Fig 4
Pre-flare, flare, and post-flare spectra from J1150.9-7411 near Hα. The pre-flare spectrum is an average of 6 spectra taken U.T. 15.78 to 16.42 (J.D. 244 9748.153-J.D. 244 9748.184). The flare spectrum is an average of 6 spectra taken U.T. 16.86 to 17.41 (J.D. 244 9748.202-J.D. 244 9748.225). The spectra are normalised to the local continuum. The line-profile of Hα is basically symmetric before and during the flare. However, the flare-spectrum does not include data from the first half an hour after the beginning of the flare.
Source publication
Results are presented from a monitoring program looking for variations
of the equivalent width and flux of Hα, and of the continuum flux,
in 18 classical and 18 weak line T Tauri stars, and one Herbig Ae/Be
star, on time scales down to 5 minutes. The stars were observed
simultaiously for 14 hours using the multiobject-spectrograph FLAIR on
the UK S...
Similar publications
In magnetic semiconductors the optical spectrum and, in particular, the absorption edge representing the band-gap are strongly affected by the onset of the magnetic order. This contribution to the band-gap energy has hitherto been described theoretically in terms of a Heisenberg Hamiltonian, in which a delocalized conduction carrier is coupled to t...
Citations
... The related mass was estimated to be in the order of ∼ 10 18 g. Another event was then presented by Guenther and Emerson [128] on an M-type weak-line T-Tauri star, showing a projected bulk velocity of ∼600 km s −1 and a prominence mass in the order of 10 18 -10 19 g. Both the Houdebine et al. [25] and Guenther and Emerson [128] events were certainly events which left the star, as both were above the stars' escape velocities. ...
... Another event was then presented by Guenther and Emerson [128] on an M-type weak-line T-Tauri star, showing a projected bulk velocity of ∼600 km s −1 and a prominence mass in the order of 10 18 -10 19 g. Both the Houdebine et al. [25] and Guenther and Emerson [128] events were certainly events which left the star, as both were above the stars' escape velocities. A 250 km s −1 emission event was detected on the dM star AT Mic but interpreted by the authors as an evaporation event, not as a prominence eruption. ...
... To increase efficiency, observing several stars simultaneously is alternative approach. Such multi-object observations have been performed by Guenther and Emerson [128], Leitzinger et al. [142], Korhonen et al. [143], Vida et al. [144]. Furthermore, also dedicated searches in data archives have been performed. ...
Flares, sometimes accompanied by coronal mass ejections (CMEs), are the result of sudden changes in the magnetic field of stars with high energy release through magnetic reconnection, which can be observed across a wide range of the electromagnetic spectrum from radio waves to the optical range to X-rays. In our review, we attempt to collect some fundamental new results, which can largely be linked to the Big data era that has arrived due to the expansion of space photometric observations of the last two decades. We list the different types of stars showing flare activity, their observation strategies, and discuss how their main stellar properties relate to the characteristics of the flares (or even CMEs) they emit. Our goal is to focus, without claiming to be complete, on those results that may in one way or another challenge the "standard" flare model based on the solar paradigm.
... 6,24,47 for reviews). In other stars, such as M-type stars [18][19][20][21]21,[48][49][50][51][52][53][54][55][56] , K-type stars 57 , T Tauri stars 58,59 , close binaries 60,61 and giant stars 23 , some observational candidates for stellar filament eruptions/CMEs have been reported, although confirmations of filament eruptions/CMEs in analogy with solar observations are still rare. We also note that some other studies have tried to detect a signature of stellar filament eruptions/CMEs in various ways but have not succeeded in robust detection [62][63][64][65][66][67][68][69] . ...
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. An energetic eruptive filament on EK Draconis most probably launched a coronal mass ejection with a mass ten times larger than the largest solar coronal mass ejection. Studying such ejections provides insight into stellar angular momentum loss and the habitability of orbiting planets.
... . In other stars, such as M-type stars18-21, 21, 53-61 , K-type stars52 , T-Tauri stars62,66 , close binaries67,71 , and giant stars22 , some observational candidates of stellar filament eruptions/CMEs have been reported, although confirmations of filament eruptions/CMEs in analogy with solar observations are still rare. We also note that some other studies have tried to detect a signature of stellar filament eruptions/CMEs in various ways but have not succeeded in robust detection[73][74][75][76][77][78][79][80] .A signature of CME was reported from a blue-shifted emission component of the cool X-ray O VIII line (4 MK) in the late phase of stellar flare on an evolved giant star HR 9024 22 . ...
Solar flares are often accompanied by filament/prominence eruptions ($\sim10^{4}$ K and $\sim 10^{10-11}$ cm$^{-3}$), sometimes leading to coronal mass ejections (CMEs) that directly affect the Earth's environment. `Superflares' are found on some active solar-type (G-type main-sequence) stars, but the association of filament eruptions/CMEs has not been established. Here we show that our optical spectroscopic observation of the young solar-type star EK Draconis reveals the evidence for a stellar filament eruption associated with a superflare. This superflare emitted a radiated energy of $2.0\times10^{33}$ erg, and blue-shifted hydrogen absorption component with a large velocity of $-510$ km s$^{-1}$ was observed shortly after. The temporal changes in the spectra greatly 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 CME occurred. The erupted filament mass of $1.1\times10^{18}$ g is 10 times larger than those of the largest solar CMEs. The massive filament eruption and an associated CME provide the opportunity to evaluate how they affect the environment of young exoplanets/young Earth and stellar mass/angular-momentum evolution.
... Different approaches have been explored in attempts to observe signatures of stellar CMEs. So far, the most promising one is the Doppler signal produced by CME-related plasma motions detected on a few main-and pre-main-sequence M stars in optical [10][11][12][13][14][15] and ultraviolet spectra 16,17 , as well as one X-ray detection on a giant star 18 . Searches for type II radio bursts generated by shock fronts driven by fast CMEs have not yet succeeded 19,20 . ...
... This research has produced systematic detections of coronal dimmings on Sun-like and late-type flaring stars, which are suggestive of flare-related CME occurrence and mass loss. In total, we identified 21 CME candidates on 13 different stars, which is larger than the total number of all previous stellar CME detections reported [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . The accordance of the characteristics of the stellar dimmings with solar dimmings identified in Sun-as-a-star broadband EUV data and their relation to the spatially resolved EUV imagery, as well as the close association between dimmings and CMEs that we established for the Sun, strongly support the interpretation that the stellar dimmings are caused by CMEs. ...
Coronal mass ejections (CMEs) are huge expulsions of magnetized matter from the Sun and stars, traversing space with speeds of millions of kilometres per hour. Solar CMEs can cause severe space weather disturbances and consumer power outages on Earth, whereas stellar CMEs may even pose a hazard to the habitability of exoplanets. Although CMEs ejected by our Sun can be directly imaged by white-light coronagraphs, for stars this is not possible. So far, only a few candidates for stellar CME detections have been reported. Here we demonstrate a different approach that is based on sudden dimmings in the extreme ultraviolet and X-ray emission caused by the CME mass loss. We report dimming detections associated with flares on cool stars, indicative of stellar CMEs, and which are benchmarked by Sun-as-a-star extreme ultraviolet measurements. This study paves the way for comprehensive detections and characterizations of CMEs on stars, which are important factors in planetary habitability and stellar evolution.
... The onset of this event was not time-resolved, apparently occurring entirely between successive points. This constrains the time for the appearance of the ¯are to less than 1.8 h, a time-scale consistent with the rise time of typically 30 min reported by Guenther & Emerson Guenther & Emerson 1997. The event lasted for two successive points at the end of night 1, and had diminished entirely by the following night. ...
... The lifetime of the event was therefore at least 2.1 h. This is also consistent with the decay times of 2.5 h reported by Guenther & Emerson (1997). The SU Aur outburst was seen at Ha, Hb and to a certain extent Hg, as well as Ca II H and K, but was not visible at Hd. ...
... This event was most probably a strong magnetic ¯are. Such phenomena are known to occur in weak-line T Tauri systems (Gahm 1994; Guenther & Emerson 1997). See also Section 4.3. ...
We have monitored the optical spectra of six T Tauri stars, AA Tau, BP Tau, CI Tau, DR Tau, RY Tau and SU Aur, approximately hourly over five successive nights. Our spectral range extends from 3800 to 7300 Å, including the Balmer series lines from H to H δ, CaII H+K and various Fe II lines. We construct time series of equivalent widths for each species to study the variations of the strengths of the different lines, and the correlations between them. We can discern a range of physical processes at work, such as the slow rotation of the stars (time-scales of days), magnetic flaring activity (time-scales of about an hour), variable accretion (time-scales of several hours) and obscuration by circumstellar material (again, time-scales of several hours). The sample objects show a range of activity in each of these categories, from DR Tau (dominated entirely by hour-time-scale activity) to those with only slowly varying line activity consistent with rotation (AA Tau). For objects between these extremes, we differentiate the activity according to time-scale, short time-scale events often appearing superimposed on longer time-scale variations. We examine the correlation in time between the rapid activity of the different emission features, which are formed under a wide range of excitation conditions. The lower Balmer lines (H and H β) and Ca II K are usually strongly correlated with one another, as are the higher Balmer lines (H and H δ), but the behaviour of these two groups sometimes becomes decoupled. In one particular case, for the active object DR Tau, we see well-correlated but time-lagged activity, occurring sequentially with the high-energy lines varying first, followed by lines of successively lower excitation temperature. We tentatively conclude that this may be the signature of an accretion shock moving over the stellar limb.
... The X-ray-discovered star V826 Tau exhibited an excursion of U = 0.5 in 40 min (Rydgren & Vrba 1983) and later, a 1-h X-ray flare (Carkner et al 1996). Sudden increases in Balmer continuum and line emission have also been seen with total power around 10 33 -10 34 ergs (Gahm et al 1995, Guenther & Emerson 1997. Third, there has been recent success in measurements of Zeeman effects on photospheric absorption lines. ...
Observational studies of low-mass stars during their early stages of evolution, from protostars through the zero-age main sequence, show highly elevated levels of magnetic activity. This activity includes strong fields covering much of the stellar surface and powerful magnetic reconnection flares seen in the X-ray and radio bands. The flaring may occur in the stellar magnetosphere, at the star-disk interface, or above the circumstellar disk. Ionization from the resulting high-energy radiation may have important effects on the astrophysics of the disk, such as promotion of accretion and coupling to outflows, and on the surrounding interstellar medium. The bombardment of solids in the solar nebula by flare shocks and energetic particles may account for various properties of meteorites, such as chondrule melting and spallogenic isotopes. X-ray surveys also improve our samples of young stars, particularly in the weak-lined T Tauri phase after disks have dissipated, with implications for our understanding of star formation in the solar neighborhood. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
Coronal mass ejections (CMEs) are huge expulsions of magnetized matter from the Sun and stars, traversing space with speeds of millions of kilometers per hour. Solar CMEs can cause severe space weather disturbances and consumer power outages on Earth, whereas stellar CMEs may even pose a hazard to the habitability of exoplanets. While CMEs ejected by our Sun can be directly imaged by white-light coronagraphs, for stars this is not possible. So far, only a few candidates for stellar CME detections are reported. Here we demonstrate a different approach, based on sudden dimmings in the extreme-ultraviolet (EUV) and X-ray emission caused by the CME mass loss. We report dimming detections associated with flares on cool stars, indicative of stellar CMEs and benchmarked by Sun-as-a-star EUV measurements. This study paves the way for comprehensive detections and characterizations of CMEs on stars, important for planetary habitability and stellar evolution.
CME activity of the Sun is known to be an important impacting factor for
the magnetospheres, atmospheres, and surfaces of solar system planets. Following
an idea of a solar-stellar analogy, CME phenomena are expected on other stars as
well. The main planetary impact factors of the stellar CMEs include the associated
interplanetary shocks, plasma density and velocity disturbances, energetic particles
accelerated in the shock regions, as well as distortions of the magnetic field direction
and modulus. All these factors should be properly taken into account during the
study of evolutionary processes on exoplanets and their atmospheric and plasma
environments. The planetary impact of the stellar CME activity may vary depending
on stellar age, stellar spectral type and the orbital distance of a planet. Because of
the relatively short range of propagation of the majority of CMEs, they affect most
strongly the magnetospheres and atmospheres of close-orbit (< 0.1 AU) exoplanets.
In this chapter we discuss an issue of the stellar CME activity in the context of
several actual problems of modern exoplanetology, including planetary atmosphere
mass loss, planet survival at close orbits, and definition of a criterion for habitability.
In this paper we investigate the origin of the mid-infrared (IR) hydrogen
recombination lines for a sample of 114 disks in different evolutionary stages
(full, transitional and debris disks) collected from the {\it Spitzer} archive.
We focus on the two brighter {H~{\sc i}} lines observed in the {\it Spitzer}
spectra, the {H~{\sc i}}(7-6) at 12.37$\mu$m and the {H~{\sc i}}(9-7) at
11.32$\mu$m. We detect the {H~{\sc i}}(7-6) line in 46 objects, and the {H~{\sc
i}}(9-7) in 11. We compare these lines with the other most common gas line
detected in {\it Spitzer} spectra, the {[Ne~{\sc iii}]} at 12.81$\mu$m. We
argue that it is unlikely that the {H~{\sc i}} emission originates from the
photoevaporating upper surface layers of the disk, as has been found for the
{[Ne~{\sc iii}]} lines toward low-accreting stars. Using the {H~{\sc
i}}(9-7)/{H~{\sc i}}(7-6) line ratios we find these gas lines are likely
probing gas with hydrogen column densities of 10$^{10}$-10$^{11}$~cm$^{-3}$.
The subsample of objects surrounded by full and transitional disks show a
positive correlation between the accretion luminosity and the {H~{\sc i}} line
luminosity. These two results suggest that the observed mid-IR {H~{\sc i}}
lines trace gas accreting onto the star in the same way as other hydrogen
recombination lines at shorter wavelengths. A pure chromospheric origin of
these lines can be excluded for the vast majority of full and transitional
disks.We report for the first time the detection of the {H~{\sc i}}(7-6) line
in eight young (< 20~Myr) debris disks. A pure chromospheric origin cannot be
ruled out in these objects. If the {H~{\sc i}}(7-6) line traces accretion in
these older systems, as in the case of full and transitional disks, the
strength of the emission implies accretion rates lower than
10$^{-10}$M$_{\odot}$/yr. We discuss some advantages of extending accretion
indicators to longer wavelengths.
