Related papers: Helium-Core White Dwarfs in the Globular Cluster N…

We have conducted a photometric survey of the globular cluster NGC 6397 in a search for variable stars. We obtained ~11h of time-resolved photometric images with one ne European Southern Observatory-Very Large Telescope using the FOcal…

If NGC 6397 contains a large fraction of "second generation" stars (>70% according to recent analysis), the helium abundance of its stars might also be affected, show some star-to-star variation, and be larger than the standard Big Bang…

Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational-wave radiation. However, a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass…

White dwarfs (WDs) are the stellar core remnants of low mass stars. They are typically divided into three main composition groups: Oxygen Neon (ONe), Carbon Oxygen (CO) and Helium (He) WDs. The evolution of binary systems can significantly…

Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258 white dwarfs (WDs) in the Galactic globular cluster M4. Fields at three radial distances from the cluster center were observed and sizeable WD populations were…

Double helium white dwarfs (He WDs) are one type of gravitational wave source and are greatly important in the studies of binary interaction, particularly in the common envelope (CE) ejection physics. Most double He WDs with mass ratios of…

Context: The metal-rich bulge globular cluster NGC6388 shows a blue horizontal branch (HB). Helium (He) enrichment, which is correlated with changes in other light elements, might explain this feature. The hot HB stars in the metal-poor…

We collected F606W- and F814W-band time-series data of the Sagittarius low-reddening window in the Galactic bulge with the Advanced Camera far Surveys mounted on the Hubble Space Telescope. We sampled the region approximately every two…

We report on the spectroscopic confirmation of 68 new bright ($G=13.5-17.2$ mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the hottest ($T_{\mathrm{eff}} \geq 60$kK) known WDs brighter…

Globular clusters contain vast repositories of metal-poor stars that represent some of the oldest stellar generations in the Universe. The archaeological footprint of early Galactic evolution may be retained in the measurable properties of…

We use Hubble Space Telescope (HST) to reach the end of the white dwarf (WD) cooling sequence (CS) in the solar-metallicity open cluster NGC 6819. Our photometry and completeness tests show a sharp drop in the number of WDs along the CS at…

We describe here the reduction methods that we developed to study the faintest red dwarfs and white dwarfs in an outer field of NGC6397, which was observed by \hst for 126 orbits in 2005. The particular challenge of this data set is that…

The present work is designed to explore the evolution of helium-core white dwarf (HeWD) stars for the case of metallicities much lower than the solar one (Z=0.001 and Z=0.0002). Evolution is followed in a self-consistent way with the…

We present a study of the white dwarf (WD) cooling sequence (CS) in the globular cluster (GC) Omega Centauri, the primary goal of a dedicated Hubble Space Telescope (HST) programme. Our analysis has revealed that the peak at the termination…

We present color-magnitude diagrams (CMD) of the globular cluster NGC 6388 based on HST multiband photometry (F255W, F336W, F439W, F555W). In this paper we focus our attention on the peculiar horizontal branch of this cluster. After a…

Searches for planetary transits carried out in open and globular clusters have yielded to date only a handful of weak, unconfirmed candidates. These results have been interpreted either as being insignificant, or as evidence that the…

We have used deep high-resolution multiband images taken at the ESO Very Large Telescope to identify the optical binary companion to the millisecond pulsar (PSR J1911-5958A) located in the halo of the Galactic Globular Cluster NGC6752. The…

(abridged) The metal-rich bulge globular cluster NGC6388 shows a distinct blue horizontal-branch tail with a strong upward tilt in its colour-magnitude diagram. Several noncanonical scenarios have been proposed to explain these puzzling…

White Dwarfs (WD) capture Dark Matter (DM) as they orbit within their host halos. These captured particles may subsequently annihilate, heating the stellar core and preventing the WD from cooling. The potential wells of WDs are considerably…

From deep color-magnitude arrays made from V and I images taken with the Hubble Space Telescope's WFPC2 camera we have determined luminosity functions (LFs) down to a level that corresponds to about 0.13 solar masses, for the…