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Patricia Whitelock Freddy Marang 《Monthly notices of the Royal Astronomical Society》2001,323(1):L13-L16
The binary companion to the peculiar F supergiant HD 172481 is shown to be a Mira variable with a pulsation period of 312 d. Its characteristics are within the normal range found for solitary Miras of that period, although its pulsation amplitude and mass-loss rate ̇ ∼3×10−6 M⊙ yr−1 are higher than average. Reasons are given for suspecting that the F supergiant, which has L ∼104 L⊙ , is a white dwarf burning hydrogen accreted from its companion. 相似文献
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Freddy J. Gathorne-Hardy Egill Erlendsson Peter G. Langdon Kevin J. Edwards 《Journal of Paleolimnology》2009,42(3):413-426
Ecosystem variability must be assessed over a range of timescales in order to fully understand natural ecosystem processes.
Long-term climate change, at millennial and centennial scales, is a major driver of natural ecosystem variability, but identifying
evidence of past climate change is frequently confounded by human-induced impacts on the ecosystem. Iceland is a location
where it is possible to separate natural from anthropogenic change in environmental archives, as the date of settlement is
accepted to be around AD 874, prior to which the island was free from proven human impacts. We used a lake sediment core from
Breieavatn, near Reykholt, a major farm of the Norse period in western Iceland, to examine landscape development. A change
in pollen concentration in the sediments, especially the decline in Betula, indicated initial landscape degradation immediately post-settlement, whereas the chironomid fauna and reconstructed temperatures
were relatively complacent during this period. The pollen evidence is corroborated by 14C analyses, which indicate an increase in older carbon entering the lake, inferred to have been caused by increased erosion
following settlement. Further decreases in Betula pollen occurred around AD 1300, pre-dating a drop in chironomid-inferred temperatures (CI-T) of ~1°C over 100–200 years.
The CI-T reconstruction also shows a significant cooling after ~AD 1800, likely indicative of the coldest phase of the Little
Ice Age. The evidence suggests that the chironomid record was relatively unaffected by the increased landscape degradation
and hence reveals a temperature reconstruction independent of human impact. 相似文献
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Freddy Rey 《山地科学学报》2018,15(2):225-236
Improving knowledge on the ability of bioengineering structures made of willow cuttings to enhance efficient and sustainable sediment trapping in marly gullies in the Southern French Alps under a mountainous Mediterranean climate, to decreasesediment trapped per experiment, the mean annual values reached 0.25, 0.14 and 0.08 m3 yr-1 in experiments C, A and B, respectively. Maximum values for one structure reached 1.94 m3 per year in experiment C. The significance of the volumes ofsediment yield at their outlets, is a key issue today for the international scientific community working in geosciences and ecology. This study therefore aims to assess three real-size experiments(A, B and C) carried out between 2003 and 2013 in this environment. A total of 157 bioengineering structures using purple and white willow(Salix purpurea and Salix incana)cuttings – which have been shown to resprout and survive more than 2 years after their installation,corresponding to brush layers with brush mats on wooden sills(BLM), 1.2 m wide and 2 m long,installed on the floors of 33 experimental marly gullies, were monitored. The results showed that sediment trapping occurred upstream of the vegetation barriers from the 1 st year onwards.Considering the depth of sediment trapped per experiment, the mean annual values reached 11.2 cm yr-1 after 3 years in experiment A, 7.7 cm yr-1 after 2–4 years in experiment C and 5.1 cm yr-1 after 5 years in experiment B. Occasionally, BLMs showed that they could trap up to 16 and 15 cm yr-1 in experiments A and C, respectively. Considering the volumes oftrapped sediment and the sustainability of sediment trapping are discussed, and rules for bioengineering strategies are proposed. 相似文献
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Chris Koen Ruby Van Rooyen Francois Van Wyk Freddy Marang 《Monthly notices of the Royal Astronomical Society》1999,309(4):1051-1062
HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes. 相似文献
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Michael W. Feast Patricia A. Whitelock Freddy Marang 《Monthly notices of the Royal Astronomical Society》2003,346(3):878-884
JHKL observations of the mass-losing carbon Mira variable IRAS 15194–5115 (II Lup) extending over about 18 yr are presented and discussed. The pulsation period is 575 d and has remained essentially constant over this time span. The star has undergone an extensive obscuration minimum during this time. This is complex and, like such minima in similar objects (e.g. R For), does not fit the model predictions of a simple long-term periodicity. Together with the high-resolution observations of Lopez et al., the results suggest that the obscuration changes are caused by the formation of dust clouds of limited extent in the line of sight. This is an R Coronae Borealis-type (RCB-type) model. The effective reddening law at J and H is similar to that found for R For. 相似文献
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Michael Feast Patricia Whitelock Freddy Marang 《Monthly notices of the Royal Astronomical Society》2001,322(4):741-748
Spectra (1951–78) of the central object in η Car, taken by A. D. Thackeray, reveal three previously unrecorded epochs of low excitation. Since 1948, at least, these states have occurred regularly in the 2020-d cycle proposed by Damineli et al. They last about 10 per cent of each cycle. Early slit spectra (1899–1919) suggest that at that time the object was always in a low state. JHKL photometry is reported for the period 1994–2000. This shows that the secular increase in brightness found in 1972–94 has continued and its rate has increased at the shorter wavelengths. Modulation of the infrared brightness in a period near 2020 d continues. There is a dip in the JHKL light curves near 1998.0, coincident with a dip in the X-ray light curve. Evidence is given that this dip in the infrared repeats in the 2020-d cycle. As suggested by Whitelock & Laney, the dip is best interpreted as an eclipse phenomenon in an interacting binary system; the object eclipsed being a bright region ('hotspot'), possibly on a circumstellar disc or produced by interacting stellar winds. The eclipse coincides in phase and duration with the state of low excitation. It is presumably caused by a plasma column and/or by one of the stars in the system. 相似文献