Near-infrared interferometric observation of the Herbig Ae star HD 144432 with VLTI/AMBER

Abstract

Aims. We study the sub-AU-scale circumstellar environment of the Herbig Ae star HD 144432 with near-infrared VLTI/AMBER observations to investigate the structure of its inner dust disk. Methods. The interferometric observations were carried out with the AMBER instrument in the H and K band. We interpret the measured H-and K-band visibilities, the near-and mid-infrared visibilities from the literature, and the spectral energy distribution (SED) of HD 144432 by using geometric ring models and ring-shaped temperature-gradient disk models with power-law temperature distributions.Results. We derive a K-band ring-fit radius of 0.17 ± 0.01 AU and an H-band radius of 0.18 ± 0.01 AU (for a distance of 145 pc). This measured K-band radius of ∼0.17 AU lies in the range between the dust sublimation radius of ∼0.13 AU (predicted for a dust sublimation temperature of 1500 K and gray dust) and the prediction of models including backwarming (∼0.27 AU). We find that an additional extended halo component is required in both the geometric and temperature-gradient modeling. In the best-fit temperaturegradient model, the disk consists of two components. The inner part of the disk is a thin ring with an inner radius of ∼0.21 AU, a temperature of ∼1600 K, and a ring thickness ∼0.02 AU. The outer part extends from ∼1 AU to ∼10 AU with an inner temperature of ∼400 K. We find that the disk is nearly face-on with an inclination angle of <28 • . Conclusions. Our temperature-gradient modeling suggests that the near-infrared excess is dominated by emission from a narrow, bright rim located at the dust sublimation radius, while an extended halo component contributes ∼6% to the total flux at 2 μm. The mid-infrared model emission has a two-component structure with ∼20% of the flux originating from the inner ring and the rest from the outer parts. This two-component structure is indicative of a disk gap, which is possibly caused by the shadow of a puffed-up inner rim.

Resolving the inner disk of UX Orionis

“…The extended halo component contributes with 13 ± 2% (DDN model)/16 ± 4% (geometric model) to the total flux, similar as found in other young stellar objects with extended halo emission (∼9-16%, e.g. Monnier et al 2006;Chen et al 2012;Vural et al 2012Vural et al , 2014a that is interpreted as scattered emission from the outer disk surface or material outside the disk plane, for example, a dusty disk wind (e.g., Bans & Königl 2012).…”

“…[ • ] 1498 ±70 25.9 ± 5.8 −1.79 ± 0.12 4.02 ± 0.12 0.60 ± 0.04 0.13 ± 0.02 70 ± 5 133 ± 5 (see, e.g., Chen et al 2012). This introduces one additional parameter, the halo flux ratio f h that defines the emitted halo flux F halo = f h (F + F rim ), where F denotes the stellar flux and F rim the flux emitted from the inner rim.…”

A study of dust properties in the inner sub-au region of the Herbig Ae star HD 169142 with VLTI/PIONIER

“…In the best-fit model the flux fraction of the halo is ∼12%, only slightly higher than the estimate of ∼8% in Lazareff et al (2017). Halo components, representing scattered light from extended (> 1 au) cold material, are frequently detected in NIR interferometric observations of Herbig stars, with typical flux ratios of 5%-20% (e.g., Monnier et al 2006;Chen et al 2012;Kreplin et al 2016). Plausible origins of the halo material include an infalling remnant envelope, dust entrained in the stellar wind or outflow (Monnier et al 2006), or a flaring outer disk that scatters the stellar light (Pinte et al 2008).…”

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

“…For the star SED, we adopt the same Kurucz model as in our previous paper (Chen et al 2012). The dust consists of astronomical silicate (Draine & Lee 1984) and amorphous carbon (Jager et al 1998).…”

“…In our previous simple temperature-gradient model of HD 144432 derived from infrared (IR) interferometric observations (Chen et al 2012), the disk consists of two components. The inner region of the model disk is a narrow ring with an inner radius of ∼0.21 AU, and an inner temperature of ∼1600 K. The outer disk region extends from ∼1 AU to ∼10 AU with an inner-edge temperature of ∼400 K. The lack of IR emission in the region from ∼0.23 AU to ∼1 AU is possibly a signature of a discontinuity in the dust distribution, and therefore a signature of the pre-transitional nature of the disk.…”