Astron. Astrophys. 363, 800-814 (2000)

Characteristics of solar coronal streamers

Element abundance, temperature and density from coordinated CDS and UVCS SOHO observations

S. Parenti ¹, B.J.I. Bromage ¹, G. Poletto ², G. Noci ³, J.C. Raymond ⁴ and G.E. Bromage <sup>1

1</sup> Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK
² Osservatorio Astrofisico di Arcetri, 50125 Firenze, Italy
³ Universita' di Firenze, 50125 Firenze, Italy
⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA

Received 23 August 2000 / Accepted 19 September 2000

Abstract

This paper presents the results from coordinated observations of streamers acquired by the SOHO Coronal Diagnostic Spectrometer (CDS) and UltraViolet Coronograph Spectrometer (UVCS) experiments. Data from different altitudes within the solar corona were taken, with the purpose of determining their physical parameters - densities, electron temperatures and element abundances - and their changes over the altitude range between 1.02 and 1.6 . Further UVCS streamer data, taken about two months later are used for comparison with the behaviour seen in two different streamers. Whenever possible, alternative methods have been adopted to determine the same physical parameter, as a cross check. In particular, the DEM technique has been applied to UVCS data, in order to compare abundance values derived in this way, with those obtained using the method of Raymond et al. (1997). We conclude that abundances in the low corona covered by CDS data do not show evidence for abundance variation, with respect to photospheric values, while, at UVCS altitudes, a depletion of all element abundances is clearly evident. No clear evidence of a FIP effect in streamers was found; we get contrasting results from the only two high FIP elements present in our spectra.

Key words: Sun: abundances Sun: atmosphere Sun: corona Sun: UV radiation

Send offprint requests to: S. Parenti

Correspondence to: sparenti@uclan.ac.uk

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. The observations
  • 2.1. UVCS observations
  • 2.2. CDS observations
  • 2.3. Correspondence between CDS and UVCS March data
• 3. Spectroscopic diagnostics
  • 3.1. Collisional and radiative components of the line intensity
  • 3.2. Temperature diagnostics
  • 3.3. Density diagnostic
  • 3.4. Determining element abundances
• 4. Results and discussion
  • 4.1. Temperatures
  • 4.2. Densities
  • 4.3. Element abundance
• 5. Conclusions
  • 5.1. Electron temperatures
  • 5.2. Densities
  • 5.3. Composition
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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