Search Publications
Three-dimensional Inversion of Time-Distance Helioseismology Data: Ray-Path and Fresnel-Zone Approximations
Kosovichev, A. G.; Birch, A. C.; Zhao, J. +1 more
Time-distance helioseismology has provided important new insight into the subphotospheric structure and dynamics of sunspots, active regions, supergranular cells, and large-scale flows. These inferences have been made by using either the ray-path or Fresnel-zone approximations. We present inversion results of travel-time perturbations of wavepacke…
Identification of emission lines in the low-ionization strontium filament near Eta Carinae
Smith, N.; Johansson, S.; Hartman, H. +2 more
We have obtained deep spectra from 1640 to 10 100 Å with the Space Telescope Imaging Spectrograph (STIS) of the strontium filament, a largely neutral emission nebulosity lying close to the very luminous star Eta Carinae and showing an uncommon spectrum. Over 600 emission lines, both permitted and forbidden, have been identified. The majority origi…
Spectroscopic measurement of the plasma electron density and outflow velocity in a polar coronal hole
Giordano, S.; Antonucci, E.; Noci, G. +2 more
A new spectroscopic method, aimed to derive the plasma electron density and outflow velocity in expanding solar coronal regions, is discussed in this paper. The method is based on the analysis of a pair of coronal lines emitted via collisional and radiative excitation by the same ion, such as the O VI 1032, 1037 Å, doublet. The merit of this techn…
Effect of spatial resolution on estimating the Sun's magnetic flux
Solanki, S. K.; Krivova, N. A.
A critical question related to a possible secular trend in the Sun's total magnetic flux and consequently in solar irradiance is the total amount of magnetic flux present on the Sun and how it is distributed between active regions and the quiet Sun. NSO/Kitt Peak synoptic charts have in the past been used to estimate the total flux and the fractio…
The Recent Cluster Formation Histories of NGC 5253 and NGC 3077: Environmental Impact on Star Formation
Conselice, Christopher J.; Calzetti, Daniela; Gallagher, John S., III +2 more
We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field Planetary Camera 2 in both broadband (F300W, F547M, and F814W) and narrowband (F487N and F656N) filters. By comparing the photometry with theoretical population synthesis mod…
The nuclear ring in the unbarred galaxy NGC 278: Result of a minor merger?
Knapen, J. H.; van der Hulst, J. M.; de Blok, W. J. G. +1 more
We present fully sampled high angular resolution two-dimensional kinematics in the Hα spectral line, optical and near-infrared imaging, as well as 21 cm atomic hydrogen data of the spiral galaxy NGC 278. This is a small non-barred galaxy, which has a bright star forming inner region of about 2 kpc in diameter, reminiscent of nuclear rings seen mai…
A faint red stellar halo around an edge-on disc galaxy in the Hubble Ultra Deep Field
Zibetti, Stefano; Ferguson, Annette M. N.
We analyse the detailed structure of a highly-inclined (i>~ 80°) disc galaxy that lies within the Hubble Ultra Deep Field (UDF). The unprecedented depth of the UDF data allow disc and extraplanar emission to be traced reliably to surface brightness levels of µV,i,z~ 29-30 mag arcsec-2 (corresponding to rest-frame equ…
X-Ray Observations of the Compact Source in CTA 1
Hughes, John P.; Slane, Patrick; Gaensler, Bryan M. +3 more
We have studied the point source RX J0007.0+7302, at the center of supernova remnant CTA 1, using the X-Ray Multi-mirror Mission (XMM-Newton). The X-ray spectrum of the source is consistent with that of a neutron star and is well described by a power law with the addition of a soft thermal component that may correspond to emission from hot polar c…
A Multiwavelength Perspective of Flares on HR 1099: 4 Years of Coordinated Campaigns
Ayres, Thomas R.; Brown, Alexander; Skinner, Stephen L. +7 more
We report on four years of multiple wavelength observations of the RS CVn system V711 Tau (HR 1099) from 1993, 1994, 1996, and 1998. This combination of radio, ultraviolet, extreme ultraviolet, and X-ray observations allows us to view, in the most comprehensive manner currently possible, the coronal and upper atmospheric variability of this active…
Counterstreaming electrons in magnetic clouds near 5 AU
Forsyth, R.; Crooker, N. U.; Gosling, J. T. +2 more
Suprathermal electron pitch angle spectrograms were searched for counterstreaming signatures in 31 magnetic clouds identified in Ulysses data when the spacecraft was located ∼5 AU from the Sun. Under the assumption that counterstreaming indicates closed field lines, that is, field lines attached to the Sun at both ends, we find that the clouds ran…