 Greetings and welcome to the introduction to astronomy. In this video we are going to look at one of the lab websites that we use for the lab and this one looks at extrasolar planets. So we're looking at planets outside the solar system and there's a number of a bit of information here. Don't forget that some of the questions on your worksheet will require you to look at the main content pages. You do want to look at those and mostly what I want to look at here briefly are the two simulators that we will use. The radiovelocity simulator and the transit simulator. So we'll take a look at each of those in turn very briefly. And what we want to look at first is the exoplanet radiovelocity simulator. So when we open that up you'll see a number of different windows that open and we'll see a couple of things here. First of all we'll see an image of the planet and star system, the star at the center and the planet orbiting it. And we will also see the radial velocity curve, which is just the radial velocity how fast the planet is moving either towards or away from the earth as it moves around the star. So the phase is not like the phase of the moon but the phase just means the location of where it is in its orbit. And it goes from zero all the way around to one and then starts over again and the process will continue. So the phase just tells you where it is in its orbit. Now there are a number of different things to look at here and what we see are a number of different controls including things like the system orientation. So you can change the inclination, how the system is tilted and its longitude. If we change the inclination what you can see is that what it changes is how things are apparently tilted. So we're changing the earth's view there. Now if you notice the curve doesn't seem to change at all for the most part but if you look at the radial velocity it is changing. So when you're close to 90 degrees you get a very high radial velocity and as you bring that down to smaller and smaller values the radial velocity will decrease. So it's a lot harder to detect a planet if it's not tilted at 90 degrees and 90 degrees means we're really seeing it edge on. As you can turn here at 90 degrees we're looking at it edge on so that a star is coming right towards us and then right away from us and that will give us the maximum value of the radial velocity. We can still detect it at other inclinations. So if we are looking at it at another inclination we're not seeing it at John we're seeing it at some other value then we're going to get only a lower limit on the mass of the planet when we try to determine that. Now if we look at the others we can also look at changing the longitude which is just how we're looking at it and you can see how that kind of shifts a little bit as you're coming around depending on the orbit but mostly changes the positioning as to where the phases are. Now we can also change things like the star properties. So if we look over here at the properties of the star right now it starts out with a star of one solar mass. Well we can change that if we like and that can then be make it a higher or lower mass and we want to do is look at how that will change the radial velocity. So if we make the star more massive the radial velocity becomes less. Now if you think about that that's because the radial velocity we're measuring is not the velocity of the planet. We are not getting the radial velocity of the planet here but the radial velocity of the star that's the object we can see. So when the star when the star is more massive it's going to move slower and when the star is less massive it's going to move faster. So if we bring this in and look here for a star much less massive than the Sun the radial velocity numbers have increased. Now you can also use this and you can use the numbers here to get an idea of what that value is. So if you want to measure what the radial velocity is at a certain point you don't have to try to guess. You can just bring the cursor over there match it up and read off what your value is for the radial velocity. Some of the other things that we can show here are you can change things like the mass and semi-major axis and eccentricity of the planet so we can change some of those and we can take a quick look at what those will do. If we make the mass of the planet larger what is that going to do? That's going to make the star move more so we're going to get a higher radial velocity. If we make it less it's going to make the planet the planet's tug on the star a little bit less so we're going to get a lower radial velocity. So it's going to be a lot easier to detect a very massive planet than it is a very low mass planet. What happens if we change the semi-major axis? Well if we make it very small or very large again we're changing the radial velocity so a small semi-major axis is very easy to detect whereas a large one is a lot harder to detect. One of the other things to look at in this is that it also gives you the system period. This is also very important because it takes time to be able to make these observations. You have to observe a complete cycle and generally several complete cycles to be confident that there is a planet there and in this case if we observe it for 245 days that's a little less than a year. That's something certainly doable. However if we look for some of these very large ones we are talking thousands of days 11,000 days and it would take many many years just to see one cycle. So something with a major semi-major axis of 10 astronomical units like Saturn in our solar system would really not be detectable at this point. Now one of the other things, last thing I wanted to show here very quickly is the simulated measurements. So you can put some simulated measurements in there which will add in a certain amount of noise because no measurement is perfect. So if there's a little bit of noise there we can see and if we take off our curve there do you see the pattern. So can we see that there is somewhat of a pattern going up and down here and it can be a little harder to see as the noise level increases. So if we increase that noise level then we would see that it is much harder to see that there is any kind of pattern there and we essentially just get random values. If we get it down lower and lower then we'll see that there is a much better curve and we can much more easily follow and predict where that theoretical curve might be. So that shows the radial velocity simulator and works with some of the controls there. The other thing we want to look at is the transit simulator. You'll look at this as well it has very similar boxes to what we saw in the previous one. There is the showing the system and here is showing in this case not the radial velocity curve but the light curve of the star. So how the star's brightness changed. You have very similar controls. You can change the planet properties, the star properties, and the system orientation just as we did with the other. And you will do that for some of the different questions that we'll give and it also has ways to change the to add in simulated measurements and to look at the various noise level and how many observations you want to look at. So if you change some of these what we can see is that for example if you change the mass of the planet it doesn't do anything. The mass of the planet would have no impact on depth of the light curve. So we want to see how far this goes down. Changing the planet mass does nothing in terms of detecting this type of planet as it did with using the radial velocity simulator. What if we change the size of the planet? Well we do see some changes now because we are looking for an eclipse and that would be how much of the star is this planet blocking out. Well if we make the planet bigger, larger in size then it is going to block out a larger percentage of the star's light making the light curve easier to see. One of the other things we'll note is that it also changes the shape of the curve along the edge here. As we change that size of the planet and make it smaller that becomes much steeper and that's because the planet hits the star and is almost immediately in front of it. A very large planet will take a certain amount of time to begin to block out the star. Changing things like the semi-major axis. What will that do? Well not a whole lot. It does change a little bit on the shape of the curve and it's more where the planet is located across this changing that semi-major axis but it doesn't really change the depth of the light curve at all. What it does change is how long the orbit is so if you look at the numbers underneath here that does change when we look at the semi-major axis how long the eclipse takes and how often this will occur. So making it a much shorter one will make it a much smaller semi-major axis will make it easier to detect. Now we can also add in things like changing the star properties. We looked at that before what does that do if we make a more massive star? Well the massive star is going to be more it's going to be brighter and therefore not going to be the planet is going to drop block out a smaller percentage of its light and if we go down to a smaller star it's going to block out more of its light. And the last thing we can look at is if we look at the simulated measurements again so you can put some simulated measurements in to see how well you can see this. So while it looks very obvious here we can see the theoretical curve. If we add a little bit of noise in all of a sudden can you really see any pattern there? And the idea to tell that is take off the theoretical curve. Can you see any pattern in that without the theoretical curve there? In this case I'd say you probably couldn't but if you can decrease the amount of noise you may be able to begin to start to see some kind of pattern present here as you can see how it kind of goes down and then comes back up so depending on how long it is you can see that. So you want to be able to see the pattern very clearly even without the theoretical curve. So that concludes this video just showing a little bit on how the exoplanet transit simulator and the radial velocity simulator work and we'll be using that for one of our labs in the class. So and we'll be back again next time to look at another one of these labs. So until then have a great day everyone and I will see you in class!