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Register a new userProbing the wind launching regions of the Herbig Be star HD 58647 with high spectral resolution interferometry
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We present a study of the wind launching region of the Herbig Be star HD 58647 using high angular (lambda/2B=0.003) and high spectral (R=12000) resolution interferometric VLTI-AMBER observations of the near-infrared hydrogen emission line, Br-gamma. The star displays double peaks in both Br-gamma line profile and wavelength-dependent visibilities. The wavelength-dependent differential phases show S-shaped variations around the line centre. The visibility level increases in the line (by ~0.1) at the longest projected baseline (88 m), indicating that the size of the line emission region is smaller than the size of the K-band continuum-emitting region, which is expected to arise near the dust sublimation radius of the accretion disc. The data have been analysed using radiative transfer models to probe the geometry, size and physical properties of the wind that is emitting Br-gamma. We find that a model with a small magnetosphere and a disc wind with its inner radius located just outside of the magnetosphere can well reproduce the observed Br-gamma profile, wavelength-dependent visibilities, differential and closure phases, simultaneously. The mass-accretion and mass-loss rates adopted for the model are Mdot_a = 3.5 x 10^{-7} Msun/yr and Mdot_dw = 4.5 x 10^{-8} Msun/yr, respectively (Mdot_dw/Mdot_a =0.13). Consequently, about 60 per cent of the angular momentum loss rate required for a steady accretion with the measured accretion rate is provide by the disc wind. The small magnetosphere in HD 58647 does not contribute to the Br-gamma line emission significantly.
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We present spatially and spectrally resolved Br-gamma emission around the planet-hosting, transitional Herbig Ae/Be star HD 100546. Aiming to gain insight into the physical origin of the line in possible relation to accretion processes, we carried out Br-gamma spectro-interferometry using AMBER/VLTI from three different baselines achieving spatial and spectral resolutions of 2-4 mas and 12000. The Br-gamma visibility is larger than that of the continuum for all baselines. Differential phases reveal a shift between the photocentre of the Br-gamma line -displaced 0.6 mas (0.06 au at 100 pc) NE from the star- and that of the K-band continuum emission -displaced 0.3 mas NE from the star. The photocentres of the redshifted and blueshifted components of the Br-gamma line are located NW and SE from the photocentre of the peak line emission, respectively. Moreover, the photocentre of the fastest velocity bins within the spectral line tends to be closer to that of the peak emission than the photocentre of the slowest velocity bins. Our results are consistent with a Br-gamma emitting region inside the dust inner rim (<0.25 au) and extending very close to the central star, with a Keplerian, disc-like structure rotating counter-clockwise, and most probably flared (25 deg). Even though the main contribution to the Br-gamma line does not come from gas magnetically channelled on to the star, accretion on to HD 100546 could be magnetospheric, implying a mass accretion rate of a few 10^-7 Msun/yr. This value indicates that the observed gas has to be replenished on time-scales of a few months to years, perhaps by planet-induced flows from the outer to the inner disc as has been reported for similar systems.
The region surrounding the well-known reflection nebula, NGC 7023, illuminated by a Herbig Be star, HD 200775, located in the dark cloud L1174 is studied in this work. Based on the distances and proper motion values from Gaia DR2 of 20 previously known young stellar object candidates, we obtained a distance of 335$pm$11 pc to the cloud complex L1172/1174. Using polarization measurements of the stars projected on the cloud complex, we show additional evidence for the cloud to be at $sim$ 335 pc distance. Using this distance and proper motion values of the YSO candidates, we searched for additional comoving sources in the vicinity of HD 200775 and found 20 new sources which show low infrared excess emission and are of age $sim$ 1 Myr. Among these, 10 YSO candidates and 4 newly identified comoving sources are found to show X-ray emission. Three of the four new sources for which we have obtained optical spectra show H$alpha$ in emission. About 80% of the total sources are found within $sim$ 1 pc distance from HD 200775. Spatial correlation of some of the YSO candidates with the Herschel dust column density peaks suggests that star formation is still active in the region and may have been triggered by HD 200775.
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.
The physical processes occurring within the inner few astronomical units of proto-planetary disks surrounding Herbig Ae stars are crucial to setting the environment in which the outer planet-forming disk evolves and put critical constraints on the processes of accretion and planet migration. We present the most complete published sample of high angular resolution H- and K-band observations of the stars HD 163296 and HD 190073, including 30 previously unpublished nights of observations of the former and 45 nights of the latter with the CHARA long-baseline interferometer, in addition to archival VLTI data. We confirm previous observations suggesting significant near-infrared emission originates within the putative dust evaporation front of HD 163296 and show this is the case for HD 190073 as well. The H- and K-band sizes are the same within $(3 pm 3)%$ for HD 163296 and within $(6 pm 10)%$ for HD 190073. The radial surface brightness profiles for both disks are remarkably Gaussian-like with little or no sign of the sharp edge expected for a dust evaporation front. Coupled with spectral energy distribution analysis, our direct measurements of the stellar flux component at H and K bands suggest that HD 190073 is much younger (<400 kyr) and more massive (~5.6 M$_odot$) than previously thought, mainly as a consequence of the new Gaia distance (891 pc).
The more massive counterparts of T Tauri stars, Herbig Ae/Be stars, are known to vary in a complex way with no variability mechanism clearly identified. We attempt to characterize the optical variability of HD~37806 (MWC 120) on time scales ranging between minutes and several years. A continuous, one-minute resolution, 21 day-long sequence of MOST (Microvariability & Oscillations of STars) satellite observations has been analyzed using wavelet, scalegram and dispersion analysis tools. The MOST data have been augmented by sparse observations over 9 seasons from ASAS (All Sky Automated Survey), by previously non-analyzed ESO (European Southern Observatory) data partly covering 3 seasons and by archival measurements dating back half a century ago. Mutually superimposed flares or accretion instabilities grow in size from about 0.0003 of the mean flux on a time scale of minutes to a peak-to-peak range of <~0.05 on a time scale of a few years. The resulting variability has properties of stochastic red noise, whose self-similar characteristics are very similar to those observed in cataclysmic binary stars, but with much longer characteristic time scales of hours to days (rather than minutes) and with amplitudes which appear to cease growing in size on time scales of tens of years. In addition to chaotic brightness variations combined with stochastic noise, the MOST data show a weakly defined cyclic signal with a period of about 1.5 days, which may correspond to the rotation of the star.
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