1,389 research outputs found
Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows
We have obtained radial gradients in the spectral features D4000 and Mg2 for
a sample of 11 central cluster galaxies (CCGs). The new data strongly confirm
the correlations between line-strength indices and the cooling flow phenomenon
found in our earlier study. We find that such correlations depend on the
presence and characteristics of emission lines in the inner regions of the
CCGs. CCGs in cooling flow clusters exhibit a clear sequence in the D4000-Mg2
plane, with a neat segregation depending on emission-line types and blue
morphology. This sequence can be modelled, using stellar population models with
a normal IMF, by a recent burst of star formation. In CCGs with emission lines,
the gradients in the spectral indices are flat or positive inside the
emission-line regions, suggesting the presence of young stars. Outside the
emission-line regions, and in cooling flow galaxies without emission lines,
gradients are negative and consistent with those measured in CCGs in clusters
without cooling flows and giant elliptical galaxies. Index gradients measured
exclusively in the emission-line region correlate with mass deposition rate. We
have also estimated the radial profiles of the mass transformed into new stars
which are remarkably parallel to the radial behaviour of the mass deposition
rate. A large fraction (probably most) of the cooling flow gas accreted into
the emission-line region is converted into stars. We discuss the evolutionary
sequence suggested by McNamara (1997), in which radio triggered star formation
bursts take place several times during the lifetime of the cooling flow. This
scenario is consistent with the available observations.Comment: 19 pages, 18 PostScript figures, accepted for publication in MNRA
The circumstellar medium of the peculiar supernova SN1997ab
We report the detection of the slow moving wind into which the compact
supernova remnant SN 1997ab is expanding. Echelle spectroscopy provides clear
evidence for a well resolved narrow (Full Width at Zero Intensity, FWZI ~ 180
km/s) P-Cygni profile, both in Ha and Hb, superimposed on the broad emission
lines of this compact supernova remnant. From theoretical arguments we know
that the broad and strong emission lines imply a circumstellar density (n ~
10^7 cm^-3). This, together with our detection, implies a massive and slow
stellar wind experienced by the progenitor star shortly prior to the explosion.Comment: 10 pages, 2 figures, acepted for publication in MNRAS. Uses
referee.sty, psfig.sty and mn.sty. A postscript file can also be retrieved at
http://www.strw.LeidenUniv.nl/~salamanc/latest.htm
An analytical approach to the external force-free motion of pendulums on surfaces of constant curvature
The dynamics of external force free motion of pendulums on surfaces of constant Gaussian curvature is addressed when the pivot moves along a geodesic obtaining the Lagrangian of the system. As an application it is possible the study of elastic and quantum pendulums
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