Melina Rice
HWO working group update: Exoplanet Demographics

All right.
So we've gone from excited about planets with hwo to excited about stars all the way back to excited about planets.
So I will be speaking about exoplanet demographics and also architectures with hwo.
I am Milena Rice.
I'm an assistant professor in the Yale Department of Astronomy, and I also lead the efforts looking at the demographics and architectures science cases that are being developed with HWO, in conjunction with Jesse Christensen.
Is also leading a sub working group that has been looking into these science cases.
I wanted to mention that this is a small part of a much, much larger effort. Oh, I don't.
It's just a lag.
So there there are quite a few science working groups that are currently working on hwo science cases and that have really just submitted their science cases for review.
This is the different science working groups that are under the umbrella of Hwo efforts right now and we.
From Eric a bit about living worlds that has several self working groups within it, and so Eric is one of the Co leads of this target. Stars and systems group.
What I'm going to be talking about is this demographics and architectures group.
That's the third down in the pink column, but I just wanted to really highlight there.
There's a huge amount of effort that is going into hwo at the moment and we're really just talking about a pretty small subset in this particular talk and also that, that, that effort is not restricted to exoplanets and so quite a bit of it is.
The the name might make it sound like it's an exoplanet mission, but there's actually a huge amount of work that's being put into looking at at galaxies and stars and other science cases that are beyond exoplanets themselves.
So the demographics and architecture is a working group is actually under this umbrella of solar systems in context that's being led by Azanya, Shkolnik and Ty Robinson.
I have them to thank actually for some of these slides.
So thank you very much for letting me use them and we have several different subgroups within that that are are looking at different aspects of planetary systems.
This is just the goal.
Of solar systems in context more broadly, which is to develop strategy to answer solar system and exoplanet science questions.
And what we're really trying to do right now is develop a vision of what we want, hwo to do and sort of our best case scenario, what are the things that we hope to be able to accomplish in the twenty 40s with hwo that we don't expect to.
Be able to accomplish with any of the other missions leading up to that, and then after that, figure out what? What is it going to take technically to actually make some of those things happen and what is the give and take.
Of what we expect to be able to realistically accomplish, in addition to sort of these visionary goals of.
What we think would be really amazing to have our next flagship mission do. So the science case development documents are really starting off with you know, what are our lofty goals.
What are the things that we want to be able to accomplish and then go digging into?
What does it actually take technically to to make those things happen?
There are a lot of people who are interested in exoplanet science with HW. Many within this room as well, and quite a few people who are directly working on these science case development documents that.
Were recently turned in.
That are now being in many cases actually turned into papers, and so we'll talk about some of that as well.
So just within solar systems, in context, this is our list of the the Scdd science case development documents that have been developed by this group.
I'm really just going to be focusing on this demographics and architecture subset that's at the bottom.
So we have 4 different science case development documents that we submitted that are really guided by these after 2020 goals.
So. So what are those big questions that we're trying to address and and what are some of the things that we?
HW is going to potentially be able to do that. Will not be done before that.
OK.
So our sub working groups specific goal is to synthesize current knowledge of exoplanet occurrence rates and system architectures for the types of stars the hwo will target.
This is largely fgkm and to assess the sensitivity and accessibility that is required to constrain system architectures.
So in addition to looking for those earth like planets that are in the habitable zones of nearby stars.
We are also really interested in figuring out what are some of the fundamental questions that we can learn about the demographics of what is a typical planetary system like and what what do these architectures look like and what can that tell us not only about habitat.
But also more generally about those planetary systems.
So these are the the members of our sub working group which is small but mighty.
It is led by myself and Jesse Christensen, but really the bulk of the work that has gone into what I'll be talking about has been through these leads.
Sarah Blunt at UC Santa Cruz.
Eric Nielsen at University of New Mexico, who fled an earth like atmosphere.
Demographic science case Sabina Saganbaev at Stony Brook, Stephen Kane at UC Riverside working on giant exoplanet.
Evolution, tanzu, Dalen, Washington University and Romey Rodriguez at CFA. Looking at occurrence rates of small exoplanets and Elizabeth Newton, our mighty lead on this hefty topic of occurrence rates in binary systems.
OK.
So I'll talk a little bit about each of those.
So. So these are just brief overviews of our our four science cases that we have been working on. The first of those is looking at occurrence rates of small exoplanets and specifically this question of what fraction of small habitable habitable.
Own planets exist in architecture similar to that of the solar system, so we're interested in not just how common those exoplanets are, which is part of this question, but also what the context is within which they lie. Looking at which of those planets have outer giant planets for.
Example, potentially even pushing to some of the smaller planets that that are not just the earths within those planets as well.
So we've got Mercury, Venus and Mars within the solar system too.
So the the main goal there is really just to find those, find those planets in the first place.
So the contrast is really important, as is sort of the range of where you're looking.
So in the figure we're seeing semi major, a major axis versus distance and this is sort of a red histogram of where the star.
164 star except list fall as well as just where the solar system would lie. For context, at 10 parsec distance and you can see the angular separation of planets as a function of of these other properties to see if you have a set inner and.
Outer working angle and arc seconds.
What would you actually be able to see with that?
So the science case is really probing what we would need in terms of the the field of view.
As well as the contrast sensitivity, though that we'd need to address this case.
The second one here is looking at occurrence rates in binary star systems.
So we know that 50% or more sunlight stars and higher mass stars are actually in binary star systems, which means that earth like planets around those stars will not necessarily follow the same demographics that they do in single star systems.
So the big question here is whether the formation of potentially habitable planets is suppressed, enhanced or unaffected by the presence of a stellar companion, which is probably at least to some extent a.
A function of the distance of your stellar companion.
So this is just some of our breakthrough requirements of what we actually expect to need to be able to do the the main limiting factor is probably whether you can actually suppress the Starlight of your companion star and avoid having substantial additional contamination when you're looking at a.
Star of interest for planets there. And that means that if you're not able to look at, for example, these very close separation binaries that are.
Three to five arc seconds as our sort of optimistic.
Like you would probably need new technology to be able to do that, whereas outside of 10 or seconds you probably don't.
We we expect to be able to accomplish that and orange is sort of in between. But if you if you need to look at the wider binaries or or the ones that are at these wider separations that's going to substantially change your target stars list. And so this.
Is sort of looking at what volume do we need to be considering targets for hwo in order to actually consider those binary systems and.
Also be able to answer questions about occurrence rates in those binary systems.
So another science case we've been looking at is in addition to just individual planets and what their atmospheres look like, figuring out at what point these earth like atmospheres actually arise.
So if we have oxygen on our planetary atmospheres, when that oxygen actually shows up, and if it's common for our planets to get these oxygen rich atmospheres kind of early on.
Or if they don't typically arise, if if they're very prevalent or or very not prevalent throughout.
And so this is again some of our breakthrough requirements, something I really want to highlight here is that UV coverage is really important to get this.
25 Micron ozone feature in order to be able to actually get those oxygen detections.
And here we we are specifically interested in looking at ages as well, which is really more of a precursor science case where you would need to characterize those stars in advance of hwo.
But we expect to need to push actually the number of stars that were looking at a little bit and the number of detected Earth analogues to be able to put really good constraints on these atmospheric demographics. So just.
An example simulation of how we actually quantified this.
Here we're looking at in Gray in these left panels, just a distribution of the mean and standard deviation of an assumed universe, where oxygen tends to arrive at something like 2 billion years with some standard deviation. And in that case you would expect to get some number of.
Of oxygen that happen after that Gray line and then non detections that are at or before that Gray line and what?
What Sarah did was she simulated looking at the number of Earth analogs that you have in your sample versus the age precision to which you know how old your stars are, how well you can actually constrain the the mean and the standard deviation of the oxygen onset this.
Is actually a a paper that's in review right now.
Where what we end up finding is the punch line.
But it helps to have better ages.
So we we were looking at this optimistic case of about 20% age uncertainties for all of those stars.
But what really matters is being able to look at a larger number of targets and you you can see that the the uncertainties drop pretty dramatically as you start looking at beyond 25 stars going up to ideally about 40.
And then the last case that I wanted to talk about is looking at the orbital evolution of giant exoplanets.
And so Sabina Sagginbaeva and Stephen Kane also have a paper in prep looking at.
What we would need to do in order to characterize both the outer giant planets orbits as well as the inner planets, and so really the limiting factor here is going to be our inner and outer working angle.
And so we, we need to have a certain contrast.
We need to be able to detect those objects, but we also need to have a sufficiently large field of view to see not just one planet, but ideally more than one planet, and to characterize the orbits of both.
So. So they've done some nice simulations to actually look at how many epics you would need to return to those systems as well.
Generally they find about 6:00 to 8:00 ethics necessary to get useful constraints on those orbits and also provide good habitable zone characterization at that particular separation.
But this is going to depend a little bit again on the cadence of when you're doing those observations.
How spread out those epics actually are and exactly how eccentric, for example, and inclines your orbit is going to be.
OK. So general outlook, just a couple of takeaways.
Hwo has the potential to provide really transformative advances to not just the detection of individual habitable zone planets, but also our understanding of these architectures and demographics on a very large scale?
This probably is going to require us to look at more than the nominal 100 star search.
And so we've been looking into what what you can actually gain from from pushing the number of stars that you're looking at.
We we argue that there's a lot to be gained really, if you start going to at least 160 to 200 stars.
To get this diversity of systems and precursor observations are going to be really, really important. To lay this foundation for future HW observations to to really get the most out of hwo 20 years from now or whenever it launches. And some of the ones that we specifically point.
Out from from our science cases are we would love to get great ages, extended RV monitoring and stellar companion characterization.
And those are all really critical for.
This context for the system.
So I will end there and thank you all and I'll take any questions.
Thanks, melina.
Do we have any quick questions?
Sorry Jonathan Lane at JPL.
Is there any benefit that you will get from the microlensing surveys that will be done by Nancy Roman in the sense of providing the context for the proportion of systems that have giant planets in the right?
Distance range from their stars that you know would provide some of what we heard before in terms of habitability, lack of habitability and other things as well.
How would you fold that into your group?
Yeah, that's a good question.
So microlensing will be useful for figuring out for these wider orbiting planets how common you expect both the giant planets and the smaller planets to be.
And so, while it's not likely to actually give us the specific planets in these very nearby star systems, it will tell us what what to expect on a statistical level for similar types of stars.
And so it'll be useful for.
Guiding how many stars we actually need to look at to get the the science cases done that we're interested in.
So in in that sense, it will be extremely useful for just giving us like number wise how many stars you need to look at across different stellar types.
Unfortunately, that's all the time we have.
So let's thank Melina again. Thank you.