Search Publications
Divergence and Vorticity of Solar Subsurface Flows Derived from Ring-Diagram Analysis of MDI and GONG Data
Howe, R.; Komm, R.; Hill, F. +3 more
We measure the relation between divergence and vorticity of subsurface horizontal flows as a function of unsigned surface magnetic flux. Observations from the Michelson Doppler Imager (MDI) Dynamics Program and Global Oscillation Network Group (GONG) have been analyzed with a standard ring-diagram technique to measure subsurface horizontal flows f…
XMM-Newton Discovery of 7 s Pulsations in the Isolated Neutron Star RX J1856.5-3754
Mereghetti, Sandro; Tiengo, Andrea
Thanks to the high counting statistics provided by a recent XMM-Newton observation of RX J1856.5-3754, we have discovered that this isolated neutron star pulsates at a period of 7.055 s. This confirms that RX J1856.5-3754 is similar in nature to the other six thermally emitting, nearby neutron stars discovered in soft X-rays with ROSAT. The pulsat…
ACS Photometry of Newly Discovered Globular Clusters in the Outer Halo of M31
Mackey, A. D.; Tanvir, N. R.; Ferguson, A. M. N. +6 more
We report the first results from deep ACS imaging of 10 classical globular clusters in the far outer regions (15 kpc<~Rp<~100 kpc) of M31. Eight of the clusters, including two of the most remote M31 globular clusters presently known, are described for the first time. Our F606W, F814W color-magnitude diagrams extend ~3 mag below th…
Star Counts in the Globular Cluster ω Centauri. I. Bright Stellar Components
Degl'Innocenti, S.; Castellani, M.; Piersimoni, A. M. +17 more
We present a photometric investigation on HB, RGB, and MSTO stars in ω Cen=NGC 5139. The center of the cluster was covered with a mosaic of F435W, F625W, and F658N band data collected with HST ACS. The outer reaches were covered with a mosaic of U-, B-, V-, and I-band data collected with the 2.2 m ESO/MPI telescope. The final catalog includes ~1.7…
Low-Energy Cutoffs and Hard X-Ray Spectra in High-z Radio-loud Quasars: The Suzaku View of RBS 315
Maraschi, L.; Tagliaferri, G.; Ghisellini, G. +4 more
We present the results from the Suzaku observation of the powerful radio-loud quasar RBS 315 (z=2.69), for which a previous XMM-Newton observation showed an extremely flat X-ray continuum up to 10 keV (photon index Γ=1.26) and indications of strong intrinsic absorption (NH~1022 cm-2, assuming neutral gas). The inst…
Electrons and Protons in Solar Energetic Particle Events
Ling, A. G.; Cliver, E. W.
A plot of 0.5 MeV peak electron intensity versus >10 MeV peak proton intensity for well-connected solar energetic particle (SEP) events from 1997 to 2003 reveals two distinct populations: (1) a group of events with peak proton intensities <3 protons cm-2 s-1 sr-1 that have electron-to-proton (e/p) ratios rang…
Swift XRT Observation of 34 New INTEGRAL IBIS AGNs: Discovery of Compton-Thick and Other Peculiar Sources
Gehrels, N.; Bird, A. J.; Fiocchi, M. +7 more
For a significant number of the sources detected at high energies (>10 keV) by the INTEGRAL IBIS and Swift BAT instruments there is either a lack information about them in the 2-10 keV range or they are totally unidentified. Herein, we report on a sample of 34 IBIS AGNs or AGN candidate objects for which there is X-ray data in the Swift XRT arc…
Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters
Schweizer, François; Miller, Bryan W.; Trancho, Gelys +1 more
We present Gemini optical spectroscopy of 23 young star clusters in NGC 3256. We find that the cluster ages range from few to ~150 Myr. All these clusters are relatively massive [(2-40)×105 Msolar] and appear to be of roughly 1.5 Zsolar metallicity. The majority of the clusters in our sample follow the same rotatio…
The Surprising External Upturn of the Blue Straggler Radial Distribution in M55
Dalessandro, E.; Ferraro, F. R.; Lanzoni, B. +3 more
By combining high-resolution HST and wide-field ground-based observations in ultraviolet and optical bands, we study the blue straggler star (BSS) population of the low-density galactic globular cluster M55 (NGC 6809) over its entire radial extent. The BSS projected radial distribution is found to be bimodal, with a central peak, a broad minimum a…
On the Characteristics of the Solar Gravity Mode Frequencies
García, R. A.; Mathur, S.; Turck-Chièze, S. +1 more
Gravity modes are the best probes for studying the dynamics of the solar radiative zone, and especially the nuclear core. This paper shows how specific physical processes influence the theoretical g-mode frequencies for the l=1 and l=2 modes over a large range of radial orders n from -46 to -1, corresponding to potential SOHO observations. To this…