The planetary albedo is partitioned into a component due to atmospheric reflection and a component due to surface reflection by using shortwave fluxes at the surface and top of the atmosphere in conjunction with a simple radiation model. The vast majority of the observed global average planetary albedo (88%) is due to atmospheric reflection. Surface reflection makes a relatively small contribut...

Long-baseline interferometry at optical and near-infrared wavelengths is an emerging technology which is quickly becoming a useful tool to investigate stellar atmospheres and to compare observations with models. Stellar atmosphere models have so far mainly been constrained by comparisons with stellar spectra which are integrated over the stellar disks. Interferometric observations provide spati...

Planetary nebulae (PNe) have the potential to revolutionize our understanding of extragalactic stellar populations. Indeed, in many systems, bright PNe are the only individual objects identifiable from the ground, and, even more often, they are the only stars that are amenable to spectroscopy. We review the ways in which ensembles of PNe can be used to probe the metallicity, age, and history of...

We study the interaction between the atmospheres of Venus-like, non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using a multi-species MHD model. We focus our investigation on the effect of enhanced stellar wind and enhanced EUV flux as the planetary distance from the star decreases. Our simulations reveal different topologies of the planetary space environment for suban...

The d iffractometer cryostat described earlier has been modified to provide a means for controlling temperature and fo r confining the vapor in equilibrium wit h volatile samples. Materials with vapor pressures as great as 1 atmosphere (atm) can be handled without loss of insulatin g vacuu m, a nd temperatures can be controlled with an accuracy of ± 0.1 OK in t he range 4 to 20 OK dec reasing t...

The planetary albedo is partitioned into a component due to atmospheric reflection and a component due to surface reflection by using shortwave fluxes at the surface and top of the atmosphere in conjunction with a simple radiation model. The vast majority of the observed global average planetary albedo (88%) is due to atmospheric reflection. Surface reflection makes a relatively small contribut...

A significant fraction of planetary nebulae (PNe) show jet-like features. These features are usually interpreted as fast collimated outflows, although their true space velocities are uncertain, as their measured radial velocities cannot be properly corrected for projection effects. We have compiled the measured expansion velocities and radial distances of collimated outflows for a sample of 33 ...

Our understanding of the formation of planetary nebulae (PNe) has been profoundly influenced in recent years by the detection of high-velocity, collimated outflows in these objects. Outflows reaching expansion velocities of several hundred km s and evidences of episodic, multiple ejection events since the proto-PNe stage, have radically modified our previous concepts of the evolution of post-AG...

Five planetary nebulae (PNe) have been discovered in the nearby dwarf irregular galaxy. Emission line images were obtained using the Wide Field Camera of the 2.5m Isaac Newton Telescope (INT) at La Palma (Spain). The candidate PNe were identified by their pointlike appearance and relatively strong [O iii] emission-line fluxes. They are located within a galactocentric distance of 2.8 arcmin, cor...

Distant planetary nebulae (PNe) are used to measure distances through the PN luminosity function, as kinematic tracers in determining the mass distribution in elliptical galaxies, and most recently, for measuring the kinematics of the diffuse stellar population in galaxy clusters. This article reviews the photometric and spectroscopic survey techniques that have been used to detect PNe beyond t...