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ABSTRACT: Optical interferometry is the only means of directly measuring the sizes of stars. The most precise angular diameter measurements, however, depend on measuring complex fringe visibilities V at spatial frequencies where Re(V ) crosses zero. We can then use the spatial frequency Bperp/$lambda$$_0$ of the zero crossing as a measure of the stellar diameter via thetas$_UD$,0 asymp 1.22$lambda$$_0$/Bperp, where $lambda$$_0$ and is the wavelength at which Re(V ) = 0 when observed with a baseline length Bperp projected toward the star, and thetas$_UD$,$_0$ is the equivalent uniform disk diameter. The variation in limb darkening with wavelength leads to a corresponding variation in thetas$_UD$,$_0$ with $lambda$, even at fixed B, which allows us to measure the limb darkening in detail and probe the structure of the atmosphere. However, in order to take meaningful data at those spatial frequencies, we need some form of bootstrapping, in wavelength, baseline length, or both. Reduction of these bootstrapped data benefits greatly from the increase in SNR offered by coherent averaging. We demonstrate the effect of limb darkening on thetas$_UD$,$_0$($lambda$) with simulated observations based on model atmospheres, and compare them to coherently averaged NOI data.
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2012
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ABSTRACT: Previous ground-based observations of the Seyfert 2 galaxy Mrk 78 revealed a double set of emission lines, similar to those seen in several active galactic nuclei (AGNs) from recent surveys. Are the double lines due to two AGNs with different radial velocities in the same galaxy, or are they due to mass outflows from a single AGN? We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of Mrk 78 using observations from the Space Telescope Imaging Spectrograph (STIS) and Faint Object Camera aboard the Hubble Space Telescope as part of an ongoing project to determine the kinematics and geometries of AGN outflows. From the spectroscopic information, we determined the fundamental geometry of the outflow via our kinematics modeling program by recreating radial velocities to fit those seen in four different STIS slit positions. We determined that the double emission lines seen in ground-based spectra are due to an asymmetric distribution of outflowing gas in the NLR. By successfully fitting a model for a single AGN to Mrk 78, we show that it is possible to explain double emission lines with radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual supermassive black holes.
The Astrophysical Journal 01/2011; 727(2):71. · 6.02 Impact Factor
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ABSTRACT: We present a study of reddening and absorption towards the Narrow Line Regions (NLR) in active galactic nuclei (AGN) selected from the Revised Shapley-Ames, 12mu, and Swift/Burst Alert Telescope samples. For the sources in host galaxies with inclinations of b/a > 0.5, we find that mean ratio of [O III] 5007A, from ground-based observations, and [O IV] 28.59mu, from Spitzer/Infrared Spectrograph observations, is a factor of 2 lower in Seyfert 2s than Seyfert 1s. The combination of low [O III]/[O IV] and [O III] 4363/5007 ratios in Seyfert 2s suggests more extinction of emission from the NLR than in Seyfert 1s. Similar column densities of dusty gas, NH ~ several X 10^21 cm^-2, can account for the suppression of both [O III] 5007A and [O III] 4363A, as compared to those observed in Seyfert 1s. Also, we find that the X-ray line OVII 22.1A is weaker in Seyfert 2s, consistent with absorption by the same gas that reddens the optical emission. Using a Hubble Space Telescope/Space Telescope Imaging Spectrograph slitless spectrum of the Seyfert 1 galaxy NGC 4151, we estimate that only ~ 30% of the [O III] 5007A comes from within 30 pc of the central source, which is insufficient to account for the low [O III]/[OIV] ratios in Seyfert 2s. If Seyfert 2 galaxies have similar intrinsic [OIII] spatial profiles, the external dusty gas must extend further out along the NLR, perhaps in the form of nuclear dust spirals that have been associated with fueling flows towards the AGN. Comment: 33 pages, 7 figures. accepted for publication in the Astrophysical Journal
11/2010;
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ABSTRACT: Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a double set of emission lines, similar to those seen in several AGN from recent surveys. Are the double lines due to two AGN with different radial velocities in the same galaxy, or are they due to mass outflows from a single AGN?We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of Mrk 78 using observations from Space Telescope Imaging Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space Telescope(HST) as part of an ongoing project to determine the kinematics and geometries of active galactic nuclei (AGN) outflows. From the spectroscopic information, we deter- mined the fundamental geometry of the outflow via our kinematics modeling program by recreating radial velocities to fit those seen in four different STIS slit positions. We determined that the double emission lines seen in ground-based spectra are due to an asymmetric distribution of outflowing gas in the NLR. By successfully fitting a model for a single AGN to Mrk 78, we show that it is possible to explain double emission lines with radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual supermassive black holes. Comment: 22 pages, 7 figures (2 color), accepted for publication in The Astrophysical Journal
11/2010;
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ABSTRACT: We have detected a satellite via optical interferometry for the first time, using a 16 m baseline of the Navy Prototype Optical Interferometer (NPOI) to observe the geostationary communications satellite DirecTV-9S during the "glint" seasons of February-March 2008 and 2009 when the sun-satellite-NPOI geometry was favorable for causing specular reflections from geostationary satellites. We used the US Naval Observatory Flagstaff Station 1 m telescope to generate accurate positions for steering the NPOI. Stars are the easiest targets for optical/infrared interferometers because of their high surface brightness. Low surface brightness targets are more difficult: if they are small enough not to be resolved out by typical baselines, they are likely to be too faint to produce detectable fringes in an atmospheric coherence time. The 16 m NPOI baseline, the shortest available at the time of our observations, resolves out structures larger than ~ 1.5 m at the geostationary distance, while a typical size for the solar panel arrays is 2 m x 30 m. Our detection indicates that a small fraction of the satellite glinted, not surprising given that the solar panels are not accurately flat. Our fringe data are consistent with a two-component image consisting of a 1 to 1.3 m higher surface brightness component and a significantly larger lower surface brightness component. The brightness of the glints (2.m 4 and < or ~ 1.m 5 for the two detections in March 2009) and the size scale suggest that the compact component has an albedo of 0.06 to 0.13, while the larger-scale component is much darker, if circular geometry is assumed.
06/2010;
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ABSTRACT: We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 573, and its interaction with an in- ner dust/gas disk, based on Hubble Space Telescope (HST) WFPC2 and STIS observations. From the spectroscopic and imaging information, we determined the fundamental geometry of the outflow and inner disk, via two modeling pro- grams used to recreate the morphology of these regions imaged with HST. We also determined that the bicone of ionizing radiation from the Active Galactic Nucleus (AGN) intersects with the inner disk, illuminating a section of the disk including inner segments of spiral arms, fully seen through structure mapping, which appear to be outflowing and expanding. In addition, we see high velocities at projected distances of \geq 2'' (- 700 pc) from the nucleus, which could be due to rotation or to in situ acceleration of gas off the spiral arms. We find that the true half opening angle of the ionizing bicone (53 degrees) is much larger than the apparent half-opening angle (34 degrees) due to the above geometry, which may apply to a number of other Seyferts as well. Comment: 20 pages, 5 figures (1 color), to be published in The Astronomical Journal
06/2010;
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ABSTRACT: We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4 GHz (3.6 cm) and 1.4 GHz (20 cm), the [O IV] 25.89um, [Ne III] 15.56um and [Ne II] 12.81um emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4GHz/[O IV] ratio, assuming that [O IV] scales with the luminosity of the AGN. From this we find that Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and Seyfert 2's (i.e., Seyfert 1.8's, 1.9's, and 2.0's) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne II] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more "radio loud", by a factor of ~2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4GHz/[O IV], or alternatively, 1.4GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables. Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal. The paper contains 11 figures and 5 tables.
03/2010;
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ABSTRACT: RESUMEN Las estrellas masivas se encuentran insertas en materia gaseosa circunstelar; a veces también se encuentra polvo y moléculas. Aunque los discos son a veces demasiado pequeños para ser detectados directamente, este material puede ser detectado en el espectro de la radiación que observamos de la estrella. A menudo, el material circunestelar posee una distribución tipo disco, pero el proceso físico que forma y mantiene estos discos no es bien entendido. Las estrellas Be son un ejemplo de rotadores rápidos, estrellas calientes, cuyo espéctro en longitudes de ondá optica muestra ambas líneas de hidrógeno en emisión y frecuentemente, líneas de emisión de metales una vez ionizados, debido a la presencia del disco. Hemos calculado modelos teóricos computacionales de discos circunestelares de estrellas Be, usando un código que incorpora un número de mejoras sobre tratamientos previos de la estructura térmica del disco, incluyendo una composición química realista. Estos modelos pueden predecir los perfiles de línea espectrales y anchos equivalentes, la distribución espectral de energía y la polarización del continuo. Los modelos con es-tructura térmica precisa y campos de radiación son esenciales para interpretar correctamente las observaciones. Estos modelos pueden también predecir imágenes en el plano del cielo en importantes longitudes de onda y por lo tanto están idealmente adecuados para compararlos con observaciones interferométricas. Demuestro que nuestros modelos pueden ser restringidos por comparación directa con observaciones interferométrica opticas para la región que emite Hα y por perfiles de línea Hα contemporáneos. Las comparaciones detalladas de nues-tras predicciones con interferometría y espectroscopía de Hα entregan ajustadas restricciones a los parámetros libres del modelo para estos sistemas estrella-disco. ABSTRACT Many massive stars are embedded within gaseous circumstellar matter; sometimes dust and molecules are also present. Though the disks are sometimes too small to be detected directly, this material can be detected in the spectrum of radiation we observe from the star. Often, the circumstellar material has a disk-like distribution, but the physical processes that form and maintain these disks are not well understood. Be stars are an example of rapidly rotating, hot stars, whose spectra at optical wavelengths show both hydrogen emission lines and, frequently, emission lines from singly ionized metals due to the presence of a disk. We have computed theoretical models of circumstellar disks for Be stars, using a non-LTE radiative transfer code which incorporates a number of improvements over previous treatments of the disk thermal structure, including a realistic chemical composition. These models can predict spectral line profiles and equivalent widths, spectral energy distributions, and continuum polarization. Models with accurate thermal structures and radiation fields are essential to interpreting observations correctly. These models can also predict images on the plane of the sky in important wavelengths and are therefore ideally suited for comparison with interferometric observations. I will demonstrate that our models can be constrained by direct comparison with optical interferometric observations for the Hα emitting region and by contemporaneous Hα line profiles. Detailed comparisons of our predictions with Hα interferometry and spectroscopy place very tight constraints on the model free parameters for these star-disks systems.
Th. Rivinius & M. Cure RevMexAA (Serie de Conferencias). 01/2010; 38:92-95.
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ABSTRACT: During the last decade spectroscopic and high resolution HST observations have established a clear link between the starburst
phenomenon and the activity of the central AGN. We report here on our investigation of the nature of the near-UV light in
these objects, its relation to the circumnuclear starburst phenomenon, and the connection of this to the evolution and growth
of the galaxy bulge and central black hole.
12/2009: pages 259-261;
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ABSTRACT: We present a study of the resolved emission-line regions and an inner dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope observations. We show that the extended narrow-line region (ENLR), spanning ~4 kpc, is defined by the intersection of the ionizing bicone of radiation from the AGN and the inner disk, which is not coplanar with the large-scale stellar disk. This intersection leads to different position and opening angles of the ENLR compared to the narrow-line region (NLR). A number of emission-line arcs in the ENLR appear to be continuations of dust lanes in the disk, supporting this geometry. The NLR, which consists of outflowing emission-line knots spanning the central ~650 pc, is in the shape of a backwards S. This shape may arise from rotation of the gas, or it may trace the original fueling flow close to the nucleus that was ionized after the AGN turned on. Comment: 22 page, 7 figures, accepted for publication in the Astronomical Journal
12/2009;
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ABSTRACT: We present a study of the radial velocity offsets between narrow emission lines and host galaxy lines (stellar absorption and H I 21-cm emission) in Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of the Seyferts in the sample show [O III] emission lines with blueshifts with respect to their host galaxies exceeding 50 km/s, whereas only 6% show redshifts this large, in qualitative agreement with most previous studies. We also find that a greater percentage of Seyfert 1 galaxies show blueshifts than Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2 galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models of their narrow-line regions (NLRs) and inner galactic disks, and show how these models can explain the blueshifted [O III] emission lines in collapsed STIS spectra of these two Seyferts. We conclude that the combination of mass outflow of ionized gas in the NLR and extinction by dust in the inner disk (primarily in the form of dust spirals) is primarily responsible for the velocity offsets in Seyfert galaxies. More exotic explanations are not needed. We discuss the implications of this result for the velocity offsets found in higher redshift AGN. Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical Journal
11/2009;
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ABSTRACT: We present a study of the radial velocity offsets between AGN-related narrow emission lines and host-galaxy emission and absorption lines in Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of the Seyferts in the sample show [O iii] emission lines with blueshifts with respect to their host galaxies exceeding 50 km s−1, whereas only 6% show redshifts this large, in qualitative agreement with most previous studies. We also find that a greater percentage of Seyfert 1 galaxies show blueshifts than Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2 galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models of their narrow-line regions (NLRs) and inner galactic disks and show how these models can explain the blueshifted [O iii] emission lines in collapsed STIS spectra of these two Seyferts. We conclude that the combination of mass outflow of ionized gas in the NLR and extinction by dust in the inner disk (primarily in the form of dust spirals) is primarily responsible for the velocity offsets in Seyfert galaxies.
Proceedings of the International Astronomical Union 07/2009; 5:387 - 392.
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ABSTRACT: We study the nature of the extended near-UV emission in the inner kiloparsec of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow band [OIII] high resolution Hubble images. For the majority of the objects we find a very similar morphology in both bands. From the [OIII] images we construct synthetic images of the nebular continuum plus the emission line contribution expected through the F330W filter, which can be subtracted from the F330W images. We find that the emission of the ionised gas dominates the near-UV extended emission in half of the objects. A further broad band photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that the remaining emission is dominated by the underlying galactic bulge contribution. We also find a blue component whose nature is not clear in 4 out of 15 objects. This component may be attributed to scattered light from the AGN, to a young stellar population in unresolved star clusters, or to early-disrupted clusters. Star forming regions and/or bright off-nuclear star clusters are observed in 4/15 galaxies of the sample. Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRAS
07/2009;
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ABSTRACT: We have examined the physical conditions within a bright emission-line knot
in the inner narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 573 using
optical spectra and photoionization models. The spectra were obtained with the
Hubble Space Telescope/Space Telescope Imaging Spectrograph with the G430L and
G750M gratings. Comparing the spatial emission-line profiles, we found [Fe X]
6734 barely resolved, [O III] 5007 centrally peaked, but broader than [Fe X],
and [O II] 3727 the most extended. The spectra reveal that [Fe X] is broader in
velocity width and blue-shifted compared with lines from less ionized species.
Our estimate of the bolometric luminosity indicates that the active galactic
nucleus (AGN) is radiating at or above its Eddington Luminosity, which is
consistent with its identification as a hidden Narrow-Line Seyfert 1. We were
able to successfully match the observed emission line ratios with a
three-component photoionization model. Two components, one to account for the
[O III] emission and another in which the [Fe X] arises, are directly ionized
by the AGN, while [O II] forms in a third component, which is ionized by a
heavily absorbed continuum. Based on our assumed ionizing continuum and the
model parameters, we determined that the two directly-ionized components are ~
55 pc from the AGN. We have found similar radial distances for the central
knots in the Seyfert 2 galaxies Mrk 3 and NGC 1068, but much smaller radial
distances for the inner NLR in the Seyfert 1 galaxies NGC 4151 and NGC 5548.
Although in general agreement with the unified model, these results suggest
that the obscuring material in Seyfert galaxies extends out to at least tens of
parsecs from the AGN.
03/2009;
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ABSTRACT: We present a study of the intrinsic UV absorption and emission lines in an
historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we
obtained in 2004 February at high spatial and spectral resolution with the
Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. We
isolate a component of emission with a width of 680 km/s (FWHM) that arises
from an "intermediate line region" (ILR), similar to the one we discovered in
NGC 4151, at a distance of ~1 pc from the central continuum source. From a
detailed analysis of the five intrinsic absorption components in NGC 5548 and
their behavior over a span of 8 years, we present evidence that most of the UV
absorbers only partially cover the ILR and do not cover an extended region of
UV continuum emission, most likely from hot stars in the circumnuclear region.
We also find that four of the UV absorbers are at much greater distances (>70
pc) than the ILR, and none have sufficient N V or C IV column densities to be
the ILR in absorption. At least a portion of the UV absorption component 3, at
a radial velocity of -530 km/s, is likely responsible for most of the X-ray
absorption, at a distance < 7 pc from the central source. The fact that we see
the ILR in absorption in NGC 4151 and not in NGC 5548 suggests that the ILR is
located at a relatively large polar angle (~45 degrees) with respect to the
narrow-line region outflow axis.
02/2009;
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ABSTRACT: We have studied the relationship between the high- and low-ionization [O IV] λ25.89 μm, [Ne III] λ15.56 μm, and [Ne II] λ12.81 μm emission lines with the aim of constraining the active galactic nuclei (AGNs) and star formation contributions for a sample of 103 Seyfert galaxies. We use the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas. We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than Seyfert 1 galaxies. This result suggests two possible scenarios: (1) Seyfert 2 galaxies have intrinsically weaker AGNs, or (2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGNs and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of ~1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation, we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continua and found that [Ne II] is well correlated with the continuum luminosity at 60 μm and that both [Ne III] and [O IV] are better correlated with the 25 μm luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGNs and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence.
The Astrophysical Journal 12/2008; 689(1):95. · 6.02 Impact Factor
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ABSTRACT: Recovering images from optical interferometric observations is one of the major challenges in the field. Unlike the case of observations at radio wavelengths, in the optical the atmospheric turbulence changes the phases on a very short time scale, which results in corrupted phase measurements. In order to overcome these limitations, several groups developed image reconstruction techniques based only on squared visibility and closure phase information, which are unaffected by atmospheric turbulence. We present the results of two techniques used by our group, which employed coherently integrated data from the Navy Prototype Optical Interferometer. Based on these techniques we were able to recover complex visibilities for several sources and image them using standard radio imaging software. We describe these techniques, the corrections applied to the data, present the images of a few sources, and discuss the implications of these results.
10/2008;
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ABSTRACT: We report a tentative interferometric detection of an earth-orbiting artificial satellite using optical interferometry. We targeted four geosynchronous communications satellites with the Navy Prototype Optical Interferometer (NPOI) near Flagstaff, AZ, and obtained interferometric fringes on one of them, DIRECTV-9S. We used an east-west 15.9-meter baseline of the NPOI and took data in 16 spectral channels covering the 500-850 nm wavelength range. Observations took place during the "glint season" of 28 February to 3 March 2008, when the geometry of the solar panel arrays and the Sun's position creates glints as bright as 2nd magnitude of a few minutes' duration each night. We detected fringes on the satellite at approximately the 2 sigma level on 1 March at magnitude 4.5. Subsequent analysis shows that the fringe amplitudes are consistent with a size scale of 2 meters (50 nanoradians at GEO) in an east-west direction. This detection shows that interferometric detection of satellites at visual wavelengths is possible, and suggests that a multi-baseline interferometer array tailored to the angular size and brightness of geosynchronous satellites could lead to images of these satellites.
08/2008;
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ABSTRACT: We have studied the relationship between the high- and low-ionization [O IV] lambda 25.89 micron, [Ne III] lambda 15.56 micron and [Ne II] lambda 12.81 micron emission lines with the aim of constraining the active galactic nuclei (AGN) and star formation contributions for a sample of 103 Seyfert galaxies. We used the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas. We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than those of Seyfert 1 galaxies. This result suggests two possible scenarios: 1) Seyfert 2 galaxies have intrinsically weaker AGN, or 2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGN and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of ~1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continua and find that [Ne II] is well correlated with the continuum luminosity at 60 micron and that both [Ne III] and [O IV] are better correlated with the 25 micron luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGN, and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence. Comment: Accepted for publication in The Astrophysical Journal
08/2008;
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ABSTRACT: We present a numerical model describing a circularly symmetric gaseous disk around the Be star chi Ophiuchi. The model is constrained by long-baseline interferometric observations that are sensitive to the H-alpha Balmer line emission from the disk. For the first time our interferometric observations spatially resolve the inner region of the circumstellar disk around chi Ophiuchi and we use these results to place a constraint on the physical extent of the H-alpha-emitting region. We demonstrate how this in turn results in very specific constraints on the parameters that describe the variation of the gas density as a function of radial distance from the central star. Comment: Accepted for publication in ApJ
07/2008;
