A distance to the Large Magellanic Cloud that is precise to one per cent.

In the era of precision cosmology, it is essential to determine the Hubble constant empirically with an accuracy of one per cent or better. At present, the uncertainty on this constant is dominated by the uncertainty in the calibration of the Cepheid period-luminosity relationship (also known as the Leavitt law). The Large Magellanic Cloud has traditionally served as the best galaxy with which to calibrate Cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale.

SPICA, Stellar Parameters and Images with a Cophased Array: a 6T visible combiner for the CHARA array.

High angular resolution studies of stars in the optical domain have highly progressed in recent years. After the results obtained with the visible instrument Visible spEctroGraph and polArimeter (VEGA) on the Center for High Angular Resolution Astronomy (CHARA) array and the recent developments on adaptive optics and fibered interferometry, we have started the design and study of a new six-telescope visible combiner with single-mode fibers. It is designed as a low spectral resolution instrument for the measurement of the angular diameter of stars to make a major step forward in terms of magnitude and precision with respect to the present situation.

The expanding fireball of Nova Delphini 2013.

A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common-envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion.

An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent.

In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately.

RR-Lyrae-type pulsations from a 0.26-solar-mass star in a binary system.

RR Lyrae pulsating stars have been extensively used as tracers of old stellar populations for the purpose of determining the ages of galaxies, and as tools to measure distances to nearby galaxies. There was accordingly considerable interest when the RR Lyrae star OGLE-BLG-RRLYR-02792 (referred to here as RRLYR-02792) was found to be a member of an eclipsing binary system, because the mass of the pulsator (hitherto constrained only by models) could be unambiguously determined. Here we report that RRLYR-02792 has a mass of 0.