The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85 000 (63 000 for the low-resolution fibre), a spectral coverage from 377 to 900 nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.

The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution 1 . The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars 2 . Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum 3 . Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clearcut profile.The young massive star HD 50230 is poorly studied, but it is known to have spectral type B3V and a visual magnitude of 8.95. HD 50230 is in its central nuclear-burning phase, just like the Sun, transforming hydrogen into helium in its core (the so-called main sequence phase). This important evolutionary phase covers about 90% of the life of the star, and the detailed internal structure of the star during this phase determines its ultimate fate 1,2 . This star is at the limiting mass of ending either as core-collapse supernova or as a white dwarf, enriching the interstellar medium with helium and heavy metals in the former case and carbon in the latter. A highquality continuous photometric light curve with 32-s sampling and with a span of 137 days has been obtained for the star by the Convection Rotation and Planetary Transits (CoRoT 4 ) satellite. A linear downward trend was removed from the data, after outliers were excluded from the light curve. The duty cycle of the final set of measurements analysed here is 88.6% and the noise has an amplitude of 1 mmag (Fig. 1). The light curve reveals the presence of numerous oscillation modes.Stellar oscillations have been found to occur at different stages of stellar life, for a range of stellar masses 5 . The best known case is that of the solar oscillations, which are acoustic modes with periods near 5 min (refs 6-9). The seismic interpretation of the detected solar oscillations led to a drastic improvement in the knowledge of the internal structure of the Sun 10,11 . Meanwhile, similar acoustic modes have been detected in various types of distant stars [12][13][14] . Gravity modes, on the other hand, probe much deeper layers inside stars and in principle allow the study of the core properties of stars far better than acoustic modes. Although such modes have been detected in massive stars similar to HD 50230 15,16 , where they have typical periods of half a day to a few days, their seismic potential could not be exploited because the number of detected modes in one star was far too lo...

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Context. Fomalhaut is a young (2 ± 1 × 10 8 years), nearby (7.7 pc), 2 M star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 and 36.7 at wavelengths between 70 μm and 500 μm. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.

The O9V star HD 46202, which is a member of the young open cluster NGC 2244, was observed by the CoRoT satellite in October/November 2008 during a short run of 34 days. From the very high-precision light curve, we clearly detect β Cep-like pulsation frequencies with amplitudes of ∼0.1 mmag and below. A comparison with stellar models was performed using a χ 2 as a measure for the goodness-of-fit between the observed and theoretically computed frequencies. The physical parameters of our best-fitting models are compatible with the ones deduced spectroscopically. A core overshooting parameter α ov = 0.10 ± 0.05 pressure scale height is required. None of the observed frequencies are theoretically excited with the input physics used in our study. More theoretical work is thus needed to overcome this shortcoming in how we understand the excitation mechanism of pulsation modes in such a massive star. A similar excitation problem has also been encountered for certain pulsation modes in β Cep stars recently modelled asteroseismically.