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Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution
Perlman, Eric S.; Sparks, William B.; Macchetto, F. Duccio +2 more
We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry observations of the M87 jet taken during 1994-1995. The angular resolution of both observations is ~0.2", which at the distance of M87 corresponds to 15 pc. Many knot regions are very highly polarized (~40%-50%, approaching the theoretical maximum for optically thin synchrotro…
A secondary clump of red giant stars: why and where
Girardi, Léo
Based on the results of detailed population synthesis models, Girardi et al. recently claimed that the clump of red giants in the colour-magnitude diagram (CMD) of composite stellar populations should present an extension to lower luminosities, which goes down to about 0.4mag below the main clump. This feature is made of stars just massive enough …
The Star Formation History of I ZW 18
Aloisi, Alessandra; Tosi, Monica; Greggio, Laura
The star formation history in I ZW 18 has been inferred from Hubble Space Telescope Wide Field Planetary Camera 2 archival data. This is done by comparing the derived V, B-V and V, V-I color-magnitude diagrams and luminosity functions with synthetic ones, based on various sets of stellar evolutionary tracks. At a distance of 10 Mpc, the stars reso…
The Metallicity Distribution in the Halo Stars of NGC 5128: Implications for Galaxy Formation
Harris, William E.; Harris, Gretchen L. H.; Poole, Gregory B.
We have used the Hubble Space Telescope to obtain WFPC2 V, I photometry for stars in the halo of NGC 5128, the nearest giant elliptical galaxy. The resulting color-magnitude diagram (CMD) of this field, which lies ~21 kpc from the center of the galaxy, contains more than 10,000 stars and reaches almost 3 mag down the red giant branch (RGB). From t…
Migration of Zonal Flows Detected Using Michelson Doppler Imager F-Mode Frequency Splittings
Schou, J.
The small-scale zonal flows in the outer part of the solar convection zone were recently detected by Kosovichev & Schou using f-mode frequency splittings. Results from five 72 day time series (Schou et al.) show a slight drift of the pattern toward the equator in a manner similar to that seen in the so-called torsional oscillation observed usi…
The domain of γ Doradus variables in the Hertzsprung-Russell diagram
Handler, G.
70 new γ Doradus candidates were identified from Hipparcos photometry, which represents more than a doubling of the presently known number. Selecting the objects with good evidence for multiperiodicity, it is found that these stars, together with bona fide members of the class, occupy a well-defined region in a colour-magnitude diagram. This domai…
The star formation history of the Hubble sequence: spatially resolved colour distributions of intermediate-redshift galaxies in the Hubble Deep Field
Fabian, A. C.; Glazebrook, K.; Abraham, R. G. +2 more
We analyse the spatially resolved colours of distant galaxies of known redshift in the Hubble Deep Field, using a new technique based on matching resolved four-band colour data to the predictions of evolutionary synthesis models. Given some simplifying assumptions, we demonstrate how our technique is capable of probing the evolutionary history of …
Comparison of Two Coronal Mass Ejections Observed by EIT and LASCO with a Model of an Erupting Magnetic Flux Rope
Chen, J.; Howard, R. A.; Wood, B. E. +3 more
We present observations of two coronal mass ejections (CMEs) observed by the LASCO and EIT instruments on board the Solar and Heliospheric Observatory. One was observed on 1997 April 30 and the other on 1997 February 23. The latter CME is accompanied by a spectacular prominence eruption and reaches velocities of about 900 km s-1, while …
Carbon in Spiral Galaxies from Hubble Space Telescope Spectroscopy
Terlevich, E.; Garnett, D. R.; Skillman, E. D. +5 more
We present measurements of the gas-phase abundance ratio C/O in six H II regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope. The ratios of C to O increase systematically with O/H in both galaxies, from log C/O~-0.8 at log O/H=-4.0 to log C/O~-0.1 at …
Solar minimum streamer densities and temperatures using Whole Sun Month coordinated data sets
Bagenal, F.; Fludra, A.; Gibson, S. E. +3 more
We model electron densities of the simplest, most symmetric solar minimum streamer structure observed during the Whole Sun Month (WSM) campaign, using coronal observations of both visible white light and extreme ultraviolet (EUV) emission. Using white light data from the SOHO/LASCO/C2 and HAO/Mauna Loa Mark 3 coronagraphs, we determine electron de…