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Solar and Heliospheric Observatory/Coronal Diagnostic Spectrograph and Ground-based Observations of a Two-Ribbon Flare: Spatially Resolved Signatures of Chromospheric Evaporation
Andretta, V.; Teriaca, L.; Falchi, A. +3 more
During a coordinated observing campaign (Solar and Heliospheric Observatory, SOHO JOP 139), we obtained simultaneous spectroheliograms of a solar active region in several spectral lines, sampling levels from the chromosphere to the corona. Ground-based spectroheliograms were acquired at the Dunn Solar Tower of the National Solar Observatory/Sacram…
X-Ray Absorption by the Low-Redshift Intergalactic Medium: A Numerical Study of the Λ Cold Dark Matter Model
Davé, Romeel; Weinberg, David H.; Chen, Xuelei +1 more
Using a hydrodynamic simulation of a cold dark matter universe with a cosmological constant, we investigate the ``X-ray forest'' absorption imprinted on the spectra of background quasars by the intervening intergalactic medium (IGM), at redshift z~0. In agreement with previous studies, we find that O VII and O VIII produce the strongest absorption…
Observation of coronal loop torsional oscillation
Zaqarashvili, T. V.
We suggest that the global torsional oscillation of solar coronal loop may be observed by the periodical variation of a spectral line width. The amplitude of the variation must be maximal at the velocity antinodes and minimal at the nodes of the torsional oscillation. Then the spectroscopic observation as a time series at different heights above t…
The Contribution of Polar Plumes to the Fast Solar Wind
Lemaire, P.; Gabriel, A. H.; Bely-Dubau, F.
The Doppler dimming technique is used for the first time to study ultraviolet polar plumes in the height range of 1.05-1.35 Rsolar, using observations from the spectrometer SUMER on the Solar and Heliospheric Observatory. It is found that, contrary to a number of published suggestions, outflow velocities in the plumes exceed those in th…
Ram pressure stripping and the formation of cold fronts
Churazov, E.; Forman, W.; Heinz, S. +2 more
Chandra and XMM-Newton observations of many clusters reveal sharp discontinuities in the surface brightness, which, unlike shocks, have lower gas temperature on the X-ray brighter side of the discontinuity. For this reason, these features are called `cold fronts'. It is believed that some cold fronts are formed when a subcluster merges with anothe…
The extra-galactic Cepheid distance scale from LMC and Galactic period-luminosity relations
Tanvir, N. R.; Kanbur, S. M.; Ngeow, C. +2 more
In this paper, we recalibrate the Cepheid distance to some nearby galaxies observed by the HST Key Project and the Sandage-Tammann-Saha group. We use much of the Key Project methodology in our analysis but apply new techniques, based on Fourier methods to estimate the mean of a sparsely sampled Cepheid light curve, to published extra-galactic Ceph…
Observability of Scattered-Light Echoes around Variable Stars and Cataclysmic Events
Sugerman, Ben E. K.
Scattered-light echoes from variable and cataclysmic stars offer one of the most effective means to probe the structure and composition of circumstellar and interstellar media. I build a simple model of light-echo surface brightness by considering the source spectrum and the dust density, geometry, and scattering efficiency. I use this model to in…
Probing AGB nucleosynthesis via accurate Planetary Nebula abundances
Pottasch, S. R.; Tielens, A. G. G. M.; Marigo, P. +2 more
The elemental abundances of ten planetary nebulae, derived with high accuracy including ISO and IUE spectra, are analysed with the aid of synthetic evolutionary models for the TP-AGB phase. The accuracy on the observed abundances is essential in order to make a reliable comparison with the models. The advantages of the infrared spectra in achievin…
On the nature of moving magnetic feature pairs around sunspots
Solanki, S. K.; Zhang, Jun; Wang, Jingxiu
Employing data recorded by the Michelson Doppler Imager (MDI) instrument on the Solar and Heliospheric Observatory (SOHO), we have identified 144 pairs of opposite magnetic polarity moving magnetic features (MMFs) in two active regions (NOAA ARs 8375 and 9236). The following results are obtained: (1) The majority of MMF pairs first appears at a di…
Compositions of Saturn's rings A, B, and C from high resolution near-infrared spectroscopic observations
Poulet, F.; French, R. G.; Cruikshank, D. P. +2 more
We used the NASA IRTF spectrograph SpeX to obtain near-infrared spectra (0.9-5.4 mu m) of Saturn's rings, achieving spectral resolution lambda / Delta lambda of about 2000. The spatial resolution (about 1 arcsec) is sufficient to distinguish the three main ring components (A, B and C rings) from one another. These new observations of Saturn's ring…