- And the last speakers for the session are Nestor Espinoza and Ben Rackham.

- Can you hear me? Can you see.

- We hear you and we see you're not full screen mode, now we see you.

- All right, awesome.

- All right, I'll give you a two minute warning before.

- Right, thank you. So, we're happy to be here with Ben Rackham also online, to share with you an update on the SAG21, this study analysis group on the Effect of Stellar Contamination on Space-based Transmission Spectroscopy. The outline of our talk is very simple, we'll just give an overview of what SAG21 has been doing. Timeline and first look at the report then Ben is gonna jump in to describe then dissect the summary of the main findings of the report. And then we're gonna go with the conclusions as usual. So, for those of you folks that don't know what SAG21 is, So, SAG21 has in mind this challenge of stellar contamination. So, during a transit, planets go over one part of surface of the star and that might not be the perfect mirror of the entire surface of this stellar in which there might be, spots, faculae and other stellar heterogeneities that impact the transit depth that you measure. And this is important because during one of the techniques that it's gonna be widely used and is already been on used by HST, by grant-based officer surgeries, and it's gonna be used by doodled UST, it's going to be changed spectroscopy and these stellar contamination can hardly impact transit spectroscopy. So here we have one figure from the paper from Ben Rackham back in 2018, and I want you to focus on the right hand plot, the one with the green on, on gray plots. So that's a chain six spectrum waving in the x-axis transit does in the y-axis. And depending on how much animal genius your story is, how much your comedy spots, what's the common fraction, what's the temperature you might actually observe different contaminated. We call it spectrum than the true blender is spectrum in gray, so this is heavily impactful. And so we set up this side of the study analysis group to actually, you know, get together people from different communities, the solar heliospheric, the planetary distiller and the exoplanet. Are your communities to talk to each other and figure it out like one sort of a roadmap through these effect. So the main question that we're asking with SAG21, is to what extent will this impact space-based transit in spectroscopy, transmission spectra? In this case, and the main deliverable of SAG21, it's a report to NASA. So SAG21 is actually composed of five subgroups, this SG subgroup. So there's one group on stellar for photospheric and chromospheric heterogeneity. And you really need to focus on the actual physical processes, how these heterogeneity in stars happen, how they behave, what do we know? What do we don't know? And what do we need? then I think when our subgroup was found, was formed in around steller and Planetary Retrievals. So once you get a chance at spectrum, you can go on to retrieve the properties of the planet, but also not only from the planet, but also you can get the properties from this thought and it's contaminated your spectrum. So the idea was to, you know, have a detailed subject, look at what we know what we don't, what we should expand on et cetera. Then we have a sub, two sub groups, three and four on both occulted and unocculted active region. So it might be that during a transit you might have caused, a spot or faculae and even out of transit, if you take long-term photometry or spectroscopy, you might actually see a variations as a function of wavelength and amplitude in time because of these spots going on in and out of view. And then the fifth subgroup, it's kind of like a one that involves the rest in terms of future complimentary observations. So which observations, we should go and focus on, in order to overcome this challenge. The original timeline of SAG21 started back in September 3rd, 2020 We had a kickoff meeting and then from there to November, we have a definition of this subgroups and questions. Then the subgroups were formed, we selected leads for that and the subgroup started working on what should be actually green And in the report, we presented all that in a community symposium in March 1st of last year, 2021, which was very successful. I'm gonna stop in a minute on that and then we had a draft report around June, August that we wanted to submit by then. So before going into that detail, because you haven't here, everything reported yet. So there's some news on that. The community symposium right away, it was a very successful, we got her, like there were more than a hundred attendees, we presented talks, we gave, contributed talks by different members of the community. A lot of that is recorded, you can go and check that out and decide that up here, I think it was a very, very fructiferous meeting. We had a number of discussion between the different subgroups, So I totally recommend you check it out. So in terms of the report, we had to move it a little bit to allow for more time from some subgroups and also for us as chairs of SAG21 to basically finalize the report. And now I can proudly claim that, the entire team has reached a kind of a consensus. We've gone through the editing process and we have like a final report that we're actually, we aren't currently, we passed it around SATAG EC for feedback. So we expected, submitted soon. So their report is this beautiful 90 plus pages full of figure, as fun as well. It has five main chapters, one person group, and he has over 40 major contributors. like over a hundred scientists from the Helio excellent plan guided communities that got these together in their report. So now to comment on the main findings of the report, Ben Rackham is gonna give us an overview of the summary of the main findings.

- Yeah sir, so our report ended up with a total of 14 findings. And what we call a finding is this contextualize statement of a need that we've identified, which we can, we can address in order to make the best use of space, space transmission spectrum. We've boiled down for the purposes of this talk to summarize. We boiled down those 14 findings into seven questions, scientific questions that they all feed into. And really those fit into three themes, three topics. The sun, studies of the sun as a stellar benchmark. The theme of what we know about the surface heterogeneities of other stars. And then how do we map our stellar knowledge to applications of exoplanet transits and vice versa? What can we learn about stars from transits markets? Next slide please, so I'm gonna go through these three themes and just touch on the, the, the total seven science questions that we identified. So the first thing is the sun is a seller benchmark, four of our findings end up fitting into this, and we boiled them down into two science questions. The first question we'd like to, that we need to address in order to make the best use of the transmission spectrum from space-based facilities is what are the spectral properties of the solar photospheric and chromospheric heterogeneities as functions of both time and location. And one of the surprising things for the exoplanet people in this group is to find that some of this knowledge just isn't out there yet. You would think that we, we know these things about the sun, but the truth is, because of the different focuses of exoplanet research and solar research, the types of data that are most useful for us just haven't yet been collected for this time. Also there's a, there's a technical issue there because what we would like as exoplanet astronomers is to know the, the spectrum of a spot at. Resolutions comparable to the HST or James Webb from UV to the near infrared. And what we actually get from solar observations is either the contrast of a spot, the photosphere, and a narrow photometric band as shown on the left panel here with some images from the Swedish solar telescope, and that you necessarily need to focus on a narrow band to get this kind of imaging data. Or if you want to look at the total solar radiance, we have that data over a wide wavelength range, but it's not for resolved areas of the sun. If we can tell you how the sun's brightness overall changes with time and as a function of wavelength, these are going to be addressed by the, when, when DKIST is fully online, we'll have new capabilities that will help us get a better handle on this, but also just talking to solar experts from the perspective of exoplanets. Now we've started some investigation where we're going to be looking into collecting a spectrum of a solar spot, collecting the spectrums of solar calculate and using those inputs in an exoplanet research. Okay, and the next question that's related is, what are the spectral properties of solar granules? Again, we know about the power spectrum of the sons like her and that's what she has shown on the left here though, the high frequency variations of those solar brightness, I'll do two granulations. And now we have even like more beautiful images than before resolves images from DKIST of solar granules covering very narrow wavelength region. There's some concern now among some folks that granulation might present, well, granulation could present two types of noise signals and transit data, which we'll get to in a moment and to really understand the second type of noise signal, we need to know the spectral properties of granules. So what is the spectral contrast of a granule in the UV optical and near infrared? And that kind of data doesn't yet exist, we have it in narrow phometric bands, but that's something that we can look at on the sun to inform our studies of exoplanets. Okay, next please. The next topic is surface heterogeneities of other stars, basically, what do we know the other stars? And five of our findings fit this category. I'll summarize them into these three questions, so basically wanna know how those spectra of spots and factually change with different properties of the host star. The left panel here shows some recent MHD simulations for three different spectral types that show that we're able to produce spots that, what you've being tone in the channels, is the spot to photosphere contrast is a function of photosphere. And that generally trends with what we've seen through doppler imaging studies, but to actually extract the spectrum of the spot, we need to have these MHD simulations in order to get a realistic spectrum that we can use as inputs. On the right is just a summary plot from another recent MHD study that looked at secular spectra as for a solar twin with different magnetic field strengths. And what you see with these different colored lines here is that the spectrum of the faculty can change pretty drastically, depending on the magnetic field strength as a star and that's interesting because most of the known exoplanet host stars, their activity is gonna be dominated by factor contributions, not by spots. So it really understanding how the spectrum of the faculae region depends on the magnetic field strength of the star is going to be important when we need to expand on these recent models. This is another example on this next slide of our second question is what are the spectral properties? A spot with faculty on specific high priority exoplanet host stars? So this is another example of recent MHD work that is expanding models originally tuned for the sun to other spectral types. What's being shown are spots on a GAK and M door. And using these like expanding grids of MHD models, we can begin to understand what the spot spectrum, what the secular spectrum might look like for a specific complainant host star that's, you know, essentially the best studied exoplanets are gonna have to have the best studied stars as well. And we need to really work on that second category here. Then you have two minutes, okay. And we need to know about granulation. There's some studies that have shown that granulation doesn't induce a flicker type noise floor, just like in radio lesson studies that extends the transit studies as well, but also there's a spectral bias that can be introduced by granulation, and that's less well studied. It might be as a level of one to two PPM, but we, we really need to look into this some more, it's an open question. All right, we can go to the last category nester, which is mapping stellar knowledge to transits and vice versa. This was really the biggest bucket. Nine of our findings fit into this And we've boiled them down to two questions. How are we going to translate our knowledge of stars to planets? And this is just a smartest board of different stellar studies that we can leverage to get a better idea of what the impact of spots are on exoplanets. We have a transit of the sun with, by Venus and the left panel there. We really need to leverage the existing data, it's data we have on finance, transiting the sun, and collect more. It sets if we can, middle panel is showing a recent MHD study. That's looking at magnetic regions as a function of field strength and spectral type. We need to leverage these MHD studies to produce spectrum of spots and faculty, which we use for inputs on our exoplanets studies as seen on the right panel there. The final question that we summarized is what can we learn? What unique trends on stellar heterogeneity are enabled by transit? So what can we learn about stars with these nice spatial probes of their photo spheres, the exoplanets are, and this is a, this is a great way to provide inputs into these steller models that don't have the same sort of ground-truthing that we have for the sun. So as we expand these models to other spectral types of activity levels, we can use exoplanets to try to get some ground truth parameters. And what we can do is we can look at the contrast of spots and the size of spots as in this left panel here from Morris et al.. And because we're doing transmission spectrum for getting a transit spectrum, we can look at the wavelength of tenent contrast of spotted regions and secular regions like in the right panels from Espinoza and all. So that is a very quick summary of the main points of this large analysis. And in conclusion, we just want to reiterate three takeaways from this talk that we're basically done. The report has been submitted to the ExoPAG EC, we're going to incorporate the final feedback and this week, and it will be on archives very soon. If you wanna see it before the end of the week, just let us know. And we'll share the link with you, and this SAG has produced a lot of valuable assets to the community, including the report and the community symposium, which all the talks are available online. Just look for the SAG21 website and finally, yes, again, the report is going to be out there on the archives within the month, so thank you and we can take some questions.

- Hey, thank you very much for our speakers. Let's give them a virtual applause and let's move to the questions. The first question could exoplanet contaminate Stellar data as well? So can things go the other way round?

- I'll take a stab nester, yeah, I, they definitely do. I would, I would say that we, we use a stellar contamination shorthand, 'cause it's a idea that people understand that, there's a lot of discussion actually within the group is like, should just not use that word because there're stellar signals and there're planetary signals and both are special and important, we on study both. I think I will say that I think, you know, planets generate smaller signals and stars. So maybe if you're studying stars, you have to worry less about the signals that are introduced by your planets. But when you're studying planets, you certainly have to worry about the signals introduced by stars.

- Okay, next questions do spots and faculae always occur together? Could you expand a bit on how they are related or different?

- I don't know if you want to take this bit or not, but they can occur together and they might lose one might win over the other. The thing is that it might depend on age and spectral type and to be completely honest with you, we have like a general understanding of when faculae win over the spots, but the detail analysis on each X-Plan holster is what really, really matters with this kind of work. There's many unknowns yet, but yes, there can be like a faculty dominated star has more faculae than spots and so on and the other way around, so it's a complicated matter in general.

- Okay, Don't have any other questions I'm just gonna ask or highlight. I would assume that interdisciplinary communication here is extremely important, right?

- Yeah, it certainly is. And we made our best effort to reach out specifically to people from different communities that deal with Helio physics and astrophysics communities, as well as issues, some general calls to, you know, the type of listservs that, that might, you know, focus on people from those fields. And a big part of our work was, was trying to make sure that we are understanding each other cause terminologies vary slightly between the disciplines and the focus of what, what people are trying to extract can be different and that leads to different techniques and we want to just make sure that we're on the same page and it was a, it was a big, big part of this work was getting everybody to talk.

- Okay, thank you. So I would suggest that we will unmute now and give a big real round of applause to all of our speakers. Michael do you have any announcement?

- No, just to, to thank Nestor and Ben for that excellent presentation on both SAG21 and SAG22 for all the extraordinary work they've done in the past year, it's really a Marvel to see what they have done. And the thank you Ofer and all the speakers from the session, it was excellent. And I think we are on a 15 minute break.