Which jet launching mechanism(s) in T Tauri stars?

Abstract

Aims. We examine whether ejection phenomena from accreting T Tauri stars can be described by only one type of self-collimated jet model. Methods. We present analytical kinematic predictions valid soon after the Alfvén surface for all types of steady magnetically selfconfined jets. Results. We show that extended disc winds, X-winds, and stellar winds occupy distinct regions in the poloidal speed vs. specific angular momentum plane. Comparisons with current observations of T Tauri jets yield quantitative constraints on the range of launching radii, magnetic lever arms, and specific energy input in disc and stellar winds. Implications on the origin of jet asymmetries and disc magnetic fields are outlined. Conclusions. We argue that ejection phenomena from accreting T Tauri stars most likely include three dynamical components: (1) an outer self-collimated steady disc wind carrying most of the mass-flux in the optical jet (when present); confining (2) a pressure-driven coronal stellar wind; and (3) a hot inner flow made of blobs sporadically ejected from the magnetopause. If the stellar magnetic moment is parallel to the disc magnetic field, then the highly variable inner flow resembles a "Reconnection X-wind", that has been proven to efficiently brake down an accreting and contracting young star. If the magnetic moment is anti-parallel, then larger versions of the solar coronal mass ejections are likely to occur. The relative importance of these three components in the observed outflows and the range of radii involved in the disc wind are expected to vary with time, from the stage of embedded source to the optically revealed T Tauri star phase.

Observational and numerical tests of jet models in young stars

“…Synthetic predictions calculated for steady solutions compare well with high resolution observations such as: apparent jet widths (Garcia et al 2001, Ray et al 2007, Stute et al 2009, maximum poloidal speeds and drop in velocity away from the jet axis (Cabrit 2007), and atomic jet rotation signatures (Pesenti et al 2004). The latter require "warm" disk winds with a moderate magnetic lever arm λ 13, launched out to a maximum radius of 0.1-3 AU, yielding an ejection to accretion ratio 4%-13% in the observed range (Ferreira et al 2006). However, T Tauri jet rotation signatures are still tentative due to possible contamination by shock asymmetries (e.g.…”

“…However, launching from the stellar surface meets three caveats in explaining observed jets: (i) energetic difficulty to eject >1% of the accretion rate (Cranmer 2009, Ferreira et al 2006, (ii) lack of dust, whereas iron and calcium depletion is measured in several jets (Podio et al 2006, Dionatos et al 2009), (iii) insufficient collimation (Bogovalov & Tsinganos 2001, Fendt 2009, Cabrit 2007 …”

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

“…Disk photoevaporation by X-ray and UV photons potentially provides an inside-out dispersal mechanism, although this is proposed to be efficient only beyond the radius where the gas is gravitationally bound to the star (1-2 au in disks around solar-mass stars). Another removal mechanism could be through portions of MHD winds (e.g., Ferreira et al 2006;Bai 2016) that may be probed at optical wavelengths through a low-velocity component in the forbidden oxygen lines (Simon et al 2016). A slow disk wind has been proposed to contribute also to the CO narrow component in double-component disks (Bast et al 2011;Pontoppidan et al 2011a), and may play a role in the depletion of molecular gas in inner disks.…”

“…After a gap is opened, the inner disk is expected to be drained onto the central star by viscous accretion, and the inner hole would rapidly grow to larger radii under the effect of photoevaporation. Disks may also disperse under removal of gas by magnetohydrodynamic (MHD) winds (e.g., Ferreira et al 2006;Bai 2016). Another process that has been shown to open gaps in disks is the formation of giant planets (e.g., Lin & Papaloizou 1986;Kley & Nelson 2012, among several others).…”

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…This review does not deal with jet-launching processes nor with the general properties of jets and their relation to accretion disks. These topics are reviewed and studied in many other papers where more references can be found (e.g., Mirabel & Rodríguez 1999;Fender & Belloni 2004;Ferreira et al 2006;Livio 2011;Fender & Belloni 2012;Pudritz et al 2012;McKinney et al 2013;Zanni & Ferreira 2013;Frank et al 2014;Lasota et al 2014;Lovelace et al 2014;McKinney et al 2014). I assume that whenever the accreted gas has a large enough specific angular momentum jets are launched.…”