Two families of exocomets in the β Pictoris system.

The young planetary system surrounding the star β Pictoris harbours active minor bodies. These asteroids and comets produce a large amount of dust and gas through collisions and evaporation, as happened early in the history of our Solar System. Spectroscopic observations of β Pictoris reveal a high rate of transits of small evaporating bodies, that is, exocomets.

An extended upper atmosphere around the extrasolar planet HD209458b.

The planet in the system HD209458 is the first one for which repeated transits across the stellar disk have been observed. Together with radial velocity measurements, this has led to a determination of the planet's radius and mass, confirming it to be a gas giant. But despite numerous searches for an atmospheric signature, only the dense lower atmosphere of HD209458b has been observed, through the detection of neutral sodium absorption.

Deficiency of molecular hydrogen in the disk of beta Pictoris.

Molecular hydrogen (H2) is by far the most abundant material from which stars, protoplanetary disks and giant planets form, but it is difficult to detect directly. Infrared emission lines from H2 have recently been reported towards beta Pictoris, a star harbouring a young planetary system. This star is surrounded by a dusty 'debris disk' that is continuously replenished either by collisions between asteroidal objects or by evaporation of ices on Chiron-like objects.

A high deuterium abundance at redshift z = 0.7.

Of the light elements, the primordial abundance of deuterium relative to hydrogen, (D/H)p, provides the most sensitive diagnostic for the cosmological mass density parameter, omegaB. Recent high-redshift D/H measurements are highly discrepant, although this may reflect observational uncertainties. The larger primordial D/H values imply a low omegaB (requiring the Universe to be dominated by non-baryonic matter), and cause problems for galactic chemical evolution models, which have difficulty in reproducing the steep decline in D/H to the present-day values.

Pre-Main-Sequence Star Candidates in the Bar of the Large Magellanic Cloud.

Candidate pre-main-sequence stars were observed in the bar of the Large Magellanic Cloud during the search for dark matter in the galactic halo. Seven blue stars of apparent visual magnitude 15 to 17 had irregular photometric variations and hydrogen emission lines in their optical spectra, which suggested that these stars are pre-main-sequence stars of about 10 solar masses. These stars are slightly more massive and definitely more luminous than are Herbig AeBe pre-main-sequence stars in our own galaxy.