TY - BOOK
T1 - 3D Radiative Transfer Modeling of Embedded Protostellar Regions
AU - Jacobsen, Steffen Kjær
PY - 2018
Y1 - 2018
N2 - The formation of stars and planetary systems is a physical as well as
a chemical process. Through decades of research, our understanding
of star formation has greatly improved, though many aspects are still
unknown or heavily debated. Stable, rotationally supported disks of
gas and dust around protostars are routinely observed in the intermediate
and later stages of star formation. However, the exact details of
how early and how they form, are still open questions. Concurrently
with these issues, Complex Organic Molecules (COMs), and even prebiotic
molecules such as simple sugars, have been observed in the gas
phase of early, protostellar cores. Their exact formation route and the
physical origin of their arrival to the gas phase are heavily debated. It
is not known if the observed COMs are linked to the warm disk atmosphere
of settled protoplanetary disks, or if they predominantly exist
in the gas phase in the warmest, inner regions of protostellar cores,
before the emergence of a protoplanetary disk. These questions are
important, as the protostellar chemistry acts as a chemical precursor
for the composition of the material that ends up in planet formation,
and may explain the rich chemistry we see in our own Solar System.
Using high angular resolution observations with the Atacama
Large Millimeter/submillimeter Array (ALMA), together with complex
3D radiative transfer codes, we can investigate the innermost
environment of young protostars, and hopefully answer some of the
questions stated above.
In this thesis I present research focusing on the two low-mass protostellar
cores, IRAS 16293-2422 and L483, in terms of their dust and
gas density, temperature structures, and chemistries. Two of the three
research papers presented in this thesis concentrate on IRAS 16293-
2422, with one focusing on the 3D modeling of the envelope, the bridge
of dust and gas conjoining the two protostars, and the disk-like
emission around each protostar, as well as their individual luminosities.
A 3D dust density model is presented, which morphologically
matches the 868 μm continuum emission and explains the observed
C17O emission through a jump abundance model. This model emulates
freeze-out of molecules upon the dust grains, when the temperature
drops beneath the sublimation temperature of CO on the dust
ice-mantles. The individual luminosities of the deeply embedded protostars
in IRAS 16293-2422 are found to be LA >18 L! and LB 63 L!,
for radiation source A and B, respectively, which presents the first estimation
of the individual luminosities.
The second research paper on IRAS 16293-2422 focuses on the outflows
and the kinematics of the observed gas line emission from the
different molecules in the gas phase, and their relation to the bridge
of dust and gas. Molecular gas line emission of CO, H2CO, HCN, CS,
SiO and C2H reveal that only the dust continuum and C17O emission
have a physical origin in the bridge of dust and gas, while all
other molecular transitions are found to be related to the outflows
emanating from radiation source A. The lack of outflow activity from
radiation source B leads us to conclude that it is likely on a lower
evolutionary stage than radiation source A.
The last research paper describes ⇠ 0.100 observations of L483 with
ALMA, which reveal that the COMs observed towards L483 reside in
the innermost hot region of the envelope, within 40–60 au of the central
protostar, and arise from thermal sublimation of the icy mantle
around the dust grains. By analyzing the kinematics of the H13CN
J = 4–3 and CS J =7–6 gas line emission, the presence of a Keplerian
disk is excluded down to at least a 15 au radius. This means that
the observed COMs cannot come from an abrupt transition region between
the collapsing envelope and a Keplerian disk, as hypothesized
by an earlier research team, or from a warm disk atmosphere. Within
15 au, a small Kepler disk could hypothetically reside.
Suggestions are made for future research projects targeting IRAS
16293-2422 and L483, to further constrain the spatial distribution of
COMs (which constrains their formation routes), and the timeline for
the emergence of protoplanetary disks.
AB - The formation of stars and planetary systems is a physical as well as
a chemical process. Through decades of research, our understanding
of star formation has greatly improved, though many aspects are still
unknown or heavily debated. Stable, rotationally supported disks of
gas and dust around protostars are routinely observed in the intermediate
and later stages of star formation. However, the exact details of
how early and how they form, are still open questions. Concurrently
with these issues, Complex Organic Molecules (COMs), and even prebiotic
molecules such as simple sugars, have been observed in the gas
phase of early, protostellar cores. Their exact formation route and the
physical origin of their arrival to the gas phase are heavily debated. It
is not known if the observed COMs are linked to the warm disk atmosphere
of settled protoplanetary disks, or if they predominantly exist
in the gas phase in the warmest, inner regions of protostellar cores,
before the emergence of a protoplanetary disk. These questions are
important, as the protostellar chemistry acts as a chemical precursor
for the composition of the material that ends up in planet formation,
and may explain the rich chemistry we see in our own Solar System.
Using high angular resolution observations with the Atacama
Large Millimeter/submillimeter Array (ALMA), together with complex
3D radiative transfer codes, we can investigate the innermost
environment of young protostars, and hopefully answer some of the
questions stated above.
In this thesis I present research focusing on the two low-mass protostellar
cores, IRAS 16293-2422 and L483, in terms of their dust and
gas density, temperature structures, and chemistries. Two of the three
research papers presented in this thesis concentrate on IRAS 16293-
2422, with one focusing on the 3D modeling of the envelope, the bridge
of dust and gas conjoining the two protostars, and the disk-like
emission around each protostar, as well as their individual luminosities.
A 3D dust density model is presented, which morphologically
matches the 868 μm continuum emission and explains the observed
C17O emission through a jump abundance model. This model emulates
freeze-out of molecules upon the dust grains, when the temperature
drops beneath the sublimation temperature of CO on the dust
ice-mantles. The individual luminosities of the deeply embedded protostars
in IRAS 16293-2422 are found to be LA >18 L! and LB 63 L!,
for radiation source A and B, respectively, which presents the first estimation
of the individual luminosities.
The second research paper on IRAS 16293-2422 focuses on the outflows
and the kinematics of the observed gas line emission from the
different molecules in the gas phase, and their relation to the bridge
of dust and gas. Molecular gas line emission of CO, H2CO, HCN, CS,
SiO and C2H reveal that only the dust continuum and C17O emission
have a physical origin in the bridge of dust and gas, while all
other molecular transitions are found to be related to the outflows
emanating from radiation source A. The lack of outflow activity from
radiation source B leads us to conclude that it is likely on a lower
evolutionary stage than radiation source A.
The last research paper describes ⇠ 0.100 observations of L483 with
ALMA, which reveal that the COMs observed towards L483 reside in
the innermost hot region of the envelope, within 40–60 au of the central
protostar, and arise from thermal sublimation of the icy mantle
around the dust grains. By analyzing the kinematics of the H13CN
J = 4–3 and CS J =7–6 gas line emission, the presence of a Keplerian
disk is excluded down to at least a 15 au radius. This means that
the observed COMs cannot come from an abrupt transition region between
the collapsing envelope and a Keplerian disk, as hypothesized
by an earlier research team, or from a warm disk atmosphere. Within
15 au, a small Kepler disk could hypothetically reside.
Suggestions are made for future research projects targeting IRAS
16293-2422 and L483, to further constrain the spatial distribution of
COMs (which constrains their formation routes), and the timeline for
the emergence of protoplanetary disks.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011893295&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - 3D Radiative Transfer Modeling of Embedded Protostellar Regions
PB - The Niels Bohr Institute, Faculty of Science, University of Copenhagen
ER -