{"title":"Optical Analysis of Cluster Mergers","authors":"M. Girardi, A. Biviano","doi":"10.1007/0-306-48096-4_2","DOIUrl":"https://doi.org/10.1007/0-306-48096-4_2","url":null,"abstract":"","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129806558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-07-01DOI: 10.1017/S1539299600013927
C. Sneden, F. Primas
Abstract Supersolar oxygen-to-iron ratios are known to exist in nearly all metal-poor stars. But there is no general agreement on the magnitude of these relative overabundances. New high resolution spectra of evolved stars over a large metallicity range have been gathered, from which lines of [O I], Sc II, and Fe II have been measured. Abundance ratios [O/Sc] and [O/Fe], insensitive to most model atmospheric uncertainties, have been derived and correlated with overall metallicity. These ratios both are consistent with earlier studies of the [O I] lines in metal-poor stars: [O/Sc]≃[O/Fe]≃+0.4, with possibly a small upward trend with decreasing [Fe/H].
{"title":"Oxygen abundances: new results from [O I] lines","authors":"C. Sneden, F. Primas","doi":"10.1017/S1539299600013927","DOIUrl":"https://doi.org/10.1017/S1539299600013927","url":null,"abstract":"Abstract Supersolar oxygen-to-iron ratios are known to exist in nearly all metal-poor stars. But there is no general agreement on the magnitude of these relative overabundances. New high resolution spectra of evolved stars over a large metallicity range have been gathered, from which lines of [O I], Sc II, and Fe II have been measured. Abundance ratios [O/Sc] and [O/Fe], insensitive to most model atmospheric uncertainties, have been derived and correlated with overall metallicity. These ratios both are consistent with earlier studies of the [O I] lines in metal-poor stars: [O/Sc]≃[O/Fe]≃+0.4, with possibly a small upward trend with decreasing [Fe/H].","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130680863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-07-01DOI: 10.1017/S1539299600013964
S. Balachandran, J. Carr, B. Carney
Abstract Oxygen abundances are derived from the vibrational–rotational OH lines in the infrared. The flat trend of [O/Fe] between −2.5
氧的丰度是由红外波段的振动-旋转OH谱线得出的。[O/Fe]在−2.5之间呈平坦趋势
{"title":"Oxygen Abundances from Infrared OH Lines","authors":"S. Balachandran, J. Carr, B. Carney","doi":"10.1017/S1539299600013964","DOIUrl":"https://doi.org/10.1017/S1539299600013964","url":null,"abstract":"Abstract Oxygen abundances are derived from the vibrational–rotational OH lines in the infrared. The flat trend of [O/Fe] between −2.5","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133319645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-03-08DOI: 10.1017/S1539299600013563
A. Sweigart
We discuss the impact of mixing and rotation along the red-giant branch (RGB) on the properties of horizontal-branch (HB) stars with emphasis on two problems: the nature of the unexpected blue HB population in the metal-rich globular clusters (GCs) NGC 6388 and NGC 6441 and the cause of the low gravities in the blue HB stars. New stellar models indicate that the sloped HBs in NGC 6388 and NGC 6441 might arise from a spread in metallicity, implying that these GCs may be metal-rich analogues of omega Cen. The low gravity problem can be largely explained by the radiative levitation of Fe in the atmospheres of the blue HB stars. We show that the onset of radiative levitation and the drop in HB rotation velocities at Teff ~ 11,000 K coincide with the disappearance of surface convection. The low rotation velocities of the hotter HB stars may be due to the spin down of the surface layers by a weak stellar wind induced by the radiative levitation of Fe. We conclude that the impact of mixing and rotation on the HB remains to be clearly established.
{"title":"Horizontal branch models as a test of mixing on the RGB","authors":"A. Sweigart","doi":"10.1017/S1539299600013563","DOIUrl":"https://doi.org/10.1017/S1539299600013563","url":null,"abstract":"We discuss the impact of mixing and rotation along the red-giant branch (RGB) on the properties of horizontal-branch (HB) stars with emphasis on two problems: the nature of the unexpected blue HB population in the metal-rich globular clusters (GCs) NGC 6388 and NGC 6441 and the cause of the low gravities in the blue HB stars. New stellar models indicate that the sloped HBs in NGC 6388 and NGC 6441 might arise from a spread in metallicity, implying that these GCs may be metal-rich analogues of omega Cen. The low gravity problem can be largely explained by the radiative levitation of Fe in the atmospheres of the blue HB stars. We show that the onset of radiative levitation and the drop in HB rotation velocities at Teff ~ 11,000 K coincide with the disappearance of surface convection. The low rotation velocities of the hotter HB stars may be due to the spin down of the surface layers by a weak stellar wind induced by the radiative levitation of Fe. We conclude that the impact of mixing and rotation on the HB remains to be clearly established.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"101 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130576898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-01-05DOI: 10.1017/S1539299600014076
S. M. Fall
This article reviews three related topics: the extragalactic background l ight and its sources, evolution models for the dust absorption and emission in galaxies, and empirical constraints on these transfer pr ocesses in nearby starburst galaxies. It is intended that the material presented here will serve as an introduction to this Joint Discussion.
{"title":"Dust absorption and emission in galaxies at high and low redshifts","authors":"S. M. Fall","doi":"10.1017/S1539299600014076","DOIUrl":"https://doi.org/10.1017/S1539299600014076","url":null,"abstract":"This article reviews three related topics: the extragalactic background l ight and its sources, evolution models for the dust absorption and emission in galaxies, and empirical constraints on these transfer pr ocesses in nearby starburst galaxies. It is intended that the material presented here will serve as an introduction to this Joint Discussion.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130299197","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-12-07DOI: 10.1017/S1539299600014246
Haida Liang
We will discuss the properties and origins of halos and relics including estimates of the cluster magnetic fields, and present results for a few recently discovered halos and relics. The electrons in the suprathermal high energy tail of the thermal gas distribution are likely to provide the seed particles for acceleration through mergers and turbulences to relativistic energies. These relativistic particles are then responsible for the synchrotron emission of the halos.
{"title":"Diffuse cluster-wide radio halos","authors":"Haida Liang","doi":"10.1017/S1539299600014246","DOIUrl":"https://doi.org/10.1017/S1539299600014246","url":null,"abstract":"We will discuss the properties and origins of halos and relics including estimates of the cluster magnetic fields, and present results for a few recently discovered halos and relics. The electrons in the suprathermal high energy tail of the thermal gas distribution are likely to provide the seed particles for acceleration through mergers and turbulences to relativistic energies. These relativistic particles are then responsible for the synchrotron emission of the halos.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125803268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-12-03DOI: 10.1017/S1539299600014842
K. Subramanian
Using a closure model for the evolution of magnetic correlations, we uncover an interesting plausible saturated state of the small-scale fluctuation dynamo (SSD) and a novel anology between quantum mechanical tunneling and the generation of large-scale fields. Large scale fields develop via the $alpha$-effect, but as magnetic helicity can only change on a resistive timescale, the time it takes to organize the field into large scales increases with magnetic Reynolds number. This is very similar to the results which obtain from simulations using full MHD.
{"title":"Synthesis of Small and Large Scale Dynamos","authors":"K. Subramanian","doi":"10.1017/S1539299600014842","DOIUrl":"https://doi.org/10.1017/S1539299600014842","url":null,"abstract":"Using a closure model for the evolution of magnetic correlations, we uncover an interesting plausible saturated state of the small-scale fluctuation dynamo (SSD) and a novel anology between quantum mechanical tunneling and the generation of large-scale fields. Large scale fields develop via the $alpha$-effect, but as magnetic helicity can only change on a resistive timescale, the time it takes to organize the field into large scales increases with magnetic Reynolds number. This is very similar to the results which obtain from simulations using full MHD.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134410135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-11-02DOI: 10.1017/S1539299600014003
M. Asplund
The formation of [O I], O I and OH lines in metal-poor stars has been studied by means of 3D hydrodynamical model atmospheres. For O I detailed 3D non-LTE calculations have been performed. While the influence of 3D model atmospheres is minor for [O I] and O I lines, the very low temperatures encountered at low metallicities have a drastic impact on the OH lines. As a result, the derived O abundances are found to be systematically overestimated in 1D analyses, casting doubts on the recent claims for a monotonic increase in [O/Fe] towards lower metallicities.
{"title":"Oxygen Line Formation in 3D Hydrodynamical Model Atmospheres","authors":"M. Asplund","doi":"10.1017/S1539299600014003","DOIUrl":"https://doi.org/10.1017/S1539299600014003","url":null,"abstract":"The formation of [O I], O I and OH lines in metal-poor stars has been studied by means of 3D hydrodynamical model atmospheres. For O I detailed 3D non-LTE calculations have been performed. While the influence of 3D model atmospheres is minor for [O I] and O I lines, the very low temperatures encountered at low metallicities have a drastic impact on the OH lines. As a result, the derived O abundances are found to be systematically overestimated in 1D analyses, casting doubts on the recent claims for a monotonic increase in [O/Fe] towards lower metallicities.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123631516","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2000-11-02DOI: 10.1017/S1539299600014283
T. Ensslin
The strong activity of radio galaxies should have led to a nearly ubiquitous presence of fossil radio plasma in the denser regions of the inter-galactic medium as clusters, groups and filaments of galaxies. This fossil radio plasma can contain large quantities of relativistic particles (electrons and possibly protons) by magnetic confinement. These particles might be released and/or re-energized under environmental influences as turbulence and shock waves. Possible connections of such processes to the formation of the observed sources of diffuse radio emission in clusters of galaxies (the cluster radio halos and the cluster radio relics) are discussed.
{"title":"Particle Acceleration and Diffusion in Fossil Radio Plasma","authors":"T. Ensslin","doi":"10.1017/S1539299600014283","DOIUrl":"https://doi.org/10.1017/S1539299600014283","url":null,"abstract":"The strong activity of radio galaxies should have led to a nearly ubiquitous presence of fossil radio plasma in the denser regions of the inter-galactic medium as clusters, groups and filaments of galaxies. This fossil radio plasma can contain large quantities of relativistic particles (electrons and possibly protons) by magnetic confinement. These particles might be released and/or re-energized under environmental influences as turbulence and shock waves. Possible connections of such processes to the formation of the observed sources of diffuse radio emission in clusters of galaxies (the cluster radio halos and the cluster radio relics) are discussed.","PeriodicalId":422890,"journal":{"name":"Highlights of Astronomy","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121223524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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