Stellar Activity on the Young Suns of Orion: COUP Observations of K5‐7 Pre–Main‐Sequence Stars

Wolk, S. J.; Harnden, F. R.; Flaccomio, E.; Micela, G.; Favata, F.; Shang, Hsien; Feigelson, E. D.

doi:10.1086/432099

Cited by 204 publications

(360 citation statements)

References 62 publications

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“…The temporal behavior of COUP sources is often very complex, with high-amplitude, rapidly changing flares superposed on apparent quiescent or slowly variable emission as studied in detail by Wolk et al (2005), Favata et al (2005), and Flaccomio et al (2005). For the purpose of the present study, the individual features of the light curves are not of interest.…”

Section: The Coup Observationmentioning

confidence: 99%

“…A strict and fully convincing definition for ''quiescent'' X-ray emission is not possible, especially since any apparently quiescent emission may, in reality, just be a superposition of numerous unresolved small flares. Wolk et al (2005) empirically establish a proxy for the quiescent emission levels by determining a ''characteristic level'' in each light curve, which is essentially defined as the average count rate over periods where the count rate is not significantly elevated. An estimate for the characteristic X-ray luminosity can then be obtained by multiplying the temporally averaged X-ray luminosity, as determined from the spectral analysis, with the ratio of the characteristic count rate from the MLB analysis to the mean count rate over the COUP exposure.…”

Section: The Coup Observationmentioning

confidence: 99%

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The Origin of T Tauri X‐Ray Emission: New Insights from the Chandra Orion Ultradeep Project

Preibisch

Kim

Favata

et al. 2005

ASTROPHYS J SUPPL S

480

673

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The Chandra Orion Ultradeep Project (COUP) provides the most comprehensive data set ever acquired on the X-ray emission of pre-main-sequence stars. In this paper, we study the nearly 600 X-ray sources that can be reliably identified with optically well-characterized T Tauri stars (TTSs) in the Orion Nebula Cluster. With a detection limit of L X; min $ 10 27:3 ergs s À1 for lightly absorbed sources, we detect X-ray emission from more than 97% of the optically visible late-type (spectral types F-M) cluster stars. This proves that there is no ''X-ray-quiet'' population of late-type stars with suppressed magnetic activity. We use this exceptional optical, infrared, and X-ray data set to study the dependencies of the X-ray properties on other stellar parameters. All TTSs with known rotation periods lie in the saturated or supersaturated regime of the relation between activity and Rossby numbers seen for mainsequence ( MS) stars, but the TTSs show a much larger scatter in X-ray activity than that seen for the MS stars. Strong near-linear relations between X-ray luminosities, bolometric luminosities, and mass are present. We also find that the fractional X-ray luminosity L X /L bol rises slowly with mass over the 0:1 2 M range. The plasma temperatures determined from the X-ray spectra of the TTSs are much hotter than in MS stars but seem to follow a general solar-stellar correlation between plasma temperature and activity level. The scatter about the relations between X-ray activity and stellar parameters is larger than the expected effects of X-ray variability, uncertainties in the variables, and unresolved binaries. This large scatter seems to be related to the influence of accretion on the X-ray emission. While the X-ray activity of the nonaccreting TTSs is consistent with that of rapidly rotating MS stars, the accreting stars are less X-ray active (by a factor of $2-3 on average) and produce much less well-defined correlations than the nonaccretors. We discuss possible reasons for the suppression of X-ray emission by accretion and the implications of our findings on long-standing questions related to the origin of the X-ray emission from young stars, considering in particular the location of the X-ray-emitting structures and inferences for pre-main-sequence magnetic dynamos.

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Section: The Coup Observationmentioning

confidence: 99%

Section: The Coup Observationmentioning

confidence: 99%

The Origin of T Tauri X‐Ray Emission: New Insights from the Chandra Orion Ultradeep Project

Preibisch

Kim

Favata

et al. 2005

ASTROPHYS J SUPPL S

480

673

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“…No evidence of short term variability is found and the resulting probability weighted light curves are shown as black squares. We also applied a maximumlikelihood block algorithm that divides the event list into blocks of constant count rate (Wolk et al 2005). Each epoch is reproduced by a single block (grey bar), which also in- Count rate (ct s −1 ) 6.1 +0.6 −0.6 × 10 −3 8.7…”

Section: Timing Analysismentioning

confidence: 99%

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

Petit

Cohen

Wade

et al. 2015

Mon. Not. R. Astron. Soc.

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We observed NGC 1624-2, the O-type star with the largest known magnetic field (B p ∼ 20 kG), in X-rays with the ACIS-S camera onboard the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Hα emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterise the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are: (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star θ 1 Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30% lower at the Hα minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (∼1-3×10 22 cm −2 ). This combination is necessary to reproduce both the prominent Mg and Si spectral features, and the lack of flux at low energies. NGC 1624-2 is intrinsically luminous in X-rays (log L em X ∼33.4) but 70-95% of the X-ray emission produced by magnetically confined wind shocks is absorbed before it escapes the magnetosphere (log L ISMcor X ∼32.5). (iii) The high X-ray luminosity, its variation with stellar rotation, and its large attenuation are all consistent with a large dynamical magnetosphere with magnetically confined wind shocks.

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“…In its form for time-tagged data, this algorithm was used for example to characterize the X-ray light curves of young pre-main sequence stars observed by the Chandra Orion Ultra-Deep Project (COUP, Getman et al 2005) in the Orion Nebula Cluster (ONC). A modified version of the S98 algorithm, based on a Maximum Likelihood rather than a Bayesian approach, was recently employed in other studies of stellar X-ray light curves (Wolk et al 2005;Favata et al 2005;Stelzer et al 2006). We will refer to this algorithm as the Maximum Likelihood Blocks (MLBs) and we introduce here a variant that is suitable for the analysis of binned light curves.…”

Section: Representation Of the Light Curve: Maximum Likelihood Blocksmentioning

confidence: 99%

“…Sometimes periods of no variable activity are defined in the literature as "quiescent". As discussed for example in (Wolk et al 2005), the meaning of quiescent emission is ambiguous. An apparently quiescent level can be due to a superposition of numerous unresolved flares.…”

Section: Interpretation Of the Light Curve: Flares Versus Characterismentioning

confidence: 99%

The classification of flaring states of blazars

Resconi¹,

Franco

Groß

et al. 2009

A&A

Self Cite

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Aims. The time evolution of the electromagnetic emission from blazars, in particular high-frequency peaked sources (HBLs), displays irregular activity that has not yet been understood. In this work we report a methodology capable of characterizing the time behavior of these variable objects. Methods. The maximum likelihood blocks (MLBs) is a model-independent estimator that subdivides the light curve into time blocks, whose length and amplitude are compatible with states of constant emission rate of the observed source. The MLBs yield the statistical significance in the rate variations and strongly suppresses the noise fluctuations in the light curves. We applied the MLBs for the first time on the long term X-ray light curves (RXTE/ASM) of Mkn 421, Mkn 501, 1ES 1959+650, and 1ES 2155-304, more than 10 years of observational data (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007). Using the MLBs interpretation of RXTE/ASM data, the integrated time flux distribution is determined for each single source considered. We identify in these distributions the characteristic level, as well as the flaring states of the blazars. Results. All the distributions show a significant component at negative flux values, most probably caused by an uncertainty in the background subtraction and by intrinsic fluctuations of RXTE/ASM. This effect concerns in particular short time observations. To quantify the probability that the intrinsic fluctuations give rise to a false identification of a flare, we study a population of very faint sources and their integrated time-flux distribution. We determine duty cycle or fraction of time a source spent in the flaring state of the source Mkn 421, Mkn 501, 1ES 1959+650 and 1ES 2155-304. Moreover, we study the random coincidences between flares and generic sporadic events such as high-energy neutrinos or flares in other wavelengths.

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Stellar Activity on the Young Suns of Orion: COUP Observations of K5‐7 Pre–Main‐Sequence Stars

Cited by 204 publications

References 62 publications

The Origin of T Tauri X‐Ray Emission: New Insights from the Chandra Orion Ultradeep Project

The Origin of T Tauri X‐Ray Emission: New Insights from the Chandra Orion Ultradeep Project

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

The classification of flaring states of blazars

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