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A search for X-ray variability in the open cluster NGC 2516
Ramsay, Gavin; Harra, Louise; Kay, Hilary
We present the results of a search for X-ray variability in the Galactic open cluster NGC 2516. This cluster has been observed on eight occasions using XMM-Newton, making it an excellent target for such a study. We find four sources that show significant variability, implying the detection of one significantly variable source every 25 ks. All sour…
Predictions for the Counts of Faint, High-Redshift Galaxies in the Mid-Infrared
Spergel, David N.; Turner, Edwin L.; Haiman, Zoltán
Deep mid-infrared (MIR) observations could reveal a population of faint, high-redshift (z>3), dusty starburst galaxies that are the progenitors of present-day spheroids or bulges and are beyond the reach of current instruments. We utilize a semianalytic galaxy formation scheme to find a range of models for the MIR galaxy counts, down to a flux …
A study of velocity fields in the transition region of ɛ Eri (K2 V)
Jordan, C.; Sim, S. A.
Analyses of the widths and shifts of optically thin emission lines in the ultraviolet spectrum of the active dwarf ɛ Eri (K2 V) are presented. The spectra were obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. The linewidths are used to find the non-thermal energy …
Solar cycle variations of the energetic H/He intensity ratio at high heliolatitudes and in the ecliptic plane
Lario, D.; Roelof, E. C.; Maclennan, C. G. +3 more
We study the variability of the heliospheric energetic proton-to-helium abundance ratios during different phases of the solar cycle. We use energetic particle, solar wind, and magnetic field data from the Ulysses, ACE and IMP-8 spacecraft to compare the H/He intensity ratio at high heliographic latitudes and in the ecliptic plane. During the first…
A possible way of understanding the differential motion of minor ions in the solar wind
Tu, C. -Y.; Marsch, E.; Wang, L. -H.
Measurements with Solar and Heliospheric Observatory (SOHO)/Charge, Element, and Isotope Analysis System (CELIAS) in high-speed solar wind show that some minor ions such as O6+ have a relatively high drift velocity; however, other ions such as Fe9+ tend to lag behind oxygen by a few tens of km/s [, 1998]. This subtle observat…
The optical jet in 3C 31 on 15 arcsec scales
Croston, J. H.; Birkinshaw, M.; Davies, R. L. +1 more
Evidence has been found for optical emission from the northern radio jet of 3C 31, the radio source associated with NGC 383. The jet emerges from the dust disc and ring of emission at a radius of 5 arcsec, and within 10.4 arcsec is measured to have a B-band flux of 2.1 µJy and an R-band flux of 2.3 µJy. The radio-to-optical spectral in…
Heliospheric Langmuir wave observations from the Ulysses spacecraft
McComas, D. J.; Lin, Naiguo; MacDowall, R. J.
Langmuir waves are electrostatic plasma oscillations produced by unstable electron beams in the solar wind and elsewhere. Typical electron sources are solar flares, shocks, and magnetic holes. In this paper, we present an overview of the Langmuir waves observed by Ulysses during both its solar minimum and solar maximum orbits. Langmuir waves in ma…
Atomic Data and Spectral Line Intensities for S XI
Bhatia, A. K.; Landi, E.
Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for S XI. The configurations included are 2s22p2, 2s2p3, 2p4, 2s22p3l, and 2s22p4l (l=s, p, d), giving rise to 72 fine-structure levels in intermediate coup…
CCD-Based Astrometric Measurement of Photographic Plates
Calderón, J. H.; Bustos Fierro, I. H.
We have developed a methodology for the astrometric measurement of photographic plates making use of a CCD camera. In order to measure a complete 2°x 2° plate a mosaic of 8×8 frames with 50% overlap in both coordinates was taken. The detection and centering of stellar images was performed with SExtractor, and by means of our own software triple …
Using Optical and Near-Infrared Photometry to Test MACHO Lens Candidates
Sarajedini, Ata; von Hippel, Ted; Ruiz, Maria Teresa
We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars and adjacent LMC field regions. After combining our near-IR photometry with Hubble Space Telescope/PC BVRI optical photometry, we compared the MACHO objects to the adjacent field stars in a variety of color-magnitude and color-color diagrams. These diagnostic diagrams we…