arXiv subjects

K. -H. Hofmann

Publications and source records attributed to K. -H. Hofmann.

At least 37 records · Page 2Linked to original sources

arXiv2017

Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk

We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris. The visibility data indicate a broadly circular resolved stellar disk with a complex substructure. The observed AMBER squared visibility values show drops at the positions of CO and CN bands, indicating that these lines form in extended layers above the photosphere. The AMBER visibility values are best fit by a model without a wind. The PIONIER data are consistent with the same model. We obtain a Rosseland angular diameter of 8.9+-0.3 mas, corresponding to a Rosseland radius of 355+-55 Rsun, an effective temperature of 2640+-80 K, and a luminosity of log L/Lsun=3.74+-0.18. These parameters match evolutionary tracks of initial mass 1.5+-0.5 Msun and current mass 1.3+-0.7 Msun. The reconstructed PIONIER images exhibit a complex structure within the stellar disk including a dominant bright spot located at the western part of the stellar disk. The spot has an H-band peak intensity of 40% to 60% above the average intensity of the limb-darkening-corrected stellar disk. The contrast between the minimum and maximum intensity on the stellar disk is about 1:2.5. Our observations are broadly consistent with predictions by dynamic atmosphere and wind models, although models with wind appear to have a circumstellar envelope that is too extended compared to our observations. The detected complex structure within the stellar disk is most likely caused by giant convection cells, resulting in large-scale shock fronts, and their effects on clumpy molecule and dust formation seen against the photosphere at distances of 2-3 stellar radii.

astro-ph.SR↗

arXiv2016

VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12000. Studies of the primary star wind and innermost wind-wind collision

Context. The mass loss from massive stars is not understood well. Eta Car is a unique object for studying the massive stellar wind during the LBV phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Methods. Observations of Eta Car were carried out with the ESO VLTI and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision. Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Br Gamma 2.166 micrometer emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately -140 to -376 km/s measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of -277 km/s, the position angle of the symmetry axis of the fan is ~ 126 degree. The fan-shaped structure extends approximately 8.0 mas (~ 18.8 au) to the southeast and 5.8 mas (~ 13.6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three-dimensional hydrodynamical, radiative transfer models of the massive interacting winds of Eta Car.

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arXiv2016

Science with MATISSE

We present an overview of the scientific potential of MATISSE, the Multi Aperture mid-Infrared SpectroScopic Experiment for the Very Large Telescope Interferometer. For this purpose we outline selected case studies from various areas, such as star and planet formation, active galactic nuclei, evolved stars, extrasolar planets, and solar system minor bodies and discuss strategies for the planning and analysis of future MATISSE observations. Moreover, the importance of MATISSE observations in the context of complementary high-angular resolution observations at near-infrared and submillimeter/millimeter wavelengths is highlighted.

astro-ph.IM↗

arXiv2016

An overview of the mid-infrared spectro-interferometer MATISSE: science, concept, and current status

MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal.

astro-ph.IM↗

arXiv2016

Tracing jet emission at the base of a high-mass YSO. First AMBER/VLTI observations of the Brγemission in IRAS 13481-6124

To probe the circumstellar environment of IRAS 13481-6124, a 20 M_sun high-mass young stellar object (HMYSO) with a parsec-scale jet and accretion disc, we investigate the origin of its Brγ-emission line through NIR interferometry. We present the first AMBER/VLTI observations of the Brγ-emitting region in an HMYSO at R~1500. Our AMBER/VLTI observations reveal a spatially and spectrally resolved Brγ-line in emission with a strong P Cygni profile, indicating outflowing matter with a terminal velocity of ~500 km/s. Visibilities, differential phases, and closure phases are detected in our observations within the spectral line and in the adjacent continuum. Both total visibilities (continuum plus line emitting region) and pure-line visibilities indicate that the Brγ-emitting region is more compact (2-4 mas in diameter or ~6-13 au at 3.2 kpc) than the continuum-emitting region (~5.4 mas or ~17 au). The absorption feature is also spatially resolved at the longest baselines (81 and 85 m) and has a visibility that is slightly smaller than the continuum-emitting region. The differential phases at the four longest baselines display an \u2018S\u2019-shaped structure across the line, peaking in the blue- and red-shifted high-velocity components. The calibrated photocentre shifts are aligned with the known jet axis, i.e they are probably tracing an ionised jet. The high-velocity components (v_r~100-500 km/s) are located far from the source, whereas the low-velocity components (0-100 km/s) are observed to be closer, indicating a strong acceleration of the gas flow in the inner 10 au. Finally, a non-zero closure phase along the continuum is detected. By comparing our observations with the synthetic images of the continuum around 2.16 um, we confirm that this feature originates from the asymmetric brightness distribution of the continuum owing to the inclination of the inner disc.

astro-ph.SR↗

arXiv2015

Monte-Carlo radiative transfer simulation of the circumstellar disk of the Herbig Ae star HD 144432

Studies of pre-transitional disks, with a gap region between the inner infrared-emitting region and the outer disk, are important to improving our understanding of disk evolution and planet formation. Previous infrared interferometric observations have shown hints of a gap region in the protoplanetary disk around the Herbig Ae star HD~144432. We study the dust distribution around this star with two-dimensional radiative transfer modeling. We compare the model predictions obtained via the Monte-Carlo radiative transfer code RADMC-3D with infrared interferometric observations and the {\SED} of HD~144432. The best-fit model that we found consists of an inner optically thin component at $0.21\enDash0.32~\AU$ and an optically thick outer disk at $1.4\enDash10~\AU$. We also found an alternative model in which the inner sub-AU region consists of an optically thin and an optically thick component. Our modeling suggests an optically thin component exists in the inner sub-AU region, although an optically thick component may coexist in the same region. Our modeling also suggests a gap-like discontinuity in the disk of HD~144432.

astro-ph.SR↗

arXiv2015

AMBER/VLTI high spectral resolution observations of the Br$γ$ emitting region in HD 98922. A compact disc wind launched from the inner disc region

We analyse the main physical parameters and the circumstellar environment of the young Herbig Be star HD 98922. We present AMBER/VLTI high spectral resolution (R =12000) interferometric observations across the Br$γ$ line, accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted near-infrared integral field spectroscopic data. To interpret our observations, we develop a magneto-centrifugally driven disc-wind model. Our analysis of the UVES spectrum shows that HD 98922 is a young (~5x10^5 yr) Herbig Be star (SpT=B9V), located at a distance of 440(+60-50) pc, with a mass accretion rate of ~9+/-3x10^(-7) M_sun yr^(-1). SINFONI K-band AO-assisted imaging shows a spatially resolved circumstellar disc-like region (~140 AU in diameter) with asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate that the Br$γ$ emitting region (radius ~0.31+/-0.04 AU) is smaller than the continuum emitting region (inner dust radius ~0.7+/-0.2 AU), showing significant non-zero V-shaped differential phases (i.e. non S-shaped, as expected for a rotating disc). The value of the continuum-corrected pure Br$γ$ line visibility at the longest baseline (89 m) is ~0.8+/-0.1, i.e. the Br$γ$ emitting region is partially resolved. Our modelling suggests that the observed Br$γ$ line-emitting region mainly originates from a disc wind with a half opening angle of 30deg, and with a mass-loss rate of ~2x10(-7) M_sun yr^(-1). The observed V-shaped differential phases are reliably reproduced by combining a simple asymmetric continuum disc model with our Br$γ$ disc-wind model. The Br$γ$ emission of HD 98922 can be modelled with a disc wind that is able to approximately reproduce all interferometric observations if we assume that the intensity distribution of the dust continuum disc is asymmetric.

astro-ph.SR↗

arXiv2015

The LEECH Exoplanet Imaging Survey. Further constraints on the planet architecture of the HR 8799 system

Context. Astrometric monitoring of directly-imaged exoplanets allows the study of their orbital parameters and system architectures. Because most directly-imaged planets have long orbital periods (>20 AU), accurate astrometry is challenging when based on data acquired on timescales of a few years and usually with different instruments. The LMIRCam camera on the LBT is being used for the LEECH survey to search for and characterize young and adolescent exoplanets in L' band, including their system architectures. Aims. We first aim to provide a good astrometric calibration of LMIRCam. Then, we derive new astrometry, test the predictions of the orbital model of 8:4:2:1 mean motion resonance proposed by Goździewski & Migaszewski, and perform new orbital fitting of the HR 8799 bcde planets. We also present deep limits on a putative fifth planet interior to the known planets. Methods. We use observations of HR 8799 and the Theta1 Ori C field obtained during the same run in October 2013. Results. We first characterize the distortion of LMIRCam. We determine a platescale and a true north orientation for the images of 10.707 +/- 0.012 mas/pix and -0.430 +/- 0.076 deg, respectively. The errors on the platescale and true north orientation translate into astrometric accuracies at a separation of 1 of 1.1 mas and 1.3 mas, respectively. The measurements for all planets are usually in agreement within 3 sigma with the ephemeris predicted by Goździewski & Migaszewski. The orbital fitting based on the new astrometric measurements favors an architecture for the planetary system based on 8:4:2:1 mean motion resonance. The detection limits allow us to exclude a fifth planet slightly brighter/more massive than HR 8799 b at the location of the 2:1 resonance with HR 8799 e (~9.5 AU) and about twice as bright as HR 8799 cde at the location of the 3:1 resonance with HR 8799 e (~7.5 AU).

astro-ph.EP↗

arXiv2014

The inner circumstellar disk of the UX Ori star V1026 Sco

The UX Ori type variables (named after the prototype of their class) are intermediate-mass pre-main sequence objects. One of the most likely causes of their variability is the obscuration of the central star by orbiting dust clouds. We investigate the structure of the circumstellar environment of the UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is large enough to explain the UX Ori variability. We observed the object in the low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument and derived H- and K-band visibilities and closure phases. We modeled our AMBER observations, published Keck Interferometer observations, archival MIDI/VLTI visibilities, and the spectral energy distribution using geometric and temperature-gradient models. Employing a geometric inclined-ring disk model, we find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the K band. The best-fit temperature-gradient model consists of a star and two concentric, ring-shaped disks. The inner disk has a temperature of 1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23 +- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner temperature of 334^{+35}_{-17} K. The derived inclination of 48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band). The position angle of the fitted geometric and temperature-gradient models are 163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg, respectively. The narrow width of the inner ring-shaped model disk and the disk gap might be an indication for a puffed-up inner rim shadowing outer parts of the disk. The intermediate inclination of ~50deg is consistent with models of UX Ori objects where dust clouds in the inclined disk obscure the central star.

astro-ph.SR↗

arXiv2013

Evidence of an asymmetrical Keplerian disk in the Brγ and He I emission lines around the Be star HD 110432

Context. HD 110432 was classified as a "γCas X-ray analog" since it has similar peculiar X-ray and optical characteristics, i.e. a hard-thermal X-ray variable emission and an optical spectrum affected by an extensive disk. Lopes de Oliveira et al. (2007) suggest that it might be a Be star harboring an accreting white dwarf or that the X-rays may come from an interaction between the surface of the star and its disk. Aims. To investigate the disk around this Be star we used the VLTI/AMBER instrument, which combines high spectral (R=12000) and high spatial (θmin =4 mas) resolutions. Methods. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. Results. We obtain a disk extension in the Brγ line of 10.2 D\ast and 7.8 D\ast in the He I line at 2.05 μm assuming a Gaussian disk model. The disk is clearly following a Keplerian rotation. We obtained an inclination angle of 55\degree, and the star is a nearly critical rotator with Vrot /Vc =1.00$\pm$0.2. This inclination is greater than the value found for γCas (about 42\degree, Stee et al. 2012), and is consistent with the inference from optical Fe II emission profiles by Smith & Balona (2006) that the inclination should be more than the γCas value. In the near-IR continuum, the disk of HD 110432 is 3 times larger than γCas's disk. We have no direct evidence of a companion around HD 110432, but it seems that we have a clear signature for disk inhomogeneities as detected for ζ Tau. This asymmetrical disk detection may be interpreted within the one-armed oscillation viscous disk framework. Another finding is that the disk size in the near-IR is similar to other Be stars with different spectral types and thus may be independent of the stellar parameters, as found for classical Be stars.

astro-ph.SR↗

arXiv2012

AMBER/VLTI observations of the B[e] star MWC 300

Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC 300 with the VLTI/AMBER instrument in the H and K bands and compared these observations with temperature-gradient models to derive model parameters. Results. The measured low visibility values, wavelength dependence of the visibilities, and wavelength dependence of the closure phase directly suggest that MWC 300 consists of a resolved disk and a close binary. We present a model consisting of a binary and a temperature-gradient disk that is able to reproduce the visibilities, closure phases, and spectral energy distribution. This model allows us to constrain the projected binary separation (~4.4 mas or ~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature power-law index, and other parameters.

astro-ph.SR↗

arXiv2012

VLTI/AMBER observations of the Seyfert nucleus of NGC 3783

Context. The putative tori surrounding the accretion disks of active galactic nuclei (AGNs) play a fundamental role in the unification scheme of AGNs. Infrared long-baseline interferometry allows us to study the inner dust distribution in AGNs with unprecedented spatial resolution over a wide infrared wavelength range. Aims. Near- and mid-infrared interferometry is used to investigate the milli-arcsecond-scale dust distribution in the type 1.5 Seyfert nucleus of NGC 3783. Methods. We observed NGC 3783 with the VLTI/AMBER instrument in the K-band and compared our observations with models. Results. From the K-band observations, we derive a ring-fit torus radius of 0.74 +/- 0.23 mas or 0.16 +/- 0.05 pc. We compare this size with infrared interferometric observations of other AGNs and UV/optical-infrared reverberation measurements. For the interpretation of our observations, we simultaneously model our near- and mid-infrared visibilities and the SED with a temperature/density-gradient model including an additional inner hot 1400 K ring component.

astro-ph.GA↗

arXiv2011

Spatially resolving the outer atmosphere of the M giant BK Vir in the CO first overtone lines with VLTI/AMBER

The mass-loss mechanism in normal K--M giant stars with small variability amplitudes is not yet understood, although they are the majority among red giant stars. We present high-spatial and high-spectral resolution observations of the 2.3 micron CO lines in the M7 giant BK Vir with a spatial resolution of 9.8 mas and a spectral resolution of 12000, using AMBER at the Very Large Telescope Interferometer (VLTI). The angular diameters observed in the CO lines are 12--31% larger than those measured in the continuum. We also detected asymmetry in the CO line-forming region. The data taken 1.5 months apart show possible time variation on a spatial scale of 30 mas (corresponding to 3 x stellar diameter) at the CO band head. Comparison of the observed data with the MARCS photospheric model shows that whereas the observed CO line spectrum can be well reproduced by the model, the angular sizes observed in the CO lines are much larger than predicted by the model. Our model with two additional CO layers above the MARCS photosphere reproduces the observed spectrum and interferometric data in the CO lines simultaneously. This model suggests that the inner CO layer at ~1.2 stellar radii is very dense and warm with a CO column density of ~10^{22} cm^{-2} and temperatures of 1900--2100K, while the outer CO layer at 2.5--3.0 stellar radii is characterized by column densities of 10^{19}--10^{20} cm^{-2} and temperatures of 1500--2100K. Our AMBER observations of BK Vir have spatially resolved the extended molecular outer atmosphere of a normal M giant in the individual CO lines for the first time. The temperatures derived for the CO layers are higher than or equal to the uppermost layer of the MARCS photospheric model, implying the operation of some heating mechanism in the outer atmosphere.

astro-ph.SR↗

arXiv2011

Constraining the structure of the planet-forming region in the disk of the Herbig Be star HD 100546

Studying the physical conditions in circumstellar disks is a crucial step toward understanding planet formation. Of particular interest is the case of HD 100546, a Herbig Be star that presents a gap within the first 13 AU of its protoplanetary disk, that may originate in the dynamical interactions of a forming planet. We gathered a large amount of new interferometric data using the AMBER/VLTI instrument in the H- and K-bands to spatially resolve the warm inner disk and constrain its structure. Then, combining these measurements with photometric observations, we analyze the circumstellar environment of HD 100546 in the light of a passive disk model based on 3D Monte-Carlo radiative transfer. Finally, we use hydrodynamical simulations of gap formation by planets to predict the radial surface density profile of the disk and test the hypothesis of ongoing planet formation. The SED and the NIR interferometric data are adequately reproduced by our model. We show that the H- and K-band emissions are coming mostly from the inner edge of the internal dust disk, located near 0.24 AU from the star, i.e., at the dust sublimation radius in our model. We directly measure an inclination of $33^{\circ} \pm 11^{\circ}$ and a position angle of $140^{\circ} \pm 16^{\circ}$ for the inner disk. This is similar to the values found for the outer disk ($i \simeq 42^{\circ}$, $PA \simeq 145^{\circ}$), suggesting that both disks may be coplanar. We finally show that 1 to 8 Jupiter mass planets located at $\sim 8$ AU from the star would have enough time to create the gap and the required surface density jump of three orders of magnitude between the inner and outer disk. However, no information on the amount of matter left in the gap is available, which precludes us from setting precise limits on the planet mass, for now.

astro-ph.SR↗

arXiv2011

Imaging the dynamical atmosphere of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER

We present the first 1-D aperture synthesis imaging of the red supergiant Betelgeuse in the individual CO first overtone lines with VLTI/AMBER. The reconstructed 1-D projection images reveal that the star appears differently in the blue wing, line center, and red wing of the individual CO lines. The 1-D projection images in the blue wing and line center show a pronounced, asymmetrically extended component up to ~1.3 stellar radii, while those in the red wing do not show such a component. The observed 1-D projection images in the lines can be reasonably explained by a model in which the CO gas within a region more than half as large as the stellar size is moving slightly outward with 0--5 km s^-1, while the gas in the remaining region is infalling fast with 20--30 km s^-1. A comparison between the CO line AMBER data taken in 2008 and 2009 shows a significant time variation in the dynamics of the CO line-forming region in the photosphere and the outer atmosphere. In contrast to the line data, the reconstructed 1-D projection images in the continuum show only a slight deviation from a uniform disk or limb-darkened disk. We derive a uniform-disk diameter of 42.05 +/- 0.05 mas and a power-law-type limb-darkened disk diameter of 42.49 +/- 0.06 mas and a limb-darkening parameter of (9.7 +/- 0.5) x 10^{-2}. This latter angular diameter leads to an effective temperature of 3690 +/- 54 K for the continuum-forming layer. These diameters confirm that the near-IR size of Betelgeuse was nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size. The continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulations.

astro-ph.SR↗

arXiv2011

VLTI/AMBER spectro-interferometry of the Herbig Be star MWC 297 with spectral resolution 12 000

Circumstellar disks and outflows play a fundamental role in star formation. Infrared spectro-interferometry allows the inner accretion-ejection region to be resolved. We measured interferometric visibilities, wavelength-differential phases, and closure phases of MWC 297 with a spectral resolution of 12000. To interpret our MWC 297 observations, we employed disk-wind models. The measured continuum visibilities confirm previous results that the continuum-emitting region of MWC 297 is remarkably compact. We derive a continuum ring-fit radius of ~2.2 mas (~0.56 AU at a distance of 250 pc), which is ~5.4 times smaller than the 3 AU dust sublimation radius expected for silicate grains (in the absence of radiation-shielding material). The strongly wavelength-dependent and asymmetric Br gamma-emitting region is more extended (~2.7 times) than the continuum-emitting region. At the center of the Br gamma line, we derive a Gaussian fit radius of ~6.3 mas HWHM (~1.6 AU). To interpret the observations, we employ a magneto-centrifugally driven disk-wind model consisting of an accretion disk, which emits the observed continuum radiation, and a disk wind, which emits the Br gamma line. The calculated wavelength-dependent model intensity distributions and Br gamma line profiles are compared with the observations (i.e., K-band spectrum, visibilities, differential phases, and closure phases). The closest fitting model predicts a continuum-emitting disk with an inner radius of ~0.3 AU and a disk wind ejection region with an inner radius of ~0.5 AU (~17.5 stellar radii). We obtain a disk-wind half-opening angle (the angle between the rotation axis and the innermost streamline of the disk wind) of ~80 degrees, which is larger than in T Tau models, and a disk inclination angle of ~20 degrees (i.e., almost pole-on).

astro-ph.SR↗

arXiv2009

Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R CrA

Models predict that in the innermost AU of the disk around Herbig Ae/Be star, the dust disk forms a "puffed-up" inner rim, which should result in a strongly asymmetric brightness distribution for disks seen under intermediate inclination. Using the VLTI/AMBER long-baseline interferometer, we obtained 24 near-infrared (H- and K-band) spectro-interferometric observations on the Herbig Ae star R CrA. In the derived visibility function, we detect the signatures of an extended (25 mas) and a compact component (5.8 mas), with the compact component contributing about 2/3 of the total flux. The brightness distribution is highly asymmetric, as indicated by the strong closure phases (up to 40 deg) and the detected position angle dependence of the visibilities and closure phases. To interpret these asymmetries, we employ geometric as well as physical models, including a binary model, a skewed ring model, and a puffed-up inner rim model with a vertical or curved rim shape. Our curved puffed-up rim model can reasonably well reproduce the interferometric observables and the SED simultaneously and suggests a luminosity of 29 L_sun and the presence of relatively large (> 1.2 micron) Silicate dust grains. Perpendicular to the disk, two bow shock-like structures appear in the associated reflection nebula NGC 6729, suggesting that the resolved sub-AU size disk is the driving engine of a large-scale outflow. Detecting, for the first time, strong non-localized asymmetries in the inner regions of a Herbig Ae disk, our study supports the existence of a puffed-up inner rim in YSO disks.

astro-ph.SR↗

arXiv2009

Resolving the asymmetric inner wind region of the yellow hypergiant IRC+10420 with VLTI/AMBER in low and high spectral resolution mode

We obtained near-infrared long-baseline interferometry of IRC+10420 with the AMBER instrument of ESO's Very Large Telescope Interferometer (VLTI) in low and high spectral resolution (HR) mode to probe the photosphere and the innermost circumstellar environment of this rapidly evolving yellow hypergiant. In the HR observations, the visibilities show a noticeable drop across the Brackett gamma (BrG) line on all three baselines, and we found differential phases up to -25 degrees in the redshifted part of the BrG line and a non-zero closure phase close to the line center. The calibrated visibilities were corrected for AMBER's limited field-of-view to appropriately account for the flux contribution of IRC+10420's extended dust shell. We derived FWHM Gaussian sizes of 1.05 +/- 0.07 and 0.98 +/- 0.10 mas for IRC+10420's continuum-emitting region in the H and K bands, respectively, and the BrG-emitting region can be fitted with a geometric ring model with a diameter of 4.18 +0.19/-0.09 mas, which is approximately 4 times the stellar size. The geometric model also provides some evidence that the BrG line-emitting region is elongated towards a position angle of 36 degrees, well aligned with the symmetry axis of the outer reflection nebula. The HR observations were further analyzed by means of radiative transfer modeling using CMFGEN and the 2-D Busche & Hillier codes. Our spherical CMFGEN model poorly reproduces the observed line shape, blueshift, and extension, definitively showing that the IRC+10420 outflow is asymmetric. Our 2-D radiative transfer modeling shows that the blueshifted BrG emission and the shape of the visibility across the emission line can be explained with an asymmetric bipolar outflow with a high density contrast from pole to equator (8-16), where the redshifted light is substantially diminished.

astro-ph.SR↗