Karin Oberg: There are still a few people coming, but I think it's time to to go ahead and get started so once again, you know warm welcome to everyone who has joined us for this.
Karin Oberg: awesome defense of our thesis that Ellen price, I will be giving in the in the coming 45 to 15 minutes or so.
Karin Oberg: And, of course, doing this remotely and it's not as much fun as doing it in person.
Karin Oberg: But it does have the silver lining that people can call in from further away so a special welcome to those of you who are calling in from not not Cambridge, of course, the people in Cambridge we're super happy to see you too.
Karin Oberg: and
Karin Oberg: Also, a special thank you to to ellen's committee at his here, so we have.
Karin Oberg: Sean Andrews, David will nerve damage our SAS will have her here locally and Ralph goodreads is our special external exterminator.
Karin Oberg: But then we actually have two more external members that are talking a little bit more about in a moment, but also leaves and destiny Rogers will come as well.
Karin Oberg: And so Ellen first approached me to do her her thesis with me I guess that a little bit more than five years ago.
Karin Oberg: And I was going at first, I felt a little bit of trepidation, because I see we'll find out Ellen is very much a theorist and I am very much not and I had some columns you know whether I could.
Karin Oberg: Give Ellen the device that you're supposed to give us an advisor for her her thesis and there were two things that pushed me over the edge to to say yes.
Karin Oberg: What was the obvious talent on ellen's ellen's part and I guess it's a outgrowth of that my realization oh that together with Ellen.
Karin Oberg: We could do things that I just could never have done on myself or with anyone else that I was working with, and that was.
Karin Oberg: That was too much of a temptation those two things together to to say no to and and I see Oh, I see I see, I am like I am very happy I said yes, and I think you will understand that in the next few minutes SEC ellen's work.
Karin Oberg: But London did a very clever thing, which is that she did realize that I was not the theories and therefore assemble sort of devising a team right and end up relying.
Karin Oberg: Only only on me at and her effective co advisors Professor illicit cleaves at the University of Virginia and Professor nestle Rogers at university of Chicago.
Karin Oberg: are both here and both part of ellen's committees is full, I want to acknowledge that this was really you know advising team effort that that helped us get a gift here today.
Karin Oberg: So Ellen Ellis thesis is really, really on the development of different kinds of numerical numerical methods, I to trade dress and to me really fascinating problems in what the chemical environment is like work planets and planetesimals assemble as well as what the.
Karin Oberg: structure or really bizarre planets are like that then forming this discs and that we can detect in different different ways.
Karin Oberg: So Ellen loves developing these kind of methods so i'm going to paraphrase a conversation that we had at some points this I unfortunately didn't take notes at the time, but it was something like this to illustrate this this characteristic.
Karin Oberg: So we're having our usual meeting and Ellen is trying to figure out some theoretical problem that I still haven't treated fully understood what it was and.
Karin Oberg: She tells me that she thinks she has found the method that she needs to solve this problem and I, you know that that's exciting, but by by things like what's.
Karin Oberg: what's the issue what why don't you know yet that this is, this is the right solution and then Alan on suspect well.
Karin Oberg: The article I found is in Russian and I don't speak Russian so I still need to figure out if it's actually applicable, but you know equations equations, so I think I can figure it out.
Karin Oberg: She did, and this ended up being part I think now, but she wants to do not necessarily did as part of her thesis applying this weird method, but what she wants to continue to do as opposed to just one of many I guess.
Karin Oberg: meetings during the past few years, where.
Karin Oberg: I have.
Karin Oberg: been pushed well out of my comfort zone into into theory land by by Ellen and i'm just so grateful to have been part of this journey together and to really be I have made uncomfortable especially we consider, I think the really.
Karin Oberg: Really cool cool results that has come out of it so in a thank you Alan for continuously pushing my horizons and understanding in the past.
Karin Oberg: few years and I can say with some certainty that there's no way I would have entered this deep into theory land.
Karin Oberg: Without you and it's been you know it's been lots of fun to do that together, but without any further stories or embarrassment I do want to hand it over to.
Karin Oberg: Ellen to tell tell us something about but her work that she has been receiving in the past few years, so Ellen, the floor is yours okay.
Ellen Price: So, can you just give me a thumbs up if you see my slide and only my slide.
Ellen Price: Okay, great.
Ellen Price: um alright.
Ellen Price: So.
Ellen Price: Thank you for the lovely introduction card i'm.
Ellen Price: Good morning, everyone Thank you so much for logging in from various time zones, I really do appreciate your support today welcome to my dissertation colloquium.
Ellen Price: And as card mentioned today i'll be telling you about my research for the last six years, and if if we have time but definitely in the private Defense I can talk a little bit about where i'll be going from here.
Ellen Price: But first, there are, of course, as is tradition, a few people that i'd like to thank and i'm going to try not to cry when I do it.
Ellen Price: So first i'd like to thank my family, they have encouraged me and supported me emotionally and financially until I was able to support myself.
Ellen Price: My parents paid for me to attend caltech which was really challenging for me, but it helped make me more competitive as a Grad school candidate, so I really appreciate that.
Ellen Price: And even before that you know my parents really enabled me helping me go to a really good high school helping me do.
Ellen Price: All the extracurricular things that I wanted to do that made me, you know, a competitive candidate to get into caltech so they've really been pushing my career for this whole time.
Ellen Price: Next i'd like to thank my fellow graduate students and maiming everyone who is, let me invade their offices to talk about my latest math problem.
Ellen Price: Which is something I do pretty frequently would take more time than I really have today so i've just offered to list a few of particularly close colleagues who've been especially helpful over the last six years.
Ellen Price: Thank you for letting me bombard you with confusing math and allowing me to fix your various computer problems.
Ellen Price: I actually have a little short thing to say to each of you over on the side, so I hope you're here.
Ellen Price: So Jimmy let you have been my writing partner for basically a year now, since a pandemic started um it's been great talking to you, everyday about my latest plot or the latest code bow that I fixed and thanks for letting me talk your ear off sometimes to.
Ellen Price: lock your a wonderful human being and you brighten up my day, every time we see each other, thank you for celebrating with me and never making me feel like I had to hide, who I really am.
Ellen Price: roxanna you're an amazing officemate and I miss seeing you there every day, I hope we can enjoy a reunion, before we proceed to our respective next stops.
Ellen Price: Jane I always looked up to you in group meeting and wondered how you knew so many awesome things, especially about bugs in Casa, which you know so many of those you may not have realized that then, but you were always really inspirational to me on a daily basis.
Ellen Price: NASA i've always admired your faith and your kindness and I love all the walks and chats we had together getting coffee getting chocolate all those times that we spent together.
Ellen Price: And finally, fair and you've been an all around terrific friend, a fellow gamer and upstairs office neighbor is joining you there to plan PC bills and talk about our research there's a couple other colleagues i'd like to mention, which are rob shoulders and peg hurley.
Ellen Price: When I was sick you made taking leave completely painless until I was ready to come back and you've carefully maneuvered the bureaucracy at Harvard to make this a good experience for everyone involved, so thank you very much.
Ellen Price: I also have a large group of friends outside work that i'd like to thank for their support during my PhD some of them are here today.
Ellen Price: i'd like to thank Nick Copernicus Parker Max the young Jacob shanker cedric Vermont Charles dehart and Kelly mauser to make up my former study group at caltech, also known as the physics group.
Ellen Price: I also think Juliet better than you on grace Tang and Alina Wang for their continued friendship and support long after we graduated.
Ellen Price: None of this would have been possible, of course, without my various mentors going all the way back to high school and i'd especially like to thank my first work steady mentors Perry Derek enos and chrissy richie who supervise my first foray into real research.
Ellen Price: Next john Johnson and Leslie Rogers who advise me and undergrad and got me interested in planetary scale astronomy.
Ellen Price: Finally, Elsa cleaves a former CFO a postdoc and current oberg My thesis advisor for been incredibly helpful and it taught me so much about this field, so I hope I make you all proud today.
Ellen Price: And finally, many of you are familiar with my cat my perpetually sick cat Kelly she's been thrilled about all this work from home time during the pandemic so i'd be remiss if I didn't also thank her for tolerating my presence in the apartment.
Ellen Price: And last but certainly not least, I want to take a minute to talk about the person that I dedicated My thesis to.
Ellen Price: rhiannon Johnson was a very dear friend of mine in high school and she died rather suddenly after a long struggle with chronic illness.
Ellen Price: She wanted to be a medical doctor and help heal others who are sick, and I think that was based on her own experiences, ideally, what she'd gotten that chance, but I know she's in a better place and feels no pain now.
Ellen Price: With that i'll transition into the meat of this talk by telling you a little bit about protoplanetary discs and how I simulate them.
Ellen Price: So a protoplanetary this or discs of gas and dust that surround the young Star and then information sides of planets.
Ellen Price: The gases largely made up of molecular hydrogen and helium but the less abundant species are also very important in the context of planet formation.
Ellen Price: On this slide I believe will just a couple of effects that will be focusing on today, the creation and grain drift.
Ellen Price: As well as dust settling i'll talk more about those later so don't worry it's also important to know that stellar radiation creates a strong temperature gradient and the disc indicated here by a color gradient.
Ellen Price: And i've labeled the three vertical sort of zones that we typically think about in the disc the MID plane, which lies at the middle vertically is comparatively cool events, and this is where all my work will focus because it's very important for planet formation.
Ellen Price: In the mid playing lots of chemical species are frozen out on to dust grains the density is in the disk or low enough that we don't even worry about a liquid phase everything's either is or guess.
Ellen Price: Even species, you might not think of is traditional ICES like carbon monoxide can be frozen out at such a low temperatures.
Ellen Price: above that we have above the MID plane, we have a rich molecular layer for gas phase chemistry can be important, because it's warmer.
Ellen Price: And at the top, is a hot ins layer which is bombarded by stellar and interstellar radiation and is therefore very warm.
Ellen Price: The solid component of the disk the dust grains usually about point one microns in size but they grow They fragment they collide bounce settle and drift not independently as a gas, but not perfectly couple of either and i'll talk more about that in a later section.
Ellen Price: So that's a little picture that I showed them the last slide really doesn't do this justice, though, in terms of their variety.
Ellen Price: The D sharp survey which observed several discs at high angular resolution found asymmetries are actually quite common and discs.
Ellen Price: i'm showing a few of the images from the survey here, where we can see some kind of weird symmetric blob of a gap a gap and some kind of bright spot.
Ellen Price: Another gap and two brains when I simulate this I always assume as an equal symmetry which is symmetry in the sort of around direction of the desk but here we can see that that assumption can easily fail for any given this.
Ellen Price: So why should you care about protoplanetary discs in the first place, I thought of a few reasons they might interest you, so I hope one of these applies to you.
Ellen Price: First, for the purposes of questions about origins of life protoplanetary this chemistry sets the composition and chemistry available to the planets that form in discs.
Ellen Price: So if you're curious about whether or not we're alone or how we got here, you might care about this.
Ellen Price: Second, maybe you're an astronomer and another subfield and to you i'd say that accretion discs which protoplanetary discouraging discs also surround black holes, for example.
Ellen Price: So even if protoplanetary this aren't your focus the modeling efforts might still be interesting because nature loves to repeat things.
Ellen Price: And finally, on that same thread discs are an incredible modeling challenge spanning many orders of magnitude and spatial and temporal scales.
Ellen Price: This is interesting in its own right, but it could also inform modeling problems and other fields, or even industry, so no matter what your interest this option have something for you.
Ellen Price: If you're skeptical at planet formation, let me reassure you astronomers have observed actively creating proto planets in the PDF 70 disk which is shown here.
Ellen Price: i'm indicating the bright spots with green arrows Those are two pro planets the other boxes you don't really need to worry about but um it's very encouraging that we've actually seen some foreign proto planets.
Ellen Price: And finally they're just so many exoplanets in our galaxy i'll talk a little more later about how they're discovered.
Ellen Price: But today we've confirmed 4375 planets with 165 of those being terrestrial planets the sample helps put our own planet and solar system in a broader context, so we can understand our place in the universe.
Ellen Price: Now i'm going to indulge in a little thought experiment which I hope you find illuminating because I certainly do um What if we wanted to simulate a disk perfectly what would that take.
Ellen Price: So we need the equations of fluid dynamics to describe the gas component those non obvious stokes equations that you may be familiar with.
Ellen Price: We also need the rate of transfer equation to describe how radiation moves through the dusty material and sets its temperature chemistry is important this is kind of an astro chemistry talk so we're going to need some chemical species abundances and some chemical reactions to model.
Ellen Price: The solids in the disc like I mentioned before, can grow and fragment so we'll need an equation for that too.
Ellen Price: And that's before we even get into things like turbulence and stellar evolution and my medic fields, all of which play a role too so let's just go with these these four things that i've listed here and and see where we get.
Ellen Price: So we want to model, all these things simultaneously the independent variables in this in this simulation are pretty easy to identify we're going to need time and space.
Ellen Price: But also frequency and angle for going to do radiation that because of six independent variables for the dependent variables they're just so so many of them.
Ellen Price: In addition to the fluids density momentum and energy and the radiation intensity, we need to track every chemical abundance of which there could be hundreds or even thousands depending on your ambition.
Ellen Price: And as many grains size bins as possible to simulate a continuous distribution of sizes, I should mention that computers and distributions are just a little bit difficult so we're going to break our distribution and convince and call it a day.
Ellen Price: So let's say we've written down some giant partial differential equation, and all those variables as well posed, and we have boundary conditions and we're ready to march through time.
Ellen Price: How much can you computer memory, would we spend storing a single snapshot of this disk.
Ellen Price: assuming a spatial grid in three dimensions, with 100 subdivisions in each direction and the thousand dependent variables to track.
Ellen Price: noting that neither of those are nearly enough like we sort of covered on the previous slide the state vector of this this disc is going to be eight gigabytes.
Ellen Price: Which is about the total amount of memory, on your standard laptop computer.
Ellen Price: If we need some operator a matrix that tells us how to get from one snapshot to the next that's going to be eight exabytes in size, if we store it densely.
Ellen Price: For the uninitiated is that is just unimaginably large but wolfram alpha does estimate that one X invite is about the information content of all the words ever spoken.
Ellen Price: So how do we actually simulate this, the point I want to convey is that the approach in this thought experiment isn't the right way.
Ellen Price: In reality, we make various approximations we exploit cemeteries eliminate unimportant variables and solve simplified versions of the full system to make forward progress, and I hope you'll see today that that's exactly what i've done.
Ellen Price: I solve sort of.
Ellen Price: Simplified systems to understand one effect.
Ellen Price: And then move on.
Ellen Price: In this talk i'm going to discuss four separate projects, here are some key ideas I hope you'll take away.
Ellen Price: In the first section i'll try to convince you that accretion is an important effect that can change the results of modeling and protoplanetary this.
Ellen Price: Next i'll show you the grain drift provides a simple and robust explanation for enhanced commentary carbon monoxide.
Ellen Price: Then i'll switch gears and tell you about how the Roche limit can help us constrain exoplanets compositions and finally i'll demonstrate that the shape of an exoplanet Terry transit changes in a predictable way when the planet is distorted away from a spherical shape.
Ellen Price: Without further ado let's get started with my first project which focuses on the process of the creation in protoplanetary discs.
Ellen Price: The motivation for this project came when I noticed that lots of disk models will simulate either chemistry or dynamics, but rarely but.
Ellen Price: I wondered how this might change things and car and suggested working with Elsa to implement accretion and an existing this model, but I actually ended up redeveloping that model from scratch, because I just can't work with for trade code.
Ellen Price: But it was a great learning experience, and I hope I can impress upon you, the number of moving parts involved in this model.
Ellen Price: So I mentioned the creation, a few times, but I haven't told you what it is and creating this because one more material is falling on to the central start.
Ellen Price: In the discovery modeling of a section this gets evolution is important to.
Ellen Price: This this evolution is it a fusion process and it moves material, both in words toward the star were to create on to the Star and our words away from the star.
Ellen Price: You can sort of think of diffusion is like a spreading out process to illustrate this i've put together the short animation.
Ellen Price: Instead of the discs usual profile will start with a thin ring of material which you see in yellow here the velocity field at the desk is shown in the colored streets i've also put in three test points which you'll see in the green orange and red colors.
Ellen Price: i'm going to sample the temperature the surface density and the velocity of the material at the test points um.
Ellen Price: For this illustration it's useful to see what happens to material that both that starts inside the ring on the ring and outside the ring, which is why I chose those three locations.
Ellen Price: You can watch these gauges on the left side on the right side to see how the fields change of colored each needle to correspond to a test point so let's see what happens as time goes forward.
Ellen Price: So if we pause here for just a second, you can see what the disk material quickly last spring, structure and spreading out in space.
Ellen Price: I should mention that all these frames are taking it equally space time points so you'll see that the first the first sample is a rather dramatic change, but the others are pretty subtle.
Ellen Price: So it's it's spreading out it's lost its ring structure that's the diffusion I mentioned before, so let's go.
Ellen Price: let's pause again, you can hopefully tell it the green test point is getting closer to the star, which has not shown but it's at the Center of the disk.
Ellen Price: But weren't shot in the state at roughly the same radio position, while the red.is moving outward when I finished the animation the green dot will almost have created on to the central star, but the red dot will have disappeared from the image.
Ellen Price: This is the final frame of the animation and as you've seen the temperature has increased for the Green point and decrease for the others, because the green point is getting closer to the star.
Ellen Price: The density just decreases since the material is spreading out and getting thinner.
Ellen Price: Another thing you should take away from this animation Is it the three points which originated very close together never crossed paths and that's very important for how we're going to simulate the creation, this.
Ellen Price: So when we think about simulating a disk we might imagine doing a global simulation kind of like what I presented in the thought experiment at the beginning of the talk.
Ellen Price: We already established that those are very expensive and probably not practical.
Ellen Price: and other two options are reducing the chemical network or the physics, to help simplify things but it's difficult to know at the beginning, what might be safe to exclude him but simulated anything yet So how do we really know.
Ellen Price: So instead we choose to do a local simulation That means that we track the physics and chemistry longer trajectory much like the trajectories of the points in the animation.
Ellen Price: And then sample a few trajectories to learn what's going on in the disk overall, this only works, because the trajectories or accretion streams don't interact with each other, will break that assumption in a later project.
Ellen Price: Now I mentioned radio transferred the beginning of this talk, but I didn't say much about it so let's dive a little deeper into this topic with the goal of understanding.
Ellen Price: Why the protoplanetary discs temperature is really hard to determine so let's suppose we have a star surrounded by some dusty claps.
Ellen Price: A drawing of a separate the clouds here, but in reality the material should be sort of continuous, this is, this is a cartoon of sort of a disc that's a little clumpy.
Ellen Price: The star ratings, which he teeth cloud.
Ellen Price: See you'll see their colors change as they are heating up oranges sort of hotter than the blue is hotter than purple you get the idea.
Ellen Price: The clouds absorb and scattered radiation according to their absorption and scattering coefficients but the clouds also reradiate at a temperature lower than the stars.
Ellen Price: At the end it's very difficult to say exactly what the temperature of each cloud should be because of their mutual influence on each other, I say it's difficult but it's not impossible and that's where the radio transfer equation comes in.
Ellen Price: This is the radio transfer.
Ellen Price: It encodes how the radiation intensity changes with time space angle and frequency.
Ellen Price: The details of the equation are not super important for the purposes of this talk, but I just want to communicate how difficult this equation is to solve hidden in the symbols B and J or the temperature of the dust and the integral of the radiation field over.
Ellen Price: angle, making this.
Ellen Price: An INTEGRA differential equation, these are just notoriously difficult to deal with there isn't a really good numerical method for them that I have ever heard.
Ellen Price: Furthermore, the temperature is set by the radiation field like we discussed on the previous slide, so now we have a dependency loop.
Ellen Price: And we decided to use an iterative procedure and a code called rat and see 3D to find the equilibrium solution to this equation, rather than solving it directly.
Ellen Price: Random CDs of Monte Carlo code for you to transfer, that means that it simulates a random set of photon packets drawn from the black body distribution of the Star and propagates them through the material.
Ellen Price: After thousands or even millions of photons the temperature will begin to converge and that's all we really need for the disk simulation we don't need the full radiation people.
Ellen Price: So this is how the full temperature iteration that then proceeds, we began with a temperature guests, like a power law with a negative index, which means that the temperature falls off as we move further from the star.
Ellen Price: Next, people on the code that's all for the evolution of the surface density of the disk using the classical Linden Belen pringle formulation for an accretion disk.
Ellen Price: Then we run random see 3D to get the temperature, as I mentioned before a Monte Carlo code is inherently random there's gonna be some numerical noise in the temperatures.
Ellen Price: Instead of using that data directly we developed the flexible function that captures the overall behavior at the temperature in time and space.
Ellen Price: At the end of the iteration we check to see if the new temperatures match the last generations temperatures when they do we're not.
Ellen Price: But if they don't we lose save it for the last set of temperatures for the next iteration the surprisingly actually converges pretty rapidly.
Ellen Price: And it gives us an analytic form for the temperature, which is really useful when we need to say take the derivative of the temperature, which is something that we will need to do.
Ellen Price: So here i'm just summarizing the local simulation method, once the temperature structure is set, we solve for the surface density without any chemistry is a function of space and time.
Ellen Price: That the chemistry doesn't feedback on the surface density, which is why we can do this.
Ellen Price: Then we choose a few radio positions to start the parcel trajectories, just like the test particles in the animation.
Ellen Price: We find that the innermost track tend to be the most scientifically interesting but we simulated a few others to.
Ellen Price: Finally, we trace the trajectory so the disk storing the abundance of abundances of all 644 chemical species, and each time step.
Ellen Price: With rates computed from the local conditions in the disk like temperature and surface density volume density.
Ellen Price: But it's important to remember that the chemistry is almost surely going to depend on the history of the parcel as well as on its current environment.
Ellen Price: And that's exactly what we found in our results move it to the disk tend to enable different chemistry than if we held the parcel at some fixed location.
Ellen Price: So what are these accretion tracks actually look like.
Ellen Price: Here i'm showing the radio physicians have a few accretion streams as time.
Ellen Price: As well as some other fields but i'm pointing to the what I would consider to be the most scientifically interesting track, which is in this dark blue.
Ellen Price: We found that cosmic rays play a very important role in driving chemistry for our innermost track.
Ellen Price: While the rate is pretty much constant for the other three tracks, the innermost ones he's a factor of about 100 reduction in the cosmic Ray rate over its lifetime.
Ellen Price: That happens because the increasing surface density of the disk will block more and more of the cosmic rays impinging on the desk.
Ellen Price: The innermost track also sees a dramatic increase in its global temperature, both because it's approaching the Star and because of the effects of stellar evolution.
Ellen Price: i'd like to give you an idea of what we found and before I just throw a giant pot up on the screen i'm going to show you just a single panel to give you a flavor of it.
Ellen Price: um each bubble on this plot represents a chemical species in the model i've labeled a few but you'll see that.
Ellen Price: you'll see in the minute that they've been colored by the heaviest atom in the molecule so orange, for example, corresponds to carbon and the blue ring actually refers to the fact that it's a hydrocarbon which could have been scientifically interesting.
Ellen Price: Species but fall along the great ash fine didn't see an appreciable change in their abundance in the dynamic this model where we follow the introductory versus a static this model where we hold the packets fixed in space.
Ellen Price: All you can see that water and carbon monoxide fall into this group, where they're very abundant but they see very little change depending on on the movement of the parcel.
Ellen Price: But for someone less abundant species, we start to see pretty well variations around the line meaning enhancement above the line or depletion bloodline and you'll see actually formaldehyde sort of down the bottom.
Ellen Price: is particularly depleted in this particular panel.
Ellen Price: As you move further to the left of the plot the sort of variations around the line aren't as scientifically important because the species aren't as abundant.
Ellen Price: So an enhancement or depletion isn't a significant for something that wasn't very abundant anyway, unless it's several orders of magnitude, but you can see that there are a few of those two.
Ellen Price: So what does all this mean of this indicates that accretion is an important process to simulate.
Ellen Price: But we can't predict, from the beginning, what affects the would be effects of adding accretionary particular model will be now when I put this plot, in the context.
Ellen Price: you'll see that.
Ellen Price: The there isn't a clear trend among all these four panels with the color with the species it's It really seems pretty random, and of course it's not random it's based on a simulation.
Ellen Price: But all I really want to tell you is that accretion does turn out to be very important for the simulation we just can't predict it the beginning.
Ellen Price: What speeches will be enhanced, which ones will be depleted which ones, you know change um so you know if you're a modeler take accretion into account.
Ellen Price: Oh now let's move on the next project where we'll have to take a very different modeling approach on this project also results in a more testable hypothesis about the prevalence of carbon monoxide enhanced comments, but we'll get to that in a minute.
Ellen Price: So the idea for this work I can't take credit for it really it was else's idea comes from the fact that we have just a few observations of comments for the carbon monoxide, the water ratio is particularly high.
Ellen Price: So if you're i'm just pointing with an arrow to the carbon monoxide bar on this plot i'm comments usually have a pretty low carbon monoxide abundance as its shown in this bar graph.
Ellen Price: you'll notice that this plot is on a log scale, so the carbon monoxide is going to be around 1% relative abundance to water, with a maximum observational little over 10%.
Ellen Price: And yet we have this small population of comments for the seal abundance is much higher than that.
Ellen Price: too I Borisov is an interstellar a comment or a comment from another planetary system but see 2016 are two pan-starrs originates here in our own solar system.
Ellen Price: We wanted to know dust drift could explain these observations, without invoking special physics or extraordinary local conditions.
Ellen Price: One of the explanations for to enforce offs unusual compensation is that it could be typical of its own system, maybe it just had more carbon monoxide.
Ellen Price: That doesn't help us explain the other one that originates here a much more scientifically satisfying explanation would apply to both columns.
Ellen Price: So why does just drift at all i've mentioned district, but I haven't told you why so does drifts because solids don't feel pressure force the way gases do.
Ellen Price: The solids want to orbit they complain velocities, which I represent here, by a very narrow.
Ellen Price: Pressure forces make the gas gas orbit at a slightly some capillary and velocity represented here by a blue arrow.
Ellen Price: The solids will feel a headwind from the gas, which is the difference between those philosophies are presented by the orange arrow when that happens, the solids will lose angular momentum and begin to drift towards the star radio.
Ellen Price: So i've mentioned before, that we can use a local simulation for the last project, because the equation streams never cross each other.
Ellen Price: Once the dust is decoupled even slightly from the gas that just isn't the case anymore so for this disk we chose to use a produce chemical network.
Ellen Price: So this model only contains CEO and water, but it includes the full physics, that we wanted to simulate the physical model actually comes from a semi analytic prescription for districts, taken from.
Ellen Price: So, in the last project we use an iterative method to solve for the temperature structure like I should.
Ellen Price: And that was possible because we only needed to run a small subset of the simulation to get the surface density evolution.
Ellen Price: Unfortunately, that simply isn't possible for this project, because we need to run the entire simulation just to find the best surface density, but just what matters for the temperature evolution.
Ellen Price: So we don't want to run this this entire simulation multiple times it's computationally expensive.
Ellen Price: Instead of doing that, we took a similar approach, we were inspired by a classical paper by changing gold right, as well as the assumption that the surface density doesn't evolve too much over the disc lifetime.
Ellen Price: So we just ran the random see 3D coat on the initial condition and then scale by a factor F, the depends on the seller radius and temperature.
Ellen Price: As the young star evolves it contracts and becomes harder changing the factor F, with time i'm showing a plot of the two regimes we found in the eyes of crumbs used to compute F an interpolation between them that just moves things out over time.
Ellen Price: So here i'm again showing just one panel of a bigger plot to give you a flavor of what's involved in the modeling.
Ellen Price: We need to track the surface density of gas, just like before and that's what i'm showing here for our for mutual or sort of normal this model.
Ellen Price: All you can do as a surface entity falls off rapidly at large rainy I like it should.
Ellen Price: The different colors are showing you snapshots at different times up to 1 million years and the lightest color, but when we put this plot in context, you can see the interesting features develop in the surface entities of the small desk and larger pebbles.
Ellen Price: The two solid sizes that we considered as time progresses, this has to do with how differently sized screens will drift at different speeds, according to a dimension last number called stokes number.
Ellen Price: Okay check revealed that the gap like region in the surface density opens where the stokes numbers about one we're grateful address the fastest.
Ellen Price: Each column of this finger corresponds to a different parameter configuration and i'll talk about that more in a second.
Ellen Price: um the roads are the different surface entities gas at the top, that was in the middle that's at the bottom, so you can see, we really do need to track all all of these to get a full flavor of the simulation.
Ellen Price: So finally i'm going to show you the main results with this paper skipping over any remaining methods and almost every combination of parameters, we tested we tested several.
Ellen Price: We found that it's possible to get a region of enhance CEO in the single panel, you see the log of the CO2 water ratio over space and time that funnel shaped purple region is where CO2 water is about one.
Ellen Price: on the side of integrated over space, so you can just see how the total budget evolves with time, nothing was caught in his place, you can see that the funnel feature persists are various parameter changes.
Ellen Price: And all of these are labeled by the parameter that we changed we experimented with the initial amount of seo the viscosity the drift efficiency and the temperature and and the feature persists, except maybe in the low CEO case where it's not a strong.
Ellen Price: So here's what we think is happening.
Ellen Price: What are isolating grains are drifting in words at the beginning of the simulation meanwhile CEOs inside it's the line and supplements off grains and back into the gas phase.
Ellen Price: The snow line is where sort of the radial tipping point between solid and gas, so when CEOs inside it's the line it's going to supplement into gas face.
Ellen Price: This is spreading, if you remember that from earlier carries the CEO gas back across this nine where it's going to freeze on whatever greens and left.
Ellen Price: So this creates a region where water is already left but CEO is just freezing out mean that we haven't had CO2 water.
Ellen Price: This cleaner robust results shows that maybe co enhance comments artists, whereas we thought so almost like form at the right place in time in the disk.
Ellen Price: On this paper was just accepted and should be published in an object and in the future, we hope to add brain growth and fragmentation, to the model, as well as some simple chemical reactions and working with species.
Ellen Price: So switching gears just a little bit I mentioned in the beginning of this call that there are lots of exoplanets with the confirmed once numbering in the thousands.
Ellen Price: But I didn't say how they're discovered, and I think it's important to have a little more context on that before diving into the next section, which will be about planets.
Ellen Price: Here i'm showing the kepler telescope which exceeded expectations and its primary mission before sadly losing control of too many reaction wheels.
Ellen Price: After that, the K two mission allowed more planets to be discovered by balancing the telescope no longer able to balance itself against solar radiation which is just really cool.
Ellen Price: Here i'm showing these so called kepler ori.
Ellen Price: Which is not a video that I made it has the attribution up at the top i'm Basically, this is showing the variety of different planetary systems that kepler discovery over its lifetime.
Ellen Price: And you'll see that some of them are you know much smaller than our solar system, the solar system has shown with the dashed lines for reference.
Ellen Price: you'll also see that you know, some of them have have really big planets some of them have very small planets.
Ellen Price: it's really just just stuff really diverse that's really, all I can say about this and that's All I want you to take away from this movie is that kepler discovered very diverse exoplanets all throughout wealth all throughout the galaxy in the one spot that it was looking for them.
Ellen Price: So the currently active exoplanet searching telescope is test the transiting exoplanet survey satellite.
Ellen Price: It is appropriately imagined here in front of a lava planet orbiting it star because we're going to get to extreme exoplanets like that one in a few minutes.
Ellen Price: Like kepler it's looking for transit light curves of exoplanets but exoplanets are discovered through other methods like direct imaging renew velocity surveys and even microlensing these days we're going to stick with the transit method for this work, though.
Ellen Price: So we're going to switch gears talk about planets and we're going to specifically focus on planets that orbit very close to your stars.
Ellen Price: See you probably remember from a middle school science class the earth has a core a mantle and across these multiple layers mean the Earth is differentiated.
Ellen Price: And, most of them that are exoplanets do the same and also differentiated for this project will consider planets that have iron which course maybe larger than our score.
Ellen Price: And one would let the upper layers like cross oceans atmospheres entirely so in this picture the whole planet is just the Irish core and the silicate mantle.
Ellen Price: Now, when this planet is very close to it start what's going to happen.
Ellen Price: If it's not ripped apart, it made a form assuming a non spherical shape.
Ellen Price: Now, getting this close to your star isn't a theoretical situation at all our model planet is kayla 18 43.03 which wasn't around at star every 4.2 hours and let's just take a second to appreciate that fact a year for kayla 18 43.03 is just 4.2 hours for us of crazy.
Ellen Price: This discovery paper, where I grabbed this table also estimated the radius of the planet, but they didn't take into account the possibility of a non spherical shape.
Ellen Price: To 18 43.3 belongs to a class of planets called ultra short period planets or usp planets which have orbital periods, less than a day in our paper we analyze a few other usp plan it's the.
Ellen Price: Has the shortest smell orbital period today so i'll just focus on that one for this talk.
Ellen Price: So I mentioned before, that was possible for the planet people depart and the rush limit is the radial tipping point between the planet surviving and being destroyed the equation i'm showing is a very classical result um it comes from a very old paper by Roche.
Ellen Price: But it assumes a constant density incompressible fluid body we know the earth isn't constant density or incompressible so if we sort of assume that our exoplanets are somewhat like Earth.
Ellen Price: we're going to assume that they aren't constant constant density or incompressible either we're going to need a more sophisticated approach if we want to simulate new planet shapes.
Ellen Price: So we base our method on an older paper which was actually interested in modeling stars and multiple systems.
Ellen Price: stars like planets could be pulled into non spiritual shapes by the strong gravitational field of the companion.
Ellen Price: But the key differences between the methods are that first we needed to break a particular cemetery in the system to add a stellar companion to our planet.
Ellen Price: And second we needed to use a different equation of state or a function that relates them to be in pressure.
Ellen Price: rocky planets, just like the rocks in your backyard have a nonzero density at zero pressure me equation of state used by the cheesy the authors that paper for polly Tropic stars has zero density of zero pressure.
Ellen Price: For some of our mineral sin, we chose a simple modified polycom equation of state which is described in this paper secret l 2007.
Ellen Price: Which just adds a constant to the classical poly trope and creates the desired effect once we've chosen our minerals and their equation of state the procedure goes like this.
Ellen Price: We start with some density for the whole planet it doesn't need to be an accurate guess, so we could just pick confidence V sphere lead as an example, then we compute the gravitational potential of the planet.
Ellen Price: it's important to remember that any extended body exerts a gravitational force on itself and so has a gravitational potential.
Ellen Price: This step is by far the most computationally intensive part of the calculation and we spent a lot of time figuring out how to do it and optimize way.
Ellen Price: Next week compute the Info B, which depends on stellar gravitational potential and centrifugal potential remember that the planet is spending very quickly around it start.
Ellen Price: And by enforcing the right boundary conditions on the envelope view we can compute the consistent seller properties, like the stellar mass.
Ellen Price: It will be can be converted to density and the cycle continues until it converges usually that takes a few iterations.
Ellen Price: So one of the coolest results of this modeling is that by assuming kale 18 43.03 is at the Roche limit, we can say something about it's probable composition.
Ellen Price: We took a large sample of planets simulated with pure iron cores and silicate mantels and generated this plot from the ones that were just about to be pulled apart.
Ellen Price: The different colored lines here are different compositions yellow is more silicate and black is more iron.
Ellen Price: The vertical Gray line here represents the range of parameters for kayla 18 43.3.
Ellen Price: We can see that measured transit radius an orbital period correspond to the composition of about 70% iron by mass with some margin for error allowed for the error bars on the transit radius, which is why it's a vertical line and not a point.
Ellen Price: But when we change the core composition, the iron sulfide something interesting happens note that I have the same line here in the same place.
Ellen Price: Now kayla 18 43.03 is only compatible with the pure iron sulfide core if it's radius measurement is a little off, and it would essentially be pure iron so fun.
Ellen Price: We can't rule out that composition, but pure iron sulfide cores are a very extreme case anyway.
Ellen Price: The earth score, for example, is polluted by light element, maybe sulfur, but it is a pure iron sulfide by testing the to end Member cases of pure iron and pure iron sulfide we gain some insight into what could happen at an intermediate composition kind of like that, as the earth's core.
Ellen Price: In general, as we make the core of the planets more massive keeping constant radius they become less distorted.
Ellen Price: Even then kayla 18 43.03 could be almost pure iron and still be distorted because it's been such an extreme environment.
Ellen Price: aspect ratio on the y axis here is defined as the long radius of the planet along the planet star access to the short radius of the planet towards the polls.
Ellen Price: If we measured Saturn the same way as an example, it has an aspect ratio of about 1.1 and I think that's the most extreme one in the solar system.
Ellen Price: So i'm a lot of drama how a few of these planets might look if you slice them open down the middle.
Ellen Price: You can see the more distorted the planet, the more mantle that has the mantle in this case is form of silicon and specifically for off sentence to type.
Ellen Price: And that's more easily to forms an iron after the previous sections, you might well be wondering how planet like these usp planets could possibly form and, quite frankly, we don't know.
Ellen Price: There are several theories, but there's no definitive answer yet so stay tuned because we might figure it out.
Ellen Price: Finally, i'm going to present very quickly some work in progress modeling the transit shapes of distorting planets.
Ellen Price: You may already be familiar with the transit method of discovering planets as a planet moves across the face of it, star some amount of light from the stars blocked, resulting in the character this characteristic shape and think at the bottom.
Ellen Price: This is a transit light curve of the ingress and egress part of the transit which i've highlighted here.
Ellen Price: Are where the planet is only partially covering this color disk and between those times there wouldn't be any difference in flux, is the star were perfectly uniform.
Ellen Price: it's not and we'll get to that later, but for now, you can assume that the transit will mostly look like this first vehicle planet.
Ellen Price: When the planet is no longer a sphere, though, something really cool happens the projected area of the planet changes as it moves around the star.
Ellen Price: producing this characteristic the wii U shaped transit gonna play that again a little slower and I want you to watch the Cross section of the planet, as it crosses the star.
Ellen Price: You can see it becomes a circular area at the midpoint as elongated into an oval elsewhere that's what produces the bump in the middle of the transit and it's also see this is exactly what happens when we simulate these transits.
Ellen Price: to measure the transit shape personally to transit we're using a sophisticated Ray tracing library and specialized hardware.
Ellen Price: But rephrasing is actually a pretty simple concept understand we simulate virtual photons or raise being emitted from a stellar disk so shown here on the right and orange.
Ellen Price: Let me check to see if the razor blocked by the planet we some of the photons that make it to some virtual detector shown here and blue and normalize and we're done well in for the normalize flux that's the sum of all the photon fluxes that make it to the detector or observer.
Ellen Price: So let's finally look at some simulated distorted transits again these results to kind of preliminary but they're so cool.
Ellen Price: As you can see the characteristic w shaped is present they're not flat.
Ellen Price: The curves are colored by the CNS of the planet, yellow in this case corresponds to the nearly pure iron case and black corresponds to about 70% higher.
Ellen Price: than if I felt the difference between the distorted transit and simple standard model which is shaped like a trap avoid.
Ellen Price: We see that the maximum discrepancy is maybe 100 parts per million, which is the same as the transit death itself roughly.
Ellen Price: So you might need some very specialized equipment to actually measure this effect for a real planet and that's something we're looking into.
Ellen Price: In addition to increase sensitivity you might also need higher cadence or frequency of observations, then we would get with kepler tests, again, this is something we're looking into.
Ellen Price: Now real stars aren't uniform discs like what I use and the Ray tracing and and the examples limb darkening as the name suggests, darkens the limb or edge of the star compared to the Center which changes the intensity of the photons as a function of the angle around the star.
Ellen Price: Furthermore, if the planet doesn't cut the star exactly at the Center but instead crosses at some other height along the desk.
Ellen Price: will see a shadow or transits and so lemons darker I know also be shorter, since the longest path across the star is the diameter, the effects of limbo marketing and transit inclination both need to be explored before this paper is going to be ready for publication.
Ellen Price: So finally let's just wrap up quickly.
Ellen Price: I hope i've successfully communicated these four big ideas to you, but you might still wonder how all this work that's together in the Grand scheme of things in one sense i've shown you for projects that span two different topics, but consider the following.
Ellen Price: We don't understand completely how planets, for we theorize barriers to planet formation that are obviously overcome we see exoplanets but we don't yet know how.
Ellen Price: studying this some plans together is, how will hopefully fit the pieces together and gain a deeper understanding of our place in the universe.
Ellen Price: So i'm not saying it all that I have everything figured out, but I think studying planet formation from both sides from this and from form planets will be really important as this field moves further.
Ellen Price: So I have a few ideas for what i'll do next rate equation chemistry, is what I use throughout my disc projects, but it only applies in certain limits and when we relax those assumptions things become very complex very quickly.
Ellen Price: Great growth and fragmentation are important phenomena for planet formation so it'd be a great step forward to incorporate those into the grain drift model I presented earlier.
Ellen Price: Now, if everything goes well today i'll be heading to the University of Chicago to work with Professor friend ciesla funded by a 51 pegasi bs postdoctoral fellowship from the highest and simon's foundation to pursue projects like these time listening and more.
Ellen Price: So with that i'll conclude and thank you for your time.
Karin Oberg: That was a beautifully crafted talk Ellen well we're worthy of the beautiful science that you were showing so, the floor is now open for questions.
Karin Oberg: theron.
Theron Weng-Hong Carmichael: healing great talk OK, so my question is about the work that is most preliminary but i'm curious I think it's a simple one, so you mentioned that the magnitude of the w shaped for the when you have a distorted planet transiting right is roughly 100 parts per million.
Theron Weng-Hong Carmichael: So that's where something about the size of the okay ky 18 something.
Theron Weng-Hong Carmichael: So if you what if you did that for you giant planet somebody is that is that magnitude larger enough that you know you expect that to be a lot easier to sort of explore that just that phenomenon of a distorted planet moving and try and and.
Theron Weng-Hong Carmichael: Using your technique to like understand that better.
Ellen Price: yeah, so I think that work is actually already been done and I couldn't tell you the reference off the top of my head, but someone did do this for giant planets already.
Ellen Price: i'm sort of seeing what their shape would be and what a transitive them and look like our results are pretty much consistent with theirs, and that, like there is a distortion, but obviously it's not as big.
Ellen Price: Also, I will point out that, even though the distortion is about 100 parts per million it's not necessarily at the Center of the w shaped it actually might be in the ingress egress part.
Ellen Price: Which is interesting and not what I was expecting um so the actual the depth what you're talking about if this row Center of the w is actually probably different and less so when I say we need sophisticated equipment i'm not kidding.
Karin Oberg: Jennifer.
Jennifer Yee: hi on that was a very interesting talk, I was also curious about the transits since you're dealing with these ultra short period transiting planets are you in a regime that you're getting like weird other relativistic effects because there's like some weird stuff that happens to transit.
Ellen Price: There is a.
Ellen Price: cleansing and.
Jennifer Yee: Some other staff.
Ellen Price: Like sort of having flashbacks like the rossiter mclaughlin effect, I don't even know if that matters here but that's one of the ones I remember from back in the day we haven't thought about that at all, but that's a great question.
Ellen Price: um we're sort of just simulating like literally just the blockage of light from the star right now, but it could be interesting to see if you know for such a small planet if those effects matter I honestly don't know.
Ellen Price: I would hope they wouldn't because that'll probably be things like limb darkening is like to but we'll see.
Jennifer Yee: Okay.
Jennifer Yee: Thank you very clear talk.
Karin Oberg: Are there any additional questions for for Ellen.
Karin Oberg: I don't see any other race hands are one.
Karin Oberg: Please.
Karin Oberg: We can't hear you still having microphone image.
Irwin I. Shapiro: I keep forgetting to unmute i'm sorry.
Irwin I. Shapiro: I may have misheard you, but I thought at one point, you said something like you are considering 640 different kinds of molecules.
Irwin I. Shapiro: Yes, but yet you seem to only discuss a couple.
Ellen Price: Yes, so in the paper we go into a little more detail about a couple of molecules um I think.
Ellen Price: The more important result is just that there isn't a clear trend with with the composition of each molecule.
Ellen Price: So we can't really say anything definitive about like Oh well, if you include accretion formaldehyde is is enhance we can't say that.
Ellen Price: um, so I think the the bigger issue is just seeing that there isn't really a trend um That being said, like technically, we have all the data to see exactly what happens to all 644 species that we can simulate.
Ellen Price: But i'm not sure you know, since there isn't a clear trend it's difficult to tell a cohesive story unless you pick out a few that you're interested in.
Irwin I. Shapiro: You do it all worry about the interactions between the molecules so that, for example, what the sensitivity would be of your results to leaving out some of the molecules.
Ellen Price: I mean when you say worried.
Ellen Price: I try not to worry but i'm certainly it is possible if we've left out some chemistry that actually is important.
Ellen Price: Even though we try to be as comprehensive as we can with this particular network, it could be the case that we're missing something important and then.
Ellen Price: All of this could be wrong, I guess, but we try not to worry about that too much people much smarter than me put together this network, and so we sort of just use it and trust that it's it's probably as.
Ellen Price: as comprehensive as possible to be right now.
Irwin I. Shapiro: I was just thinking of the sensitivity, so that you could see, for example, if you'd omitted some what effects they may have.
Ellen Price: I mean it's it's kind of hard to say it would depend on the kind of the reaction um and even then, there are a lot of numerical.
Ellen Price: Issues that came up with that project, including an interesting one, where the order of the chemical reactions as they were entered into the network actually mattered for some reason.
Ellen Price: which was horrifying until I figured out why that happened.
Ellen Price: So, certainly, it is possible, even with these small seemingly insignificant tweaks to get slightly different results and um yeah we were just need to test it on a different chemical network or rube important chemical reaction see how see how things changed.
Irwin I. Shapiro: Thank you.
Karin Oberg: Any last question.
Karin Oberg: Gary please oh.
Gary Melnick: ELENA was a beautiful talk, I very much enjoyed it, I may have missed it because I got called away for two minutes but i'm wondering if you could say briefly.
Gary Melnick: The effect of cosmic rays on the results, I know you mentioned it briefly, but obviously these discs are forming planets all over the galaxy.
Gary Melnick: And in different cosmic Ray environments, presumably so i'm just wondering if you could summarize, in a few sentences, the extreme differences, you see as a function of cosmic Ray rates.
Ellen Price: So basically what we think is happening with the cosmic rays, is essentially.
Ellen Price: A packet that starts further out in the disk is going to be exposed to more cosmic rays, then when it gets to the interior of it is because the surface density there is higher.
Ellen Price: So what we did is we actually were able to track back for back through time what was causing some species to be enhanced, and all of them seems to trace back to an initial cosmic Ray ionization.
Ellen Price: And then the subsequent train of reactions as things warmed up and the packet moved inward and that's why I mentioned the cosmic rays um basically the fact that a packet is exposed to cosmic rays beginning of its lifetime and then warms up towards the end.
Ellen Price: Really enable some different chemistry than what we would have seen without the cosmic rays, we also did test a model with higher cosmic rays, we didn't talk about it much in the paper we also took out cosmic rays, to see what would happen.
Ellen Price: And I think we just confirmed that basically cosmic rays are driving a lot of this this chemistry.
Gary Melnick: Thank you.
Karin Oberg: So I that brings us just a little bit past the hour so so perfect timing I don't see any additional hands raised, and so what will happen next, is that well, first of all, if you want to unmute again and again congratulate Ellen on.
Karin Oberg: This beautiful presentation.
Karin Oberg: And me especially for ellen's friends and family that are calling in what will happen next, is it will go into private Defense with the committee.
Karin Oberg: And you know if everything goes well there will then be.
Karin Oberg: In those zoom celebration later and afternoon, so those of you have to see a look for the thief a.
Karin Oberg: Wide email For those of you who are not the CFA i'm counting on ELENA will indeed forward to the information so if she doesn't you know bite her about that, and that will happen servant into early or the afternoon.
Karin Oberg: But yeah without further ado fantastic work and Ellen and the committee, I think.
Karin Oberg: Committee will reconvene and I think about six minutes or so, and if you don't if you can't find a link email me and i'll send it to you.
Karin Oberg: Take care everyone.
Ellen Price: Thanks for coming everyone.