How to Form a Habitable Planet 3 21 23

our happiest lectures of the year with the bach prize award um because this is a chance to welcome back a graduate of the department who's gone off to do wonderful things and this year's awardee is Meredith McGregor who I hope many of you uh recognize from her time but Meredith was actually was here for quite a while because she was not just a graduate student but she was an undergraduate with us graduating in 2011. she won both the Junior and senior Goldberg prizes for research including a senior thesis with Edo uh and then she came here for a PhD and uh with David Wallner she won a graduate National Science Foundation graduate research Fellowship she won a bunch of different teaching accolades with her teaching and graduated in 2017 with a really I think a landmark piece of work on the discs with Alma she then went to be a NSF postdoctoral fellow and Carnegie post doctoral at DTM and finished there in 2020 and moved to the join the faculty at the University of Colorado in January 2020 very good timing got to meet your colleagues in person before the curtain fell but Americus has really distinguished herself uh since her thesis with her continued work in the formation and habitability of planetary systems uh Shield I don't want to steal her Thunder but I mean to me the the picture is from Alma of these protoplanetary discs I think are really one of the Highlight in just astronomical imaging in the last 10 years I'm not going to vote on the science exactly but you know I think aside from m87 maybe some folks might have might have a dog in the race but I really think that the picture is from Alma on the on the photo planter so just just completely evocative and I'm sure we'll see a bunch of those uh in the talk um and she's also made made her Mark in the uh impacts of Stellar activity on the habitability of planets and I think we'll hear some about that as well so let me uh Meredith for coming today we have uh certificate and uh and so thank you [Applause] okay let me put this over here um great it's fun to be back I realize this is the first time I've been back here since I graduated so it's like been a minute especially after I spent a whole solid 10 years here it's like a simultaneously weird Deja Vu feeling but like also it's different but it's still kind of the same so it's been an interesting 24 hours so um I gave this talk this like pretty vague and grandiose title that we're going to discuss how to form a habitable planet and the reason I did that is because my research group at CU Boulder is pretty diverse in what we work on um so we use essentially any telescope that I can convince someone to give me access to to try and understand all pieces of planetary systems so really trying to draw connections between these Planet flowering discs and the actual planets that form from them and the star that's in the middle that's irradiating everything and I always show this talk because a lot of the wonderful science that I get to show is now done by my amazing research group so here's all of the names of all of my students and our like Zoom covid picture because since I started in January 2020 most of my students started working with me on zoom and we had really fantastic Zoom group meetings and that is the picture we have um so at the moment I have uh three full-time grad students one who's doing um some side projects with me a postdoc five current undergrads and then three undergrads who've actually come done on a thesis and left all during the pandemic and so you'll see their names in the bottom of the slides because a lot of the things that I get to show are things that they've worked on as part of their projects okay so um I always start with an overview of how we form planetary systems here that's maybe not as necessary because there's a lot of expertise here but we'll go through the same the same thing so we think that planetary systems form from giant molecular clouds we're pieces of that cloud get over dense and they collapse and we form a new star and that star is surrounded by this disc of dust and gas we call protoplanetary disk this is the phase where there's enough material to actually form new planetary systems lasts for somewhere on the order of one to ten million years very large error bar on that and then most of that material is cleared away and we're left with a main sequence star any planets that formed during this earlier phase of evolution and then what we call a debris which is really kind of the remnant material left over so if you'd like compare those two populations of disks on the left these are all the d-sharp images of forming protoplanetary disks so these are all pre-made sequence Stars they have a lot of gas in them which is primordial material only time that we actually have enough material in these discs to form giant planets certainly and so I always like to call protoplendria sort of the reservoirs of Planet formation whereas on the right now these are all the images of debris discs these are main sequence Stars they do actually have gas in them at mostly lower levels and the picture we have is that actually these are sort of like our Kuiper Belt where you have asteroids and comets that are now colliding and grinding and as they Collide they also out gas ice and so we're seeing outgassed Co from these commentary collisions there's certainly not enough material to form giant planets here maybe we could form terrestrial planets and so I like to call it breed as sort of the fossil record of Planet formation because what's left the structure of these discs is really like shaped by the plant information process that happened earlier and we can observe all of these discs that across the entire electromagnetic spectrum so here are four Images all of the same debris disc this is aumek one of only one of a one of a few to breeders known around an m-type star the top image is taken with sphere so this is where we're actually seeing scattered light in the near IR off of tiny Micron sized dust grains and then if we move to the bottom panels This is Herschel Alma and the vla so moving out from 70 microns to a centimeter in wavelength where you're actually seeing thermal emission now from larger dust screens so we're tracing different emission mechanisms that we move through different wavelengths and you're also tracing different grain sizes and that lets you get this really multiply resolved picture of Planet formation right because we can spatially resolve these systems as a function of different grain sizes but of course a lot of the images that I get to show you are from Alma because Alma has completely revolutionized how we think about planet formation so here's Alma which we're all intimately familiar with um but really Alma has amazing angular resolution and sensitivity which allows us to take this gallery of debris discs which is pre-alma none of these images are from Oma and some things look interesting and a lot of things look like blobs and then turn them into the now Alma View where these are all the exact same discs and you can see that things that are blobs now have eccentricities and gaps and structure and we have a completely different view of the systems that we're trying to study okay so that's the disk introduction but I framed this talk is like how to form a habitable planet so what does that mean we astronomers really like to make the simplest definition of habitability which is this right we Define habitability based upon if I have an Earth-like planet with an Earth-like atmosphere where can I place that planet in its orbit that it will have the appropriate surface temperature to allow for liquid water on the surface so if I move the planet a little bit too close it's going to get too hot all the water is going to boil off if I move the planet a little bit too far away everything freezes and you get this nice observational test right we can go out we can measure planetary properties and see where they are in their orbits and we can say maybe they're habitable maybe they're not but there were a lot of descriptors that I put into that right I said it's an Earth-like planet with an Earth-like atmosphere and really habitability is a much more complicated picture right just moving in orbit around tells us some information but it doesn't really give us a complete picture of habitability and if we want to answer that question we need to get into a lot more details if I look at our planetary system technically there are three planets in the solar system that have at some point been in that habitable zone I would get Venus Earth end bars and only one of those has humans on it sitting in a cloquium talk so clearly something's different between these right Venus is a little bit too close in so it dried out the surface of the planet which made it not have plate tectonics and so there's no carbon cycle on Venus there's no CO2 cycle to actually pull CO2 out of the atmosphere so the atmosphere of the planet is 96 CO2 and it's a horrible place and Mars is a little bit too small so Mars cooled completely has a solid core and as a result it lost its magnetic field which allowed the solar wind to completely strip away the atmosphere of the planet so there's a lot of other factors that I'd put up if I wanted to tackle the question of is something habitable or not and where I like to try and do my work is using different parts of planetary systems to tackle some of these things that we can't get at by just looking at say Transit light cares effects of planets so let's I'm going to start with highlighting two different factors here oh the first is do other planetary systems have outer giant planets which seems like a really basic question to ask but we don't actually have the statistics to be able to answer this right now why do we even care so in our Earth's history where we formed would not have had any water built into the planet because we're within the snow line of the solar system which is actually out in the asteroid belt which means that all of Earth's water has to have been delivered to it and so you need Jupiter to suddenly go on this Motion in the outer solar system and stir things up in order to deliver water this is our typical exoplanet plot which shows the mass of exoplanets as a function of period and they're color-coded by Discovery method there's really like three main ways we discover exoplanets we can look for transits we're actually trying to look for the planet Crossing in front of the star we can look for radio velocities where we're seeing the star and the planet the planet actually tug on the star and seeing the shift the Doppler shift in the Stellar lines or in some cases we can actually block out the life from the Star and take a direct image in the exoplanet itself and all of these have some significant biases which you can see when you look at this plot right if we're looking for transits in RV we want to see multiple transits or multiple wobbles so you're biased towards looking for things on short orbits and for looking for things that are quite massive so you end up with this huge pileup of planets on like really short orbits and with RVs you end up with this giant population of like close in giant planets but we're completely missing the area that overlaps with where our giant planets are in the solar system right we're not detecting any Uranus or Neptune or Saturn analogues and a lot of that is just you know I'm not going to sit here for 140 years and look for transits we haven't even known about exoplanets that long so that means we need some other way to try and get a handle on the outer parts of planetary systems and where my interest lies is actually trying to use the structure of these evolved discs to then actually model that structure understand the Dynamics of it and say something about whether there could be giant planets that are shaping these disks okay so if you imagine having a planet sitting on the inner edge of an outer debris disc it's going to gravitationally perturb that dust and you might expect to see structure there right things like eccentricities or warps or resonant clumping and we do see this in some systems right the left here is beta pictoris which has a directly imaged exoplanet in it and the exoplanet is on a tilted orbit relative to the plane of the disk and so there's actually a warp in the inner part of the disc caused by that planet and even in our own hyper belt the kyber belt that we Define as the classical Kuiper Belt which is the red and the Blue Points here is actually very narrow and it's narrow because it's confined between orbital and resonances with Neptune so as the solar system had its initial dynamical instability and everything moved outwards Neptune basically snow plowed all this material into these resonances that has been maintained in so it's not crazy that we might expect to go look at other debrita C structure and then model that and be able to say something about planetary systems so let's look at some examples of debris discs what do they look like so this first disc is formal hot fomo hot is one of the most famous debrideous it was one of the first ones imaged it looks a little like the eye of Sauron in this Hubble image and Omaha is interesting because it's eccentric so the diamond there is showing the center of the disc and the star is then labeled by the white symbol and they're offset there's it's enough of an eccentric disc that you can visibly see the offset between the center of the disc and the actual Stellar position and it had a tentative directly image Planet which then is now maybe a dust Clump because it's not present in the current Hubble images but it was an intriguing system if there was really a planet orbiting on the inner Edge causing this eccentricity so back in my PhD work we made the first sort of millimeter map of this uh which was a mosaic image made with Oma and so I've overlaid that on top the pink here is now the disc Center so you can still visibly see that offset between the center of the disc and the star and then there's the planet question mark and we now have new data from Alma which one of my grad students is working on analyzing right now so the disc is visibly eccentric right it's clearly eccentric and what you notice is that actually it's brighter at the epicenter side of the disc than the Perry Center side of the disk so when I play with a super elongated elliptical orbit here planets on elliptical orbits actually move slower at Apple Center farther from the Star this is keplerian Dynamics and they move faster when they come closer to the star and so if you imagine a lot of comments that are all in eccentric orbits they're going to move slower at the Apple Center side faster at Perry Center and you would predict that there should be a surface density difference in the disk that you'd actually see the surface density be higher at Apple Center than a Perry Center because now you're probing the material from the disk what's interesting is that now with these new images we can get even better resolution so we're down to having roughly 1au resolution and depending upon the planetary orbit that's interior to that disc If there really is a planet shaping it you actually don't just predict that there should be this difference in surface density but that you should see as a methyl change in the width of the disc because depending upon the planetary orbit like in our solar system you basically pinch the orbits at Perry Center with Neptune a lot of these eccentric hyperbolt objects all have the same pericenter position and then they extend their orbits and Alpha centers so you actually end up seeing this like difference in the width of the disc as you go out so what I've done here is taken that Alma image but I'm only showing the Perry Center and the alpha Center sides and like flashing between the two of them and you can actually see that with this there's a significant difference between the width and the surface density profile between epicenter and Perry Center so for the first time we're actually like really probing down to the resolution we need to consider those Dynamics okay so there's also other structures we might see in disks that are shaped by planets one possibility is that planets might carve out gaps in a disk like we see in those d-sharp images so this disc was studied again with Hubble and what was notable about it is that it's actually two times is extended on the right side as it is on the left so it's like twice as extended on the right as on the left side and that was thought to be because maybe this disc is interacting with the interstellar medium that it's actually like colliding with a dense clump of ism gas and it's like dragging grains out in some kind of ram pressure stripping so we imagined it with Alma to try and see where the larger particles were like where are those millimeter size grains so now on the right is the alma image and then it's overlaid as Contours on the left surprising if it looks nothing like the Hubble image at all in fact there's no evidence of this extension in the alma image and instead it looks quite Blobby I stare at pictures of discs all the time but not everybody does so we get my donut primer so if you imagine the left disc is totally faced on it has a zero degree inclination if I pick any line of sight through that donut I'm going to see the same amount of material the same thickness of donut now if I take the donut and I incline it so it's Edge onto your line of sight inhalation of 90 degrees if I pick a line of sight through the center I'm going to see donut and then whole and then more donut but if I pick a line inside I'm like the far right this is going to be donut all the way down so in an optically thin disc you should see this what we call onsai or limb brightening basically that comes from having more material where there's not a hole and if we see then like these sort of brightening on the edges of a disc that indicates that there's a gap in the middle of it when viewed Edge on so I can go back to this Blobby looking disc the center here is actually the star and then there's two onsai on either side of the star with a gap in between them and this has been best fit by having a model where there's an inner disc a clear Gap and then an outer disk okay so that's nice because we can then try and say imagine that there's a planet sitting in this disc like could it explain this Gap that we see so we can then actually use the properties of that Gap the radius and the depths and the width to actually place a direct constraint on the planet Mass which is what's at the top here and then we can run dynamical and body simulations with rebound to actually see does that work so this is showing a 0.16 Jupiter Mass Planet inserted into a disc that's about the exact same properties as we see with Oma and then run for a million years and it does in fact open a gap you can play around with it a little more if you allow the eccentricity to increase so this has a slight eccentricity which allows you to open up a bigger Gap with a slightly smaller plant but it seems to sort of make consistent sense okay now I showed you do so those two examples for a reason because most recently we've been looking at this disc which is just truly bizarre and seems to have both so this is hd53143 and it's a sun-like star that's about a billion years old so it's like a young solar analog and this is the Hubble image I would almost squint at this and you probably can't necessarily tell that there's actually a disc in that image it looks terrible there's basically like two clumping of material on the like lower left and the upper right and this was thought to maybe be like a face-on disc where we're seeing like resonant gloves so we imaged it with Alma it doesn't look like that at all this is the alma data now overlaying on top of the HST data and the center point is the star again so this disc is extremely eccentric it's about twice as eccentric as follow hot is the star is quite offset from the center of the disk and we see that same brightening at the epicenter side of the disc um we then imaged it again with HST better chronographic image and this is now the HST image again overlaid so we've improved the catch is that it still doesn't match the alma data if you fit the alma data allowing for a vertical thickness to the disc you get that the disc should be extremely thin and if you fit the Hubble data it wants to be really puffy so it actually has like a significant vertical height to it which means that the large grains and the small grains are actually in different places there's some you know confined plane with the larger millimeter grains and then this elevated population of small grains in this considerably eccentric disk okay but it gets even more fun so this is the actual model fit to the data where we fit an eccentric disk model to this disk so it's showing the data on the left and then the model at full resolution and then the model image like the data and then the residuals on the far right and those residuals are up to Six Sigma so they're significant the dashed line to guide your eye is actually the inner and the outer radius of that outer disc so if we were fitting the outer disk well we shouldn't see anything in that dashed region which we don't so we're like net overall fitting that outer disk but there's a lot of emission coming from inside of that that we cannot explain through an eccentric disk model so it's not immediately clear what's going on the best guess that makes some dynamical sense is actually that there's an inner disc in this system as well and that what we're seeing in those two Contours is basically the onside of an inclined inner disc that same like limb brightening phenomena if that's true that means that the outer disk is eccentric and then there's an inner disc that's actually Mutual like inclined relative to the outer disc and then there's a gap in between them so this was the helpful artist's impression that nrao put together for our press release the double last meeting last summer and that there's now this outer disk and then this incline inner disc and then the hypothetical undetected planet um good news is that we will get new Alma data on this system soon provided that Alma doesn't have any more shutdowns and uh then we'll be able to actually go back to the system with that 1au resolution that we used for formal hot to get a really high resolution view which would be good enough to actually resolve that inner disk if there is an inner disk so if we take all of the disks that we have seen an image with Alma it seems like structure is pretty much ubiquitous like we see it in almost all of these disks there's a lot of rings and gaps and I can wildly extrapolate and infer Planet masses for all of those rings and gaps and plot them down on the same Planet Mass exoplanet diagram so this is the same thing it's mass as a function of same major axis all of the great points are those known exoplanets the black points are the known solar system planets and all of the colored symbols are the planets that are inferred by just modeling the gaps in structure in these disks and many of these may not actually be planets but they do very nicely fill in this space where we have these giant planets that we have in our solar system when we don't know whether they exist in other planetary systems and I'm particularly excited a number of people here involved in this there's a large program happening on Alma right now to actually image a large sample of debris discs with high resolution and look for structure and debris discs to do this even more now what else can we say that's interesting about disks and exoplanets so my one undergraduate student did his honors thesis where he was actually trying to look at whether discs are inclined relative to their star so you might expect that nothing crazy has happened your Stellar axis is straight up and down and your disc would be perpendicular and everything would make sense there's a large question about what forms these sort of hot Jupiters these giant planets that are close to their star and one option is having dynamical instabilities that actually move them inwards that they form further out and then get scattered in and if that was the case then it might end up leaving an imprint on the remnant disk by basically like sending things out of alignment people had tried to do this previously with pretty small samples and largely found that things were aligned and so everything made sense my undergrad went back and used the test data to actually measure the Stellar inclination angles and then we took all of the resolved debris with Alma and fit inclination to them and this is what we get so it's just inclination as a function of celery inclination everything that's in blue and along that line is like Mutual inclinations are the same and the red points that are now off are things that have significant offsets in their inclination um where there's clear evidence that the disk is not aligned with the star anymore okay and of course I would be very remiss if I just said everything was planets because clearly it might not be there's lots of other things that can produce structure and disks that we need to understand in order to really conclusively say that anything is planets so this is a project I've been working on with Anne-Marie Madigan who developed a model of an inclination instability for the outer solar system basically a way to explain the orbits of outer solar system bodies without needing to add planet nine where if you have a large enough population of stuff you can actually have mutual self-gravity and it excites this instability which you can see progressing through these model panels at the top so basically you end up exciting like a wing where the orbits from the self-gravity get perturbed slightly out of the plane of the disc and then they get pertured the other direction and they sort of like flap to this mutually inflated disc over time and I show this because I mean that's cool but also because we see debris discs that have very similar structure so this is a real HST image of HD 61005 called The Moth because it has this wing-like structure to it um and so this is just an example of another way that we could produce structures that we'd like to say might be planets but just through the self-gravity of bodies in the outer parts of these solar systems okay so I'm going to take an Abrupt turn into the center part of planetary systems because in the middle of all these discs and all of those lovely Alma images I showed you there's a bright point source which is the star why do we care about stars so much so Stars including our sun flare they send out bursts of high energy radiation they also send out charged particles what we call coronal mass ejections or CMEs and they travel out into space and they hit your planet's magnetosphere and can come into the atmosphere and actually dissociate molecules in the atmosphere so they can split apart things like ozone and water and on Earth this is what produces the Aurora right it's coronal mass ejections from the Sun actually ionizing parts of Earth's atmosphere dissociating these molecules and giving us beautiful Northern Lights on many of our exoplanet systems the star in the middle is not a sun-like star it's an m-type star and M stars are much more active they send out bursts and flares that are thousands of times more energetic than anything we've ever seen from our sun and so it starts to kind of throw into some question this idea of habitability because you might be getting irradiated by your star so in order to really like tackle this we need to think about stars in a multi-wavelength way because Stars emit across the entire electromagnetic spectrum and in fact different wavelengths of light are actually tracing different emission processes and even different places in a flare Loop so the left is sort of the cartoon picture of a flare right where we have magnetic field lines that are actually threading through the photos here of the Star as the surface convex those foot points move around and that twists the field lines eventually they twist up and they snap and reconnect we'll call our reconnection event and we get this like nice loop-like structure there's electrons and charged particles that are actually accelerated around the top of the loop we'd expect to see synchrotron emission that's traced by say millimeter and UV light and then heating is actually propagated down the loop back into the Photosphere of the star and heats up those foot points and produces thermal black body emission that we see in say like the near infrared and the optical this is just our sun where we can actually resolve flare structures and this is a tiny wavelength range from 130 angstroms to 1600 but you can see this flare Loop looks completely different even across that small wavelength range okay so how did I end up working on Stars because of our nearest Stellar neighbor or Proxima Centauri so Proxima is an M SAR it's at 1.3 parse X it has three exoplanets now known orbiting around it and the one that everybody's very excited about is approxima B because it's a roughly Earth Mass planet and it's in that habitable zone it's the right distance from the Star to allow it to have liquid water if it's in Earth Mass planet so a group went and took a deep Oma image of the system to try and see whether there was any dust because we have a multiple Planet system around this nearby star we might expect there to be Remnant Kuiper belts in this system as well and so they went to try and look for these discs so the left image is the sort of published image from that paper they used about 13 hours of all my time so they pointed at this star for 13 hours and then took all the data and averaged it together and what you get is a point source in the middle that is bright it's like 340 micro janskates which is significantly above what the Stellar Photosphere should be the Photosphere should be about 70 micro danskies if you're it's just an M photosphere if you look at just the first 12 hours of data you get the middle panel which now looks quite different there is actually nothing detected above three sigma in that middle image and if you look at just the last hour you get the right panel where now there's an even brighter point source for the Flux Of roughly a milligansky so something's clearly varying in time now Alma actually has a one second integration time so instead of looking at total observations we can actually look at each of those Integrations separately and if you do that you get this which is now the time and it's about six minutes of data there's only a mission from the Star for about two minutes the rest of the time the star is actually not detected at all and we see this series of sort of small hiccups and then this giant burst where the star brightens by a factor of almost a thousand and then it decays away to nothing and we have no more emission from the star so that clearly indicates that there's not a disc in this system because discs don't do that but it was the first time that we'd actually detected millimeter flaring emission from these m-type Stars which was exciting and maybe a new way to try and understand stars and their activity levels but in order to do that we needed to actually place that in some kind of context because I can't just say yes Stars flare in the millimeter but I have no idea what that correlates to or what's coming from right so we undertook this large campaign to actually go back to Proxima but now with the millimeter and a range of wavelengths so we had 40 hours of time where I tried to convince every telescope to point at Proxima at the same time it was fun we had Alma several ground-based telescopes doing optical photometry and spectroscopy tests in space so we actually coordinate this the test window and Tess was looking at Proxima and then we used Hubble and Swift to cover the UV and then Swift and Chandra to cover the X-ray so everything from the radio all the way through the X-ray and all of these were executed completely simultaneously so we just pointed at Proxima for the exact same time and when you do that it turns out that you get really interesting data sets so this is an example of the first flare that we pulled out of this survey so this is stepping through wavelength here on the left with Alma the longest at the top going through tests and then Dupont looking at the H Alpha and helium one lines and then Hubble with Continuum and silicon four emission and the right is now just zooming in on the Hubble and the alma data together and there's a lot of really interesting things to take away from this plot so the flare is enormous in the alma and Hubble it's the largest Flair we've ever seen from Proxima with Hubble it brightens by a factor of almost 15 000. in the Hubble light curve and it blinds by a factor of more than a thousand in the alma light curve each of these points is a one second integration so the entire event lasts eight seconds so it bursts and has that 14 000 times brightening in about four seconds before decaying away the optical light is very different it's very small actually the like a mission increase in the optical is Tiny and there's actually a significant delay between when we see the peak and the Hubble and the Almond data and when we see the peak in the optical so there's actually a gap in time they don't occur simultaneously but they all know the Hubble data are like strikingly locked together um it makes I think physical sense because if they're both coming from synchrotron emission then we would expect to see this and if the optical is actually coming from say black body heating that's propagating down then it's maybe not surprising that there is this delay and difference between the emission at those wavelengths what's interesting because we typically observe players in the optical and then we wildly extrapolate to say now we know the UV emission because it's the UV that we actually want to know when we think about atmospheric stripping and photochemistry Optical light doesn't do that so we scale optical flares all the time into the UV and if they aren't actually linked then that makes me feel a little uncomfortable about that and if the millimeter turns out to actually be a better Tracer that would be very exciting because it's a lot easier to do millimeter observations and in fact all these CMB surveys are going to suddenly be observing tons and tons of millimeter flares they already are publishing millimeter flares out of spt and we could get a lot of data very quickly with millimeter flux measurements of nearby Stars okay so just to highlight that that Optical is really different this is what we call a flare frequency distribution which is number of flares as a function of energy and amplitude so really big flares are all the way over here on the right they're rare and really tiny flares are all the way on the left which occur pretty much daily from Proxima and these are all of the flares that were detected from Proxima in the entire test time that it looked at the start and the green line is that flare I just showed you that brightened by 15 000 times with Hubble so in the optical 75 of the flare is detected from Proxima are brighter than that flare and in fact we would estimate that basically we'd see that flare once a day if the optical and the UV are connected we can also use Alma to say some more interesting things about the emission mechanisms of the star because with Alma we get a spectral band pass where we observe across a range of frequencies so we can actually then calculate a spectral index so how the flux varies as a function of frequency and we can try and recreate a lower limit on the linear polarization by taking the XX and YY polarizations so this is three different flares the left panel is a previous layer from Proxima this is a flare from aumic in the middle and then this is that new Proxima flare on the right the top is just showing that light curve again so flux is a function of time here's the spectral index and then the linear polarization and we see some very clear changes as the flare happens the spectral index changes from being like a really jeans black body tail to noticeably negative and then recovers and there's an indication that there's actually a change in the polarization of the star and they all look pretty similar so we're starting to build up a sample where they all appear to have pretty comparable properties and this is consistent with a picture of either having synchrotron or gyrosynchrotron emission we would expect to see this sort of spectral index change and this linear polarization if we're really seeing this sort of emission mechanism now we've been like continuing to comb through the data from that survey so this is a paper that my postdoc put out earlier which is actually the first Alma and x-ray flare so this is Chandra data that we got at the same time as Oma so the right curve is on the far left showing Chandra lcogt and Oma it's a very different flare because it's actually quite small and it's like total energy it's about similar to like an x-class flare on the sun which is the largest flares that our sun puts out but like small for an mdorf and now because it's actually comparable to the sun we can start looking at it in kind of the landscape of solar flares so this is showing here these sort of typical godell Ben's relationships we plot x-ray Luminosity as a function of radial luminosity and it's interesting because the alma data in quiescence like when the star isn't flaring seems to be roughly consistent but when the star flares it like really jumps up in the flaring emission so it seems like there's some kind of overproduction of millimeter emission happening they're using during these events compared to like solar flares and I don't actually have an explanation for that except that we are starting to get the data that we can look at that what else can we do so now this is like brand new and like not published at all so take that what it is but my postdoc has been working on jwst observations turns out that when you try and take a mission transmission Spectra of your mdorf exoplanets you still have the mdorf in the middle and it can flare in the middle of your transmission spectroscopy so the top light curve is the actual like initial Liker from jwst and you can see this like Peak up right as it's going into the transit this is a model where we've actually tried to take out the transit life curve because the exoplanet people would really like to just take out that flare and like see what happens in the stealth like exoplanet atmosphere which you can't do if there's this flare sitting on top so the hope is that if we understand the flare we can better model it and remove it but then also the dangerous T data on the flare is like astounding to me because we detect like every spectral line ever so this is H Alpha we have all the passion lines down to like passion Epsilon this is a bracket beta line helium and suddenly we can see like all of these emission lines and how they vary as a function of time and wavelength and we can actually use these to inform these like radiative transfer models and actually say things about the magnetic field of the star at the time of the event how many particles were accelerated the energies that were released during that mdorfs aren't the only ones that actually flare at millimeter wavelengths so this is just a highlight from a paper um looking at Epsilon eridani on the left which is a sunlight star where we reanalyze the alma data and found several flares happen from the star and this is actually hd53143 that really crazy debris disc I showed you turns out has a crazy Star as well so we observed that for like eight hours with Alma and the flux on the star changes dramatically in the middle which we think is also due to a flare the background here is actually test data because it turned out that Tess was observing it the exact same time as Alma by complete chance so we can actually look at the optical light curve at the same time and what's surprising is that for a billion Euro sunlight start has an enormous amount of spot modulation um so much so that it really messed up the HST chronographic Imaging because the reference star was failing because the star was actually like changing color due to the spot modulation so I think that there's lots of places to go from this one thing I'm really excited about is like thinking about what kind of new telescope we might want and to me the really interesting lever arm here is getting the multi-wave the mission but that's very hard right now we have to like try and coordinate eight different telescopes and it would be nice if we didn't have to do that so I'm working on a new Mission concept with JPL called aspects which is focused on looking at Young stars to study young exoplanets young discs and young Stellar activity and it's meant to be a multi-band instrument with near IR Optical and near UV and fast Cadence less than 30 seconds Cadence staring at all of these sources with all of those bands at the same time so we don't have to try and make multiplayer like course we just get them and then like the next step is to connect this to an actual understanding of astrobiology right because it's great to just understand stars but we'd really like to think about how they alter atmospheres so this is a project I've been working on with Laura Schaefer also fellow Alum here where we're trying to actually model what these flares do to Atmosphere chemistry specifically looking at oxygen because oxygen is talked about a lot as a biosignature since it's really tightly linked to the rise of life on Earth we had no oxid in the atmosphere and then plants happened and then we get oxygen but you can actually basically produce a giant oxygen column density just by allowing these flares to propagate through the atmosphere because they dissociate water and then you can drive hydrogen Escape in these young exoplanets you lose the hydrogen and you're just left with a ton of oxygen and we are then also collaborating with the geneticist at the University of Minnesota to try and do this in a lab where we're actually going to like use a UV flash bulb to try and simulate UV flares in a lab and see what damage it might actually do to DNA okay so I like Whirlwind tour of two of these things but there's many other items on this list right that we'd like to get at and we can't so what gives two things that I think are of particularly key interest they're trying to understand the water and volatile abundance because you need to have water and volatiles to create life on a planet so how do we get at that well discs are complicated places I like to show this figure and then say like we're not going to talk about all of it because it's deeply complicated it's showing a debris disc on the right and a protonplanatory disc on the left and like different wavelengths of light are tracing different temperatures so we're seeing different parts of discs with different telescopes these young discs are like flared right so we're seeing different depths into the disk and so trying to actually understand the chemistry of discs is complicated and there's certain things that were completely missing right now because we don't actually have the right choices that we can access from the ground so I've been working on another mission concept as the deputy API called first which is the far infrared spectroscopic survey telescope which is designed to do high resolution spectroscopy in the far IR with the goal of really like getting at Planet formation chemistry and why is that interesting important so one point here is that we don't actually have a great understanding of the masses of Planet forming discs which is a pretty fundamental property I just showed you all the stuff about planet formation and it makes it seem like this is really solved but actually there's a lot of uncertainty so these are all measurements done of TW Hydra which is our like best studied protoplanetary disc and they are all disc masses that use different tracers and this is a logarithmic scale so these Mass derived estimates span several orders of magnitude which is problematic because you go from like having a decently sized disc to having a disc that's not going to form any giant planets at all depending upon which Tracer you've used and maybe that's not super surprising because a lot of these use like dust masses and then try and scale that to a gas mask or we use tracers like Co and then assume that we know the co to H2 abundance and that Co isn't optically thick we really want to actually measure the hydrogen Reservoir we can't do that the so thought to be best option is to use a molecule called HD which is deuterated hydrogen and unfortunately HD only hens transitions in the far IR at 56 and 112 microns so it's been used in TW Hydra with Herschel which is the top but otherwise we have like two other discs that have ever had HD measurements of and so one key here is that using HD you really need to know the temperature of your materials you really need to know its location in the disk so you need to have really high spectral resolving power so we've been targeting first as this really exquisitely high resolution spectrograph to be able to do this the other really exciting thing to mention is water because water is pretty fundamental to life however this is the landscape of water transitions that we can actually observe so this is in energy bin so hotter water at the bottom colder at the top the left is jwst where basically there's a few water lines but they're at really high temperatures so they're not great for looking in disk environments the right is Alma where technically there are water lines but we're looking through a water atmosphere so this is tough and then all of the transitions of water basically are in the far IR so without a foreigner telescope we have no way to really Trace water in Star formation or plant information or any environment so like one big question is trying to look at the origin of water in disks and what are the abundances of discs where we don't actually have a good handle and then we can also do this with um comets so we're even trying to look through uh comments in our own solar system where the question is really like where did Earth's water come from and the way to get at that is to measure the ratio of deuterated water to normal water so we call the D to H ratio and um we've done this a lot for asteroids but not that much for comets the comet population is pretty sparse and we don't really have the sensitivities so we're also trying to Target doing Comet science to really like measure the ddh ratios in a significant sample of cots and the hope would be that if we combine all those things together with what we've done with Alma now we can really put together a complete picture of plant information so with that I will leave up my take-home slides and I'm happy to take questions [Applause] any questions particularly want to encourage early career folks good enough so um the HD line should be optically thin um and it has been used pretty successfully in TW Hydra the real like problem here and why there is still scatter is because of the temperature so it's really sensitive to the temperature that you put into deriving a mass and Pax only had a resolution of like a thousand at 112 and like 1500 at 56 microns so not very good um which means that there's a lot of like uncertainty then in like deriving that mass so you end up with that which is why we're trying to go for like higher spectral resolution to really robustly determine like where in the disk the mission is coming from and that's the temperature and thus the actual mass you could also spatially resolve it but we can't do that for a billion dollars has much larger bins and at that time but if you had higher occasions observation observations in the optical that would change that picture at all or you think that that is yeah so that's a good question um so the X error bars here are actually the time bin of the data so with tests that says two minute Cadence data with a Dupont it's bad because we're using a spectrograph so we're actually like trying to detect an mdorf so you need to stare at it for like eight minutes to get a decent Spectrum um so there's multiple pieces on like the it's definitely a coarser spectrum even with that the time delay is significant they don't overlap like there's no overlap between the alma flare and the test flare um and so even if like we were just not sampling it well enough we should be able to have seen that and we don't so that offset is real um definitely the energy could be higher in the optical because you're you know sampling an eight second flare with a coarser Cadence and adding a lot of noise in there so you lower the significance of it um not enough to make this agree but there certainly could be a higher energy which is why like Fast Cadence is really key for flare work because you lose a lot when we look at these flares with these course observations please uh on this flare um did you have overlapping genre data and if so did you detect it in the X-ray we did not that's what I was suspicious yep um we only had a little bit of chandranada and so um not overlap this time it didn't overlap with this um the other like this is the same campaign just on a different day right we did this over like 12 different days and so this time Chandra overlapped but it was a tiny flare but like we still were able to get the overlap just not unfortunately for that really big one so the few flares that you showed were all main sequence Stars I wondered if you could say something more about the evolution of flaring at the time and whether or not there are any campaigns of younger stars to see how involved yeah that's an excellent question so in general Stellar activity declines as stars get older so Stars start off and they're spinning really rapidly and they're generally more magnetically active and then there's some like tail off right eventually they slow down and they spin down and then their activity level goes down so technically Proxima should not be so active it definitely is much more active than you might expect in that simple picture there have been some work done with Kepler to look at young Stellar clusters you know like tens of million year age to try and like map this Evolution like how active like how does this trend down but I would say less than you might expect which is why this particular Mission we are specifically targeting young clusters and by Young I mean like one to 100 million years at that time when like you would expect to be able to still detect like disc accretion and Stellar activity and also be looking at these exoplanets when they have puffed up atmospheres with the goal on this to really like look at the early Evolution um and like sample you know six ten different clusters that span like one two five ten 100 million years so that you can really like try and study that there's an online question which we'll do quickly uh Bob Wilson asked can you use 13 Co to measure mass to avoid problems with Optical so yes they're like in this this plot I sort of like didn't go into this but like every single one of these things is totally using a different traits there or some overlapping tracers some of them are 12co some of them are dust masses some of them are 13 Co like c17 like name your isotopolog and they certainly like 13 CR should be more optically thin than 12co but you still run into the problem that you're like using CO as a tracer for an underlying hydrogen Reservoir and we don't know the scaling between those things particularly well so you still end up with them significant error when when we look at lower Mass substellar objects flaring usually at lower frequency than gigahertz frequencies we oftentimes find at these very short duration flares are 100 circularly polarized and so I was wondering if with Alma you can extract robust circular polarization I would love to because that very well could be I mean like that's just the lower limit by like using the XX and YY that you get for free with Alma it says nothing about the cross products and like it could very well just be circular polarization that we're detecting just have to actually convince oh there goes the slides convince uh Alma to let me stare at an unresolved point source with full polarization capabilities that may or may not flare which is why I have not been able to get that data but yes that would be the best thing to do last question from Melissa um that's great um just curious all of these systems show them you know look isolated except for that one slide where you showed me there's some secretion so I'm just curious like is there any interaction with binaries or with instantly accreting material or anything from outside that matters in like the various disk sources yeah good question I mean most of these are at this point like isolated field stars um but they certainly didn't form that way so it's a good question there are some discs that have very weird structure that people like try and claim are Stellar flybys it's a tough one because you can never really like a hundred percent prove that that's the case because you're seeing it now billions of years later um but maybe probably right I mean stars form in dense environments so I'm sure that plays a role we just haven't all right half the half hour so uh let's take Meredith one more time [Applause]

Channel: CfA Colloquium

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Id: uYT9pxf0s5U

Length: 56min 33sec (3393 seconds)

Published: Wed May 24 2023