Using publicly available data from NASA of actual satellite observations of astronomical x-ray sources, we explore some of the mysteries of the cosmos, including neutron stars, black holes, quasars and supernovae. We will analyze energy spectra and time series data to understand how these incredible objects work. We utilize an imaging tool called DS9 to explore the amazing diversity of astronomical observations that have made x-ray astronomy one of the most active and exciting fields of scientific investigation in the past 50 years. Each week we will explore a different facet of x-ray astronomy. Beginning with an introduction to the nature of image formation, we then move on to examples of how our imaging program, DS9, can aid our understanding of real satellite data. You will using the actual data that scientists use when doing their work. Nothing is "canned". You will be able to appreciate the excitement that astronomers felt when they made their important discoveries concerning periodic binary x-ray sources, supernovae and their remnants, and extragalactic sources that have shaped our understanding of cosmology.
Lecture 6 Introduction to DS9--Part II
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From the course by Rutgers the State University of New Jersey
Analyzing the Universe
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From the lesson
Light and the Nature of Images....Plus, an Introduction to DS9
Welcome to Week 1 of "Analyzing the Universe!" This week we explore the nature of light, and how we get astronomical information from the images we obtain. The lectures and "wiki" material address these themes: light, image formation, and DS9. Dive right in!
Meet the Instructors
Dr. Terry A. MatilskyProfessor
Physics and Astronomy
[BLANK_AUDIO]
Okay, gang.
Well, now that you have DS9, you're going to want to see how to use it.
Next week, we will have an in-depth tutorial on all of the
things that DS9 can do. But, I thought it would be interesting for
you to finish out this week with just a general broad overview about the structure
of the software and some of the neat things that you can
actually do with it. So, let's go over to our screen and
see what DS9 is up to. We
open DS9 and usually the first thing that you're going to want
to do is go to this menu bar here.
And, under Analysis, you're going to scroll down and click on
the Virtual Observatory. This will bring up a window
that allows you to connect to the hundreds and hundreds of
observations that Chandra has made over the years.
ATTENTION! News Flash!
We interrupt this broadcast, to bring you a special bulletin.
DS9's Virtual Observatory needs to have a
parameter set in order to function properly.
It's easy and here's how to do it for both Mac and Windows systems.
If you have a Macintosh, this is what you do.
When you start DS9, you go to Analysis,
click on the Virtual Observatory, and before you check
Rutgers Primary MOOC X-ray Analysis Server, just make sure
that this radio button here that's says, Connect To
VO Servers through the remote Web Server, is initialized.
When you do that, DS9 will function properly.
If you don't want to
do that every single time you initialize DS9, every single
time you use it, you can change in your Preferences a parameter
that allows you to do it automatically and you don't have to worry about it anymore.
The way you do it is as follows.
You go to SAOImage DS9 ion your top menu bar and
click on Preferences. When you do that, you will see a dialogue
box, and one of the possibilities under Preferences is VO, Virtual Observatory.
Click on that.
When you click on that, you can then enable your connect using Web
Proxy radio button over here, and after you click right
there, you will then be able to Save it. That's
it. For a Windows machine, it's almost
identical. You go to Analysis.
Click on Virtual Observatory. Then you get your dialogue box, and before
you click on Rutgers Primary MOOC X-ray Analysis Server, make sure that you click
on this radio button that says, Connect Using Web
Proxy. If you don't want to do that every single
time you start DS9 for this course, you can change
the parameter in your Preferences so it will do that automatically.
The way you do that, is by going to Edit, Preferences.
And when you do that, and click on it, you will see a Preferences dialogue box.
And you can select the O for Virtual Observatory.
When you do that, you'll get another box and you just make sure that this little
radio button here that says, Connect Using Web Proxy, is enabled.
You Save it and
you're done. That's it.
And now, back to our regular programming.
First thing you're going to do, is connect to the Rutger's
Primary MOOC X-ray Analysis Server. Make sure that
you click on this radio button that says, Connect Using
Web Proxy. And when you do that, you
will get another screen that now lists all
of these Observations. Let me kind of
position things, so we can see everything usefully.
And, here is a listing of
hundreds and hundreds of Observations that have made
with the satellite, and in order to see what some of these things
look like, we're going to click on the first one, ACIS
Observation of CAS A. Now, you
see immediately, an image is loaded into
our viewing area. And we can,
for instance, change its color by selecting different color
schemes and doing all sorts of
interesting kinds of displays in that way.
Also, we can change something that's called the Scale.
I'm going to select the Square Root Scale, and we'll talk about that next week.
But, you can
see that this display now changes and
you can look at this particular object, which is a supernova
remnant, in its entirety. Notice as I cruise
around with my Pointer, lots of things are changing
in the informational area at near the top left of
your window. You see something called Alpha and Delta,
which is the position in the sky, and you also see the actual
pixel that is being looked at or pointed
to, and you can see that more clearly in a magnification
box that is at the upper right hand corner
of your main window. Also, what you'll see as we cruise
around, is the Value of the intensity at the particular
point that the arrow is looking at, and you
can see that value change as I go from one
place in the supernova remnant to another.
Now, it's hard to select a particular point
using the mouse. Things kind of jump around a little bit.
But, what you can do is, for instance, we can click
setting down a region here. We'll talk about regions
and that's going to be the area in the object
that you're actually going to examine the data for.
And if you click again, after clicking once, you can see that now
you have selected that region and there's four little
handles on the region that allow you to change your
position, that region, wherever you want, and you can go up or down,
one pixel at a time, by just using your up and down arrows on your keyboard.
So, notice what happens in the informational box when we do this.
The Value changes, meaning the brightness of the supernova is changing
as we look at different parts of it. You can see in the magnification
box what we're actually looking at
magnified, so you actually can see the pixel structure.
You can see the position in the sky is changing, it's Alpha and Delta.
And, the actual pixel number that identifies where we are
in the actual photograph or image, also changes.
So, you can use your up and down arrows,
left and right, to move one pixel at a time.
Now, if you accidentally put down a
region that you want to get rid of, all you have to do is select
that region, by clicking again within it, and hitting the Delete key.
And then, boom! The region is gone.
And, you can still pan up and down.
And now, notice here, this is interesting, this little tiny, tiny white
dot, almost one pixel in size, actually a couple of pixels
in size, but definitely tiny, and geez, it looks really
close to what might be the center of this object.
We're going to have more to say about that, as time goes
on. But now, in order to see what the values
of the brightness-es are in the regions surrounding
where you're pointing, you can actually go to View
and have the horizontal and vertical
parts of the image explicitly shown
to you, and here I'm going to lift this up a little bit.
This is going to be a little tricky because
my screen is a little bit too small for this, but I
think you can see what's going to happen. Watch what
happens when I go back into the area
that is denoted by the supernova remnant. I can, for instance,
set down a region and go back and forth and look
at a slice, through the supernova remnant, both
vertically and horizontally,
as things change, as I move one pixel at a time.
So, let's go back to this central point here.
And now, in order to see what the actual Values
are of the region surrounding it, let's go to
Analysis and look at the Pixel
Table. If I drag that Pixel Table over to here,
you can see now that you get a little box which gives
you, along the top and left side of that box,
the actual image pixel numbers. And you can actually,
if you want, go back and forth by one pixel at a
time, to see what the intensity of the supernova is,
in this particular case, very close to the
center of the remnant. Lets see, how close it really
is to the center? We'll just grab one of these little
handles here and drag our region
out to make it bigger. Boy, it really does look pretty
close to being in the very center of this big blob in the sky.
But, there's some other stuff, like what's going on here?
That doesn't look like it's part of some kind of spherically symmetric object.
So, these are all things that we will explore in the future, and
this gives you at least some idea about what can be
done using DS9. To look at another
source, lets do the following. First, lets get rid of our Pixel Table.
And, lets also get rid of our Horizontal Graph,
and our Vertical Graph. Bring this back
down a little bit, and now lets load a different
Observation. What we're going to do here, is instead of
looking at Cas A, we're going to look at another supernova
remnant, called Tycho. And, we'll load Tycho
into our observation box, here.
And Color, we'll, I guess, leave at HE, and
Scale, well, let's see what it looks like. That looks pretty good.
Okay, now notice that there are these kind of like gaps in the data, over here.
And, that is actually a reflection of the chips
in the Chandra satellite, and the fact that these chips are located side by side,
and there are some parts of the sky then that fall between the chips.
So, sometimes you'll see these X types of patterns that really
don't mean anything as far as the actual X-ray source is concerned.
But, now, I want to show you something interesting.
Lets go back to Analysis, and now we're going to look at an Image Server.
This is a set of data that actually consists
of other types of optical or
radio images of the same area in the sky.
So, if for instance we scroll down to NRAO NVSS
and click on that. What we end up with is
another little window, and it will now allow us
to retrieve that part of the sky that corresponds
to the Alpha and Delta, or the position
coordinates of the Tycho supernova remnant.
So, if we click on Retrieve, you now see a little
box. That is the radio image of the exact same
part of the sky, as we see here on the left.
So, what I'm going to do here, we can do something even
neater than just displaying it. I'm going to click on this left frame,
which is our original X-ray image. And now, if I go to frames,
and scroll down to Match Frames,
and I click on WCS, which is World Coordinate System,
boom! Look at what happened to our radio image.
It got slightly larger, and it got slightly larger in exact proportion
to the size of the X-ray image. So, now, we are seeing
the exact same areas in the sky in, at exactly
the same magnification. Now, we can do something
that's even more interesting. And that is, if we go to
Edit and change our Pointer to a Crosshair, now we
have a set of Crosshairs that can link up the radio
image over here with the X-ray image over here.
And, we can lock the two together. So, if we go
to Frame> Lock> Crosshairs, now we can
cruise around one of those images, picking
out regions say, here in the X-rays, and
seeing exactly what corresponds to that part
of the image in X-rays, in the radio regime.
So, you can cruise around the entire area and select
out regions of the sky that might be of interest to you.
Now, one of the things you'll notice right
away here, is that this radio image looks blurry.
It's not really blurry, it's just the fact that radio waves
have much longer wavelengths than X-rays, and because of
this, it's just a fact of life that you don't get the same
types of resolution for your images.
Things don't look quite as good in some radio images,
as they might have look in some X-ray images.
But, radio astronomers have a lot of tricks up their sleeves, and they
can use interferometry to make these radio images
appear very, very pristine and accurate, indeed.
So, this is really our first cut
at what DS9 can do. And,
I hope you will use DS9 on your own, and starting next week,
we will have an in-depth tutorial about what this really
nifty piece of software can do for us. So, we'll see you then.
[BLANK_AUDIO]
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