ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic evidence for protostellar infall (1996)
    Springer
    Astrophysics and space science 237 (1996), S. 299-318 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The observational evidence for infall associated with star formation is discussed. Whilst spectral energy distributions of young protostellar objects are consistent with infall, the best direct evidence comes from millimetre and sub-millimetre spectral line observations. Considerations of the formation of the line profiles and the chemical effects of gas-grain interactions suggest that there is only a very short ‘window’ in the evolutionary track of a protostellar object during which infall is directly observable. This may explain why so few infall candidates have been detected. It is argued that self-consistent models of the dynamical and chemical evolution of collapsing cores, coupled to multiple high resolution line observations, will provide definitive evidence for the presence of infall in these objects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02424436
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Dust Evolution in Nova Cassiopeia 1993 (1997)
    Springer
    Astrophysics and space science 251 (1997), S. 303-309 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present UKIRT spectroscopy of Nova Cassiopeia 1993 (= V705 Cas) in KLNQ bands, taken in 1994 and 1995. Fitting the continuum indicates a dust temperature T ∼ 740 – 750 K in the latter part of 1994; this is similar to earlier measurements, and consistent with the “isothermal” behaviour observed in novae with optically thick dust shells. The β-index drops from 0.8 to 0.4 over the same period. This suggests grain growth; grain diameter increases from 〈 0.54 µm around day 256, to 〉 0.57 µm by day 342. The UIR features differ from those in other Galactic sources, and are similar to those in V842 Cen. This suggests fundamental differences between the UIR carriers, or environments, in novae and other Galactic sources. The silicate feature is consistent with an amorphous structure, in contrast to previous novae. We believe that grains in V705 Cas form two populations: silicates, and hydrocarbons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1000787528827
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Dust processing in nova winds (1995)
    Springer
    Astrophysics and space science 224 (1995), S. 543-544 
    Details
    ISSN: 1572-946X
    Keywords: Novae ; Dust ; Interstellar Medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have radically re-assessed the conditions required for the formation and growth of carbon grains in the ejecta of novae. The stability and hence the ultimate fate of the grains is primarily determined by the degree to which they are annealed by the nova's ultraviolet radiation field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667946
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Gas-grain interaction in the low mass star-forming region B335 (1994)
    Springer
    Astrophysics and space science 216 (1994), S. 155-157 
    Details
    ISSN: 1572-946X
    Keywords: stars ; chemistry ; dust
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have modelled chemical abundances and line profiles in the Bok globule B335. The chemical characteristics of this star-forming core are largely determined by gas-grain interaction in the inflowing material. By comparing high resolution observational data with our model it should be possible to determine the evolutionary status of B335 and to establish the role that surface chemistry plays in protostellar clouds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00982487
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Molecular diagnostics of diffusive boundary layers (1995)
    Springer
    Astrophysics and space science 233 (1995), S. 161-164 
    Details
    ISSN: 1572-946X
    Keywords: Stars ; Chemistry ; Diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have assessed the role of diffusion in determining chemical abundances in molecular interface regions. Chemical models have been developed which include the appropriate diffusion terms and that are appropriate to a narrow diffusion region (∼0.01pc) that may exist at the interface between a dark core and a hot, shocked T-Tauri wind. We have assumed pressure balance throughout and have calculated the chemical abundances as functions of time and position through the interface. The results show that significant enhancements of detectable molecules/transitions are expected (e.g. CO J=6→5, OH and CH). Using a realistic value of the diffusion coefficient a diffusive region of dimension 0.01pc may be established within about 104 years. In general it seems likely that diffusion processes are highly significant on these and smaller lengthscales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00627344
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    facet.materialart.
    Unknown
    Unified models of molecular emission from Class 0 protostellar outflow sources (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-17
    Description: Low-mass star-forming regions are more complex than the simple spherically symmetric approximation that is often assumed. We apply a more realistic infall/outflow physical model to molecular/continuum observations of three late Class 0 protostellar sources with the aims of (a) proving the applicability of a single physical model for all three sources and (b) deriving physical parameters for the molecular gas component in each of the sources. We have observed several molecular species in multiple rotational transitions. The observed line profiles were modelled in the context of a dynamical model which incorporates infall and bipolar outflows, using a three-dimensional radiative transfer code. This results in constraints on the physical parameters and chemical abundances in each source. Self-consistent fits to each source are obtained. We constrain the characteristics of the molecular gas in the envelopes as well as in the molecular outflows. We find that the molecular gas abundances in the infalling envelope are reduced, presumably due to freeze-out, whilst the abundances in the molecular outflows are enhanced, presumably due to dynamical activity. Despite the fact that the line profiles show significant source-to-source variation, which primarily derives from variations in the outflow viewing angle, the physical parameters of the gas are found to be similar in each core.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    Is acetylene essential for carbon dust formation? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-15
    Description: We have carried out an investigation of the chemical evolution of gas in different carbon-rich circumstellar environments. Previous studies have tended to invoke terrestrial flame chemistries, based on acetylene (C 2 H 2 ) combustion to model the formation of carbon dust, via polycyclic aromatic hydrocarbons (PAHs). In this work, we pay careful attention to the accurate calculation of the molecular photoreaction rate coefficients to ascertain whether there is a universal formation mechanism for carbon dust in strongly irradiated astrophysical environments. A large number of possible chemical channels may exist for the formation of PAHs, so we have concentrated on the viability of the formation of the smallest building block species, C 2 H 2 , in a variety of carbon-rich stellar outflows. C 2 H 2 is very sensitive to dissociation by UV radiation. This sensitivity is tested, using models of the time-dependent chemistry. We find that C 2 H 2 formation is sensitive to some of the physical parameters and that in some known sources of dust formation it can never attain appreciable abundances. Therefore, multiple (and currently ill-defined) dust-formation channels must exist.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Champagne flutes and brandy snifters: modelling protostellar outflow-cloud chemical interfaces (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-08
    Description: A rich variety of molecular species has now been observed towards hot cores in star-forming regions and in the interstellar medium. An increasing body of evidence from millimetre interferometers suggests that many of these form at the interfaces between protostellar outflows and their natal molecular clouds. However, current models have remained unable to explain the origin of the observational bias towards wide-angled ‘brandy snifter’ shaped outflows over narrower ‘champagne flute’ shapes in carbon monoxide imaging. Furthermore, these wide-angled systems exhibit unusually high abundances of the molecular ion HCO + . We present results from a chemodynamic model of such regions where a rich chemistry arises naturally as a result of turbulent mixing between cold, dense molecular gas and the hot, ionized outflow material. The injecta drives a rich and rapid ion–neutral chemistry in qualitative and quantitative agreement with the observations. The observational bias towards wide-angled outflows is explained naturally by the geometry-dependent ion injection rate causing rapid dissociation of CO in the younger systems.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Simulated observations of young gravitationally unstable protoplanetary discs (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-14
    Description: The formation and earliest stages of protoplanetary discs remain poorly constrained by observations. Atacama Large Millimetre/sub-millimetre Array (ALMA) will soon revolutionise this field. Therefore, it is important to provide predictions which will be valuable for the interpretation of future high sensitivity and high angular resolution observations. Here, we present simulated ALMA observations based on radiative transfer modelling of a relatively massive (0.39 M ) self-gravitating disc embedded in a 10 M dense core, with structure similar to the pre-stellar core L1544. We focus on simple species and conclude that C 17 O 3-〉2, HCO + 3-〉2, OCS 26-〉25 and H 2 CO 4 04 -〉3 03 lines can be used to probe the disc structure and kinematics at all scales.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    A radical route to interstellar propylene formation (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-23
    Description: Complex organic molecules, such as propylene (CH 3 CHCH 2 ), are detected in molecular clouds (such as TMC1) with high fractional abundances (~2 10 –9 , relative to hydrogen) that cannot be explained by gas-phase chemical reactions under normal dark-cloud conditions. To obtain such high abundances requires an efficient grain-driven chemistry to be operating, coupled with effective desorption of the complex organics back into the gas phase. We propose that the mechanism that we have previously described – rapid high-density gas-phase chemistry in the gas released following sudden, total, ice mantle sublimation – can explain the high abundances, without recourse to ill-defined surface chemical pathways. Our model provides a natural explanation for why it is that some sources harbour high abundances of propylene, whilst others do not, based on the age and level of dynamical activity within the source (which affects the ice composition), and the chemical composition of the ambient gas.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...