---
abstract: 'We determine the proton and helium nuclei release times at the Sun for
  25 SEP events within the time period May 8, 1996-June 20, 2001, and compare them
  to each other. The event onset times at 1 AU are determined with a Poisson-CUSUM
  method, and the solar release times are obtained by the velocity dispersion analysis.
  Velocity dispersions were derived in the energy range 14-51 MeV/n. If the release
  times of protons and helium nuclei do not overlap within their error limits, and
  if protons are released earlier than helium, then the helium event is defined as
  ``delayed''''. Seventeen helium events (68\%) were found to be ``delayed'''' and
  only eight (32\%) ``non-delayed''''. The average delay was (34 \ensuremath\pm
  18) minutes. The event-related flare location had an important role in the ``non-delayed''''
  events. A significant difference was found in the helium-to- proton ratios at the
  time of maximum intensity of the ``delayed'''' and ``non-delayed'''' events. No
  clear evidence was found that the ``delayed'''' and ``non-delayed'''' events would
  correspond the classical gradual-impulsive division of SEP events. We find that
  the delay is related to the poor magnetic connection between the flare site and
  the spacecraft.'
adsnote: Provided by the SAO/NASA Astrophysics Data System
adsurl: https://ui.adsabs.harvard.edu/abs/2005A&A...442..673H
authors:
- K. Huttunen-Heikinmaa
- E. Valtonen
- T. Laitinen
category: publications
date: '2005-11-01'
doi: 10.1051/0004-6361:20042620
draft: false
featured: false
journal: A&A
month: November
number: '2'
pages: 673-685
projects: []
publication: A&A
publication_types:
- '2'
tags:
- Acceleration of particles
- 'Methods: data analysis'
- 'Sun: coronal mass ejections (CMEs)'
title: 'Proton and helium release times in SEP events observed with SOHO/ERNE'
type: ARTICLE
volume: '442'
year: '2005'
---