arXiv subjects

Sidney van den Bergh

Publications and source records attributed to Sidney van den Bergh.

At least 19 recordsLinked to original sources

arXiv2012

A Search for OB Associations Near Southern Long-Period Cepheids. V. AQ Puppis and V620 Puppis

A photometric UBV survey is presented for 610 stars in a region surrounding the Cepheid AQ Puppis and centered southwest of the variable, based upon photoelectric measures for 14 stars and calibrated iris photometry of photographic plates of the field for 596 stars. An analysis of reddening and distance for program stars indicates that the major dust complex in this direction is ~1.8 kpc distant, producing differential extinction described by a ratio of total-to-selective extinction of R=Av/E(B-V)=3.10+-0.20. Zero-age main-sequence fitting for the main group of B-type stars along the line of sight yields a distance of 3.21+-0.19 kpc (Vo-Mv=12.53+-0.13 s.e.). The 29.97d Cepheid AQ Pup, of field reddening E(B-V)=0.47+-0.07 (E(B-V)(B0)=0.51+-0.07), appears to be associated with B-type stars lying within 5' of it as well as with a sparse group of stars, designated Turner 14, centered south of it at J2000.0 = 07:58:37, -29:25:00, with a mean reddening of E(B-V)=0.81+-0.01. AQ Pup has an inferred luminosity as a cluster member of =-5.40+-0.25 and an evolutionary age of 3x10^7 yr. Its observed rate of period increase of 300.1+-1.2 s/yr is an order of magnitude larger than what is observed for Cepheids of comparable period in the third crossing of the instability strip, and may be indicative of a high rate of mass loss or a putative fifth crossing. Another sparse cluster, designated Turner 13, surrounds the newly-recognized 2.59d Cepheid V620 Pup, of space reddening E(B-V)=0.64+-0.02 (E(B-V)(B0)=0.68+-0.02), distance 2.88+-0.11 kpc (Vo-Mv=12.30+-0.08 s.e.), evolutionary age 10^8 yr, and an inferred luminosity as a likely cluster member of =-2.74+-0.11. V620 Pup is tentatively identified as a first crosser, pending additional observations.

astro-ph.SR↗

arXiv2012

Luminosities of Barred and Unbarred S0 Galaxies

Lenticular galaxies with M_B < -21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be ~0.4 mag brighter than than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An E galaxy might be misclassified as an S0, or an S0 as an E. However, an E will never be misclassified an SB0, nor will an SB0 ever be called an E. This asymmetry is important because elliptical (E) galaxies are typically twice as luminous as lenticular (S0) galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.

astro-ph.CO↗

arXiv2012

Sizes of Galactic Globular Clusters

A study is made of deviations from the mean power-law relationship between the Galactocentric distances and the half-light radii of Galactic globular clusters. Surprisingly, deviations from the mean R_h versus R_gc relationship do not appear to correlate with cluster luminosity, cluster metallicity, or horizontal branch morphology. Differences in orbit shape are found to contribute to the scatter in the R_h versus R_gc relationship of Galactic globular clusters.

astro-ph.GA↗

arXiv2011

Hubble and Shapley - Two Early Giants of Observational Cosmology

Observational cosmology of the first decades of the Twentieth Century was dominated by two giants: Edwin Hubble and Harlow Shapley. Hubble's major contributions were to the study and classification of individual galaxies with large telescopes, whereas Shapley is best remembered for his work on groups and clusters of galaxies using telescopes of more modest aperture.

physics.hist-ph↗

arXiv2011

Discovery of the Expansion of the Universe

The myth that the expansion of the Universe was discovered by Hubble was first propagated by Humason (1931). The true nature of this discovery turns out to have been both more complex and more interesting.

physics.hist-ph↗

arXiv2011

Some Systematics of Galactic Globular Clusters

The global properties of all known Galactic globular clusters are examined. The relationship between the luminosities and the metallicities of Galactic globular clusters is found to be complex. Among luminous clusters there is a correlation in the sense that the oldest clusters are slightly more metal deficient than are younger clusters. However, no such clear-cut relationship is found among the faintest globular clusters. The central concentration index C of globular clusters is seen to be independent of metallicity. The dependence of the half-light radii of globular clusters on their Galactocentric distances can be approximated by the relation $R_h α R^{2/3}_{gc}$. Clusters with collapsed cores are mostly situated close to the Galactic nucleus. For $R_{gc} < 10$ kpc the luminosities and the radii of clusters appear to be uncorrelated. The Galaxy differs from the LMC and the SMC in that it appears to lack highly flattened luminous clusters. Galactic globular clusters with ages $\geq$ 13.0 Gyr are all of Oosterhoff type II, whereas almost all of those with ages $<$ 13.0 Gyr have been assigned to Oosterhoff type I. Globular clusters with ages $<$11.5 Gyr are all located in the outer Galactic halo, have below-average luminosities and above-average radii. On the other hand the very old globular cluster NGC 6522 is situated close to the Galactic nucleus.

astro-ph.GA↗

arXiv2011

The Curious Case of Lemaitre's Equation No. 24

The 1927 discovery of the expansion of the Universe by Lemaitre was published in French in a low-impact journal. In the 1931 high-impact English translation of this article a critical equation was changed by omitting reference to what is now known as the Hubble constant. That the section of the text of this paper dealing with the expansion of the Universe was also deleted from that English translation suggests a deliberate omission by the unknown translator.

physics.hist-ph↗

arXiv2011

A Fundamental Line for Elliptical Galaxies

Recent studies have shown that massive galaxies in the distant universe are surprisingly compact, with typical sizes about a factor of three smaller than equally massive galaxies in the nearby universe. It has been suggested that these massive galaxies grow into systems resembling nearby galaxies through a series of minor mergers. In this model the size growth of galaxies is an inherently stochastic process, and the resulting size-luminosity relationship is expected to have considerable environmentally-dependent scatter. To test whether minor mergers can explain the size growth in massive galaxies, we have closely examined the scatter in the size-luminosity relation of nearby elliptical galaxies using a large new database (Nair & Abraham 2010) of accurate visual galaxy classifications. We demonstrate that this scatter is much smaller than has been previously assumed, and may even be so small as to challenge the plausibility of the merger driven hierarchical models for the formation of massive ellipticals.

astro-ph.CO↗

arXiv2011

How Different are Normal and Barred Spirals?

No significant color differences are found between normal and barred spirals over the range of Hubble stages a - ab - b - bc. Furthermore, no significant difference is seen between the luminosity distributions of normal and barred galaxies over the same range of Hubble stages. However, SBc galaxies are found to be systematically fainter than Sc galaxies at 99% confidence. The observation that normal and barred spirals with Hubble stages a - ab - b - bc have indistinguishable intrinsic colors hints at the possibility that the bars in such spiral galaxies might be ephemeral structures. Finally, it is pointed out that lenticular galaxies of types S0 and SB0 are systematically fainter than are other early-type galaxies, suggesting that such galaxies are situated on evolutionary tracks that differ systematically from those of galaxies that lie along the E - Sa - Sb -Sc and E - SBa - SBb - SBc sequences.

astro-ph.CO↗

arXiv2010

A Strange Mènage Á Trois

The Magellanic Clouds may have joined our Milky Way system quite recently. The Large Magellanic Cloud turns out to be a remarkably luminous object that is close to the upper luminosity limit of the class of magellanic irregular galaxies.

astro-ph.CO↗

arXiv2010

A Comparison Between the Half-Light Radii, Luminosities, and UBV Colors of Globular Clusters in M31 and the Galaxy

The Milky Way System and the Andromeda galaxy experienced radically different evolutionary histories. Nevertheless, it is found that these two galaxies ended up with globular cluster systems in which individual clusters have indistinguishable distributions of half-light radii. Furthermore globulars in both M31 and the Galaxy are found to have radii that are independent of their luminosities. In this respect globular clusters differ drastically from early-type galaxies in which half-light radius and luminosity are tightly correlated. Metal-rich globular clusters in M31 occupy a slightly larger volume than do those in the Galaxy. The specific globular cluster frequency in the Andromeda galaxy is found to he significantly higher than it is in the Milky Way System. The present discussion is based on the 107 Galactic globular clusters, and 200 putative globulars in M31, for which UBV photometry was available.

astro-ph.CO↗

arXiv2010

The Environmental Dependence of the Luminosity-Size Relation for Galaxies

We have examined the luminosity-size relationship as a function of environment for 12150 SDSS galaxies with precise visual classifications from the catalog of Nair & Abraham (2010a). Our analysis is subdivided into investigations of early-type galaxies and late-type galaxies. Early-type galaxies reveal a surprisingly tight luminosity-size relation. The dispersion in luminosity about the fiducial relation is only ~0.14 dex (0.35 mag), even though the sample contains galaxies which differ by a factor of almost 100 in luminosity. The dispersion about the luminosity-size relation is comparable to the dispersion about the fundamental plane, even though the luminosity-size relation is fundamentally simpler and computed using purely photometric parameters. The key contributors to the dispersion about the luminosity-size relation are found to be color and central concentration. Expanding our analysis to the full range of morphological types, we show that the slope, zero point, and scatter about the luminosity-size relation is independent of environmental density. Our study thus indicates that whatever process is building galaxies is doing so in a way that preserves fundamental scaling laws even as the typical luminosity of galaxies changes with environment. However, the distribution of galaxies along the luminosity-size relation is found to be strongly dependent on galaxy environment. This variation is in the sense that, at a given morphology, larger and more luminous galaxies are rarer in sparser environments. Our analysis of late-type galaxy morphologies reveals that scatter increases towards later Hubble types. Taken together, these results place strong constraints on conventional hierarchical models in which galaxies are built up in an essentially stochastic way.

astro-ph.CO↗

arXiv2009

Lenticular Galaxies and Their Environments

It is widely believed that lenticular (S0) galaxies were initially spirals from which the gas has been removed by interactions with hot cluster gas, or by ram-pressure stripping of cool gas from spirals that are orbiting within rich clusters of galaxies. However, problems with this interpretation are that: (1) Some lenticulars, such as NGC 3115, are isolated field galaxies rather than cluster members. (2) The distribution of flattening values of S0 galaxies in clusters, in groups and in the field are statistically indistinguishable. This is surprising because one might have expected most of the progenitors of field S0 galaxies to have been flattened late-type galaxies, whereas lenticulars in clusters are thought to have mostly been derived from bulge-dominated early-type galaxies. (3) It should be hardest for ram-pressure to strip massive luminous galaxies with deep potential wells. However, no statistically significant differences are seen between the luminosity distributions of early-type Shapley-Ames galaxies in clusters, groups and in the field. (4) Finally, both ram-pressure stripping and evaporation by hot intra-cluster gas would be most efficient in rich clusters. However, the small number of available data in the Shapley-Ames sample appears to show no statistically significant differences between the relative frequencies of dust-poor S0_1 and dust-rich S0_3 galaxies in clusters, groups and in the field. It is tentatively concluded that ram-pressure stripping, and heating by intra-cluster gas, may not be the only evolutionary channels that lead to the formation of lenticular galaxies. It is speculated that gas starvation, or gas ejection by active nuclei, may have play a major role in the formation of a significant fraction of all S0 galaxies.

astro-ph.CO↗

arXiv2009

What Are S0 Galaxies?

The data collected in the Shapley-Ames catalog of bright galaxies show that lenticular (S0) galaxies are typically about a magnitude fainter than both elliptical (E) and early spiral (Sa) galaxies. Hubble (1936) was therefore wrong to regard S0 galaxies as being intermediate between morphological types E and Sa. The observation that E5-E7 galaxies are significantly fainter than objects of sub-types E0-E5 suggests that many of the flattest 'ellipticals' may actually be misclassified lenticular galaxies. In particular it is tentatively suggested all E7 galaxies might actually be misclassified S0_1 (7) galaxies. The present results are consistent with the view that galaxies belonging to the S0 class evolved in environments in which they typically lost more than half of their original luminous material.

astro-ph.CO↗

arXiv2008

How Do Galaxies Form?

It is currently believed that galaxies were assembled via chaotic hierarchical mergers between massive cold dark matter halos, in which baryonic star forming matter was embedded. One would therefore expect the properties of individual galaxies to be determined by numerous independent factors such as star forming history, merger history, mass, angular momentum, size and environment. It is therefore surprising to find that galaxies actually appear to form an (almost) one parameter family in which galaxy mass is the dominant factor.

astro-ph↗

arXiv2008

The Magnitude-Diameter Relation of Galaxies

We investigate the dependence of the luminosity-diameter relation of galaxies on the environment. This study is based on a comparison between the 80 galaxies in the Shapley-Ames Catalog that are located within a distance of 10 Mpc, and the luminosity-diameter relation for galaxies in great clusters such as Virgo and Coma. A relatively tight linear correlation is observed between the absolute magnitudes and the logarithms of the linear diameters of galaxies located within 10 Mpc. Surprisingly this observed power-law relationship appears to be almost independent of environment and local mass density as defined by Karachentsev & Malakov. However, at a given luminosity, early-type galaxies are (on average) slightly more compact than are objects of a later type. Unexpectedly the present results appear to indicate that the luminosity-diameter relation for the galaxies within 10 Mpc is indistinguishable from what is observed in the much denser Virgo cluster. Galaxies appear to form an almost one-dimensional family in parameter space. It remains a mystery why the luminosity-diameter relation for galaxies is so insensitive to environment.

astro-ph↗

arXiv2008

Luminosity-Diameter Relations for Globular Clusters and Dwarf Spheroidal Galaxies

It is shown that globular clusters and the dwarf spheroidal companions of the Galaxy have a different distribution of flattening values, and appear to occupy adjacent regions of the M_v versus log R_h plane that can be separated by what will be referred to as the Shapley line. Surprisingly, typical dwarf spheroidal companions to the Milky Way System are fainter than the average Galactic globular cluster.

astro-ph↗

arXiv2008

The Flattening of Globular Clusters

In the three nearest luminous galaxies, the Milky Way System, the Andromeda Galaxy and NGC 5128 the brightest globular clusters are rounder than the faintest ones. On the other hand (contrary to some previous results) the flattening of individual LMC clusters is found to be independent of their luminosities. This suggests the possibility that the relationship between the flattening and luminosity of clusters might depend on host galaxy luminosity. No significant differences are found between the intrinsic flattening distributions of Galactic old halo, Galactic young halo and Galactic bulge/disk clusters. Such a dependence might perhaps have been expected if tidal forces (which are largest at small Galactocentric distances) removed angular momentum from globular clusters. The preliminary conclusion by Norris that clusters with blue horizontal branches are more flattened than red HB clusters is not confirmed by the larger data base that is now available. In other words there is no evidence for the puzzling claimed correlation between the flattening and the horizontal branch morphology of Galactic globular clusters.

astro-ph↗