arXiv subjects

Sidney van den Bergh

Publications and source records attributed to Sidney van den Bergh.

95 records · Page 6Linked to original sources

arXiv1995

A New Method for the Determination of the Hubble Parameter

By chance, the slope of the Mv(max) versus (B-V)max relation for recent theoretical models of supernovae of Type Ia (SNe Ia) by Hoflich & Khokhlov is indistinguishable from the slope of a reddening line in the V versus B-V plane. This coincidence allows one to determine a parameter Mv*(max) for SNe Ia that is independent of both supernova detonation model and of interstellar reddening. Calibrating Mv*(max) with observations of SNe Ia by Hamuy et al. yields values of the Hubble parameter Ho in the range 55 - 60 km s-1 Mpc-1 . The discrepancy between this result, and values of Ho recently obtained from observations of Cepheids in the Virgo cluster, suggests that either (1) the Cepheid distance scale is wrong, (2) the SN Ia models of Hoflich & Khokhlov are too bright by ~ 0.75 mag near maximum light, or (3) their models are too red by \~ 0.25 mag in B-V.

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arXiv1995

The Age of the Universe

It is found that the ages of the most metal-poor Galactic globular clusters are probably around 18 Gyr. On the other hand a Hubble parameter of 82 +/- 8 km/sec/Mpc (in conjunction with the standard Einstein-de Sitter model with an Omega =1 and Lambda =0) yields and age of the Universe of about 8 Gyr. Some possible reasons for this discrepancy are explored.

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arXiv1995

PERIGALACTIC DISTANCES OF GLOBULAR CLUSTERS

Luminosities and tidal radii of globular clusters have been used to estimate the perigalactic distances P of well-observed Galactic globulars that do not have collapsed cores. It is found that the cluster metallicity [Fe/H] correlates somewhat more strongly with P than it does with the present Galactocentric distances R of globular clusters. It is also found that both P and R correlate more strongly with the cluster half-light radii rh than they do with [Fe/H]. This suggests that cluster radii are mainly determined by global parameters of the (proto)Galaxy, whereas [Fe/H] may have been more strongly affected by local evolutionary effects. The strong correlation (P) = 0.70 +/- 0.05 between the perigalactic distances and half-light radii of globular clusters is particularly striking. The half-light radii rh of globular clusters in the outer halo of the Galaxy are found to correlate with R, and even more strongly with P. It is not yet clear how this result is to be reconciled with the Searle-Zinn scenario for the formation of the outer halo of the Galaxy. The tidal radii of clusters with collapsed cores appear to have been systematically over-estimated, resulting in perigalactic distances that are too large. Halo globulars with P > 15 kpc are (with the exception of NGC 2419) typically an order of magnitude less luminous than the clusters with P < 15 kpc that are associated with the main body of the Galaxy. The population of nuclear globular clusters with P < 1 kpc appears to be deficient in objects fainter than MV ~ -7. Clusters with well-determined ages having P > 15 kpc have ages in the range 9 - 16 Gyr, whereas globulars with P < 15 kpc all appear to have ages that are restricted to the narrower range 13 < T < 16 Gyr.

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arXiv1995

A PRELIMINARY CLASSIFICATION SCHEME FOR THE CENTRAL REGIONS OF LATE-TYPE GALAXIES

The large-scale prints in The Carnegie Atlas of Galaxies have been used to formulate a classification scheme for the central regions of late-type galaxies. Systems that exhibit small bright central bulges or disks (type CB) are found to be of earlier Hubble type and of higher luminosity than galaxies that do not contain nuclei (type NN). Galaxies containing nuclear bars, or exhibiting central regions that are resolved into individual stars and knots, and galaxies with semi-stellar nuclei, are seen to have characteristics that are intermediate between those of types CB and NN. The presence or absence of a nucleus appears to be a useful criterion for distinguishing between spiral galaxies and Magellanic irregulars.

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arXiv1993

Lyman Alpha Absorption and Tidal Debris

It is suggested that a significant fraction of the low column-density absorption features seen in the spectra of quasars are produced in pressure-confined tidal debris, that was built up in small groups and clusters of galaxies over a Hubble time. We show that the space-density and cross-section of tidal tails in groups of galaxies are large enough that they could constitute a major source of the low redshift Ly$α$ absorption features that are associated with galaxies. The space-density of groups within 10 Mpc of our galaxy is found to be 2.4 $\times 10^{-3}$ Mpc$^{-3}$, which is close to the $\sim 6 \times 10^{-3}$ Mpc$^{-3}$ space-density calculated for Ly$α$ absorbers, assuming they have a 1 Mpc radius. Other observational constraints on the properties of Ly$α$ absorber such as their velocity dispersion, correlation properties, dimensions and abundances, are shown to be consistent with this hypothesis.

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