The double helium-white dwarf channel for the formation of AM CVn binaries     

Xian-Fei Zhang  Jin-Zhong Liu  C.Simon Jeffery  Philip D.Hall  Shao-Lan Bi 《天文和天体物理学研究(英文版)》2018,(1)

Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer.Such stable mass transfer between two helium white dwarfs(He WDs) provides one channel for the production of AM CVn binary stars.In previous calculations of double He WD progenitors,the accreting He WD was treated as a point mass.We have computed the evolution of 16 double He WD models in order to investigate the consequences of treating the evolution of both components in detail.We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach.By comparing with observed periods and mass ratios,we redetermine masses of eight known AM CVn stars by our double He WDs channel,i.e.HM Cnc,AM CVn,V406 Hya,J0926,J1240,GP Com,Gaia14 aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240,GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double He WD channel.The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna(LISA) project.  相似文献   

Abundance analyses of three helium-rich sdB stars     

Naslim N.  C. S. Jeffery  A. Ahmad  N. Behara  T. Şahìn 《Astrophysics and Space Science》2010,328(1-2):119-122

We present some preliminary results based on the CoRoT observations of the young distant cluster Dolidze 25. The light curve for the 28 stars observed by the satellite have been analyzed and the relevant periodogram presented. As a result we have found two binary, three Pulsating Be, three SPB, two Spotted and one ellipsoidal variables. Noteworthy, we have also identified one PMS δ Scuti candidate.  相似文献   

Holocene lake-level trends in the Rocky Mountains, U.S.A.     

Bryan Shuman  Anna K. Henderson  Steven M. Colman  Jeffery R. Stone  Sherilyn C. Fritz  Lora R. Stevens  Mitchell J. Power  Cathy Whitlock   《Quaternary Science Reviews》2009,28(19-20):1861-1879

The availability of water shapes life in the western United States, and much of the water in the region originates in the Rocky Mountains. Few studies, however, have explicitly examined the history of water levels in the Rocky Mountains during the Holocene. Here, we examine the past levels of three lakes near the Continental Divide in Montana and Colorado to reconstruct Holocene moisture trends. Using transects of sediment cores and sub-surface geophysical profiles from each lake, we find that mid-Holocene shorelines in the small lakes (4–110 ha) were as much as 10 m below the modern lake surfaces. Our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000–2000 years ago. We also discuss evidence for millennial-scale moisture variation, including an abruptly-initiated and -terminated wet period in Colorado from 4400 to 3700 cal yr BP, and find only limited evidence for low-lake stands during the past millennium. The extent of low-water levels during the mid-Holocene, which were most severe and widespread ca 7000–4500 cal yr BP, is consistent with the extent of insolation-induced aridity in previously published regional climate model simulations. Like the simulations, the lake data provide no evidence for enhanced zonal flow during the mid-Holocene, which has been invoked to explain enhanced mid-continent aridity at the time. The data, including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium, confirm the ability of large boundary-condition changes to push western water supplies beyond the range of recent natural variability.  相似文献   

Optical Spectroscopy of V4334 Sgr: 1996–2000     

C.S. Jeffery  D. Pollacco 《Astrophysics and Space Science》2002,279(1-2):15-30

Due to a combination of rapid expansion and changes in chemical composition, the optical spectrum of V4334 Sgr changed rapidly between discovery in 1996 Februaryand extinction during 1999. As one of the most rapidly evolving stars ever observed, optical spectroscopy must answer a range of important questions.The development of the optical spectrum and its implications are discussedthrough a review of published literature. A previously unpublished sequence of spectra from near discovery through 1996 demonstrates the thermal evolution of V4334 Sgr, while detailed analysis of an unpublished echelle spectrumobtained in 1996 May raises questions about the model atmospheres used to date.As a result, requirements for future models of the atmosphere of V4334 Sgr are analysed. The future evolution of V4334 Sgr and the dispersion of its dustycocoon are briefly discussed.  相似文献   

Colour and radial velocity variations in pulsating subluminous B stars     

C. Simon Jeffery 《Astrophysics and Space Science》2004,291(3-4):403-410

The utility of pulsations for the investigation of the structure and evolution of subdwarf B stars is considerable. However, the small number of detected modes generally limits the potential for a traditional seismological analysis such as that carried out for the Sun. Therefore, it is crucial to acquire additional primary data to characterise the stellar oscillations more completely. We review recent studies of radial velocity amplitudes and introduce new multi-colour photometry of small-amplitude sdBV stars. We also discuss a set of models for radial velocity and colour variations and demonstrate how these may be used to infer the spherical and azimuthal degrees of observed pulsations.  相似文献   

A Drowned Lagunar Channel in the Southern Brazilian Coast in Response to the 8.2-ka Event: Diatom and Seismic Stratigraphy     

Cristiane Bahi dos Santos-Fischer  Jair Weschenfelder  Iran Carlos Stalliviere Corrêa  Jeffery Robert Stone  Beatriz Appel Dehnhardt  Eduardo Calixto Bortolin 《Estuaries and Coasts》2018,41(6):1601-1625

Drowning of the coast was initiated by a marine inundation after the Last Glacial Maximum (marine isotope stage (MIS) 2) and has continued during the mid-Holocene and highstand (MIS 1). Detailed analyses of two previously examined core stratigraphy and seismic profiles combined with new grain-size and detailed diatom analyses are used to study the history of the Barra Falsa paleochannel over the last 11,000 years BP and to document the peculiar deposition within the channel fill. A rapid sea-level rise was responsible for flooding the coast in 11,180–10,780, 8420–7930, 8150–7870, and 7640–7430 cal years BP, infilling a low topographic back-barrier region. High deposition rates suggest a rapid filling of the channel, which coincides with an accelerated period of sea-level rise, closely linked to the global 8.2-ka event. The morphology of the channel is recognized by facies units in the underlying strata related to one episode of cut and fill during a single cycle of base-level fall and rise. An overall transgressive sequence above the regional surface is related to marine and marine-brackish sediments, which corresponds to a seaward/central basil fill of a wave-dominated estuary.  相似文献   

F. Carlos Lázaro and Maria J. Arévalo (eds.): Binary Stars: Selected Topics on Observations and Physical Processes,EADN School XII,Lecture Notes in Physics,Vol. 563.     

Jeffery  C. Simon 《Earth, Moon, and Planets》2000,88(3):185-186

Earth, Moon, and Planets -  相似文献   

Abundance analyses of cool extreme helium stars     

Gajendra Pandey  N. Kameswara Rao  David L. Lambert  C. Simon Jeffery  Martin Asplund 《Monthly notices of the Royal Astronomical Society》2001,324(4):937-959

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PIANCALDOLI METEORITE: CHEMISTRY,MINERALOGY AND PETROLOGY     

Marcello Carapezza  P. Mario Nuccio  Mariano Valenza 《Meteoritics & planetary science》1976,11(3):195-205

The fall occurred near Piancaldoli, Florence, Italy, at 19.14 U.T. on the 10th August 1968. The fireball broke up in the atmosphere producing a cloud like a balloon. The trajectory and the terminal point were calculated, leading to the recovery of three small meteoritic fragments, found on the roof of a house. Chemical analysis gave the following results: SiO₂ 40.80; TiO₂ 0.15; Al₂O₃ 2. 70; Cr₂O₃ 0.47; FeO 17.20; MnO 0.07; MgO 25.18; CaO 1.95; Na₂O 0.64; K₂O 0.07; P₂O₅ 0.20; NiS 0.93; FeS 6.24; Fe° 2.40; Ni° 0.40; Co 0.05; sum 99.45. In the lithic portion of the meteorite the following minerals were found: both clino and orthopyroxenes (En = 76 to 98%), olivines (Fo = 66 to 98%), troilite, pyrrhotite, pentlandite, kamacite, ilmenite, apatite, merillite, schreibersite, chromite and Henderson phase. From all the mineralogical and petrological data, we conclude that the Piancaldoli meteorite is an “unequilibrated ordinary chondrite,” LL3. The microbrecciated structure of the rock and some shock features were observed, while the rock as a whole is unshocked, suggesting that these features were caused by impact events which took place during the accretion of the parent body.  相似文献   

Stability of Strain-Meter Mounts     

G. J. Jeffery  P. H. Sydenham 《Geophysical Journal International》1973,33(2):185-193

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