Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system
A. O. BenzS. BrudererE. F. van DishoeckP. StäuberS. F. WampflerM. MelchiorC. DedesF. WyrowskiS. D. DotyF. van der TakW. BächtoldA. CsillaghyA. MegejC. MonsteinMauro SoldatiR. BachillerA. BaudryM. BenedettiniE. A. BerginP. BjerkeliG. A. BlakeS. BontempsJ. BraineP. CaselliJ. CernicharoC. CodellaF. DanielA. M. Di GiorgioP. DielemanC. DominikP. EncrenazM. FichA. FuenteT. GianniniJ. R. GoicoecheaTh. de GraauwF. HelmichG. J. HerczegF. HerpinM. R. HogerheijdeT. JacqWillem JellemaDoug JohnstoneJ. K. JørgensenL. E. KristensenBengt LarssonD. C. LisR. LiseauM. MarseilleC. McCoeyGary J. MelnickDavid A. NeufeldB. NisiniM. OlbergV. OssenkopfB. PariseJ. C. PearsonR. PlumeC. RisacherJ. Santiago-GarcíaP. SaracenoR. SchiederR. ShipmanJ. StützkiM. TafallaA. G. G. M. TielensT. A. van KempenR. VisserU. A. Yíldíz
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Context: Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation. Methods: W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (about 2500 s) in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds. Conclusions: The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.Keywords:
Protostar
Young stellar object
Outflow
Line (geometry)
Protostar
Outflow
Accretion disc
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We present deep near- and mid-infrared images of six high-mass young stellar objects (YSOs) in order to help understand the physical mechanisms of their formation. We have searched for shocked H2 emission around such massive protostars. All but one of these regions exhibit series of molecular hydrogen emission knots, either in perfect alignment or in more complex configurations. In the case of the Class I object Mol 7, the protostars driving a couple of highly bipolar collimated outflows appear to be members of a binary or multiple system. A similar scenario appears to apply to Mol 143. The protostar Mol 12 drives a large little-collimated bipolar outflow with a number of H2 emission nebulosities. In two other methanol cores studied here, we also found shocked molecular hydrogen knots driven by highly embedded YSOs, some of them in clusters. From their near-IR to millimetre-wavelength spectral energy distributions, we derived stellar masses and temperatures, extinctions, luminosities, disc masses, and accretion rates. We provide photometric evidence that the dense dust core housing Mol 12, a Class I YSO, has eclipsed the light of an early-type main-sequence star. The latter is probably a physical companion to the protostar, as indicated by both having nearly identical coordinates and parallaxes as measured by Gaia (DR2) in the case of the star and by VLBI techniques in the case of the water maser associated with the YSO. This eclipse lasted about 15 years (1985–2000) and amounted to ΔAV ≃ 22. Since the year 2002, no further significant variations have been recorded.
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Young stellar object
Bipolar outflow
Spectral energy distribution
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In order to study how outflows from protostars influence the physical and chemical conditions of the parent molecular cloud, we have observed the Barnard 1 (B1) main core, which harbors four Class 0 and three Class I sources, in the CO (J = 1 − 0), CH3OH (JK = 2K − 1K), and the SiO (J = 1 − 0) lines using the Nobeyama 45 m telescope. We have identified three CO outflows in this region: one is an elongated (∼0.3 pc) bipolar outflow from a Class 0 protostar B1-c in the submillimeter clump SMM 2, another is a rather compact (∼0.1 pc) outflow from a Class I protostar B1 IRS in the clump SMM 6, and the other is an extended outflow from a Class I protostar in SMM 11. In the western lobe of the SMM 2 outflow, both the SiO and CH3OH lines show broad redshifted wings with the terminal velocities of 25 km s−1 and 13 km s−1, respectively. It is likely that the shocks caused by the interaction between the outflow and ambient gas enhance the abundance of SiO and CH3OH in the gas phase. The total energy input rate by the outflows (1.1 × 10−3 L☉) is smaller than the energy-loss rate (8.5 × 10−3 L☉) through the turbulence decay in the B1 main core, which suggests that the outflows cannot sustain the turbulence in this region. Since the outflows are energetic enough to compensate the dissipating turbulence energy in the neighboring, more evolved star-forming region NGC 1333, we suggest that the turbulence energy balance depends on the evolutionary state of the star formation in molecular clouds.
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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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Stellar mass
Bipolar outflow
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Distribution of the CH3OH (JK = 2K–1K, 96.7 GHz) emission has been investigated toward NGC 1333 IRAS4B, a low-mass Class 0 protostar which harbors a hot corino, with Nobeyama Millimeter Array. The CH3OH emission is found to be prominent in the shocked region caused by an impact of the molecular outflow from the protostars. The direction of the outflow which is responsible for the shock seems to be opposite to that of a compact outflow known previously in the CO (J = 2–1), HCN (J = 1–0), H2CO (312–211), and CH3OH (JK = 7K–6K) emissions, whereas it is the same as that of the faint second outflow found in the H2CO emission. This double outflow structure can be interpreted most naturally by the existence of more than two protostars in IRAS4B. On the other hand, a centrally condensed component associated apparently with IRAS4B cannot be recognized in our CH3OH observation. Our observation suggests that, in this source, the CH3OH (JK = 2K–1K) emission preferentially traces the shocked regions rather than the hot corino around the protostar.
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Submillimeter Array
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We aim to characterize the outflow properties of a sample of early Class 0 phase low-mass protostars in Orion first identified by the Herschel Space Observatory. We also look for signatures of infall in key molecular lines. CO $J$=3-2 and $J$=4-3 maps toward 16 very young Class 0 protostars were obtained using the Atacama Pathfinder EXperiment (APEX) telescope. We search the data for line wings indicative of outflows and calculate masses, velocities, and dynamical times for the outflows. We use additional HCO$^+$, H$^{13}$CO$^+$, and NH$_3$ lines to look for infall signatures toward the protostars. We estimate the outflow masses, forces, and mass-loss rates based on the CO $J$=3-2 and $J$=4-3 line intensities for 8 sources with detected outflows. We derive upper limits for the outflow masses and forces of sources without clear outflow detections. The total outflow masses for the sources with clear outflow detections are in the range between 0.03 and 0.16 $M_\odot$ for CO $J$=3-2, and in the range between 0.02 and 0.10 $M_\odot$ for CO $J$=4-3. The outflow forces are in the range between $1.57\times10^{-4}$ and $1.16\times10^{-3}$ $M_\odot$ km s$^{-1}$ yr$^{-1}$ for CO $J$=3-2 and in the range between $1.14\times10^{-4}$ and $6.92\times10^{-4}$ $M_\odot$ km s$^{-1}$ yr$^{-1}$ for CO $J$=4-3. Nine protostars in our sample show asymmetric line profiles indicative of infall in HCO$^+$, compared to H$^{13}$CO$^+$ or NH$_3$. The outflow forces of the protostars in our sample show no correlation with the bolometric luminosity, unlike those found by some earlier studies for other Class 0 protostars. The derived outflow forces for the sources with detected outflows are similar to those found for other - more evolved - Class 0 protostars, suggesting that outflows develop quickly in the Class 0 phase.
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The evolution of protostellar outflow is investigated with resistive magneto-hydrodynamic nested-grid simulations that cover a wide range of spatial scales (∼1 au–1 pc). We follow cloud evolution from the pre-stellar core stage until the infalling envelope dissipates long after the protostar formation. We also calculate protostellar evolution to derive protostellar luminosity with time-dependent mass accretion through a circumstellar disc. The protostellar outflow is driven by the first core prior to protostar formation and is directly driven by the circumstellar disc after protostar formation. The opening angle of the outflow is large in the Class 0 stage. A large fraction of the cloud mass is ejected in this stage, which reduces the star formation efficiency to ∼50 per cent. After the outflow breaks out from the natal cloud, the outflow collimation is gradually improved in the Class I stage. The head of the outflow travels more than ∼105 au in ∼105 yr. The outflow momentum, energy and mass derived in our calculations agree well with observations. In addition, our simulations show the same correlations among outflow momentum flux, protostellar luminosity and envelope mass as those in observations. These correlations differ between Class 0 and I stages, which are explained by different evolutionary stages of the outflow; in the Class 0 stage, the outflow is powered by the accreting mass and acquires its momentum from the infalling envelope; in the Class I stage, the outflow enters the momentum-driven snow-plough phase. Our results suggest that protostellar outflow should determine the final stellar mass and significantly affect the early evolution of low-mass protostars.
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We present a detailed kinematical study and modeling of the emission of the molecular cores at ambient velocities surrounding IRAS 21391+5802, an intermediate-mass protostar embedded in IC 1396N. The high-density gas emission is found in association with three dense cores associated with the YSOs BIMA 1, BIMA 2, and BIMA 3. The CS () and CH3OH () emission around BIMA 1 has been modeled by considering a spatially infinitely thin ring seen edge-on by the observer. From the model we find that CS is detected over a wider radii range than CH3OH. A bipolar outflow is detected in the CS () line centered near BIMA 1. This outflow could be powered by a yet undetected YSO, BIMA 1W, or alternatively could be part of the BIMA 1 molecular outflow. The CS and CH3OH emission associated with the intermediate-mass protostar BIMA 2 is highly perturbed by the bipolar outflow even at cloud velocities, confirming that the protostar is in a very active stage of mass loss. For YSO BIMA 3 the lack of outflow and of clear evidence of infall suggests that both outflow and infall are weaker than in BIMA 1, and that BIMA 3 is probably a more evolved object.
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Bipolar outflow
High mass
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In order to study the morphology and the dynamics of the molecular outflow associated with IRAS 18162−2048, a wide area of ∼95 arcmin2 around the source has been mapped by means of CO and 13CO (1–0) lines, and has been complemented by a map of a smaller region surrounding the high-mass object using the C18O (1–0) and CH3OH (2k–1k) and (3k–2k) transitions. The lines profile reveals the presence of several velocity components among which two major line components at 11.9 and 12.8 km s−1 have been detected in all the tracers.
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Line (geometry)
High mass
Bipolar outflow
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We present multi-line and continuum observations of the circumstellar environment within 10^4 AU of a sample of protostars to investigate how the effects of outflows on their immediate environment changes over time. 12CO(1-0) emission probes the high-velocity molecular outflows near the protostars and demonstrate that the outflow opening angle widens as the nascent star evolves. Maps of the 13CO(1-0) and HCO+(1-0) outflow emission show that protostellar winds erode the circumstellar envelope through the entrainment of the outer envelope gas. The spatial and velocity distribution of the dense circumstellar envelope, as well as its mass, is traced by the C18O(1-0) emission and also displays evolutionary changes. We show that outflows are largely responsible for these changes, and propose an empirical model for the evolution of outflow-envelope interactions. In addition, some of the outflows in our sample appear to affect the chemical composition of the surrounding environment, enhancing the HCO+ abundance. Overall, our results confirm that outflows play a major role in the star formation process through their strong physical and chemical impacts on the environments of the young protostars.
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Outflow
Circumstellar envelope
Envelope (radar)
Entrainment (biomusicology)
Low Mass
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