ABSTRACT Although more than 5000 TESS Objects of Interest have been catalogued, no comprehensive survey of the flare rates of their host stars exists. We perform the first flare survey of all 2250 non-retired TOIs with 2-min cadence light curves to measure or place upper limits on their flare rates. We find 93 candidates orbit flare stars and measure their flare frequency distributions. Across the sample, TOIs of ≤1.5R⊕ orbit flare stars more frequently than do TOIs of 1.5 &amp;lt; R&amp;lt; 2.75R⊕, 2.75 &amp;lt; R&amp;lt; 4R⊕, or R≥ 4R⊕. We sort all TOI host stars by their flare rate/upper limit, stellar mass, and distance to create a flare ranking metric (FRM) to determine suitability for follow-up. The FRM of each TOI is then checked against the expected signal-to-noise of atmospheric features in transmission spectroscopy to locate the most promising targets. We find 1/4 of terrestrial M-dwarf planets amenable to transmission spectroscopy orbit flare stars. However, none of the M-dwarf hosts to terrestrial planets are currently flaring at sufficient levels for &amp;gt;99.9 per cent atmospheric ozone depletion. We give the first upper limits on the flare rate of the host star to TOI 700 d and explore the flare rates incident on young planets such as DS Tuc Ab. 

OUP accepted manuscript


 We present a magnetic activity study of GJ 436 using spectroscopic data from HARPS, spanning over 14 years, and additional data from NARVAL, falling within the HARPS observations. We study the CaII H&K, HeID3, NaI doublet, Hα and CaII IRT triplets lines and explore linear correlations between them. Using the full HARPS dataset, we found indices Hα versus CaII H&K & Hα versus HeI to correlate positively. From the NARVAL dataset, covering one observing epoch, we found CaII IRT3 versus CaII IRT2 & CaII IRT3 versus Hα index to correlate negatively. We investigate long and short-term periodicity in these index variations using the Generalised Lomb-Scargle periodogram. For CaII H&K, NaI and Hα indices, we detect long-term periods of 2470.7d (∼ 6.8 years), 1861.6d (∼ 5.1 years) and 2160.9d (∼ 5.9 years) respectively, consistent with GJ 436’s photometric cycle of ∼ 7.4 years. Applying the ‘Pooled Variance’ technique to Hα & NaI indices, we found ∼ 2500d to be the period of an activity cycle mechanism, in good agreement with the detected 2470.7d period. For CaII H&K and Hα indices, we detect short-term periods of $39.47^{+0.11}_{-0.15}$d and $40.46^{+0.44}_{-0.52}$d respectively, identified as the stellar rotation period. The stellar rotation is detected after prewhitening the long-term periodicity. It is detected as well in the analysis of individual observing epochs.

/pdf/a-study-of-the-magnetic-activity-and-variability-of-gj-436-1awlu9ry.pdf

A study of the magnetic activity and variability of GJ 436

In Lammer et al. (2024), we defined Earth-like habitats (EHs) as rocky exoplanets within the habitable zone of complex life (HZCL) on which Earth-like N 

Eta-Earth Revisited II: Deriving a Maximum Number of Earth-Like Habitats in the Galactic Disk

Abstract A gold standard for the study of M dwarfs is the eclipsing binary CM Draconis. It is rare because it is bright (Jmag = 8.5) and contains twin fully convective stars on an almost perfectly edge-on orbit. Both masses and radii were previously measured to better than 1 per cent precision, amongst the best known. We use 15 sectors of TESS data to show that CM Draconis is the gift that keeps on giving. Our paper has three main components. First, we present updated parameters, with radii and masses constrained to previously unheard of precisions of ≈0.06 per cent and ≈0.12 per cent, respectively. Second, we discover strong and variable spot modulation, suggestive of spot clustering and an activity cycle on the order of ≈4 years. Third, we discover 163 flares. We find a relationship between the spot modulation and flare rate, with flares more likely to occur when the stars appear brighter. This may be due to a positive correlation between flares and the occurrence of bright spots (plages). The flare rate is surprisingly not reduced during eclipse, but one flare may show evidence of being occulted. We suggest the flares may be preferentially polar, which has positive implications for the habitability of planets orbiting M dwarfs. 

The benchmark M dwarf eclipsing binary CM Draconis with TESS: Spots, flares and ultra-precise parameters

We studied the light curve of the star CD-36 3202, which was observed by TESS for the presence of stellar spots and to analyze the rotationally modulated flare that took place on TBJD (TESS Barycentric Julian Date) 1486.93. Our main aims are to model the light curve of this flare and to estimate its location regarding stellar spots. The flare lasted approximately 27$\,$h. Using our new tool findinc\_mc we managed to estimate the inclination angle of the star to $70^ With BASSMAN we modeled the light curve of the CD-36 3202 and estimated that three spots are present on its surface. The mean temperature of the spots was about $4000 765\,$K, and their total area amounted to $11.61 on average. We created a new tool, named MFUEA to model rotationally modulated flares, and used it to estimate the latitude of the long-duration flare event (LDE), finding $69^ \,$deg. Our estimation of the flare location is the first recreation of the exact position of a flare in relation to starspots. The flare is placed 12$^ from the center of the coolest spot. This means that the flare is related to the magnetic processes above the active region represented by the spot. Removing the effects of rotational modulation from the flare light curve allowed us to correct the estimation of bolometric energy released during the event from $(1.15 \,$erg to $(3.99 \,$erg.

Unveiling the spectacular over 24 hour flare of star CD-36 3202

Photometric space missions like Kepler and TESS continuously discover new exoplanets and advance the search for a second habitable world. The light curves recorded by these telescopes also reveal signs of magnetic activity, such as star spot modulation and flares, which can influence habitability. Searching for these characteristics, we analyzed TESS light curves of 112 M dwarfs selected according to the criterion that TESS can spot planet transits over their entire habitable zone (HZ). We detected 2532 flare events, occurring on 35 stars, thus the flare incidence rate is $\approx32\%$. For only $\approx11\%$ of our stars, we found rotation periods. We calculated bolometric flare energies and luminosities, flare energy frequency distributions (FFDs) and the bolometric flux reaching the HZ at the peak of the flare. We estimated the effects of flaring on the atmosphere of an Earth-like planet in the HZ in the view of both ozone depletion and the enabling of chemical reactions necessary to build ribonucleic acid (RNA). None of our targets exhibits highly energetic flares at a frequency large enough to trigger ozone depletion or RNA formation. The flux reaching the inner HZ edge during flare events goes up to $\approx 4.5$ times the quiescent solar flux at 1\,au.

Effects of flares on the habitable zones of M dwarfs accessible to TESS planet detections

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Effects of flares on the habitable zones of M dwarfs accessible to TESS planet detections

Effects of flares on the habitable zones of M dwarfs accessible to TESS planet detections