568 research outputs found
Resolving the nucleus of Centaurus A at mid-IR wavelengths
We have observed Centaurus A with the MID-infrared Interferometric instrument
(MIDI) at the Very Large Telescope Interferometer (VLTI) at resolutions of 7 -
15 mas (at 12.5 micron) and filled gaps in the (u,v) coverage in comparison to
earlier measurements. We are now able to describe the nuclear emission in terms
of geometric components and derive their parameters by fitting models to the
interferometric data. With simple geometrical models, the best fit is achieved
for an elongated disk with flat intensity profile with diameter 76 +/- 9 mas x
35 +/- 2 mas (1.41 +/- 0.17 pc x 0.65 +/- 0.03 pc) whose major axis is oriented
at a position angle (PA) of 10.1 +/- 2.2 degrees east of north. A point source
contributes 47 +/- 11 % of the nuclear emission at 12.5 micron. There is also
evidence that neither such a uniform nor a Gaussian disk are good fits to the
data. This indicates that we are resolving more complicated small-scale
structure in AGNs with MIDI, as has been seen in Seyfert galaxies previously
observed with MIDI. The PA and inferred inclination i = 62.6 +2.1/-2.6 degrees
of the dust emission are compared with observations of gas and dust at larger
scales.Comment: Accepted for the PASA special issue on Centaurus
Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust
We present new interferometric data obtained with MIDI (MID infrared
Interferometric instrument) for the Seyfert II galaxy NGC 1068, with an
extensive coverage of sixteen uv points. These observations resolve the nuclear
mid-infrared emission from NGC 1068 in unprecedented detail with a maximum
resolution of 7 mas. For the first time, sufficient uv points have been
obtained, allowing us to generate an image of the source using maximum entropy
image reconstruction. The features of the image are similar to those obtained
by modelling. We find that the mid-infrared emission can be represented by two
components, each with a Gaussian brightness distribution. The first, identified
as the inner funnel of the obscuring torus, is hot (800K), 1.35 parsec long,
and 0.45 parsec thick in FWHM at a PA=-42 degrees (from north to east). It has
an absorption profile different than standard interstellar dust and with
evidence for clumpiness. The second component is 3 by 4 pc in FWHM with T=300K,
and we identify it with the cooler body of the torus. The compact component is
tilted by 45 degrees with respect to the radio jet and has similar size and
orientation to the observed water maser distribution. We show how the dust
distribution relates to other observables within a few parsecs of the core of
the galaxy such as the nuclear masers, the radio jet, and the ionization cone.
We compare our findings to a similar study of the Circinus galaxy and other
relevant studies. Our findings shed new light on the relation between the
different parsec-scale components in NGC 1068 and the obscuring torus.Comment: Accepted to MNRA
Observing the Seyfert 2 nucleus of NGC 1068 with the VLT Interferometer
Dusty tori have been suggested to play a crucial role in determining the
physical characteristics of active galactic nuclei (AGN), but investigation of
their properties has stalled for lack of high resolution mid-IR imaging.
Recently, a long-awaited breakthrough in this field was achieved: NGC 1068, a
nearby AGN, was the first extragalactic object to be observed with a mid-IR
interferometer, thereby obtaining the needed angular resolution to study the
alleged torus.
In this proceeding, first the field of AGN research is briefly reviewed, with
an emphasis on models of dusty tori. Second, the general properties of the key
object NGC 1068 are discussed. Third, the MIDI mid-IR interferometric data set
is presented together with a first attempt to interpret this data in the
context of tori models. Fourth, preliminary MIDI interferometric spectra of the
nucleus of the nearby starbursting galaxy Circinus are presented. Finally, we
briefly discuss the prospects of ESA's Darwin mission for observing nearby and
distant AGN. This mission will allow detailed mapping of tori of low luminosity
AGN such as NGC 1068 up to redshifts of 1 - 2 and more luminous AGN up to
redshift of 10 and beyond (abridged).Comment: 10 pages, 3 figures, published in Proceedings of SPIE Volume 5491
"New Frontiers in Stellar Interferometry
International Secured Transactions and Insolvency
The following article surveys some of the significant developments in the field of cross-border insolvencies and secured financing during the twelve months prior to December 1, 2005. The most publicized and long-awaited bankruptcy development was the enactment of legislation in the United States to adopt the UNCITRAL framework for the recognition of foreign insolvency proceedings. Even with the adoption of the UNICTRAL framework, American courts continued to render significant decisions under the former law which may, over time, inform practice, under the UNICTRAL provisions. Brazil also enacted significant bankruptcy reforms during 2005. The international law of secured transactions experienced a tremendous breakthrough in 2005 when the first protocol under the UNIDROIT Convention on International Interests in Mobile Equipment, specifically the aircraft protocol, received approval by a sufficient number of states to come into force and to establish a benchmark effective date
International Secured Transactions and Insolvency
The following article surveys some of the significant developments in the field of cross-border insolvencies and secured financing during the twelve months prior to December 1, 2005. The most publicized and long-awaited bankruptcy development was the enactment of legislation in the United States to adopt the UNCITRAL framework for the recognition of foreign insolvency proceedings. Even with the adoption of the UNICTRAL framework, American courts continued to render significant decisions under the former law which may, over time, inform practice, under the UNICTRAL provisions. Brazil also enacted significant bankruptcy reforms during 2005. The international law of secured transactions experienced a tremendous breakthrough in 2005 when the first protocol under the UNIDROIT Convention on International Interests in Mobile Equipment, specifically the aircraft protocol, received approval by a sufficient number of states to come into force and to establish a benchmark effective date
Large stellar disks in small elliptical galaxies
We present the rotation velocities V and velocity dispersions sigma along the
principal axes of seven elliptical galaxies less luminous than M_B= -19.5.
These kinematics extend beyond the half-light radii for all systems in this
photometrically selected sample. At large radii the kinematics not only confirm
that rotation and "diskiness" are important in faint ellipticals, as was
previously known, but also demonstrate that in most sample galaxies the stars
at large galactocentric distances have (V/sigma)_max of about 2, similar to the
disks in bona-fide S0 galaxies. Comparing this high degree of ordered stellar
motion in all sample galaxies with numerical simulations of dissipationless
mergers argues against mergers with mass ratios <=3:1 as an important mechanism
in the final shaping of low-luminosity ellipticals, and favors instead the
dissipative formation of a disk.Comment: 11 pages LaTex with 4 Postscript figure
Influence of near-surface stratigraphy on coastal landslides at Sleeping Bear Dunes National Lakeshore, Lake Michigan, USA
This paper is not subject to U.S. copyright. The definitive version was published in Journal of Coastal Research 20 (2004): 510-522, doi:10.2112/1551-5036(2004)020[0510:IONSOC]2.0.CO;2.Lake-level change and landslides are primary controls on the development of coastal environments along the coast of northeastern Lake Michigan. The late Quaternary geology of Sleeping Bear Dunes National Lakeshore was examined with high-resolution seismic reflection profiles, ground-penetrating radar (GPR), and boreholes. Based on sequence-stratigraphic principles, this study recognizes ten stratigraphic units and three major unconformities that were formed by late Pleistocene glaciation and postglacial lake-level changes. Locally high sediment supply, and reworking by two regressions and a transgression have produced a complex stratigraphy that is prone to episodic failure. In 1995, a large landslide deposited approximately 1 million m3 of sediment on the lake floor. The highly deformed landslide deposits, up to 18 m thick, extend 3–4 km offshore and unconformably overlie well-stratified glacial and lacustrine sediment. The landslide-prone bluff is underlain by channel-fill deposits that are oriented nearly perpendicular to the shoreline. The paleochannels are at least 10 m deep and 400 m wide and probably represent stream incision during a lake-level lowstand about 10.3 ka B.P. The channels filled with sediment during the subsequent transgression and lake-level highstand, which climaxed about 4.5 ka B.P. As lake level fell from the highstand, the formation of beach ridges and sand dunes sealed off the channel and isolated a small inland lake (Glen Lake), which lies 5 m above the level of Lake Michigan and may be a source of piped groundwater. Our hypothesis is that the paleochannels act as conduits for pore water flow, and thereby locally reduce soil strength and promote slope failure.Generous support for this project was provided by Max Holden and Steve Yancho of Sleeping Bear Dunes National Lakeshore
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