The structure of disks around intermediate-mass young stars from mid-infrared interferometry

Abstract

Context. The disks around Herbig Ae/Be stars are commonly divided into group I and group II based on their far-infrared spectral energy distribution, and the common interpretation for that is flared and flat disks. Our understanding of the evolution of these disks is rapidly changing. Recent observations suggest that many flaring disks have gaps, whereas flat disks are thought to be gapless. Aims. The different groups of objects can be expected to have different structural signatures in high-angular-resolution data, related to gaps, dust settling, and flaring. We aim to use such data to gain new insight into disk structure and evolution. Methods. Over the past 10 years, the MIDI instrument on the Very Large Telescope Interferometer has collected observations of several tens of protoplanetary disks. We modeled the large set of observations with simple geometric models and compared the characteristic sizes among the different objects. A population of radiative-transfer models was synthesized for interpreting the midinfrared signatures. Results. Objects with similar luminosities show very different disk sizes in the mid-infrared. This may point to an intrinsic diversity or could also hint at different evolutionary stages of the disks. Restricting this to the young objects of intermediate mass, we confirm that most group I disks are in agreement with being transitional (i.e., they have gaps). We find that several group II objects have mid-infrared sizes and colors that overlap with sources classified as group I, transition disks. This suggests that these sources have gaps, which has been demonstrated for a subset of them. This may point to an intermediate population between gapless and transition disks. Conclusions. Flat disks with gaps are most likely descendants of flat disks without gaps. Potentially related to the formation of massive bodies, gaps may therefore even develop in disks in a far stage of grain growth and settling. The evolutionary implications of this new population could be twofold. Either gapped flat disks form a separate population of evolved disks or some of them may evolve further into flaring disks with large gaps. The latter transformation may be governed by the interaction with a massive planet, carving a large gap and dynamically exciting the grain population in the disk.

Fingerprints of giant planets in the photospheres of Herbig stars

“…Interferometric observations reveal radial gaps on (sub-)au scales in both (Chen et al 2012;Schegerer et al 2013;Menu et al 2015). They are thus small-scale transitional disks with outer disks similar to group II sources.…”

“…Initially, group I was thought to evolve to group II as dust particles grew Appendix A is available in electronic form at http://www.aanda.org and settled (Meeus et al 2001;Dullemond & Dominik 2004a,b). The emerging view from recent debates is that group I disks are transitional, i.e., have radial cavities or gaps strongly depleted in millimetre-sized dust and perhaps gas (e.g., Keane et al 2014;Maaskant et al 2014;Banzatti & Pontoppidan 2015;Menu et al 2015;van der Plas et al 2015). As yet, no group II source is known to be a transition disk (TD), while all resolved TDs are group I sources.…”

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

“…The photospheric template, where used for photospheric correction, is shown in magenta at the top, broadened and veiled. Maaskant et al 2013;Menu et al 2015), as well as to recent model explorations (Antonellini et al 2016).…”

“…One major implication of this analysis is that the low frequency of water vapor detections in disks around  > M 1.5  M is found to be linked to inner disk regions depleted in molecular gas out to or even beyond the water snow line, differently from most disks around solar-mass stars. Other independent techniques find signatures of inner holes in dust emission in a growing number of disks around intermediatemass stars (e.g., Maaskant et al 2013;Menu et al 2015). With the analysis of disks that have CO emission observed at 4.7 μm and H 2 O at 2.9 μm and/or 10-33 μm (Table 6), we also find that the depletion scenario is not limited to the known transitional disks or to disks around intermediate-mass stars.…”

Resolving the inner disk of UX Orionis

“…The observation log is shown in Table 1. For modeling and interpretation, we complemented our near-infrared AMBER data with archival mid-infrared MIDI data (published in the survey paper of Menu et al 2015). We re-reduced this data set of five MIDI measurements using custom IDL routines (Kishimoto et al 2011) that incorporates parts of the standard software EWS 2 .…”