ESO and European astronomy: four decades of reciprocity     

C. Sterken 《Astronomische Nachrichten》2002,323(6):555-558

This paper describes and discusses some key facts in the early history of the European Southern Observatory: the founding phase leading to the establishment of the “nucleus” of telescopes in Chile, the role and impact of the “parallel line” of national telescopes, the mission of ESO and the impact of the organisation as a maecenas to European astronomy. With specific focus on the foundation of A & A as a refereed journal foregoing page charges, the support of national telescopes of all classes, the allotment of telescope time on the sole basis of proposal quality, the free travel and technical support, the free distribution of “The Messenger”, the development and free distribution of MIDAS, and the personal dedication of some early foster persons.  相似文献   

Multisite campaign on the open cluster M67 – II. Evidence for solar-like oscillations in red giant stars     

D. Stello  H. Bruntt  H. Kjeldsen  T. R. Bedding  T. Arentoft  R. L. Gilliland  J. Nuspl  S.-L. Kim  Y. B. Kang  J.-R. Koo  J.-A. Lee  C. Sterken  C.-U. Lee  H. R. Jensen  A. P. Jacob  R. Szabó  S. Frandsen  Z. Csubry  Z. E. Dind  M. Y. Bouzid  T. H. Dall  L. L. Kiss 《Monthly notices of the Royal Astronomical Society》2007,377(2):584-594

Measuring solar-like oscillations in an ensemble of stars in a cluster, holds promise for testing stellar structure and evolution more stringently than just fitting parameters to single field stars. The most-ambitious attempt to pursue these prospects was by Gilliland et al. who targeted 11 turn-off stars in the open cluster M67 (NGC 2682), but the oscillation amplitudes were too small (<20 μmag) to obtain unambiguous detections. Like Gilliland et al. we also aim at detecting solar-like oscillations in M67, but we target red giant stars with expected amplitudes in the range 50–  500 μmag  and periods of 1 to 8 h. We analyse our recently published photometry measurements, obtained during a six-week multisite campaign using nine telescopes around the world. The observations are compared with simulations and with estimated properties of the stellar oscillations. Noise levels in the Fourier spectra as low as  27 μmag  are obtained for single sites, while the combined data reach  19 μmag  , making this the best photometric time series of an ensemble of red giant stars. These data enable us to make the first test of the scaling relations (used to estimate frequency and amplitude) with an homogeneous ensemble of stars. The detected excess power is consistent with the expected signal from stellar oscillations, both in terms of its frequency range and amplitude. However, our results are limited by apparent high levels of non-white noise, which cannot be clearly separated from the stellar signal.  相似文献   

Sampling effort required to recover the main gradients in marine benthic species composition          下载免费PDF全文

Thijs Christiaan van Son  Rune Halvorsen  Torgeir Bakke 《Marine Ecology》2016,37(2):329-335

Marine benthic surveys and monitoring programs may have several goals. When the aim of such studies is to reveal and describe gradients in species composition, the gain in ecological insight achieved by the study depends on how well the spatial variability of species’ occurrence and abundance within the study area is covered by the sampling design. The common practice in such programs is to collect four or five grab samples from each visited site to capture the site's species composition. The rationale for this practice is based on the aim of capturing a large proportion of species at a specific site (i.e. point). We argue that this practice has been established without taking Iterative approaches into account, such as decreasing the sampling effort at each site and instead increase the number of sites visited. The collection and processing of data from marine sediment ecosystems are time‐consuming and, thus, expensive. Therefore, finding the optimal trade‐off between the number of sites visited and the number of samples per site is important. We examined this trade‐off by exploring how reduction of sampling effort per site affects the stability and recovery of gradients in species composition of marine benthic macrofauna. Our full data set consisted of four grab samples from each of 28 sites from the inner part of the Oslofjord, SE Norway. Procrustes analysis and calculation of Kendall's rank correlation coefficients showed that the main gradient in species composition extracted by detrended correspondence analysis of data sets with reduced per‐site sampling effort closely resembled the main gradient extracted for the full data set. Our results therefore suggest that marine benthic surveys that aim to identify the main gradient structure of species composition and relate this structure to main environmental complex gradients are likely to benefit from reducing the sampling effort at each site and, instead, increasing the number of visited sites. We argue that coverage of both the variation in species composition and the environment in the study area will then be improved. Monitoring programs with other aims than to identify the main gradients in species composition may also benefit from the adoption of a many‐sites, one‐sample sampling strategy. This may be particularly true if additional sampled sites are based on a stratified sampling strategy that ensures that the spatial variability in the study area is accounted for.  相似文献   

Cometary nuclear magnitudes from sky survey observations     

Michael Weiler  Heike Rauer  Christiaan Sterken 《Icarus》2011,212(1):351-366

The determination of the nuclear magnitudes of comets, and with it nuclear size frequency distributions, is strongly complicated by cometary activity. By now, only nuclear size frequency distributions for Jupiter Family comets are available, and they are still subject of uncertainties. For comets of other dynamical classes, nuclear magnitudes are known for only a few comets. The size frequency distributions are thus not well constrained.In this work we study whether nuclear magnitudes of comets can be constrained from sky survey observations as published by the Minor Planet Center. Observations from sky survey programs in which the comet was classified as a point-like source are analyzed in this respect.From the available published observations from 1998 to 2008, we derive nuclear magnitudes, as well as nuclear radii, for 84 comets. Among these are comets of the Jupiter Family, dynamically old and new isotropic comets, Halley-type comets and Centaurs. For Jupiter Family comets and for isotropic comets, the size frequency distributions are presented.Uncertainties of derived nuclear magnitudes arise from photometry and from potentially undetected activity. However, a comparison with objects with well known nuclear parameters shows that, despite substantial observational uncertainties, nuclear magnitudes are constrained to ±0.6 mag, thereby providing first indications for nuclear sizes. This is particularly relevant for isotropic comets with so far ill-constrained size distributions. Exponents of the differential size frequency distributions of for Jupiter Family comets and for isotropic comets are presented. The values derived here form a basis for future, dedicated observational studies which provide higher measurement accuracy.  相似文献