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PH700 Projects
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.
The formation of massive stars in the present day and in the primordial Universe:
observation and theory. Using an IDL code to calculate evolutionary paths of massive
stars as they form. Concentrating on aspects such as relationship to cluster formation,
outflow, accretion rate.
PROJECT
The formation of high mass stars remains a key unsolved problem in the field of
astrophysics. The widely accepted paradigm for the formation of solar-type stars via
spherical or disc accretion predicts an evolution from cores to protostars, and finally
pre-main sequence stars. The peak of the Spectral Energy Distribution shifts from
wavelengths longward of 100 microns for Class 0 objects toward shorter wavelengths
as the Young Stellar Object (YSO) emerges from an obscuring cloud approaches the
Main Sequence.
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 characteristic
distances, exceeding one kiloparsec.
Young massive stars create Ultracompact (UC) H II regions which have radii less
than 0.1 pc and high radio surface brightness. Recent radio continuum observations
have suggested that H II regions can contract, change in shape, or expand
anisotropically over intervals of as little as ~10 yr. If the regions were to expand at the
sound speed of ionized gas, ci ~ 10 km s–1, they would have lifetimes of roughly 104 yr.
However, surveys find numbers in our Galaxy consistent with over 10% of OB stars
being surrounded by them or equivalently, lifetimes of ~105 yr if this model is correct.
Extracted from:
http://adsabs.harvard.edu/cgi-bin/bib_query?2010ApJ...719..831P
These PH700 projects will be directed at one or more of the projects A to H below
under some things to do now
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.
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YOU WILL NEED IDL software. This runs on all platforms, OS,
You will need to make an appointment with Dr Mark Price to get the software installed
on your laptop. That is easiest since you can then work on the code anywhere..
email: mcp2@star.kent.ac.uk
Alternatively you can gain a UNIX account for the PCs in SPS106 and work in there
when it is open. Again, you will need to request an account on these PCs through Dr
Price. He will probably not do this until after you have completed the Health & safety in
Week 1. I have a UNIX primer if you request it to learn the basic UNIX commands.
Machines should run IDL.
The project will be based on an aspect of:
How do stars more massive than the Sun form?
Or:
How do stars like the Sun form?
Watch talks by Testi, testi.mp4 in:
http://astro.kent.ac.uk/mds/Modules/1314/
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?
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
Stage 1
Review Subject: literature from journals.
Use ADS system to perform literature review.
http://adsabs.harvard.edu/abstract_service.html
Anything else referred to below is contained in:
http://astro.kent.ac.uk/mds/Modules/1415/PH700/
Read Emily Tipper’s and Tom Brown’s Intro from 2011-12 and 12-13. Note that you
must build on this and will not be allowed to copy anything from these. These
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demonstrate the standard required.
PH700-2012-Tipper.pdf
PH700-brown.pdf
What is a massive star ?
Why are massive stars important?
Here is a very good review:
http:// .harvard.edu/abs/2007ARA%26A..45..481Z
How do we observe them and their effects?
Read:
http://adsabs.harvard.edu/abs/2014MNRAS.443.1555U
How do they form?
What models are there for massive star formation?
What are the issues that still need resolving?
Stage 2: Understand the Model
Read
http://adsabs.harvard.edu/abs/2000IrAJ...27...25S
We will 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. This needs to be done sometime.
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!
The Latest version of the Code is explained here:
http://adsabs.harvard.edu/abs/2014MNRAS.438.1051S
Evolutionary tracks of massive stars during formation
A model for massive stars is constructed by piecing together evolutionary algorithms
for the protostellar structure, the environment, the inflow and the radiation feedback.
The framework requires the accretion rate from the clump to be specified. We
investigate constant, decelerating and accelerating accretion rate scenarios and
consider both hot and cold accretion, identified with spherical free-fall and disk accretion, respectively. We find that accelerated accretion is not favoured on the basis of
the often-used diagnostic diagram which correlates the bolometric luminosity and
clump mass. Instead, source counts as a function of the bolometric temperature can
distinguish the accretion mode. Specifically, accelerated accretion yields a relatively
high number of low-temperature ob jects. On this basis, we demonstrate that
evolutionary tracks to fit Herschel Space Telescope data require the generated stars to
be three to four times less massive than in previous interpretations. We also find that
neither spherical nor disk accretion can explain the high radio luminosities of many
protostars. Nevertheless, we discover a solution in which the extreme ultraviolet flux
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needed to explain the radio emission is produced if the accretion flow is via free-fall on
to hot spots covering less than 20% of the surface area. Moreover, the protostar must
be compact, and so has formed through cold accretion. This suggest that massive
stars form via gas accretion through disks which, in the phase before the star bloats,
download their mass via magnetic flux tubes on to the protostar.
Questions for you:
What does the Unification Scheme / Capsule Model 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.
Some of the latest data to be modeled is here:
http://adsabs.harvard.edu/abs/2014arXiv1406.5078U
Stage 3: Understand the Code
What is IDL and how does it work?
Look at files in:
http://astro.kent.ac.uk/mds/Modules/1415/PH700/idl/
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
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Find wherever you put intro.pro and click on that. it appears in the main grey area,
where it can be edited.
This IDL file 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.
**************************************************
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. Take a look at
how the programme is constructed.
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.
Question: What is The Unification Code – what algorithms are used? How is it put
together? See caps-smith131029.pptx
MAKING IDL DO THE WORK FOR YOU
This is important to make things work properly – be precise.
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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 two .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 idl-notes.pdf for the full instructions....it all worked on my toshiba.
++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++
Final Code Stage: set up the working code
My set up:
C:\Documents and Settings\Michael\My Documents\Capsule
contains
Code
and
setup.pro
This new setup.pro has two added lines which make the figures appear in reverse
video – black lines.
Then,
Capsule contains
caps.pro
When run this displays to screen and saves a jpeg file (at the end, it dumps the
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window to the d****.jpg)
- all set up already.
caps.pro (old version was : massive.pro) chooses accretion rate and time from
Data/inputA-accB.d
Data/inputA-accB.l …are chosen if ilowmass=1 is set at top ocf caps.pro
where A=1,2,3,4 track parameters eg maximum accretion rate
and B = accretion type eg power-law, constant accretion,….the time function
The Model is determined by:
iaccmodel0 (= 1 for power law etc….)
What it decides to do is now controlled directly from the main programme: caps.pro
where you can read the full list.
Ilnumber = 4
This yields 4 tracks ( lines ) for accretion rates/parameters shown on the screen as it
runs.
Try it. See where d*******.jpg turns up.
Reminder – to try start the IDL application
( hopefully it is set to automatically run the new setup.pro)
Open: caps.pro
Run caps.pro ( compiles caps)
Type caps in the lower command line.
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++++++++++++++++++++++++++++++++++++++++++++
Final Stage: Research –
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 – as set up
with iflag=12 ….see what the different iflag settings do
4. Include periodic outbursts, each 1000 years, have a 100 year outburst in which
most of the accretion occurs. This will need outburst = 'sine' to be set
5. Determine number of objects in each Class. Class 0 spectral energy distributions
(SEDs) are typically well characterized by single temperature blackbodies with
15 ≤Td≤ 30 K and where Td is the dust temperature (or Tbol in our model). For
further distinction, bolometric temperature is also used to characterize
evolutionary class, where Tbol < 70 K for Class 0 objects and 70 < Tbol < 650 K
for Class I (Chen et al. 1995).
Some Things to do now:
A Outflows:
1. Jet Velocity – as a function of stellar mass? Chi=1 set in massiv.pro
…plot22.pro…done 100 to 1000 km/s
2. Jet section is in environment.pro
Outflow age is short, 10^4 years for jet?
3. Jet power – momentum – H2 luminosity
4. Maser outflows?
5. Do outflow and radio/EUV phases overlap? Yes if accretion/jet generates the hot
spots/EUV.
6. Thermal radio jets – see below
B Most massive? VMS ? Properties? Very high accretion rates perhaps could have
giant swollen phase as in Kuiper & Yorke 2013. Does this destroy the disc? Eddington
limit? See Section 4 of HYO, The Astrophysical Journal, 721:478–492, 2010
LIMIT ON MASS INFLOW & Eddington Limit
Most massive? VMS ? Properties? Very high accretion rates perhaps could have giant
swollen phase as in Kuiper & Yorke 2013. Does this destroy the disc? Eddington limit?
See Section 4 of HYO, The Astrophysical Journal, 721:478–492, 2010
Interesting is that spherical accretion must fight against the full energy released
from star and gravity from free-fall accretion- release. But Hosokawa et al 2010 use
only the stars energy for cold accretion, assuming that energy released from accretion
disc leaks out.....in effect the radiation pressure would blow out the outermost layer of
the star if the accretion rate is too high. But this depends on accretion type? We can
test.
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C Low mass stars – redo IrishApJ paper with new code, reconsider the statistics for
Tbol
D Clump formation. Note that Mclump is rather arbitrary – depends mainly on one
parameter – how long the clump survives, assumed to dissipate linearly in time.
Why?We take an already formed clump. But cannot happen like that. Formation time
is 0.5pc/3 km/s perhaps or 200,000 years – longer than formation period of massive
star!
Take Mclump = (1 – exp(-t/to) ) ( 1 – t/t1 ) Mo
To = 10^5 yr, t1 = 10^6 year ??
131116: added to code uner option: ifixclump = 3
See line 250 of envelope.pro
mcor(*) = (10.^logmcluster - mstarfinal) *exp(-10.*t(*))
Set iflag = 72 to see Lbol/Mclump diagram – see elia et al 2010
E Clump mass appears as dense filaments (perhaps) rather than smooth spherical
distribution. Mclump measures all the mass (dust emission) whereas the Tbol depends
on radiation escaping through the lower bdenity inter-filamentary medium, so can be
higher. So perhaps we should use Lbol/Mclump as evolutionary measure rather than
Tbol.
F Binarity – most OB stars are in binaries. Either they attract companions, or the disk
is so massive that it fragments. So: investigaye disk: when does disk become selfgravitating and what mass would grow? Planets could also form from core-accretion in
inner disk?
G radio continuum observations of young stellar objects with known outflows
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2012.20935.x/full
Low-mass radio from jets: no EUV. ‘thermal radio jets’
We present 16 GHz (1.9 cm) deep radio continuum observations made with the
Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets.
80 per cent of the objects in this sample have spectral indices consistent with free–free
emission. Strong correlation with envelope mass – WHY?
Class 0 spectral energy distributions (SEDs) are typically well characterized by single
temperature blackbodies with 15 ≤Td≤ 30 K and where Td is the dust temperature (or
Tbol in our model). For further distinction, bolometric temperature is also used to
characterize evolutionary class, where Tbol < 70 K for Class 0 objects and 70 < Tbol <
650 K for Class I (Chen et al. 1995).
H Do massive stars rotate fast or at break-up?
http://iopscience.iop.org/0004-637X/753/1/51/fulltext/
J The student will (1) investigate the observations of the radio emission and the
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growing luminosity of the massive star, (2) build a code to predict the radio emission as
the massive star evolves, (3) determine the observable properties of the first stars to
form in the Universe (primordial star formation).
The observational project will look at published data for sizes and luminosities, and
consider how to modify standard theory of H II regions to accommodate the data. The
second project will involve an IDL code reconstructed to account for variable accretion
rates on to the massive star. The third project will investigate cosmological star
formation, largely reviewing recent changes and discussing how this may influence our
future approach.
APPENDIX A: Talks from PP6
Watch talks here:
http://www.mpia-hd.mpg.de/homes/ppvi/prognew.php
Most massive star links
http://adsabs.harvard.edu/abstract_service.html
http://adsabs.harvard.edu/abs/2010ApJ...722.1556K
http://adsabs.harvard.edu/abs/2013ApJ...772...61K
http://www.mpia-hd.mpg.de/homes/ppvi/talks/
http://www.mpia-hd.mpg.de/homes/ppvi/prognew.php
ALMA Press Release:
http://www.eso.org/public/news/eso1331/
Mergers:
http://adsabs.harvard.edu/abs/2012MNRAS.425.2778M
300 solar mass stars??? See…..
http://arxiv.org/abs/1302.2021
Paper 1:
http://arxiv.org/abs/1311.3352
APPENDIX B LOW-MASS CODE ………
LOW MASS STARS
The aim of this project is to investigate how low mass stars like our Sun and brown
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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.
Low mass: need the power-law accretion Model 1 only.
Control with m_o and alpha
Try hot and cold to see if there is a difference.
Set up acc1: power law with alpha = 1.75
Input1 to input5: 1, 4, 2, 0.5, and 0.25 solar masses
tostar = 3 x 10^4 years
Set up acc6: constant with alpha = 1.75
Input1 to input5: 1, 4, 2, 0.5, and 0.25 solar masses
tostar = 10^5 years
So how does the CLUMP lose its mass? Synchronised with star gain?
In envelope.pro:
if ifixclump eq 4 then begin ; mass loss at constant rate from surrounding clump
;;;;;;; menvi is total envelope mass menv(i) is env mass at
;;;;;;; timestep i
mextra = 3.0
mclump = mextra*mstarfinal ;; total gas mass including envelope/core
mcordot = mclump - menvi)/to ; constant massloss rate from clump
mcor(*) = menv(*) + mcordot*(to - to*t(*))
endif
if ifixclump eq 5 then begin ; clump mass proportional to envelope mass
;;;;;;; menvi is total envelope mass menv(i) is env mass at
;;;;;;; timestep i
mextra = 3.0
mclump = mextra*mstarfinal ;; total gas mass including envelope/core
mcor(*) = mclump*menv(*)/menvi
endif
HOW TO FIX?
Dunham et al 2013 PP6: http://arxiv.org/pdf/1401.1809.pdf
Class 0+1 lifetime is 480,000 years if Class II is 2 Myr
Class 0 is 150,000 yr
You will revisit the low-mass and brown dwarf formation scenario, add new
observational data sets and update the theory. Previously ISO data were compared to
the model:
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!
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There are many subsequent issues and problems:
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 one-dimensional 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 color-magnitude 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 Low-Mass, 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, two-dimensional 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.
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