The UV and X-ray activity of the M dwarfs within 10 pc of the Sun

Stelzer, B.; Marino, A.; Micela, G.; López‐Santiago, J.; Liefke, C.

doi:10.1093/mnras/stt225

Cited by 183 publications

(215 citation statements)

References 69 publications

(96 reference statements)

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“…TWA 29 was not detected and an upper limit was given by Stelzer et al (2007). For the remaining four targets without X-ray detection we assumed an upper limit to the RASS count rate of 0.02 cts/s, corresponding to the sensitivity limit for a typical RASS exposure time of ≈400−500 s (see Stelzer et al 2013). The matches and table handling was carried out in the Virtual Observatory environment Topcat (Taylor 2005) and in idl 1 .…”

Section: Ancillary X-ray Datamentioning

confidence: 99%

“…9 the Hα and X-ray activity indices of our Class III sample are shown as a function of T eff and are compared with two samples of field M dwarfs. Shown as crosses and plus symbols is the "10-pc sample" of Stelzer et al (2013), which comprises all M dwarfs within 10 pc of the Sun from the proper motion survey of Lépine & Gaidos (2011). The Hα measurements of these stars have been compiled from the literature by Stelzer et al (2013), while they extracted the X-ray data from public data archives.…”

Section: Level Of Hα and X-ray Activitymentioning

confidence: 99%

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X-shooter spectroscopy of young stellar objects

Stelzer

Frasca

Alcalá

et al. 2013

A&A

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Context. Traditionally, the chromospheres of late-type stars are studied through their strongest emission lines, Hα and Ca ii HK emission. Our knowledge on the whole emission line spectrum is more elusive as a result of the limited spectral range and sensitivity of most available spectrographs. Aims. We intend to reduce this gap with a comprehensive spectroscopic study of the chromospheric emission line spectrum of a sample of non-accreting pre-main sequence stars (Class III sources). Methods. We analyzed X-shooter/VLT spectra of 24 Class III sources from three nearby star-forming regions (σ Orionis, Lupus III, and TW Hya). We determined the effective temperature, surface gravity, rotational velocity, and radial velocity by comparing the observed spectra with synthetic BT-Settl model spectra. We investigated in detail the emission lines emerging from the stellar chromospheres and combined these data with archival X-ray data to allow for a comparison between chromospheric and coronal emissions. Results. For some objects in the sample the atmospheric and kinematic parameters are presented here for the first time. The effective temperatures are consistent with those derived for the same stars from an empirical calibration with spectral types. Small differences in the surface gravity found between the stars can be attributed to differences in the average age of the three star-forming regions. The strength of lithium absorption and radial velocities confirm the young age of all but one object in the sample (Sz 94). Both X-ray and Hα luminosity as measured in terms of the bolometric luminosity are independent of the effective temperature for early-M stars but decline toward the end of the spectral M sequence. For the saturated early-M stars the average emission level is almost one dex higher for X-rays than for Hα: log (L x /L bol ) = −2.85 ± 0.36 vs. log (L Hα /L bol ) = −3.72 ± 0.21. When all chromospheric emission lines (including the Balmer series up to H11, Ca ii HK, the Ca ii infrared triplet, and several He i lines) are summed up the coronal flux still dominates that of the chromosphere, typically by a factor 2−5. Flux-flux relations between activity diagnostics that probe different atmospheric layers (from the lower chromosphere to the corona) separate our sample of active pre-main sequence stars from the bulk of field M dwarfs studied in the literature. Flux ratios between individual optical emission lines show a smooth dependence on the effective temperature. The Balmer decrements can roughly be reproduced by an NLTE radiative transfer model devised for another young star of similar age. Future, more complete chromospheric model grids can be tested against this data set.

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Section: Ancillary X-ray Datamentioning

confidence: 99%

Section: Level Of Hα and X-ray Activitymentioning

confidence: 99%

X-shooter spectroscopy of young stellar objects

Stelzer

Frasca

Alcalá

et al. 2013

A&A

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“…The installation of COS renewed interest in observing low-activity stars in the UV (e.g. France et al 2013;Linsky et al 2013;Stelzer et al 2013;Fossati et al 2015b).…”

Section: Introductionmentioning

confidence: 99%

Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 System*

Fossati

Koskinen

Cubillos

et al. 2018

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WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (<1 Gyr), the star presents an anomalously low stellar activity level: the measured log R ′ HK activity parameter lies slightly below the basal level; there is no significant time-variability in the log R ′ HK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of Hubble Space Telescope aimed at explaining this anomaly. From the star's spectral energy distribution, we infer the extinction (E(B − V) ≈ 0.01 mag) and then the interstellar medium (ISM) column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5 Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s . For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape.

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“…This strong UV and X-ray emission has its origins in a combination of stellar magnetic and accretion activity. As low-mass pre-MS stars descend to the main sequence, their deep convective envelopes combine with differential rotation to produce strong magnetic dynamos and, hence, high levels of chromospheric and coronal activity; the former is a source of bright UV emission, while the latter generates strong X-ray emission (e.g., Stelzer et al 2013, and references therein). In the case of T Tauri stars that are actively accreting from circumstellar disks, shocks at the bases of accretion columns can also significantly contribute to UV and soft X-ray emission (Günther et al 2007;Sacco et al 2010).…”

Section: Introductionmentioning

confidence: 99%

M Stars in the Tw Hya Association: Stellar X-Rays and Disk Dissipation

Kastner¹,

Principe²,

Punzi³

et al. 2016

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To investigate the potential connection between the intense X-ray emission from young low-mass stars and the lifetimes of their circumstellar planet-forming disks, we have compiled the X-ray luminosities (L X ) of M stars in the ∼8 Myr old TW Hya Association (TWA) for which X-ray data are presently available. Our investigation includes analysis of archival Chandra data for the TWA binary systems TWA 8, 9, and 13. Although our study suffers from poor statistics for stars later than M3, we find a trend of decreasing L L X bol with decreasing T eff for TWA M stars, wherein the earliest-typeand then ( ) L L log X bol decreases, and its distribution broadens, for types M4 and later. The fraction of TWA stars that display evidence for residual primordial disk material also sharply increases in this same (mid-M) spectral type regime. This apparent anticorrelation between the relative X-ray luminosities of low-mass TWA stars and the longevities of their circumstellar disks suggests that primordial disks orbiting early-type M stars in the TWA have dispersed rapidly as a consequence of their persistent large X-ray fluxes. Conversely, the disks orbiting the very lowest-mass pre-MS stars and pre-MS brown dwarfs in the Association may have survived because their X-ray luminosities and, hence, disk photoevaporation rates are very low to begin with, and then further decline relatively early in their pre-MS evolution.

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The UV and X-ray activity of the M dwarfs within 10 pc of the Sun

Cited by 183 publications

References 69 publications

X-shooter spectroscopy of young stellar objects

X-shooter spectroscopy of young stellar objects

Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 System*

M Stars in the Tw Hya Association: Stellar X-Rays and Disk Dissipation

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