The Charge, Element, and Isotope Analysis System CELIAS on SOHO
Courtesy of SOHO/CELIAS/(sensor name) team. SOHO is a mission of international cooperation between ESA and NASA.
The CTOF sensor determines for every charged particle entering the sensor its mass, charge and energy. To show the ionic and elemental composition of the minor ions in the solar wind we plot a histogram of registered particles in mass and mass/charge, thus integrating over energy. A compilation of all PHA data for the time period between DOY 150 and DOY 199 of 1996 is shown in the figure below.
Clearly, the prominent minor ions carbon, oxygen, silicon and iron can be identified easily, with their respective charges. But even less abundant minor ions, e.g. Ne or Mg can be identified.
In the following panels the iron freeze-in temperature and the mean charge of the iron ion charge states are shown. They are derived from SOHO/CELIAS/CTOF data and are ordered in Carrington rotations. Both the freeze-in temperature and the mean charge are calculated from the individual iron ion densities (Fe8+ - Fe16+) and smoothed with a boxcar average of two hours width.
Movie showing iron charge state distribution for DOY 150 until 221 of 1996 in daily images. The E/Q axis is a measure for the velocity of the iron ions. The "horizontal" lines are drawn for ion velocities of 300, 400 500, and 600 km/s from bottom to top, as indicated. The "vertical" lines give the charge state of the iron ion, as indicated. The charge state distribution is a measure of the electron temperature in the corona. If the charge state distribution is centered at high charges, the electron temperature is high and vice versa. Note the correlation of the average charge of the charge state distribution and ion velocity (pretty much the same as the solar wind proton velocity).
Here you can download
In the following picture the distribution of iron charges states is shown for DOY 196 of 1996 using CTOF PHA data. On this particular day even Fe16+ can be identified.
This CELIAS/MTOF spectrum was accumulated over a three day period (these values are uncorrected for efficiencies). The MTOF sensor was set in a mode that was optimized for observing solar wind species with masses above that of sulfur. This is why the peaks for Calcium (mass 40) and Iron (mass 56) are so dominant compared to, for example, Oxygen. In this color version of the figure, the peaks that are simply linedrawn are the elements commonly observed by in situ solar wind experiments: Carbon (mass 12 amu), Oxygen (mass 16 amu), Neon (mass 20), Magnesium (mass 24), Silicon (mass 28), and Iron (mass 56).
The elements and isotopes for which SOHO MTOF has given the first in situ spacecraft solar wind observations are in red. These include the Silicon isotopes (masses 29, 30), the element Phosphorus (mass 31), a Sulfur isotope (mass 34), the element Chlorine (mass 35) and its isotope (mass 37), an Argon isotope (mass 38), the Calcium isotopes (masses 42 and 44), the element Titanium (mass 48), the element Chromium (mass 52) and its isotope (mass 53), the Iron isotope (mass 54, there is also a shoulder for mass 57), the element Manganese (mass 55), the element Nickel (mass 58) and its isotopes (masses 60, 62). [For all but Argon 38, these are the first in situ solar wind observations by any means. There was a measurement of Argon 38 in the Apollo foil experiments, but it had a large uncertainty, and is not frequently quoted by the foil experimenters themselves for solar wind abundance measurements.]
The elements and isotopes that are shaded green are not observed routinely by conventional solar wind experiments. These include the element Nitrogen (mass 14), a Neon isotope (mass 22), the element Sodium (mass 23), the Magnesium isotopes (masses 25, 26), the element Aluminum (mass 27), the Sulfur element (mass 32), the Argon element (mass 36), and the Calcium element (mass 40). Measurements for Sulfur 32 have been made with the Ulysses SWICS experiment, by accumulating over several months of data, and using extensive fitting techniques (it is not really resolved from Iron and Magnesium). 22Ne and 36Ar were measured by the Apollo foil experiments. The remainder were first observed in the in situ solar wind by the MTOF prototype sensor, which was launched on WIND about 13 months before SOHO. However, MTOF has a major advantage over its prototype regarding temporal resolution, because of its higher collection power.
At the end of April 1998 a sequence of large CMEs was observed with SOHO/LASCO: On April 29 (DOY 119) a halo CME, on May 2 (DOY 122) a large CME, and on May 6 (DOY 126) another halo CME. With some delay these events were observed with spacecraft particle experiments of SOHO and ACE at L1. Using data from the CELIAS/STOF sensor onboard SOHO we can study for the first time the energy spectra and the charge state distribution of suprathermal particles in the energy range from 35 to 660 keV/e just above the solar wind distribution and below the low energy flare particle energies.
We made the following observations:
The He+/He++ ratio was strongly enhanced during the first halo CME. After a sudden rise it dropped successively to approximately zero. The May 2-3 CME shows much less enrichment of He+ in the suprathermal particles. In contrast, in the CME-related solar wind of May 2-3, 1998, a significant enhancement of He+ for an interval of more than 24 hours was found. The mean charge state of Fe of the pre-CME time period is lower than during and after the May 2-3 CME. In the second halo CME two kinds of material can be distinguished in time: One with higher charge states Fe and one with lower. During the time periods with shocks (DOY 121 and 124) and the first halo CME very hard spectra were observed with spectral indices of about 2 for He++. Simultaneously the SWICS and SWIMS instruments on the Advanced Composition Explorer (ACE) observed a most unusual elemental and charge state composition in the solar wind related to the May 2-3 CME: high and low charge states for all elements (e.g., Fe3+ to Fe16+), an enhanced 3He/4He ratio and a prolongued He+ enhancement measured by ACE/SWEPAM.
Here you can download some movies showing the data sets from the three CME events. Note that the fluxes are not yet fully calibrated.
Or all data sets in one movie:
Summary data, also called Key Parameter data, are part of the International Solar-Terrestrial Physics ( ISTP) program key parameter data set. From the CELIAS sensor data from SEM, CTOF, STOF, and the PM are provided with 5 minute time resolution. Starting with 16 July 1996, data files in CDF format are located in the SOHO Summary Database.
Heavy ion flux: This KP gives the integral flux of solar wind ions ranging from carbon up to iron in two energy bands. For each of the two energy bands, the ion flux is integrated over the entire energy range of the sensor. One component (data from the CTOF sensor) spans from 100 eV up to 50 keV, the other band (data from the HSTOF sensor) spans from 100 keV up to ~ 5 MeV. This Key Parameter is very helpful to identify particle events on the sun.Solar EUV emission: This KP gives the absolute photon flux of the full solar disk in two wavelength bands as measured by the Solar EUV Monitor (SEM).
The narrow band centers at the prominent and scientifically important He II 30.4 nm line (bandwidth of ± 4.0 nm), the wide band covers the absolute integral photon flux between 0.1 and 77 nm.