- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Imaging the disk around IRAS?20126+4104 at subarcsecond resolution
摘要： Context. The existence of disks around high-mass stars has yet to be established on a solid ground, as only few reliable candidates are known to date. The disk rotating about the ～104 L⊙ protostar IRAS 20126+4104 is probably the most convincing of these. Aims. We would like to resolve the disk structure in IRAS 20126+4104 and, if possible, investigate the relationship between the disk and the associated jet emitted along the rotation axis. Methods. We performed observations at 1.4 mm with the IRAM Plateau de Bure interferometer attaining an angular resolution of ～0.″4 (～660 AU). We imaged the methyl cyanide J = 12 → 11 ground state and vibrationally excited transitions as well as the CH3 13CN isotopologue, which had proved to be disk tracers. Results. Our findings confirm the existence of a disk rotating about a ～7–10 M⊙ star in IRAS 20126+4104, with rotation velocity increasing at small radii. The dramatic improvement in sensitivity and spectral and angular resolution with respect to previous observations allows us to establish that higher excitation transitions are emitted closer to the protostar than the ground state lines, which demonstrates that the gas temperature is increasing towards the centre. We also find that the material is asymmetrically distributed in the disk and speculate on the possible origin of such a distribution. Finally, we demonstrate that the jet emitted along the disk axis is co-rotating with the disk. Conclusions. We present iron-clad evidence of the existence of a disk undergoing rotation around a B-type protostar, with rotation velocity increasing towards the centre. We also demonstrate that the disk is not axially symmetric. These results prove that B-type stars may form through disk-mediated accretion as their low-mass siblings do, but also show that the disk structure may be significantly perturbed by tidal interactions with (unseen) companions, even in a relatively poor cluster such as that associated with IRAS 20126+4104.
关键词： ISM: individual objects: IRAS 20126+4104,ISM: jets and outflows,stars: formation
更新于2025-09-23 15:23:52
-
Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
摘要： Context. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. Aims. We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. Methods. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. Results. A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ～ 105, and very low ionisation, xe ～ 0.02?0.05, which combine to give a total density up to nH ～ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2'' from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, ˙Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of ˙Mj ～ 8 ± 4× 10?9 M☉ yr?1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of ˙Lj ～ 2.9 ± 1.5 × 10?6 M☉ yr?1 AU km s?1. We discuss implications of these findings for jet launch theories. Conclusions. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.
关键词： ISM: jets and outflows,Herbig-Haro objects,stars: pre-main sequence,stars: formation
更新于2025-09-23 15:22:29
-
ESO-H <i>α</i> 574 and Par-Lup 3-4 jets: Exploring the spectral, kinematical, and physical properties
摘要： In this paper a comprehensive analysis of VLT/X-Shooter observations of two jet systems, namely ESO-Hα 574 a K8 classical T Tauri star and Par-Lup 3-4 a very low mass (0.13 M☉) M5 star, is presented. Both stars are known to have near-edge on accretion disks. A summary of these first X-shooter observations of jets was given in a 2011 letter. The new results outlined here include flux tables of identified emission lines, information on the morphology, kinematics and physical conditions of both jets and, updated estimates of ?out/?acc. Asymmetries in the ESO-Hα 574 flow are investigated while the Par-Lup 3-4 jet is much more symmetric. The density, temperature, and therefore origin of the gas traced by the Balmer lines are investigated from the Balmer decrements and results suggest an origin in a jet for ESO-Hα 574 while for Par-Lup 3-4 the temperature and density are consistent with an accretion flow. ?acc is estimated from the luminosity of various accretion tracers. For both targets, new luminosity relationships and a re-evaluation of the effect of reddening and grey extinction (due to the edge-on disks) allows for substantial improvements on previous estimates of ?acc. It is found that log(?acc) = ?9.15 ± 0.45 M☉ yr?1 and ?9.30 ± 0.27 M☉ yr?1 for ESO-Hα 574 and Par-Lup 3-4 respectively. Additionally, the physical conditions in the jets (electron density, electron temperature, and ionisation) are probed using various line ratios and compared with previous determinations from iron lines. The results are combined with the luminosity of the [SII]λ6731 line to derive ?out through a calculation of the gas emissivity based on a 5-level atom model. As this method for deriving ?out comes from an exact calculation based on the jet parameters (measured directly from the spectra) rather than as was done previously from an approximate formula based on the value of the critical density at an assumed unknown temperature, values of ?out are far more accurate. Overall the accuracy of earlier measurements of ?out/?acc is refined and ?out/?acc = 0.5 (+1.0)(?0.2) and 0.3 (+0.6)(?0.1) for the ESO-Hα 574 red and blue jets, respectively, and 0.05 (+0.10)(?0.02) for both the Par-Lup 3-4 red and blue jets. While the value for the total (two-sided) ?out/?acc in ESO-Hα 574 lies outside the range predicted by magneto-centrifugal jet launching models, the errors are large and the effects of veiling and scattering on extinction measurements, and therefore the estimate of ?acc, should also be considered. ESO-Hα 574 is an excellent case study for understanding the impact of an edge-on accretion disk on the observed stellar emission. The improvements in the derivation of ?out/?acc means that this ratio for Par-Lup 3-4 now lies within the range predicted by leading models, as compared to earlier measurements for very low mass stars. Par-Lup 3-4 is one of a small number of brown dwarfs and very low mass stars which launch jets. Therefore, this result is important in the context of understanding how ?out/?acc and, thus, jet launching mechanisms for the lowest mass jet driving sources, compare to the case of the well-studied low mass stars.
关键词： ISM: jets and outflows,line: identification,accretion, accretion disks,stars: formation
更新于2025-09-23 15:22:29
-
VLBA imaging of the 3 mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I
摘要： Context. High-mass star formation remains poorly understood due to observational difficulties (e.g. high dust extinction and large distances) hindering the resolution of disk-accretion and outflow-launching regions. Aims. Orion Source I is the closest known massive young stellar object (YSO) and exceptionally powers vibrationally-excited SiO masers at radii within 100 AU, providing a unique probe of gas dynamics and energetics. We seek to observe and image these masers with Very Long Baseline Interferometry (VLBI). Methods. We present the first images of the 28SiO v = 1, J = 2?1 maser emission around Orion Source I observed at 86 GHz (λ3 mm) with the Very Long Baseline Array (VLBA). These images have high spatial (～0.3 mas) and spectral (～0.054 km s?1) resolutions. Results. We find that the λ3 mm masers lie in an X-shaped locus consisting of four arms, with blue-shifted emission in the south and east arms and red-shifted emission in the north and west arms. Comparisons with previous images of the 28SiO v = 1, 2, J = 1?0 transitions at λ7 mm (observed in 2001–2002) show that the bulk of the J = 2?1 transition emission follows the streamlines of the J = 1?0 emission and exhibits an overall velocity gradient consistent with the gradient at λ7 mm. While there is spatial overlap between the λ3 mm and λ7 mm transitions, the λ3 mm emission, on average, lies at larger projected distances from Source I (～44 AU compared with ～35 AU for λ7 mm). The spatial overlap between the v = 1, J = 1?0 and J = 2?1 transitions is suggestive of a range of temperatures and densities where physical conditions are favorable for both transitions of a same vibrational state. However, the observed spatial offset between the bulk of emission at λ3 mm and λ7 mm possibly indicates different ranges of temperatures and densities for optimal excitation of the masers. We discuss different maser pumping models that may explain the observed offset. Conclusions. We interpret the λ3 mm and λ7 mm masers as being part of a single wide-angle outflow arising from the surface of an edge-on disk rotating about a northeast-southwest axis, with a continuous velocity gradient indicative of differential rotation consistent with a Keplerian profile in a high-mass proto-binary.
关键词： stars: formation,masers,ISM: jets and outflows,radio lines: stars,ISM: individual objects: Orion BN/KL (except planetary nebulae)
更新于2025-09-23 15:21:21
-
The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). IV. Free–Free Emission from Protostars: Links to Infrared Properties, Outflow Tracers, and Protostellar Disk Masses
摘要： Emission from protostars at centimeter radio wavelengths has been shown to trace the free–free emission arising from ionizing shocks as a result of jets and outflows driven by protostars. Therefore, measuring properties of protostars at radio frequencies can provide valuable insights into the nature of their outflows and jets. We present a C-band (4.1 and 6.4 cm) survey of all known protostars (Class 0 and Class I) in Perseus as part of the VLA Nascent Disk and Multiplicity (VANDAM) Survey. We examine the known correlations between radio flux density and protostellar parameters, such as bolometric luminosity and outflow force, for our sample. We also investigate the relationship between radio flux density and far-infrared line luminosities from Herschel. We show that free–free emission most likely originates from J-type shocks; however, the large scatter indicates that those two types of emission probe different time and spatial scales. Using C-band fluxes, we removed an estimation of free–free contamination from the corresponding Ka-band (9 mm) flux densities that primarily probe dust emission from embedded disks. We find that the compact (<1″) dust emission is lower for Class I sources (median dust mass 96 M⊕) relative to Class 0 (248 M⊕), but several times higher than in Class II (5–15 M⊕). If this compact dust emission is tracing primarily the embedded disk, as is likely for many sources, this result provides evidence of decreasing disk masses with protostellar evolution, with sufficient mass for forming giant planet cores primarily at early times.
关键词： techniques: interferometric,radio continuum: stars,stars: protostars,protoplanetary disks,stars: winds, outflows,stars: formation
更新于2025-09-19 17:15:36
-
Far-infrared CO and H <sub/>2</sub> O emission in intermediate-mass protostars
摘要： Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions. Aims. Our aim is to analyze excitation of CO and H2O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs. Methods. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of Lbol ～ 102?103 L☉. The maps cover spatial scales of ～104 AU in several CO and H2O lines located in the ～55–210 μm range. Results. Rotational diagrams of CO show two temperature components at Trot ～ 320 K and Trot ～ 700–800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a single component at Trot ～ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in Trot are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs. Conclusions. Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 × 103 AU scales, suggesting similar shock conditions in all those sources.
关键词： stars: protostars,ISM: jets and outflows,ISM: molecules
更新于2025-09-19 17:15:36
-
Distinguishing circumstellar from stellar photometric variability in Eta Carinae
摘要： The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from long-term brightening, the light curve shows periodic orbital modulation (?V ～ 0.6 mag) attributed to the wind-wind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time scales of 2-3 and 8-10 yr and low amplitude, ?V < 0.2 mag, are superimposed on the brightening light-curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light curve analysis shows no evidence of 'shell ejections' at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 ± 4 yr, when the star will be brighter than in the 1600's by up to ?V ～ 1 mag.
关键词： stars: individual (η Carinae),stars: winds, outflows,(stars:) binaries: general,stars: evolution,(ISM:) dust, extinction
更新于2025-09-19 17:15:36
-
Optimization of Processing Parameters of Laser Skin Welding in vitro Combining the Response Surface Methodology with NSGA- II
摘要： The broadband afterglow of GW170817/GRB 170817A is believed to be from an off-axis structured jet. The central engine of a gamma-ray burst usually launches a pair of outflows that move oppositely. It is reasonable to consider the emission from double-sided structured jets, with a near-jet moving toward us and a counter-jet moving away from us. Assuming that the two branches of the jet have the same physical parameters, we have calculated their radio emission. It is found that the counter-jet component will emerge in the radio light curves ～2500 days post-merger. It typically leads to a plateau in the light curve, thus it could be revealed by high accuracy radio observations. We have also considered the possibilities that both branches have different parameters, and found that if some of the physical parameters of the counter-jet are evaluated more favorably than those of the near-jet, then the counter-jet emission will be enhanced and will clearly show up as an obvious plateau or even a rebrightening. For example, when the circumburst medium encountered by the counter-jet is assumed to be 100 times denser than that of the near-jet, a remarkable radio plateau will appear at ～600 days. However, in X-ray bands, the counter-jet component is generally too faint to be discerned. It is argued that the late radio observations of GW170817/GRB 170817A can help determine the key parameters and diagnose the environment of the event.
关键词： gamma-ray burst: individual (GRB 170817A),ISM: jets and outflows,methods: numerical
更新于2025-09-19 17:13:59
-
ALMA Observations of Polarized Emission toward the CW Tau and DG Tau Protoplanetary Disks: Constraints on Dust Grain Growth and Settling
摘要： We present polarimetric data of CW Tau and DG Tau, two well-known Class II disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) at 870 μm and 0 2 average resolution. In CW Tau, the total and polarized emission are both smooth and symmetric, with polarization angles almost parallel to the minor axis of the projected disk. In contrast, DG Tau displays a structured polarized emission, with an elongated brighter region in the disk’s near side and a belt-like feature beyond about 0 3 from the source. At the same time, the total intensity is spatially smooth, with no features. The polarization pattern, almost parallel to the minor axis in the inner region, becomes azimuthal in the outer belt, possibly because of a drop in optical depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4% in DG Tau. Our results are consistent with polarization from self-scattering of the dust thermal emission. In this hypothesis, the maximum size of the grains contributing to polarization is in the range 100–150 μm for CW Tau and 50–70 μm for DG Tau. The polarization maps combined with dust opacity estimates indicate that these grains are distributed in a geometrically thin layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such settling is not yet apparent for DG Tau. These results advocate polarization studies as a fundamental complement to total emission observations, in investigations of the structure and the evolution of protoplanetary disks.
关键词： ISM: jets and outflows,protoplanetary disks,polarization
更新于2025-09-10 09:29:36
-
Far-infrared molecular lines from low- to high-mass star forming regions observed with <i>Herschel</i>
摘要： Aims. Our aim is to study the response of the gas-to-energetic processes associated with high-mass star formation and compare it with previously published studies on low- and intermediate-mass young stellar objects (YSOs) using the same methods. The quanti?ed far-IR line emission and absorption of CO, H2O, OH, and [O i] reveals the excitation and the relative contribution of di?erent atomic and molecular species to the gas cooling budget. Methods. Herschel/PACS spectra covering 55–190 μm are analyzed for ten high-mass star forming regions of luminosities Lbol ～ 104?106 L(cid:4) and various evolutionary stages on spatial scales of ～104 AU. Radiative transfer models are used to determine the contribution of the quiescent envelope to the far-IR CO emission. Results. The close environments of high-mass protostars show strong far-IR emission from molecules, atoms, and ions. Water is detected in all 10 objects even up to high excitation lines, often in absorption at the shorter wavelengths and in emission at the longer wavelengths. CO transitions from J = 14?13 up to typically 29?28 (Eu/kB ～ 580?2400 K) show a single temperature component with a rotational temperature of Trot ～ 300 K. Typical H2O excitation temperatures are Trot ～250 K, while OH has Trot ～ 80 K. Far-IR line cooling is dominated by CO (～75%) and, to a smaller extent, by [O i] (～20%), which becomes more important for the most evolved sources. H2O is less important as a coolant for high-mass sources because many lines are in absorption. Conclusions. Emission from the quiescent envelope is responsible for ～45–85% of the total CO luminosity in high-mass sources compared with only ～10% for low-mass YSOs. The highest?J lines (Jup ≥ 20) originate most likely in shocks, based on the strong correlation of CO and H2O with physical parameters (Lbol, Menv) of the sources from low- to high-mass YSOs. The excitation of warm CO described by Trot ～ 300 K is very similar for all mass regimes, whereas H2O temperatures are ～100 K high for high-mass sources compared with low-mass YSOs. The total far-IR cooling in lines correlates strongly with bolometric luminosity, consistent with previous studies restricted to low-mass YSOs. Molecular cooling (CO, H2O, and OH) is ～4 times greater than cooling by oxygen atoms for all mass regimes. The total far-IR line luminosity is about 10?3 and 10?5 times lower than the dust luminosity for the low- and high-mass star forming regions, respectively.
关键词： stars: protostars,infrared: ISM,molecular processes,astrochemistry,ISM: jets and outflows
更新于2025-09-10 09:29:36