HIGH-RESOLUTION 25μM IMAGING OF THE DISKS AROUND HERBIG AE/BE STARS

Abstract

We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 µm using Subaru/COMICS and Gemini/T-ReCS. Our sample consists of equal numbers of objects belonging to the two categories defined by Meeus et al. (2001); 11 group I (flaring disk) and II (flat disk) sources. We find that group I sources tend to show more extended emission than group II sources. Previous studies have shown that the continuous disk is hard to be resolved with 8 meter class telescopes in Q-band due to the strong emission from the unresolved innermost region of the disk. It indicates that the resolved Q-band sources require a hole or gap in the disk material distribution to suppress the contribution from the innermost region of the disk. As many group I sources are resolved at 25 µm, we suggest that many, not all, group I Herbig Ae/Be disks have a hole or gap and are (pre-)transitional disks. On the other hand, the unresolved nature of many group II sources at 25 µm supports that group II disks have continuous flat disk geometry. It has been inferred that group I disks may evolve into group II through settling of dust grains to the mid-plane of the proto-planetary disk. However, considering growing evidence for the presence of a hole or gaps in the disk of group I sources, such an evolutionary scenario is unlikely. The difference between groups I and II may reflect different evolutionary pathways of protoplanetary disks.

Candidate Water Vapor Lines to Locate the H2O Snowline Through High-dispersion Spectroscopic Observations. II. The Case of a Herbig Ae Star

“…They pointed out that there is no significant difference in age between groups I and II sources (Meeus et al 2001;Honda et al 2015). Therefore, recent studies (e.g., Maaskant et al 2013;Honda et al 2015) suggested that both group I and II sources had experienced different evolutionary paths from some common primordial and continuous flaring disks. Here we note that Menu et al (2015), Isella et al (2016), and Zhang et al (2016) suggested that some geometrically flat disks (group II disk) have gaps.…”

“…On the other hand, there is little evidence for inner holes and/or gaps reported toward group II disks, and they seem to have a radially continuous structure (e.g., Honda et al 2015). Honda et al (2012) and Maaskant et al (2013) suggested that most group I sources can be classified as (pre-)transitional disks.…”

Dust Continuum Emission and the Upper Limit Fluxes of Submillimeter Water Lines of the Protoplanetary Disk around HD 163296 Observed by ALMA

“…Our target HD 163296 is an isolated, young (∼5 Myr), and intermediate mass (∼2.3M ) Herbig Ae star and has no evidence of a stellar binary companion. It is relatively nearby, and it is surrounded by a well-studied gas-rich disk with no hint of an inner hole (group II, e.g., Honda et al 2015). Here we note that according to the recent Gaia data release 2 2 , the distance obtained by Hipparcos measurement in the past (d ∼122 pc, e.g., Perryman et al 1997;van den Ancker et al 1997) was corrected to d ∼101.5 pc (Gaia Collaboration et al 2018).…”

Observing the linked depletion of dust and CO gas at 0.1–10 au in disks of intermediate-mass stars

“…In disks around young intermediate-mass stars (Herbig Ae/Be stars), the far-IR excess of the SED, tracing colder material at larger radii, has been adopted by Meeus et al (2001) to classify disks into Group I (GI, with high excess) and Group II (GII, with moderate excess). The current understanding of this empirical classification is that it reflects a different disk structure, with GI having a large disk cavity that allows the irradiation of the disk at 10 au, and GII having no or at most small inner cavities (Maaskant et al 2013;Menu et al 2015;Honda et al 2015;Garufi et al 2017).…”