Extreme Active Molecular Jets in L1448c

Abstract

The protostellar jet driven by L1448C was observed in the SiO J=8-7 and CO J=3-2 lines and 350 GHz dust continuum at ∼1 ′′ resolution with the Submillimeter Array (SMA). A narrow jet from the northern source L1448C(N) was observed in the SiO and the high-velocity CO. The jet consists of a chain of emission knots with an inter-knot spacing of ∼2 ′′ (500 AU) and a semi-periodic velocity variation. These knots are likely to be the internal bow shocks in the jet beam that were formed due to the periodic variation of the ejection velocity with a period of ∼15-20 yr. The innermost pair of knots, which are significant in the SiO map but barely seen in the CO, are located at ∼1 ′′ (250 AU) from the central source, L1448C(N). Since the dynamical time scale for the innermost pair is only ∼10 yr, SiO may have been formed in the protostellar wind through the gas-phase reaction, or been formed on the dust grain and directly released into the gas phase by means of shocks. It is found that the jet is extremely active with a mechanical luminosity of ∼7 L ⊙ , which is comparable to the bolometric luminosity of the central source (7.5 L ⊙ ). The mass accretion rate onto the protostar derived from the mass-loss rate is ∼10 −5 M ⊙ yr −1 . Such a high mass accretion rate suggests that the mass and the age of the central star are 0.03-0.09 M ⊙ and (4-12)×10 3 yr, respectively, implying that the central star is in the very early stage of protostellar evolution. The low-velocity CO emission delineates two Vshaped shells with a common apex at L1448C(N). The kinematics of these shells are reproduced by the model of a wide opening angle wind. The co-existence of the highly-collimated jets and the wide-opening angle shells can be explained by the "unified X-wind model" in which highly-collimated jet components correspond to the on-axis density enhancement of the wide-opening angle wind. The CO J=3-2 map also revealed the second outflow driven by the southern source L1448C(S) located at ∼8.3 ′′ (2000 AU) from L1448C(N). Although L1448C(S) is

Water in low-mass star-forming regions withHerschel(WISH-LM)

“…The RADEX models that match the H 2 O line emission best predict that the filling factor for the EHV component is very small, <0.01. Such low values agree with high spatialresolution observations showing this component to be confined to the molecular jet and consisting of several sub-arcsec knots (e.g., Hirano et al 2010). The model furthermore predicts that the ground-state transitions have optical depths in excess of 100 (Fig.…”

“…In the lower-T scenario, H 2 O will not form in the quantities observed here implying that the temperature is high in the bullets or that H 2 O is not formed in the gas phase. The gas-phase production of H 2 O is in agreement with models of continuous spherical wind models of Glassgold et al (1991), where the formation takes place from a dust-free atomic gas in sufficient quantities if the mass-loss rate exceeds 10 −5 M yr −1 , which is to be compared to the time-averaged mass-loss rate in the jet of ∼10 −6 M yr −1 (Hirano et al 2010). The mass loss rate traced directly by the bullets is episodic (and thus higher than the time-averaged value) and the wind is not spherical, i.e., it is plausible that the H 2 O abundance is consistent with production in the IWS from atomic gas.…”

“…Low-mass star formation is accompanied by the launch of powerful jets that drive strong shocks into the parental material (e.g., Arce et al 2007), both in the form of shell shocks that interact with the molecular envelope, and in the form of the jet itself (e.g., Hirano et al 2010). The jets are generally not uniform, but consist of small condensations ("bullets" 1 ), that can be attributed to internal working surfaces caused by episodic ejection of material from the protostar (Santiago-García et al 2009).…”

“…The bullets are clearly visible in other shock tracers such as SiO (e.g. Nisini et al 2007), and have been imaged at high spatial resolution using interferometers (e.g., Guilloteau et al 1992;Hirano et al 2010 programme further explore the chemical and excitation conditions of shocked gas in low-mass star-forming regions.…”

First results from the CALYPSO IRAM-PdBI survey

“…So far, a quite limited number of Class 0 jets has been observed at sub-arcsecond angular resolution (needed to disentangle the jet and the outflow cavities): HH211 (Lee et al 2007(Lee et al , 2009(Lee et al , 2010, HH212 Lee et al 2008), IRAS04166+2706 (Tafalla et al 2010), and L1448-C (Maury et al 2010;Hirano et al 2010). The IRAM Plateau de Bure Interferometer (PdBI) large program CALYPSO 1 (Continuum and Lines from Young ProtoStellar Objects) is correcting this situation by providing the first sub-arcsecond statistical study of inner jet properties in nearby low-luminosity Class 0 sources in combination with studies of the envelopes, disks, and multiplicity structure.…”