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  • 1
    Electronic Resource
    Electronic Resource
    Water-maser emission from a planetary nebula with a magnetized torus (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 414 (2001), S. 284-286 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A star like the Sun becomes a planetary nebula towards the end of its life, when the envelope ejected during the earlier giant phase becomes photoionized as the surface of the remnant star reaches a temperature of ∼30,000 K. The spherical symmetry of the giant phase is lost in the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35104518
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Spherical episodic ejection of material from a young star (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 411 (2001), S. 277-280 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The exact processes by which interstellar matter condenses to form young stars are of great interest, in part because they bear on the formation of planets like our own from the material that fails to become part of the star. Theoretical models suggest that ejection of gas during early phases ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35077020
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  • 3
    Electronic Resource
    Electronic Resource
    Compact protoplanetary disks around the stars of a young binary system (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 395 (1998), S. 355-357 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Planet formation is believed to occur in the disks of gas and dust that surround young solar-type stars. Most stars, however, form in multiple systems, where the presence of a close companion could affect the structure of the disk and perhaps interfere with planet formation. It has been ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/26421
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  • 4
    Electronic Resource
    Electronic Resource
    Long-slit spectroscopy of the compact planetary nebula Hu 2-1 (1995)
    Springer
    Astrophysics and space science 224 (1995), S. 517-518 
    Details
    ISSN: 1572-946X
    Keywords: ISM: kinematics and dynamics ; planetary nebulae: individual (Hu 2-1)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Long-slit spectra of high spectral and spatial resolution of the compact planetary nebula Hu 2-1, are presented. The analysis of the [NII] 6583 emission line detected in the spectra allows us to identify the kinematical components present in the nebula and to deduce their basic geometry. We use position-velocity maps of the [NII] 6583/Hα line intensity ratio in order to identify nebular regions in which shock-excitation and/or overabundace of N exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667933
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular clouds around outflow sources (1990)
    Springer
    Astrophysics and space science 171 (1990), S. 161-162 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The (J, K)=(1,1) ammonia transition emission has been observed toward six regions with signs of active star formation (AFGL 5142, HH 33/40, AFGL 5157, AFGL 6366S, HHL 73, and S140N), using the 37 m antenna of the Haystack Observatory. We detected and mapped the ammonia emission in all of these sources with the exception of HH 33/40. The (J, K)-(2,2), ammonia transition was also observed at the peak position of each source in order to obtain the rotational temperature of the ammonia clumps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646838
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  • 6
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    SMA observations towards the compact, short-lived bipolar water maser outflow in the LkH{alpha}234 region (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-03
    Description: We present Submillimeter Array (SMA) 1.35 mm subarcsecond angular resolution observations towards the LkHα234 intermediate-mass star-forming region. The dust emission arises from a filamentary structure of ~5 arcsec (~4500 au) enclosing VLA 1-3 and MM 1, perpendicular to the different outflows detected in the region. The most evolved objects are located at the southeastern edge of the dust filamentary structure and the youngest ones at the northeastern edge. The circumstellar structures around VLA 1, VLA 3, and MM 1 have radii between ~200 and ~375 au and masses in the ~0.08–0.3 M range. The 1.35 mm emission of VLA 2 arises from an unresolved ( r 135 au) circumstellar disc with a mass of ~0.02 M . This source is powering a compact (~4000 au), low radial velocity (~7 km s –1 ) SiO bipolar outflow, close to the plane of the sky. We conclude that this outflow is the ‘large-scale’ counterpart of the short-lived, episodic, bipolar outflow observed through H 2 O masers at much smaller scales (~180 au), and that has been created by the accumulation of the ejection of several episodic collimated events of material. The circumstellar gas around VLA 2 and VLA 3 is hot (~130 K) and exhibits velocity gradients that could trace rotation. There is a bridge of warm and dense molecular gas connecting VLA 2 and VLA 3. We discuss the possibility that this bridge could trace a stream of gas between VLA 3 and VLA 2, increasing the accretion rate on to VLA 2 to explain why this source has an important outflow activity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Not a galaxy: IRAS 04186+5143, a new young stellar cluster in the outer Galaxy (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-16
    Description: We report the discovery of a new young stellar cluster in the outer Galaxy located at the position of an IRAS Point Source Catalog source that has been previously misidentified as an external galaxy. The cluster is seen in our near-infrared imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the young stellar nature of the sources detected. There is also evidence of subclustering seen in the spatial distributions of young stars and of gas and dust. Near- and mid-infrared photometry indicates that the stars exhibit colours compatible with reddening by interstellar and circumstellar dust and are likely to be low- and intermediate-mass young stellar objects (YSOs) with a large proportion of Class I YSOs. Ammonia and CO lines were detected, with the CO emission well centred near the position of the richest part of the cluster. The velocity of the CO and NH 3 lines indicates that the gas is Galactic and located at a distance of about 5.5 kpc, in the outer Galaxy. Herschel data of this region characterize the dust environment of this molecular cloud core where the young cluster is embedded. We derive masses, luminosities, and temperatures of the molecular clumps where the young stars reside and discuss their evolutionary stages.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    A very young, compact bipolar H2O maser outflow in the intermediate-mass star-forming LkH{alpha} 234 region (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-06
    Description: We report multi-epoch Very Long Baseline Interferometry (VLBI) H 2 O maser observations towards the compact cluster of young stellar objects (YSOs) close to the Herbig Be star LkHα 234. This cluster includes LkHα 234 and at least nine more YSOs that are formed within projected distances of ~10 arcsec (~9000 au). We detect H 2 O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact (~0.2 arcsec = ~180 au), bipolar H 2 O maser outflow emerging from the embedded YSO Very Large Array (VLA) 2. We estimate a kinematic age of ~40 yr for this bipolar outflow, with expanding velocities of ~20 km s –1 and momentum rate M w V w ~= 10 –4 –10 –3 M  yr –1 km s –1  (/4), powered by a YSO of a few solar masses. We propose that the outflow is produced by recurrent episodic jet ejections associated with the formation of this YSO. Short-lived episodic ejection events have previously been found towards high-mass YSOs. We show now that this behaviour is also present in intermediate-mass YSOs. These short-lived episodic ejections are probably related to episodic increases in the accretion rate, as observed in low-mass YSOs. We predict the presence of an accretion disc associated with VLA 2. If detected, this would represent one of the few known examples of intermediate-mass stars with a disc–YSO–jet system at scales of a few hundred astronomical units.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    H2O maser emission associated with the planetary nebula IRAS 16333-4807 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-14
    Description: We present simultaneous observations of H 2 O maser emission and radio continuum at 1.3 cm carried out with the Australia Telescope Compact Array towards two sources, IRAS 16333–4807 and IRAS 12405–6219, catalogued as planetary nebula (PN) candidates, and where single-dish detections of H 2 O masers have been previously reported. Our goal was to unambiguously confirm the spatial association of the H 2 O masers with these two PN candidates. We detected and mapped H 2 O maser emission in both fields, but only in IRAS 16333–4807 the maser emission is spatially associated with the radio continuum emission. The properties of IRAS 16333–4807 provide strong support for the PN nature of the object, hereby confirming it as the fifth known case of an H 2 O maser-emitting PN. This source is bipolar, like the other four known H 2 O maser-emitting PNe, indicating that these sources might pertain to a usual, but short phase in the evolution of bipolar PNe. In IRAS 12405–6219, the H 2 O maser and radio continuum emission are not associated with each other and, in addition, the available data indicate that this source is an H  ii region rather than a PN.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Formation and evolution of the water maser outflow event in AFGL 2591 VLA 3-N (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-02
    Description: In this paper we analyse multi-epoch very long baseline interferometry water maser observations carried out with the Very Long Baseline Array towards the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~0.5 arcsec north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission towards the region VLA 3-N shows two bow-shock-like structures, northern and southern, separated from each other by ~100 mas (~330 au). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of 7 yr. The northern bow shock has a somewhat irregular morphology, while the southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~1.3 mas yr –1 (~20 km s –1 ). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centres of star formation activity. We made a detailed model for the southern structure, proposing two different kinematic models to explain the three-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures and (2) two independent driving sources, one of them exciting the northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and moulding the remarkably smoother southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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