Search Publications
The Distribution of Nearby Stars in Velocity Space Inferred from HIPPARCOS Data
Dehnen, Walter
The velocity distribution f(v) of nearby stars is estimated, via a maximum likelihood algorithm, from the positions and tangential velocities of a kinematically unbiased sample of 14,369 stars observed by the Hipparcos satellite. The distribution f shows rich structure in the radial and azimuthal motions, v_R and v_phi, but not in the vertical vel…
The Sun's total irradiance: Cycles, trends and related climate change uncertainties since 1976
Fröhlich, Claus; Lean, Judith
A composite record of the Sun's total irradiance compiled from measurements made by five independent space-based radiometers since 1978 exhibits a prominent 11-year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the…
New models of Jupiter's magnetic field constrained by the Io flux tube footprint
Connerney, J. E. P.; Satoh, T.; Acuña, M. H. +1 more
Spherical harmonic models of the planetary magnetic field of Jupiter are obtained from in situ magnetic field measurements and remote observations of the position of the foot of the Io flux tube in Jupiter's ionosphere. The Io flux tube (IFT) footprint locates the ionospheric footprint of field lines traced from Io's orbital radial distance in the…
Detailed Mass Map of CL 0024+1654 from Strong Lensing
Tyson, J. Anthony; Kochanski, Greg P.; Dell'Antonio, Ian P.
We construct a high-resolution mass map of the z=0.39 cluster 0024+1654, based on a parametric inversion of the associated gravitational lens. The lens creates eight well-resolved subimages of a background galaxy, seen in deep imaging with the Hubble Space Telescope.1 Excluding mass concentrations centered on visible galaxies, more than 98% of the…
Steps toward interstellar silicate mineralogy. IV. The crystalline revolution
Waters, L. B. F. M.; Mutschke, H.; Henning, Th. +3 more
Mid- and far-infrared spectra gained by the Short Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO) satellite have provided striking evidence for the presence of crystalline silicates in comets, circumstellar envelopes around young stars and, most of all, evolved stars and planetary nebulae. Since optical properties of astrophy…
The Age of Globular Clusters in Light of Hipparcos: Resolving the Age Problem?
Chaboyer, Brian; Demarque, P.; Kernan, Peter J. +1 more
We review five independent techniques that are used to set the distance scale to globular clusters, including subdwarf main-sequence fitting utilizing the recent Hipparcos parallax catalog. These data together all indicate that globular clusters are farther away than previously believed, implying a reduction in age estimates. We now adopt a best-f…
The spectrum of the young star HD 100546 observed with the Infrared Space Observatory
Waters, L. B. F. M.; Vandenbussche, B.; Waelkens, C. +3 more
It is generally assumed that planets form in the dusty disks that surround young stars (Beckwith & Sargent 1996). The Infrared Space Observatory (Kessler et al. 1996) now enables us to determine the characteristics of these disks with unprecedented spectral resolution and signal-to-noise. We present here ISO spectra of the disk that surrounds …
High-z Lyalpha Emitters. I. A Blank-Field Search for Objects near Redshift Z = 3.4 in and around the Hubble Deep Field and the Hawaii Deep Field SSA 22
Cowie, Lennox L.; Hu, Esther M.
We present deep narrowband (lambda = 5390 Å, Deltalambda = 77 Å) and multicolor observations of the Hubble Deep Field and the Hawaii Deep Field SSA 22 obtained with the LRIS instrument at the 10 m Keck II Telescope. It is shown that there is a substantial population of galaxies at z ~ 3.4 that can be selected by Lyalpha emission. Comparison with c…
The Nature and Evolution of Ultraluminous Infrared Galaxies:A Mid-Infrared Spectroscopic Survey
Lutz, D.; Genzel, R.; Rigopoulou, D. +2 more
We report the first results of a low-resolution mid-infrared spectroscopic survey of an unbiased, far-infrared-selected sample of 60 ultraluminous infrared galaxies (ULIRGs) (LIR>1012 Lsolar) using ISOPHOT-S on board the Infrared Space Observatory (ISO). We use the ratio of the 7.7 µm ``polycyclic aromatic…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XIII. The Metallicity Dependence of the Cepheid Distance Scale
Illingworth, Garth D.; Huchra, John P.; Madore, Barry F. +22 more
Uncertainty in the metal-abundance dependence of the Cepheid variable period-luminosity (PL) relation remains one of the outstanding sources of systematic error in the extragalactic distance scale and in the Hubble constant. To test for such a metallicity dependence, we have used the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telesc…