Download ph600-12 - University of Kent

PH700 Project
Prof Michael D. Smith
Centre for Astrophysics & Planetary Science
University of Kent
Towards a resolution of a burning issue in Astrophysics, from the fields of solar
system, galactic or extragalactic astronomy.
Recent problems between observational data and theory provide a rich source
of issues to be investigated. This project will focus on a specific phenomenom
of high interest and motivation, in one of extragalactic astronomy, galactic
astronomy, or solar system astronomy. The study will begin with a review of
recent publications which address the issue and an evaluation of possible
solutions. To achieve this, all major physical processes involved will be
understood in depth and detail. Then, data will be obtained from an appropriate
source and analysed in order to generate, in an original way, fresh evidence for
or against the available solutions. The study will then consider new or hybrid
solutions before considering how these can be tested. The relevance of new
ground-based telescopes or space missions will be discussed.
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The aim of this PH600 project is to investigate how low mass stars like our Sun and
brown dwarves are formed. Models for the formation of such stars through infall from a
molecular core into an envelope and then via a spinning accretion disc on to the
protosatr can be tested by comparing predictions to a range of observational parameters.
These include the bolometric and extreme ultraviolet luminosities, the core, envelope
and disc mass, and the jet and outflow momentum and energy. If there is a gradual
evolution, these parameters should undergo coordinated changes. Or, if there are short
superimposed outbursts, the effects on the statistics should be apparent.
The specific method is to further develop a code written in the IDL language (similar to
matlab) to determine possible evolutionary tracks on assuming the variation with time of
the accretion rate from the clump on to the star and calculating how the star, envelope
and outflow evolve. This is achieved by making analytical prescriptions for the
components based on current knowledge.
Learning Outcomes:
Experience in computational physics.
Experience in undertaking a literature review
Detailed knowledge of an area of astrophysics
Experience in obtaining new data, data analysis and presenting data
Experience in communicating findings through a written report
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The project will be based on an aspect of:
How do stars like the Sun form?
Watch talks by Testi, Garay, and try others:
http://www.eso.org/sci/meetings/2012/ESOat50/program.html
From a cloud, into a clump, into a core where angular momentum holds it up - it forms the
spinning disc from which material slowly accretes on to the star.
How is the angular momentum extracted? through jets?
Diverted into planets? Or diffused out through the accretion disc?
As our starting point, we could take:
http://adsabs.harvard.edu/abs/2000IrAJ...27...25S
and update or reconstruct using IDL which is very similar to matlab.
I am doing the case of massive stars at this moment. You could revisit the low-mass brown
dwarf formation scenario, add new observational data sets and update the theory.
http://adsabs.harvard.edu/abs/2006MNRAS.368..435F
There is plenty in those papers so dont worry if you get lost - we have a habit of not explaining
things properly except to the initiated!
http://adsabs.harvard.edu/abs/2011AAS...21734035B
http://adsabs.harvard.edu/abs/2005ApJ...627..293Y
Evolutionary Signatures in the Formation of Low-Mass Protostars
Authors:
Young, Chadwick H.; Evans, Neal J., II
We present an evolutionary picture of a forming star. We assume
a singular isothermal sphere as the initial state of the core
that undergoes collapse, as described by Shu. We include the
evolution of a first hydrostatic core at early times and allow a
disk to grow, as predicted by Adams & Shu. We use a onedimensional radiative transfer code to calculate the spectral
energy distribution for the evolving protostar from the
beginning of collapse to the point when all envelope material
has accreted onto the star + disk system. Then, we calculate
various observational signatures (Tbol, Lbol/Lsmm, and infrared
colors) as a function of time. As defined by the bolometric
temperature criterion, the Class 0 stage should be very short,
while the Class I stage persists for much of the protostar's
early life. We present physical distinctions among the classes
of forming stars and calculate the observational signatures for
these classes. Finally, we present models of infrared colormagnitude diagrams, as observed by the Spitzer Space Telescope,
that should be strong discriminators in determining the stage of
evolution for a protostar.
http://adsabs.harvard.edu/abs/2010ApJ...710..470D
Evolutionary Models of the Formation of Protostars out of LowMass, Dense Cores: Towards Reconciling Models and Observations
Authors:
Dunham, M. M.; Evans, N. J., II; Terebey, S.; Dullemond, C. P.;
Young, C. H.
A long-standing problem in low-mass star formation is the
“luminosity problem,” whereby protostars are underluminous
compared to the expected accretion luminosity. Motivated by this
problem, we present a set of evolutionary models describing the
collapse of low-mass, dense cores into protostars, using the
evolutionary models describing the collapse of low-mass, dense
cores into protostars, using the Young & Evans (2005)
evolutionary models as our starting point. We calculate the
radiative transfer, spectral energy distributions, and
observational signatures of the collapsing cores to directly
compare to observations. We incorporate several additions to the
Young & Evans (2005) model in an effort to better match
observations, including: (1) the opacity from scattering, (2) a
circumstellar disk directly in the 2-D radiative transfer, (3) a
two-dimensional, rotationally flattened envelope, (4) mass-loss
and the opening of outflow cavities, and (5) a simple treatment
of episodic mass accretion. We find that scattering, twodimensional geometry, mass-loss, and outflow cavities all affect
the model predictions, as expected, but none resolve the
luminosity problem. On the other hand, a cycle of episodic mass
accretion similar to that predicted by recent theoretical work
can resolve this problem and bring the model predictions into
better agreement with observations.
http://adsabs.harvard.edu/abs/2012ApJ...747...52D
Resolving the Luminosity Problem in Low-mass
Star Formation
Authors:
Dunham, Michael M.; Vorobyov, Eduard I.
dddd
Resolving the Luminosity Problem in Low-mass
Star Formation
Authors:
Dunham, Michael M.; Vorobyov, Eduard I.
http://adsabs.harvard.edu/abs/2012ApJ...747.
..52D
Resolving the Luminosity Problem in Low-mass
Star Formation
Authors:
Dunham, Michael M.; Vorobyov, Eduard I.
.
Stage 1
Review Subject: literature from journals
Read Emily Tipper’s Intro to the Code. Note that you must build on this and will not be
allowed to copy anything from this.
What is a low mass star ?
Why are they important?
How do we observe them and their effects?
How do they form?
What models are there for star formation?
What are the issues that still need resolving?
Use ADS system to perform literature review.
http://adsabs.harvard.edu/abstract_service.html
Stage 2: Understand the Model
Read 2001ureview.pdf
http://adsabs.harvard.edu/abs/2000IrAJ...27...25S
massive120930.pdf
What does the Unification Scheme do?
What is it good for and what are its limitations?
Are there alternative schemes?
The widely accepted paradigm for the formation of solar-type stars via spherical
accretion (Shu et al. 1987) predicts an evolution from cores to protostars, and finally
pre-main sequence stars. The peak of the SED shifted from wavelengths longward of
100 m for Class 0 objects toward shorter wavelengths the more the YSO approaches
the Main Sequence (MS).
Establishing a similar scenario for high-mass YSOs is much more difficult due to the
clustered environments in which they are born and to the large ( kpc) characteristic
distances exceeding one kiloparsec.
Stage 3: Understand the Code
What is IDL and how does it work?
Quick Start:
IDL Introduction
What it is and why is it so good?
http://www.astro.virginia.edu/class/oconnell/astr511/IDLguide.html
All IDL programmes have the explicit extension '.pro'.
http://chaos.swarthmore.edu/courses/phys6_2004/IDL_Notes_P6.pdf
There are many other IDL guides on the internet. Find your favourite.
e.g. http://www.dfanning.com/
There is also the help associated with the installed programme.
What you need to know….quick confidence booster:
Save the programme
intro.pro
Click on your IDL icon to start IDL.
Go to the top bar and 'file' 'open...'
and open intro.pro
Find wherever you put intro.pro and click on that. it appears in the main grey area,
where it can be edited.
This is just a calculator, reading in useful constants and then calculated a density near
the end and giving print commands.
To run it:
Go to the top bar and choose Run, compile intro.pro
The answer comes in the middle window.
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Next level;
More complicated:
open intro-cosmo
run intro-cosmo
In the middle window appears the names of two modules: PARAMETERS and
COSMO
These are the two separate programmes contained in intro-cosmo.pro. In this case,
actually, running PARAMETERS will ask it to also run COSMO before finishing. You
can see that if you scan through it.
To run the programme, go to the command line right at the bottom ....the one-liner with
IDL>
Type just the one word:
parameters
Then you should see that it calculates, in the middle window, the complete set of
parameters for 3c465 ....this is my own tool for calculating the distance of a quasar or
galaxy from its redshift - you have to integrate from us to the object
to do it. There is a loop in the code over 30000 steps which does the integration - dont
worry about that - its the whole concept of programming contained here.
More help ideas:
http://vis.lbl.gov/NERSC/Software/idl/help/docs6.0/getstart.pdf
eg there are commands to write images into various formats…..lots to get familiar with.
What is The Unification Code – what algorithms are used? How is it put together? See
Ph700-2012-Tipper pdf.
MAKING IDL DO THE WORK FOR YOU
Make a directory in some tidy place where it can stay.
Put the attached setup.pro in it. Open it up in IDL and change the first line.to YOUR
directory.
Save it. Put the other *.pro files in the same directory
Having set up setup.pro ............
(2) START IDL
In IDL select Preferences under the File menu.
(3) Click STARTUP.
Click SELECT WORKING DIRECTORY and browse and select your working folder.
Click SELECT STARTUP FILE and browse and select the file
setup.pro
(4) Click PATHS
Click INSERT and browse and select your working folder
Click the box in the window next to the listing of your working folder (check mark
should appear)
(5) Click APPLY
Click SAVE
Click OK - if it asks.
(6) Restart IDL
Now it should automatically choose the directory
In the future setup.pro may contain anything you always use, loaded in at the start
automatically.
Neat...see attached idl-notes.pdf for the full instructions....it all worked on my toshiba.
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Final Code Stage: set up the working code
My set up:
C:\Documents and Settings\Michael\My Documents\Massiv
contains
Massive Code
and
setup.pro
This new setup.pro has two added lines which make the figures appear in reverse
video – black lines.
Then,
Massive contains
massiv.pro
This now displays to screen and saves a jpeg file (at the end, it dumps the window to
the d****.jpg) ( display to screen set by iprint=0 in input.d.
- all set up already.
THE REST BELOW IS WRONG AND NEEDS UPDATING …………..
massive.pro chooses accretion rate and time from Data/inputA-accB.d
where A=1,2,3,4 track parameters eg maximum accretion rate
and B = accretion type eg power-law, conastant accretion,….
What it decides to do is now controlled directly from the main programme: massiv.pro
This yields three lines for accretion rates 10^-3, 10^-4 and 10^-5 10^-5 Msun/year
For a 100 solar mass – final stellar mass.
Try it. See where diag.jpg turns up.
Reminder – to try start the IDL application
( hopefully it is set to automatically run the new setup.pro)
Open: massiv.pro
Run massiv.pro ( compiles unify)
Type unify in the lower command line.
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Final Stage: Research –
The Issue or Problem
1. Data: use the code to calculate tracks but concentrate on getting new sets of
data and reading them in.
2. Use data present but ask what if ………………..
3. . Do Luminosity – Clump mass analysis for different accretion types.
4. Include periodic outbursts, each 1000 years, have a 100 year outburst in which
most of the accretion occurs.
5. ……….