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- Adelman, S J, et al.
(author)
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Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
- 2004
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In: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 155:1, s. 179-189
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Journal article (peer-reviewed)abstract
- Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
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- Dolk, Linus, et al.
(author)
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On the elemental abundance and isotopic mixture of mercury in HgMn stars
- 2003
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 402:1, s. 299-313
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Journal article (peer-reviewed)abstract
- Optical region spectra of 31 HgMn stars have been studied for the abundance and isotope mixture of mercury. In the course of the investigation the lines Hg I lambda 4358 and Hg Ii lambda lambda3984,6149 have been studied, with abundances established for all three lines in several HgMn stars. The mercury isotope mixture has been determined from high resolution spectra of the lambda 3984 line.Possible signs of an ionization anomaly have been detected by the comparison of the abundance derived from the Hg I line and the Hg Ii lines in seven of the observed HgMn stars. A possible correlation of the mercury abundance with Teff has been detected. Possible signs of a weak anticorrelation of the manganese and mercury abundance in HgMn stars have been found, which could be interpreted as a sign of inhomogeneous surface distribution of these elements. For a number of the HgMn stars in this study the mercury abundance and isotope mixture are reported for the first time.
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- Dolk, Linus, et al.
(author)
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The presence of Nd and Pr in HgMn stars
- 2002
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 385:1, s. 111-130
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Journal article (peer-reviewed)abstract
- Optical region spectra for a number of upper main sequence chemically peculiar (CP) stars have been observed to study singly and doubly ionized praseodymium and neodymium lines. In order to improve existing atomic data of these elements, laboratory measurements have been carried out with the Lund VUV Fourier Transform Spectrometer (FTS). From these measurements wavelengths and hyperfine structure (hfs) have been studied for selected , and lines of astrophysical interest. Radiative life times for some excited states of have been determined with the aid of laser spectroscopy at the Lund Laser Center (LLC) and have been combined with branching fractions measured in the laboratory to calculate gf values for some of the stronger optical lines of . With the aid of the derived gf values and laboratory measurements of the hfs, a praseodymium abundance was derived from selected lines in the spectrum of the Am star 32 Aqr. This abundance was used to derive astrophysical gf values for selected lines in 32 Aqr, and these gf values were used to get a praseodymium abundance for the HgMn star HR 7775. The praseodymium abundance in HR 7775 was then utilized to derive astrophysical gf values for all observable lines in this star. The neodymium abundance, derived from unblended lines of in HR 7775, has been utilized to establish astrophysical gf values for observed lines in the optical region of this star. Selected and lines have been identified and studied in a number of HgMn stars and three hot Am stars. The praseodymium and neodymium abundance change rapidly from an approximate 1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement for the cool HgMn stars, indicating a well-defined boundary between the hot Am and HgMn stars in the vicinity of 10 500 K. The enhancement of praseodymium and neodymium in Am and HgMn stars may be explained by diffusive processes active in the stellar atmosphere, while the observed discontinuity might be explained by a thin hydrogen convection zone thought to be present for the Am stars, but absent in the HgMn stars. The absence of a convection zone would cause the diffused elements to gather higher in the atmosphere of HgMn stars compared to Am stars, and explain the observed increase in abundance.
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- Jankowska, Elzbieta, et al.
(author)
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A confocal and electron microscopic study of contacts between 5-HT fibres and feline dorsal horn interneurons in pathways from muscle afferents.
- 1997
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In: The Journal of comparative neurology. - 0021-9967. ; 387:3, s. 430-8
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Journal article (peer-reviewed)abstract
- Morphological substrates of actions of serotonin upon dorsal horn interneurons with input from group II muscle afferents were investigated by using two experimental approaches. Twelve interneurons were intracellularly labelled with rhodamine-dextran, and serotoninergic fibres were identified by immunofluorescence. Appositions between the serotoninergic axons and these interneurons were examined with a dual-channel confocal microscope. A further four interneurons were intracellularly labelled with horseradish peroxidase, and serotoninergic axons were identified by immunocytochemistry; these neurons were prepared for combined light and electron microscopy. Confocal microscopy revealed serotoninergic varicosities in apposition to both cell bodies and dendrites. Similar total numbers of appositions were found on the soma, and on dendrites within 100 microm from the soma, on the most completely labelled neurons. The number of appositions on 100-microm segments of dendrites decreased with increasing distances from the soma (from 14.6 within 100 microm, to 3.8 and 2.4 at 100-300 microm, and more than 300 microm distances, respectively). Electron microscopic analysis of two neurons revealed that few of the apparent contacts on cell bodies were synaptic, but, in contrast, many varicosities apposed to proximal dendrites formed synapses. The evidence suggests that serotonin may have more powerful synaptic effects upon the dendrites of this class of dorsal horn interneurons than on their cell bodies.
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- Jankowska, Elzbieta, et al.
(author)
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Contacts between serotoninergic fibres and dorsal horn spinocerebellar tract neurons in the cat and rat: A confocal microscopic study
- 1995
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In: Neuroscience. - 0306-4522. ; 67, s. 477-487
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Journal article (peer-reviewed)abstract
- Contacts between serotoninergic nerve fibres and dorsal horn dorsal spinocerebellar tract neurons were analysed in order to investigate the morphological basis of actions of serotonin upon dorsal spinocerebellar tract neurons. In a series of experiments dorsal spinocerebellar tract neurons were labelled with intracellularly injected rhodamine-dextran in the cat. The neurons were monosynaptically excited by group II muscle afferents and cutaneous afferents and were identified by antidromic activation following stimuli applied in the cerebellum. In the second series of experiments dorsal spinocerebellar tract neurons were labelled by retrograde transport of Fluorogold injected into the cerebellum in the rat. In both series, serotoninergic fibres were labelled by using a specific anti-serotonin antiserum and were revealed by immunofluorescence. Appositions between the serotoninergic fibres and the cells were inspected with a dual channel confocal microscope. The merged images obtained with the two channels of the microscope were viewed in single optical planes 2 μm apart and in rotated three-dimensional reconstructions. Serotoninergic nerve fibres were found in apposition to cell bodies of all feline dorsal spinocerebellar tract neurons (n = 7) and of 75% of rat dorsal spinocerebellar tract neurons (n = 90). The numbers of putative contacts on cell bodies varied between less than 100 and nearly 300 (mean 160) in the cat and between about five and 30 in the rat. Contacts with dendrites of feline neurons were seen on 96% of 72 dendrites within 300 μm from soma and on 91% of 23 dendrites at distances of 300-500 μm. The number of such contacts varied from less than five to 150 on a single dendrite within these ranges of distances. Their total number within 100 μm from the soma was comparable or exceeded the number of contacts on the soma. © 1995 IBRO.
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