ORCID Profile
0000-0002-2149-2660
Current Organisation
Chalmers University of Technology
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Publisher: American Astronomical Society
Date: 25-11-2019
Publisher: American Astronomical Society
Date: 12-2021
Abstract: With a mass of ∼1000 M ⊙ and a surface density of ∼0.5 g cm −2 , G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μ m Dark High-mass Clumps in Early Stages. We have conducted ∼1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M ⊙ . Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H 2 CO and CH 3 OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8–19 M ⊙ ). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.
Publisher: American Astronomical Society
Date: 21-02-2017
Publisher: American Astronomical Society
Date: 13-02-2020
Publisher: American Astronomical Society
Date: 06-2021
Abstract: We present a spatio-kinematical analysis of the CO ( J = 2 → 1) line emission, observed with the Atacama Large Millimeter/submillimeter Array (ALMA), of the outflow associated with the most massive core, ALMA1, in the 70 μ m dark clump G010.991–00.082. The position–velocity (PV) diagram of the molecular outflow exhibits a peculiar S -shaped morphology that has not been seen in any other star-forming region. We propose a spatio-kinematical model for the bipolar molecular outflow that consists of a decelerating high-velocity component surrounded by a slower component whose velocity increases with distance from the central source. The physical interpretation of the model is in terms of a jet that decelerates as it entrains material from the ambient medium, which has been predicted by calculations and numerical simulations of molecular outflows in the past. One side of the outflow is shorter and shows a stronger deceleration, suggesting that the medium through which the jet moves is significantly inhomogeneous. The age of the outflow is estimated to be τ ≈ 1300 yr, after correction for a mean inclination of the system of ≈57°.
Publisher: American Astronomical Society
Date: 28-04-2023
Abstract: We present the spectral and spatial evolution of H 2 O masers associated with the water fountain source IRAS 18043−2116, found in observations with the Nobeyama 45 m Telescope and the Australia Telescope Compact Array. We have found new highest-velocity components of the H 2 O masers (at the redshifted side V LSR ≃ 376 km s −1 and at the blueshifted side V LSR ≃ −165 km s −1 ), and the resulting velocity spread of ≃540 km s −1 breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow (∼60°). The evolution of the maser cluster separation of ∼2.9 mas yr −1 and the compact (∼0.″2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (∼30 yr) timescale of the outflow. We also confirmed an increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed.
Publisher: American Astronomical Society
Date: 09-11-2020
Publisher: American Astronomical Society
Date: 06-2023
Abstract: The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12 and 7 m arrays from the Atacama Large Millimeter/submillimeter Array. The targets are 70 μ m dark massive (220–4900 M ⊙ ), dense ( 4 cm −3 ), and cold (∼10–20 K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 M ⊙ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass ( M ⊙ ), whereas ≲1% (7/839) are high-mass (≳27 M ⊙ ). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within in idual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.
Publisher: EDP Sciences
Date: 22-08-2019
DOI: 10.1051/0004-6361/201834632
Abstract: Context. Water-fountain nebulae are asymptotic giant branch (AGB) and post-AGB objects that exhibit high-velocity outflows traced by water-maser emission. Their study is important for understanding the interaction between collimated jets and the circumstellar material that leads to the formation of bipolar and/or multi-polar morphologies in evolved stars. Aims. The aim of this paper is to describe the three-dimensional morphology and kinematics of the molecular gas of the water-fountain nebula IRAS 16342−3814. Methods. Data was retrieved from the ALMA archive for analysis using a simple spatio-kinematical model. The software SHAPE was employed to construct a three-dimensional, spatio-kinematical model of the molecular gas in IRAS 16342−3814, and to then reproduce the intensity distribution and position-velocity diagram of the CO emission from the ALMA observations to derive the morphology and velocity field of the gas. Data from CO( J = 1 → 0) supported the physical interpretation of the model. Results. A spatio-kinematical model that includes a high-velocity collimated outflow embedded within material expanding at relatively lower velocity reproduces the images and position-velocity diagrams from the observations. The derived morphology is in good agreement with previous results from IR and water-maser emission observations. The high-velocity collimated outflow exhibits deceleration across its length, while the velocity of the surrounding component increases with distance. The morphology of the emitting region, the velocity field, and the mass of the gas as function of velocity are in excellent agreement with the properties predicted for a molecular outflow driven by a jet. The timescale of the molecular outflow is estimated to be ~70–100 yr. The scalar momentum carried by the outflow is much larger than it can be provided by the radiation of the central star. An oscillating pattern was found associated with the high-velocity collimated outflow. The oscillation period of the pattern is T ≈ 60–90 yr and its opening angle is θ op ≈ 2°. Conclusions. The CO ( J = 3 → 2) emission in IRAS 16342−3814 is interpreted in terms of a jet-driven molecular outflow expanding along an elongated region. The position-velocity diagram and the mass spectrum reveal a feature due to entrained material that is associated with the driving jet. This feature is not seen in other more evolved objects that exhibit more developed bipolar morphologies. It is likely that the jet in those objects has already disappeared since it is expected to last only for a couple hundred years. This strengthens the idea that water fountain nebulae are undergoing a very short transition during which they develop the collimated outflows that shape the circumstellar envelopes. The oscillating pattern seen in the CO high-velocity outflow is interpreted as due to precession with a relatively small opening angle. The precession period is compatible with the period of the corkscrew pattern seen at IR wavelengths. We propose that the high-velocity molecular outflow traces the underlying primary jet that produces such a pattern.
Publisher: American Astronomical Society
Date: 04-2022
Publisher: Oxford University Press (OUP)
Date: 21-09-2018
Publisher: American Astronomical Society
Date: 24-01-2022
Abstract: In this paper, we report new detections of SiO v = 1 and v = 2 J = 1 → 0 masers in the “water fountain” source IRAS 16552−3050, which was observed with the Nobeyama 45 m telescope during 2021 March–April. Water fountains are evolved stars whose H 2 O maser spectra trace high-velocity outflows of km s −1 . This is the second known case of SiO masers in a water fountain, after their prototypical source, W 43A. These SiO masers should shed light on the evolutionary status of this category of evolved stars, which are likely to be at the end of the asymptotic giant branch phase, when the star exhibits the most copious stellar mass loss, followed by development of the complicated morphologies of planetary nebulae. The origin of a large (up to 25 km s −1 ) velocity offset of the SiO masers with respect to the systemic velocity derived from the spectrum of CO J = 2 → 1 line is discussed here.
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317009589
Abstract: We briefly introduce the VLBI maser astrometric analysis of IRAS 18043–2116 and IRAS 18113–2503, two remarkable and unusual water fountains with spectacular bipolar bow shocks in their high-speed collimated jet-driven outflows. The 22 GHz H 2 O maser structures and velocities clearly show that the jets are formed in very short-lived, episodic outbursts, which may indicate episodic accretion in an underlying binary system.
Publisher: Oxford University Press (OUP)
Date: 11-09-2013
Location: United States of America
No related grants have been discovered for Daniel Tafoya.