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Register a new userOn the asymmetry of the OH ro-vibrational lines in HD 100546
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D. Fedele
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We present multi-epoch high-spectral resolution observations with VLT/CRIRES of the OH doublet $^2Pi_{3/2}$ P4.5 (1+,1-) (2.934 $mu$m) towards the protoplanetary disk around HD 100546. The OH doublet is detected at all epochs and is spectrally resolved while nearby H$_2$O lines remains undetected. The OH line velocity profile is different in the three datasets: in the first epoch (April 2012, PA=26$^{circ}$) the OH lines are symmetric and line broadening is consistent with the gas being in Keplerian rotation around the star. No OH emission is detected within a radius of 8-11 au from the star: the line emitting region is similar in size and extent to that of the CO ro-vibrational lines. In the other two epochs (March 2013 and April 2014, PA=90$^{circ}$ and 10$^{circ}$, respectively) the OH lines appear asymmetric and fainter compared to April 2012. We investigate the origin of these line asymmetries which were taken by previous authors as evidence for tidal interaction between an (unseen) massive planet and the disk. We show that the observed asymmetries can be fully explained by a misalignment of the slit of order 0farcs04-0farcs20 with respect to the stellar position. The disk is spatially resolved and the slit misalignment is likely caused by the extended dust emission which is brighter than the stellar photosphere at near-infrared wavelengths which is the wavelength used for the pointing. This can cause the photo-center of HD 100546 to be mis-aligned with the stellar position at near-infrared wavelengths.
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We present observations of ro-vibrational OH and CO emission from the Herbig Be star HD 100546. The emission from both molecules arises from the inner region of the disk extending from approximately 13 AU from the central star. The velocity profiles of the OH lines are narrower than the velocity profile of the [O I] 6300 Angstrom line indicating that the OH in the disk is not cospatial with the O I. This suggests that the inner optically thin region of the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO emission lines, the OH lines are highly asymmetric. We show that the average CO and average OH line profiles can be fit with a model of a disk comprised of an eccentric inner wall and a circular outer disk. In this model, the vast majority of the OH flux (75%) originates from the inner wall, while the vast majority of the CO flux (65%) originates on the surface of the disk at radii greater than 13 AU. Eccentric inner disks are predicted by hydrodynamic simulations of circumstellar disks containing an embedded giant planet. We discuss the implications of such a disk geometry in light of models of planet disk tidal interactions and propose alternate explanations for the origin of the asymmetry.
HD 141569 is a Herbig Ae/Be star that straddles the boundary between the transition disks and debris disks. It is a low dust mass disk that reveals numerous structural elements (e.g. gaps and rings) that may point to young planets. It also exhibits a reservoir of CO gas observed at both millimeter and IR wavelengths. Previous observations (Goto et al. 2006) reported a possible asymmetry in the CO gas emission. Herein the IR ro-vibrational emission lines are analyzed and modeled both spectroscopically and spectroastrometrically. We find emission features from both 12CO and 13CO isotopologues heated to a temperature of approximately 200 K in the radial extent of 13 to 60 au. We do not see evidenceof the previously reported asymmetry in CO emission, our results being consistent with a Keplerian, axisymmetric emitting region. This raises the question of whether the emission profile may be evolving in time, possibly as a result of an orbiting feature in the inner disk such as a planet.
We present a study of ro-vibrational OH and CO emission from 21 disks around Herbig Ae/Be stars. We find that the OH and CO luminosities are proportional over a wide range of stellar ultraviolet luminosities. The OH and CO line profiles are also similar, indicating that they arise from roughly the same radial region of the disk. The CO and OH emission are both correlated with the far-ultraviolet luminosity of the stars, while the PAH luminosity is correlated with the longer wavelength ultraviolet luminosity of the stars. Although disk flaring affects the PAH luminosity, it is not a factor in the luminosity of the OH and CO emission. These properties are consistent with models of UV-irradiated disk atmospheres. We also find that the transition disks in our sample, which have large optically thin inner regions, have lower OH and CO luminosities than non-transition disk sources with similar ultraviolet luminosities. This result, while tentative given the small sample size, is consistent with the interpretation that transition disks lack a gaseous disk close to the star.
We present analysis of commissioning $M-$band data acquired with the infrared echelle spectrograph (iSHELL) on {it NASAs Infrared Telescope Facility}. In this paper we describe the delivered performance of the instrument for these $M-$band observations and the data reduction process. The feasibility of using iSHELL for spectro-astrometry is tested on the Herbig Ae/Be star HD~179218 and we show that sub-milliarcsecond fidelity is achievable.
We have studied the emission of CO ro-vibrational lines in the disc around the Herbig Be star HD100546 with the final goal of using these lines as a diagnostic to understand inner disc structure in the context of planet formation. High-resolution IR spectra of CO ro-vibrational emission at eight different position angles were taken with CRIRES at the VLT. From these spectra flux tables, CO ro-vibrational line profiles, and population diagrams were produced. We have investigated variations in the line profile shapes and line strengths as a function of slit position angle. We used the thermochemical disc modelling code ProDiMo based on the chemistry, radiation field, and temperature structure of a previously published model for HD100546. Comparing observations and the model, we investigated the possibility of disc asymmetries, the excitation mechanism (UV fluorescence), the geometry, and physical conditions of the inner disc. The observed CO ro-vibrational lines are largely emitted from the inner rim of the outer disc at 10-13 AU. The line shapes are similar for all v levels and line fluxes from all vibrational levels vary only within one order of magnitude. All line profile asymmetries and variations can be explained with a symmetric disc model to which a slit correction and pointing offset is applied. Because the angular size of the CO emitting region (10-13 AU) and the slit width are comparable the line profiles are very sensitive to the placing of the slit. The model reproduces the line shapes and the fluxes of the v=1-0 lines as well as the spatial extent of the CO ro-vibrational emission. It does not reproduce the observed band ratios of 0.5-0.2 with higher vibrational bands. We find that lower gas volume densities at the surface of the inner rim of the outer disc can make the fluorescence pumping more effcient and reproduce the observed band ratios.
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