12 research outputs found
Perspective from a Younger Generation -- The Astro-Spectroscopy of Gisbert Winnewisser
Gisbert Winnewisser's astronomical career was practically coextensive with
the whole development of molecular radio astronomy. Here I would like to pick
out a few of his many contributions, which I, personally, find particularly
interesting and put them in the context of newer results.Comment: 14 pages. (Co)authored by members of the MPIfR (Sub)millimeter
  Astronomy Group. To appear in the Proceedings of the 4th
  Cologne-Bonn-Zermatt-Symposium "The Dense Interstellar Medium in Galaxies"
  eds. S. Pfalzner, C. Kramer, C. Straubmeier, & A. Heithausen (Springer:
  Berlin
Varying constants, Gravitation and Cosmology
Fundamental constants are a cornerstone of our physical laws. Any constant
varying in space and/or time would reflect the existence of an almost massless
field that couples to matter. This will induce a violation of the universality
of free fall. It is thus of utmost importance for our understanding of gravity
and of the domain of validity of general relativity to test for their
constancy. We thus detail the relations between the constants, the tests of the
local position invariance and of the universality of free fall. We then review
the main experimental and observational constraints that have been obtained
from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites
dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic
microwave background and big bang nucleosynthesis. At each step we describe the
basics of each system, its dependence with respect to the constants, the known
systematic effects and the most recent constraints that have been obtained. We
then describe the main theoretical frameworks in which the low-energy constants
may actually be varying and we focus on the unification mechanisms and the
relations between the variation of different constants. To finish, we discuss
the more speculative possibility of understanding their numerical values and
the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit
The Primordial Helium-4 Abundance from Observations of a Large Sample of Blue Compact Dwarf Galaxies
Book Review: Nocturnal Malagasy primates: Ecology, physiology and behavior. By P. Charles-Dominique, H. M. Cooper, A. Hladik, C. M. Hladik, E. Pages, G. S. Pariente, A. Petter-Rousseaux, J. J. Petter, and A. Schilling. Academic Press, New York, 1980
An accurate value of the deuterium/hydrogen (D/H) ratio in the local
interstellar medium (LISM) and a better understanding of the D/H variations
with position in the Galactic disk can provide essential information on the
primordial D/H ratio in the Galaxy at the time of the protosolar nebula, and
the amount of astration and mixing in the Galaxy over time. Recent measurements
have been obtained with UV spectrographs on FUSE, HST, and IMAPS using hot
white dwarfs, OB stars, and late-type stars as background light sources against
which to measure absorption by D and H in the interstellar medium along the
lines of sight. Recent analyses of FUSE observations of seven white dwarfs and
subdwarfs provide a weighted mean value of D/H = (1.52 +/- 0.08) 10(-5) (15.2
+/- 0.8 ppm), consistent with the value of (1.50 +/- 0.10) 10(-5) (15.0 +/- 1.0
ppm) obtained from analysis of lines of sight toward nearby late-type stars.
Both numbers refer to the ISM within about 100 pc of the Sun, which samples
warm clouds located within the Local Bubble. Outside of the Local Bubble at
distances of 200 to 500 pc, analyses of far-UV spectra obtained with IMAPS
indicate a much wider range of D/H ratios between 0.8 to 2.2 ppm, providing
information on inhomogeneous astration in the Galactic disk.Comment: 12 pages, 3 figure
