[MUSIC] Okay gang, now that you've downloaded DS9, let's put it through its paces. What I would like you to do with this lecture or presentation is use it throughout the course as kind of a reference guide. You can see what DS9 is capable of doing and we'll be presenting some other parts of its features as well. But this will give you a general overview as to what the capabilities are and how you can go about using it. I encourage you to download other sources, and we'll see how that's done shortly. And just play with it because it's a lot of fun, and you can learn a lot just by doing these particular types of steps with more than one observation. Okay, so now we go to our screen and we start DS9. When you start DS9, you will see a blank screen, very intimidating. The first thing, usually, that we will do is we will go to this upper menu bar here and notice that there are lot of choices, File, Edit, View, Frame. These are also repeated for convenience on this bar over here. So you can actually do a lot of your analysis from both or either of those two places. But right now, usually the first thing that we will do Is click on Analysis. When you click on Analysis you will see a dropdown menu. This a very handy convenient thing. It's kind of like a scissors and you can take that scissors. And by clicking on it, you can now have your analysis commands at your disposal without having to always click on the menu bar over here. Now this may or may not work for some of your operating systems. You can try it and if it doesn't work, no big deal, you just go to Analysis and you'll get that drop down menu, okay. So now the first thing, usually, that we will do is load an image, and we do so from the Virtual Observatory. If we click on the Virtual Observatory, first of all notice before we do that that the menu stops where it says Load Analysis Commands and Clear Analysis Commands. There's nothing else underneath that. Let's see what happens when we go to the Virtual Observatory. We click on it, and now we are presented with a list of servers that contain the data that we will be using for the course. The analysis server that you should always attempt to log in with, at least initially, is the Rutgers Primary MOOC X-Ray Analysis server. The others ones are there just in case something goes wrong here, but if you click on one of these servers, and only click on one, watch what happens. Another window comes up immediately. And you now have a screen that contains all of the observations that you might want to utilize. We don't need this particular window anymore, so we'll minimize it. And now, we see that, let me move this over here so we can see what's going to happen, okay? There's a whole list of observations that have been done with Chandra of different objects, hundreds and hundreds of observations that have been done over the years using this satellite. And if there's one that you don't see, you can actually enter that observation yourself but for now and the purposes of our demonstration of DS9 capability. We're going to click on the first observation, this was the first light that Chandra ever saw when it was launched over a decade ago and it consists of an observation of a supernova called Cas A. And I'm just going to move this over a little bit so you'll see that something is going to be happening in the window. Okay, we're going to click on the asis observation of cast A, and there it is, displayed in black and white and notice what happened in our analysis table here? We now have loaded the Chandra Add Analysis Tools and we can use them as a guide for what we do with our data. Okay, so let's minimize this window, we don't need it anymore, and now let's look at the Chandra Add Analysis Tools. Once again we have a little scissors that we can click on and bring that window over so that we can see what those analysis commands are. And now we deal with our object, CAS A. Well, one of the first things that you probably ask about CAS A is What is it and where is it? Well, the where it is is a little bit easier except for we don't quite have a very easy way to get a distance to it. But just like on the surface of the Earth where we have latitude and longitude, we have a coordinates system in space. And this coordinates system is displayed here in this box. And now it's blank because I am not on the source itself, but you can see that as I cruise around this source that alpha and delta change. What is alpha and delta? It's the equivalent of our latitude and longitude here on the earth. The delta is the latitude of the source and we get that latitude by imagining that we take the earth slicing it through the equator and extending that slice out to the celestial sky. So, we measure latitude north or south of the celestial equator We also need a prime meridian where on the earth, we use the Greenwich meridian as the zero point in longitude. In astronomy, we use the position of the sun when it crosses the vernal equinox. In other words, as the sun moves through the sky on a yearly basis, it crosses the celestial equator in March, going upward or northward, or in September, going southward. The zero point of longitude is selected as the vernal equinox, and that marks the coordinate that we call right ascension, or alpha over here. Delta is the declination, alpha is the right ascension. To see this more clearly, we can go to Analysis, and you see one of the possibilities is setting up a coordinate grid. When we click on that Coordinate Grid, we now have a numerical and graphical position of what we know to be the position of CAS A in the sky. Now, sometimes, we need a different coordinate system altogether. And the reason is, is that we are looking sometimes to see where an object is relative to galactic coordinates instead of Earth-based coordinates, which is what the celestial equator and right ascension system tells us. With respect to the galaxy, things are very different. If we choose the galactic center as the prime meridian for our analysis and anything north or south of the galactic equator, which represents the disk of the Milky Way, and we can see a photograph of what that looks like for a typical spiral galaxy here, we get a completely different coordinate system. Looking at this, let's see the coordinate grid parameters. Here, we can actually select out various coordinates. Here, you see we have selected what's called WCS, World Coordinate System, but we can also click on Galactic coordinates. Watch what happens to our display of grids when we click on Galactic coordinates. You see that the coordinate system has changed. This is because the Earth is tipped with respect to the plane of the galaxy, and that tipping is reflected in a change of our coordinate system. So now, let's talk a little bit about this object itself. It turns out that this is a supernova remnant, a star that has gone through its lifetime of evolution, ranging from 10 million years to sometimes 10 billion years, and has exploded in a tremendous catastrophic event that spews out all of the material that was in the star itself into interstellar space. And it becomes the breeding ground for yet another generation of stars. We're going to talk more in detail about this object in the coming weeks. But right now, I just want to use the image to demonstrate some of the capabilities of DS9. It turns out that this is an object that across from one side to the other is a distance of about five parsecs. Now, a parsec is about three light years. So this distance in the sky from one end of CAS A to the other is about 15 light years. And if you need a handle on how far, how distant a lightyear is, how many miles or kilometers it is, just remember that light goes around the Earth, if you could put a light beam circling the Earth, it would circle the Earth seven times in one second. Imagine something that is so vast that light would take 15 years to go from one end of the supernova remnant to another. The distance is even more staggering. We have estimated the distance to CAS A at about 3.5 kiloparsecs, 3,500 parsecs, or over 10,000 light years. In other words, light traveling to us, right now, from CAS A left that object over 10,000 years ago, pretty staggering. Okay, well now, we see this image, and it is displayed in black and white. The grey scale on the bottom here demonstrates the actual intensity of the object from black with no photons to white where the intensity is the greatest. However, we don't necessarily want to use a gray scale to look at our object, and what we can do instead is click on Color, either here or here. If we click on Color, we have at our disposal a number of representations of this data. Here is color coded A, here's color coded B, here's color coded BB. This one is particularly useful, and we're going to look at it in detail for a lot of our images. It's HE, and you can see now that the same data is represented by a different color scale. If it's very, very faint, it's black or red or purple, and as it gets brighter and brighter, the areas of the representation of the image get greener and lighter green until they get To almost white. Now what's interesting about this is that we don't have to display even the same colors in exactly the same way. It turns out that if you look at this bar here. These are more or less evenly spaced in a linear fashion. If we now click on scale however, we don't have to use a linear scale. And the reason for that, we sometimes don't want a linear scale is provided for you in a brief interlude to a PowerPoint slide. Let's go to that slide now and see why we might want to choose a scale other than a linear one. Let's imagine that we have a bright point and its intensity is 100. So, in a linear scale we would have a bright point with 100 brightness units and our faint point is four units of brightness. Now you can see that the ratio of the bright to the faint object is therefore 25:1. Now, let's select a square root scale. You can see that the bright point will translate into 10 units. The faint point will translate into two units. And now the ratio instead of being 25:1, it's 5:1. Therefore we have enhanced the faint object in the square root scale. Let's see how that functions in practice by going back to DS9. Okay, so now you see why we might want a different type of representation, and let's see what happens if we go from a linear representation to a square root representation. Watch closely to see what happens to our bar at the bottom and then numbers associated with it. You can see that now we are seeing much, much, fainter parts of the image. And in fact this purple region is nothing more than the background photons that Chandra has collected and it's completely off the actual supernova remnant all together. And we can toggle back and forth and see how we can represent or see more faint parts of the image by using a square root or even a logarithmic scale. So we can actually display this data in many, many different ways. Also what is possible is to be able to change our contrast, and how we display the image as far as how quickly we get it to go from one intensity to another. Very similar to a high contrast image such as you get in looking at a type written page to a lower contrast image when you look at certain photographs. Here's our gray scale image. And we're going to click on color and look at the color map parameters. If you do that, you get a dialogue box in which you can change your contrast and your bias. Now pay particular attention to what happens on this menu bar when I utilize the contrasts slider. If I increase the contrast, notice what happens is that the bar from black to white gets compressed. And you see the object goes from black to white almost immediately, so that there's very little grey in between. That changes the contrast. Bias, what bias does is it changes the place at which the gray scale starts to change. So let's see what happens when I move the bias slider. So you can play around with these particular representations, changing the contrast, changing the bias. To display the image in a very myriad number of ways, and depending on what you want to see, you can represent faint parts of the images or bright parts of the images. And we'll be utilizing this way of looking at things extensively. Another way of doing this that's probably better when you get a little feel for it, is to instead of looking at these two things separately. If you go back to your image and right-click on it you can actually by scrolling left and right and up and down you can invoke the color map changes on your own. So right-click, now watch what happens when I go left and right. Look it, I'm changing the bias. Look at the bias dialogue box that you have there. And now if I go up and down, I am changing the contrast. So you can kind of manipulate things to your desire depending on how you want to view the object. [MUSIC]
