LESIA - Observatoire de Paris

Observations of the interplanetary hydrogen during solar cycles 23 and 24. What can we deduce on the local interstellar medium ?

mardi 25 juin 2013, par Frédéric Vincent (IAP)

Mardi 3 septembre 2013 à 11h00 , Lieu : Salle de conférence du bât. 17

The motion of the Sun within the Milky Way allows to probe the local interstellar medium (LISM) that interacts with the heliosphere and whose physical parameters may vary during the journey of the Sun. Hence, recent observations of interstellar helium atoms by the IBEX spacecraft indicate that the LISM velocity vector may have changed since previous measurements by the Ulysses spacecraft about 20 years ago. The interplanetary hydrogen (IPH), a population of neutrals that fill the space between planets inside the heliosphere, carries the signature of the LISM and the heliospheric interface. More than 40 years of space-based studies of the backscattered solar Lya emission from the IPH provided limited access to the velocity distribution, with the first partial temporal map of the IPH line-shift during the solar cycle 23. I will present the results of last IPH observations made by the Space Telescope Imaging Spectrograph during the solar cycle 24. These results have been compiled with previous measurements and the whole set has been compared to physically realistic models to test the LISM physical parameters as measured by Ulysses and IBEX. This comparison suggests that the LISM velocity vector has not changed significantly since Ulysses measurements. At last, I will briefly present the spatial heterodyne spectrometer, an emerging technique of interferometry, that can be used to obtain all-sky IPH Lya maps in order to improve the study of the heliosphere and its surroundings.