Showing papers by "Margarita Karovska published in 2003"
TL;DR: In this article, the Magellan 6.5 m telescope with the MIRAC/BLINC camera has been used to detect mid-IR emission from a compact region surrounding the active galactic nucleus (AGN).
Abstract: In this Letter, we present results from our exploratory mid-IR study of Centaurus A circumnuclear environment using high angular resolution imaging at the Magellan 6.5 m telescope with the MIRAC/BLINC camera. We detected emission from a compact region surrounding the nuclear source and obtained photometry at 8.8 μm and in the N band. Our analysis suggests that the nuclear region is resolved with a size of ≈3 pc. The mid-IR emission from this region is likely associated with cool dust with an estimated temperature of ~160 K, surrounding the central "hidden" active galactic nucleus (AGN). We discuss the characteristics of this emission in relation to other mid-IR observations and the implications on models of dust formation in AGNs.
9 citations
TL;DR: In this article, the Magellan 6.5m telescope with the MIRAC/BLINC camera was used to detect mid-IR emission from a compact region surrounding the nuclear source and obtained photometry at 8.8 microns.
Abstract: In this paper we present results from our exploratory mid-IR study of Centaurus A circumnuclear environment using high-angular resolution imaging at the Magellan 6.5m telescope with the MIRAC/BLINC camera. We detected emission from a compact region surrounding the nuclear source, and obtained photometry at 8.8 microns and in the N band. Our analysis suggests that the nuclear region is resolved with a size of approximately 3 pc. The mid-IR emission from this region is likely associated with cool dust with an estimated temperature of \~160 K, surrounding the central ``hidden'' AGN. We discuss the characteristics of this emission in relation to other mid-IR observations and the implications on models of dust formation in AGNs.
7 citations
TL;DR: In this paper, a new method using interferometric measurements of quasars is presented, which allows the determination of direct geometrical distances on cosmic scales using a "meter rule" with which to measure the metric of the Universe.
Abstract: 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.
2 citations
TL;DR: In this paper, Far Ultraviolet Spectroscopic Explorer (FUSE) observations of Mira A's wind-accreting companion star, Mira B, were used to refine estimates of the physical properties of the emitting H2 gas.
Abstract: We present new Far Ultraviolet Spectroscopic Explorer (FUSE) observations of Mira A's wind-accreting companion star, Mira B. We find that the strongest lines in the FUSE spectrum are H2 lines fluoresced by H I Lyman-alpha. A previously analyzed Hubble Space Telescope (HST) spectrum also shows numerous Lyman-alpha fluoresced H2 lines. The HST lines are all Lyman band lines, while the FUSE H2 lines are mostly Werner band lines, many of them never before identified in an astrophysical spectrum. We combine the FUSE and HST data to refine estimates of the physical properties of the emitting H2 gas. We find that the emission can be reproduced by an H2 layer with a temperature and column density of T=3900 K and log N(H2)=17.1, respectively. Another similarity between the HST and FUSE data, besides the prevalence of H2 emission, is the surprising weakness of the continuum and high temperature emission lines, suggesting that accretion onto Mira B has weakened dramatically. The UV fluxes observed by HST on 1999 August 2 were previously reported to be over an order of magnitude lower than those observed by HST and the International Ultraviolet Explorer (IUE) from 1979--1995. Analysis of the FUSE data reveals that Mira B was still in a similarly low state on 2001 November 22.
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TL;DR: This article showed that quasar winds may be a major source of dust at high redshifts, obviating a difficulty with current observations, and requiring far less dust to exist at early epochs.
Abstract: Winds from AGN and quasars will form large amounts of dust, as the cool gas in these winds passes through the (pressure, temperature) region where dust is formed in AGB stars. Conditions in the gas are benign to dust at these radii. As a result quasar winds may be a major source of dust at high redshifts, obviating a difficulty with current observations, and requiring far less dust to exist at early epochs.
TL;DR: In this paper, a method to compute wavelength and phase-dependent limb darkening corrections for classical Cepheids is presented, derived from hydrodynamic simulations and radiative transfer modeling with a full set of atomic and molecular opacities.
Abstract: We present a new method to compute wavelength- and phase-dependent limb darkening corrections for classical Cepheids. These corrections are derived from hydrodynamic simulations and radiative transfer modeling with a full set of atomic and molecular opacities. Comparison with hydrostatic models having the same stellar parameters show a larger limb darkening for most phases in our models, and temporal variations related to the hydrodynamics of the stellar pulsation. We assess the implications of our results with respect to the geometric Baade-Wesselink method, which uses interferometric measurements of Cepheid angular diameters to determine their distances and radii. The relevance of the hydrodynamic effects predicted by our model on the limb darkening of pulsating Cepheids is finally discussed in terms of the predicted capabilities of the VLTI.
TL;DR: In this paper, a method to compute wavelength and phase-dependent limb darkening corrections for classical Cepheids is presented, derived from hydrodynamic simulations and radiative transfer modeling with a full set of atomic and molecular opacities.
Abstract: We present a new method to compute wavelength- and phase-dependent limb darkening corrections for classical Cepheids. These corrections are derived from hydrodynamic simulations and radiative transfer modeling with a full set of atomic and molecular opacities. Comparison with hydrostatic models having the same stellar parameters show a larger limb darkening for most phases in our models, and temporal variations related to the hydrodynamics of the stellar pulsation. We assess the implications of our results with respect to the geometric Baade-Wesselink method, which uses interferometric measurements of Cepheid angular diameters to determine their distances and radii. The relevance of the hydrodynamic effects predicted by our model on the limb darkening of pulsating Cepheids is finally discussed in terms of the predicted capabilities of the VLTI.
TL;DR: In this paper, a new method using interferometric measurements of quasars is presented, which allows the determination of direct geometrical distances on cosmic scales using a "meter rule" with which to measure the metric of the Universe.
Abstract: 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.