 All good. All good. Perfect. Seamless. I won't make any mistakes. Okay. Thank you, John. It's nice to talk to you all. I'm going to talk for, you know, 45-ish minutes about some stellar activity work that I've done and others along with me have done. I'll get citations throughout. I think this would be a lot of review for some of you. I hope it's exciting for some of you. Kepler, K2, and I'm including Gaia even though it's not, I think, officially part of the missions that I've worked on, but everybody uses Gaia data now, and so it's this combination of this amazing space-based data, which Gaia certainly qualifies as, and I need a couple of years. We'll be rewriting this talk with doubling the data with Gaia. So I think this is a really special time and special opportunity to study stars and stellar activity and try to understand things around other stars like we do on our own sun. But first, let me give just a brief introduction to myself. Here is some fancy stock footage that I found on the University of Washington's website. This is our building. This is the physics and astronomy building. We are on the third floor here. The bird just flew above us. We're at my offices. So sort of in the middle of the building, we have the third floor. Physics is above and below us, but that's okay. We try not to feel offended that they get more space than we do. And on the top floor is the eScience, the interdisciplinary eScience Institute, which combines data science and computer science and astronomy and other domain sciences. So I am, as John said, the associate director of the Dirac Institute, which exists within the astronomy department. It's the data intensive research in astrophysics and cosmology. I don't know anything about cosmology, but I got the rest of it. And we try to bring together people who are interested in programs like LST and severe ruben observatory, missions like tests, other sources of large data sets, time domain astronomy, things like that are our focus. It is a great acronym. If you're into acronyms, it's a great acronym. We've got a nice hoodie. It's very cozy hoodie. If you come out and visit, I'll give you one of these hoodies. It is, however, a difficult acronym in the fact that Dirac, the actual scientist Dirac didn't work on anything related to the stuff that we do and actually was a theorist and didn't work on any data. So it's actually a terrible acronym if you think about the namesake. Thankfully, I'm not responsible for the acronym. I just keep the place running. So come out and visit. I swear it looks like this every day in Seattle. Okay. So I'm going to talk about what is, and this is a punny title here, a revolution that has happened in stellar rotation over the past roughly 10, maybe 12 years. And that is that our knowledge starts in sort of the time of Galileo, learning that the sun in fact rotates. Here pictured is the sun rotating. This is a several days movie from Solar Dynamics Observatory. You can see some very boring, normal star spots. It's a little more active than the sun is right now. Unfortunately, sun's pretty boring right now. And so our knowledge of stellar activity and stellar magnetic fields really is born out of this fact that the star that we orbit rotates. And a lot of things and timescales are driven out of this rotation and different rotation and all the other physics that are going on in the sun. The revolution comes in that before, in 2009 when Kepler launched, before Kepler launched, there was something like order of a thousand stars for which we could measure the rotation period. This was difficult work by today's standards. You had to go take a spectrum, a pretty high resolution spectrum and the line broadening of that spectrum would give you something like the surface velocity modulo, the inclination. So you'd get v sine i. And then you could play some games and maybe do a little better and constrain the inclination somehow. But really it was of order of a thousand, maybe a couple of thousand stars period of which this measurement had been done and was possible. And so rotation was not seen as something that we used to characterize stars. We had things like color and temperature, maybe luminosity. But the rotation rate was not something that we could do in an ensemble statistical sense, enter these amazing space based photometric missions like Kepler and then Tess and Gaia. And this has really revolutionized our ability to measure this fundamental stellar property, this really fundamental facet that drives a lot of activity on the sun, which is rotation. So how do you measure the rotation from light curves alone? We can't see the spots moving over the surface. Instead, we can imply their presence. This is an old gift that I made of a circular spot rolling around on a perfectly uniform sphere. And you can see when the spot is away from you, the star is bright. And when the spot rolls into view, the brightness goes down. You get this sort of sinusoidal like modulation. And we see this in data. We see here is an example figure from Lucy on Walk, which is paper on em dwarfs. This is a paper that kind of changed my life and blew my mind when I first saw this here is just four random em dwarfs from the very first quarter, the Q zero data of Kepler. And it kind of looks like a cartoon almost. It looks like the data that you would manufacture if you were trying to teach a class on this. You've got quasi sinusoidal modulation from that spot or spot features rolling around on the surface. And then here we have flares. Now, I've done a lot of work on flares and I'll come back to them at the very end. But today I really just want to talk and focus on rotation because I think this is where a lot of the future is. And it's a really big point of, I think, the Kepler and soon the test legacy. So this is just four em dwarfs, four random no name em dwarfs. And the real revolution, I think, began in about 2013 and 2014 when Amy McQuillan, for her thesis work with Susanna Grain and Oxford, published this incredible now benchmark catalogue of 30, 34,000 roughly rotation periods from Kepler. So in this lovely cyan diagram, which they call the shrimp, which I think is very cute. They call this the shrimp diagram because I think it looks like or maybe they call it the prawn, I guess they're in the UK. Anyway, so here's the shrimp or the prawn. It looks like the legs of a shrimp, I guess, or the tail. And you can see there's a wide range of masses here from above higher than solar mass all the way down to sort of the mid em dwarfs. The sun is in this red star here. So it's sort of on the upper edge of this diagram with a rotation period, a sort of average rotation period around 25 days. There's overlays here of various clusters and subpopulations that don't matter. To orient you in this diagram, this is the diagram we're going to come back to over and over and over throughout this talk. This is the the characteristic rotation period versus age diagram. And to give you some some some orientation here, we think that through the the classical rules of angular momentum loss, things should slow down. But if you spin a top on the table, it should lose angular momentum. In the case of a table, it's because of friction and wobble and air resistance and all these things. In the case of a star, it loses angular momentum because of winds and particles flying off. It's like the figure skater putting their arms out, slowing themselves down. You have a torque from mass literally leaving the surface. And so we look at this diagram and we think we see evidence of age that stars should move effectively vertically on this diagram. They should be born with some initial rapid rotation and they should slow down over time. And the degree to which that is smooth and consistent and uniform develops a technique that we call gyro chronology or the spin clock, spin down, as it's called. I like this figure from this manifold from soren my bomb that kind of maps this out that there is a mass and age or a color and age dependency. And here, 10 years ago, you could see the sort of three or four open clusters that were used to sort of benchmark this. And the sun is like one infinitesimal little dot there in age and mass space. So this is gyro chronology. And this is another one of those papers that like causes you to drop what you're doing and change the course of your career, if you're me. So this is a really cool data set. And one thing that McQuillan at all noticed was that there was a bimodality in a period. They first noticed this in the Emdwarf. So here in the right, I've highlighted just that little sliver of the prawn of the shrimp diagram where you can maybe see that there's kind of two clumps. There's a higher clump and a lower clump. And then here on the left, I put the big red circle around the histogram and log period space. And you can see there's sort of two populations of stars. The bottom panels show this in terms of scatter. So trying to see if it's something to do with the spot amplitudes and there doesn't seem to be any correlation there. In fact, I think I've drawn misleading ovals here. So anyways, there's two populations, this bimodality or or equivalently a gap. There is maybe a smooth underlying population and a gap right in the middle. At first, we thought about this as a bimodality. First, they observed it in 2013 in the Emdwarfs. Then they expanded their sample to the full 30,000 stars from Kepler that could have rotation periods measured. And they saw evidence here. This is kind of a dense diagram. But the point is here on the right that the K in the Emdwarfs showed evidence of this bimodality and that by the time you got into sort of the G and the F stars, there was no indication of a bimodality. So the mystery deepened. Why is there a gap or two clumps of stars as it were in this age period space? What might that mean? And why does it seem to only occur for the K in the Emdwarfs and not the F and the G stars? Which have been theorized to all from anywhere. There's a convective envelope. So from mid F down to Emdwarfs, anywhere there's a convective envelope, we think this sort of angular momentum loss mechanism should work and this gyrochronology to an extent should hold. So so the question that was posed in 2013 and has remained an active question in area investigation. Is gyrochronology broken? Is there something fundamentally wrong about our assumption of angular momentum loss? Now this model was proposed and really in detail in the 1970s that there should be this smooth, wind-driven angular momentum loss or breaking of the spin, breaking like pedaling the brakes on your car. And so this bimodal distribution suggests one of two things. Number one, the simplest explanation I think is that it is encoding the gyrochronology does work and that it's encoding the star formation history. So that if this vertical direction on the diagram is time or age, this would indicate a burst of star formation recently, then a gap in star formation and then another burst. And maybe it's in logarithmic time or something. So they're log bursts of star formation. Okay, that's the easiest read of this diagram. The second is that the gap is actually, that there is no gap in star formation. Instead the gap is a break in the stellar spin down that somehow angular momentum loss does not proceed uniformly. And stars are jumping over this point that this is a sort of semi-forbidden region in angular momentum space for the star. This is completely unsupported by any predictions 10 years ago. Similarly, proposition number one is also unsupported. We have other estimates of the star formation history of the Milky Way and the disc of our galaxy. And there's no indication that there was a really recent localized burst of star formation in the last half a gig a year or so. I think we would have probably noticed a big cluster of young stars right in our face. And there is not an indication of that in the field. So number one totally clashes with our understanding of the galaxy. And number two is completely unsupported by our understanding of angular momentum and wins from stars, not that we know them that well. So I love that both of these are perplexing or problematic explanations because that is what we call job security. And so we've got ADAP, NASA ADAP award about three or four years ago to study this to try to expand our understanding of this feature. Where is it from? Okay, so further evidence that gyrochronology is potentially broken came from another group from Jen Van Seder's work. This was a really cool nature paper. So other evidence that gyrochronology that this spin down is perhaps not smooth and there's some, so other funny business going on is that at the very top edge of this diagram, here I've highlighted that in this sort of purple marker streak, we see sort of a hard edge, that there are F stars that could have a spin down rates of 20 or 30 days that we would have been sensitive to in Kepler and we don't see them. Instead we see this hard sort of upper edge. And this is supported by in the handful of stars where there are independent age measurements. This is hard work to get independent age measurements. But here for F, G and K stars, there seems to be, and this was much debated, there seems to be a break from the expected spin down if you, these curves here and colors are a spin down, I think the black line is spin down for just wind driven angle momentum loss. And what we see is that the G stars right after the age of the sun for the middle panel here, right after about four giga years, the G stars stop spinning down as efficiently. Instead they fall below that black line. And so Jen's work was in trying to figure out what could be the cause and what rotation period or what we would say what rosby number this occurs at. And there does seem to be some point at which the star, they could, she called it, she called it broken breaking where it no longer can lose angle momentum as efficiently as it did. So whatever the wind that it's producing either turns off or becomes much less efficient in terms of dragging angle measurements from the star. So this was a cool independent line of reasoning that maybe spin down is not as simple as just a steady wind flying off the star for all time. That of course, nature is tricky. So when my work picked up a few years ago was in trying to explore this first conundrum which is why did in the Kepler sample we only see this for the K and the M stars and not really for the G and the F stars. Why is there a mass dependence? Is this real? And so enter this other helpful mission Kepler plus Gaia. What we noticed when we started looking at the sample of rotation periods that McQuillan had all had generated that Amy had worked on for a thesis. There is a wonderful range here. This is the Gaia DR2 color magnitude diagram. There's a wonderful range here of spectral types of masses. You can definitely see a cluster of potentially equal mass binary stars up there above the main sequence, which is really fun. But there's this big cloud of dots up above this sort of notional zero age main sequence in black here for the G stars here with colors bluer than about one brightness is above absolute magnitude of four. We call this the sub giant branch. This is the turnoff in the sub giants. And there's a lot of work and fascinating work about what happens to the envelope of a star when fusion starts turning off and support from fusion starts to go away and the envelope changes its size. There are many PhD theses to be written here about understanding this. What happens when a star journeys from the main sequence to the giant branch. But for us, for those interested in trying to age date the stars on the main sequence, this is all noise. These stars are out of bounds because they aren't experiencing the same wind driven angle momentum loss. And so by just taking a nice little box here in pink and throwing out all the stuff in blue, these sub giants or anything that's a post main sequence object, just being a really strict about throwing out the binaries as best you can and just getting the main sequence stars. Then we start realizing that the contamination in these G stars was super high. There's a ton of sub giants that were stuck in the Kepler data that weren't known to be sub giants. And so we find this was with the DR one results for Gaia but with the same thing was true in DR two. So here is the histogram of rotation periods on the left centered around that the rotation period of the gap for those stars. So it's in sort of obtuse units here, I apologize. And the point is in orange was the histogram before which is equivalent to what McQuillan and all had seen for F and G stars that there is no bimodality it's just a smooth distribution of periods. And after we throw out all the sub giants you get a nice bimodal peak right where you expect it or bimodal gap or whatever, right where you expect it that there is a population of rapid rotators to the left and slow rotators to the right where you expect them and it was just sub giants in the way interfering with our understanding of rotation period space. So sorry sub giants out you go. So we whittled this sample from about in half down to the most likely single main sequence objects we can. And what we can see here I've highlighted it because it gets a little hard to see in the higher mass stars is there is a nice little gap this is my PowerPoint gyro crone we call them it's like an isochrone, a gyro crone that nicely traces out this bimodality and seems to follow nearly a single age sequence very fascinating that looks roughly like a 600 million year old gap. This at the time in 2018 we wrote this suggested to us that maybe it is star formation it was kind of wild that this gap seemed to follow the prediction of a single age in the gyro chronology model that there might be a gap that might have been a burst of star formation somewhat locally or down in the disc. There was other evidence that higher up in the disc you didn't see this gap as much when you started to get to the sort of the thick disc as it's called region. So this was very suggestive that maybe it was age maybe this is just simply star formation history encoding itself and this gap or this bimodality is just simply star formation history. There's other problems which we'll return to but this was very interesting. One problem though is that Kepler just stared at one field of view for four years. It was a great data set and really wonderful if you wanted to understand rotation period you could come back month after month, year after year and make sure that your signal was good that you had the right rotation period no matter what the star spots were doing but it is one field of view and you don't know when you have a sample of one like so many things in science we don't know if that sample is representative maybe this localized burst star formation just happened in the direction of the Kepler field maybe we were looking into some cluster or some feature that we didn't understand or hadn't detected yet. So the next challenge was to figure out was this feature ubiquitous and the next successor to Kepler and here I'll turn the spacecraft was the K2 mission. So Kepler lost its ability to point at its single stable field of view which it had stared at throughout its main mission for four years but the very crafty engineers of Ball Aerospace and with NASA figured out a way to get the spacecraft to point semi-stably for something like 70 to 90 day periods by keeping its back to the wind and essentially used to the solar radiation pressure to sort of keep itself sailing quasi-stable. So it could point to these fields of view along the ecliptic for something like a quarter or three months roughly of the year and then they would have to turn the spacecraft to keep its back to the sun. So over the course of four years Kepler doubled its sample size in terms of observation and it vastly expanded the numbers of lines of sight. It went from one line of sight that was kind of up above the galactic plane to 20 or 18, I guess 19 technically, 19 lines of sight that it surveyed over the four years giving us many fingers, many pencil beams, many fingers of observation throughout the galaxy that we could test this basic question of does this bimodality exist only in the Kepler field or is this something to do with the construction of our galaxy more generally? Now, of course there is one degeneracy left which is the same spacecraft and we'll return to that at the end. So it's possible that Kepler itself is somehow haunted and it gives us the signal. I don't think that's the case. So what follows is work that a student I've been working with, Tyler Gordon has submitted, you can find it on the archive, it's undergoing a favorable rough re-review right now. We set out to model every light curve from K2 which had not been done to model the light curves to do a uniform robust search for rotation periods from every light curve in K2 just like what was done in 2013 and 2014 with Kepler roughly 200,000 light curves in Kepler. So we've doubled the sample of observable stars. We don't have years of data instead we only have about 70 to 80 days per star. So you need to be a lot more careful and a lot more sure that the rotation periods you pull out are real. So we used a much more sophisticated method than was used before. In Kepler, they used the autocorrelation function which has become sort of a now standard approach for measuring rotation periods. And here instead, Tyler as part of his thesis work is using a Gaussian process with a periodic kernel. So it's a semi parametric flexible model which only encodes sort of with a characteristic time scale but it doesn't enforce a strict periodicity in the light curve. So here you can see there's an example on the left of sort of a moderate rotation period something like 12 days on the right, a rapid rotation period with strong spot evolution as well. And it's able to capture both of these features very robustly. So this is a great data product in itself even for stars we don't have robust rotation periods. If you wanted to go do a new search for exoplanets or eclipsing binaries or other weird things that go pump in the night. This is a great data set and we're releasing the detrended light curves the Gaussian process models for all the light curves as a byproduct of this data. So if you're interested in modeling things with K2 this is a great data set to check out. One of the byproducts just to take a very short tangent here is that the Gaussian process also quantifies how stable the features are in time. And so the so-called quality factor or Q that is used in the hyper parameter of the Gaussian process. This hyper parameter characterizes how stable the features are from period to period. So here on the right is just like 10 examples of the same periodic signal but drawn from different models with different Qs. And so on the bottom where the quality factor is low you just get random noise. The noise terms dominate and on the top where the quality factor is very high you have an incredibly high quality stable periodic signal that looks here just kind of like a damped sine wave a very in phase very stable. And so this is I think a really interesting way of quantifying how stable star spots are how stable things like differential rotation might be I think there's a lot of future here. So again, there's great data products here even for stars we're not sure if the rotation period is super robust. But what's cool is even using really strict cutoffs about the quality factor and the error bars we did the Gaussian process with MCMC so we have big error bars that we can explore. So even requiring great Gaia measurements and great rotation periods we're able to add almost 9,000 new rotating stars to the sort of Kepler family of rotation periods. So again, compared to 10 years ago this would have been a groundbreaking sample adding eight almost 9,000 new stars of rotation periods would have just dominated any measurements of rotation in the field. And we have many lines of sight which is really exciting. So we did the same sort of game using the Gaia Color-Managed Diagram cut out the subgiants cut out the obvious binaries just look for the most likely main sequence single stars that we can. And the drum roll the whole reason we set out to write this proposal and this paper was we can see the rotation period by modality very, very clearly in the K2 data. So here is the ensemble of all 8,943 high quality high fidelity rotation periods measured using the Gaussian process. We do compare it with the autocorrelation function of Lone Scarlet you can see these features as well. And you can see very clearly or at least I hope you can see very clearly that the prawn that the shrimp is there that there is this gap sort of slanted with the rotation period envelope especially prominent in the K and M dwarfs here starting with colors of about 0.8 out to one. So this is a huge victory and I'm super duper excited about this. So I hope you all will check out Tyler's paper just for this figure alone cause I think it's a total slam dunk and it makes me really excited. We can see the bimodality and other stars beyond just the Kepler field. Now again, there is a possibility that Kepler is haunted. This feature has not been detected robustly with any other telescope yet at least in the published literature that I'm aware of but it's really exciting that we can see it with totally different data processing and totally different lines of sight. We have different lines of sight and so if we start measuring where the gap is and how wide the gap or how far apart the bimodality is or where the middle of that gap is we can do a precise tracing of where the gap is within each line of sight cause again, we're probing many lines of sight throughout the galaxy out to about a kiloparsec in each direction. And the figure on the right, the takeaway here is that on average when we sort of take a kernel density smoothing of these features the gap is roughly in the same direction. So this suggests to us since if you look a kiloparsec in one direction a kiloparsec in another direction in the galaxy in the leading and the trailing direction in the galaxy there's no time dependence. This is not a feature of star formation rolling through a spiral arm or anything like that. If you look through the sort of the, whoop, the sort of Q zero, that's a sector zero, sector 13 compared to sector nine, sort of leading and trailing edges in the galaxy there is no dependence on where you're looking or how high you're looking the gap is always in the same place. And so we think this pretty conclusively rules out star formation history by itself. We think this really favors something going wrong or unexpected with spin down with gyrochronology. So is gyrochronology broken? Yes, yes, we think it is. We think this is more evidence. There's other evidence in the literature as we mentioned earlier there's other evidence that gyrochronology appears to be broken that the stars are somehow reaching a critical point and not able to efficiently lose angular momentum and spin through that place in the diagram. So that's really great. So good for our annual report to NASA but now the physicist inside of us has to ask why? What's happening? Just from these lines of sight alone we can't figure out why this is the case. We don't know independently the ages of all these stars. These are field stars. We don't know any of the other properties of these stars really. So we need to turn to another set of observations. And this is open clusters is sort of the benchmark that you would next naturally go to or this is what we went to and what others have gone to. So this is again a diagram from Tyler's paper where he's just reproducing with his periods the handful of well-published clusters that have shown up in the K2 data. There's other clusters as well in the K2 and the Kepler data. But here are just a few and you can see again vaguely in the background you can see the sort of the prawn, the gap, the bimodality, whatever you wanna call it. And then you can see these two clusters and you see 6811 with an age of around a gig a year and Pricepe with an age of around 700 million years. And you can see that they at around 1.1 solar masses they are split, they are offset from each other. One sort of seems to be on the top edge of the gap and one is on the bottom edge begin with about 300 million years separation for the low mass stars for the 0.8 solar masses, K dwarfs these all appear to be on the lower edge of the diagram. They are on the other side. You would naively expect all those green dots on the right to be above the gap and instead they're on the below the gap. And so you can see that something is transitioning from the high mass to the low mass at this somewhere around a gig a year or just before a gig a year. Here's I think a cleaner diagram that Jason Curtis made just showing again this stall, this kind of break in the rotation evolution. So it looks like if we were to read this right diagram it looks like that the 6811 stars here in the red and the blue dots that they for the higher mass ones, the hotter ones they have transitioned as you expect they've continued to spin down but the lower mass ones have stalled. That's what the, I think they use the word term stall or they've broken their breaking as Jen Van Seder said. So this is really interesting. What happened? Why did they stop losing angular momentum? They certainly have star spots they certainly have magnetic fields we can see the star spots that's how we're making these measurements. So what's going on? Another example again using Prisepi and comparing it to the Hyades. So the Hyades and Prisepi are often considered sort of like sibling clusters they have roughly the same age right around 700 million years and what Stephanie Douglas noted in her 2019 paper using again K2 data K2 has really been revolutionary for this that the G dwarfs so on the right diagram the G dwarfs of the hotter end at the left side their age you would infer from gyrochronology is about 70 million years older than in the case of the highs this is the Hyades age minus the Prisepi age you're subtracting this is kind of a confusing thing you're subtracting the distributions of the two clusters and the point being that the higher mass stars appear a little older than the lower mass stars while we think the cluster should have formed all at once we don't think there's a 70 million year age spread in one cluster and the other but this goes in the same direction as Jason's diagram here. Another third example of clusters being very revealing here when we get out to older ages now when you get to older ages so this is the case of NGC 6819 and Ruprecht 147 these are two clusters with ages of around two to two and a half maybe 2.7 billion years so not quite to the solar age but several giga years old. This becomes really difficult work as the stars get older the magnetic field gets weaker and the star spots get smaller and it becomes harder and harder to detect rotation period so our sample is very biased towards having lots of measurements of rapid rotating young stars and not so many measurements of these older stars but again here on the right panel you would expect if we extended the Prisepi model to this age you would see that it would go up in this gray line instead you get this sort of black curve where the stars seem to have stalled out as compared to where they should be. So our takeaway from all these clusters and there's other cluster work that fits into this diagram as well is that this McQuillan gap where the bimodality has something to do with some kind of mass dependent stall in angular momentum loss that these features seem to line up with this gap and it seems to be mass and age dependent the fact that it traced a 600 million year old gyro crone in my model is just kind of dumb luck. It actually looks like this is a feature that takes place starting at a few hundred million years and continues out to several giga years when you get to the M dwarfs. This is what we're seeing in the field we're seeing all these ages and star formation history artifacts all mixed together and so there's some kind of age dependent evolution that's going on. What's really encouraging is that this doesn't seem to be completely outside of possibility anymore. These kinds of observations especially the ones in the clusters have driven some theorists to take up the mantle here and I'm really still trying after a year now of reading this paper I'm still trying to digest all the implications of this model from a spot on Lanzifam a rotational coupling between the convective and the radiative zone. So using a rotating stellar evolution model and letting the radiative core have some kind of time dependent coupling to the convective envelope. And so what happens here is the star forms it contracts and then there's some phase of coupling where the radiative zone and the convective zone can kind of talk to each other or angular momentum is transferred from that more rapidly rotating radiative zone more efficiently into the convective zone. And so the analogy here is that the radiative zone is able to provide extra angular momentum to the radiative zone to the convective zone which it's trying to lose angular momentum by winds the spots and the activity is driving off mass and the winds are driving angular momentum away from the envelope away from the surface that we would see but the convective zone is gaining angular momentum at space from the radiative zone. So something is going on at that sort of interface layer called the tackle Klein. Something's happening at this point which is propping up the rotation period here. And you see it here, did I highlight it? No, I didn't highlight it here. You see it here, right by the Pleiades, this black line is M dwarf line. The Pleiades shows the M dwarf line right at that sort of stall. And so the rotation evolution stalls out because these things can talk to each other. So it's a really interesting, it's a little semi empirical or phenomenological you would say, but it's really interesting because it seems to fit the, I mean it's tuned to fit the open clusters but it does seem to kind of generally fit this evolution. You can see here, again, comparing orange or just pricepi to green, which is 6811. It's not as tight as in the observations that Jason Curtis and Stephanie Douglas had made but this general model, this general framework does seem to be populating this diagram and in the way that we expect from our observations that there does seem to be some mass dependent, time dependent break or stall in the spin down which is really interesting. Quick question. Yes, please. So I'm a little bit confused because what you showed seemed to indicate there was this gap where there weren't stars of that rotation period for that age. And that would suggest to me rather than a stalling, a speeding up of the spin down, sort of like crossing the Hertzsprung gap and stellar evolution. Yes. It goes across there. But you are talking about these in terms of stalling models, I would think that would be more of a pile up where you can get in a maximum rather than a gap. And so could you explain how that's understood or? No, I can't explain it because I think this is exactly one of the issues. I think you've hit the nail on the head and let me go ahead and go to my next slide. You've perfectly anticipated my next slide. I thought I was missing something, but no, no, you're following along perfectly. Thank you for that totally perfect question, which is this, here I've highlighted this feature, this stall, this stall does create a pile up, we think, a pile up, especially for the low mass stars. But the gap, there's not no stars, it's not truly forbidden, but things must move quickly through this diagram to get a gap. And so you kind of can see this suggested here, and again in the M dwarf line, you can see that it hits the stall and then it speeds up really quick, or not speeds up, I guess it slows down really quickly because we're losing angular momentum. So the period increases quickly. And so if you were to average through this and ignore this little shoulder, you would have this smooth evolution that you would expect, and instead it must accelerate through this. You can kind of see it in the pink line, which would be a M zero or something, or a K seven or something like that. But this speed up is not part of their model, is not tuned in part of their model. And so an open question that I have, that I think a lot of us have, is if you take this grid of spin down models and you propagate it with a realistic, smooth star formation history, do you just get a pile up and then a smooth, slow tail to rotation, or do you get a gap? This especially for these higher mass stars, these curves in red and purple and blue, don't seem to have the right shape to produce the kind of gap that we expect. So I think this is exactly the right question is, sure, we've got the bottom edges of the prawn of the shrimp populated with a stall, but we need also a quick resurgence of rotation, angular momentum loss to get to the gap to actually appear. And so a toy implementation of this that I've made for this talk. So this is not referee, this is just what I was playing with to illustrate this point. On the right, if you take the spot on Lanza fame, gyro crone grid that they publish and you populate it with a uniform star formation history and then you interpolate it into the period diagram on the left, you get something, I mean, there's lots of artifacts because it's not a smooth grid, you don't get a gap, you get a pile up there for the low mass stars in the bottom and then just a smooth smearing. You don't get this gap. And so at least with this toy star formation history that I've injected, it doesn't quite seem to tell the whole story that we're seeing in the field. So I like this general model that they propose, I'm adding one feature to this model. So they propose this, I think good diagram of the generalized evolution of rotation for a star, which I think has a lot of the right pieces that we see. There is some initial rotation period. Now their model assumed every star had eight days, which is not what we see from young clusters and things. So already the model is incomplete. There is some phase of contraction where the star is settling onto the main sequence. And then we see the bottom of the diagram here, the rotation period bottoms out at the zero age main sequence and begins its wind driven angular momentum loss. And then there is some stall, which occurs at some kind of fixed Rosby number or fixed point of confluence between the convective and the radiative zones. The tackle client gets blurred or something is able to pull angular momentum up and you get a stall or something. And then there must be some rapid resumption of spin down. It has to join this angular momentum loss trajectory again and then continue to resume its sort of wind driven breaking until it reaches some sort of final phase of what I'm calling, what I've labeled as broken breaking here, which has been seen in sort of the oldest stars, again by Jen Vansators. At what point this no longer seems to evolve anymore in a coherent or a steady fashion. And so rather than the sort of like T to the one half smooth line that was proposed in the 70s, we see that this diagram has lots of structure and we're probably missing features as well, as we've noted here, that this resumption of spin down needs to be faster to get a gap in the field diagram. But this gives you an idea of the kind of grid of stellar evolution models that we need to actually use gyrochronology to interpret the age of any random field star. We can't just take its rotation period and its color and interpolate based on a few clusters. We have to actually have a complicated realistic model just like we do for isochrones. And of course, just like for isochrone modeling there's all kinds of garbage to do with or opportunity to do with metallicity, which Sean Matt's group seems to be finding a lot of dependence on spin down. So the ability to launch winds is heavily dependent on opacities. And so metallicity plays a strong role. So we're gonna see a metallicity correlation here. Of course, binaries throw everything for a loop, which is both a hindrance and also a great opportunity. So from David Fleming's work here at the University of Washington from a couple of years ago, just doing binary evolution modeling using simple gyrochronology evolution, you can populate the diagram in all kinds of ways with binaries. Even a small fraction of binaries can pollute this diagram in all sorts of interesting ways. So those are confounding things. And we have very few clusters, right? The figure on the right here, even though it has more than three lines from Soren Maibalm's work a decade ago, we've only got about six lines. This is still very sparsely populated at some very interesting phases, particularly even at the rapid rotating end. We have very few clusters. We really, really need more data, says the observer forever. And so enter our new best friend, which is the Transiting Exoplanet Survey Satellite, which has been the last couple of minutes talking about here. Tess is going to answer our prayers, I hope. Now Tess launched about two and a half, almost three years ago now, and is serving something like 80% of the sky, not for four-year chunks for something like 27-day chunks. Tess, I think I will assert is the next frontier for stellar rotation, at least for the next few years. Here are just six random stars that I pulled out of my own little period finding script. Ignore all the labeling, just look at the fuzzy wiggly sinusoidal lines and agree with me and nod your head that these look like sine waves. Good. Tess is going to find a lot of rotation periods. This is fantastic. This is exciting. Tess has already observed more stars than the Kepler mission. It's about 300,000 stars. In total, if you only include the two minute short cadence data, if you include the full frame 30-minute data which is being released as we speak, Tess has resolved something like 10 million stars, something on order of that. And so this really is going to push rotation periods from even 30,000 into hopefully 100 or a couple of 100,000 stars we should have rotation periods for in the next few years. This is a huge revolution. Now there's a challenge with 27-day observing sectors for most stars. Here is Tyler's diagram where the K2 data with 70 or 80-day observations, you can get up to almost 30 days of rotation periods. But sort of the Nyquist frequency is something like 13 days. You can't get rotation periods very robustly for any stars with periods longer than about 13 days in Tess with a single sector. And here on the right, we've just plotted the Tess periods we've measured compared to the known periods for the handful of Kepler stars. We can treat Kepler as the ground truth but we're gonna do the same exercise with K2 soon. And there's not that many stars in this diagram. This is a diagram of like 20 points or something. They do fall the one-to-one line generally, a few down at the one-to-two alias, this happens. The only star that we had in our sample that gets out to a period in Tess of teens of days actually is an alias of a Kepler period that should be out about 25 days. And you can see one star that we should have measured, we measured it to have a very rapid rotation period in Tess but it actually has a slow rotation period. This is contamination. Tess has really huge pixels and contamination is a really big problem. So Tess is gonna solve a lot of problems but it is not a free lunch. Now there's some hope. Tess does have these overlapping sectors and at the equatorial poles, the continuous viewing zones. And so here is one example of a long period eclipsing binary that we found. I think Asasin actually found it first unfortunately. So there is some hope that with multiple sectors of data you can sort of stitch these together. It's not easy, calibrating fraction of a percent photometry over long periods of time is not an easy task but there is some hope. Christina Hedges and with Angus and others have published what they call the systematic insensitive periodogram or SIP systematic insensitive periodogram where you were both detrending the data here originally in pink at the bottom, you're detrending it and measuring the periodogram at the same time. You're creating a linear model with both the periodogram and the detrending at the same time. And here they've recovered a known rotator, a known slow rotator with 50 day, 52 day rotation using many, almost a year's worth of test data, many sectors of test data. So this is still computationally expensive but it is hopeful at least for the fraction of stars at the sort of poles or in the petals of this flower if you can see the overlapping sort of the things and up to about green in this sky map. Tests also might answer our prayers in terms of observing many more young clusters. So this is an example of an ancillary data set that's now available on MAST. The cluster difference imaging photometric survey are CDIPS by Obama at all. They've got a few releases now of this data, a few hundred thousand stars with light curves generated for known young stars and clusters and moving groups in tests most with multiple sectors of data you can see here and all the blue dots are the targets they've gotten. And I think this is a wealth that there's more than 150 clusters here that we can sample. Some of them are going to have great rotation periods. So this is work that we're interested in. I know other people are interested in as well. So this is an area I think where we're definitely excited for some collaboration that this is something you're interested in. But this will fill I think our need for having many more clusters to populate that evolution to look for that change in the stall and the spin down. Now, this long duration data set as my title suggested allows you to find some rare things or some slowly moving things. Here is just a shameless advertisement for a paper that we're working on that is, I swear I'm gonna send it back to the referee any day now. But this is a evolving eclipsing binary called HS Hydra. This is now a former eclipsing binary. On the left is the historical data from the 1970s all the way into the 2000s. And then on the right is the data from tests. And you can see the eclipses are so small they look like exoplanet transits. And now the eclipses are gone. There are lots of systems like this to be found and also the opposite happening where the inclination is changing and the eclipses will begin. So there will be newly born eclipsing binaries as systems have pivoting, shifting, processing inclinations. This is very cool. There's lots to do here that you can do finally with a 10 year space baseline. And then finally, the last thing I'll show is just with 10 year baseline, you can start to look for changes within a single star itself. Here I have shown stuff for the sun. This is the well-known 11 year activity cycle on the sun. And I won't spend any time explaining this other than the left most diagram is the flare distribution. And you can see there's lots of flares and then there's less flares based on solar max and solar min. And we have at least one candidate where over several years of data from the Kepler mission give you early data in blue, later data in the Kepler data in red and the Kepler mission in red. And then in tests, we have flares down in black. We think this star is undergoing flare occurrence changes which is exciting. And so I'll just wrap up by saying there's a huge opportunity space in this combination of Kepler and tests. Both individual missions are still under tapped. So lots of astrophysics to be done. And then the combination of the two with 10 year baseline allows us to see things changing. Space based geometry is produced the rotation revolution. I think that's a really cheesy thing, but I love it. There's lots of interesting results here in rotation about breaking, spin down, maybe fixing it, seeing the gap in K2 data. And I'm just so excited that tests is going to solve all of our problems with the little asterisks being that whenever you start solving problems you find more problems. And again, students, this is what we call job security. And so with that, I would love to take any questions. Thank you.