Jets from massive protostars: clues on their role in the formation process from masers and high resolution radio / NIR imaging (original) (raw)
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Radio observations of jets from massive young stars
Proceedings of the International Astronomical Union, 2010
The formation of low mass stars takes place with the assistance of an accretion disk that transports gas and dust from the envelope of the system to the star, and a jet that removes angular momentum and allows accretion to proceed. In the radio, these ionized jets can be studied very close to the star via the thermal (free-free) emission they produce and at larger scales by the molecular outflows that result from their interaction with the surrounding medium. Is the same disk-jet process responsible for the formation of massive stars? I will review recent evidence for the presence of collimated jets and accretion disks in association with forming massive stars. The jets in massive protostars have large velocities that could produce a synchrotron component and I discuss the evidence for the presence of this non-thermal process in the jet associated with the HH 80-81 system.
An Infrared Jet from a High-Mass Young Star
The Astrophysical Journal, 2001
Jets are a direct consequence of accretion in the inner regions of circumstellar disks. They trace the structure of the accretion disk and, indirectly, the star formation mechanism. Here we report on the discovery of a nearinfrared jet from a young B1 star, one of the most luminous young stars known to exhibit such a structure. The jet is seen in LЈ images of IRAS 18556ϩ0136 in the G35.2Ϫ0.74N region; a significant fraction of the emission is due to Bra line emission. At shorter wavelengths, the jet is obscured: the colors of the bipolar nebula are consistent with 25 mag visual extinctions to the near lobe and 40 mag to the far lobe. A previously detected radio continuum source and an elongated clump of OH maser spots coincide with a break in the jet. This is interpreted as the location of the circumstellar disk surrounding the embedded young star. A lower limit of ∼170 mag is derived for the extinction to the exciting source. This provides an estimate of 0.15 M for the mass , of the circumstellar disk within ∼1500 AU of the central source. Emission knots on either side of a second, weaker radio continuum source offset ∼3Љ from the jet source suggests the presence of a second outflow source in the region. The lack of known jets in high-mass protostars, in contrast to their prevalence among low-mass systems, points to a difference in the star formation process, e.g., mergers. The jet from this B1 star suggests that the mechanisms that form low-mass stars can operate up to at least 10 M stars. , Subject headings: accretion, accretion disks -H ii regions -ISM: individual (G35.2Ϫ0.74N) -ISM: jets and outflows -stars: formation
Collimated molecular jets from high-mass young stars: IRAS?18151-1208
Astronomy and Astrophysics, 2004
Recent near-IR images of massive star forming regions have revealed two collimated jets in the IRAS 18151-1208 region, one of which is almost a parsec in length (Varricatt et al.). Follow-up high-spectral-resolution echelle spectroscopy and 2-dimensional "integral field" spectroscopy of the associated molecular shock features are presented here. From these data kinematic information and excitation maps are extracted, which show that the two jets are morphologically, kinematically and energetically similar to their counterparts from low mass protostars. The close association between the H 2 emission features and the high-velocity CO emission presented by Beuther et al. also suggests that the CO represents gas entrained by these two very collimated jets. From the mass and momentum of the molecular gas, and the luminosity of the H 2 features, it is clear that the flows must be powered by massive sources. To all intents and purposes, the molecular jets appear to be scaled-up versions of low-mass YSO jets. Collectively, the observations add further support to the idea that massive stars are formed through vigorous disk accretion, and that, while in their earliest stages of evolution, massive protostars drive collimated jets.
The Formation of High-Mass Stars: from High-Mass Clumps to Accretion Discs and Molecular Outflows
High-mass stars play a significant role in the evolution of the Universe and the process that leads to the formation of such objects is still an open question in Astrophysics. The details of the structures connected to the central sources, such as the circumstellar discs and the morphology of the jets at their launching points, still lack of observational evidence. In this thesis, the high-mass star forming process is investigated in terms of the evolution of high-mass clumps selected from the ATLASGAL survey based on their 12 CO emission in the sub-millimetre. While single-dish sub-millimetre observations provide a large-scale view of the high-mass star formation process, higher angular resolution observations are required to disentangle the details of the protostars within the clumps. For this, threedimensional infrared spectroscopy was obtained for a group of RMS sources to characterise the circumstellar environment of high-mass YSOs in linear scales of ∼100-1000 AU. The ATLASGAL TOP100 sample offers a unique opportunity to analyse a statistically complete sample of high-mass clumps at different evolutionary stages. APEX data of three rotational J transitions of the CO (the CO (4-3), CO (6-5) and CO (7-6)) were used to characterise the properties of their warm gas (155 K) content and to derive the relations between the CO and the clump properties. The CO line luminosities were derived and the analysis indicated that the CO emission increases as a function of the evolutionary stage of the clumps (from infrared-weak to H ii regions) and as a function of the bolometric luminosity (L bol) and mass of the sources (M clump). The comparison of the TOP100 with low-mass objects observed in the CO (6-5) and CO (7-6), together with CO (10-9) data observed for a complementary sample of objects indicated that the dependency of the CO luminosity (L CO) with the bolometric luminosity of the sources gets steeper towards higher-J transitions. Although the CO luminosity of more luminous clumps are systematically larger than the values obtained for the less luminous sources, the individual analysis of each subsample suggests a similar dependency of L CO versus L bol for each luminosity regime. Finally, the presence of high-velocity CO emission observed for the TOP100 suggests that ∼85% of the sources are driving molecular outflows. The selection of isolated high-mass objects undergoing mass accretion is fundamental to investigate if these objects are formed through an accretion disc or if they are formed by merging of low-mass YSOs. The near-infrared window provides one of the best opportunities to investigate the interior of the sub-mm clumps and study in details their individual members. Thanks to the relatively high-resolution obtained in the K-band and the moderate reddening effectsin the K-band, a sample of eight (8) HMYSOs exhibiting large-scale H 2 outflows were selected to follow-up K-band spectroscopic observations using the NIFS spectrometer (Gemini North). All sources exhibit extended continuum emission and exhibit atomic and molecular transitions typical of embedded objects, such as Brγ, H 2 and the CO lines. The H 2 lines are tracing the launching point of the large-scale jets in scales of ∼ 100 AU in five of eight sources (63%). The identification of jets at such small scales indicates that these objects are still undergoing mass accretion. The Brγ emission probes the ionised gas around the HMYSOs. The analysis of the Brγ spectro-astrometry at sub-pixel scales suggests that the line arises from the cavity of the outflows or from rotating structures perpendicular to the H 2 jets (i.e., disc). Five sources also exhibit CO emission features (63%), and three HMYSOs display CO absorption features (38%), indicating that they are likely associated with circumstellar discs. By further investigating the kinematics of the spatially resolved CO absorption features, the Keplerian mass of three sources was estimated in 5±3, 8±5 and 30±10 M ⊙. These results support that high-mass stars are formed through discs, similarly as observed towards low-mass stars. The comparison between the collimation degree of the molecular jets or outflows detected in the NIFS data with their large-scale counterparts indicate that these structures present a relatively wide range of collimation degrees.
THE INTERMEDIATE-MASS YOUNG STELLAR OBJECT 08576nr292: DISCOVERY OF A DISK–JET SYSTEM
The Astrophysical Journal, 2011
We present observations of the embedded massive young stellar object (YSO) candidate 08576nr292, obtained with X-shooter and SINFONI on the ESO Very Large Telescope (VLT). The flux-calibrated, medium-resolution X-shooter spectrum (300-2500 nm) includes over 300 emission lines, but no (photospheric) absorption lines, and is consistent with a reddened disk spectrum. Among the emission lines are three hydrogen series and helium lines, both permitted and forbidden metal lines, and CO first-overtone emission. A representative sample of lines with different morphologies is presented. The Hα and Ca ii triplet lines are very strong, with profiles indicative of outflow and-possibly-infall, usually observed in accreting stars. These lines include a blueshifted absorption component at ∼−125 km s −1 . The He i and metal-line profiles are double peaked, with a likely origin in a circumstellar disk. The forbidden lines, associated with outflow, have a single blueshifted emission component centered at −125 km s −1 , coinciding with the absorption components in Hα and Ca ii. SINFONI H-and K-band integral-field spectroscopy of the cluster environment demonstrates that the [Fe ii] emission is produced by a jet originating at the location of 08576nr292. Because the spectral type of the central object cannot be determined, its mass remains uncertain. We argue that 08576nr292 is an intermediate-mass YSO with a high accretion rate (Ṁ acc ∼ 10 −6 -10 −5 M yr −1 ). These observations demonstrate the potential of X-shooter and SINFONI to study in great detail an accretion disk-jet system, rarely seen around the more massive YSOs.
Structure and Physical Conditions in MHD Jets from Young Stars
Journal of the Korean Astronomical Society
We have constructed the foundations to a series of theoretical diagnostic methods to probe the jet phenomenon in young stars as observed at various optical forbidden lines. We calculate and model in a self-consistent manner the physical and radiative processes which arise within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk of a young sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. This work can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between many very sophiscated numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST and Adaptic Optics.
Observations of Jets and Outflows from Young Stars
This review concentrates on observations of outflows from young stars during the last 6 years. Recent developments include detections of an increasing number of Herbig-Haro flows at X-rays and UV wavelengths, high resolution studies of irradiated jets with HST, wide-field imaging of parsec-scale outflows with ground-based CCDs and near-IR imagers, complete surveys of visual and near-IR emission from shocks in the vicinity of entire molecular clouds with wide-field imagers, far infrared studies with ISO and the Spitzer Space Telescope, and high angular sub-mm, mm, and cm wavelength aperture synthesis array data-cubes showing both the spatial and velocity structure of jets and outflows.
2013
We have constructed the foundations to a series of theoretical diagnostic methods to probe the jet phenomenon in young stars as observed at various optical forbidden lines. We calculate and model in a self-consistent manner the physical and radiative processes which arise within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk of a young sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. This work can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between many very sophiscated numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST and Adaptic Optics.
Star and jet multiplicity in the high-mass star forming region IRAS 05137+3919
Astronomy & Astrophysics, 2015
Context. We present a study of the complex high-mass star forming region IRAS 05137+3919 (also known as Mol8), where multiple jets and a rich stellar cluster have been described in previous works. Aims. Our goal is to determine the number of jets and shed light on their origin, and thus determine the nature of the young stars powering these jets. We also wish to analyse the stellar clusters by resolving the brightest group of stars. Methods. The star forming region was observed in various tracers and the results were complemented with ancillary archival data. The new data represent a substantial improvement over previous studies both in resolution and frequency coverage. In particular, adaptive optics provides us with an angular resolution of 80 mas in the near IR, while new mid-and far-IR data allow us to sample the peak of the spectral energy distribution and thus reliably estimate the bolometric luminosity. Results. Thanks to the near-IR continuum and millimetre line data we can determine the structure and velocity field of the bipolar jets and outflows in this star forming region. We also find that the stars are grouped into three clusters and the jets originate in the richest of these, whose luminosity is ∼2.4 × 10 4 L. Interestingly, our high-resolution near-IR images allow us to resolve one of the two brightest stars (A and B) of the cluster into a double source (A1+A2). Conclusions. We confirm that there are two jets and establish that they are powered by B-type stars belonging to cluster C1. On this basis and on morphological and kinematical arguments, we conclude that the less extended jet is almost perpendicular to the line of sight and that it originates in the brightest star of the cluster, while the more extended one appears to be associated with the more extincted, double source A1+A2. We propose that this is not a binary system, but a small bipolar reflection nebula at the root of the large-scale jet, outlining a still undetected circumstellar disk. The gas kinematics on a scale of ∼0.2 pc seems to support our hypothesis, because it appears to trace rotation about the axis of the associated jet.
This paper is one of a series in which we report on near infrared imaging of outflow complexes in the H2 v=I-0 S(I) (2.l2Jlm) emission line. Here we discuss observations of HHI and HH2, HH34, HH46 and HH47, HHII0, HHlll and HH144, which are associated with well collimated jets. We observe molecular hydrogen emission associated with regions within the highly collimated, blue-shifted jets ofHHl, HH46 and HHlll. This low excitation emission is most simply explained in terms of bow shocks within a periodic outflow. Molecular emission is also found associated with the Mach disks HH47D and HH46C implying the existence of H2 molecules within the HH46/HH47 flow. The edges of the red-shifted outflow cavity of HH46 and HH47 are clearly outlined by molecular hydrogen emission. This extends from the working surface back towards the reflection nebulosity close to the source. This emission may result from entrainment of ambient material at the flow edges or from material within the flow being obl...