Evidence for Accretion: High‐Resolution X‐Ray Spectroscopy of the Classical T Tauri Star TW Hydrae

Kastner, Joel H.; Huenemoerder, David P.; Schulz, Norbert S.; Canizares, C. R.; Weintraub, David A.

doi:10.1086/338419

Cited by 347 publications

(498 citation statements)

References 31 publications

Supporting

Mentioning

446

Contrasting

Order By: Relevance

“…and Batalha et al (2002) derived a higher value, 1−5 × 10 −9 M yr −1 , based on UV data, in agreement with the mass accretion rate inferred from the Hα line width by Jayawardhana et al (2006). The X-ray emission of TW Hya shows clear evidence of high-density plasma (n e ∼ 10 13 cm −3 ) at low temperatures (Kastner et al 2002;Stelzer & Schmitt 2004).…”

Section: Targetssupporting

confidence: 76%

X-ray optical depth diagnostics of T Tauri accretion shocks

Argiroffi

Maggio

Peres

et al. 2009

A&A

View full text Add to dashboard Cite

Context. In classical T Tauri stars, X-rays are produced by two plasma components: a hot low-density plasma, with frequent flaring activity, and a high-density lower temperature plasma. The former is coronal plasma related to the stellar magnetic activity. The latter component, never observed in non-accreting stars, could be plasma heated by the shock formed by the accretion process. However its nature is still being debated. Aims. Our aim is to probe the soft X-ray emission from the high-density plasma component in classical T Tauri stars to check whether this plasma is heated in the accretion shock or whether it is coronal plasma. Methods. High-resolution X-ray spectroscopy allows us to measure individual line fluxes. We analyze X-ray spectra of the classical T Tauri stars MP Muscae and TW Hydrae. Our aim is to evaluate line ratios to search for optical depth effects, which are expected in the accretion-driven scenario. We also derive the plasma emission measure distributions EMD, to investigate whether and how the EMD of accreting and non accreting young stars differ. The results are compared to those obtained for the non-accreting weakline T Tauri star TWA 5. Results. We find evidence of resonance scattering in the strongest lines of MP Mus, supporting the idea that soft X-rays are produced by plasma heated in the accretion shock. We also find that the EMD of MP Mus has two peaks: a cool peak at temperatures expected for plasma heated in the accretion shock, and a hot peak typical of coronal plasma. The shape of the EMD of MP Mus appears to be the superposition of the EMD of a pure coronal source, like TWA 5, and an EMD alike that of TW Hya, which is instead dominated by shock-heated plasma.

show abstract

Section: Targetssupporting

confidence: 76%

X-ray optical depth diagnostics of T Tauri accretion shocks

Argiroffi

Maggio

Peres

et al. 2009

A&A

View full text Add to dashboard Cite

show abstract

“…Hence, we favor the latter interpretation of the soft X-ray component, i.e., that this component has its origin in accretion shocks. As in the case of TW Hya (Kastner et al 2002;Brickhouse et al 2010), our pole-on view of the EX Lup star-disk system indeed probably provides a direct view of the relatively cool plasma associated with these shocks.…”

Section: The Origin Of the Soft X-ray Component Of Ex Lupsupporting

confidence: 53%

A few days before the end of the 2008 extreme outburst of EX Lupi: accretion shocks and a smothered stellar corona unveiled by XMM-Newton

Grosso

Hamaguchi

Kastner

et al. 2010

A&A

View full text Add to dashboard Cite

Context. EX Lup is a pre-main sequence star that exhibits repetitive and irregular optical outbursts driven by an increase in the mass accretion rate in its circumstellar disk. In mid-January 2008, EX Lup, the prototype of the small class of eruptive variables called EXors, began an extreme outburst that lasted seven months. Aims. We attempt to characterize the X-ray and UV emission of EX Lup during this outburst. Methods. We observed EX Lup during about 21 h with XMM-Newton, simultaneously in X-rays and UV, on August 10-11, 2008 -a few days before the end of its 2008 outburst -when the optical flux of EX Lup remained about 4 times above its pre-outburst level. Results. We detected EX Lup in X-rays with an observed flux in the 0.2-10 keV energy range of 5.4 × 10 −14 erg s −1 cm −2 during a low-level period. This observed flux increased by a factor of four during a flaring period that lasted about 2 h. The observed spectrum of the low-level period is dominated below ∼1.5 keV by emission from a relatively cool plasma (∼4.7 MK) that is lightly absorbed (N H 3.6 × 10 20 cm −2 ) and above ∼1.5 keV by emission from a plasma that is ∼ten times hotter and affected by a photoelectric absorption that is 75 times larger. The intrinsic X-ray luminosity of the relatively cool plasma is ∼4 × 10 28 erg s −1 . The intrinsic X-ray luminosity of EX Lup, ∼3.4 × 10 29 erg s −1 , is hence dominated by emission from the hot plasma. During the X-ray flare, the emission measure and the intrinsic X-ray luminosity of this absorbed plasma component is five times higher than during the low-level period. We detected UV variability on timescales ranging from less than one hour up to about four hours. We show from simulated light curves that the power spectral density of the UV light curve can be modeled with a red-noise spectrum with a power-law index of 1.39 ± 0.06. None of the UV events observed on August 10-11, 2008 correlate unambiguously with simultaneous X-ray peaks. Conclusions. The soft X-ray spectral component is most likely associated with accretion shocks, as opposed to jet activity, given the absence of forbidden emission lines of low-excitation species (e.g., [O i]) in optical spectra of EX Lup obtained during outburst. The hard X-ray spectral component, meanwhile, is most likely associated with a smothered stellar corona. The UV emission is reminiscent of accretion events, such as those already observed with the Optical/UV Monitor from other accreting pre-main sequence stars, and is evidently dominated by emission from accretion hot spots. The large photoelectric absorption of the active stellar corona is most likely due to high-density gas above the corona in accretion funnel flows.

show abstract

“…However, we find that the lowest FIP elements have intermediate abundances, as does the high-FIP element Ar, relative to the other elements. AR Lac seems to be more moderate in terms of abundance anomalies compared with other active stars such as II Peg or HR 1099, being less deficient in iron and having a lower neon abundance ratio to iron (see Kastner et al 2002 for collections of HETGS spectra qualitatively ordered by iron to neon abundance ratio). 6 The trend of increasing abundance with FIP is opposite to what has been seen in the solar corona (see, e.g., Feldman & Laming 2000;Feldman 1992;Feldman, Widing, & Lund 1990, for reviews).…”

Section: Discussionmentioning

confidence: 98%

The Coronae of AR Lacertae

Huenemoerder

Canizares

Drake

et al. 2003

ApJ

Self Cite

View full text Add to dashboard Cite

We observed the coronally active eclipsing binary AR Lac with the High Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV spectra and photometry were also obtained with the Extreme Ultraviolet Explorer. Significant variability in both X-ray and EUV fluxes were observed, dominated by at least one X-ray flare and one EUV flare. We saw no evidence of primary or secondary eclipses, but exposures at these phases were short and intrinsic variability compromised detection of any geometric modulation. X-ray flux modulation was largest at high temperature, indicative of flare heating of coronal plasma rather than changes in emitting volume or global emission measure. Analysis of spectral line widths interpreted in terms of Doppler broadening suggests that both binary stellar components are active. On the basis of line fluxes obtained from total integrated spectra, we have modeled the emission measure and abundance distributions. The EUV spectral line fluxes were particularly useful for constraining the parameters of the '' cool '' ( 2 Â 10 6 K) plasma. A strong maximum was found in the differential emission measure, characterized by two apparent peaks at log T ¼ 6:9 and 7.4, together with a weak but significant cooler maximum near log T ¼ 6:2 and a moderately strong hot tail from log T ¼ 7:6 8:2. Coronal abundances have a broad distribution and show no simple correlation with first ionization potential. While the resulting model spectrum generally agrees very well with the observed spectrum, there are some significant discrepancies, especially among the many Fe L lines. Both the emission measure and abundance distributions are qualitatively similar to prior determinations from other X-ray and ultraviolet spectra, indicating some long-term stability in the overall coronal structure.

show abstract

Evidence for Accretion: High‐Resolution X‐Ray Spectroscopy of the Classical T Tauri Star TW Hydrae

Cited by 347 publications

References 31 publications

X-ray optical depth diagnostics of T Tauri accretion shocks

X-ray optical depth diagnostics of T Tauri accretion shocks

A few days before the end of the 2008 extreme outburst of EX Lupi: accretion shocks and a smothered stellar corona unveiled by XMM-Newton

The Coronae of AR Lacertae

Contact Info

Product

Resources

About