Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leonis

Crespo‐Chacón, I.; Montes, D.; García-Álvarez, D.; Fernández-Figueroa, M. J.; López‐Santiago, J.; Foing, B. H.

doi:10.1051/0004-6361:20053615

Cited by 52 publications

(65 citation statements)

References 62 publications

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“…This is larger than the typical short-term Hα variations (of a factor of two in Δt ≤ 1 h) observed on M dwarfs (e.g. Crespo-Chacón et al 2006;Lee et al 2010;Kruse et al 2010). These differences are probably due to the much shorter timescales examined in these latter studies and observational biases in our sample in favor of UCDs that have caught attention because of their flaring activity either in Hα or X-rays.…”

Section: Observed Balmer Decrementsmentioning

confidence: 64%

The ultracool dwarf DENIS-P J104814.7-395606

Stelzer

Alcalá

Biazzo

et al. 2012

A&A

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Context. Several diagnostics ranging from the radio to the X-ray band are suitable for investigating the magnetic activity of late-type stars. Empirical connections between the emission at different wavelengths place constraints on the nature and efficiency of the emission mechanism and the physical conditions in different atmospheric layers. The activity of ultracool dwarfs, at the low-mass end of the main-sequence, is poorly understood. Aims. We perform a multi-wavelength study of one of the nearest M9 dwarfs, DENIS-P J104814.7-395606 (4 pc), to examine its position within the group of magnetically active ultracool dwarfs, and, in general, advance our understanding of these objects by comparing them to early-M type dwarf stars and the Sun. Methods. We obtained an XMM-Newton observation of DENIS-P J104814.7-395606 and a broad-band spectrum from the ultraviolet to the near-infrared with X-Shooter. From this dataset, we derive the X-ray properties, stellar parameters, kinematics, and the emission-line spectrum tracing chromospheric activity. We integrate these data by compiling the activity parameters of ultracool dwarfs from the literature. Results. Our deep XMM-Newton observation provides the first X-ray detection of DENIS-P J104814.7-395606 (log L x = 25.1), as well as the first measurement of its V band brightness (V = 17.35 mag). The flux-flux relations between X-ray and chromospheric activity indicators are here for the first time extended into the regime of the ultracool dwarfs. The approximate agreement of DENIS-P J104814.7-395606 and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests that the same heating mechanisms work in the atmospheres of ultracool dwarfs, albeit weaker as judged from their lower fluxes. The observed Balmer decrements of DENIS 1048-3956 are compatible with optically thick plasma in local thermal equilibrium (LTE) at low, nearly photospheric temperature or optically thin LTE plasma at 20 000 K. Describing the decrements with case B recombination requires different emitting regions for Hα and the higher Balmer lines. The high observed Hα/Hβ flux ratio is also poorly fitted by the optically thin models. We derive a similarly high value for the Hα/Hβ ratio of vB 10 and LHS 2065 and conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P J104814.7-395606 to the list of ultracool dwarfs detected in both the radio and the X-ray band. The Benz-Güdel relation between radio and X-ray luminosity of late-type stars is well-known to be violated by ultracool dwarfs. We speculate on the presence of two types of ultracool dwarfs with distinct radio and X-ray behaviors.

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Section: Observed Balmer Decrementsmentioning

confidence: 64%

The ultracool dwarf DENIS-P J104814.7-395606

Stelzer

Alcalá

Biazzo

et al. 2012

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“…For the He i lines at 3819.6, 4026.2, and 6678.1 Å the line amplitudes are not strong enough to reveal a broad component, although the latter at least shows a second component. These broad component has been noted mostly in M-dwarf flares (Crespo-Chacón et al 2006;Fuhrmeister et al 2008Fuhrmeister et al , 2011, but also for young K-dwarfs (Montes et al 1999 and references therein). They can be blue-or (more often) red-shifted, and are often ascribed to a moving turbulent plasma component.…”

Section: Broad Line Componentsmentioning

confidence: 84%

“…Other flare studies usually concentrate on high resolution or high cadence; e.g. Crespo-Chacón et al (2006) studied flares on AD Leo with a cadence of typically 3 min, but with R of ∼3500 in the wavelength range of 3500 to 5176 Å. Also Kowalski et al (2010) observed a white light mega-flare on YZ CMi with a resolving power below 1000 but a cadence of 30 s covering a wavelength range from 3350 to 9260 Å.…”

Section: Introductionmentioning

confidence: 99%

A multi-wavelength view of AB Doradus outer atmosphere

Lalitha

Fuhrmeister

Wolter

et al. 2013

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Aims. We study the chromosphere and corona of the ultra-fast rotator AB Dor A at high temporal and spectral resolution using simultaneous observations with XMM-Newton in the X-rays, VLT/UVES in the optical, and the ATCA in the radio. Our optical spectra have a resolving power of ∼50 000 with a time cadence of ∼1 min. Our observations continuously cover more than one rotational period and include both quiescent periods and three flaring events of different strengths. Methods. From the X-ray observations we investigated the variations in coronal temperature, emission measure, densities, and abundance. We interpreted our data in terms of a loop model. From the optical data we characterised the flaring chromospheric material using numerous emission lines that appear in the course of the flares. A detailed analysis of the line shapes and line centres allowed us to infer physical characteristics of the flaring chromosphere and to coarsely localise the flare event on the star. Results. We specifically used the optical high-cadence spectra to demonstrate that both turbulent and Stark broadening are present during the first ten minutes of the first flare. Also, in the first few minutes of this flare, we find short-lived (one to several minutes) emission subcomponents in the Hα and Ca ii K lines, which we interpret as flare-connected shocks owing to their high intrinsic velocities. Combining the space-based data with the results of our optical spectroscopy, we derive flare-filling factors. Finally, comparing X-ray, optical broadband, and line emission, we find a correlation for two of the three flaring events, while there is no clear correlation for one event. Also, we do not find any correlation of the radio data to any other observed data.

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“…For example, the H α line peaks approximately 2.5 minutes before both Ca ii H & K lines. In an analysis of several flares on AD Leo, Crespo-Chacón et al (2006) find that the flare peaks in the Ca ii H & K lines were delayed with respect to that of the Balmer lines by up to 5 ± 3 min; in particular, this refers to the delay of the Ca ii K line with respect to H β. If anything, our observation indicates a similar trend.…”

Section: Evolution Of the Balmer And Ca II Linesmentioning

confidence: 98%

“…Similarly, Johns-Krull et al (1997) report on a GOES M7.7 class solar flare also finding the He i D3 line to be in absorption throughout the entire event and absent during quies-During flares on other stars the He i D3 line has been observed in emission. For instance, Crespo-Chacón et al (2006) detect the line studying flares on the active M-type star AD Leo and Montes et al (1999) report He i D3 emission during a flare on the K2 dwarf LQ Hya. Our observations indicate a potential small increase in the He i D3 flux during the rise phase of the flare, which would be consistent with observations of strong flares on the Sun, thereafter a phase of increasing absorption follows.…”

Section: The Behavior Of He I D3mentioning

confidence: 99%

Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

Klocová

Czesla

Khalafinejad

et al. 2017

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Context. HD 189733 is an exoplanetary system consisting of a transiting hot Jupiter and an active K2V-type main sequence star. Rich manifestations of a stellar activity, like photometric spots or chromospheric flares were repeatedly observed in this system in optical, UV and X-rays. Aims. We aim to use VLT/UVES high resolution (R = 60 000) echelle spectra to study a stellar flare. Methods. We have performed simultaneous analyses of the temporal evolution in several chromospheric stellar lines, namely, the, H (3970 Å), the Ca ii infrared triplet line (8498, 8542 and 8662 Å), and He i D3 (5875.6 Å). Observations were carried out with a time resolution of approximately 1 min for a duration of four hours, including a complete planetary transit. Results. We determine the energy released during the flare in all studied chromospheric lines combined to be about 8.7 × 10 31 erg, which puts this event at the upper end of flare energies observed on the Sun. Our analysis does not reveal any significant delay of the flare peak observed in the Balmer and Ca ii H & K lines, although we find a clear difference in the temporal evolution of these lines. The He i D3 shows additional absorption possibly related to the flare event. Based on the flux released in Ca ii H & K lines during the flare, we estimate the soft X-ray flux emission to be 7 × 10 30 erg. Conclusions. The observed flare can be ranked as a moderate flare on a K-type star and confirms a rather high activity level of HD 189733 host star. The cores of the studied chromospheric lines demonstrate the same behavior and let us study the flare evolution. We demonstrate that the activity of an exoplanet host star can play an important role in the detection of exoplanet atmospheres, since these are frequently discovered as an additional absorption in the line cores. A possible star-planet interaction responsible for a flare occurrence during a transit can neither be confirmed nor ruled out.

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Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leonis

Cited by 52 publications

References 62 publications

The ultracool dwarf DENIS-P J104814.7-395606

The ultracool dwarf DENIS-P J104814.7-395606

A multi-wavelength view of AB Doradus outer atmosphere

Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

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