Heating and Ionization of<i>X</i>‐Winds

Shang, Hsien; Glassgold, A. E.; Shu, Frank H.; Lizano, Susana

doi:10.1086/324197

Cited by 159 publications

(168 citation statements)

References 79 publications

Supporting

Mentioning

155

Contrasting

Unclassified

Order By: Relevance

“…It is, however, very difficult to estimate whether any of these models can explain the observed properties of the LVC emitting region derived in this paper or, even more, to use the observations to discriminate between the various mechanisms that can trigger an MHD wind and constrain the model parameters. In very few cases have the results of the MHD models and simulations been coupled with calculations of the temperature (Safier 1993a,b;Shang et al 1998Shang et al , 2002Cabrit et al 1999Cabrit et al , 2007Garcia et al 2001;Pesenti et al 2004;Pyo et al 2003Pyo et al , 2006Panoglou et al 2012), and they generally focused on jet-tracing lines for luminous, highly accreting TTS.…”

Section: Wind Modelsmentioning

confidence: 99%

X-shooter spectroscopy of young stellar objects

Natta

Testi

Alcalá

et al. 2014

A&A

126

View full text Add to dashboard Cite

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.

show abstract

Section: Wind Modelsmentioning

confidence: 99%

X-shooter spectroscopy of young stellar objects

Natta

Testi

Alcalá

et al. 2014

A&A

126

View full text Add to dashboard Cite

show abstract

“…As shown in Sauty & Tsinganos (1994, hereafter ST94), these self-similar models can be seen as a combination of stellar wind and X-wind models. Conversely to formal X-winds (Shu et al 1994;Shang et al 2002), they do not require that all fieldlines emerge from a single point of the disk in the form of a fan. Instead there is a smooth transition between the stellar wind and the disk jet.…”

Section: Stellar Jet Theorymentioning

confidence: 99%

Nonradial and nonpolytropic astrophysical outflows

Sauty

Méliani

Lima

et al. 2011

A&A

View full text Add to dashboard Cite

Context. A large sample of T Tauri stars exhibits optical jets, approximately half of which rotate slowly, only at ten per cent of their breakup velocity. The disk-locking mechanism has been shown to be inefficient to explain this observational fact. Aims. We show that low mass accreting T Tauri stars may have a strong stellar jet component that can effectively brake the star to the observed rotation speed. Methods. By means of a nonlinear separation of the variables in the full set of the MHD equations we construct semi-analytical solutions describing the dynamics and topology of the stellar component of the jet that emerges from the corona of the star. Results. We analyze two typical solutions with the same mass loss rate but different magnetic lever arms and jet radii. The first solution with a long lever arm and a wide jet radius effectively brakes the star and can be applied to the visible jets of T Tauri stars such as RY Tau. The second solution with a shorter lever arm and a very narrow jet radius may explain why similar stars, either weak line T Tauri stars (WTTS) or classical T Tauri stars (CTTS) do not all have visible jets. For instance, RY Tau itself seems to have different phases that probably depend on the activity of the star. Conclusions. First, stellar jets seem to be able to brake pre-main sequence stars with a low mass accreting rate. Second, jets may be visible only part time owing to changes in their boundary conditions. We also suggest a possible scenario for explaining the dichotomy between CTTS and WTTS, which rotate faster and do not have visible jets.

show abstract

“…We also include secondary heating of X-rays due to photoionization from the n = 2 state of atomic hydrogen and follow exactly the treatment of Shang et al(2002).…”

Section: B1 X-ray Spectrummentioning

confidence: 99%

Models of Chemistry, Thermal Balance, and Infrared Spectra from Intermediate‐Aged Disks around G and K Stars

Gorti¹,

Hollenbach²

2004

ApJ

138

171

View full text Add to dashboard Cite

We model gas and dust emission from regions 0.3−20 AU from a central low mass star in intermediate-aged (∼10 7 years) disks whose dust is fairly optically thin to stellar radiation. The models treat thermal balance and chemistry selfconsistently, and calculate the vertical density and temperature structure of the gas in a disk. The gas and dust temperatures are calculated separately. The models cover gas masses 10 −3 − 1 M J , dust masses 10 −7 − 10 −4 M J , and treat solar type (G and K) stars. We focus on mid-infrared and far-infrared emission lines from various gas species such as the rotational lines of H 2 , OH, H 2 O and CO molecules and the fine structure lines of carbon, oxygen, sulfur, iron, and silicon atoms and ions. These lines and the dust continuum are observable by the Spitzer Space Telescope, and future missions including SOFIA and the Herschel Space Observatory. We find that the [SI]25.23µm line is the strongest emission line for a wide range of disk and stellar parameters, followed by emission from [SiII]34.8µm, [FeII]26µm, and [OI]63µm. [FeI]24µm and rotational lines of OH and H 2 O are strong when gas masses are high ( 0.1 M J ). Emission from the rotational lines of H 2 is more difficult to detect, unless disk gas masses are substantial ( 0.1 M J ). For emission from H 2 lines to be observable and yet the dust be optically thin in stellar light, the ratio of gas to small sub-millimeter sized dust particle mass in the disk needs to be 1000, or at least an order of magnitude higher than that in the interstellar medium. This may be possible at intermediate stages in disk evolution, such as in the gas gathering stage of the core accretion scenario for giant planet formation, where most of the dust has coagulated into larger objects (≫ 1mm) but the gas has not yet fully dispersed. Whereas the absolute fluxes observed in some lines such as [FeI]24µm and H 2 S(0) 28µm primarily measure the gas mass in the disks, various line ratios diagnose the inner radius of the gas, and the radial temperature and surface density distribution of the gas. Many -2 -lines become optically thick and/or suffer chemical or thermal effects such that the line luminosities do not increase appreciably with increasing gas mass. We predict it may be difficult for the Spitzer Space Telescope to detect 1 M J of gas in optically thin (in dust) disks at distances 150 pc. The models presented here will be useful in future infrared studies of the timescale for the dispersion of gas in a planet-forming disk, and testing core accretion models of giant planet formation.

show abstract

Heating and Ionization ofX‐Winds

Cited by 159 publications

References 79 publications

X-shooter spectroscopy of young stellar objects

X-shooter spectroscopy of young stellar objects

Nonradial and nonpolytropic astrophysical outflows

Models of Chemistry, Thermal Balance, and Infrared Spectra from Intermediate‐Aged Disks around G and K Stars

Contact Info

Product

Resources

About