منابع مشابه
On the distances of planetary nebulæ
Reconsidering calibration of statistical distance scales for planetary nebulæ leads naturally to examining precision and especially the systematic errors of other methods. Here we present a different calibration strategy based on the precise trigonometric parallaxes for sixteen central stars published by Harris et al. (2007) of USNO, with four improved by Benedict et al. using the Hubble Space ...
متن کاملMinimum Mass Solar Nebulæ and Planetary Migration
The Minimum Mass Solar Nebula (MMSN) is a protoplanetary disk that contains the minimum amount of solids necessary to build the planets of the Solar System. Assuming that the giant planets formed in the compact configuration they have at the beginning of the “Nice model”, Desch (2007) built a new MMSN. He finds a decretion disk, about ten times denser than the well-known Hayashi MMSN. The disk ...
متن کاملHigh-excitation nebulæ around Magellanic Wolf-Rayet stars
The SMC harbours a class of hot nitrogen-sequence Wolf-Rayet stars (WNE) that display only relatively weak broad emission lines. This indicates low mass-loss rates and makes them also hard to detect. However, such stars are possible emitters of strong He Lyman continua that in turn could ionize observable He iii regions, i.e. highly excited H ii regions emitting nebular He iiλ4686 emission. We ...
متن کاملThe Missing “Missing Middle”
T he notion that the distribution of firm size in poor countries is characterized by a bimodal distribution with a “missing middle” is a widely accepted fact in development economics (for example, see Krueger 2013). The idea of the missing middle is that there are a large number of small firms, some large firms, but very few medium-sized firms. The purported fact about the missing middle is cit...
متن کاملCase Report: Congenitally Missing Teeth
Congenitally missing of maxillary lateral incisors is one of the most common patterns of hypodontia. This paper presents a nine year old boy with congenital missing of lateral incisors. Familial history showed that, his mother, aunts, uncle and grandmother have also congenital absence of lateral incisors.
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ژورنال
عنوان ژورنال: Nature
سال: 1879
ISSN: 0028-0836,1476-4687
DOI: 10.1038/019290b0