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Spectral analyses of central stars of planetary nebulae of early WC-type NGC 6751 and Sanduleak 3.
Hamann, W. -R.; Koesterke, L.
The two Wolf-Rayet type central stars of the planetary nebulae NGC 6751 and Sanduleak 3, showing the early spectral subtypes [WC4] and [WC2-3], respectively, are analyzed by means of non-LTE models for spherically expanding atmospheres. Complex model atoms of helium, carbon, oxygen and nitrogen are taken into account. For the atmospheric compositi…
First Results on it P Modes from GOLF Experiment
Baudin, F.; García, R. A.; Pérez Hernández, F. +17 more
The GOLF experiment on the SOHO mission aims to study the internal structure of the Sun by measuring the spectrum of global oscillations in the frequency range 10-7 to 10-2 Hz. Here we present the results of the analysis of the first 8 months of data. Special emphasis is put into the frequency determination of the p modes, as…
Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations with Ulysses Observations
Baring, Matthew G.; Forsyth, Robert J.; W. Ogilvie +1 more
Various theoretical techniques have been devised to determine distribution functions of particles accelerated by the first-order Fermi mechanism at collisionless astrophysical shocks. The most stringent test of these models as descriptors of the phenomenon of diffusive acceleration is a comparison of the theoretical predictions with observational …
Collimation of Astrophysical Jets: The Proto-Planetary Nebula He 3-1475
Borkowski, Kazimierz J.; Harrington, J. Patrick; Blondin, John M.
The proto-planetary nebula He 3-1475 was imaged in the [N II] λ6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical j…
On the Patterns of the Solar Granulation and Supergranulation
Title, Alan M.; Schrijver, Carolus J.; Hagenaar, Hermance J.
We study the cellular patterns of the white light granulation and of the chromospheric Ca II K supergranular network. We apply a gradient-based tessellation algorithm to define the cell outlines. The geometry of the patterns formed by the associated granular and supergranular flows are very similar, in spite of the substantial difference in length…
HST Imagery of the Non-Expanding, Clumped "Shell" of the Recurrent Nova T Pyxidis
Williams, Robert E.; Zurek, David R.; Moffat, Anthony F. J. +3 more
The "shell" of the recurrent nova T Pyxidis has been resolved with HST imagery into more than two thousand individual knots. Hydrogen and [N II] emission have very similar spatial distributions. Four epochs of observation allow us to place an upper limit of 40 km/s on the systematic expansion velocity of the knots. This is in contrast to our 1985 …
Molecular Hydrogen in the Direction of ζ Orionis A
Jenkins, Edward B.; Peimbert, Antonio
A spectrum of ζ Ori A over the wavelength interval 950-1150 Å recorded by the Interstellar Medium Absorption Profile Spectrograph (IMAPS) on the ORFEUS-SPAS I mission shows Lyman and Werner band absorption features from molecular hydrogen in rotational levels J = 0, 1, 2, 3, and 5. Most of the molecules are found in two distinct velocity component…
First View of the Solar Core from GOLF Acoustic Modes
Baudin, F.; Christensen-Dalsgaard, J.; Eff-Darwich, A. +16 more
After 8 months of nearly continuous measurements the GOLF instrument, aboard SOHO, has detected acoustic mode frequencies of more than 100 modes, extending from 1.4 mHz to 4.9 mHz. In this paper, we compare these results with the best available predictions coming from solar models. To verify the quality of the data, we examine the asymptotic seism…
Solar-type stars with planetary companions: 51 Pegasi and 47 Ursae Majoris.
Fuhrmann, K.; Pfeiffer, M. J.; Bernkopf, J.
Accurate stellar parameters are presented for the solar-type stars 51 Peg and 47 UMa. The announcement of the detection of jovian planets around these objects has recently caused much attention to extrasolar planet research. From the analysis of high resolution spectrograms we obtain for 51 Peg: T_eff_=5793+/-70K, log(g)=4.33+/-0.1, [Fe/H]=+0.20+/…
The Structure of the Super-Star Clusters in NGC 1569 from Hubble Space Telescope WFPC2 Images
Leitherer, Claus; Clampin, Mark; Nota, Antonella +3 more
We present high-resolution observations of the super-star clusters in the nearby irregular galaxy NGC 1569, obtained with the WFPC2 on board the Hubble Space Telescope. Our analysis shows that the brightest of these clusters, NGC 1569A, results from the superposition of two clusters with an angular separation of ~0.2". Recent ground-based spectros…