Search Publications
Reconstructing galaxy histories from globular clusters
Jordán, Andrés; Marzke, Ronald O.; Côté, Patrick +1 more
Nearly a century after the true nature of galaxies as distant `island universes' was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study the ubiquitous globular star clusters that surround most galaxies. Globular clusters are compa…
Bright Points in the Internetwork Quiet Sun
Muller, R.; Márquez, I.; Sánchez Almeida, J. +2 more
High-resolution G-band images of the interior of a supergranulation cell show ubiquitous bright points (BPs; some 0.3 BPs per Mm2). They are located in intergranular lanes and often form chains of elongated blobs whose smallest dimension is at the resolution limit (135 km on the Sun). Most of them live for a few minutes, having peak int…
The SUMER spectral atlas of solar coronal features
Curdt, W.; Landi, E.; Feldman, U.
We present a spectral atlas of the solar corona in the far-ultraviolet (FUV) and extreme ultraviolet (EUV) wavelength range. The atlas is based on observations obtained between 670 Å and 1609 Å in first order of diffraction and between 465 and 670 Å in second order with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph o…
The HELLAS2XMM survey. VI. X-ray absorption in the 1df AGN sample through a spectral analysis
Maiolino, R.; Perola, G. C.; Fiore, F. +13 more
The spectroscopic analysis of 117 serendipitous sources in the HELLAS2XMM 1df (1 degree field) survey is described. Of these, 106 sources, of which 86% have a spectroscopic redshift, are used to evaluate the fraction of X-ray absorbed (log NH>22) Active Galactic Nuclei (AGN) in the 2-10 keV flux range 0.8-20×10-14 erg cm
Extreme-Ultraviolet and X-Ray Spectroscopy of a Solar Flare Loop Observed at High Time Resolution: A Case Study in Chromospheric Evaporation
Phillips, Kenneth J. H.; Brosius, Jeffrey W.
We present extreme-ultraviolet (EUV) and X-ray light curves and Doppler velocity measurements for a GOES class M2 solar flare observed in NOAA Active Region 9433 on 2001 April 24 at high time resolution with the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) satellite (9.83 s) and the Bragg Crystal Spe…
Jupiter's low-frequency radio spectrum from Cassini/Radio and Plasma Wave Science (RPWS) absolute flux density measurements
Kurth, W. S.; Cecconi, B.; Zarka, P.
We apply the calibration method developed by [2001] to the data from the Cassini/Radio and Plasma Wave Science (RPWS) High-Frequency Receiver in order to derive flux density measurements of six components of the Jovian low-frequency radio spectrum over the full frequency range of the instrument (3.5 kHz to 16.1 MHz). The estimated accuracy is bett…
Two New Low Galactic D/H Measurements from the Far Ultraviolet Spectroscopic Explorer
Blair, William P.; Wood, Brian E.; Linsky, Jeffrey L. +3 more
We analyze interstellar absorption observed toward two subdwarf O stars, JL 9 and LS 1274, using spectra taken by the Far Ultraviolet Spectroscopic Explorer (FUSE). Column densities are measured for many atomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, Fe II, and H2), but our main focus is on measuring the D/H ratios f…
Ring-Diagram Analysis of the Structure of Solar Active Regions
Basu, Sarbani; Antia, H. M.; Bogart, Richard S.
We measure differences in structure between active and quiet regions of the Sun using the frequencies of high-degree modes determined from ring-diagram analyses. We find that both the speed of sound and the adiabatic index Γ1 differ in active regions as compared with quiet regions. In the immediate subsurface layers, the sound speed is …
Discovery of the galaxy counterpart of HDF 850.1, the brightest submillimetre source in the Hubble Deep Field
Muxlow, T. W. B.; Smail, I.; Smith, G. P. +14 more
Despite extensive observational efforts, a convincing optical/infrared identification of the brightest submm source in the Hubble Deep Field, HDF 850.1, has remained elusive after almost four years. This failure is all the more notable given the availability of supporting multifrequency data of unparalleled depth, and subarcsec positional accuracy…
The initial helium abundance of the Galactic globular cluster system
Salaris, M.; Riello, M.; Piotto, G. +1 more
In this paper we estimate the initial He content in about 30% of the Galactic globular clusters (GGCs) from new star counts we have performed on the recently published HST snapshot database of Colour Magnitude Diagrams (Piotto et al. \cite{Piotto02}). More specifically, we use the so-called R-parameter and estimate the He content from a theoretica…