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Lecture 6 Introduction to DS9--Part II

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Analyzing the Universe

Rutgers the State University of New Jersey

4.7 (77 ratings) | 5.9K Students Enrolled

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.

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4.7 (77 ratings)

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DA

Feb 01, 2017

A very good course to start with while analyzing the astrophysical data with opensource software..... a must learn by all astrophysics student.

K

Oct 28, 2018

Thank You! Very good course, different with actual data to handle. Thank You Terry Matilsky for your lessons. They were excellent.

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!

Lecture 1 The Nature of Images 13:45

Lecture 2 Image Formation 14:45

Lecture 3 Skipping Stones and X-ray Images 10:22

Lecture 4 The Perception of Images 17:33

Lecture 5 Introduction to DS9--Part I 6:06

Lecture 6 Introduction to DS9--Part II 20:02

Taught By

Dr. Terry A. Matilsky
Professor

Transcript

[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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