Search Publications
Temporal variations in the Sun's rotational kinetic energy
Antia, H. M.; Gough, D. O.; Chitre, S. M.
Aims: We study the variation of the angular momentum and the rotational kinetic energy of the Sun, and associated variations in the gravitational multipole moments, on a timescale of the solar cycle.
Methods: These quantities are determined by inverting helioseismic rotational splitting data obtained by the Global Oscillation Network Group and…
Variations of the solar granulation motions with height using the GOLF/SoHO experiment
Jiménez-Reyes, S. J.; García, R. A.; Mathur, S. +2 more
Context: Below 1 mHz, the power spectrum of helioseismic velocity measurements is dominated by the spectrum of convective motions (granulation and supergranulation) and it is difficult to detect the low-order acoustic modes and gravity modes.
Aims: We attempt to understand more clearly the behavior of solar granulation as a function of observi…
The long-term X-ray variability properties of AGNs in the Lockman Hole region
Papadakis, I. E.; Georgantopoulos, I.; Markowitz, A. +2 more
Context: We present the results from a detailed X-ray variability analysis of 66 AGN in the Lockman Hole, which have optical spectroscopic identifications.
Aims: We compare, quantitatively, their variability properties with the properties of local AGN, and we study the “variability - luminosity” relation as a function of redshift, and the “var…
Young star clusters in interacting galaxies - NGC 1487 and NGC 4038/4039
Lehnert, M. D.; Vacca, W. D.; Chandar, R. +3 more
We estimate the dynamical masses of several young (≈10 Myr) massive star clusters in two interacting galaxies, NGC 4038/4039 (“The Antennae”) and NGC 1487, under the assumption of virial equilibrium. These are compared with photometric mass estimates from K-band photometry assuming a standard Kroupa IMF. The clusters were selected to have near-inf…
Density structure of an active region and associated moss using Hinode/EIS
Young, P. R.; Mason, H. E.; Del Zanna, G. +1 more
Context: Studying the problem of active region heating requires precise measurements of physical plasma parameters such as electron density, temperature, etc. It is also important to understand the relationship of coronal structures with the magnetic field. The Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode provides a rare opportunit…
Tracing jet-ISM interaction in young AGN: correlations between [O III] λ 5007 Å and 5-GHz emission
Labiano, A.
Aims: I study the interaction between young AGN and their host galaxies based on their ionized gas and radio emission, and analyze possible implications for radio galaxy evolution.
Methods: The [O III] λ 5007 Å line and 5-GHz radio properties are compared and studied for a large, representative sample of GPS and CSS (i.e., young) quasars and r…
X-ray and optical observations of M55 and NGC 6366: evidence for primordial binaries
Lewin, W. H. G.; Verbunt, F.; Pooley, D. +3 more
We present Chandra X-ray Observatory ACIS-S3 X-ray imaging observations and VLT/FORS2 and Hubble Space Telescope optical observations of two low-density Galactic globular clusters; NGC 6366 and M 55. We detect 16 X-ray sources with 0.5-6.0 keV luminosities above L_ {X}= 4 × 1030 erg s-1 within the half-mass radius of M 55, of…
On the absorption of X-ray bright broad absorption line quasars
Cappi, M.; Vignali, C.; Giustini, M.
Context: Most X-ray studies of broad absorption line quasars (BALQSOs) found significant (NH∼ 1022-24 cm-2) intrinsic column densities of gas absorbing an underlying typical power-law continuum emission, in agreement with expectations from radiatively driven accretion disk wind models. However, direct spectral anal…
Discovery of heavily-obscured AGN among seven INTEGRAL hard X-ray sources observed by Chandra
Sunyaev, R.; Revnivtsev, M.; Sazonov, S. +4 more
Aims: We identify hard X-ray sources discovered by the INTEGRAL all-sky survey. We complete identification of a unique sample of active galactic nuclei (AGN) selected in the hard X-ray band (17-60 keV) with minimal effects from absorption. Subsequently, we determine the fraction of obscured AGN in the local Universe.
Methods: We observed 7 INT…
Time evolution of the line emission from the inner circumstellar ring of SN 1987A and its hot spots
Lundqvist, P.; Spyromilio, J.; Gröningsson, P. +4 more
We present seven epochs between October 1999 and November 2007 of high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A. The fluxes of most of the narrow lines from the unshocked gas decreased by a factor of 2-3 during this period, consistent with the decay from the initial ionization by the shock break-out. However, [O…