First <scp>eROSITA‐<i>TESS</i></scp> results for M dwarfs: Mass dependence of the X‐ray activity rotation relation and an assessment of sensitivity limits

Magaudda, E.; Stelzer, B.; Raetz, St.

doi:10.1002/asna.20220049

Cited by 4 publications

(3 citation statements)

References 29 publications

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“…A hint of this dichotomy is also visible in Fig. 4 of Magaudda et al (2020) and extensively discussed in Magaudda et al (2022a).…”

Section: Rotation-activity Relationsmentioning

confidence: 54%

“…For example, rapid rotation is usually associated with youth and high levels of activity. There have been many recent efforts to characterize these relationships for latetype stars (e.g., Reiners & Basri 2008;McQuillan et al 2013a;Newton et al 2016bNewton et al , 2017Newton et al , 2018Stelzer et al 2016;Astudillo-Defru et al 2017a;Suárez Mascareño et al 2018;Wright et al 2018;González-Álvarez et al 2019;Raetz et al 2020;Magaudda et al 2020Magaudda et al , 2022aMedina et al 2020;Ramsay et al 2020;Popinchalk et al 2021;Boudreaux et al 2022;Pass et al 2022). For instance, McQuillan et al (2013a) showed a well-defined upper limit in P rot for early-M dwarfs that depends monotonically and continuously on stellar mass.…”

Section: Introductionmentioning

confidence: 99%

“…Newton et al (2016b) pointed out that the period distribution of fully convective field M dwarfs hints at a rapid spin-down phase from <10 d to >50 d. Several authors noticed a very tight correlation between Ca ii H&K emission and P rot for slow rotators (Astudillo-Defru et al 2017a;Suárez Mascareño et al 2018), which is useful for predicting P rot whenever R HK ( ≡ L Ca ii H&K /L bol ) could be readily measured. According to Magaudda et al (2022a), the X-ray saturation regime shows hints of mass-dependent behaviour. However, few of these aforementioned studies involved by themselves a large sample that spans the entire range of M dwarf spectral subtypes, ages, and rotation periods, or had at their disposal stellar properties that have been comprehensively and uniformly characterized.…”

Section: Introductionmentioning

confidence: 99%

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CARMENES input catalog of M dwarfs

Shan,

Revilla,

Skrzypinski

et al. 2024

A&A

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Knowledge of rotation periods ($P_ rot $) is important for understanding the magnetic activity and angular momentum evolution of late-type stars, as well as for evaluating radial velocity signals of potential exoplanets and identifying false positives. We measured photometric and spectroscopic $P_ rot $ for a large sample of nearby bright M dwarfs with spectral types from M0 to M9, as part of our continual effort to fully characterize the Guaranteed Time Observation programme stars of the CARMENES survey. We analyse light curves chiefly from the SuperWASP survey and TESS data. We supplemented these with our own follow-up photometric monitoring programme from ground-based facilities, as well as spectroscopic indicator time series derived directly from the CARMENES spectra. From our own analysis, we determined $P_ rot $ for 129 stars. Combined with the literature, we tabulated $P_ rot $ for 261 stars, or 75<!PCT!> of our sample. We developed a framework to evaluate the plausibility of all periods available for this sample by comparing them with activity signatures and checking for consistency between multiple measurements. We find that 166 of these stars have independent evidence that confirmed their $P_ rot $. There are inconsistencies in 27 periods, which we classify as debated. A further 68 periods are identified as provisional detections that could benefit from independent verification. We provide an empirical relation for the $P_ rot $ uncertainty as a function of the $P_ rot $ value, based on the dispersion of the measurements. We show that published formal errors seem to be often underestimated for periods longwards of $ 10$\,d. We examined rotation-activity relations with emission in X-rays, Halpha , Ca ii H K, and surface magnetic field strengths for this sample of M dwarfs. We find overall agreement with previous works, as well as tentative differences in the partially versus fully convective subsamples. We show $P_ rot $ as a function of stellar mass, age, and galactic kinematics. With the notable exception of three transiting planet systems and TZ Ari, all known planet hosts in this sample have $P_ rot 15$\,d. Inherent challenges in determining accurate and precise stellar $P_ rot $ means independent verification is important, especially for inactive M dwarfs. Evidence of potential mass dependence in activity-rotation relations would suggest physical changes in the magnetic dynamo that warrants further investigation using larger samples of M dwarfs on both sides of the fully convective boundary. Important limitations need to be overcome before the radial velocity technique can be routinely used to detect and study planets around young and active stars.

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“…A hint of this dichotomy is also visible in Fig. 4 of Magaudda et al (2020) and extensively discussed in Magaudda et al (2022a).…”

Section: Rotation-activity Relationsmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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CARMENES input catalog of M dwarfs

Shan,

Revilla,

Skrzypinski

et al. 2024

A&A

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Simultaneous X-ray and optical variability of M dwarfs observed with eROSITA and TESS

Joseph,

Stelzer,

Magaudda

et al. 2024

A&A

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M-dwarf stars are the most numerous stars in the Galaxy, and are highly magnetically active. They exhibit bursts of radiation and matter, called flares and coronal mass ejections which have the potential to strongly affect the habitability of their planets. We investigate variability through simultaneous optical and X-ray observations, forming the largest statistical sample of M dwarfs observed in this way so far. Such simultaneous observations at different wavelengths, which correspond to emissions from different layers of the stellar atmosphere, are required to constrain the flare frequency and energetics and to understand the physics of flares. We used light curves from the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission (SRG) and the Transiting Exoplanet Survey Satellite (TESS) for a sample of M dwarfs observed simultaneously with both instruments. Specifically, we identified 256 M dwarfs in the TESS Southern Continuous Viewing Zone (SCVZ), which corresponds to a sky area of 452.39 ($ deg^2 $), with simultaneous TESS and eROSITA detection. For this work, we selected the $25$ X-ray brightest or most X-ray variable stars. We used photometric data from Gaia and 2MASS to obtain stellar parameters such as distances, colours, masses, radii, and bolometric luminosities. X-ray fluxes and luminosities were determined from observed eROSITA count rates using appropriate rate-to-flux conversion factors. We defined and examined various variability diagnostics in both wavebands and how these parameters are related to each other. Our stars are nearby (mostly within $ 100$\,pc ), rotating fast rot < 9$\,d), and display a high optical flare frequency, as expected from the selection of particularly X-ray-active objects. The optical duty cycle -- defined as the fraction of observing time in which the stars were in a high activity state -- is well correlated with the optical flare rate and was therefore used as proxy for optical variability. The X-ray and optical duty cycles are positively correlated, and there is a trend of faster rotators tending to have higher X-ray and optical variability. For stars with many X-ray flaring events, the chances of these events being found together with optical flares are high. A quantitative variability study of individual flares in the X-ray light curves is severely affected by data gaps due to the low (4\,h) cadence during the eROSITA all-sky survey. To mitigate this, we made use of the optical flares observed with TESS combined with knowledge accumulated from solar flares to put additional constraints on the peak flux and timing of X-ray events. With this method we could perform an exponential fit to X-ray light curves in the aftermath of an optical flare, and we find that the energies for these X-ray flares are well correlated with the corresponding optical flare energy. We also found two peculiar flaring events with uncharacteristically long duration and high energies observed in both their X-ray and optical light curves. Despite the substantial uncertainties associated with our analysis, which are mostly related to the poor sampling of the eROSITA light curves, our results showcase in an exemplary way the relevance of simultaneous all-sky surveys in different wavebands for obtaining unprecedented quantitative information on stellar variability.

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The corona of a fully convective star with a near-polar flare

Ilin,

Poppenhäger,

Stelzer

et al. 2024

A&A

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In 2020, the Transiting Exoplanet Survey Satellite (TESS) observed a rapidly rotating M7 dwarf, TIC 277539431, producing a flare at $81^ circ $ latitude, the highest latitude flare located to date. This is in stark contrast to solar flares that occur much closer to the equator, typically below $30^ circ $. The mechanisms that allow flares at high latitudes to occur are poorly understood. We studied five sectors of TESS monitoring, and obtained 36 ks of XMM-Newton observations to investigate the coronal and flaring activity of TIC 277539431. From the observations, we infer the optical flare frequency distribution; flare loop sizes and magnetic field strengths; the soft X-ray flux, luminosity, and coronal temperatures; as well as the energy, loop size, and field strength of a large flare in the XMM-Newton observations. We find that the corona of TIC 277539431 does not differ significantly from other low-mass stars on the canonical saturated activity branch with respect to coronal temperatures and flaring activity, but shows lower luminosity in soft X-ray emission by about an order of magnitude, consistent with other late M dwarfs. The lack of X-ray flux, the high-latitude flare, the star's viewing geometry, and the otherwise typical stellar corona taken together can be explained by the migration of flux emergence to the poles in rapid rotators like TIC 277539431 that drain the star's equatorial regions of magnetic flux, but preserve its ability to produce powerful flares.

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First eROSITA‐TESS results for M dwarfs: Mass dependence of the X‐ray activity rotation relation and an assessment of sensitivity limits

Cited by 4 publications

References 29 publications

CARMENES input catalog of M dwarfs

CARMENES input catalog of M dwarfs

Simultaneous X-ray and optical variability of M dwarfs observed with eROSITA and TESS

The corona of a fully convective star with a near-polar flare

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