arXiv subjects

Sebastian Hoenig

Publications and source records attributed to Sebastian Hoenig.

12 recordsLinked to original sources

arXiv2025

GRAVITY+ adaptive optics (GPAO) tests in Europe

We present in this proceeding the results of the test phase of the GRAVITY+ adaptive optics. This extreme AO will enable both high-dynamic range observations of faint companions (including exoplanets) thanks to a 40x40 sub-apertures wavefront control, and sensitive observations (including AGNs) thanks to the addition of a laser guide star to each UT of the VLT. This leap forward is made thanks to a mostly automated setup of the AO, including calibration of the NCPAs, that we tested in Europe on the UT+atmosphere simulator we built in Nice. We managed to reproduce in laboratory the expected performances of all the modes of the AO, including under non-optimal atmospheric or telescope alignment conditions, giving us the green light to proceed with the Assembly, Integration and Verification phase in Paranal.

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arXiv2024

The Galaxy Activity, Torus, and Outflow Survey (GATOS). VII. The 20-214 $\mu$m imaging atlas of active galactic nuclei using SOFIA

We present a 19.7 - 214 $\mu$m imaging atlas of local (4 - 181 Mpc; median 43 Mpc) active galactic nuclei (AGN) observed with FORCAST and HAWC+ on board the SOFIA telescope with angular resolutions ~ 3"- 20". This atlas comprises 22 Seyferts (17 Type 2 and 5 Type 1) with a total of 69 images, 41 of which have not been previously published. The AGN span a range of luminosities of log$_{10}$ ($L_{bol}$ [erg/s]) = [42, 46] with a median of log$_{10}$ ($L_{bol}$ [erg/s]) = 44.1 $\pm$ 1.0. We provide total fluxes of our sample using aperture photometry for point source objects and a 2-D Gaussian fitting for objects with extended host galaxy emission, which was used to estimate the unresolved nuclear component. Most galaxies in our sample are point-like sources, however, four sources (Centaurus A, Circinus, NGC 1068, and NGC 4388) show extended emission in all wavelengths. The 30 - 40 $\mu$m extended emission in NGC 4388 is coincident with the narrow line region at PA ~ 50$^{\circ}$, while the dusty extension at longer wavelengths arises from the host galaxy at PA ~ 90$^{\circ}$. Our new observations allow us to construct the best sampled spectral energy distributions (SEDs) available between 30 - 500 $\mu$m for a sample of nearby AGN. We estimate that the average peak wavelength of the nuclear SEDs is ~ 40 $\mu$m in $\nu$F$_{\nu}$ , which we associate with an unresolved extended dusty region heated by the AGN.

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arXiv2023

Chromatically modelling the parsec scale dusty structure in the centre of NGC1068

The Very Large Telescope Interferometer (VLTI) has been providing breakthrough images of the dust in the central parsecs of Active Galactic Nuclei (AGN), a key component of the AGN unification scheme and AGN host galaxy interaction. In single IR bands, the images can have multiple interpretations some of which could challenge the unification scheme. This is the case for the archetypal type 2 AGN of NGC1068. The ambiguity is reduced by multi-band temperature maps which are hindered by uncertainty in intra-band alignment. We create a chromatic model capable of simultaneously explaining the VLTI GRAVITY+MATISSE 2$\mu$m-13$\mu$m observations of the AGN in NGC1068. We use a simple disk and wind geometry populated with spherical black body emitters and dust obscuration to create a versatile multi-wavelength model for IR interferometric data of dusty objects. This simple geometry is capable of reproducing the K-N-band VLTI data, explains the complex single band images, and solves the alignment between bands. We find that the resulting geometry is consistent with previous studies. Compared to molecular gas emission, our model wind position angle (PA) of $22^3_2{\deg}$ is close to the mas scale outflowing CO(6-5) PA of ~33{\deg} seen with the ALMA. The equivalent 90{\deg} offset model disk PA is also consistent with the CO(6-5) disk axis of 112{\deg} as well as the mas scale disk axis from CO(2-1), CO(3-2), and HCO$^+$(4-3) of 115$\pm$5{\deg}. Furthermore, the resulting model visually resembles the equivalent achromatic image reconstructions. We conclude that the IR emitting structure surrounding the AGN can indeed be explained by the clumpy disk+wind iteration of the AGN unification scheme. Within the scheme, we find it is best explained as a type 2 and the obscuring dust chemistry is consistent with a mix of olivine silicates and 16$\pm$1% amorphous carbon.

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arXiv2022

The dust sublimation region of the Type 1 AGN NGC4151 at a hundred micro-arcsecond scale as resolved by the CHARA Array interferometer

The nuclear region of Type 1 AGNs has only been partially resolved so far in the near-infrared (IR) where we expect to see the dust sublimation region and the nucleus directly without obscuration. Here we present the near-IR interferometric observation of the brightest Type 1 AGN NGC4151 at long baselines of ~250 m using the CHARA Array, reaching structures at hundred micro-arcsecond scales. The squared visibilities decrease down to as low as ~0.25, definitely showing that the structure is resolved. Furthermore, combining with the previous visibility measurements at shorter baselines but at different position angles, we show that the structure is elongated *perpendicular* to the polar axis of the nucleus, as defined by optical polarization and a linear radio jet. A thin-ring fit gives a minor/major axis ratio of ~0.7 at a radius ~0.5 mas (~0.03 pc). This is consistent with the case where the sublimating dust grains are distributed preferentially in an equatorial plane in a ring-like geometry, viewed at an inclination angle of ~40 deg. Recent mid-IR interferometric finding of polar-elongated geometry at a pc scale, together with a larger-scale polar outflow as spectrally resolved by the HST, would generally suggest a dusty, conical and hollow outflow being launched presumably in the dust sublimation region. This might potentially lead to a polar-elongated morphology in the near-IR, as opposed to the results here. We discuss a possible scenario where an episodic, one-off anisotropic acceleration formed a polar-fast and equatorially-slow velocity distribution, having lead to an effectively flaring geometry as we observe.

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arXiv2022

Building a GRAVITY+ Adaptive Optics Test Bench

We present the testbench aimed at integrating the GRAVITY+ adaptive optics GPAO. It consists of two independent elements, one reproducing the Coud{é} focus of the telescope, including the telescope deformable mirror mount (with its surface facing down), and one reproducing the Coud{é} room opto-mechanical environment, including a downwards-propagating beam, and the telescope mechanical interfaces in order to fit in the new GPAO wavefront sensor. We discuss in this paper the design of this bench and the solutions we adopted to keep the cost low, keep the design compact (allowing it to be fully contained in a 20 sqm clean room), and align the bench independently from the adaptive optics. We also discuss the features we have set in this bench.

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arXiv2019

Exploring Active Supermassive Black Holes at 100 Micro-arcsecond Resolution

Super-high spatial resolution observations in the infrared are now enabling major advances in our understanding of supermassive black hole systems at the centers of galaxies. Infrared interferometry, reaching resolutions of milliarcseconds to sub-milliarcseconds, is drastically changing our view of the central structure from a static to a very dynamic one by spatially resolving to the pc-scale. We are also starting to measure the dynamical structure of fast moving gas clouds around active supermassive black holes at a scale of less than a light year. With further improvements on resolution and sensitivity, we will be able to directly image the exact site of the black hole's feedback to its host galaxy, and quantify the effect of such interaction processes. Near-future high angular resolution studies will definitely advance our mass determinations for these black holes, and we might even witness the existence of binary black hole systems at the center of galaxies.

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arXiv2018

WISE view of Narrow-Line Seyfert 1 galaxies: mid-infrared color and variability

We present the color and flux variability analysis at 3.4 μm (W1-band) and 4.6 μm (W 2-band) of 492 narrow-line Seyfert 1 (NLSy1) galaxies using archival data from the Wide-field Infrared Survey Explorer (WISE). In the WISE color-color, (W1 - W2) versus (W2 - W3) diagram, ~58% of the NLSy1 galaxies of our sample lie in the region occupied by the blazar category of active galactic nuclei (AGN). The mean W1 - W2 color of candidate variable NLSy1 galaxies is $0.99 \pm 0.18$ mag. The average amplitude of variability is $0.11 \pm 0.07$ mag in long-term (multi-year) with no difference in variability between W1 and W2-bands. The W1 - W2 color of NLSy1 galaxies is anti-correlated with the relative strength of [O III] to Hβ, strongly correlated with continuum luminosity, black hole mass, and Eddington ratio. The long-term amplitude of variability shows weak anti-correlation with the Fe II strength, continuum luminosity and Eddington ratio. A positive correlation between color as well as the amplitude of variability with the radio power at 1.4 GHz was found for the radio-detected NLSy1 galaxies. This suggests non-thermal synchrotron contribution to the mid-infrared color and flux variability in radio-detected NLSy1 galaxies.

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arXiv2018

Determination of the size of the dust torus in H0507+164 through optical and infrared monitoring

The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V -band and NIR J, H and Ks bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using cross-correlation techniques, we found delayed responses of the J, H and Ks light curves to the V -band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be $27.1^{+13.5}_{-12.0}$ days (V vs. J), $30.4^{+13.9}_{-12.0}$ days (V vs. H) and $34.6^{+12.1}_{-9.6}$ days (V vs. K ). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the τ - MV plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN.

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arXiv2017

Science cases for a visible interferometer

High spatial resolution is the key for the understanding various astrophysical phenomena. But even with the future E-ELT, single dish instruments are limited to a spatial resolution of about 4 mas in the visible. For the closest objects within our Galaxy most of the stellar photosphere remains smaller than 1 mas. With the success of long baseline interferometry these limitations were soom overcome. Today low and high resolution interferometric instruments on the VLTI and CHARA offer an immense range of astrophysical studies. Combining more telescopes and moving to visible wavelengths broadens the science cases even more. With the idea of developing strong science cases for a future visible interferometer, we organized a science group around the following topics: pre-main sequence and main sequence stars, fundamental parameters, asteroseismology and classical pulsating stars, evolved stars, massive stars, active galactic nuclei (AGNs) and imaging techniques. A meeting was organized on the 15th and 16th of January, 2015 in Nice with the support of the Action Specific in Haute Resolution Angulaire (ASHRA), the Programme National en Physique Stellaire (PNPS), the Lagrange Laboratory and the Observatoire de la Cote d'Azur, in order to present these cases and to discuss them further for future visible interferometers. This White Paper presents the outcome of the exchanges. This book is dedicated to the memory of our colleague Olivier Chesneau who passed away at the age of 41.

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arXiv2016

Planet Formation Imager (PFI): science vision and key requirements

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to about 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.

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arXiv2008

Phase Closure Image Reconstruction for Future VLTI Instrumentation

Classically, optical and near-infrared interferometry have relied on closure phase techniques to produce images. Such techniques allow us to achieve modest dynamic ranges. In order to test the feasibility of next generation optical interferometers in the context of the VLTI-spectro-imager (VSI), we have embarked on a study of image reconstruction and analysis. Our main aim was to test the influence of the number of telescopes, observing nights and distribution of the visibility points on the quality of the reconstructed images. Our results show that observations using six Auxiliary Telescopes (ATs) during one complete night yield the best results in general and is critical in most science cases; the number of telescopes is the determining factor in the image reconstruction outcome. In terms of imaging capabilities, an optical, six telescope VLTI-type configuration and ~200 meter baseline will achieve 4 mas spatial resolution, which is comparable to ALMA and almost 50 times better than JWST will achieve at 2.2 microns. Our results show that such an instrument will be capable of imaging, with unprecedented detail, a plethora of sources, ranging from complex stellar surfaces to microlensing events.

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arXiv2008

Phase Referencing in Optical Interferometry

One of the aims of next generation optical interferometric instrumentation is to be able to make use of information contained in the visibility phase to construct high dynamic range images. Radio and optical interferometry are at the two extremes of phase corruption by the atmosphere. While in radio it is possible to obtain calibrated phases for the science objects, in the optical this is currently not possible. Instead, optical interferometry has relied on closure phase techniques to produce images. Such techniques allow only to achieve modest dynamic ranges. However, with high contrast objects, for faint targets or when structure detail is needed, phase referencing techniques as used in radio interferometry, should theoretically achieve higher dynamic ranges for the same number of telescopes. Our approach is not to provide evidence either for or against the hypothesis that phase referenced imaging gives better dynamic range than closure phase imaging. Instead we wish to explore the potential of this technique for future optical interferometry and also because image reconstruction in the optical using phase referencing techniques has only been performed with limited success. We have generated simulated, noisy, complex visibility data, analogous to the signal produced in radio interferometers, using the VLTI as a template. We proceeded with image reconstruction using the radio image reconstruction algorithms contained in AIPS IMAGR (CLEAN algorithm). Our results show that image reconstruction is successful in most of our science cases, yielding images with a 4 milliarcsecond resolution in K band. (abridged)

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