Search Publications
NOTE: HST/FGS Observations of the Asteroid (216) Kleopatra
Lattanzi, M. G.; Tanga, P.; Berthier, J. +4 more
Interferometric observations of asteroid (216) Kleopatra were performed in January 2000 using the Fine Guidance Sensors (FGS) aboard HST. The FGS data obtained clearly suggest that (216) Kleopatra is composed of two lobes in contact, in agreement with the radar data (Ostro et al. 2000, Science288, 836-839), and provide more precise constraints on …
The first ISO ERO: A dusty quasar at z = 1.5
Cesarsky, C.; Lidman, C.; Pierre, M. +9 more
We report the discovery of an extremely red object (ERO) in a medium-deep ISOCAM extragalactic survey. The object is also a radio source. Subsequent VLT NIR spectroscopy revealed a prominent Hα line giving a redshift of 1.5. We present the spectrum and photometric data points and discuss evidence that ISO J1324-2016 is a quasar harbouring a signif…
The Tolman Surface Brightness Test for the Reality of the Expansion. I. Calibration of the Necessary Local Parameters
Sandage, Allan; Lubin, Lori M.
The extensive CCD photometry by Postman & Lauer in the Cape/Cousins R photometric band for first-ranked cluster elliptical and S0 galaxies in 118 low redshift (<z>=0.037) clusters is analyzed for the correlations between average surface brightness, linear radius, and absolute magnitude. The purpose is to calibrate the correlations betwee…
The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the Local Void
Greggio, Laura; Hopp, Ulrich; Schulte-Ladbeck, Regina E. +2 more
We find that NGC 6789 is the most nearby example of a blue compact dwarf galaxy known to date. With the help of the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope, we resolve NGC 6789 into over 15,000 point sources in the V and I bands. The young stars of NGC 6789 are found exclusively near the center of the galaxy. The red giant …
Cyclic and secular variation in the temperatures and radii of extreme helium stars
Pollacco, Don; Jeffery, C. Simon; Starling, Rhaana L. C. +1 more
The ultraviolet properties of 17 extreme helium stars have been examined using 150 IUE spectra. Combining short-wave and long-wave image pairs and using a grid of hydrogen-deficient model atmospheres and a χ2 minimization procedure, 70 measurements of effective temperature (Teff), angular diameters (θ) and interstellar extinc…
Dual Flows and Oscillations in the Sunspot Transition Region
Wilhelm, K.; Kjeldseth-Moe, O.; Brynildsen, N. +1 more
New knowledge about sunspot transition region lines that deviate significantly from a Gaussian shape are presented. Attention is given to ``multiple flows,'' a line profile phenomenon in which two or more distinct velocities are observed within the same spatial resolution element. We observe line profiles that are well represented by two Gaussian …
Structural evolution in elliptical galaxies: the age-shape relation
Forbes, Duncan A.; Ryden, Barbara S.; Terlevich, A. I.
We test the hypothesis that the apparent axial ratio of an elliptical galaxy is correlated with the age of its stellar population. We find that old ellipticals (with estimated ages t>7.5Gyr) are rounder on average than younger ellipticals. The statistical significance of this shape difference is greatest at small radii; a Kolmogorov-Smirnov tes…
Relation between Thermal and Magnetic Properties of Active Regions as a Probe of Coronal Heating Mechanisms
Shibata, Kazunari; Yashiro, Seiji
We study the relation between thermal and magnetic properties of active regions in the corona observed with the soft X-ray telescope aboard Yohkoh. We derive the mean temperature and pressure of 64 mature active regions using the filter ratio technique, and examine the relationship of region size with temperature and pressure. We find that the tem…
Hubble Space Telescope Imaging in the Chandra Deep Field-South. I. Multiple Active Galactic Nucleus Populations
Marconi, A.; Gilli, R.; Tozzi, P. +9 more
We present preliminary results from imaging three Hubble Space Telescope (HST) Wide Field Planetary Camera 2 fields in V and I within the Chandra Deep Field-South (CDF-S). HST's sensitivity and resolution are sufficient to reveal optical counterparts for 24 of the 26 CDF-S X-ray sources detected in the 300 ks X-ray catalog and determine the morpho…
XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504
O'Brien, P. T.; Reeves, J. N.; Brinkmann, W. +4 more
We present the temporal analysis of X-ray observations of the radio-loud Narrow-Line Seyfert 1 galaxy (NLS1)