The small-scale HH34 IRS jet as seen by X-shooter

Abstract

Context. Atomic jets are a common phenomenon among young stars, being intimately related to disk accretion. Most studies have been performed on jets from pre-main sequence stars. However, to date very little detailed information has been gathered on jets from young embedded low mass sources (the so-called class I stars), especially in the inner jet region. Aims. We exploit a diagnostic analysis based on multiwave spectroscopic observations to infer kinematics and physical conditions of the inner region of the prototypical class I jet from HH34 IRS. Methods. We use a deep X-shooter spectrum covering the wavelength range 350−2300 nm at resolution between ∼8000 and ∼18 000 (i.e., ∆V ∼ 17−27 km s −1 ), which allows us to detect lines in a wide range of excitation conditions (from E up ∼ 8000 to ∼31 000 cm −1 ) and to study their kinematics. Statistical equilibrium and ionization models are adopted to derive the jet main physical parameters. Results. We separately derive the physical conditions for the extended high velocity jet (HVC, V r ∼ −100 km s −1 ) and for the low velocity and compact gas (LVC, V r ∼ −20−50 km s −1 ) located on-source. Close to the jet base (<200 AU from source) the HVC gas is mostly neutral (x e < 0.1) and very dense (n H > 5 × 10 5 cm −3 ). The LVC gas has the same density and A V as the HVC, but it is at least a factor of two colder. Iron abundance in the HVC is consistent with the solar value, while it is a factor of 3 subsolar in the LVC, suggesting an origin of the LVC gas from a dusty disk. From the derived total density we infer that the jet mass flux rate is >5 × 10 −7 M yr −1 . We find that the relationships between accretion luminosity and permitted line luminosity derived for T Tauri stars cannot be directly extended to class I sources embedded in reflection nebulae since the permitted lines are seen through scattered light. An accretion rate of ∼7 × 10 −6 M yr −1 is instead derived from an empirical relationship connectingṀ acc with L([O i])(HVC).Conclusions. The class I HH34 IRS jet at small scale shares many kinematical and physical properties with the jets from the most active classical T Tauri (CTT) stars. However, the HH34 IRS jet is denser as a consequence of the larger mass ejection rate with respect to typical values in CTTs jets. These findings suggests that the acceleration and excitation mechanisms in collimated jets are not influenced by evolution and are similar in CTTs and in still embedded sources with high accretion rates.

Connection between jets, winds and accretion in T Tauri stars

“…The log(L [O i]HVC ) vs. logṀ acc correlation is particularly useful to indirectly estimate the mass accretion rate in moderately embedded sources driving jets, where the permitted lines or the LVC emission region might be subject to large extinctions or scattering (e.g. Nisini et al 2016).…”

GIARPS High-resolution Observations of T Tauri stars (GHOsT)

“…Optical high-resolution observations of CTT stars have mainly addressed the kinematic properties of the [O i]630 line or performed a diagnostic analysis based on very few lines and exploiting a limited diagnostic range (e.g., Fang et al 2018, Banzatti et al 2019). On the other hand, recent VLT/X-shooter observations have shown the potential of combining several diagnostic forbidden lines in the optical and infrared (IR) ranges to constrain the physical properties of the emitting gas associated with the jets (Bacciotti et al 2011, Giannini et al 2013, Nisini et al 2016.…”

“…Therefore, the measurement of the depletion degree in the different velocity components is crucial to shed light on jet formation, as it depends upon both the location of the launching region and the ability of the jet to destroy the dusty disk material. Several observations have indicated that a significant degree of dust depletion occurs in the jet region close to the disk (e.g., Nisini et al 2005, Podio et al 2006, Giannini et al 2013, and that the depletion might decrease with jet velocity (Agra-Amboage et al 2011, Nisini et al 2016), suggesting that high-velocity jet channels preferentially originate in dust-free disk regions.…”

Stacked Average Far-infrared Spectrum of Dusty Star-forming Galaxies from the Herschel/SPIRE Fourier Transform Spectrometer∗

“…Because the bolometric temperature is not much higher than the Class 0/I boundary (70 K), the age of this protostar may be somewhat older than the typical lifetime of the Class 0 phase (∼10 5 years; Evans et al 2009). The prominent HH 34 jet has been studied extensively (Reipurth et al 1986(Reipurth et al , 2002Rodríguez & Reipurth 1996;Nisini et al 2016). The jet extends to a parsec-scale outflow that has a dynamic age of ∼10,000 years (Bally & Devine 1994;Devine et al 1997).…”