Abstract
Context. A good constraint of when the growth of dust grains from sub-micrometer to millimeter sizes occurs, is crucial for planet formation models. This provides the first step towards the production of pebbles and planetesimals in protoplanetary disks. Currently, it is well established that Class II objects have large dust grains. However, it is not clear when in the star formation process this grain growth occurs. Aims. We use multi-wavelength millimeter observations of a Class I protostar to obtain the spectral index of the observed flux densities αmm of the unresolved disk and the surrounding envelope. Our goal is to compare our observational results with visibility modeling at both, 1.3 and 2.7 mm simultaneously. Methods. We present data from NOEMA at 2.7 mm and SMA at 1.3 mm of the Class I protostar, Per-emb-50. We model the dust emission with a variety of parametric and radiative-transfer models to deduce the grain size from the observed emission spectral index. Results. We find a spectral index in the envelope of Per-emb-50 of αenv = 3.3 ± 0.3, similar to the typical ISM values. The radiative-transfer modeling of the source confirms this value of αenv with the presence of dust with a amax ≤ 100 μm. Additionally, we explore the backwarming effect, where we find that the envelope structure affects the millimeter emission of the disk. Conclusions. Our results reveal grains with a maximum size no larger than 100 μm in the inner envelope of the Class I protostar Per-emb-50, providing an interesting case to test the universality of millimeter grain growth expected in these sources.
Highlights
Disks and envelopes around protostars play a fundamental role in the process of planet formation since they contain the ingredients out of which planets are formed (Testi et al 2014).Thanks to detailed studies of protoplanetary disks at several sub-millimeter and millimeter wavelengths such as HL Tau (Carrasco-González et al 2016), CY Tau, DoAr 25, and FT Tau (Pérez et al 2015; Tazzari et al 2016) it is well established that the radial profiles of their grain-size distributions are compatible with millimeter-sized grains
Our results reveal grains with a maximum size no larger than 100 μm in the inner envelope of the Class I protostar Per-emb-50, providing an interesting case to test the universality of millimeter grain growth expected in these sources
– For the envelope uv analysis we find a spectral index similar to the typical interstellar medium (ISM) values, αmm = 3.3 ± 0.3
Summary
Thanks to detailed studies of protoplanetary disks at several sub-millimeter and millimeter wavelengths such as HL Tau (Carrasco-González et al 2016), CY Tau, DoAr 25, and FT Tau (Pérez et al 2015; Tazzari et al 2016) it is well established that the radial profiles of their grain-size distributions are compatible with millimeter-sized grains. It is not yet clear at which stage of the star and planet formation process dust grains start to efficiently coagulate and evolve from micrometer-sized particles to macroscopic dimensions. This is explored recently in Chacón-Tanarro et al (2017), where they calculate the grain size in the center of the pre-stellar core L1544, finding that only in the central 300 AU, can grain size grow to about 200 μm
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