Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra

Ingleby, Laura; Calvet, Nuria; Herczeg, Gregory J.; Blaty, Alex; Walter, Frederick M.; Ardila, D. R.; Alexander, Richard D.; Edwards, Suzan; Espaillat, Catherine; Gregory, S. G.; Hillenbrand, Lynne A.; Brown, Alexander

doi:10.1088/0004-637x/767/2/112

Cited by 214 publications

(331 citation statements)

References 94 publications

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“…6.2. This relation extends also to the more massive TTS analyzed by Gullbring et al (1998) and Ingleby et al (2013) and to the low-mass ( < ∼ 0.15 L ) . L acc as function of L star for objects in Lupus (red dots) and σ Ori (filled blue squares).…”

Section: The Samplesupporting

confidence: 60%

X-shooter spectroscopy of young stellar objects

Natta

Testi

Alcalá

et al. 2014

A&A

126

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Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been identified, one characterized by velocity shifts of tens to hundreds of km s −1 (HVC) and one with a much lower velocity of a few km s −1 (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly lowmass young stars in Lupus and σ Ori observed with the X-shooter ESO spectrometer. We detect forbidden line emission of O , O , S , N , and N , and characterize the line profiles as LVC, blueshifted HVC, and redshifted HVC. We focus our study on the LVC.We show that there is a good correlation between line luminosity and both L star and the accretion luminosity (or the mass accretion rate) over a large interval of values (L star ∼ 10 −2 −1 L ; L acc ∼ 10 −5 −10 −1 L ;Ṁ acc ∼ 10 −11 −10 −7 M /yr). The lines show the presence of a slow wind (V peak < 20 km s −1 ) that is dense (n H > 10 8 cm −3 ), warm (T ∼ 5000−10 000 K), mostly neutral. We estimate the mass of the emitting gas and provide a value for the maximum volume it occupies. Both quantities increase steeply with the stellar mass, from ∼10 −12 M and ∼0.01 AU 3 for M star ∼ 0.1 M , to ∼3 × 10 −10 M and ∼1 AU 3 for M star ∼ 1 M , respectively. These results provide quite stringent constraints to wind models in low-mass young stars, that need to be explored further.

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Section: The Samplesupporting

confidence: 60%

X-shooter spectroscopy of young stellar objects

Natta

Testi

Alcalá

et al. 2014

A&A

126

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“…Depending on whether the stars used for the calibration are dominated by continuum or line veiling, the accretion rate could be lower. Although veiling-by-lines tends to occur in strong accretors Ingleby et al 2013), EX Lupi demonstrates that objects with low accretion rates can also have significant line-dependent veiling.…”

Section: Discussionmentioning

confidence: 98%

Accretion dynamics of EX Lupi in quiescence

Sicilia‐Aguilar¹,

Fang²,

Roccatagliata³

et al. 2015

A&A

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Context. EX Lupi is a young, accreting M0 star and the prototype of EXor variable stars. Its spectrum is very rich in emission lines, including many metallic lines with narrow and broad components. The presence of a close companion has also been proposed, based on radial velocity signatures. Aims. We use the metallic emission lines to study the accretion structures and to test the companion hypothesis. Methods. We analyse 54 spectra obtained during five years of quiescence time. We study the line profile variability and the radial velocity of the narrow and broad metallic emission lines. We use the velocity signatures of different species with various excitation conditions and their time dependency to track the dynamics associated with accretion. Results. We observe periodic velocity variations in the broad and the narrow line components, consistent with rotational modulation. The modulation is stronger for lines with higher excitation potentials (e.g. He II), which are likely produced in a confined area very close to the accretion shock. Conclusions. We propose that the narrow line components are produced in the post-shock region, while the broad components originate in the more extended, pre-shock material in the accretion column. All the emission lines suffer velocity modulation due to the rotation of the star. The broad components are responsible for the line-dependent veiling observed in EX Lupi. We demonstrate that a rotationally modulated line-dependent veiling can explain the radial velocity signature of the photospheric absorption lines, making the close-in companion hypothesis unnecessary. The accretion structure is locked to the star and very stable during the five years of observations. Not all stars with similar spectral types and accretion rates show the same metallic emission lines, which could be related to differences in temperature and density in their accretion structure(s). The contamination of photospheric signatures by accretion-related processes can be turned into a very useful tool for determining the innermost details of the accretion channels in the proximity of the star. The presence of emission lines from very stable accretion columns will nevertheless be a very strong limitation for the detection of companions by radial velocity in young stars, given the similarity of the accretion-related signatures with those produced by a companion.

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“…Typical values are about 1%, but the range is wide, reaching over 10% in the most active accretors (Calvet & Gullbring 1998;Johns-Krull & Gafford 2002, Ingleby et al 2013.…”

Section: Analysis: the Structure Of The Accretion Flowmentioning

confidence: 99%

Doppler probe of accretion onto a T Tauri star

Петров¹,

Gahm²,

Herczeg³

et al. 2014

A&A

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Context. The YY Ori stars are T Tauri stars with prominent time-variable redshifted absorption components that flank certain emission lines. S CrA, one of the brightest of these stars, affords the rare opportunity of directly probing the accretion processes on the line of sight to one of the components of this wide visual pair. Aims. We followed the spectral changes in S CrA to derive the physical structure of the accreting gas. Methods. A series of high-resolution spectra of the two components of S CrA was obtained during four nights with the UVES spectrograph at the Very Large Telescope. Results. We found that both stars are very similar with regard to surface temperature, radius, and mass. Variable redshifted absorption components are particularly prominent in the SE component. During one night, this star developed a spectrum unique among the T Tauri stars: extremely strong and broad redshifted absorption components appeared in many lines of neutral and ionized metals, in addition to those of hydrogen and helium. The absorption depths of cooler, low-ionization lines peak at low velocities -while more highly ionized lines have peak absorption depths at high velocities. The different line profiles indicate that the temperature and density of the accretion stream increase as material approaches the star. We derive the physical conditions of the flow at several points along the accretion funnel directly from the spectrum of the infalling gas. We estimated mass accretion rates of about 10 −7 M /yr, which is similar to that derived from the relation based on the strength of Hα emission line. Conclusions. This is the first time the density and temperature distributions in accretion flows around a T Tauri star have been inferred from observations. Compared with predictions from standard models of accretion in T Tauri stars, which assume a dipole stellar magnetic field, we obtained higher densities and a steeper temperature rise toward the star.

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Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra

Cited by 214 publications

References 94 publications

X-shooter spectroscopy of young stellar objects

X-shooter spectroscopy of young stellar objects

Accretion dynamics of EX Lupi in quiescence

Doppler probe of accretion onto a T Tauri star

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