Bright X-Ray Flares in Orion Young Stars from COUP: Evidence for Star-Disk Magnetic Fields?

By F. Favata, E. Flaccomio, Fabio Reale, G. Micela, S. Sciortino, H. Shang, Keivan G. Stassun, Eric D. Feigelson. 2005

232 citations recorded by the source corpus.

We have analyzed a number of intense X-ray flares observed in the Chandra Orion Ultradeep Project (COUP), a 13 day observation of the Orion Nebula Cluster (ONC), concentrating on the events with the highest statistics (in terms of photon flux and event duration). Analysis of the flare decay allows to determine the physical parameters of the flaring structure, particularly its size and (using the peak temperature and emission measure of the event) the peak density, pressure, and minimum confining magnetic field. A total of 32 events, representing the most powerful ≃1% of COUP flares, have sufficient statistics and are sufficiently well resolved to grant a detailed analysis. A broad range of decay times are present in the sample of flares, with τlc (the 1/e decay time) ranging from 10 to 400 ks. Peak flare temperatures are often very high, with half of the flares in the sample showing temperatures in excess of 100 MK. Significant sustained heating is present in the majority of the flares. The magnetic structures that are found, from the analysis of the flare's decay, to confine the plasma are in a number of cases very long, with semilengths up to ≃1012 cm, implying the presence of magnetic fields of hundreds of G (necessary to confine the hot flaring plasma) extending to comparable distance from the stellar photosphere. These very large sizes for the flaring structures (length L ≫ R*) are not found in more evolved stars, where, almost invariably, the same type of analysis results in structures with L ≤ R*. As the majority of young stars in the ONC are surrounded by disks, we speculate that the large magnetic structures that confine the flaring plasma are actually the same type of structures that channel the plasma in the magnetospheric accretion paradigm, connecting the star's photosphere with the accretion disk.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cd252dc0bf0f8a3abfcd914382c348eb0a5d0607

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In Astronomy and Astrophysics

1. M. Gudel
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3. N. Calvet
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6. L. Hillenbrand
7. J. Najita
8. Eric D. Feigelson

Citations in the corpus

• CRYSTALLINE SILICATES AND DUST PROCESSING IN THE PROTOPLANETARY DISKS OF THE TAURUS YOUNG CLUSTER (2007, background): “…particularly intriguing experiment of this sort would be to acquire mid-IR silicate-feature observations of the YSOs in the Orion clouds that were detected in the COUP X-ray survey (Getman et al. 2005), as this sample is large and contains many examples of X-ray-flaring YSOs (Favata et al. 2005).”
• Accretion-powered Stellar Winds. II. Numerical Solutions for Stellar Wind Torques (2008, background): “These stars have active coronae (Feigelson & Montmerle 1999; Stassun et al. 2004; Favata et al. 2005), and it thus seems a reasonable assumption that they also drive solarlike coronal winds in which thermal pressure plays a significant role in the wind acceleration.”
• Accretion onto Pre-Main-Sequence Stars (2016, background): “Reconnection events as the star–disk magnetic fields wind up may also result in bright flares in hard X-rays on long (0.1-AU) magnetic structures (Favata et al. 2005).”
• The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project (2005, background): “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 byWolk et al. (2005), Favata et al. (2005), and Flaccomio et al. (2005).”
• Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars (2005, methodology): “Favata et al. (2005) examined the brightest flares in the COUP sample and found 100MK temperatures in half of the events.”