stars," scientists at the University of Delaware have discovered that at least one of these dim celestial objects can emit powerful flashes of light.

A research team led by John Gizis, professor in UD's Department of Physics and Astronomy, discovered an "ultracool" brown dwarf known as 2MASS 0335+23, with a temperature of only 4400°F that can generate flares stronger than the sun's. Gizis reported on the finding on June 13 at the annual meeting of the American Astronomical Society in San Diego.

"This brown dwarf is very young by star standards -- only 23 million years old," Gizis said. "It has lots of flares that are as hot as or hotter than the flares coming off full-fledged stars. This shows that the warmer brown dwarfs can generate flares from magnetic field energy just like stars. Our work shows, however, that colder brown dwarfs cannot generate flares even though they also have magnetic fields."

link.

The Host Stars of Keplers Habitable Exoplanets: Superflares, Rotation and Activity

The Host Stars of Keplers Habitable Exoplanets: Superflares, Rotation and Activity

Authors:

Armstrong et al

Abstract:

We embark on a detailed study of the lightcurves of Keplers most Earth-like exoplanet host stars using the full length of Kepler data. We derive rotation periods, photometric activity indices, flaring energies, mass loss rates, gyrochronological ages, X-ray luminosities and consider implications for the planetary magnetospheres and habitability. Furthermore, we present the detection of superflares in the lightcurve of Kepler-438, the exoplanet with the highest Earth Similarity Index to date. Kepler-438b orbits at a distance of 0.166AU to its host star, and hence may be susceptible to atmospheric stripping. Our sample is taken from the Habitable Exoplanet Catalogue, and consists of the stars Kepler-22, Kepler-61, Kepler-62, Kepler-174, Kepler-186, Kepler-283, Kepler-296, Kepler-298, Kepler-438, Kepler-440, Kepler-442, Kepler-443 and KOI-4427, between them hosting 15 of the most habitable transiting planets known to date from Kepler.

Will Flare Star Exoplanets see More Forbush Decreases?

How are Forbush decreases related with interplanetary magnetic field enhancements ?

Authors:

Arunbatu et al

Abstract:

Aims.

Forbush decrease (FD) is a transient decrease followed by a gradual recovery in the observed galactic cosmic ray intensity. We seek to understand the relationship between the FDs and near-Earth interplanetary magnetic field (IMF) enhancements associated with solar coronal mass ejections (CMEs).

Methods.

We use muon data at cutoff rigidities ranging from 14 to 24 GV from the GRAPES-3 tracking muon telescope to identify FD events. We select those FD events that have a reasonably clean profile, and magnitude greater than 0.25%. We use IMF data from ACE/WIND spacecrafts. We look for correlations between the FD profile and that of the one hour averaged IMF. We ask if the diffusion of high energy protons into the large scale magnetic field is the cause of the lag observed between the FD and the IMF.

Results.

The enhancement of the IMF associated with FDs occurs mainly in the shock-sheath region, and the turbulence level in the magnetic field is also enhanced in this region. The observed FD profiles look remarkably similar to the IMF enhancement profiles. The FDs typically lag the IMF enhancement by a few hours. The lag corresponds to the time taken by high energy protons to diffuse into the magnetic field enhancement via cross-field diffusion.

Conclusions.

Our findings show that high rigidity FDs associated with CMEs are caused primarily by the cumulative diffusion of protons across the magnetic field enhancement in the turbulent sheath region between the shock and the CME.