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Solar internal rotation rate and the latitudinal variation of the tachocline
Basu, Sarbani; Antia, H. M.; Chitre, S. M.
A new set of accurately measured frequencies of solar oscillations is used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least-squares technique with iterative refinement for both 1.5D inversion, using the splitting coefficients, and 2D inversion using individual m sp…
ΔY/ΔZ from fine structure in the main sequence based on Hipparcos parallaxes
Pagel, B. E. J.; Portinari, L.
The slope ΔY/ΔZ is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate ΔY/ΔZ from fine structure in the main sequence of nearby stars from Hipparcos data for stars with Z<=Zsolar. We find a value of about 3, which is consistent wit…
The Castor moving group. The age of Fomalhaut and VEGA
Barrado y Navascues, D.
We have recomputed the kinematic properties of several of dozens nearby stars, to try to verify if Castor (alpha Gem) indeed has a cohort of stars sharing the same space motion and age. We used kinematics, the location of the stars in Color-Magnitude Diagrams, their lithium abundances, and their activity, to establish that the moving group seems t…
The Recent Star Formation History of GR 8 from Hubble Space Telescope Photometry of the Resolved Stars
Saha, A.; Gallagher, J.; Mateo, Mario +6 more
We have used the Hubble Space Telescope to observe the resolved stars in the dwarf irregular galaxy GR 8 (DDO 155, UGC 8091). The data consisted of dithered Wide Field Planetary Camera 2 images in three bands: F439W (1 hr), F555W (30 minutes), and F814W (30 minutes). The stellar photometry was extracted with a modified version of DoPHOT. Artificia…
Weak and Post-T Tauri Stars around B-Type Members of the Scorpius-Centaurus OB Association
Martín, E. L.
I report medium-resolution (FWHM = 1.9 Å) spectroscopic observations of six Hα emission-line stars proposed in 1993 by Meyer, Wilking, & Zinnecker to be T Tauri stars formed in the vicinity of the B1 giant sigma Sco, a bright member of the Sco-Cen OB association. Using spectroscopic criteria (spectral types, Hα and Li i equivalent widths), whi…
The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxiesfrom the Hubble Space Telescope
Ferguson, Henry C.; Stiavelli, Massimo; Whitmore, Bradley C. +2 more
The specific globular cluster frequencies (SN) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group that were imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dE (dE, N) galaxies, which are spatially distributed like giant elliptical galaxi…
Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1
Da Costa, G. S.; Caldwell, Nelson; Seitzer, Patrick +1 more
The M81 Group is one of the nearest groups of galaxies, but its properties are quite different from those of the Local Group. It has therefore provided a different environment for the evolution of its member galaxies. We have carried out a CCD survey of the M81 Group to search for analogs to Local Group dwarf elliptical (dE) galaxies. All the M81 …
Cosmic-Ray Modulation in the Heliosphere A Phenomenological Study
McDonald, Frank B.
The heliospheric cosmic-ray network-Pioneer 10/11, Voyager 1/2, Ulysses and IMP 8 have provided detailed observations of galactic and anomalous cosmic rays over a period of time that now exceeds 25 years and extends to heliocentric distances beyond 65 AU. These data, when compared over consecutive 11 year solar cycles, clearly establishes the exis…
Late Spectral Evolution of SN 1987A. II. Line Emission
Fransson, Claes; Kozma, Cecilia
Using the temperature and ionization calculated in our previous paper, we model the spectral evolution of SN 1987A. We find that the temperature evolution is directly reflected in the time evolution of the lines. In particular, the IR catastrophe is seen in the metal lines as a transition from thermal to nonthermal excitation, seen most clearly in…
The Ages of the Globular Clusters in the Fornax Dwarf Galaxy
Suntzeff, N. B.; Buonanno, R.; Corsi, C. E. +3 more
From observations with the Hubble Space Telescope, color-magnitude diagrams (CMDs) have been constructed for the four most metal-poor globular clusters in the Fornax dSph galaxy. These diagrams confirm that cluster 1 has a redder horizontal-branch (HB) morphology than the other three clusters despite its similarity in metallicity (the second param…