[MUSIC] So welcome back to the latest news from Exoplanetary atmosphere. So today we're going to address the power of high spectral resolution. We are still in the troposphere of Exoplanetary Atmosphere. And previously we've seen that water can be routinely probed in these tropospheres, for hot gas giants and a few warm neptunes. But aerosols are able to mute spectroscopic features, that are obtained at low spectral resolution. So now we're going to discuss what high spectral resolution can bring to the characterization of Exoplanetary atmosphere. And I will start by showing you a comparison between the low resolution spectrum. Which has been obtained with the Hubble space telescope, imaging spectrograph called STIS. And it's the blue curve that you see in the figure here. This is a part of the transmission spectrum of the transit transmission spectrum, of the hot gas giant AG189733B. Which we're going to talk about again in one of the next part of this course. The resolution here is actually more than ten times larger, than the resolution of the near infrared spectra we've seen below. But since we are zoomed in on a much smaller wavelength domain, it does not appear with with big resolution, but it is bigger. However, it is much lower than the black spectrum that, has been obtained with a ground based telescope. The 3.6 meter telescope of the European Southern Observatory set in La Silla in Chile, where the HARPS spectrograph, is set. And HARPS has a resolution of over 100,000, and you can see two striking things by comparing the black and the blue spectrum. And we're going to forget about the red one for the moment. The first one is that the black spectrum, has much more noise in its continuum than the blue spectrum. And this is because, simply there is less light in the smaller wavelength bean, of HARPS compared to those of STIS. So there is more noise, on the other hand, what you can also see is that the spectroscopic features. Which here are the features of sodium, in yellow, are also much stronger than what is seen with STIS. And this is because, the line are not resolved with STIS, whereas they are resolved with HARPS. And resolving lines as we are going to see next is something that is quite important. Now the high resolution is also going to give us access to molecular species, that lies in the spectrum of planets. So this is an example, I'm going to zoom in on the transit transmission spectrum of the same planet, to show you what's molecular bands. So here are all the bands you see okay, the forest of lines are water vapor bands. And these bands are composed by many many individual lines, that are individually all very weak and this is just a model. So we can see them very clearly, but in real data, this is not going to happen. Because, there's going to be noise but, so the individual lines are not going to be seen. However, if you are able to make an average of all these individual lines to stack them up. This could create a signal that could be detected, and reveal the presence of the molecule. So this is again a zoom on this water band in the optical, and what we are going to do here is the same operation that we do to calculate the radial velocity of a star. Except that we are going to do it on the planet spectrum, and not on the star's spectrum. So we're going to do a cross correlation function, in other word, we're going to build to add on all these lines and, try to extract a plant signal. And the red curve on the bottom panel, show the cross-correlation function, of the spectrum that you have on the upper panel. So there is a line but can we detect it so, the gray spectrum is the transit transmission spectrum obtained with the HARPS instrument. And as you can see, it is too noisy to allow us to detect water in the optical for these planets. The prediction is that we cannot really detect it however, this is just a four meter class telescope on the ground. Next generation spectrograph such as the recently commissioned Espresso, which is also a high resolution spectrograph. But this time set at the very large telescope, although in Chile it's 4 8 meter telescope. Should be more than able to detect such a feature in the optical. And we are confident that it could because we know that this is actually achievable already in the near infrared. By using another spectrograph at the same telescope, the CRIRES spectrograph. And astronomers are currently getting pretty excited about the kind of plots that you see here. So these plots, basically represents the semi amplitude of the radial velocity of the planet, not the star. So it's KP not KS, as a function of the systemic velocity. Which is the velocity of the radial velocity of the planetary system, in the line of sight. And what each line in this 2D plot 2D image represents, each line is basically the cross correlation, of the Stellar spectrum. With a mask of here carbon monoxide line, that is shifted at the orbital velocity of the planet. And it is shifted at different velocity along the y axis. And the bright points correspond to the maximum signal that is obtained. And this maximum signal, is actually due to the planet. Because it is obtained at the systemic velocity of the planetary system. And it is obtained for a semi amplitude that corresponds, to the planet mass. And what this signal means is that, well there is carbon monoxide in the planetary atmosphere. So this is quite a powerful method, to detect molecular features in the near infrared in planetary atmospheres. And as a result, a flurry of results have been obtained using these instruments. So, some during transits of planets in transmission spectroscopy some, during eclipses of planets. So these are water and carbon monoxide that are seen in emission. And it's even possible to apply this method for non-transiting, planets. And here is one very nice example, is that the first exoplanet known 51 Pegasi b, which is not transiting. Well, it's still possible to use this technique, and actually detect water vapor in the atmosphere of this planet. So, this is what you see here, and additionally, since this method also give in the y axis. The actual semi amplitude of the planet, orbital velocity. Well you have the real mass of the planet, and you can determine the inclination of the planet. Which is something that was not previously determined. So, as a summary for this part, we've seen that high resolution spectroscopy with ground based telescope is a really powerful tool. And in particular, it allowed to spectrally identify unambiguously, molecules such as water and carbon monoxide in the tropospheres, of exoplanets, thank you. [MUSIC]
