Search Publications
A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
de Bruijne, J. H. J.; de Zeeuw, P. T.; Hoogerwerf, R.
Hipparcos parallaxes fix distances to individual stars in the Hyades cluster with an accuracy of ~ 6 percent. We use the Hipparcos proper motions, which have a larger relative precision than the trigonometric parallaxes, to derive ~ 3 times more precise distance estimates, by assuming that all members share the same space motion. An investigation …
The mass of the neutron star in Vela X-1
Kaper, L.; Telting, J. H.; Barziv, O. +2 more
We measured the radial-velocity curve of HD 77581, the B-supergiant companion of the X-ray pulsar Vela X-1, using 183 high-resolution optical spectra obtained in a nine-month campaign. We derive radial-velocity amplitudes for different lines and wavelength regions, and find all are consistent with each other, as well as with values found in previo…
A Faint Star-forming System Viewed through the Lensing Cluster Abell 2218: First Light at z~=5.6?
Ellis, Richard; Kneib, Jean-Paul; Kuijken, Konrad +1 more
We discuss the physical nature of a remarkably faint pair of Lyα-emitting images discovered close to the giant cD galaxy in the lensing cluster Abell 2218 (z=0.18) during a systematic survey for highly magnified star-forming galaxies beyond z=5. A well-constrained mass model suggests the pair arises via a gravitationally lensed source viewed at hi…
The solar neighbourhood age-metallicity relation - Does it exist?
Holmberg, J.; Feltzing, S.; Hurley, J. R.
We derive stellar ages, from evolutionary tracks, and metallicities, from Strömgren photometry, for a sample of 5828 dwarf and sub-dwarf stars from the Hipparcos Catalogue. This stellar disk sample is used to investigate the age-metallicity diagram in the solar neighbourhood. Such diagrams are often used to derive a so called age-metallicity relat…
Is the Gas in Cooling Flows Multiphase?
Molendi, Silvano; Pizzolato, Fabio
Employing XMM-Newton EPIC data we perform a detailed comparison between different spectral models to test whether the gas in cooling flows is multiphase or not. Our findings all point in the same direction, namely, that gas in cooling flows does not show the wide distribution of temperatures expected from standard multiphase models. This result ha…
Galaxy number counts - V. Ultradeep counts: the Herschel and Hubble Deep Fields
McCracken, H. J.; Campos, A.; Metcalfe, N. +2 more
We present u,b,r and i galaxy number counts and colours from both the North and South Hubble Space Telescope Deep Fields and the William Herschel Deep Field. The latter comprises a 7×7arcmin2 area of sky, reaching b~28.5 at its deepest. Following Metcalfe et al., we show that simple Bruzual & Charlot evolutionary models which assume…
Chemical abundances of planetary nebulae from optical recombination lines - III. The Galactic bulge PN M 1-42 and M 2-36
Barlow, M. J.; Liu, X. -W.; Storey, P. J. +2 more
We present deep, high-resolution optical spectra of two Galactic bulge planetary nebulae (PN), M 1-42 and M 2-36. The spectra show very prominent and rich optical recombination lines (ORLs) from C, N, O and Ne ions. Infrared spectra from [formmu10]2.4-197µm were also obtained using the Short and Long Wavelength Spectrometer (SWS and LWS) on …
The Coronal Mass Ejection of 1998 April 20: Direct Imaging at Radio Wavelengths
Pick, M.; Kerdraon, A.; Vourlidas, A. +2 more
We observed the fast coronal mass ejection (CME) of 1998 April 20 with the radioheliograph at Nançay, France, between 164 and 432 MHz. Spectroscopic data were obtained between 40 and 800 MHz by the spectrometer at Tremsdorf, Germany, and between 20 kHz and 14 MHz with the WAVES instrument on board the Wind spacecraft. Energetic particle data were …
Evolution of Two EIT/Hα Moreton Waves
Vršnak, B.; Hanslmeier, A.; Aurass, H. +1 more
Since the discovery of EIT waves, questions have remained about the driver of these disturbances and their association with the chromospheric Moreton waves. In order to resolve some of these issues, two flare-associated transient events (1997 November 3 and 1998 May 2) observed simultaneously in Hα and EIT are analyzed. The cospatiality of Moreton…
Coronal Mass Ejections Associated with Impulsive Solar Energetic Particle Events
Kahler, S. W.; Reames, D. V.; Sheeley, N. R., Jr.
An impulsive solar energetic particle (SEP) event observed on the Wind spacecraft on 2000 May 1 was associated with an impulsive solar active region M1 X-ray flare. The timing and position of a fast (v=960 km s-1), narrow CME observed in the LASCO coronagraph on SOHO make clear the connection between the CME and the flare and SEP event.…