Ultracool subdwarfs are low luminosity, late-type M and L dwarfs that exhibit spectroscopic indications of subsolar metallicity and halo kinematics. Their recent discovery and ongoing investigation have led to new insights into the role of metallicity in the opacity structure, chemistry (e.g. dust formation) and evolution of low-temperature

We study the collective kinklike normal modes of a system of several cylindrical loops using the T-matrix theory. Loops that have similar kink frequencies oscillate collectively with a frequency which is slightly different from that of the individual kink mode. On the other hand, if the kink frequency of a loop is different from that of the others

Gaia, an ESA cornerstone mission, will obtain of the order of 100 high-precision photometric observations over five years for tens of millions of stars with V 17. The vast number of red dwarfs in this data set, with their correspondingly deep (high S/N) transits, makes it worthwhile to explore the possibility of detecting transits in such data

Compared to bright star searches, surveys for transiting planets against fainter (V = 12 18) stars have the advantage of much higher sky densities of dwarf star primaries, which afford easier detection of small transiting bodies. Furthermore, deep searches are capable of probing a wider range of stellar environments. On the other hand, for a given

We observed several transits of the exoplanet TrES-1 distributed over four years from 2004 to 2007. On the basis of these observations and additional published data, we present a mid-transit time analysis. The aim is to find indications of the presence of a third body by analysing the difference between the calculated and observed transit times.

Solar irradiance changes on a wide range of time scales and is a key driver of the Earth's climate where secular variability in particular is relevant. This is, however, not well understood and our knowledge relies on reconstructions based on sunspot numbers and similar proxies. The prime candidate to produce secular variability is a change in the