Search Publications
A possible age-metallicity relation in the Galactic thick disk?
Feltzing, S.; Bensby, T.; Lundström, I.
A sample of 229 nearby thick disk stars has been used to investigate the existence of an age-metallicity relation (AMR) in the Galactic thick disk. The results indicate that that there is indeed an age-metallicity relation present in the thick disk. By dividing the stellar sample into sub-groups, separated by 0.1 dex in metallicity, we show that t…
New Hipparcos-based Parallaxes for 424 Faint Stars
Gould, Andrew; Chanamé, Julio
We present a catalog of 424 common proper-motion companions to Hipparcos stars with good (>3 σ) parallaxes, thereby effectively providing new parallaxes for these companions. Compared with typical stars in the Hipparcos catalog, these stars are substantially dimmer. The catalog includes 20 white dwarfs and an additional 29 stars with MV
The Chemical Properties of Milky Way and M31 Globular Clusters. I. A Comparative Study
Forbes, Duncan A.; Brodie, Jean P.; Beasley, Michael A. +4 more
A comparative analysis is performed between high-quality integrated spectral indices of 30 M31 globular clusters, 20 Milky Way globular clusters, and a sample of field and cluster elliptical galaxies. We find that the Lick CN indices in the M31 and Galactic clusters are enhanced relative to the bulges of the Milky Way, M31, and elliptical spheroid…
Measurement and Uncertainty of the Long-Term Total Solar Irradiance Trend
Mekaoui, Sabri; Dewitte, Steven; Crommelynck, Dominique +1 more
A possible long-term trend of the total solar irradiance could be a natural cause for climate variations on Earth. Measurement of the total solar irradiance with space radiometers started in 1978. We present a new total solar irradiance composite, with an uncertainty of ± 0.35 W m−2. From the minimum in 1995 to the maximum in 2002 the t…
On the Constancy of the Solar Diameter. II.
Scherrer, P. H.; Kuhn, J. R.; Bush, R. I. +1 more
The Michelson Doppler Imager instrument on board SOHO has operated for most of a solar cycle. Here we present a careful analysis of solar astrometric data obtained with it from above the Earth's turbulent atmosphere. These data yield the most accurate direct constraint on possible solar radius variations on timescales from minutes to years and the…
Coronal transients and metric type II radio bursts. I. Effects of geometry
Raymond, J. C.; Mancuso, S.
In this paper we investigate the relationship between type II and coronal transient activity in terms of emission originating from the top or the flanks of a bow/piston shock surface, extending just above the coronal mass ejection (CME) leading edge surface. For this purpose, we used ground-based metric type II radio burst observations of twenty-n…
A Steady, Radiative-Shock Method for Computing X-Ray Emission from Colliding Stellar Winds in Close, Massive-Star Binaries
Owocki, S. P.; Antokhin, I. I.; Brown, J. C.
We present a practical, efficient, semianalytic formalism for computing steady state X-ray emission from radiative shocks between colliding stellar winds in relatively close (orbital period up to order tens of days) massive-star, binary systems. Our simplified approach idealizes the individual wind flows as smooth and steady, ignoring the intrinsi…
Partial Covering Interpretation of the X-Ray Spectrum of the NLS1 1H 0707-495
Ueda, Yoshihiro; Tanaka, Yasuo; Gallo, Luigi +2 more
The X-ray spectrum of 1H 0707 - 495 obtained with XMM-Newton showing a deep flux drop at ∼ 7 keV (Boller et al. 2002) is studied based on the partial covering concept. The previously inferred extreme iron overabundance can be reduced down to ∼ 3× solar if the hard component gradually steepens at high energies. The spectral shape supports that 1H 0…
Anatomy of a flux transfer event seen by Cluster
Hasegawa, H.; Paschmann, G.; Sonnerup, B. U. Ö.
Data from Cluster are used to study the structure of a flux transfer event (FTE), seen near the northern cusp. We employ Grad-Shafranov reconstruction, using measured fields from all four spacecraft to produce a map of the FTE cross section. The FTE consists of a flux rope of approximate size 1RE and irregular shape, embedded in the mag…
RR Lyrae Stars in the Andromeda Halo from Deep Imaging with the Advanced Camera for Surveys
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +4 more
We present a complete census of RR Lyrae stars in a halo field of the Andromeda galaxy. These deep observations, taken as part of a program to measure the star formation history in the halo, spanned a period of 41 days with sampling on a variety of timescales, enabling the identification of short- and long-period variables. Although the long-perio…