Aims. We present mid-IR spectro-interferometry of the Seyfert type 1 nucleus of NGC 3783. The dusty circumnuclear environment is spatially resolved and the wavelength dependence of the compact ...emission is discussed. Methods. The observations were carried out with the MIDI instrument at the Very Large Telescope Interferometer in the N-band. Spectra and visibilities were derived with a spectral resolution of $\lambda/\Delta\lambda$ ~ 30 in the wavelength range from 8 to 13 μm. For the interpretation we developed a simple dusty disk model with a small and variable covering factor. Results. At baselines of 65 and 69 m, visibilities in the range of 0.4 to 0.7 were measured. The N-band spectra show a monotonic increase of the measured flux with wavelength with no apparent silicate feature around 10 μm. We find that the mid-IR emission from the nucleus can be reproduced by an extended dust disk or torus with a small covering factor of the radiating dust clouds. Conclusions. Our mid-IR observations of NGC 3783 are consistent with a clumpy circumnuclear dust environment. The interpretation in terms of a dusty torus with a low covering factor supports a clumpy version of the unified scheme for AGN. The inferred sizes and luminosities are in good agreement with dust reverberation sizes and bolometric luminosities from optical and X-ray observations.
Context. Despite their carbon-rich photospheres, silicate carbon stars show 10 μm silicate emission. They are considered to have circumbinary or circum-companion disks, which serve as a reservoir of ...oxygen-rich material shed by mass loss in the past. Aims. We present N-band spectro-interferometric observations of the silicate carbon star BM Gem using MIDI at the Very Large Telescope Interferometer (VLTI). Our aim is to probe the spatial distribution of oxygen-rich dust at high spatial resolution. Methods. Using the UT2-UT3 and UT3-UT4 configurations, BM Gem was observed with VLTI/MIDI at 44–62 m baselines. Results. The N-band visibilities observed for BM Gem decrease steeply between 8 and ~10 μm and increase gradually longward of ~10 μm, reflecting the optically thin silicate emission feature emanating from sub-micron-sized amorphous silicate grains. The differential phases obtained at baselines of ~44–46 m show significant non-zero values (∼-70°) in the central part of the silicate emission feature between ~9 and 11 μm, revealing a photocenter shift and the asymmetric nature of the silicate emitting region. The observed N-band visibilities and differential phases can be described adequately by a simple geometrical model in which the unresolved star is surrounded by a ring with azimuthal brightness modulation. The best-fit model is characterized by a broad ring (~70 mas across at 10 μm) with a bright region offset from the unresolved star by ~20 mas at a position angle of ~280°. This model can be interpreted as a system with a circum-companion disk and is consistent with the spectroscopic signatures of an accretion disk around an unseen companion, which were discovered in the violet spectrum of BM Gem.
Aims. We investigate the structure of the circumstellar disk of the T Tauri star S CrA N and test whether the observations agree with the standard picture proposed for Herbig Ae stars. Methods. Our ...observations were carried out with the VLTI/AMBER instrument in the H and K bands with the low spectral resolution mode. For the interpretation of our near-infrared AMBER and archival mid-infrared MIDI visibilities, we employed both geometric and temperature-gradient models. Results. To characterize the disk size, we first fitted geometric models consisting of a stellar point source, a ring-shaped disk, and a halo structure to the visibilities. In the H and K bands, we measured ring-fit radii of 0.73 ± 0.03 mas (corresponding to 0.095 ± 0.018 AU for a distance of 130 pc) and 0.85 ± 0.07 mas (0.111 ± 0.026 AU), respectively. This K-band radius is approximately two times larger than the dust sublimation radius of ≈0.05 AU expected for a dust sublimation temperature of 1500 K and gray dust opacities, but approximately agrees with the prediction of models including backwarming (namely a radius of ≈0.12 AU). The derived temperature-gradient models suggest that the disk is approximately face-on consisting of two disk components with a gap between star and disk. The inner disk component has a temperature close to the dust sublimation temperature and a quite narrow intensity distribution with a radial extension from 0.11 AU to 0.14 AU. Conclusions. Both our geometric and temperature-gradient models suggest that the T Tauri star S CrA N is surrounded by a circumstellar disk that is truncated at an inner radius of ≈ 0.11 AU. The narrow extension of the inner temperature-gradient disk component implies that there is a hot inner rim.
We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008–2009 using the CRIRES spectrograph mounted on the 8 m UT 1 Very Large Telescope (VLT Antu). We ...detect a strong, broad absorption wing in He i λ10833 extending up to -1900 km s-1 across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s-1) in the ultraviolet resonance lines of Si iv λλ1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si ii λλ1527, 1533 and C ii λλ1334, 1335, show absorption only up to -1200 km s-1, indicating that the absorption with velocities -1200 to -2100 km s-1 originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6 m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989–2009) also show high-velocity absorption in He i λ10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s-1 is present in the phase range 0.976 ≤ ϕ ≤ 1.023 of the spectroscopic cycle, but absent in spectra taken at ϕ ≤ 0.94 and ϕ ≥ 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of ω ~ 240°–270°. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40°–60°.
Context. Most Wolf-Rayet stars (WR) of the WC9 subtype exhibit a dusty circumstellar envelope, but it is still a matter of debate how dust can form in their harsh environment. In a few cases, a ...pinwheel-like structure of the dusty envelope has been detected; therefore, it has been suggested that dust formation in all dusty WR stars might be linked to colliding winds in a binary system. Aims. We probed the innermost region of the circumstellar dust shell of the deeply embedded WR star WR 118. Methods. We carried out spectro-interferometric observations using the AMBER instrument of ESO's Very Large Telescope Interferometer in low-spectral resolution mode ($R=35$). The K-band observations were obtained with three 1.8 m telescopes spanning projected baselines between 9.2 and 40.1 m. Results. At high spatial frequencies, the AMBER visibilities exhibit a prominent lobe, indicating that the envelope contains one or several zones with a large local intensity gradient. The strong closure phase signal clearly shows that the circumstellar envelope of WR 118 can only be described by an asymmetric intensity distribution. We show that a pinwheel nebula seen at low inclination is consistent with the AMBER data. Its size was determined to be $13.9\pm1.1$ mas. Conclusions. WR 118 possibly harbors a pinwheel nebula, which suggests a binary nature of the system. According to our best model, the period of the system would be ≈60 days (for $d=3$ kpc), making WR 118 the shortest-period pinwheel nebula known so far.
Aims.We present J, H, K spectrally dispersed interferometry with a spectral resolution of 35 for the Mira variable S Orionis. We aim at measuring the diameter variation as a function of wavelength ...that is expected due to molecular layers lying above the continuum-forming photosphere. Our final goal is a better understanding of the pulsating atmosphere and its role in the mass-loss process. Methods.Visibility data of S Ori were obtained at phase 0.78 with the VLTI/AMBER instrument using the fringe tracker FINITO at 29 spectral channels between 1.29 μm and 2.32 μm. Apparent uniform disk (UD) diameters were computed for each spectral channel. In addition, the visibility data were directly compared to predictions by recent self-excited dynamic model atmospheres. Results.S Ori shows significant variations in the visibility values as a function of spectral channel that can only be described by a clear variation in the apparent angular size with wavelength. The closure phase values are close to zero at all spectral channels, indicating the absence of asymmetric intensity features. The apparent UD angular diameter is smallest at about 1.3 μm and 1.7 μm and increases by a factor of ~1.4 around 2.0$\,\mu$m. The minimum UD angular diameter at near-continuum wavelengths is $\Theta_\mathrm{UD}=8.1 \pm 0.5$ mas, corresponding to $R\sim 420\,R_\odot$. The S Ori visibility data and the apparent UD variations can be explained reasonably well by a dynamic atmosphere model that includes molecular layers, particularly water vapor and CO. The best-fitting photospheric angular diameter of the model atmosphere is $\Theta_\mathrm{Phot}=8.3\pm0.2$ mas, consistent with the UD diameter measured at near-continuum wavelengths. Conclusions.The measured visibility and UD diameter variations with wavelength resemble and generally confirm the predictions by recent dynamic model atmospheres. These size variations with wavelength can be understood as the effects from water vapor and CO layers lying above the continuum-forming photosphere. The major remaining differences between observations and model prediction are very likely due to an imperfect match of the phase and cycle combination between observation and available models.
PURPOSE
To report a case of
Mycobacterium chelonae keratitis after laser in situ keratomileusis successfully treated with medical therapy and flap removal.
METHODS
Case report. A 36-year-old white ...woman in good health developed a paracentral keratitis in her right eye 1 month after bilateral laser in situ keratomileusis. Initial treatment included topical steroids and then intensive Ocuflox (ofloxacin ophthalmic solution; Allergan, Inc, Irvine, California) without success. Cultures were negative. The keratitis worsened, and she was referred to our institution. Interface infiltration was noted, and the flap was lifted to obtain adequate laboratory studies. Cultures were positive for
M chelonae.
RESULTS
The keratitis was treated with intensive topical amikacin sulfate 1%, topical clarithromycin 1%, and Ciloxan (ciprofloxacin HCL; Alcon Laboratories, Inc, Fort Worth, Texas) with minimal improvement in her clinical condition. She developed a toxic reaction to amikacin 1%. In order to improve antibiotic penetration, the hazy, ulcerated corneal flap was removed. The keratitis then resolved with intensive topical clarithromycin 1% and Ocuflox over 5 weeks. The patient now has visual acuity without correction of 20/50, despite superficial corneal haze.
CONCLUSION
M chelonae is a rare and insidious cause of infection after laser in situ keratomileusis. Diagnosis can be difficult and is often delayed. Aggressive medical management, with flap removal, if needed, may lead to resolution of infection.
Aims. We investigate the molecular and dusty environment of OH/IR stars in order to characterize the mass-loss process during the tip-AGB superwind phase. Methods. Employing the AMBER instrument at ...the VLT Interferometer we obtained near-infrared H- and K-band spectro-interferometric observations of the three OH/IR stars IRAS 13479-5436, IRAS 14086-6907 and IRAS 17020-5254 with a spectral resolution of about 35. We use a two-component geometrical model, consisting of a uniform disk and a Gaussian disk, to obtain characteristic angular sizes of the central stellar sources and their dust envelopes, as well as the flux ratios between these components. Results. Angular uniform disk diameters of the three central components of the objects above have values between 3.2 mas and 5.4 mas. For their dust envelopes, we find FWHM values between 17.1 mas and 25.2 mas. The three objects show significantly different flux contributions of the shells to the total near-IR flux of 61%, 38%, and 16% for IRAS 13479-5436, IRAS 14086-6907, and IRAS 17020-5254, respectively. According to distance estimates from the literature, the central stellar components have radii between 900 R⊙ and 1400 R⊙, while their dust envelopes reach FWHM values between 9000 R⊙ and 13 000 R⊙. The visibility functions of all three sources exhibit wavelength variations that resemble those of earlier VLTI/AMBER observations of semi-regular and Mira variable AGB stars. These are interpreted as characteristic of atmospheric molecular layers lying above the photosphere. Conclusions. The derived characteristic sizes of both, the central stellar atmospheres and dust envelopes are consistent with the canonical properties of OH/IR stars. The spectral visibility variations resemble those of other AGB stars and indicate the presence of molecular layers, confirming that these are a common phenomenon among AGB stars of very different luminosities and mass-loss rates, alike. We also find that the dust envelopes have a clearly larger optical depth than those known for Mira stars. We interpret this as an expected result of the “superwind” phase, the final 10 000 to 30 000 years of AGB-evolution, when the mass-loss rate increases by a factor of 10–100. By their different optical depths, the three dust shells studied here may represent different stages of the “superwind” and different initial masses.
Aims. We combined bispectrum speckle interferometry, adaptive optics (AO) imaging polarimetry, and radiative transfer modeling of polarized light to derive various physical properties of the ...proto-planetary nebula Frosty Leo. Methods. We performed bispectrum K '-band speckle interferometry and H-and K-band imaging polarimetry of Frosty Leo using the ESO 3.6 m telescope and the AO-equipped CIAO instrument of the 8 m Subaru telescope, respectively. Two-dimensional radiative transfer modeling was carried out in order to obtain a quantitative interpretation of our observations. Results. Our diffraction-limited speckle image shows distinct hourglass-shaped, point-symmetric bipolar lobes, an equatorial dust lane, and complex clumpy structures in the lobes. Our polarimetric data display a centro-symmetric polarization vector pattern with P similar to 30-50% in the bipolar lobes and a polarization disk between them. The polarization images also reveal an elongated region with low polarization along a position angle of-45 degree . The observations suggest that this region has a low dust density and was carved out by a jet-like outflow. Our radiative transfer modeling can simultaneously explain the observed spectral energy distribution, the intensity distribution of the hourglass-shaped lobes, and our polarization images if we use two grain species with sizes of 0.005 le a le 2.0 mum at latitudes between-2 degree and +2 degree , and 0.005 le a le 0.7 mum in the bipolar lobes. Assuming a distance of 3 kpc, an expansion velocity of 25 km s super(-1), and a gas-to-dust mass ratio of 160, we derive a dust mass of the disk of 2.85\times10 super(-3) M_, a gas mass-loss rate of 8.97\times10 super(-3) M_ yr super(-1), and a total envelope mass of 4.23 M_.
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