Millimetre spectral indices of transition disks and their relation to the cavity radius

Abstract

Context. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and to efficiently grow to millimetre sizes. Dynamical interactions with planet(s) have been one of the most exciting theories to explain the clearing of the inner disk. Aims. We look for evidence of millimetre dust particles in transition disks by measuring their spectral index α mm with new and available photometric data. We investigate the influence of the size of the dust depleted cavity on the disk integrated millimetre spectral index. Methods. We present the 3-mm (100 GHz) photometric observations carried out with the Plateau de Bure Interferometer of four transition disks: LkHα 330, UX Tau A, LRLL 31, and LRLL 67. We used the available values of their fluxes at 345 GHz to calculate their spectral index, as well as the spectral index for a sample of twenty transition disks. We compared the observations with two kinds of models. In the first set of models, we considered coagulation and fragmentation of dust in a disk in which a cavity is formed by a massive planet located at different positions. The second set of models assumes disks with truncated inner parts at different radii and with power-law dust-size distributions, where the maximum size of grains is calculated considering turbulence as the source of destructive collisions. Results. We show that the integrated spectral index is higher for transition disks (TD) than for regular protoplanetary disks (PD) with mean values ofᾱ TD mm = 2.70 ± 0.13 andᾱ PD mm = 2.20 ± 0.07 respectively. For transition disks, the probability that the measured spectral index is positively correlated with the cavity radius is 95%. High angular resolution imaging of transition disks is needed to distinguish between the dust trapping scenario and the truncated disk case.

Polycyclic Aromatic Hydrocarbons in Protoplanetary Disks around Herbig Ae/Be and T Tauri Stars

“…The disk is known to be pre-transitional, characterized by an inner optically thick disk (R 0.21 AU; e.g., Espaillat et al 2010) and a gap (e.g., Espaillat et al 2007). Andrews et al (2011) presented a spatially resolved cavity with a radius of ∼ 25 AU at 880 µm, also confirmed by 3 mm (100 GHz) observations (Pinilla et al 2014). The H-band polarimetric observations show a strongly polarized disk around UX Tau A which extends to ∼ 120 AU (Tanii et al 2012).…”

“…-(1) Alecian et al (2013), (2) Rigliaco et al (2015), (9) Sturm et al (2013), (10) Seok & Li (2015), (11) Maaskant et al (2014), (12) Juhász et al (2010), (13) Fairlamb et al (2015), (14) Mariñas et al (2011), (15) Verhoeff et al (2012), (16) van Boekel et al (2005), (17) Siebenmorgen et al (2000), (18) Hubrig et al (2009), (19) Folsom et al (2012, (20) Fukagawa et al (2010), (21) Seok & Li (2016), (22) Keller et al (2008), (23) Merín et al (2010), (24) Harvey et al (1984), (25) Kóspál et al(2012), (26) Boersma et al (2009), (27) Brown et al (2008), (28) Borges Fernandes et al (2007, (29) Schütz et al (2009), (30) Prato et al (2003), (31) Jeffers et al (2013), (32) Huélamo et al (2011), (33) Casey et al (1998), (34) Pinilla et al (2014), (35) Magazzu et al (1991), (36) Liu et al (2011), (37) …”

A Multi-wavelength Analysis of Dust and Gas in the SR 24S Transition Disk

“…Taking the total flux at each wavelength, the integrated spectral index is given by F F ln mm 1.3 mm 0.45 mm a = ( ) ln 0.45 mm 1.3 mm 2.02 0.13 =  ( ) (the error includes a calibration uncertainty of 10%), which is lower than the value previously reported (Pinilla et al 2014) based on SMA and ATCA observations at 0.88 and 3.0 mm Andrews et al 2011). This low value may indicate grain growth and/or a small cavity, but most likely arises from optically thick emission as discussed in Section 4.2.…”

“…For these disks, the spatially integrated spectral index is also expected to be higher for larger cavities (Pinilla et al 2014). There are few transition disks where the spectral index has been imaged, HD 142527, IRS 48, and SR 21 Pinilla et al 2015;van der Marel et al 2015), and in these few cases the spectral index decreases toward the location where the millimeter emission peaks and where a particle accumulation is expected.…”

Disk Dispersal: Theoretical Understanding and Observational Constraints

“…(There are also several definitions of what constitutes a transition disk, we adopt the definition of Espaillat et al (2014), i.e., disks with a clear deficit in short wavelength emission.) Transition disks have larger dust grains (Pinilla et al 2014), are typically millimeterbright (suggesting high disk mass) and accrete at rates a factor of ∼ 3 − 10 lower than full primordial disks (e.g. Espaillat et al 2014, Najita et al 2015.…”