PhD Project Kinematics of Young Stellar Clusters

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13 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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PhD Project

Kinematics of Young Stellar Clusters



Supervision & Contact



Dr. Estelle Moraux (
emorauxobs.ujf
-
grenoble.fr
)
, IPAG, Grenoble



Dr. Luis Manuel Sarro Baro (
lsbdia.uned.es
)
, UNED, Madrid



Dr Hervé Bouy (
hbouycab.inta
-
csic.es
)
, ESAC, Madrid

Scientific Context

It is a key
goal of modern astronomy to discover how planets and stellar populations
form and evolve. Studies of embedded clusters reveal that the vast majority of stars are
born in clusters with N

100 members while a minority form in smaller associations
(Porras et
al. 2003, Allen et al. 2007). However, only about 10% of star
-
forming regions
are destined to become bound, long
-
lived open clusters. For the remaining 90%, the
birth aggregates dissolve rapidly and the stars orbit freely in the host galaxy. Thus, to
under
stand the general rules that govern how the majority of stars form, as well as the
properties of stars that populate the Milky Way, it is crucial to decode fully the
formation and early evolution of young stellar clusters.

Spectacular advances have been m
ade in recent years in the field of
stellar cluster formation. New statistical theories of star and planet
formation have replaced the standard Shu (1987) model of isolated
star formation and offer a much more dynamic view of prompt
multiple fragmentation
driven by MHD supersonic turbulence in
molecular clouds (see Fig. 1, and e.g. Bate et al. 2003; Li et al. 2004;
Jappsen et al. 2005). Smooth particle hydrodynamics (SPH)
calculations are now able to simulate the collapse and fragmentation
of large turbulen
t molecular clouds forming several hundreds
of
stars (e.g. Bate 2009
).

However, the outcome of these simulations depend crucially on the
physical parameters of the parent molecular cloud (density,
turbulence), and i
f radiative feedback (Bate 2009
) and mag
netic field
(Hennebelle & Teyssier 2008) are taken into account. In particular,
important open issues remain:



What determines the distribution of stellar masses in
cluster?



Is there a universal mass function of stars and brown dwarfs
in all clusters?



How
does the cluster environment affect the e
volution of
the statistical
properties of young stars (e.g. disks, multiplicity,

etc.)?



Is the spatial mass
-
segregation built
-
in at birth or does it derive

from dynamical
evolution?

Fig. 1
: MHD simulation of star cluster
formation. From Bate et al., 2009.



Objectives of the PhD project

In order to address the above
questions and constrain the star formation theories, quantitative statistical
analyses of fully characterized populations of young stars are required, extending from the highest mass
objects all the way down to brown dwarfs.
Since we do not have laboratories to test the star formation
simulations and the theories behind, we have to rely on very well designed observations,
e
specially in young
stellar associations and clusters. A number of observational
quantities, which are di
rect products of the star formation
processes, can be used to
understand them.
They include:



the initial mass function (IMF, see Fig. 2)



the spatial structure of stellar clusters



the stellar and substellar velocity dispersions



the multiplicity properties o
f stars and brown dwarfs
(binaries, triple systems, ...)


This is the main aim of this research project.
We propose to
use proper motion studies to identify and characterize the
population of star forming regions and young (50 Myr) open
clusters.
Indeed,
a number of young nearby regions have mean
transverse motions of a few tens of milli
-
arcsec per year (mas/yr)
making it possible to measure their members’ motion.


The datasets and databases required for the PhD candidate are already available, ensuring
that s/he can
immediately start and successfully complete the thesis project.


The DANCe survey

Our group has been leading the
DANCe project
, an ambitious ground based survey
aiming
at measuring accurate astrometry (proper motions) and photometry from the
ground. Taking advantage of the deep wide field surveys performed in the early
2000, our group has obtained 2nd epoch observations and developed new tools to
measure proper motions
with an accuracy better than 0.5mas/yr over large
(100deg
2
) areas and to unprecedented depth (i23mag).

The DANCe survey unique sensitivity and accuracy allows, for the first time, a complete analysis of the
properties of young nearby associations. The
PhD candidate will immediately start working with the
DANCe catalogues and database.


The Gaia space mission

End of 2013, the European Space Agency will launch
Gaia
, a space mis
sion aimed at
deriving a complete census of the galaxy. Gaia will measure the position, velocities
and photometry for a billion stars with an unprecedented accuracy. Gaia will
revolutionize our view and understanding of the Galaxy, and as such, will be one
of
the most important scientific
projects
of the next decade. The proposed PhD
project is offered
with Gaia data analysis in mind, especially as 2
of the supervisors
are already involved in the preparati
on of
the
Gaia
mission.
Th
e tools developed
initially for
the DANCe database shall be extended and applied to the Gaia catalogue, once it becomes
av
ailable (first release in 2016, final release in 2020). The Gaia mission ensures that the PhD candidate will
start on a very promising field of astrophysics with excellent and ex
c
iting career perspectives.

Fig. 2:
Mass function of Taurus, IC348
and Cha I



Timeline

The PhD thesis will consist in 4 phas
es:


1.

Bibliographic exploration
of the scientific context, state of the art, learning of advanced statistical
techniques: probabilistic Bayesian inference, hierarchical models, stochastic sampling techniques and
their advantages for various problems, etc.


[2 months].

2.

Coding in R or python
of a general parallel framework for Bayesian inference of cluster probability
distributions: initial mass functions, star formation histories, kinematic properties, binarity (with the
help of existing code). The Bayesi
an hierarchical models must incorporate survey dependent models
of the observational biases (selection effects, reddening, obscuration...) and should be flexible enough
to be easily adapted to the future Gaia data. Publication of the results in the new jou
rnal Astronomy
and Computi
ng.


[8
-
10 months]

3.

Analysis of 2
-
3 clusters
of increasing complexity (start with an open cluster without gas and then add
reddening, and other biases). Scientific interpretation and discussion of results: derive the IMF; look
for wide binaries; study the
cluster internal dynamics; look for kinematic substructures that may be
associated with spatial location or age;
do the follow
-
up of interesting objects (accretors, objects with
ci
rcumstellar disk, binaries...).


[8
-
10 months for each cluster including p
ublication of results in astronomical journals]

3.

R
edaction of the thesis manuscript
.


[6 months]


Supervision and organization of the PhD

The PhD thesis will be done under the supervision of E. Moraux at the Institute of Planetology and
Astrophysics of
Grenoble (
http://ipag.osug.fr
), University of Grenoble within the stellar formation group
("FOST", the largest of the lab) and in the framework of the ANR project "DESC" (Dynamical Evolution of
Stellar Clusters;
http://ipag.osug.fr/emoraux/DESC/
).

The work will be done in close collaboration with H. Bouy (Center of Astrobiology, ESAC, Madrid) and L.M.
Sarro Baro (Centre on Intelligent Decision
-
Support Systems, UNED, M
adrid), especially for understanding
proper motion data and for the training on advanced statistical techniques.


Funding

Although the lab
s support
the PhD project, the interested student will have to apply for funding at the
Physics Doctoral School of G
renoble (
http://www.grenoble
-
univ.fr/edphys
) in June 2013 (results early July).

The main criterion for the selection process is the academic level of the candidate.

Note that other funding applications to other
institutions including Spanish ones (UNED, Spanish ministry,
etc) will also be investigated.


Joint PhD France / Spain

A cotutelle (joint
-
PhD) between Grenoble and Madrid may be organized. In that case, the student would
spend 1 year
i
n Madrid, and 2 year
s in Grenoble.