R. J. Thomas

FIRST RESULTS OF THE SUMER TELESCOPE AND SPECTROMETER ON SOHO – I. Spectra and Spectroradiometry

SUMER – the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) – observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 Å (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 Å. The second-order spectra of detectors A and B cover 330 to 805 Å and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mÅ is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona.SUMER – the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) – observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 A (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 A. The second-order spectra of detectors A and B cover 330 to 805 A and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mA is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona.

FIRST RESULTS OF THE SUMER TELESCOPE AND SPECTROMETER ON SOHO – II. Imagery and Data Management

SUMER – Solar Ultraviolet Measurements of Emitted Radiation – is not only an extreme ultraviolet (EUV) spectrometer capable of obtaining detailed spectra in the range from 500 to 1610 Å, but, using the telescope mechanisms, it also provides monochromatic images over the full solar disk and beyond, into the corona, with high spatial resolution. We report on some aspects of the observation programmes that have already led us to a new view of many aspects of the Sun, including quiet Sun, chromospheric and transition region network, coronal hole, polar plume, prominence and active region studies. After an introduction, where we compare the SUMER imaging capabilities to previous experiments in our wavelength range, we describe the results of tests performed in order to characterize and optimize the telescope under operational conditions. We find the spatial resolution to be 1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along the slit. Resolution and sensitivity are adequate to provide details on the structure, physical properties, and evolution of several solar features which we then present. Finally some information is given on the data availability and the data management system.

First Results of Tide SUMER Telescope and Spectrometer on SOHO

SUMER — the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Reliospheric Observatory (SORO) — observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 A (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 A. The second-order spectra of detectors A and B cover 330 to 805 A and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mA is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona.

Correlation of He II lyman alpha with He I 10830 Å, and with chromospheric and EUV coronal emission

This paper describes the results of comparing SERTS-3 images obtained in the transition region line of Heii 304 Å with chromospheric Hei 10830 Å absorption, with strong coronal lines of Mgix 368 Å, Fexv 284 Å and 417 Å, and Fexvi 335 Å and 31 Å, with Hα, with Caii 8542 Å, and with magnetograms in Fei 8688Hα. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the Heii 304 Å and Hei 10830 Å images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 Å than in 304 Å. In active regions, the 304 Å line follows more closely the behavior of Hα and Caii 8542 Å than the 10830 Å line.

A comparison of theoreticalCIV emission line strengths with active region observations obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical line ratios involving 2s2S - 3p2P, 2p2P - 3s2S, and 2p2S - 3d2D transitions inCiv between 312 and 420 Å are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. The potential usefulness of theCIV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed.

Abundance determination in solar active region

Abstract An improved method has been developed to evaluate element abundances from emission line intensities of thin plasmas, depending on the differential emission measure (DEM) of the source. Observations made by the SERTS Rocket EUV Spectrograph are used to perform a detailed analysis of the DEM distribution for temperatures larger than 10 5 K in a solar active region. Comparison of the DEM distributions obtained by means of lines from different elements allows the verification of relative abundances for the most common elements of the solar corona, and gives an abundance estimates for the minor components, such as Na, Al, Ar, Cr, Mn and Zn.

Mg IX emission lines in an active region spectrum obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical electron-temperature-sensitive Mgix emission line ratios are presented forRI =I(443.96 Å)/I(368.06 Å),R2 =I(439.17 Å)/I(368.06 Å),R3 =I(443.37 Å)/I(368.06 Å),R4 =I(441.22 Å)/I(368.06 Å), andR5 =I(448.28 Å)/I(368.06 Å). A comparison of these with observational data for a solar active region, obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals excellent agreement between theory and observation forR1 throughR4, with discrepancies that average only 9%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. However in the case ofR5, the theoretical and observed ratios differ by almost a factor of 2. This may be due to the measured intensity of the 448.28 Å line being seriously affected by instrumental effects, as it lies very close to the long wavelength edge of the SERTS spectral coverage (235.46−448.76 Å).

Some design and performance features of SUMER: solar ultraviolet measurements of emitted radiation

The instrument SUMER (solar ultraviolet measurements of emitted radiation) is designed to investigate structures and associated dynamical processes occurring in the solar atmosphere from the chromosphere through the transition region to the inner corona, over a temperature range from 104 to 2 multiplied by 106 K and above. The observations will be performed, on board SOHO (solar and heliospheric observatory) scheduled for launch in November 1995, by a scanning, normal-incidence telescope/spectrometer system in the wavelength range from 500 to 1610 angstrom. Spatial resolution requirements compatible with the pointing stability of SOHO are less than 1000 km corresponding to about 1-arcsec angular resolution. Doppler observations of EUV line shifts and broadenings should permit solar plasma velocity measurements down to 1 km s-1. We report here on some specific features of this instrument related to its pointing as well as its spatial and spectral resolution capabilities.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Coordinated observations with high resolution spectrographs (HRTS, SERTS, MSDP)

Abstract Observations with the High Resolution Telescope Spectrograph (HRTS) aboard Spacelab2 in 1985, and more recently with the Solar Extreme-ultraviolet Rocket Telescope and Spectrometer (SERTS) during the rocket flight of May 5, 1989 were well coordinated with the Meudon instruments, principally with the Multichannel Subtractive Double Pass (MSDP) spectrograph. These instruments allow the study of phenomena in a large temperature range and the determination of the energy budget. MSDP observations coordinated with the SERTS have permitted the analysis of physical parameters of coronal plasma surrounding dynamical chromospheric events, such as preflaring region and a filament. By combining Hα spectrograms and HRTS data, C IV flow (∼50 km s −1 ) detected at the footpoints of a prominence has been interpreted by horizontal velocities along the axis of the arches of the prominence.

Measurements of Active and Quiet Sun Coronal Plasma Properties with Serts EUV Spectra

The Solar EUV Rocket Telescope and Spectrograph (SERTS) obtained spectra and images of active regions, quiet Sun areas, and other solar features during successful flights in 1989, 1991, 1993, and 1995. The availability of multiple emission lines from eight ionization stages of iron (1) furnishes line ratio temperature diagnostic tools which are independent of elemental abundance uncertainties, (2) enables verification of the instrumental photometric calibration and atomic physics parameters through density- and temperature-insensitive ratios, (3) provides a means of deriving plasma densities, and (4) supplies input for DEM analyses. Temperatures derived from seven different line ratios are shown in Figure 1. For ratios among the higher ionization stages of iron, the derived active region temperature is greater than that of the quiet Sun; for ratios among the lower ionization stages, the active region and quiet Sun temperatures converge. Differential emission measure distributions were derived using the procedure developed by Monsignori-Fossi & Landini for SOHO. An active region DEM is shown in Fig 2. Details are provided in a paper submitted to Astrophysical Journal.