PH600
Radio galaxies project notes
Professor Michael Smith
1
Preparing for H2EX
The molecule which is by far the most abundant in our Universe is the hydrogen molecule. It is
the simplest molecule although still very complicated to understand how it influences the
structures we observe between the stars. This is partly because it is so difficult to observe: being
lightweight and symmetric, it takes considerable energy to get the molecule excited.
The Molecular Hydrogen Explorer is a low-to-medium cost satellite being planned by a worldwide consortium of astronomers interested in tracking H2. We hope to finally directly
determine many its astronomical properties. The purpose of this project is to provide a critical
review of the properties of H2 and how best to observe H2 in astrophysical phenomena. This
will first involve a literature review to come to terms with past attempts to observe it and what
those attempts tell us. Data will then be provided to be analysed with data reduction
proceeding with the AIPS software package. Images of H2 emission within regions of star
formation will then be discussed. The relation of the H2EX mission to these data or other
observing campaigns will be explored
Learning outcomes: ability to conduct a literature review; understanding of the physical
processes surrounding the molecule and astrophysical chemistry; involvement in the planning
of the science case for a (as yet unfunded) future space mission. Practical data reduction of
infrared data.
Objectives:
To understand the nature of the hydrogen molecule (how it forms, how it is
destroyed) and how we can observe it in space.
To analyse some infrared data of star formation regions and explain the origin of
the emission.
To identify the current major issues/debates in this field. To suggest solutions. To
determine the future prospects for progress in this field, especially whether H2EX
will make a coist effective contribution.
Method:
Scientific research procedures. Study some famous objects which emit H2 line
emission by acquiring their fits files from Virtual Observatories and applying
image processing techniques.
Review. Read a few journal papers and introductions to papers to build up a view
of the latest knowledge/issues.
Deepen knowledge on a specific theme through further detailed reading and use
own data to illustrate effects.
Analysis/Quantify: evaluate data .... not your own ..... producing a
histogram/graph using data from a journal paper or papers.
Training:
1 How to use Virtual Observatories: Aladin etc
PH600
Radio galaxies project notes
Professor Michael Smith
2
Skyview
SkyView is a Virtual Observatory on the Net generating images of any part of the sky at
wavelengths in all regimes from Radio to Gamma-Ray.
http://skyview.gsfc.nasa.gov/
Aladin
Aladin An interactive software sky atlas allowing the user to visualize digitized images
of any part of the sky, to superimpose entries from astronomical catalogs
http://aladin.u-strasbg.fr/aladin.gml
Multiwavelength archive/resource list
http://astro.kent.ac.uk/mds/multiwavelength
Handbook of Astronomical Image Processing (HAIP)(AIP4WIN)
Astronomical Image Processing Software (AIP4Win2.0)
www.willbell.com/aip/index.htm
2. How to use the ADS
http://adsabs.harvard.edu/abstract_service.html
3. Abstracts/reviews
This is not an easy subject to review! There are a couple of reviews…
Field 1966
Shull and Beckwith 1978
…since then…not much, so it needs synthesizing.
4. We observe H2 directly in several ways:
After excitation in collisions, it may radiate as the vibe-rotational energy
level falls back down.
After excitation by far ultraviolet, into an ‘electronicically excited state
(a continuum) , it cacades back down and through vibe/rote levels,
radiating.
After formation in an (electronically) excited state, it cascades down.
As foreground gas to a hot star, UV absorbtion lines can be detected as
the cold H2 gas absorbs photons, re-radiaitng it isotropically in various
lines.
PH600
Radio galaxies project notes
Professor Michael Smith
3
We infer H2 indirectly, by detecting CO or other molecules which radiate
at around 10K, and assume CO/H2 abundance ratio of around 0.0001.
The trouble is H2 has no dipole moment (it is a symmetric molecule), so
it doesn’t radiate like CO when cold. We observe it only when really
excited or strongly heated: rotationally (few hundred K needed) or
vibrationally (1000K needed at least).
5. What do we observe?
Very bright regions – hot and dense – conditions for collisional
excitation (e.g. shock waves).
Extended diffuse patches/ cloud edges near bright UV sources.
6. Can we illustrate these regions?
Take rho Oph?
Orion OMC-1? What can we show with image manipulation?
Optical: Orion Nebula
2MASS: K and J bands: subtract/divide to show features? Orion Bar:
PDR (UV). OMC-1 shock. Use JHK RGB color image. Will shocks
appear as different colour to UV-excited region?
Rho Ophiuchus. Use HH313 to find the 2mass images. …similoat
structures to orion.
Young Stars Swim in Pools of Molecular
Hydrogen
http://www.gemini.edu/index.php?option=content&task=view&id=235
Wednesday, 27 June 2007
Figure 1: The spectrum of ECHA J0843.3-7905 divided by that of RECX12 with the fit to the
H2 1-0 S(1) line and residuals in the lower panel.
During a search for hydrogen emission in the disks of young stars, Suzanne
K. Ramsay Howat (UK Astronomy Technology Centre) and Jane S.
Greaves (University of St. Andrews) have discovered a massive layer of
hot gas around a low-mass M3-type star in the 6 million-year-old Eta
Chamaeleontis cluster. Both the strength and the kinematics of the
emission imply that it arises from a disk illuminated by ultraviolet
PH600
Radio galaxies project notes
Professor Michael Smith
4
radiation produced by the central star.
Studying the gas content of protoplanetary disks around young stars is an
important step in understanding the formation of planetary systems.
Molecular hydrogen is one of the main constituents of the atmospheres of
giant planets and so must be present in the disks for Jupiter-like planets to
form. Moreover, the near-infrared emission from it is one of the best
indicators of warm gas that may exist in gaps carved by massive new
protoplanets. This emission may arise from excitation of gas molecules by
a passing shock wave, or by the absorption of ultraviolet radiation (or xrays) from the stars at the center of the disks.
Molecular hydrogen emission was detected from only one of the seven
sources observed by Ramsay Howat and Greaves. The researchers used
PHOENIX, the high-resolution infrared spectrograph on the Gemini South
Telescope at Cerro Pachón, Chile to make the observations. This
instrument was built by a National Optical Astronomy Observatory
(NOAO) team led by Ken Hinkle and is on loan to Gemini from NOAO.
Detecting molecular hydrogen emission associated with disks has proven
challenging, even with 8- to 10-meter class telescopes and advanced
instruments. In fact, this measurement by Ramsay Howat and Greaves is
one of very few published detections of this type of emission. Another
definite detection was recently made around the star AB Aurigae by a team
led by Marty Bitner using the very high-resolution mid-infrared
spectrograph TEXES on Gemini North.
The mass of hot molecular gas inferred around this source, named ECHA
J0843.4-7905, is about 0.03 solar mass. This is similar to the mass of the
minimum solar nebula. From the shape and width of the line profile
(Figure 1) the authors conclude that this circumstellar gas is orbiting at 2
AU (astronomical units) from the star. Since the system is ~6 million years
old, these results indicate that a significant gas reservoir persists to the age
when gas giant planets are presumed to form. Current theories show that
Jupiter-like object should form in the first ~2 million years of a disk’s life
with the thick atmosphere accreted onto the planet in around 5million
years.
More details can be found in the article “Molecular Hydrogen Emission
from Disks in the Eta Chamaeleontis Cluster”, by S. K. Ramsay Howat and
J. S. Greaves, The Monthly Notices of the Royal Astronomical Society,
2007 in press.
PH600
Radio galaxies project notes
Professor Michael Smith
panel.
Figure 1: The spectrum of ECHA J0843.3-7905 divided by that of RECX12 with the fit to the
H2 1-0 S(1) line and residuals in the lower
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