110 research outputs found
Distances on Cosmological Scales with VLTI
We present here a new method using interferometric measurements of quasars,
that allows the determination of direct geometrical distances on cosmic scales.
Quasar Broad Emission Line Regions sizes provide a "meter rule" with which to
measure the metric of the Universe. This method is less dependent of model
assumptions, and even of variations in the fundamental constants (other than
c). We discuss the spectral and spatial requirements on the VLTI observations
needed to carry out these measurements.Comment: 6 pages, 2 postscript figures, to appear in the proceedings of the
JENAM 2002 Workshop WS-VLTI "The Very Large Telescope Interferometer:
Challenges for the Future", Editors: P.J.V. Garcia, A. Glindemann, Th.
Henning, F. Malbet, Ap&SS, Kluwer, in pres
High Resolution Imaging of the Sun with CORONAS-1
We applied several image restoration and enhancement techniques, to CORONAS-I images. We carried out the characterization of the Point Spread Function (PSF) using the unique capability of the Blind Iterative Deconvolution (BID) technique, which recovers the real PSF at a given location and time of observation, when limited a priori information is available on its characteristics. We also applied image enhancement technique to extract the small scale structure imbeded in bright large scale structures on the disk and on the limb. The results demonstrate the capability of the image post-processing to substantially increase the yield from the space observations by improving the resolution and reducing noise in the images
CHEERS results on Mrk 573: Study of deep Chandra observations
We present results on Mrk 573 obtained as part of the CHandra survey of
Extended Emission-line Regions in nearby Seyfert galaxies (CHEERS). Previous
studies showed that this source features a biconical emission in the soft X-ray
band closely related with the Narrow Line Region as mapped by the [O iii]
emission line and the radio emission, though on a smaller scale; we investigate
the properties of soft X-ray emission from this source with new deep Chandra
observations. Making use of the subpixel resolution of the Chandra/ACIS image
and PSF-deconvolution, we resolve and study substructures in each ionizing
cone. The two cone spectra are fitted with photoionization model, showing a
mildly photoionized phase diffused over the bicone. Thermal collisional gas at
about ~ 1.1 keV and ~ 0.8 keV appears to be located between the nucleus and the
"knots" resolved in radio observations, and between the "arcs" resolved in the
optical images, respectively; this can be interpreted in terms of shock
interaction with the host galactic plane. The nucleus shows a significant flux
decrease across the observations indicating variability of the AGN, with the
nuclear region featuring higher ionization parameter with respect to the bicone
region. The long exposure allows us to find extended emission up to ~ 7 kpc
from the nucleus along the bicone axis. Significant emission is also detected
in the direction perpendicular to the ionizing cones, disagreeing with the
fully obscuring torus prescribed in the AGN unified model, and suggesting
instead the presence of a clumpy structure.Comment: 38 pages, 15 figures, 8 tables, accepted for publication on Ap
The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity
The Stellar Imager (SI) is a UV/Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is included as a 'Flagship and Landmark Discovery Mission' in the 2005 NASA Sun Solar System Connection (SSSC) Roadmap and as a candidate for a 'Pathways to Life Observatory' in the NASA Exploration of the Universe Division (EUD) Roadmap (May, 2005). In this paper we discuss the science goals and technology needs of, and the baseline design for, the SI Mission (http://hires.gsfc.nasa.gov/si/) its ability to image the 'Biggest, Baddest, Coolest Stars'
SI: The Stellar Imager
The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe
The Coronal Abundance Anomalies of M Dwarfs
We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As
quantified by X-ray surface flux, these are the most inactive M dwarfs ever
observed with X-ray grating spectroscopy. We focus on measuring coronal
abundances, in particular searching for evidence of abundance anomalies related
to First Ionization Potential (FIP). In the solar corona and wind, low FIP
elements are overabundant, which is the so-called "FIP effect." For other
stars, particularly very active ones, an "inverse FIP effect" is often
observed, with low FIP elements being underabundant. For both members of the GJ
338 binary, we find evidence for a modest inverse FIP effect, consistent with
expectations from a previously reported correlation between spectral type and
FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the
inverse FIP effect phenomenon, not just the active ones. We take the first step
towards modeling the inverse FIP phenomenon in M dwarfs, building on past work
that has demonstrated that MHD waves coursing through coronal loops can lead to
a ponderomotive force that fractionates elements in a manner consistent with
the FIP effect. We demonstrate that in certain circumstances this model can
also lead to an inverse FIP effect, pointing the way to more detailed modeling
of M dwarf coronal abundances in the future.Comment: to appear in The Astrophysical Journa
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