 So I'm going to keep this tightened on time. So I'm going to jump from the edge of the universe back to something more local and search for analogs in ZTF to the so-called Boyajian, or somebody who knows it as Tabi Star. Now this is the sort of title we're using on our GitHub repo, but as Keaton Bell reminded me yesterday during lunch, there's probably a better, more pithy title, which would be ZTF WTF, which I quite like. So maybe we should rename our repo this. And this is because, if this joke is not immediately obvious to you, here is the title of the discovery paper. This was Boyajian at all, hence Boyajian Star, a team effort from the Plant Hunters Citizen Science Project. This is paper 10, Where's the Flux or WTF? That's the joke. You were, ASCAP has a similar wide field protocol for weird transients. I didn't know that, but it's not as cool as this. I can say that with absolute certainty because the Atlantic said this was the most mysterious star in the galaxy. Are you sure it's in our galaxy? We are. We are. Yeah, that's right. So this has gotten quite a bit of press, so just a brief reminder of what Boyajian Star or Tabi Star is. So it's quite famous. It's got lots of good press. It's truly famous because it has Wikipedia page and its own Twitter account, so you know this is an exciting object. So a quick introduction for those who haven't been following along with the Kepler stellar literature for the last decade. Boyajian Star is a seemingly normal F-type star. This means it's a little more massive, a little hotter than the sun. Here is a detailed artist's conception of what an F-type star looks like. They're honestly fairly boring objects for most stellar astrophysics. They haven't been sort of the niche that planet hunters are usually looking at. And this seemingly boring, isolated star one day decided to go off the rails and had this very strange change in brightness as observed by the Kepler missions. This is 30-minute cadence data taken over this little inset here is many weeks. And Kepler being an exoplanet hunter, we can imagine what kind of occulting object might have moved in front of this star and what the shape would have to be to produce these strange like Batman symbol looking events. Now this was just one set of these strange dips. Here's the full light curve from the discovery paper. So this is 40 years of 30-minute cadence data from Kepler. You can see a couple, if you squint you can see a couple little events here in the first couple years that went unnoticed. And then there was this massive dip, here is the blow up of this dip, 15, 18% something like that dip for a star more massive than the sun. So whatever this was was a large or medium size but very opaque something that moved in a cult of the star and moved out over a series of a couple of days. This central core here is about a day. And it's very asymmetric which is interesting. Very smooth. And then if you go forward a few more years right at the end of the mission, a series of very strange dips, again this sort of bat symbol looking thing here, a series of sort of double peaked events which people speculated might be similar. There's sort of like one hump and then two close humps. There's a lot of hand waving and numerology going on when we look at this light curve because we don't know what it is. And there's been lots of speculation about the source of these dips worth. Again there's a couple other small little events here that went largely unnoticed. Something like 8% of the four year Kepler light curve was in one of these dipping phases and a couple of percent in total during these very deep dips. The plot thickened after the Kepler mission when we went back and so you can see this is all normalized as a delta flux mission when we went and renormalized the total light curve. It looks like, these are the calibration images. Here we've stitched this light curve through a possible solution to these calibration images. You can see that there was a slow decline of about 3% in the light curve over the course of the mission. It's a little less dramatic, but it's equally puzzling what would cause this seemingly boring isolated star to decline in brightness over 40 years, 3%. Once this was realized a slew of publications and popular science articles came out and continued monitoring has been happening on the ground. So here's an example from Tabby's follow-up paper in 2018 from ground-based monitoring. Okay, it's again, it's less dramatic, maybe less enticing than the 15, 20% dips we saw in Kepler, but it's no less puzzling. One to 2% variations like this on an F-star are unexplainable from standard stellar evolution models. There's nothing that this star should be doing that should cause it to vary like this with repeating durations. So lots of explanations have been posited. For example, the initial paper suggested maybe it was some family of large, very large comets. So we've seen cometary activity in light curves like this before that give you nice asymmetrical ingress and egress because the comet might have a big cometary tail. And so you could see some large family of comets, maybe very large comets moving in front of the star. That seems possible. What could cause such large cometary activity? Maybe something like planets smashing into each other or something like Mars running into the earth or something like this could create a large enough cloud to obscure 20% of the light from this star briefly. Whatever it has to be, it's a big cloud of something, whatever it is. This seems also possible. There have been other recalibrations of long time scale ground based data. So this is I think largely ASAS data, so the air bars are large even though it's a 12 magnitude star. Here's the calibration images from Kepler overlay. So it looks like maybe this 3% dip has sort of come back up if you believe this data and some other analysis of other ground based data have shown similar like possible repetition of this dipping feature. So this long time scale modulation might also be some large object or disc or something moving in an ad bar field of view. There was a very elegant visualization. I'm not sure if the model is super robust, but the visualization is very nice. What they suggest is that maybe this primary big smooth dip was some kind of ring system that was slightly inclined and someone had moved in front of or transited the star. You've got some sort of inclined almost like a comet like shape. And these funny little Batman symbols were the results of maybe Trojans that were in sort of proceeding and trailing in the orbit. And if this model is correct, this makes some loose predictions about what the orbital period of this thing must be. And so they predict that in the early months of 2021, which is not quite yet, but it's soon, we should see this family return and we should see a large series of dips return. They said that this should be a secondary eclipse as possible, but is weak to constraint. As far as I know, two years ago we did not see, because I didn't see a lot of Atlantic articles coming out again. So we didn't see the secondary eclipse, but that was a pretty weak constraint on this model. So potentially facilities like ZTF and others in a year and a half, early months of 2021, can constrain this model. So Voyage and Star has two mysterious behaviors. On short time scales, there are very unusual shape dips, which probably are some kind of occulting rocks or dust or something. On long time scales, there are also slow changes to brightness of the star, while a little less sexy, equally unexplainable. And what we know from a little bit of color monitoring we have here, it looks kind of like dust, is the best we've been able to say. We have a little bit of UV data, we have a little bit of infrared data, we have a lot of optical data and it looks kind of like dust, because everything else looks like dust up there. So the goal, like many of the projects we've talked about here, we haven't done anything yet, but we've started working on this for ZTF, WTF, is to use ZTF to look for other examples of this class. Now Voyage and Star at 11th magnitude is a little too bright to play this game with, or to do continued monitoring really with ZTF, but there's a lot of sky out there. It's just the Kepler footprint, but there's a lot of sky that we can monitor. So if you were to take a box of stars, so this is the Gaia CND of the Kepler data, for example, if you were to take a box, a small box of quote unquote similar stars, and look for the incidence of this activity, well if you use Kepler as the most naive statistics, Kepler observed something like, there's about 10,000 objects in that orange box that I drew it, and each with about four years of data. So if you just use very, very naive statistics, and you say there's something like 50-ish million F stars in ZTF with appropriate light curves, ZTF has about twice as much data as Kepler, which is kind of funny. You have a thousand minutes or so on each target, but you have 50 million targets versus four years on 10-ish thousand. You get about twice as much coverage assuming that this phenomenon is ubiquitous in F stars. It probably is not. And that suggests that we should see several Boyajian star like analogs in ZTF. Unfortunately, the light curves won't be as beautiful as in Kepler. Instead of seeing well resolved dips, we'll see one or two data points that are abnormally low, 10 to 20% dips. Again, if this phenomenon is ubiquitous. And so that's an enticing number. We can put an upper limit on the occurrence rate of this phenomenon just by looking at all the F stars that fall in this box and going and mining all the light curves. So the project that we've begun here using tools like AXIS we've heard about yesterday where we can easily cross match Gaia and other data sets to select stars is to go through and do this wholesale mining of the light curves. I have no results because we just started a couple weeks ago as a nice group project to introduce ourselves to AXIS and all the tool sets available. But when we're looking for things that are in the WTF category, it's worth looking at one more headline that came out from Boyajian star as an example. And it was this suggestion that perhaps astronomers have discovered aliens that instead of comets we're looking at some sort of grand designed mega structure that's orbiting around the star. Something like a Dyson sphere or a partially constructed Dyson sphere where they haven't filled in all the gaps yet. Different Dyson. So this opens the possibility that platforms like ZTF might actually be good data sets to do SETI work with. Many of you in this room have heard me make this pitch before, but I won't waste the opportunity to stand up here and make it again. From a paper that I submitted a few months ago, if you take really naive estimates about the so-called Haystack that we might be looking for needles in. So this is the nine dimensional Haystack that Jason Wright's group developed to parameterize the SETI parameter space in terms of volume and distance and time coverage and wavelength and frequency coverage that we're searching. If you plug in naive numbers for surveys like CRTS or our friend ZTF, TESS, LST and ironically the every scope wins slightly, beats LST slightly because of the constant two minute exposures. The point being here, this is in log scale. Most radio targeted radio SETI work has Haystack coverages of 10 to the minus 19, 10 to the minus 18, something like a pint glass or maybe a large bucket of water as compared to the ocean in volume differences. And here we are probing something like an Olympic swimming pool compared to the ocean. That's still a small sampling of possible parameter space but if you're trying to infer the presence of life in the universe from a bucket versus a swimming pool or if you needed to know that whales existed, you're unlikely to find a whale in your bucket. You could possibly find a whale in your swimming pool. So this suggests that ZTF might be an interesting or other surveys like this could be useful platforms. Now the literature is not well developed on what kind of SETI signals we're looking for. We're looking for things like lighthouses or runway landing strips or people waving flags in our direction but we don't have a lot of literature on what this might be. So one of the opportunities that missions like ZTF might have is developing how we look for these things. So looking for lighthouses could include off the top of my head, looking for repeating but non-periodic patterns. So here I've just drawn a cartoon of a fibonacci sequence of pulses, things that are spaced out with progressively larger and larger spaces and of course if you stick signals like this into data you can also develop tools to go look for them. So this last week I've been working on phases, version minimization for non-periodic but repeating patterns which has been a cute exercise. I'm not suggesting that aliens are out there blinking fibonacci sequences at us, I'm just suggesting that we're developing the tools to look for supernova and other things that we can do database queries with and go look for signals like this. Another example would be a project that I'm not leading but has been started by a European team called Vasco or vanishing something, something, century observations. These are stars that either disappear or are very slowly changing on century timescales. They have been looking at archival data, photographic plate data and are trying to find stars that are disappearing or popping into existence, things that just should not exist. I will also note that this team has reached out to me with interest in using like ZTF horse photometry to do validation of some of their candidates. So this might be an interesting collaboration that we can tap into. There are lots of things in nature that do look like this. There's a long list that I've just come up with, things like Voyagenstar or YSOs or our corbors can have a very peculiar activity that we're going to find, but thankfully they're also somewhat rare so you can write nature papers or other cool things with them. So it's worth looking for very strange light curves. Okay, and then with exactly 15 minutes under my belt I will say my conclusions are ZTF is a good platform and other surveys are good platforms to look for the WTFs of this world and of other worlds. We're on the hunt for Voyagenstar analogs, things that hopefully look like this but sampled once every few days. I think we should be mindful, just as a group that in a year and a half we might, with Voyagenstar particularly, might be able to go back and make some stronger predictions about what it is. And I would encourage anybody who's interested in talking about SETI or taking this idea just to touch more seriously to come talk to me safe tomorrow. On the hack day, there is no working group in the ZTF or LST community formally to do SETI, there doesn't need to be a small but growing amount of people who are taking this idea a little more seriously. So I would encourage you to come talk to me or just send me a tweet. Thank you.