Physical parameters of the Local Interstellar Medium (LISM) through coordinated
observations of the gravitational focusing cone at 1 AU
Members
- John Raymond, SOHO UVCS,
Harvard Smithsonian Center for Astrophysics, Cambridge, MA, USA
- John Vallerga, EUVE,
Space Sciences Laboratory, University of California Berkeley, Berkeley, CA
- George Gloeckler, ACE and Ulysses
SWICS,
Dept. of Physics and IPST, University of Maryland, College Park, MD, USA
& Dept. of Atmospheric, Oceanic and Space Sciences, University
of Michigan, Ann Arbor, MI, USA
- Daniel Rucinski(deceased), Maciej Bzowski,
Modeling,
Space Research Centre, Warsaw, Poland,
- Howard Ogawa, Darrell
Judge, Don McMullin, SOHO CELIAS
SEM,
Space Science Center, University of Southern California, Los Angeles, CA,
U.S.A.
- Rosine Lallement,
Jean-Loup Bertaux, EUV Absorption, SOHO SWAN, Modeling,
Service d’Aéronomie du CRNS, Verrières le Buisson, France
- William Thompson,
SOHO CDS,
Goddard Space Flight Center, Greenbelt, MD, U.S.A.
- Manfred Witte, Ulysses GAS,
Max-Planck-Institut für Aeronomie, Lindau/Harz, Germany
- Hans Fahr, Modeling,
Institut für extraterrestrische Forschung, Universität Bonn, Bonn,
Germany
- Sergei Chalov, Modeling,
Institute for Problems in Mechanics, Russian Academy of Sciences, Moscow,
Russia
- Reinald Kallenbach,
Ruedi von Steiger, ISSI,
International Space Science Institute (ISSI), Bern, Switzerland
- Eberhard Möbius, Chair,
AMPTE SULEICA, SOHO CELIAS
Institute for the Study of Earth, Oceans, and Space
& Department of Physics, University of New Hampshire, U.S.A.
- Toshio Terasawa, M.
Oka, GEOTAIL, NOSOMI,
University of Tokyo, Tokyo, Japan
- Hirotomo Noda, GEOTAIL,
NOSOMI
National Astronomical Observatory of Japan, Misuzawa, Japan
Additional participants and/or consultants:
- Vladimir Izmodenov, Modeling of interstellar
flow
Department of Mechanics and Mathematics, Moscow State University, Moscow,
Russia
- Anuschka Pauluhn, SUMER
calibration
International Space Science Institute (ISSI), Bern, Switzerland
- Lukas Saul, Pickup ions, modeling,
(graduate student at UNH)
Department of Physics, University of New Hampshire, U.S.A.
- Stephen Fuselier, IMAGE LENA observations
of interstellar gas
Lockheed Martin Advanced Technology Laboratory, Palo Alto, CA, U.S.A.
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Executive Summary
The ISSI Team has analyzed the combined data sets from coordinated campaigns
to observe the interstellar helium cone with in-situ and remote sensing methods,
including the necessary supporting observations over three years from 1998 through
2000. The data sets are comprised of observations of pickup ions with ACE and
Ulysses SWICS, neutral atoms with Ulysses GAS, UV backscattering with SOHO UVCS
and EUVE. We have made use of simultaneous monitoring of solar UV radiation
with SOHO and of the interplanetary conditions with SOHO, ACE and WIND. The
analysis is comprised of detailed modeling of the interstellar gas and its secondary
products in the heliosphere. This effort has resulted in a consistent set of
interstellar He parameters. Previous apparent differences between the complementary
observations could be traced to incomplete information on ionization rates and
solar illumination of the interstellar gas in the inner heliosphere.
The results from this work have been highlighted in a Science@NASA
feature release, entitled "Shields
Up!" and on the ESA
Science & Technology webpage as a Ulysses reseach news item.
Publications and Presentations
The results from the activity of this Team have been disseminated in
a number of publications and presentations.
Preliminary results by the Team were reported at the World Space Congress in
Houston in October 2002 in talks by G. Gloeckler, R. Lallement, and M. Witte.
The Team also presented a Poster, which is available as a PDF
File.
A series of 7 papers on the Team results is in press for a special
section in Astronomy & Astrophysics and will appear soon.
Continuation of the Team Work
A new ISSI
Team with some members of this Team is now working on a consolidation of
the interstellar H parameters.
More Details on the Work Including Links to Observations and Models
- A simplified overview about the Local Interstellar Medium can be found on
the Interstellar
Medium Page that was prepared at the University of New Hampshire by students.
- The velocity distribution of the neutral interstellar helium as it streams
through the inner heliosphere is observed as neutral particle images with
the Ulysses
/ GAS Instrument. These observations allow a deduction of the interstellar
flow vector (speed and arrival direction), He density and temperature. The
detailed analysis of these data is a key element in the work of this Team.
- The interstellar neutral He density has been derived independently from
the Neutral Gas observations from double charge exchange with solar wind He2+
through the emerging He2+ pickup ions with Ulysses SWICS. The analysis of
Ulysses SWICS data is being carried out mainly at the University
of Maryland, the University
of Michigan, the University
of Bern and at ISSI.
- Under the influence of the Sun's garvitational force the interstellar gas
flow is focused on the downwind side of the Sun. This leads to a density enhancement
(coined the "Interstellar Focusing Cone"), which the Earth traverses
on its orbit, encountering the maximum around December 4 each year. This feature
has been observed first through resonant scattering of the Sun's He I 384
nm with Pioneer Venus and Prognoz and more recently in He+ pickup ions with
AMPTE
SULEICA, ACE
SWICS, and NOZOMI.
ACE SWICS provides contiguous coverage and has led to a detailed analysis
of the cone. The shape of the cone is modeled consistently with the same interstellar
He parameters as found with Ulysses GAS and SWICS.
- The Extreme UltraViolet Explorer (EUVE)
has provided the best mapping of the He I 384 nm backscatter glow at 1 AU.
Using the Earth's exosphere as a giant absorption cell and employing Doppler
Dimming of the resonant glow, has led to independent values for the He flow
vector, which are consistent with the neutral gas observations.
- SOHO UVCS observes the Sun's
corona in the UV region of the spectrum. With this capability it also sees
the interstellar He focusing cone close to the Sun (at 0.1 - 0.2 AU). Together
with the other observations of the cone at 1 AU SOHO UVCS provides convincing
evidence that an additional ionization process (in addition to solar UV and
solar wind charge exchange) is needed with increasing importance close to
the Sun, most probably electron impact ioinization.
- SOHO / CELIAS
� SEM provides simultaneous and continuos monitoring of the UV radiation
responsible for He ionization. The ionizing radiation was also monitored with
full disk images by SOHO CDS.
The spectral shape and position of the HeI 384 nm line was determined with
SOHO SUMER.
Ionization and solar illumination had only been inferred in the past.
- The Team also discussed the interstellar neutral gas observations with IMAGE
LENA, which were reported to the Team by Stephen Fuselier and Peter Wurz.
The ongoing ISM Neutral
Discussion can be followed on the web.
Useful Links
Related ISSI Team Sites
Documents