66 research outputs found
Intégration verticale et contrats en agriculture. I. R.F. d'Allemagne = Vertical integration and contracts in agriculture. I. F.R. of Germany. Internal information on agriculture 106, June 1973. VI/3359/73-F
HST observations of star clusters in NGC 1023: Evidence for three cluster populations?
Using HST images we have carried out a study of cluster populations in the
nearby S0 galaxy NGC 1023. In two WFPC2 pointings we have identified 221
cluster candidates. The small distance (~9 Mpc) combined with deep F555W and
F814W images allows us to reach about two magnitudes below the expected
turn-over of the globular cluster luminosity function. NGC 1023 appears to
contain at least three identifiable cluster populations: the brighter clusters
show a clearly bimodal color distribution with peaks at V-I = 0.92 and at V-I =
1.15 and in addition there are a number of fainter, more extended objects with
predominantly red colors. Among the brighter clusters, we find that the blue
clusters have somewhat larger sizes than the red ones with mean effective radii
of R(eff) ~ 2 and R(eff) ~ 1.7 pc, respectively. These clusters have luminosity
functions (LFs) and sizes consistent with what is observed for globular
clusters in other galaxies. Fitting Gaussians to the LFs of the blue and red
compact clusters we find turn-over magnitudes of M(TO,blue)=-7.58 and
M(TO,red)=-7.37 in V and dispersions of sigma(V,blue)=1.12 and
sigma(V,red)=0.97. The fainter, more extended clusters have effective radii up
to R(eff) ~ 10-15 pc and their LF appears to rise at least down to M(V) ~ -6,
few of them being brighter than M(V) = -7. We suggest that these fainter
objects may have a formation history distinct from that of the brighter GCs.Comment: 27 pages, 13 figures. Accepted for publication in the Astronomical
Journa
Gravitational waves from coalescing binaries and Doppler experiments
Doppler tracking of interplanetary spacecraft provides the only method
presently available for broad-band searches of low frequency gravitational
waves. The instruments have a peak sensitivity around the reciprocal of the
round-trip light-time T of the radio link connecting the Earth to the
space-probe and therefore are particularly suitable to search for coalescing
binaries containing massive black holes in galactic nuclei. A number of Doppler
experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS
OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI
spacecraft will perform three 40 days data acquisition runs with expected
sensitivity about twenty times better than that achieved so far. Central aims
of this paper are: (i) to explore, as a function of the relevant instrumental
and astrophysical parameters, the Doppler output produced by in-spiral signals
-- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii)
to identify the most important parameter regions where to concentrate intense
and dedicated data analysis; (iii) to analyze the all-sky and all-frequency
sensitivity of the CASSINI's experiments, with particular emphasis on possible
astrophysical targets, such as our Galactic Centre and the Virgo Cluster.Comment: 52 pages, LaTeX, 19 Postscript Figures, submitted to Phys. Rev.
The interstellar medium of the Antennae Galaxies
To study the properties of the interstellar medium in the prototypical
merging system of the Antennae galaxies (NGC 4038 and NGC 4039), we have
obtained CO(1-0), (2-1) and (3-2) line maps, as well as a map of the 870 micron
continuum emission. Our results are analysed in conjunction with data from
X-ray to radio wavelengths. In order to distinguish between exact coincidence
and merely close correspondence of emission features, we compare the
morphological structure of the different emission components at the highest
available angular resolution. To constrain the physical state of the molecular
gas, we apply models of photon dominated regions (PDRs) that allow us to fit CO
and [CII] data, as well as other indicators of widespread PDRs in the Antennae
system, particularly within the super giant molecular cloud (SGMC) complexes of
the interaction region (IAR) between the two galaxies. The modeled clouds have
cores with moderately high gas densities up to 4 10^4 / cm^3 and rather low
kinetic temperatures <=25K). At present, all these clouds, including those near
the galactic nuclei, show no signs of intense starburst activity. Thermal radio
or mid-infrared emission are all observed to peak slightly offset from the
molecular peaks. The total molecular gas mass of the Antennae system adds up to
\~10^10 M_sun. In the vicinity of each galactic nucleus, the moleculargas mass,
1-2 10^9 M_sun, exceeds that of the Galactic centre region by a factorof almost
100. Furthermore, the gas does not seem to deviate much from the N_{H_2}/I_CO
ratio typical of the disk of our Galaxy rather than our Galactic centre.Comment: 15 pages, 6 figure
Star cluster versus field star formation in the nucleus of the prototype starburst galaxy M82
We analyse high-resolution Hubble Space Telescope/Advanced Camera for Surveys
imaging of the nuclear starburst region of M82, obtained as part of the Hubble
Heritage mosaic made of this galaxy, in four filters (Johnson-Cousins
equivalent B, V, and I broad bands, and an Halpha narrow-band filter), as well
as subsequently acquired U-band images. We find a complex system of ~150 star
clusters in the inner few 100 pc of the galaxy. We do not find any conclusive
evidence of a cluster-formation epoch associated with the most recent starburst
event, believed to have occurred about 4-6 Myr ago. This apparent evidence of
decoupling between cluster and field-star formation is consistent with the view
that star cluster formation requires special conditions. However, we strongly
caution, and provide compelling evidence, that the `standard' simple stellar
population analysis method we have used significantly underestimates the true
uncertainties in the derived ages due to stochasticity in the stellar initial
mass function and the corresponding sampling effects.Comment: 10 pages, A&A, in pres
Stellar population synthesis at the resolution of 2003
We present a new model for computing the spectral evolution of stellar
populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across
the whole wavelength range from 3200 to 9500 A for a wide range of
metallicities. These predictions are based on a newly available library of
observed stellar spectra. We also compute the spectral evolution across a
larger wavelength range, from 91 A to 160 micron, at lower resolution. The
model incorporates recent progress in stellar evolution theory and an
observationally motivated prescription for thermally-pulsing stars on the
asymptotic giant branch. The latter is supported by observations of surface
brightness fluctuations in nearby stellar populations. We show that this model
reproduces well the observed optical and near-infrared colour-magnitude
diagrams of Galactic star clusters of various ages and metallicities.
Stochastic fluctuations in the numbers of stars in different evolutionary
phases can account for the full range of observed integrated colours of star
clusters in the Magellanic Clouds. The model reproduces in detail typical
galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky
Survey (SDSS). We exemplify how this type of spectral fit can constrain
physical parameters such as the star formation history, metallicity and dust
content of galaxies. Our model is the first to enable accurate studies of
absorption-line strengths in galaxies containing stars over the full range of
ages. Using the highest-quality spectra of the SDSS EDR, we show that this
model can reproduce simultaneously the observed strengths of those Lick indices
that do not depend strongly on element abundance ratios [abridged].Comment: 35 pages, 22 figures, to appear in MNRAS; version with full
resolution figures available at http://www.iap.fr/~charlot/bc2003/pape
Defizite in Forschung und Lehre – Bericht aus der Arbeitsgruppe „Betriebliche Marktwirtschaft“
Akzeptanz der Ergebnisse technischer Fortschritte durch die Verbraucher – empirische Relevanz
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