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Search: authors:"A. C. Katsiyannis"

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Results of the digital co-addition of thirteen Schmidt films of the Virgo cluster of galaxies

We have digitally co-added APM scans of 13 Kodak TechPan films of the SE region of the Virgo cluster of galaxies. The field of the R-band films combined with the resolution of arcsec pixel-1 results in data file sizes of about 222 MBytes. The 13 scanned films have been aligned, co-added, corrected for vignetting effects and cleaned of stellar features. To illustrate the...

BVRI photometric analysis for the galaxy group NGC 4410

We present a BVRI CCD (Charge Coupled Device) surface photometry analysis of the galaxy group NGC 4410, which contains four galaxies in interaction. Along with our photometric study, we show residual images (after subtracting isophotal models) and unsharp masked images to uncover any hidden structures in this system of galaxies; we have also performed a two-dimensional bulge-disk...

Emission lines of Na-like ions in spectra obtained with the Solar EUV Research Telescope and Spectrograph (SERTS)

Theoretical emission-line ratios involving transitions in the 236–412 Å wavelength range are presented for the Na-like ions Ar viii, Cr xiv, Mn xv, Fe xvi, Co xvii, Ni xviii and Zn xx. A comparison of these with an extensive data set of the solar active region, quiet-Sun, subflare and off-limb observations, obtained during rocket flights by the Solar EUV Research Telescope and...

Time signatures of impulsively generated coronal fast wave trains

Impulsively generated short-period fast magneto-acoustic wave trains, guided by solar and stellar coronal loops, are numerically modelled. In the developed stage of the evolution, the wave trains have a characteristic quasi-periodic signature. The quasi-periodicity results from the geometrical dispersion of the guided fast modes, determined by the transverse profile of the loop...

Extreme ultraviolet emission lines of Ar xiv in solar active region and flare spectra

New R-matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2 and 2p3 levels of Ar xiv are presented. These data are subsequently used to derive the theoretical electron density diagnostic emission-line intensity ratios R1=I(187.95 Å)/I(194.41 Å) and R2=I(257.40 Å)/I(243.78 Å) for a range of densities (Ne= 109–1013 cm−3) and electron...

Brown dwarfs and low-mass stars in the Pleiades and Praesepe: membership and binarity

We present near-infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We flag non-members from their position in K, I−K and J, J−K colour–magnitude diagrams (CMDs), and J−H, H−K two-colour diagrams. In general, the dust-free NextGen model isochrones of the Lyon Group fit the K, I...

Results of the digital co-addition of thirteen Schmidt films of the Virgo cluster of galaxies

We have digitally co-added APM scans of 13 Kodak TechPan films of the SE region of the Virgo cluster of galaxies. The field of the R-band films combined with the resolution of arcsec pixel-1 results in data file sizes of about 222 MBytes. The 13 scanned films have been aligned, co-added, corrected for vignetting effects and cleaned of stellar features. To illustrate the...

An observational study of a magneto-acoustic wave in the solar corona

The Solar Eclipse Corona Imaging System (SECIS) observed a strong 6-s oscillation in an active region coronal loop, during the 1999 August 11 total solar eclipse. In the present paper we show that this oscillation is associated with a fast-mode magneto-acoustic wave that travels through the loop apex with a velocity of 2100 km s−1. We use near-simultaneous SOHO observations to...