Research Overview

Chondrule Formation

Chondrules are crystallized spherules that are embedded in chondritic materials. They were first described in the late 18th century. These chondritic materials are known to be few of the oldest materials that are remnant of the disk that the Solar System formed out of. Yet, after all of these times, their formation processes and evolution are still a mystery. There are clear signatures of flash heating that can be deduced from their glassy textures which can be reproduced in the laboratories. From experimental studies (see Ebel+ 2015), their cooling rates and compositional constraints can indicate some path-ways that they can form. I am invetigating whether a collision between planetesimals can produce these chondrules. Three-dimensional simulations with radiative transfer are performed to investigate the cooling rates of the fagments that are produced. In near future, the coupling of these cooling histories with chemisty can give some indications to the composition history of individual fragment that can be compared to experiments.

Formation and Physical Structure of Embedded Disks around Low-Mass Stars

The presence of accretion disks during the embedded stages of star formation have been inferred through continuum interferometric observations (eg., Jørgensen+ 2009). On the other hand, it is unclear from such observations whether these disks are similar to the evolved accretion disks around pre-main sequence stars. The combination of spatially and spectrally resolved molecular lines will give us clue to the physical and chemical structure of these young accretion disks. I have used the semi-analytical disk formation models (Visser+ 2009, 2010) and escape probability line radiative transfer (Bruderer+ 2009, 2012) to simulate molecular lines (near-IR through submm) as observed with single-dish telescopes and interferometry. The aim is to provide observational signatures of embedded rotationally supported disks and general observables as predicted by semi-analytical disk formation scenario. This is accompanied by interferometric observations using the PdBI in order to sample a number of nearby Stage I sources in order to find such disks. By combining both observation and multi-dimensional gas and dust physical models, I eventually can provide some insight into the disk formation process.

MSc: Physical and Chemical Conditions of Deeply Embedded Serpens Sources

We used the CS 3-2, CO 6-5, CO 7-6 and CS 5-4 spectra in order to study the physical and chemical conditions of four embedded young stellar objects in Serpens Core. Molecular emissions are tracing the outflow around each protostar. The morphologies of the high-J CO lines are similar to the low-J lines. Non-LTE gas and dust radiative transfers RADEX (van der Tak+ 2007) and RATRAN (Hogerheijde and van der Tak 2000) are used to determine the physical and chemical structure of the envelope around each protostar. The studies were complemented with mid- and far-IR emission due to embedded and isolated disk models using RADMC (Dullemond and Dominik 2004) and RADLite (Pontoppidan+ 2009) under LTE excitation conditions.

MSc: Gravitational Instabilities in Accretion Discs

This project investigates the gravitational transport properties of self-gravitating discs as a function of disc mass and prescribed cooling law. Self-gravitating discs are discs whose mass is comparable to the central object's mass. In such discs, gravitational instabilities can develop and transport angular momentum. We performed numerical studies of gravitational instabilities using Smoothed Particles Hydrodynamic code GADGET2. We compared the transport properties of two disc masses, 0.1 M_o and 0.5 M_o, under scale-free cooling law. The self-regulation process is efficient and the disc becomes quasi-steady. The transport in such discs is shown to be dominated by gravitational instabilities with varying spiral structures depending on disc mass. We conclude that gravitational instabilities are relevant for thin discs that cool on dynamical time scale. The overall transport properties in such disc can be described locally by viscous transport as long as the disc is quasi-steady. I have extended this research to the effect of infall on accretion disks as presented in Harsono, Alexander and Levin, MNRAS 2011.

Long time ago: Evolution of Dwarf Galaxies in Clusters

Deep HST ACS observations of Clusters of Galaxies at redshift of 0.3 have been used to investigate the faint-end of the luminosity function within 20 - 40 percent of the r₂₀₀. The lack of faint-end upturn within such scale in comparison to larger-scale studies suggest that the dwarf galaxies consist of recently infalling structures.