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First Large Scale Herbig-Haro Jet Driven by a Proto-Brown Dwarf

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First Large Scale Herbig-Haro Jet Driven by a Proto-Brown Dwarf First large scale Herbig-Haro jet driven by a proto-brown dwarf B. Riaz Max-Planck-Institut f¨urExtraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany C. Brice~no Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena, Chile E. T. Whelan Maynooth University Department of Experimental Physics, National University of Ireland Maynooth, Maynooth Co. Kildare, Ireland and S. Heathcote Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena, Chile Received ; accepted arXiv:1705.01170v1 [astro-ph.SR] 2 May 2017 { 2 { ABSTRACT We report the discovery of a new Herbig-Haro jet, HH 1165, in SOAR narrow- band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow-shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ∼36 MJup and a bolometric luminosity of ∼0.1 L . High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmet- rical morphology for HH 1165. We find a puzzling picture wherein the north-west part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system. Subject headings: Herbig-Haro objects | stars: jets | Brown dwarfs | stars: low-mass | stars: winds, outflows | open clusters and associations: individual (σ Orionis) { 3 { 1. Introduction Herbig-Haro (HH) jets are so called as they are made up of a string of shocks or HH objects which represent individual ejection events (e.g., Reipurth & Bally 2001). These atomic jets are most often associated with Class 0/I low mass young stellar objects (YSOs), and are important as they offer a way in which to study the mass loss history of the driving source (e.g., Frank et al. 2014). They can be parsec scale in length and their morphology is greatly affected by the ejection properties of the source and the environment in which they are propagating (e.g., Bally 2011). On scales of < 0.1 pc, they are characterized by closely spaced knots which show evidence of internal shock waves likely caused by supersonic velocity jumps. It can be strongly argued that these velocity jumps are a result of intrinsic ejection variability (e.g., Bally et al. 2001; 2002; Frank et al. 2014). On parsec scales, the HH objects tend to be more sparsely distributed and fragmented. Interactions with the environment can also cause the HH jets to become bent, and to take on a C- or S-shaped morphology (e.g., Bally et al. 2006). While most of what is understood about outflows comes from observations of low mass YSOs, it is now 10 years since outflows were first associated with objects at the bottom of the mass spectrum of star forming regions i.e. young brown dwarfs (0.08 M to 0.13 M ) (e.g., Whelan et al. 2005). Although numerous outflows have been detected in the mass range from brown dwarfs to very low mass stars (0.13 M to 0.2 M ), in a majority of the cases, these are micro-jets with projected lengths of ≤0.03 pc (e.g., Whelan 2014). The brown dwarfs or very low-mass stars driving these micro-jets are all optically visible, and are therefore taken to be analogous to Class II YSOs. Some notable Class II brown dwarfs and very low-mass stars that are known to drive micro-jets are Par-Lup3-4 and ISO143, with projected lengths of < 0.004 pc (Comer´on& Fern´andez2011, Joergens et al. 2012, Whelan et al. 2012; 2014). Recently, we have identified a new micro-jet, HH 1158, which is { 4 { driven by a Class Flat1 very low-mass star, and has a projected length of ∼0.01 pc (Riaz & Whelan 2015). Here we report the first observation of a large-scale (∼0.26 pc) HH jet driven by a candidate proto-brown dwarf. This jet has been designated the HH number HH 1165. The driving source of the jet is a very low-luminosity Class I object, Mayrit 1701117 (hereafter M1701117), which lies at the cusp of the stellar/sub-stellar boundary and will likely evolve into a brown dwarf. HH 1165 shows many of the characteristics of a large-scale jet including multiple knots, bow-shocks, a C-shaped morphology and a reflection nebula. The first hints of a jet driven by M1701117 were seen in moderate resolution spectra presented in Riaz et al. (2015). Follow-up UV-Visual Echelle Spectrometer (UVES) spectra provided more information on the jet close to the driving source. Images taken with SOAR have revealed the spectacular nature of the jet. In this paper, we present both the SOAR and UVES data. While the jet is not extended in the UVES data, much can still be learnt from the various accretion and outflow associated spectral line diagnostics. Sect. 2 provides further information on the driving source, and a description of the various sets of observations and the data reduction. Sect. 3 presents the results from the data analysis of spectra and images. A discussion on the morphology of the jet and the different features observed is presented in Sect. 4, along with a comparison with some of the well-known large-scale HH jets driven by protostellar objects. 1The Class Flat is considered to be an intermediate stage between Class I and II (e.g., Greene et al. 1994). { 5 { 2. Target, Observations and Data Reduction 2.1. Target properties Figure 1 shows a wide 1×1 degree view of the surroundings of the HH 1165 jet in the 0 00 WISE mid-infrared 3.4µm image. The driving source M1701117 (05h40m25s.8, -02◦48 55. 4) lies at the outer periphery of the σ Orionis cluster (387±1.3 pc; Schaefer et al. 2016; Sim´on-Diazet al. 2015). It is located ∼3.2 pc from the σ Orionis cluster core, ∼1 pc from the south-west edge of the L1630 molecular cloud in Orion B, and also lies in close proximity to the massive B2IV-type star HR 1950, just ∼0.33 pc south-east from the source (Fig. 1). M1701117 was first discovered and catalogued by Caballero (2008). Riaz et al. (2015) investigated the multi-wavelength properties of this source and concluded that it is a very low-luminosity Class I object, with a total (gas + dust) mass of ∼36 MJup, and a bolometric luminosity of only ∼0.1 L . The mass of the central object in this Class I system can be constrained to within the sub-stellar mass regime (∼0.04 { 0.08 M ), using the measured bolometric luminosity and numerical simulations of stellar evolution, as discussed in Riaz et al. (2016). Considering the very low mass reservoir in the (envelope+disk) for this system, and the fact that M1701117 drives a powerful outflow that will further dissipate the circumstellar envelope material, M1701117 will most likely evolve into a brown dwarf, and can be considered as a strong candidate proto-brown dwarf. Using multiple diagnostics observed in moderate resolution (R ∼1000) optical spectra, Riaz et al. (2015) estimated a _ −10 −1 _ mass accretion rate (Macc) of ∼ 6.4 × 10 M yr and a mass outflow rate (Mout) of ∼ −9 −1 1 × 10 M yr , for M1701117. M1701117 is still considered a \candidate" member of σ Orionis because of lying at the periphery of the cluster. The long Mayrit numbers imply that they are located far from { 6 { Fig. 1.| The WISE 3.4µm 1x1 degree image showing the surroundings of the HH 1165 jet. Also marked are the locations of the σ Orionis cluster core to the west, and the B2-type star HR 1950 located close (∼0.33 pc) to the driving source M1701117. Blue squares mark the locations of some known B-type stars located near the ionization front seen brightly towards the east of M1701117. the cluster centre, where there is contamination by other neighbouring young star-forming regions (Alnilam, Orionis, Horsehead Nebula). The latest measurement on the proper motion for M1701117 using 17 astrometric epochs from several surveys is µα cos δ, µδ = -2±2, -6.3±1.9 mas/a (J. Caballero; priv. comm.). The proper motion of M1701117 is compatible within 1.0σ-2.5σ with the mean value for the σ Orionis cluster (+2.2±1, -0.5±1.0 mas/a), but also with that of other very young region towards Orion (except for the 32 Ori association). The third Gaia data release in 2018 can disentangle the tangential { 7 { velocities of M1701117 and other young stars in the Horsehead Nebula and σ Orionis area.
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