Pulsation stability of helium-rich subdwarf B stars     

A. Ahmad  C.S. Jeffery  J.-E. Solheim  R. Østensen 《Astrophysics and Space Science》2004,291(3-4):435-439

We present results of the pulsation monitoring of helium-rich subdwarf B (He-sdB) stars using high-speed differential photometry observations made with the SAAO (1.0m), NOT (2.6m) and the IAC80 (0.8m) telescopes. Although we did not find a pulsator in our sample of He-sdB stars, some of the stars show hints of pulsations which need further investigation.  相似文献   

Multicolour high-speed photometry of pulsating subdwarf B stars with ULTRACAM     

C. S. Jeffery  V. S. Dhillon  T. R. Marsh  B. Ramachandran 《Monthly notices of the Royal Astronomical Society》2004,352(2):699-707

  相似文献   

The evolution of helium-rich subdwarf-B stars     

A. Ahmad  C.S. Jeffery 《Astrophysics and Space Science》2004,291(3-4):253-260

Helium-rich subdwarf-B (He-sdB) stars are extremely rare hot subluminous stars found in the field of our Galaxy as well as in some globular clusters. The existence of these hot helium stars cannot be explained by canonical stellar evolution theories nor can it be explained by normal sdB evolution. We discuss the existing evolutionary models for the formation of He-sdB stars—the flash mixing model and the binary white dwarf merger model in the light of new observational results. Spectral classification of objects as He-sdB stars by various authors has resulted in a range of objects, including white dwarfs, being classified as He-sdB stars. We propose a homogeneous definition for this class of objects based on the original classification scheme used in the PG catalogue. Spectral analysis of He-sdB stars in the last 15 years is also briefly reviewed.  相似文献   

Valuing climate impacts in integrated assessment models: the MIT IGSM   总被引：1，自引：0，他引：1  

John Reilly  Sergey Paltsev  Ken Strzepek  Noelle E. Selin  Yongxia Cai  Kyung-Min Nam  Erwan Monier  Stephanie Dutkiewicz  Jeffery Scott  Mort Webster  Andrei Sokolov 《Climatic change》2013,117(3):561-573

  相似文献   

On the angular momentum evolution of merged white dwarfs     

K. N. Gourgouliatos †  C. S. Jeffery † 《Monthly notices of the Royal Astronomical Society》2006,371(3):1381-1389

  相似文献   

Improved opacities and pulsation stability in subluminous B and O stars     

C. S. Jeffery  H. Saio 《Monthly notices of the Royal Astronomical Society》2007,378(1):379-383

  相似文献   

Mass loss and yield uncertainty in low-mass asymptotic giant branch stars     

Richard J. Stancliffe  C. Simon Jeffery 《Monthly notices of the Royal Astronomical Society》2007,375(4):1280-1290

  相似文献   

MSST observations of the pulsating sdB star PG 1605+072     

S.J. O’Toole  S. Falter  U. Heber  C.S. Jeffery  S. Dreizler  S.L. Schuh 《Astrophysics and Space Science》2004,291(3-4):457-464

We present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (also known as EC 14026 stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG 1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in May/June 2002 immediately following the Whole Earth Telescope Xcov22 run, which observed PG 1605+072 as an alternate target. We will first give an overview of the project and its feasibility, after which we will present the massive data set, made up of 399 h of photometry and 151 h of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and λ-dependence of photometric amplitudes, and to use these properties for mode identification.  相似文献   

Automatic Classification of Subdwarf Spectra using a Neural Network     

C. Winter  C.S. Jeffery  J.S. Drilling 《Astrophysics and Space Science》2004,291(3-4):375-378

We apply a multilayer feed-forward back propagation artificial neural network to a sample of 380 subdwarf spectra classified by Drilling et al. (Drilling, J.S., Moehler, S., Jeffery, C.S., Heber, U., and Napiwotzki, R.: in press in: R. Gray (ed.), Probing the Personalities of Stars and Galaxies), showing that it is possible to use this technique on large sets of spectra and obtain classifications in good agreement with the standard. We briefly investigate the impact of training set size, showing that large training sets do not necessarily perform significantly better than small sets.  相似文献   

Photo's from Proceedings of the Third MicroQuasar Workshop; Granada Worshop on Galactic Relativistic Jet Sources – Granada,Spain, 11–13 September 2000     

Herbert W. Schnopper  Eric Silver  Stephen Murray  Suzanne Romaine  Simon Bandler  Christine Jones  William Forman  Norman Madden  Jeffery Beeman  Eugene Haller  Finn Christensen  Niels Westergaard  Juan Fabregat  Victor Reglero  Alvaro Gimenez  Noah Brosch  Elia Liebowitz  Hagai Netzer  Marco Barbera  Alfonso Collura  Salvatore Sciortino 《Astrophysics and Space Science》2001,276(1):49-65

The X-Ray Spectroscopic Explorer (XRASE) has a unique combination of features that will make it possible to address many of NASA's scientific goals. These include how galaxy clusters form, the physics and chemistry of the ISM, the heating of stellar coronae, the amount and content of intergalactic baryonic matter, the mass of black holes and the formation of disks and jets in AGN and galactic binaries. XRASE has a thin foil, multilayered telescope with a large collecting area up to 10 keV, especially in the Fe K region (1100 cm²). Its microcalorimeter array combines high energy resolution (7 eV at 6 keV) and efficiency with a field-of-view of 26 arcmin² . A deep orbit allows for long, continuous observations. Monitoring instruments in the optical (WOM-X), UV (TAUVEX) and hard X-RAY (GRAM) bands will offer exceptional opportunities to make simultaneous multi-wavelength observations.  相似文献