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Takaishi 髙石, Daisuke 大輔, Yusuke 裕介 Tsukamoto 塚本, Miyu 未宇 Kido 城戸, et al. "Formation of Unipolar Outflow and Protostellar Rocket Effect in Magnetized Turbulent Molecular Cloud Cores." Astrophysical Journal 963, no. 1 (2024): 20. http://dx.doi.org/10.3847/1538-4357/ad187a.
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Abstract Observed protostellar outflows exhibit a variety of asymmetrical features, including remarkable unipolar outflows and bending outflows. Revealing the formation and early evolution of such asymmetrical protostellar outflows, especially the unipolar outflows, is essential for a better understanding of the star and planet formation because they can dramatically change the mass accretion and angular momentum transport to the protostars and protoplanetary disks. Here we perform three-dimensional nonideal magnetohydrodynamics simulations to investigate the formation and early evolution of the asymmetrical protostellar outflows in magnetized turbulent isolated molecular cloud cores. We find, for the first time to our knowledge, that the unipolar outflow forms even in the single low-mass protostellar system. The results show that the unipolar outflow is driven in the weakly magnetized cloud cores with the dimensionless mass-to-flux ratios of μ = 8 and 16. Furthermore, we find the protostellar rocket effect of the unipolar outflow, which is similar to the launch and propulsion of a rocket. The unipolar outflow ejects the protostellar system from the central dense region to the outer region of the parent cloud core, and the ram pressure caused by its ejection suppresses the driving of additional new outflows. In contrast, the bending bipolar outflow is driven in the moderately magnetized cloud core with μ = 4. The ratio of the magnetic to turbulent energies of a parent cloud core may play a key role in the formation of asymmetrical protostellar outflows.
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Nakamura, Fumitaka, and Zhi-Yun Li. "Protostellar turbulence in cluster forming regions of molecular clouds." Proceedings of the International Astronomical Union 2, S237 (2006): 306–10. http://dx.doi.org/10.1017/s1743921307001640.
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AbstractWe perform 3D MHD simulations of cluster formation in turbulent magnetized dense molecular clumps, taking into account the effect of protostellar outflows. Our simulation shows that initial interstellar turbulence decays quickly as several authors already pointed out. When stars form, protostellar outflows generate and maintain supersonic turbulence that have a power-law energy spectrum of Ek ~ k−2, which is somewhat steeper than those of driven MHD turbulence simulations. Protostellar outflows suppress global star formation, although they can sometimes trigger local star formation by dynamical compression of pre-existing cores. Magnetic field retards star formation by slowing down overall contraction. Interplay of protostellar outflows and magnetic field generates large-amplitude Alfven and MHD waves that transform outflow motions into turbulent motions efficiently. Cluster forming clumps tend to be in dynamical equilibrium mainly due to dynamical support by protostellar outflow-driven turbulence (hereafter, protostellar turbulence).
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Skretas, I. M., and L. E. Kristensen. "Connecting Galactic and extragalactic outflows: From the Cygnus-X cluster to active galaxies." Astronomy & Astrophysics 660 (April 2022): A39. http://dx.doi.org/10.1051/0004-6361/202141944.
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Context. Molecular outflows are commonly detected originating from both protostellar and extragalactic sources. Separate studies of low-mass, isolated high-mass, and extragalactic sources reveal scaling relations connecting the force carried by an outflow and the properties of the source that drives it, as for example the mass and luminosity. Aims. The aim of this work is twofold: first, to examine the effects, if any, of clustered star formation on the protostellar outflows and their scaling relations and, second, to explore the possibility that outflows varying in scale and energetics by many orders of magnitude are consistent with being launched by the same physical processes. Methods. To that end, high-angular resolution CO J = 3–2 observations were used of ten high-mass protostars in the Cygnus-X molecular cloud, obtained at the SubMilliMeter Array as part of the Protostellar Interferometric Line Survey of Cygnus-X (PILS-Cygnus). From these data, the outflow force, that is the momentum ejection rate, was measured. In addition, an extended sample of protostellar and extragalactic outflow-force measurements was assembled from existing literature to allow for a direct comparison of the scaling relations of the two types of outflows. Results. Molecular outflows were detected originating from all ten sources of the PILS-Cygnus survey, and their outflow forces are found to be in close agreement with measurements from the literature. In addition, the comparison of the protostellar and extragalactic sources reveals, with 95% confidence, that Class 0 protostars and extragalactic sources follow the same outflow force–bolometric luminosity correlation. Conclusions. The close agreement between the Cygnus-X sources and sources of similar envelope mass and bolometric luminosity suggests that clustered star formation has no significant effect on protostellar outflows. We find a strong indication that protostellar and extragalactic outflows are consistent with having a similar launch mechanism. The existence of such a mechanism would enable the development of a single universal outflow launch model, although more observations are required in order to verify this connection.
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Bally, John. "Protostellar Outflows." Annual Review of Astronomy and Astrophysics 54, no. 1 (2016): 491–528. http://dx.doi.org/10.1146/annurev-astro-081915-023341.
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Lin, Shuping. "Protostellar Outflows." Highlights in Science, Engineering and Technology 61 (July 30, 2023): 206–14. http://dx.doi.org/10.54097/hset.v61i.10297.
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The formation of massive stars differs from low-mass stars due to their rapid evolution, relatively low abundance, and their burial within molecular clouds, making observations more challenging. Moreover, the mechanisms give rise to the formation of O-type and B-type stars, in particular, differ from those responsible for the formation of low-mass stars. The paper presents an overview of the two main theories that have been proposed to explain the formation of massive stars: accretion and collision theories. The paper also investigates several mainstream theories of protostellar outflows during the massive star formation phase, and describe the model and their simulation of these theories. These results may provide useful references and guidance for future studies on the formation of massive stars.
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Gómez-Ruiz, A. I., A. Gusdorf, S. Leurini, et al. "Warm gas in protostellar outflows." Astronomy & Astrophysics 629 (September 2019): A77. http://dx.doi.org/10.1051/0004-6361/201424156.
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Context. OMC-2/3 is one of the nearest embedded cluster-forming regions that includes intermediate-mass protostars at early stages of evolution. A previous CO (3–2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases. Aims. The present work presents a study of the warm gas in the high-velocity emission from several outflows found in CO (3–2) emission by previous observations, determines their physical conditions, and makes a comparison with previous results in low-mass star-forming regions. Methods. We used the CHAMP+ heterodyne array on the APEX telescope to map the CO (6–5) and CO (7–6) emission in the OMC-2 FIR 6 and OMC-3 MMS 1-6 regions, and to observe 13CO (6–5) at selected positions. We analyzed these data together with previous CO (3–2) observations. In addition, we mapped the SiO (5–4) emission in OMC-2 FIR 6. Results. The CO (6–5) emission was detected in most of the outflow lobes in the mapped regions, while the CO (7–6) was found mostly in the OMC-3 outflows. In the OMC-3 MMS 5 outflow, a previously undetected extremely high-velocity gas was found in CO (6–5). This extremely high-velocity emission arises from the regions close to the central object MMS 5. Radiative transfer models revealed that the high-velocity gas from MMS 5 outflow consists of gas with nH2 = 104–105 cm−3 and T > 200 K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of nH2 > 104 cm−3 were found. Conclusions. The physical conditions and kinematic properties of the young intermediate-mass outflows presented here are similar to those found in outflows from Class 0 low-mass objects. Due to their excitation requirements, mid − J CO lines are good tracers of extremely high-velocity gas in young outflows likely related to jets.
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Nony, T., F. Motte, F. Louvet, et al. "Episodic accretion constrained by a rich cluster of outflows." Astronomy & Astrophysics 636 (April 2020): A38. http://dx.doi.org/10.1051/0004-6361/201937046.
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Context. The accretion history of protostars remains widely mysterious, even though it represents one of the best ways to understand the protostellar collapse that leads to the formation of stars. Aims. Molecular outflows, which are easier to detect than the direct accretion onto the prostellar embryo, are here used to characterize the protostellar accretion phase in W43-MM1. Methods. The W43-MM1 protocluster hosts a sufficient number of protostars to statistically investigate molecular outflows in a single, homogeneous region. We used the CO(2–1) and SiO(5–4) line datacubes, taken as part of an ALMA mosaic with a 2000 AU resolution, to search for protostellar outflows, evaluate the influence that the environment has on these outflows’ characteristics and put constraints on outflow variability in W43-MM1. Results. We discovered a rich cluster of 46 outflow lobes, driven by 27 protostars with masses of 1−100 M⊙. The complex environment inside which these outflow lobes develop has a definite influence on their length, limiting the validity of using outflows’ dynamical timescale as a proxy of the ejection timescale in clouds with high dynamics and varying conditions. We performed a detailed study of Position–Velocity diagrams of outflows that revealed clear events of episodic ejection. The time variability of W43-MM1 outflows is a general trend and is more generally observed than in nearby, low- to intermediate-mass star-forming regions. The typical timescale found between two ejecta, ~500 yr, is consistent with that found in nearby protostars. Conclusions. If ejection episodicity reflects variability in the accretion process, either protostellar accretion is more variable, or episodicity is easier to detect in high-mass star-forming regions than in nearby clouds. The timescale found between accretion events could result from instabilities associated with bursts of inflowing gas arising from the close dynamical environment of high-mass star-forming cores.
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Tokuda, Kazuki, Sarolta Zahorecz, Yuri Kunitoshi, et al. "The First Detection of a Protostellar CO Outflow in the Small Magellanic Cloud with ALMA." Astrophysical Journal Letters 936, no. 1 (2022): L6. http://dx.doi.org/10.3847/2041-8213/ac81c1.
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Abstract Protostellar outflows are one of the most outstanding features of star formation. Observational studies over the last several decades have successfully demonstrated that outflows are ubiquitously associated with low- and high-mass protostars in solar-metallicity Galactic conditions. However, the environmental dependence of protostellar outflow properties is still poorly understood, particularly in the low-metallicity regime. Here we report the first detection of a molecular outflow in the Small Magellanic Cloud with 0.2 Z ⊙, using Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.1 pc toward the massive protostar Y246. The bipolar outflow is nicely illustrated by high-velocity wings of CO(3–2) emission at ≳15 km s−1. The evaluated properties of the outflow (momentum, mechanical force, etc.) are consistent with those of the Galactic counterparts. Our results suggest that the molecular outflows, i.e., the guidepost of the disk accretion at the small scale, might be universally associated with protostars across the metallicity range of ∼0.2–1 Z ⊙.
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Rohde, P. F., S. Walch, D. Seifried, A. P. Whitworth, and S. D. Clarke. "Protostellar outflows: a window to the past." Monthly Notices of the Royal Astronomical Society 510, no. 2 (2021): 2552–71. http://dx.doi.org/10.1093/mnras/stab3572.
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ABSTRACT During the early phases of low-mass star formation, episodic accretion causes the ejection of high-velocity outflow bullets, which carry a fossil record of the driving protostar’s accretion history. We present 44 SPH simulations of $1\, {{\mathrm{M}}}_{\odot }$ cores, covering a wide range of initial conditions, and follow the cores for five free-fall times. Individual protostars are represented by sink particles, and the sink particles launch episodic outflows using a sub-grid model. The Optics algorithm is used to identify individual episodic bullets within the outflows. The parameters of the overall outflow and the individual bullets are then used to estimate the age and energetics of the outflow, and the accretion events that triggered it, and to evaluate how reliable these estimates are, if observational uncertainties and selection effects (like inclination) are neglected. Of the commonly used methods for estimating outflow ages, it appears that those based on the length and speed of advance of the lobe are the most reliable in the early phases of evolution, and those based on the width of the outflow cavity and the speed of advance are most reliable during the later phases. We describe a new method that is almost as accurate as these methods, and reliable throughout the evolution. In addition, we show how the accretion history of the protostar can be accurately reconstructed from the dynamics of the bullets if each lobe contains at least two bullets. The outflows entrain about 10 times more mass than originally ejected by the protostar.
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Myers, Philip C., Michael M. Dunham, and Ian W. Stephens. "Can Protostellar Outflows Set Stellar Masses?" Astrophysical Journal 949, no. 1 (2023): 19. http://dx.doi.org/10.3847/1538-4357/acca74.
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Abstract The opening angles of some protostellar outflows appear too narrow to match the expected core–star mass efficiency (SFE) = 0.3–0.5, if the outflow cavity volume traces outflow mass, with a conical shape and a maximum opening angle near 90°. However, outflow cavities with a paraboloidal shape and wider angles are more consistent with observed estimates of the SFE. This paper presents a model of infall and outflow evolution based on these properties. The initial state is a truncated singular isothermal sphere which has mass ≈ 1 M ⊙, freefall time ≈ 80 kyr, and small fractions of magnetic, rotational, and turbulent energy. The core collapses pressure free as its protostar and disk launch a paraboloidal wide-angle wind. The cavity walls expand radially and entrain envelope gas into the outflow. The model matches the SFE values when the outflow mass increases faster than the protostar mass by a factor 1–2, yielding protostar masses typical of the IMF. It matches the observed outflow angles if the outflow mass increases at nearly the same rate as the cavity volume. The predicted outflow angles are then typically ∼50° as they increase rapidly through the stage 0 duration of ∼40 kyr. They increase more slowly up to ∼110° during their stage I duration of ∼70 kyr. With these outflow rates and shapes, the model predictions appear consistent with observational estimates of the typical stellar masses, SFEs, stage durations, and outflow angles, with no need for external mechanisms of core dispersal.
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Duffin, Dennis F., and Ralph E. Pudritz. "Discs, outflows, and feedback in collapsing magnetized cores." Proceedings of the International Astronomical Union 6, S270 (2010): 291–95. http://dx.doi.org/10.1017/s1743921311000536.
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AbstractThe pre-stellar cores in which low mass stars form are generally well magnetized. Our simulations show that early protostellar discs are massive and experience strong magnetic torques in the form of magnetic braking and protostellar outflows. Simulations of protostellar disk formation suggest that these torques are strong enough to suppress a rotationally supported structure from forming for near critical values of mass-to-flux. We demonstrate through the use of a 3D adaptive mesh refinement code – including cooling, sink particles and magnetic fields – that one produces transient 1000 AU discs while simultaneously generating large outflows which leave the core region, carrying away mass and angular momentum. Early inflow/outflow rates suggest that only a small fraction of the mass is lost in the initial magnetic tower/jet event.
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Walawender, Josh, Grace Wolf-Chase, Michael Smutko, JoAnn OLinger-Luscusk, and Gerald Moriarty-Schieven. "PROTOSTELLAR OUTFLOWS IN L1340." Astrophysical Journal 832, no. 2 (2016): 184. http://dx.doi.org/10.3847/0004-637x/832/2/184.
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Froebrich, Dirk, Michael D. Smith, and Jochen Eislöffel. "Shocks in Protostellar Outflows." Astrophysics and Space Science 287, no. 1-4 (2003): 217–20. http://dx.doi.org/10.1023/b:astr.0000006227.85806.85.
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Mignon-Risse, R., M. González, and B. Commerçon. "Collapse of turbulent massive cores with ambipolar diffusion and hybrid radiative transfer." Astronomy & Astrophysics 656 (December 2021): A85. http://dx.doi.org/10.1051/0004-6361/202141648.
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Context. Most massive protostars exhibit bipolar outflows. Nonetheless, there is no consensus regarding the mechanism at the origin of these outflows, nor on the cause of the less-frequently observed monopolar outflows. Aims. We aim to identify the origin of early massive protostellar outflows, focusing on the combined effects of radiative transfer and magnetic fields in a turbulent medium. Methods. We use four state-of-the-art radiation-magnetohydrodynamical simulations following the collapse of massive 100 M⊙ pre-stellar cores with the RAMSES code. Turbulence is taken into account via initial velocity dispersion. We use a hybrid radiative transfer method and include ambipolar diffusion. Results. Turbulence delays the launching of outflows, which appear to be mainly driven by magnetohydrodynamical processes. We study both the magnetic tower flow and the magneto-centrifugal acceleration as possible origins. Both contribute to the acceleration and the former operates on larger volumes than the latter. Our finest resolution, 5 AU, does not allow us to get converged results on magneto-centrifugally accelerated outflows. Radiative acceleration takes place as well, dominates in the star vicinity, enlarges the outflow extent, and has no negative impact on the launching of magnetic outflows (up to M ~17 M⊙, L ~ 105 L⊙). We observe mass outflow rates of 10−5−10−4 M⊙ yr−1 and momentum rates of the order ~10−4 M⊙ km s−1 yr−1. The associated opening angles (20−30deg when magnetic fields dominate) are in a range between observed values for wide-angle outflows and collimated outflows. If confirmed with a finer numerical resolution at the outflow interface, this suggests additional (de-)collimating effects. Outflows are launched nearly perpendicular to the disk and are misaligned with the initial core-scale magnetic fields, in agreement with several observational studies. In the most turbulent run, the outflow is monopolar. Conclusions. Magnetic processes are dominant over radiative ones in the acceleration of massive protostellar outflows of up to ~17 M⊙. Turbulence perturbs the outflow launching and is a possible explanation for monopolar outflows.
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Xu, Duo, Stella S. R. Offner, Robert Gutermuth, Shuo Kong, and Hector G. Arce. "A Census of Protostellar Outflows in Nearby Molecular Clouds." Astrophysical Journal 926, no. 1 (2022): 19. http://dx.doi.org/10.3847/1538-4357/ac39a0.
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Abstract We adopt the deep learning method casi-3d (Convolutional Approach to Structure Identification-3D) to systemically identify protostellar outflows in 12CO and 13CO observations of the nearby molecular clouds, Ophiuchus, Taurus, Perseus, and Orion. The total outflow masses are 267 M ⊙, 795 M ⊙, 1305 M ⊙, and 6332 M ⊙ for Ophiuchus, Taurus, Perseus, and Orion, respectively. We show the outflow mass in each cloud is linearly proportional to the total number of young stellar objects. The estimated total 3D deprojected outflow energies are 9 × 1045 erg, 6 × 1046 erg, 1.2 × 1047 erg, and 6 × 1047 erg for Ophiuchus, Taurus, Perseus, and Orion, respectively. The energy associated with outflows is sufficient to offset turbulent dissipation at the current epoch for all four clouds. All clouds also exhibit a break point in the spatial power spectrum of the outflow prediction map, which likely corresponds to the typical outflow mass and energy injection scale.
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Machida, Masahiro N., and Takashi Hosokawa. "Failed and delayed protostellar outflows with high-mass accretion rates." Monthly Notices of the Royal Astronomical Society 499, no. 3 (2020): 4490–514. http://dx.doi.org/10.1093/mnras/staa3139.
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ABSTRACT The evolution of protostellar outflows is investigated under different mass accretion rates in the range ∼10−5–$10^{-2}\, {\rm M}_\odot$ yr−1 with 3D magnetohydrodynamic simulations. A powerful outflow always appears in strongly magnetized clouds with $B_0 \gtrsim B_{\rm 0, cr}\, =10^{-4} (M_{\rm cl}/100\, {\rm M}_\odot)$ G, where Mcl is the cloud mass. When a cloud has a weaker magnetic field, the outflow does not evolve promptly with a high-mass accretion rate. In some cases with moderate magnetic fields B0 slightly smaller than B0, cr, the outflow growth is suppressed or delayed until the infalling envelope dissipates and the ram pressure around the protostellar system is significantly reduced. In such an environment, the outflow begins to grow and reaches a large distance only during the late accretion phase. On the other hand, the protostellar outflow fails to evolve and is finally collapsed by the strong ram pressure when a massive (≳ 100 M⊙) initial cloud is weakly magnetized with B0 ≲ 100 μG. The failed outflow creates a toroidal structure that is supported by magnetic pressure and encloses the protostar and disc system. Our results indicate that high-mass stars form only in strongly magnetized clouds, if all high-mass protostars possess a clear outflow. If we would observe either very weak or no outflow around evolved protostars, it means that strong magnetic fields are not necessarily required for high-mass star formation. In any case, we can constrain the high-mass star formation process from observations of outflows.
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Sperling, T., J. Eislöffel, C. Fischer, B. Nisini, T. Giannini, and A. Krabbe. "Evolution of the atomic component in protostellar outflows." Astronomy & Astrophysics 650 (June 2021): A173. http://dx.doi.org/10.1051/0004-6361/202040048.
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Context. We present SOFIA/FIFI-LS observations of three Class 0 and one Class I outflows (Cep E, HH 1, HH 212, and L1551 IRS5) in the far-infrared [O I]63 μm and [O I]145 μm transitions. Spectroscopic [O I]63 μm maps enabled us to infer the spatial extent of warm (T ∼ 500−1200 K), low-excitation atomic gas within these protostellar outflows. Aims. Our main goal is to determine mass-loss rates from the obtained [OI]63 μm maps and compare these with accretion rates from other studies. Methods. The far-infrared [O I]63 μm emission line is predicted to be the main coolant of dense, dissociative J-shocks caused by decelerated wind or jet shocks. If proper shock conditions prevail, the instantaneous mass-ejection rate is directly connected to the [O I]63 μm luminosity. In order to unravel evolutionary trends, we analysed a set of 14 Class 0/I outflow sources that were spatially resolved in the [O I]63 emission. We compared these data with a sample of 72 Class 0/I/II outflow sources that have been observed with Herschel (WISH, DIGIT, WILL, GASPS surveys) without spatially resolving the [O I]63 μm line. Results. All our newly observed targets feature prominent [O I]63μm emission either close to the driving source (L1551 IRS5, HH 1, HH 212) or as extended jet-like or knotty emission region away from it (Cep E). The detected [O I]63 μm emission can mostly be attributed to dissociative shocks and photodissociation regions (PDRs). Flux values at 63 μm and 145 μm of all four associated continuum sources are presented. We calculated mass-loss rates connected to the low-excitation, atomic outflow component in the range of (5−50)×10−7 M⊙ yr−1. Estimated ratios between the mass loss in the outflow and the mass accretion onto the source (jet efficiency ratios) are largely in the range of Ṁout/Ṁacc ∼ 0.05 − 0.5 for the observed outflow sources, which are consistent with theoretical predictions and quoted Herschel data. Conclusions. Our new observations and a comparison with the 72 outflow sources observed with Herschel indicate that the bulk ejected material in outflows from Class 0 sources resides in the molecular component, that is mass-loss rates derived from the [O I]63 emission line significantly underestimate the total mass-loss rate during this and possibly also later phases of the star formation process.
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Gomez-Ruiz, A. I., F. Wyrowski, A. Gusdorf, S. Leurini, K. M. Menten, and R. Güsten. "Warm gas in protostellar outflows." Astronomy & Astrophysics 555 (June 19, 2013): A8. http://dx.doi.org/10.1051/0004-6361/201218824.
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Fukui, Y., T. Iwata, H. Takaba, et al. "Molecular outflows in protostellar evolution." Nature 342, no. 6246 (1989): 161–63. http://dx.doi.org/10.1038/342161a0.
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Zapata, Luis A., Johannes Schmid-Burgk, Luis F. Rodríguez, Aina Palau, and Laurent Loinard. "Molecular Outflows: Explosive versus Protostellar." Astrophysical Journal 836, no. 1 (2017): 133. http://dx.doi.org/10.3847/1538-4357/aa5b94.
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Hsieh, Cheng-Han, Héctor G. Arce, Zhi-Yun Li, et al. "The Evolution of Protostellar Outflow Cavities, Kinematics, and Angular Distribution of Momentum and Energy in Orion A: Evidence for Dynamical Cores." Astrophysical Journal 947, no. 1 (2023): 25. http://dx.doi.org/10.3847/1538-4357/acba13.
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Abstract We present Atacama Large Millimeter/submillimeter Array observations of the ∼10,000 au environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the pixel flux-tracing technique. Our results indicate that by the end of the protostellar phase, outflows will remove ∼2–4 M ⊙ from the surrounding ∼1 M ⊙ low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of cores as well-defined mass reservoirs, and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10,000 au scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.
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Arce, Héctor G. "Outflow-Circumstellar Envelope Interactions in Protostars." Symposium - International Astronomical Union 221 (2004): 345–50. http://dx.doi.org/10.1017/s0074180900241764.
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We present the results of a high angular resolution (< 5″) survey of protostars with outflows, at different evolutionary stages, using the Owens Valley Radio Observatory Millimeter Array. This survey aims to understand the evolution of the interaction between protostellar outflows and the infalling circumstellar envelopes. Our data enable us to probe the structure and kinematics of the molecular outflow and the circumstellar envelope, as well as the outflow-envelope interaction at scales of less than 0.02 pc, for every source in our sample. Our results indicate that outflows have a considerable impact on the dense circumstellar envelope. Also, we show that the nature of the outflow-envelope interaction depends on the protostar's evolutionary stage.
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Kuiper, R., and T. Hosokawa. "First hydrodynamics simulations of radiation forces and photoionization feedback in massive star formation." Astronomy & Astrophysics 616 (August 2018): A101. http://dx.doi.org/10.1051/0004-6361/201832638.
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Aims. We present the first simulations of the formation and feedback of massive stars which account for radiation forces as well as photoionization feedback (along with protostellar outflows). In two different accretion scenarios modeled, we determine the relative strength of these feedback components and derive the size of the reservoir from which the forming stars gained their masses. Methods. We performed direct hydrodynamics simulations of the gravitational collapse of high-density mass reservoirs toward the formation of massive stars including self-gravity, stellar evolution, protostellar outflows, continuum radiation transport, photoionization, and the potential impact of ram pressure from large-scale gravitational infall. For direct comparison, we executed these simulations with and without the individual feedback components. Results. Protostellar outflows alone limit the stellar mass growth only in an accretion scenario with a finite mass reservoir; when including accretion and ram pressure from large scales (>0.1 pc), protostellar outflows do not limit stellar mass growth at all. Photoionization and HII regions dominate the feedback ladder only at later times, after the star has already contracted down to the zero-age main sequence, and only on large scales. Specifically, photoionization yields a broadening of the bipolar outflow cavities and a reduction of the gravitational infall momentum by about 50%, but does not limit the stellar mass accretion. On the other hand, we find radiation forces restrain the gravitational infall toward the circumstellar disk, impact the gravito-centrifugal equilibrium at the outer edge of the disk, and eventually shut down stellar accretion completely. The most massive star formed in the simulations accreted 95 M⊙ before disk destruction; this mass was drawn-in from an accretion reservoir of ≈240 M⊙ and ≈0.24 pc in radius. Conclusions. In the regime of very massive stars, the final mass of these stars is controlled by their own radiation force feedback.
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Lora, V., T. Nony, A. Esquivel, and R. Galván-Madrid. "Shedding Light on the Ejection History of Molecular Outflows: Multiple Velocity Modes and Precession." Astrophysical Journal 962, no. 1 (2024): 66. http://dx.doi.org/10.3847/1538-4357/ad13ed.
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Abstract Variable accretion has been well studied in the evolved stages of low-mass star formation. However, the accretion history in the initial phases of star formation is still a seldom studied topic. The outflows and jets emerging from protostellar objects could shed some light on their accretion history. We consider the recently studied case of W43-MM1, a protocluster containing 46 outflows driven by 27 protostellar cores. The outflow kinematics of the individual cores and associated knots in W43-MM1 indicate episodic protostellar ejection. We take the observed parameters of an individual core system (core #8) and perform 3D hydrodynamic simulations of such a system, including episodic changes in the velocity of the outflow. The simulations consist of a collimated jet emerging from a core, taking into account one- and two-velocity modes in the variation of the ejection velocity of the jet. In addition, we investigated the effect of including the precession of the jet in the one- and two-velocity-mode models. From the simulations, we constructed position–velocity diagrams and compared them with the observations. We find that including a second mode in the ejection velocity, as well as the precession, are required to explain the positions of the outflow knots and other position–velocity features observed in core #8 in W43-MM1.
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FRANK, ADAM. "PROTOSTELLAR OUTFLOWS: NEW PERSPECTIVES ON MESOSCOPIC STRUCTURE AND MACROSCOPIC FEEDBACK." Modern Physics Letters A 24, no. 15 (2009): 1167–85. http://dx.doi.org/10.1142/s0217732309030989.
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This paper presents a brief review of new perspectives in the field of protostellar outflows concentrating on scales above those associated with the launch region (L > 10 AU ). The formation and propagation of protostellar or Young Stellar Object (YSO) jets and collimated outflows has been intensively studied over the last 30 years with enormous progress being made in both theory and observations. As both the resolution and integration of observational platforms increases new features are revealed which have shifted the emphasis of research efforts. In this paper we review results in two different domains of YSO outflows research which focus on these new perspectives. We first review attempts to model jets as intrinsically heterogeneous (clumpy) systems. The role of sub-radial clumps (rc < rj) within a jet are explored and these models are differentiated from the classic paradigm of pulsed jets. In the second section we look at YSO jets in a global, environmental context. The ability of YSO jets and outflows to generate and/or sustain turbulence in star forming environments has been suggested as a major source of feedback in young clusters. Until recently this suggestion has been untested via direct simulations. We review new work on star formation outflow feedback and discuss issues for future studies.
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Frank, A. "Hypersonic Swizzle Sticks: Protostellar Turbulence, Outflows and Fossil Outflow Cavities." Astrophysics and Space Science 307, no. 1-3 (2007): 35–39. http://dx.doi.org/10.1007/s10509-006-9283-9.
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Li, Guang-Xing, Keping Qiu, Friedrich Wyrowski, and Karl Menten. "Turbulent entrainment origin of protostellar outflows." Astronomy & Astrophysics 559 (October 30, 2013): A23. http://dx.doi.org/10.1051/0004-6361/201220581.
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Nisini, B., G. Santangelo, S. Antoniucci, et al. "Mapping water in protostellar outflows withHerschel." Astronomy & Astrophysics 549 (December 6, 2012): A16. http://dx.doi.org/10.1051/0004-6361/201220163.
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Contopoulos, I., and C. Sauty. "The origin of molecular protostellar outflows." Astronomy & Astrophysics 365, no. 2 (2001): 165–73. http://dx.doi.org/10.1051/0004-6361:20000329.
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Nakamura, Fumitaka, and Zhi‐Yun Li. "Protostellar Turbulence Driven by Collimated Outflows." Astrophysical Journal 662, no. 1 (2007): 395–412. http://dx.doi.org/10.1086/517515.
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Rawlings, J. M. C., J. E. Drew, and M. J. Barlow. "Excited Hydrogen Chemistry in Protostellar Outflows." Symposium - International Astronomical Union 150 (1992): 387–88. http://dx.doi.org/10.1017/s0074180900090446.
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Chemical models of protostellar and other outflows have been reassessed in the light of new chemical data. In particular, reactions involving excited hydrogen (2s,p) are shown to be important in hot, dense outflows. The H(n=2) + H → H2 + hv reaction is much less of a contributor to the H2 formation rate than the recently measured H(n=2) + H → H2+ + e- reaction, providing conditions allow the 0.75eV endothermicity of this reaction to be overcome.
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Bürzle, Florian, Paul C. Clark, Federico Stasyszyn, Klaus Dolag, and Ralf S. Klessen. "Protostellar outflows with smoothed particle magnetohydrodynamics." Monthly Notices of the Royal Astronomical Society: Letters 417, no. 1 (2011): L61—L65. http://dx.doi.org/10.1111/j.1745-3933.2011.01120.x.
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Dutta, Somnath, Chin-Fei Lee, Naomi Hirano, et al. "ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution." Astrophysical Journal 931, no. 2 (2022): 130. http://dx.doi.org/10.3847/1538-4357/ac67a1.
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Abstract Protostellar outflows and jets play a vital role in star formation as they carry away excess angular momentum from the inner disk surface, allowing the material to be transferred toward the central protostar. Theoretically, low-velocity and poorly collimated outflows appear from the beginning of the collapse at the first hydrostatic core (FHSC) stage. With growing protostellar core mass, high-density jets are launched, entraining an outflow from the infalling envelope. Until now, molecular jets have been observed at high velocity (≳100 km s−1) in early Class 0 protostars. We, for the first time, detect a dense molecular jet in SiO emission with low velocity (∼4.2 km s−1, deprojected ∼24 km s−1) from source G208.89–20.04Walma (hereafter G208Walma) using ALMA Band 6 observations. This object has some characteristics of FHSCs, such as a small outflow/jet velocity, extended 1.3 mm continuum emission, and N 2D+ line emission. Additional characteristics, however, are typical of early protostars: collimated outflow and SiO jet. The full extent of the outflow corresponds to a dynamical timescale of ∼ 930 − 100 + 200 yr. The spectral energy distribution also suggests a very young source having an upper limit of T bol ∼ 31 K and L bol ∼ 0.8 L ⊙. We conclude that G208Walma is likely in the transition phase from FHSC to protostar, and the molecular jet has been launched within a few hundred years of initial collapse. Therefore, G208Walma may be the earliest object discovered in the protostellar phase with a molecular jet.
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Podio, Linda, Benoit Tabone, and Claudio Codella. "Protostellar jets: A statistical view with the CALYPSO IRAM-PdBI survey." EPJ Web of Conferences 265 (2022): 00037. http://dx.doi.org/10.1051/epjconf/202226500037.
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In the context of the CALYPSO IRAM-PdBI Lai•ge Program we performed the first statistical survey of protostellar jets by analysing molecular emission in a sample of 21 protostars covering a broad range of internal luminosities (Lint from 0.035 L⊙ to 47 L⊙). We find that the outflow phenomenon is ubiquitous in our sample of protostars, with wide-angle outflows detected in CO (2 - 1) in all sources, and high-velocity collimated jets detected in SiO (5-4) in 80% of the sources with Lint > 1 L⊙. The protostellar flows have an onion-like structure, with the SiO jet (opening angle, α ~ 10°) nested into a wider angle SO (α ~ 15°) and CO (α ~ 25°) outflows. Interestingly, protostellar jets show several properties in common with the atomic jets associated with more evolved sources (106 yr), e.g. one third of the jets show velocity asymmetry of ~ 1.3-2 between the two lobes, and the mass-loss rates are ~ 1% - 50% of the mass accretion rates. This suggests that the same launching mechanism is at work and that the correlation between mass ejection and mass accretion holds along the star-formation process from 104 yr up to a few Myr.
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Lee, Seokho, Jeong-Eun Lee, Doug Johnstone, Gregory J. Herczeg, and Yuri Aikawa. "Multiple Jets in the Bursting Protostar HOPS 373SW." Astrophysical Journal 964, no. 1 (2024): 34. http://dx.doi.org/10.3847/1538-4357/ad21e3.
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Abstract We present the outflows detected in HOPS 373SW, a protostar undergoing a modest 30% brightness increase at 850 μm. Atacama Large Millimeter/submillimeter Array observations of shock tracers, including SiO 8–7, CH3OH 7k–6k, and 12CO 3–2 emission, reveal several outflow features around HOPS 373SW. The knots in the extremely high-velocity SiO emission reveal the wiggle of the jet, for which a simple model derives a 37° inclination angle of the jet to the plane of the sky, a jet velocity of 90 km s−1, and a period of 50 yr. The slow SiO and CH3OH emission traces U-shaped bow shocks surrounding the two CO outflows. One outflow is associated with the high-velocity jets, while the other is observed to be close to the plane of the sky. The misaligned outflows imply that previous episodic accretion events have either reoriented HOPS 373SW or that it is an unresolved protostellar binary system with misaligned outflows.
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Moscadelli, L., A. Sanna, C. Goddi, V. Krishnan, F. Massi, and F. Bacciotti. "Protostellar Outflows at the EarliesT Stages (POETS)." Astronomy & Astrophysics 631 (October 22, 2019): A74. http://dx.doi.org/10.1051/0004-6361/201936436.
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Context. Although recent observations and theoretical simulations have pointed out that accretion disks and jets can be essential for the formation of stars with a mass of up to at least 20 M⊙, the processes regulating mass accretion and ejection are still uncertain. Aims. The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10–100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. Methods. The outflow kinematics is studied at milliarcsecond scales through very long baseline interferometry (VLBI) observations of the 22 GHz water masers, which are ideal test particles to measure the three-dimensional (3D) motion of shocks owing to the interaction of winds and jets with ambient gas. We employed the Jansky Very Large Array (JVLA) at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission, and address its nature. Results. In about half of the targets, the water masers observed at separation ≤1000 au from the YSOs trace either or both of these kinematic structures: (1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and (2) a linear local standard of rest (LSR) velocity (VLSR) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the VLSR gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of ≤1000 au; third, the PMs of the masers delineating the VLSR gradients hint at flow motions at a speed of 10–20 km s−1 directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions. To explain this peculiar PM distribution, and in light of the observational bias strongly favoring masers moving close to the plane of sky, we propose that, in these sources, the maser emission could originate in DW-jet systems slightly inclined (≤30°) with respect to edge-on. Magneto-centrifugally driven DWs could in general account for the observed velocity patterns of water masers.
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Thieme, Travis J., Shih-Ping Lai, Sheng-Jun Lin, et al. "Accretion Flows or Outflow Cavities? Uncovering the Gas Dynamics around Lupus 3-MMS." Astrophysical Journal 925, no. 1 (2022): 32. http://dx.doi.org/10.3847/1538-4357/ac382b.
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Abstract Understanding how material accretes onto the rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how disks are formed. Magnetohydrodynamic simulations of magnetized, turbulent disk formation usually show spiral-like streams of material (accretion flows) connecting the envelope to the disk. However, accretion flows in these early stages of protostellar formation still remain poorly characterized, due to their low intensity, and possibly some extended structures are disregarded as being part of the outflow cavity. We use ALMA archival data of a young Class 0 protostar, Lupus 3-MMS, to uncover four extended accretion flow–like structures in C18O that follow the edges of the outflows. We make various types of position–velocity cuts to compare with the outflows and find the extended structures are not consistent with the outflow emission, but rather more consistent with a simple infall model. We then use a dendrogram algorithm to isolate five substructures in position–position–velocity space. Four out of the five substructures fit well (>95%) with our simple infall model, with specific angular momenta between 2.7–6.9 × 10−4 km s−1 pc and mass-infall rates of 0.5–1.1 × 10−6 M ⊙ yr−1. Better characterization of the physical structure in the supposed “outflow cavities” is important to disentangle the true outflow cavities and accretion flows.
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Arce, Héctor G. "Outflows and Turbulence in Young Stellar Clusters — An Observer's View." Proceedings of the International Astronomical Union 6, S270 (2010): 287–90. http://dx.doi.org/10.1017/s1743921311000524.
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AbstractRecent numerical studies have focused their interest on the impact outflows have on the cloud's turbulence. The contradictory results obtained by these studies indicate that it is essential for observers to provide the required data to constrain the models. Here we discuss the impact of outflows on the environment surrounding clusters of young stellar objects, from an observer's point of view. We have conducted several studies of outflows in different active star-forming regions. In all cases it is clear that outflows have the power to sustain the observed turbulence in the gas surrounding protostellar clusters. We investigate whether there is a correlation between outflow strength and star formation efficiency, as predicted by numerical simulations, for six different regions in the Perseus molecular cloud complex. We argue that results of other recent studies that use CO line maps to study the turbulence driving length should not be used to discard outflows as major drivers of turbulence in clusters.
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Pudritz, Ralph E., and Colin A. Norman. "Hydromagnetic winds from accretion disks." Canadian Journal of Physics 64, no. 4 (1986): 501–6. http://dx.doi.org/10.1139/p86-094.
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We present a hydromagnetic wind model for molecular and ionized gas outflows associated with protostars. If the luminosity of protostars is due to accretion, then centrifugally driven winds that arise from the envelopes of molecular disks explain the observed rates of momentum and energy transport. Ionized outflow originates from disk radii r ≤ 1015 cm inside of which Ly-continuum photons from the protostellar accretion shock are intercepted. Observed molecular outflows arise from the cool disk envelope at radii 1015 ≤ r ≤ 1017 cm. The mass-loss rates of these two component outflows are [Formula: see text] and [Formula: see text]. These winds solve the angular-momentum problem of star formation. We propose that the collimation of such outflows is due to "hoop" stresses generated by the increasingly toroidal magnetic field in the wind and suggest that the structure of the underlying disks makes self-similar solutions for these outflows likely. Finally, we apply this analysis to other accreting systems such as cataclysmic variables.
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Green, Joel D., Klaus M. Pontoppidan, Megan Reiter, et al. "Why Are (Almost) All the Protostellar Outflows Aligned in Serpens Main?" Astrophysical Journal 972, no. 1 (2024): 5. http://dx.doi.org/10.3847/1538-4357/ad5a02.
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Abstract We present deep 1.4–4.8 μm JWST-NIRCam imaging of the Serpens Main star-forming region and identify 20 candidate protostellar outflows, most with bipolar structure and identified driving sources. The outflow position angles (PAs) are strongly correlated, and they are aligned within ±24° of the major axis of the Serpens filament. These orientations are further aligned with the angular momentum vectors of the two disk shadows in this region. We estimate that the probability of this number of young stars being coaligned if sampled from a uniform PA distribution is 10−4. This in turn suggests that the aligned protostars, which seem to be at similar evolutionary stages based on their outflow dynamics, formed at similar times with a similar spin inherited from a local cloud filament. Further, there is tentative evidence for a systematic change in average PA between the northwestern and southeastern cluster, as well as increased scatter in the PAs of the southeastern protostars. SOFIA-HAWC+ archival dust polarization observations of Serpens Main at 154 and 214 μm are perpendicular to the dominant jet orientation in the northwestern region in particular. We measure and locate shock knots and edges for all of the outflows and provide an identifying catalog. We suggest that Serpens main is a cluster that formed from an isolated filament and due to its youth retains its primordial outflow alignment.
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Sanna, A., L. Moscadelli, C. Goddi, et al. "Protostellar Outflows at the EarliesT Stages (POETS)." Astronomy & Astrophysics 623 (March 2019): L3. http://dx.doi.org/10.1051/0004-6361/201834551.
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Centimeter continuum observations of protostellar jets have revealed knots of shocked gas where the flux density decreases with frequency. This spectrum is characteristic of nonthermal synchrotron radiation and implies both magnetic fields and relativistic electrons in protostellar jets. Here, we report on one of the few detections of a nonthermal jet driven by a young massive star in the star-forming region G035.02+0.35. We made use of the NSF’s Karl G. Jansky Very Large Array (VLA) to observe this region at C, Ku, and K bands with the A- and B-array configurations, and obtained sensitive radio continuum maps down to an rms of 10 μJy beam−1. These observations allow for a detailed spectral index analysis of the radio continuum emission in the region, which we interpret as a protostellar jet with a number of knots aligned with extended 4.5 μm emission. Two knots clearly emit nonthermal radiation and are found at similar distances, of approximately 10 000 au, at each side of the central young star, from which they expand at velocities of several hundred km s−1. We estimate both the mechanical force and the magnetic field associated with the radio jet, and infer a lower limit of 0.4 × 10−4 M⊙ yr−1 km s−1 and values in the range 0.7–1.3 mG.
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Stephens, Ian W., Michael M. Dunham, Philip C. Myers, et al. "Alignment between Protostellar Outflows and Filamentary Structure." Astrophysical Journal 846, no. 1 (2017): 16. http://dx.doi.org/10.3847/1538-4357/aa8262.
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Nisini, B., M. Benedettini, C. Codella, et al. "Water cooling of shocks in protostellar outflows." Astronomy and Astrophysics 518 (July 2010): L120. http://dx.doi.org/10.1051/0004-6361/201014603.
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Krumholz, Mark R., Christopher F. McKee, and Richard I. Klein. "How Protostellar Outflows Help Massive Stars Form." Astrophysical Journal 618, no. 1 (2004): L33—L36. http://dx.doi.org/10.1086/427555.
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Machida, Masahiro N. "PROTOSTELLAR JETS ENCLOSED BY LOW-VELOCITY OUTFLOWS." Astrophysical Journal 796, no. 1 (2014): L17. http://dx.doi.org/10.1088/2041-8205/796/1/l17.
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Sanna, A., L. Moscadelli, C. Goddi, V. Krishnan, and F. Massi. "Protostellar Outflows at the EarliesT Stages (POETS)." Astronomy & Astrophysics 619 (November 2018): A107. http://dx.doi.org/10.1051/0004-6361/201833573.
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Context. Weak and compact radio continuum and H2O masers are preferred tracers of the outflow activity nearby very young stars. Aims. We want to image the centimeter free–free continuum emission in the range 1–7 cm (26–4 GHz), which arises in the inner few 1000 au from those young stars also associated with bright H2O masers. We seek to study the radio continuum properties in combination with the H2O maser kinematics to quantify the outflow energetics powered by single young stars. Methods. We made use of the Karl G. Jansky Very Large Array (VLA) in the B configuration at K band and the A configuration at both Ku and C bands in order to image the radio continuum emission toward 25 H2O maser sites with an angular resolution and thermal rms on the order of 0.′′1 and 10 μJy beam−1, respectively. These targets add to our pilot study of 11 maser sites previously presented. The sample of H2O maser sites was selected among those regions that have accurate distance measurements, obtained through maser trigonometric parallaxes, and H2O maser luminosities in excess of 10−6 L⊙. Results. We present high-resolution radio continuum images of 33 sources belonging to 25 star-forming regions. In each region, we detect radio continuum emission within a few 1000 au of the H2O masers’ position; 50% of the radio continuum sources are associated with bolometric luminosities exceeding 5 × 103 L⊙, including W33A and G240.32 + 0.07. We provide a detailed spectral index analysis for each radio continuum source, based on the integrated fluxes at each frequency, and produce spectral index maps with the multifrequency synthesis deconvolution algorithm of CASA. The radio continuum emission traces thermal bremsstrahlung in (proto)stellar winds and jets that have flux densities at 22 GHz below 3 mJy and spectral index values between − 0.1 and 1.3. We prove a strong correlation (r > 0.8) between the radio continuum luminosity (Lrad) and the H2O maser luminosity (LH2O) of (L8 GHz∕mJy kpc2) = 103.8 × (LH2O L⊙)0.74. This power-law relation is similar to that between the radio continuum and bolometric luminosities, which confirms earlier studies. Since H2O masers are excited through shocks driven by (proto)stellar winds and jets, these results provide support to the idea that the radio continuum emission around young stars is dominated by shock ionization, and this holds over several orders of magnitude of stellar luminosites (1–105 L⊙).
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Peters, Thomas, Pamela D. Klaassen, Daniel Seifried, Robi Banerjee, and Ralf S. Klessen. "Morphologies of protostellar outflows: an ALMA view." Monthly Notices of the Royal Astronomical Society 437, no. 3 (2013): 2901–8. http://dx.doi.org/10.1093/mnras/stt2104.
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Moscadelli, L., A. Sanna, C. Goddi, V. Krishnan, F. Massi, and F. Bacciotti. "Protostellar Outflows at the EarliesT Stages (POETS)." Astronomy & Astrophysics 635 (March 2020): A118. http://dx.doi.org/10.1051/0004-6361/202037472.
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Context. 22 GHz water masers are the most intense and widespread masers in star-forming regions. They are commonly associated with protostellar winds and jets emerging from low- and high-mass young stellar objects (YSO). Aims. We wish to perform for the first time a statistical study of the location and motion of individual water maser cloudlets, characterized by typical sizes that are within a few au, with respect to the weak radio thermal emission from YSOs. Methods. For this purpose, we have been carrying out the Protostellar Outflows at the EarliesT Stages survey of a sample (38) of high-mass YSOs. The 22 GHz water maser positions and three-dimensional (3D) velocities were determined through multi-epoch Very Long Baseline Array observations with accuracies of a few milliarcsec (mas) and a few km s−1, respectively. The position of the ionized core of the protostellar wind, marking the YSO, was determined through sensitive radio continuum, multi-frequency Jansky Very Large Array observations with a typical error of ≈20 mas. Results. The statistic of the separation of the water masers from the radio continuum shows that 84% of the masers are found within 1000 au from the YSO and 45% of them are within 200 au. Therefore, we can conclude that the 22 GHz water masers are a reliable proxy for locating the position of the YSO. The distribution of maser luminosity is strongly peaked towards low values, indicating that about half of the maser population is still undetected with the current Very Long Baseline Interferometry detection thresholds of 50–100 mJy beam−1. Next-generation, sensitive (at the nJy level) radio interferometers will have the capability to exploit these weak masers for an improved sampling of the velocity and magnetic fields around the YSOs. The average direction of the water maser proper motions provides a statistically-significant estimate for the orientation of the jet emitted by the YSO: 55% of the maser proper motions are directed on the sky within an angle of 30° from the jet axis. Finally, we show that our measurements of 3D maser velocities statistically support models in which water maser emission arises from planar shocks with propagation direction close to the plane of the sky.
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Shu, Frank H., and Hsien Shang. "Protostellar X-Rays, Jets, and Bipolar Outflows." Symposium - International Astronomical Union 182 (1997): 225–39. http://dx.doi.org/10.1017/s0074180900061672.
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We review the theory of x-winds in young stellar objects (YSOs). In particular, we consider how a model where the central star does not corotate with the inner edge of the accretion disk may help to explain the enhanced emission of X-rays from embedded protostars. We argue, however, that the departure from corotation is not large, so a mathematical formulation that treats the long-term average state as steady and axisymmetric represents a useful approximation. Magnetocentrifugally driven x-winds of this description collimate into jets, and their interactions with the surrounding molecular cloud cores of YSOs yield bipolar molecular outflows.
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Rosen, A., and M. D. Smith. "Numerical simulations of highly collimated protostellar outflows." Astronomy & Astrophysics 413, no. 2 (2003): 593–607. http://dx.doi.org/10.1051/0004-6361:20031566.
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