Prof.dr. Henny J.G.L.M. Lamers
Astronomical Institute Utrecht
Princetonplein 5
NL-3584CC Utrecht
Tel: +31 30 253 5212
Fax: +31 30 253 5201
E-mail: H.J.G.L.M.Lamers[at]
Room: BBL769

Popular lectures

- Evolution of Stars and Stellar Populations
- Star Clusters & Resolved Stellar Populations

Staff member(s):
- Søren Larsen
- Henny Lamers

- Peter Anders

PhD student(s) + supervisor(s):
Diederik Kruijssen (HJGLML)

Star clusters are very useful extragalactic “chronometers”:
Some have survived since shortly after the “Big Bang” (i.e. the globular clusters), while others are still forming today. Observations allow us to measure the ages of individual star clusters and determine their chemical composition. Thus, in principle star clusters provide a unique tool which potentially allows us to reconstruct the entire star formation histories of galaxies. Our research aims to exploit this potential and quantify its shortcomings (e.g. by quantifying the important effect of cluster disruption) both from an observational and theoretical point of view.

Gieles, M., et al. 2006: Observational Evidence for a Truncation of the Star Cluster Initial Mass Function at the High Mass End, A&A 446, L9
Gieles, M. et al. 2005: The Luminosity Function of Young Star Clusters: Implications for the Maximum Mass and Luminosity of Clusters, A&A 450, 129
Anders & Fritze - v. Alvensleben 2003 view
Anders, Gieles & de Grijs 2006 view
Lamers, Anders & de Grijs 2006 view

Relevant collaborations:
SAGES group,
GALEV group
Stellar dynamics and stellar mass function group Bonn
Stellar dynamics group Amsterdam
Mark Gieles and Markus Kisler-Patig, ESO Nate Bastian, Univ College London

Relevant instruments:
Among others:

BSc project(s):
Project name: "Simulating The Appearance of Star Clusters"
Project supervisor: SL

Project description:
The idea here is to simulate the appearance of star clusters in galaxies at different distances and at different resolution (ground-based, HST, etc.).
We know that clusters follow well-defined density profiles: densities are higher in the centre and decrease outwards, typically about half of the stars are found within a radius of a few pc. The types of stars (their brightness and colour) found within a cluster depends on the age. For star clusters in our own galaxy, the stars can be resolved and studied in great detail, but in other galaxies the stars can only be partially resolved, and as we go to greater distances a cluster eventually becomes recognizable only as a slightly extended blob.
What does a star cluster look like in galaxies at different distances, observed with different instruments, and as a function of age? This is the question which will be addressed in this project.

Project name: "Resolution Effects on the Detection of Star Clusters"
Project supervisor: SL
Images from the Hubble Space Telescope allows us to study stars and star clusters in other galaxies in great detail. This also means that extended "fuzzy" blobs which may look like a cluster at poor resolution start to be resolved into sub-units in better quality data. The goal of this project is to degrade HST images of nearby galaxies to the resolution which can be achieved with ground-based data, or in more distant galaxies. Various common techniques to detect star clusters will then be applied to images at the original and degraded resolution, and the reliability of star cluster classification techniques will be tested.
More projects are listed at

Project name: "How colour transformations can influence your parameter determination" Project supervisor: PA
Project description:
Each telescope and instrument has its own set of filters and detectors, creating a unique photometric system. In order to compare observations made with different telescopes, standard stars with known photometric properties in a defined standard system have to be observed, in order to establish colour (and magnitude) transformations of observations into the defined photometric standard system. Such transformations are naturally not perfect, and available only for a certain parameter range of standard stars. No special standard photometry is available for star clusters.
By comparing photometric models of star clusters with observations, the physical parameters of clusters can be determined. This comparison can be done either in the photometric system of the observations (i.e. by creating models in the unique photometric system of the instrument used for the observations) or by transforming the observations into the standard system and compare with models in the standard system.
On the example of the colour transformations from the Hubble Space Telescope photometric system into the standard ground-based system, the student will study and quantify the effects introduced by the colour transformations. A first small-scale study (de Grijs et al. 2005) suggested already a strong impact.
The results will most likely be published as a small paper.

Project name: "Getting extinction determinations right"
Project supervisor: PA, probably additional advice by Daniela Calzetti (STScI, Baltimore, USA), a leading expert in dust extinction
Project description:
The wavelength-dependent light dimming (extinction) due to dust is usually described by analytical formulae, the strength of extinction parametrised e.g. by E(B-V) = difference between extinction in the B and in the V band.
In principle, by comparing spectra reddened by a given extinction law with a given E(B-V) to the unreddened spectra should yield the input E(B-V) value. However, first tests show that this in true only for a small range in the parameter space. Following discussions with Daniela Calzetti, this effect seems to be known of to observers, though was never systematically studied, despite errors as large as 20%.
The student will test and quantify the deviations of the real values from the input parameters. The results will be published to give observers a guide how to correct their observations accordingly.

MSc project(s):
Project name: "Simulate a Star Cluster"
Project supervisor: SL
Project description:
Same as for the bachelor project of the same name listed above, but in this master project we will go into more detail with the simulations, e.g. to test the photometric evolution of the clusters, and possibly use real N-body simulations of star cluster profiles as input.

Project name: "Properties of Faint Fuzzy Star Clusters"
Project supervisor: SL
Project description:
A rather surprising property of star clusters is that they all tend to have about the same linear dimensions, regardless of age and mass. More precisely, most star clusters have half-light radii of 2-4 pc, meaning that half their total light is concentrated within that radius. Recently, a new type of star cluster has been discovered, which are characterised by much larger half-light radii of 7-15 pc. These clusters appear to be associated mainly with lenticular galaxies, and their unique properties may provide important insight to the evolution of such galaxies. The aim of this project is to study these “faint fuzzy” star clusters in one particular galaxy, NGC 3384, for which deep imaging from the Hubble Space Telescope is now available. With these data, it will be possible to study the structural properties (sizes, central surface brightness, etc) and the luminosity function of the faint fuzzy clusters in much more detail than hitherto possible, and establish to what extent these objects represent a truly unique new type of star cluster.

Project name: "Distribution of stars in the LMC Constellation III"
Project supervisor: SL
Project description:
The so-called "Constellation III" in the Large Magellanic Cloud has a number of interesting looking arc-like structures, consisting of individual stars and star clusters. It has been proposed that these may been formed as a result of powerful explosions or a superwind from a now dissolved star cluster. However, the three-dimensional structure of these arcs is poorly known. This project would use multi-passband imaging (in the Johnson UBVI and Strömgren uvby systems) from the Danish 1.54 m telescope at ESO, La Silla, to map the density of stars across Constellation III, look for age gradients across the region, and also map variations in the foreground extinction and metallicity.

Papers   preprints

Department of Physics and Astronomy