Issue |
A&A
Volume 426, Number 3, November II 2004
|
|
---|---|---|
Page(s) | 875 - 884 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20035929 | |
Published online | 18 October 2004 |
Modeling the interstellar-interplanetary helium 58.4 nm resonance glow: Towards a reconciliation with particle measurements
1
Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson, France e-mail: rosine.lallement@aerov.jussieu.fr
2
Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS 50, Cambridge, MA 02138, USA
3
Space Sciences Laboratory, University of California, Berkeley CA 94720-7450, USA
4
Institut Leprince-Ringuet, École Polytechnique 91128 Palaiseau, France
Received:
22
December
2003
Accepted:
14
May
2004
Pioneering observations of the diffuse HeI-58.4 nm background radiation were
performed with a series of satellites in the 70's.
Today, their published results on the flow of interstellar helium atoms in the heliosphere
are still in contradiction with (i) the results of the particle experiments, i.e.
in situ detection of neutrals
and pickup ions; (ii) expectations from heliospheric models and comparison with the hydrogen flow;
(iii) results of the recent helium glow
observations with the Extreme Ultraviolet
Explorer (EUVE). Here we discuss these data sets and their modeling, together with the EUVE data
and the first
coronographic observations of the helium glow obtained with
the Ultraviolet
Coronographic Spectrometer (UVCS) on board SOHO.
We show how they can all be made compatible, and reconciled with in situ data.
We have
reanalysed the Prognoz data and we derive an updated and higher value of
the
background noise level. Based on this
we can now fit the data satisfactorily with the same set of
helium parameters as that one derived from recent EUVE and in situ data. We suggest that other early
data sets
could be reanalyzed in the same way.
Using this updated analysis,
EUVE and SOHO-UVCS measurements, we find that all glow
data are compatible with the interstellar
parameters km s-1,
K,
deg,
6.0 deg (downwind axis, ecliptic coordinates),
as well as with the solar parameters
derived from SOHO CELIAS-SEM, SUMER and CDS observations, i.e.
the helium photoionisation rate, the 58.4 nm irradiance, and the 58.4 nm Doppler width,
found to be between 60 and 90 mÅ (30 and 45 km s-1). The density is the least constrained parameter from
the glow measurements. Prognoz lateral scans, EUVE LWS and SOHO UVCS data are
compatible with an interstellar helium
density n0 in the range 0.013–0.016 cm-3. Prognoz anti-solar data and
EUVE scanner data lead to a 40% lower value, suggesting uncertainties in the calibrations.
A large part of the contradictions between particle and remote
sensing results are thus
removed, since the
above parameters are very similar to those derived from in situ data.
The high electron impact rates inferred from the
UVCS remote sensing observations imply high fluxes of newly produced helium pickup ions,
which can possibly explain in part the observed correlation between H+ and He+
pickup fluxes, and the inverse correlation between He+ fluxes and
solar wind velocity.
Key words: interplanetary medium / Sun: solar wind / plasmas / ISM: atoms / ISM: kinematics and dynamics
© ESO, 2004
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.