Search Publications
Are short-term variations in solar oscillation frequencies the signature of a second solar dynamo?
Chaplin, William J.; García, Rafael A.; Basu, Sarbani +6 more
In addition to the well-known 11-year solar cycle, the Sun's magnetic activity also shows significant variation on shorter time scales, e.g. between one and two years. We observe a quasi-biennial (2-year) signal in the solar p-mode oscillation frequencies, which are sensitive probes of the solar interior. The signal is visible in Sun-as-a-star dat…
The 17-min orbital period in the ultracompact X-ray binary 4U 0513-40
Fiocchi, M.; Ubertini, P.; Landi, R. +2 more
The ultracompact low-mass X-ray binary 4U 0513-40 in the globular cluster NGC1851 exhibits large amplitude X-ray flux variations with spectral changes from low/hard to high/soft states which have not been reported previously in other ultracompact X-ray binaries. Using BeppoSAX, Chandra and XMM-Newton archival data together with recent INTEGRAL obs…
Analysis of SOHO/MDI and TRACE Observations of Sunspot Torsional Oscillation in AR10421
Kosovichev, A. G.; Gopasyuk, O. S.
Rotation of the leading sunspot of active region NOAA 10421 was investigated using magnetograms and Dopplergrams from the MDI instrument of the Solar and Heliospheric Observatory, and white-light images from the Transition Region and Coronal Explorer (TRACE). The vertical, radial, and azimuthal axisymmetrical components of both magnetic and veloci…
A Hard and Variable X-ray Emission from the Massive Emission-line Star HD 157832
Motch, C.; Lopes de Oliveira, R.
We report the discovery with XMM-Newton of a hard-thermal (T ~ 130 MK) and variable X-ray emission from the Be star HD 157832, a new member of the puzzling class of γ-Cas-like Be/X-ray systems. Recent optical spectroscopy reveals the presence of a large/dense circumstellar disk seen at intermediate/high inclination. With a B1.5V spectral type, HD …
Comparison of Millimeter-wave and X-Ray Emission in Seyfert Galaxies
Phillips, T. G.; Blain, A. W.; Monje, R. R.
We compare the emission at multiple wavelengths of an extended Seyfert galaxy sample, including both types of Seyfert nuclei. We use the Caltech Submillimeter Observatory to observe the CO J = 2-1 transition line in a sample of 45 Seyfert galaxies and detect 35 of them. The galaxies are selected by their joint soft X-ray (0.1-2.4 keV) and far-infr…
Searching for active galactic nuclei among unidentified INTEGRAL sources
Palazzi, E.; Minniti, D.; Masetti, N. +13 more
We report on a new method to identify active galactic nuclei (AGNs) among unidentified INTEGRAL sources. This method consists of cross-correlating unidentified sources listed in the fourth Imager on Board the INTEGRAL Satellite (IBIS) Survey Catalogue first with infrared and then with radio catalogues and a posteriori verifying, by means of X-ray …
Cryoclastic origin of particles on the surface of Enceladus
Manga, M.; Degruyter, W.
Analogous to volcanic deposits on Earth, we can infer eruption characteristics on Enceladus from the relationship between particle size and distance from the vent. We develop a model in which ice particles feeding plumes are accelerated by the gas. We consider two cases: drag-limited and collision-limited acceleration, which link particle size to …
Spectroastrometry of rotating gas disks for the detection of supermassive black holes in galactic nuclei. II. Application to the galaxy Centaurus A (NGC 5128)
Marconi, A.; Capetti, A.; Axon, D. J. +3 more
We measure the black hole mass in the nearby active galaxy Centaurus A (NGC 5128) using a new method based on spectroastrometry of a rotating gas disk. The spectroastrometric approach consists in measuring the photocenter position of emission lines for different velocity channels. In a previous paper we focused on the basic methodology and the adv…
Formation of a Propeller Structure by a Moonlet in a Dense Planetary Ring
Kokubo, Eiichiro; Michikoshi, Shugo
The Cassini spacecraft discovered a propeller-shaped structure in Saturn's A ring. This propeller structure is thought to be formed by gravitational scattering of ring particles by an unseen embedded moonlet. Self-gravity wakes are prevalent in dense rings due to gravitational instability. Strong gravitational wakes affect the propeller structure.…
HST-ACS photometry of the isolated dwarf galaxy VV124=UGC 4879. Detection of the blue horizontal branch and identification of two young star clusters
Bellazzini, M.; Galleti, S.; Perina, S. +1 more
We present deep V and I photometry of the isolated dwarf galaxy VV124=UGC 4879, obtained from archival images taken with the Hubble Space Telescope - Advanced Camera for Surveys. In the color-magnitude diagrams of stars at distances greater than 40″ from the center of the galaxy, we clearly identify a well-populated, old horizontal branch (HB) for…