2 research outputs found
Observational evidence for gravitationally trapped massive axion(-like) particles
Unexpected astrophysical observations can be explained by gravitationally
captured massive particles, which are produced inside the Sun or other Stars
and are accumulated over cosmic times. Their radiative decay in solar outer
space would give rise to a `self-irradiation' of the whole star, providing the
time-independent component of the corona heating source. In analogy with the
Sun-irradiated Earth atmosphere, the temperature and density gradient in the
corona - chromosphere transition region is suggestive for an omnipresent
irradiation of the Sun. The same scenario fits other astrophysical X-ray
observations. The radiative decay of a population of such elusive particles
mimics a hot gas. X-ray observatories, with an unrivalled sensitivity below ~10
keV, can search for such particles. The elongation angle relative to the Sun is
the relevant new parameter.Comment: 35 pages, LaTeX, 9 figures. Accepted by Astroparticle Physic
On the recent star formation history of the Milky Way disk
We have derived the star formation history of the Milky Way disk over the
last 2 Gyr from the age distribution diagram of a large sample of open clusters
comprising more than 580 objects. By interpreting the age distribution diagram
using numerical results from an extensive library of N-body calculations
carried out during the last ten years, we reconstruct the recent star formation
history of the Milky Way disk. Our analysis suggests that superimposed on a
relatively small level of constant star formation activity mainly in small-N
star clusters, the star formation rate has experienced at least 5 episodes of
enhanced star formation lasting about 0.2 Gyr with production of larger
clusters. This cyclic behavior seems to show a period of 0.4+/-0.1 Gyr.Comment: Abridged abstract. Accepted by New Astronomy. Major changes. A number
of figures have been added in order to improve the discussion on error