Multiwavelength diagnostics of accretion in an X-ray selected sample of CTTSs

Curran, Rachel; Argiroffi, C.; Sacco, G. G.; Orlando, S.; Peres, G.; Reale, F.; Maggio, A.

doi:10.1051/0004-6361/201015522

Cited by 60 publications

(80 citation statements)

References 68 publications

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“…This wide scatter may reflect a real spread in the values of the secondary indicators for fixed accretion luminosity, owing to, e.g., different stellar and/or disk properties, or differences in wind/jet contributions. We investigated the possibility that this spread may depend on the stellar masses or different regimes of mass accretion, and we found that these dependencies can be ruled out, agreeing with the results found by Curran et al (2011) for higher mass objects. Despite this wide spread, for a given star all accretion luminosity indicators give values of L acc,l , which are consistent within the error bars, and the average value of L acc,l has a considerably reduced uncertainty, which is about a factor two.…”

Section: Discussionsupporting

confidence: 80%

“…In the far-ultraviolet (FUV) Herczeg et al (2002) and Yang et al (2012) found that the OIλ103.4 nm triplet, SiIVλ139.4, A&A 548, A56 (2012) 140.3 nm doublet and CIVλ154.9 nm doublet are tightly correlated with L acc . In the soft X-rays, Telleschi et al (2007) and Curran et al (2011) found that the low-density plasma component in the post-shock region correlates withṀ acc . From the near-UV to the near-IR several hydrogen recombination lines can be used to estimate L acc (Hα,Hβ,H11,Paβ,Paγ), as well as other lines CaIIλ854.2 nm, CaIIλ866.2 nm, HeIλ587.6 nm, NaIλ589.3 nm, as shown by Fang et al (2009), Mohanty et al (2005), HH08, Natta et al (2004), and Gatti et al (2008), among many others.…”

Section: Introductionmentioning

confidence: 98%

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X-shooter spectroscopy of young stellar objects

Rigliaco

Natta

Testi

et al. 2012

A&A

179

291

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We present high-quality, medium-resolution X-shooter/VLT spectra in the range 300−2500 nm for a sample of 12 very low mass stars in the σ Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without disks, with masses ranging from 0.08 to 0.3 M . The aim of this first paper is to investigate the reliability of the many accretion tracers currently used to measure the mass accretion rate in low-mass young stars and the accuracy of the correlations between these secondary tracers (mainly accretion line luminosities) found in the literature. We use our spectra to measure the accretion luminosity from the continuum excess emission in the UV and visual; the derived mass accretion rates range from 10 −9 M yr −1 down to 5 × 10 −11 M yr −1 , allowing us to investigate the behavior of the accretion-driven emission lines in very low mass accretion rate regimes. We compute the luminosity of ten accretion-driven emission lines from the UV to the near-IR, which are all obtained simultaneously. In general, most of the secondary tracers correlate well with the accretion luminosity derived from the continuum excess emission. We recompute the relationships between the accretion luminosities and the line luminosities, and we confirm the validity of the correlations given in the literature, with the possible exception of Hα. Metallic lines, such as the CaII IR triplet or the Na I line at 589.3 nm, show a larger dispersion. When looking at individual objects, we find that the hydrogen recombination lines, from the UV to the near-IR, give good and consistent measurements of L acc that often better agree than the uncertainties introduced by the adopted correlations. The average L acc derived from several hydrogen lines, measured simultaneously, have a much reduced error. This suggests that some of the spread in the literature correlations may be due to the use of nonsimultaneous observations of lines and continuum. Three stars in our sample deviate from this behavior, and we discuss them individually.

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Section: Discussionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 98%

X-shooter spectroscopy of young stellar objects

Rigliaco

Natta

Testi

et al. 2012

A&A

179

291

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“…rooted (e.g. Sacco et al 2010;Curran et al 2011;Reale et al 2013;Bonito et al 2014). Our models do not take into account this local absorption and, in fact, all of them (blue, red, and green symbols in the figure) slightly overestimate the luminosity of X-ray lines.…”

Section: X-ray and Uv Luminosity Of Selected Linesmentioning

confidence: 99%

“…Theoretical models proved that absorption of X-rays in the accretion-shock region is significant (Bonito et al 2014) but the consequences of local heating due to this absorption are still unexplored. Investigating these aspects could probably help in understanding one of the most debated issues: the evidence that the mass-accretion rates inferred from X-ray observations are systematically lower (even by one or more orders of magnitude) than those derived from near infrared (NIR)/optical/UV observations (Curran et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic modelling of accretion impacts in classical T Tauri stars: radiative heating of the pre-shock plasma

Costa

Orlando

Peres

et al. 2016

A&A

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Context. It is generally accepted that, in classical T Tauri stars, the plasma from the circumstellar disc accretes onto the stellar surface with free-fall velocity and the impact generates a shock. The impact region is expected to contribute to emission in different spectral bands; many studies have confirmed that the X-rays arise from the post-shock plasma but, otherwise, there are no studies in the literature investigating the origin of the observed UV emission which is apparently correlated to accretion. Aims. We investigated the effect of radiative heating of the infalling material by the post-shock plasma at the base of the accretion stream, with the aim to identify in which region a significant part of the UV emission originates. Methods. We developed a one-dimensional hydrodynamic model describing the impact of an accretion stream onto the stellar surface; the model takes into account the gravity, the radiative cooling of an optically thin plasma, the thermal conduction, and the heating due to absorption of X-ray radiation. The latter term represents the heating of the infalling plasma due to the absorption of X-rays emitted from the post-shock region. Results. We found that the radiative heating of the pre-shock plasma plays a non-negligible role in the accretion phenomenon. In particular, the dense and cold plasma of the pre-shock accretion column is gradually heated up to a few 10 5 K due to irradiation of X-rays arising from the shocked plasma at the impact region. This heating mechanism does not affect significantly the dynamics of the post-shock plasma. On the other hand, a region of radiatively heated gas (that we consider a precursor) forms in the unshocked accretion column and contributes significantly to UV emission. Our model naturally reproduces the luminosity of UV emission lines correlated to accretion and shows that most of the UV emission originates from the precursor.

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“…For instance, to mention a few, the mass accretion rates derived from X-rays are, in general, sensibly lower (even by few orders of magnitude) than the corresponding mass accretion rates derived from UV/optical/NIR observations [6]. Also, the spectral analysis of X-ray emission arising from the impact region of accretion streams show that the shocked plasma seems to be denser at higher temperatures, a result which has been considered in contrast with the accretion shock models.…”

Section: Introductionmentioning

confidence: 95%

Role of local absorption on the X-ray emission from MHD accretion shocks in classical T Tauri stars

Bonito¹,

Orlando²,

Argiroffi³

et al. 2014

EPJ Web of Conferences

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Abstract. Accretion processes onto classical T Tauri stars (CTTSs) are believed to generate shocks at the stellar surface due to the impact of supersonic downflowing plasma. Although current models of accretion streams provide a plausible global picture of this process, several aspects are still unclear. For example, the observed X-ray luminosity in accretion shocks is, in general, well below the predicted value. A possible explanation discussed in the literature is in terms of significant absorption of the emission due to the thick surrounding medium. Here we consider a 2D MHD model describing an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere. The model includes all the relevant physics, namely the gravity, the thermal conduction, and the radiative cooling, and a realistic description of the unperturbed stellar atmosphere (from the chromosphere to the corona). From the model results, we synthesize the X-ray emission emerging from the hot slab produced by the accretion shock, exploring different configurations and strengths of the stellar magnetic field. The synthesis includes the local absorption by the thick surrounding medium and the Doppler shift of lines due to the component of plasma velocity along the line-of-sight. We explore the effects of absorption on the emerging X-ray spectrum, considering different inclinations of the accretion stream with respect to the observer. Finally we compare our results with the observations.

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Multiwavelength diagnostics of accretion in an X-ray selected sample of CTTSs

Cited by 60 publications

References 68 publications

X-shooter spectroscopy of young stellar objects

X-shooter spectroscopy of young stellar objects

Hydrodynamic modelling of accretion impacts in classical T Tauri stars: radiative heating of the pre-shock plasma

Role of local absorption on the X-ray emission from MHD accretion shocks in classical T Tauri stars

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