| Speaker: | Prof. Ralph Neuhaeuser , University of Jena |
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| Title: | NEUTRON STAR WORK IN JENA |
| Abstract: |
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We try to constrain the nuclear Equation-of-State (EoS) by
observations of neutron stars in our galactic neighbourhood. There
are seven thermally emitting neutron stars known from X-ray and
optical observations, the so-called Magnificent Seven (M7),which are
young (few Myrs), nearby (one to few hundred pc), and radio-quiet
with blackbody-like X-ray spectra, so that we can observe their
surfaces. As bright X-ray sources, we can determine their rotational
(pulse) periods and their period derivatives from X-ray timing. From
XMM and/or Chandra X-ray spectra, we can determine their
temperatures. With precise astrometric observations using the Hubble
Space Telescope, we can determine their parallax (i.e. distance) and
optical flux (done for RXJ1856 and RXJ0720). From flux, distance, and
temperature, one can derive the radius using just the
Stefan-Boltzmann law. Then, from identifying atomic or cyclotron
absorption lines in X-ray spectra and also from rotational
phase-resolved spectroscopy, we can determine the compactness
(mass/radius) and/or gravitational redshift. This has also just been
successfully applied for one case (RBS1223). If also applied to
RXJ1856, radius (from luminosity and temperature) and compactness
(mass/radius) and/or gravitational redshift. This has also just been
successfully applied for one case (RBS1223). If also applied to
RXJ1856, radius (from luminosity and temperature) and compactness
(from X-ray data) will yield the mass and radius - for the first time
for an isolated single neutron star without previous mass exchange.
Recently, 60Fe was found in the Earth crust, which is believed to have formed in a recent nearby supernova, which may have had influence on the Earth cosmic ray flux, the climate, and possibly on life. If the time, distance, and mass of the progenitor of that supernova would be known, then one can test and constrain supernova ejecta models. Knowing the positions, proper motions, and distances of dozens of nearby neutron stars (within a few kpc), we can determine their past flight path and possible kinematic origin. For such calculations, we have to assume the otherwise unknown radial velocity (and to account for errors in the observables) through Monte-Carlo simulations. We can then find the stellar association, in which the neutron star may have been formed by a recent supernova, by tracing back its motion. If a neutron star seems to have flewn through a nearby young stellar association, where at least one supernova may have taken place given its current mass function, it may have formed there. We search for additional indications for such events, like run-away stars ejected in supernovae in binaries etc. Once the birth place of a neutron star in a supernova is found, we would have determined the distance of the supernova and the age of the neutron star (flight time as kinematic age). If all stars in such an association have formed roughly at the same time, as assumed by star formation theories, we also know the life-time and, hence, mass of the supernova progenitor star. In this way, we try to find the neutron star, which was born in the nearby recent supernova, which may have ejected the 60Fe found in the Earth crust. We can then test and calibrate supernova ejecta models. Any identification of a known neutron star with its birth association (and/or run-away star) would be interesting also to compare kinematic ages with characteristic ages, to study the formation and re-heating of the Local Bubble by supernovae, to compare the progenitor mass with the neutron star mass(if known), etc. We also compiled a catalog of all massive stars within 5 kpc around the Sun, in order to predict their final stage and, hence, the supernova rate in the solar neighborhood in the next few million years, partly also to predict small locations on the sky with slightly larger probability to detect gravitational waves. |