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Oscillations of sunspot magnetic fields
Solanki, S. K.; Scherrer, P. H.; Stenflo, J. O. +2 more
We report on velocity and magnetic field oscillations observed in sunspots using the MDI instrument onboard SOHO. In addition to the well-known velocity oscillations, the data clearly show highly localised oscillations of the magnetogram signal in different parts of the sunspots. We show that only oscillations of the magnetic field vector can prod…
Solar Wind Velocity and Anisotropic Coronal Kinetic Temperature Measured with the O VI Doublet Ratio
Giordano, S.; Antonucci, E.; Martin, R. +1 more
Doppler dimming of the O vi resonance lines (λ1032 Å, λ1037 Å) in an expanding corona is calculated including the pumping effect on the O vi λ1037.61 Å of both C ii lines at λ1036.34 Å and λ1037.02 Å, and the effect of the width of the absorption profiles of the coronal oxygen ions along the incident radiation. The pumping effect of the C ii line …
Three Populous Clusters Discovered in the Large Magellanic Cloud Age Gap
Sarajedini, Ata
In the process of searching the Hubble Space Telescope archive, we have serendipitously discovered three populous Large Magellanic Cloud (LMC) clusters with ages that place them in the LMC ``age gap.'' These clusters-NGC 2155, SL 663, and NGC 2121-turn out to have [Fe/H] ~ -1.0 and ages of ~4 Gyr. This puts them in the ``age gap'' between the inte…
Chromospheric Upflow Events Associated with Transition Region Explosive Events
Wang, Haimin; Chae, Jongchul; Schühle, Udo +2 more
Transition region explosive events are considered to be a manifestation of small-scale magnetic reconnection ubiquitously occurring--even in the quiet Sun. In this paper, we report a close association between transition region explosive events and chromospheric upflow events seen in Hα. From a comparison of the Big Bear Solar Observatory (BBSO) Hα…
HST Images of the Extremely Clumpy Radio Galaxy 1138-262 at z = 2.2
Pentericci, L.; Macchetto, F.; Spinrad, H. +4 more
We present and discuss optical continuum images made with the Hubble Space Telescope of the radio galaxy 1138-262 at z = 2.2. This object possesses one of the clumpiest optical morphologies of all known high-redshift radio galaxies, consisting of a bright nucleus aligned along the radio axis and a number of smaller components distributed over a re…
Searching for Wolf-Rayet Stars in I ZW 18: the Origin of He II Emission
Schaerer, Daniel; Leitherer, Claus; de Mello, Duília F. +1 more
I Zw 18 is the most metal-poor star-forming galaxy known and is an ideal laboratory to probe stellar evolution theory at low metallicities. Using archival Hubble Space Telescope WFPC2 imaging and Faint Object Spectrograph spectroscopy, we were able to improve previous studies. We constructed a continuum-free He II λ4686 map, which was used to iden…
Spectroscopic confirmation of redshifts predicted by gravitational lensing
Ellis, Richard; Smail, Ian; Kneib, Jean-Paul +4 more
We present deep spectroscopic measurements of 18 distant field galaxies identified as gravitationally lensed arcs in a Hubble Space Telescope image of the cluster Abell2218. Redshifts of these objects were predicted by Kneib et al. using a lensing analysis constrained by the properties of two bright arcs of known redshift and other multiply imaged…
The 1996 outburst of GRO J1655-40: the challenge of interpreting the multiwavelength spectra
Horne, Keith; Shrader, C. R.; O'Brien, K. +6 more
We report on the results of a multiwavelength campaign to observe the soft X-ray transient (SXT) and superluminal jet source GRO J1655-40 in outburst using HSTRXTECGRO together with ground-based facilities. This outburst was qualitatively quite different from other SXT outbursts and from previous outbursts of this source. The onset of hard X-ray a…
ISO-SWS spectra of the C-rich AGB star R Scl and dynamical model atmospheres
Hron, J.; Kerschbaum, F.; Aringer, B. +3 more
We have monitored the spectral variations of the carbon rich AGB star R Scl in the 2-45 mu m range using the ISO-SWS instrument. We have also computed hydrostatic and hydrodynamic model atmospheres and corresponding synthetic spectra representative for two phases of R Scl. There is good qualitative agreement between observations and models in the …
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XI. The Cepheids in NGC 4414
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P. +21 more
We report the discovery of Cepheid variable stars in the galaxy NGC 4414, as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale. Observations were obtained with the HST Wide-Field and Planetary Camera 2 (WFPC2) for 13 epochs at V (F555W) and 4 at I (F814W). Photometry was performed using two independent progra…