X-ray flares on the UV Ceti-type star CC Eridani: a “peculiar” time-evolution of spectral parameters

Colombo

López-García

2010

A&A

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Context. The members of the η Chamaleontis cluster are in an evolutionary stage in which disks are rapidly evolving. It also exhibits some peculiarities, such as the large fraction of binaries and accretion disks, probably related to the cluster formation process. Its proximity makes this stellar group an ideal target for studying the relation between X-ray emission and those stellar parameters. Aims. Our main objective is to determine the general X-ray properties of the cluster members in terms of coronal temperature, column density, emission measure, X-ray luminosity, and variability. We also aim to establish the relation between the X-ray luminosity of these stars and other stellar parameters, such as effective temperature, binarity, and the presence of accretion disks. Finally, a study of flare energies in each flare event detected during the observations and their relation with some stellar parameters is also performed. Methods. We used proprietary data from a deep XMM-Newton EPIC observation targeting the core of the η Chamaleontis cluster. Specific software for the reduction of XMM-Newton data was used to analyze our observation. To detect sources in the composed EPIC pn+mos image, we used the wavelet-based code PWDetect. General coronal properties were derived from plasma model fitting. X-ray light curves in the 0.3−8.0 keV energy range were generated for each star. Results. We determine both the coronal properties and variability of the η Chamaleontis members in the XMM-Newton EPIC field-ofview. A total of six flare-like events are clearly detected in five different stars. For them, we derived coronal properties during the flare events and pseudo-quiescent state separately. In our observations, stars that experienced a flare event have higher X-ray luminosities in the pseudo-quiescent state than cluster members of similar spectral type that exhibit no evidence of flaring independently of whether they have an accretion disk or not. Observed flare energies are typical of both pre-main-and main-sequence M stars. We detected no difference between flare energies of stars with and without an accretion disk.

Section: Flaressupporting

confidence: 87%

DeepXMM-Newtonobservation of theη Chamaleontis cluster

Colombo

López-García

2010

A&A

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“…The mean coronal temperature during the observation reached 3.3 keV (T ∼ 38 MK). This value is typical of high-energy flaring events in late-type stars (see Crespo-Chacón et al 2007, and references therein).…”

Section: X-ray Variabilitymentioning

confidence: 69%

New deepXMM-Newtonobservations to the west of the σ Orionis cluster

Caballero

2008

A&A

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Aims. The objective of this study is to determine the general X-ray properties of the young stars in the external regions of the σ Orionis cluster (τ ∼ 3 Ma, d ∼ 385 pc) and determine constraints on the X-ray emission of brown dwarfs. Methods. We carried out a careful analysis of public data obtained from an unexplored region to the west of the centre of the cluster with the three EPIC cameras onboard the XMM-Newton mission. We looked for new X-ray young stars among the 41 identified X-ray sources in the area with maximum likelihood parameters L > 15 by cross-correlation with the USNO-B1, DENIS, and 2MASS databases.Results. Based on colour-colour, colour-magnitude, and hardness ratio diagrams, and previous spectroscopic, astrometric, and infrared-flux excess information, we classified the optical/near-infrared counterparts of the X-ray sources into: young stars (15), field stars (4), galaxies (19), and sources of unknown nature (3). Most of the X-ray detections, including those of nine young stars, are new. We derived the X-ray properties (e.g. temperatures, metallicities, column densities) of the twelve young stars with the largest signal-to-noise ratios. The X-ray parameters determined here are in good agreement with those found in the cluster centre, where the stellar density is higher. There is no relation between infrared excess and column density in the X-ray measurements in our data. We detected flaring events in two young stars of the sample. One of them showed a very large (∼30) relative increase in flux. Both stars showed high coronal temperatures during the observation. Finally, we determined upper limits to the flux of the young stars and brown dwarfs not detected by our search algorithm.

“…5 5 In this power law, d N is the number of flares (per unit time) with a total energy (thermal or radiated) in the interval [ E , E + d E ] and α is greater than 0 (see section 1 in Crespo‐Chacón et al 2007, for the value of α derived by different authors and its relation with nanoflare heating of quiescent coronae). …”

mentioning

confidence: 99%

Effect of magnetic activity saturation in chromospheric flux-flux relationships

Martínez-Arnáiz

Monthly Notices of the Royal Astronomical Society

Crespo‐Chacón

et al. 2011

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We present a homogeneous study of chromospheric and coronal flux–flux relationships using a sample of 298 late‐type dwarf active stars with spectral types F to M. The chromospheric lines were observed simultaneously in each star to avoid spread as a result of long‐term variability. Unlike other works, we subtract the basal chromospheric contribution in all the spectral lines studied. For the first time, we quantify the departure of dMe stars from the general relations. We show that dK and dKe stars also deviate from the general trend. Studying the flux–colour diagrams, we demonstrate that the stars deviating from the general relations are those with saturated X‐ray emission and we show that these stars also present saturation in the Hα line. Using several age spectral indicators, we show that these are younger stars than those following the general relationships. The non‐universality of flux–flux relationships found in this work should be taken into account when converting between fluxes in different chromospheric activity indicators.