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

By T. Preibisch, Yong-Cheol Kim, F. Favata, Eric D. Feigelson, E. Flaccomio, Konstantin Getman, G. Micela, S. Sciortino, Keivan G. Stassun, B. Stelzer and 1 more. 2005

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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 LX, min ~ 1027.3 ergs s-1 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 main-sequence (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 LX/Lbol 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.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

The Evolution of X-Ray Emission in Young Stars (2005, background): “As the evolutionary time scales for PMS stars are a strong function of the stellar mass (Preibisch et al. 2005), which itself has dependencies on bolometric luminosity, we believe it is necessary to consider mass stratified subsamples to avoid confusing interrelationships.”
CRYSTALLINE SILICATES AND DUST PROCESSING IN THE PROTOPLANETARY DISKS OF THE TAURUS YOUNG CLUSTER (2007, background): “The propensity for high X-ray luminosity varies substantially among Class II YSOs of given mass or spectral type (see, e.g., Preibisch et al. 2005).”
Highlights from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) (2006, background): “The cause of Xray suppression is not clear but appears to be related to a suppression of the coronal heating efficiency by inflowing cool, accreting material (Preibisch et al. 2005; Telleschiet al. 2007a).”
Accretion in the ρ-Ophiuchi pre-main sequence stars (2006, background): “The COUP Chandra observations of Orion show that LX scales approximately as M 1.1−1.4 in the interval 0.1−2 M (Preibisch et al. 2005).”
The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime (2015, background): “…X-ray spectrum (generated by fitting the observed XMM-Newton spectrum) for the M dwarf and T Tauri stars, with a total luminosity, Lx ∼ 1030 erg s−1 (Preibisch et al. 2005) and assume Lx ≈ 3 × 1029 erg s−1 and Tx ≈ 1.0 keV for the X-ray spectrum of the Herbig Ae star (see, e.g., Zinnecker &…”
New constraints on the multiplicity of massive young stars in Upper Scorpius (2015, background): “According to the observationally established correlation between X-ray luminosity and stellar mass for coronal sources (see, e.g., Preibisch et al. 2005), these X-ray luminosities suggest companions with masses of M ∼ 1.5 M for the case of HR 6026 and M ∼ 1 M for HR 6027.”
X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, methodology): “16 of Preibisch et al. (2005).”
PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR (2008, methodology): “The X-ray luminosities of stars are fairly well determined and we use observational data to guide our choice of X-ray luminosity as a function of mass (LX ∼ 2.3 × 1030 (M∗/M )1.44 erg s−1 for M∗ 3 M and LX ∼ 10−6L∗ for M∗ 3 M ; Flaccomio et al. 2003; Preibisch et al. 2005).”
Radiation-hydrodynamic models of X-ray and EUV photoevaporating protoplanetary discs (2009, background): “…in terms either of X-ray absorption in accretion columns (Gregory et al. 2007) or confinement of the Xray producing corona in accreting systems (Preibisch et al. 2005) (in other words, it is conventionally assumed that accretion suppresses X-ray emission rather than the effect predicted here…”
On the theory of disc photoevaporation (2011, methodology): “Such an evolution is consistent with the observation that discless stars are systematically more X-ray luminous than stars still surrounded by discs (Neuhäuser et al. 1995; Stelzer & Neuhäuser 2001; Flaccomio, Micela & Sciortino 2003; Preibisch et al. 2005).”
The Sun in Time: Activity and Environment (2007, methodology): “therein), the luminosity deficit in CTTS is now thought to be real; it appears that accretion suppresses coronal heating in a fraction of the coronal volume (Preibisch et al., 2005), or at least leads to larger amounts of cooler plasma, which is perhaps the same plasma inferred from the X-ray soft e”
EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, background): “In Figure 2, the black line corresponds to a “characteristic” T-Tauri X-ray spectrum as measured at the stellar surface with temperature components corresponding to T = 9 MK and 30 MK respectively (Getman et al. 2005; Preibisch et al. 2005).”
A STELLAR CENSUS OF THE TUCANA–HOROLOGIUM MOVING GROUP (2014, background): “Selection of Young Stars with GALEX Stellar activity is known to be an indicator of youth (Preibisch et al. 2002, 2005), so X-ray and UV all-sky surveys are well-suited to finding active young stars.”
X-ray spectroscopy of stars (2009, background): “For TTS samples,LX/Lbol ≈ 10−3.5, although there is a large scatter around this saturation value, nd the subsample of accreting TTS (“classical T Tauri” stars or CTTS) reveals ratios on average 6 about a factor of 2 lower than non-accreting TTS (“weak-lined T Tauri” stars or WTTS; Preibisch et al 20”
Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars (2005, background): “The effect has also been noted in the time-integrated spectra of COUP stars (Preibisch et al. 2005a).”
The Magnetic Fields of Classical T Tauri Stars (2007, background): “…that accreting young stars as a group show X-ray emission levels that are reduced by a factor of 2Y3 relative to nonaccreting young stars, even after dependencies on mass and age are taken into account (Flaccomio et al. 2003; Stassun et al. 2004; Preibisch et al. 2005; Feigelson et al. 2007).”
TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR (2009, background): “Non-accreting stars interestingly do not show the soft X-ray excess, and their absolute and fractional X-ray luminosities are a factor of ∼ 2 − 3 higher than the CTTS (e.g., Preibisch et al. 2005, Güdel & Telleschi 2007).”
Protoplanetary disc evolution and dispersal: the implications of X-ray photoevaporation (2010, methodology): “…Neuhauser et al 1995; Stelzer & Neuhauser 2001; Flaccomio 1 Where the X-ray luminosity is taken to be in the range 0.3- 10keV for the Taurus sample and 0.5-8keV for the Orion sample, consistent with our definition which includes both the soft and hard component. et al. 2003; Preibisch et al. 2005).”