SPEAKER: Agnes Kospal (Osservatorio di Konkoly, Budapest)
TITLE: What can we learn about young stellar objects from their variability?
ABSTRACT: Variability is practically a defining property of young stellar objects. In this talk I will summarize variability statistics during pre-main sequence evolution, focusing on low and intermediate mass stars. I will present different variability patterns and their physical reasons. I will highlight three special topics: regular accretion variability of T Tauri stars, extreme accretion outbursts of young eruptive stars, and pulsed accretion observed in some young binaries. I will discuss how variability, if accompanied by significant luminosity changes in the system, may substantially alter the geometrical, mineralogical, or chemical structure of the disk, and may consequently affect the disk’s planet-forming capabilities. Finally, I will show some prospective future directions in this research field, using data from on-going or upcoming surveys.
okay okay so I think we can start um hi everybody uh it’s a pleasure for me uh today to introduce you Dr Agnes kosa and uh I’m gonna say a few words before trapping so she uh defended her PhD uh thesis in partical physics and astronomy Su um at the EOS luren University uh in Hungary in 2009 and after that she was an assistant researcher fellow at calcon observatory in Budapest Hungary uh then she was a postdoctoral researcher at Len observatory in the Netherlands and always in Len she wor the prestigious Eva Fellowship working at a sec finally she moved back to Hungary being a senior research fellow until 19 2019 and when she became researcher advisor uh tenard and this is her current position at the Observatory the research center for astronomy and scientist where she leads the stff Miss group during her career she won many awards and funds uh she has been very successful uh I just mentioned the fact that she won an NC starting rent uh which just finished um his name was saket uh was about equation and variability and her commitment in being a female Ro model for young researchers she tuted many students like was dos including me and she’s part of many International collaboration uh she’s a well recognized expert of subformation in general and varability in particular so for this reason I will stop this presentation here and I leave to her U describing your work so please the FL is yours thank you very much thank you I’m sure this is much more flattering than what time this but thank you very much for the nice introduction thank you for for the invitation it’s a a great pleasure to be here this is my first time in Naples I’m really happy to be here and to to meet you yes so so uh today I’m going to talk about uh young Stellar the variability of young Stellar objects and um but first add be a long talk so just to to summarize what I’m going to talk about I will give you a short introduction to con Observatory to where from where I I come H and then a little bit of introduction to Star formation because I know that not all of you are working on this topic and then I will um talk a little bit about uh variability of of youngst objects why we are interested in this what are the physical reasons for the variability uh how how we can observe this and what physical parameters we can constrain uh from these observations and then I will focus on on um kind of a space parameter space which is the time scale and the amplitude of the variability and then there will be different groups of of young stars in in this parameter space and I will talk about each of these these groups each of them are interesting for there are reasons and then one aspect that I will mostly focus on is is the most most extreme variability which are the armur and their effects on the circumstan which is a specific field I’m studying so I will talk a bit more about that so just to start off I’m coming from con Observatory this is the main largest astronomical institution in in Hungary it’s as mentioned part of this Research Center for astronomy and Earth Sciences so there’s the astronomical Institute and two more earth science institutes group together uh some collaboration between between us and it belongs to a a larger network of basic research institutes that uh previously used to belong to the Hungarian Academy of Sciences now it belongs basically directly under the hungan government at the moment we have 65 astronomers working at our Institute three large Institute 25 of them are permanent staff and then we have at the moment 19 postdocs PhD student students six Professor mer some support staff and U it’s a quite International and typically like four of third of of the staff the researchers at least are international and then um we work on various topics so of course one topic is Stellar physics so there are colleagues who work on Stellar pation Stellar activity nuclear astrophysics there’s a another ERC group uh which run the the same time as my group uh for nuclear astrophysics and then we work on Str environment so staring Planet formation ex planet there’s a group for solar system studies so they study asterids trans TransUnion objective and meteorites there are a few people working on extragalactic um astronomy Supernova quars and also the large structure in the universe it’s a new new uh research group uh and then there’s a little bit of instrument and satellite development I have a colleague who who builds CS so that’s uh basically what what our Institute is working on and um that is our main building where Al Ella used to work and um and we also have a mountain station about 100 kilometers from Budapest this is in Budapest capital city and then about 100 kilometers from there we have a mountain station where we have a smaller optical telescopes um basically four three three uh main instruments in these three domes and residency there um but of course we are using the international facilities as well we write observing time proposals and we use the VT use other telescopes um I wanted to also talk a little bit um about our collaboration uh with the Italian colleagues uh so basically we started I think with Al who came to Budapest and encouraged us to to build a closer connections with people mainly in Naples and Rome and then this is basically our large group who um out of which now some people left um but we are still collaborating and we have a basically weekly pelons H and our main topic so for this collaboration for these people are um photometric inspector scopic followup of Gia science alerts and not only these objects but also other young stars as well and then if you haven’t heard about Gia this is the satellite it’s an astrometric mission of of Isa so it basically scans the whole Sky several times a year makes very precise astrometric measurements but it also measures uh brightness for billions of stars and it has an allert algorithm which checks the brightness of which source it measures and then if it sees something interesting that might be a interesting for the scientific Community to follow up then it issues alerts like it published there’s a web page where you have some kind of light curve published saying that okay this this we now published and then if someone is interested they can follow it up um so we are doing that uh and then we write Jo proposals for telescopes like the lbtm TNG so facilities which are maintained or funded at least partly by aliens but also for other telescopes you using Hungarian Scopes as well and then we write Jo papers so what are we working on uh so we studed Star Planet formation and you may wonder why why is this an an interesting topic I think it’s very interesting because uh well I mean it’s clearly interesting because a St Planet formation open questions in St Planet formation of motivates the uh construction of the largest telescopes and the most sensitive instruments and um and then now uh there there has been a lot of uh development a lot of improvement of U observational and numerical techniques in the recent years which means that now we have a good general idea of how sunlike stars and their planetary systems form H which is based on basically observational evidence uh and and the underlying physics is understood using theoretical work and numerical simulations and then um like a broader motivation is that basically by studying stars and planets that are forming now in different star froming regions in the Galaxy we hope to understand better how around sun solar system and around Earth formed perhaps billions of of years ago so I’m TR an artist impression of what a young star looks like but of course now because we have fantastic instruments we have direct images spal resolved images of the star formation process most of the important steps of the star formation process uh so I’m showing that here I’m just collected some some nice real uh images of how this process happens and then basically if we concentrate on sunlike Stars so Stars which are less massive than about eight S masses so low and intermediate mass stars it starts up with molecular cloud very you have kind of filaments there the the den Parts they collapse under theity then we get Cloud cores and then at the center where the density is the highest you start forming a protar and then at the beginning it’s still embedded in its uh envelope but due to the conservation of angular momentum the the material closest to this forming star quite quickly forms a dis an accuration dis which feeds material to the forming star and this dis also becomes the birthplace of planets and once you start forming a large enough Planet as planets they start interacting with this dis that is their birthplace and then cause an interesting Str structures but eventually you build up your star you build up your planets you use up all the material that the rest disperses and why remains is a is basically a mature exoplanetary system and um and then I’m going to focus on basically this right hand side of of this graph and or series of pictures uh for those objects which we call class zero class one and class to the these are the objects where we have the protar and then we have the circum material so if you want to observe these kind of objects then um then you can measure them at different B blength and then you will find that the earliest phases at the class zero f this is the phase where where the object is is really large quite cold uh this is uh this phase last for about 10,000 years after the start of the gravitational collapse and accordingly um according to the temperature basically these objects are mostly seen at far infra the midterm B lengths and then as it progresses further after some 100 thousand years you start seeing the Photosphere of of your protar and then there are a lot of infrared and millimeter submillimeter excess which comes from the dis C conell disc on the envelope uh so now you have the higher temperatures of course um but it’s still quite large because these envelopes can be pretty large and then even later envelope disperses what you have is basically your PR and frere and then then some excess from from the disk uh which can still accrete or can be passive after a while this may last for a couple of million years and these this typically 100 days in size again you still have some temperature gradient and after a while as decoration stops you disperse your dis and then you basically have your star and then even later like after tens or hundreds of millions of years you may have some collisions between your planet as in Earth and that may produce fresh dust in this system like a Dusty disc which we call a der disc so that those discs are signs of a planet formation and then that that lasts for a long time um even even the around solar system have a have a de disc so um so you saw that this is a a quite complicated process with many many details and then one uh difficulty U about observing and modeling these systems is the the problem with the the orders of magnitude so if you look at spatial scales um the filaments that you have in molecular cloud are several parts that long you have to take something you have to take some material which is spread out at several par and then you have to compress it to basically one solar radi because that’s your that’s the size of the star and that’s I think eight orders of magnitude you have to overcome and then of course in the ism in the interest matter you have densities which are typically like a thousand particles per cubic centimeter and then you have to increase that density 26 for cubic centimeter which is density at the center of your Spar and then for the temperatures you take the the interstellar met typically 10K and then at the central usar you have to 10 milon um but even if you disregard the star the St interior which I I don’t work on and we only look at the circumstellar matter there’s still uh orders of magnitude variations in in densities in temperatures and in different physical parameters so this Evolution I I outlined takes a few million years but of course um we don’t leave that long but we do see uh variability in if you look at a young star shorter time scales which is very nice because that’s a good topic then for a PhD or a post do and indeed young Stellar objects have been defined many many decades ago as a as variable Stars they were recognized variable stars and if you look at these traditional variable stars like PTO or SE or or once you run out of the alphabet you start numbering them like the 1057 sign whatever so many of these long known variable Stars Are Young Stellar object uh typically this has been monitored at Optical wavelengths 100 years ago we only had optical telescopes um and then if you monitor these kind of stars so the um low mass young stars are called teary stars and intermediate Mass young stars are called hermic Stars virtually all of them are irregular variables uh and there variability amplitude spread from the barely detectable uh to the file magnitude or even higher and then of of course there are different reasons behind this variability uh which then cause different variability patterns so again I’m showing an artist’s impression of what a circum star environment of a young star looks like and then if you look at different parts of this system then uh you may noce accuration channels through which the accuration rate may be more efficient or less less efficient more or less material may go through this and that that means that that changes the um energy that is released when that material lands on your on your star so that causes variability and then there may be like flares which are the analoges of the solar flares that we observe in our sun but for young stars because they have much stronger magnetic fields it’s it’s much more energetic and then if you look at low M Stars you again because of their magnetic activity there may be a dark Stellar spots on them and res updates then that also causes some variability and then of course there’s a lot of circumstellar material around your young star and then if the inclination is so then parts of the material May obscure your star and that will also cause some variability and then of course all of these things may happen at the same time so what do you how do you deal with that I mean there are some objects where uh this can be nicely discerned not always but but there is this very special case that we managed to do this and this is called vut one of the young variable stars in tus here I’m showing a light curve taken with the capar K Mission it’s an optical light curve which covered about 8 years 80 sorry 80 days with a one minute Cadence it’s a great data set and we managed to discern the different variability phenomena here so the very light gray you see a kind of a sinusoidal variation which is due to the rotational modulation caused by the dark spots on the star and then in some cases you can see that the star is brighter than what you expect compared to this sinusal curve and that’s the case during those S the star was actively accreting from the dis this typically lasts for a couple of days but then there are these narrow Peaks very bright Peaks which are which last only a few hours those are spellar flares and in some cases uh the star is actually ther than what we expect like here also here here and that’s because of obscuration by the circumstellar material so everything is mixed here so it’s sometimes not easy to to to discern to to differentiate between these phenomena but sometimes uh colors sometimes time scales help now uh just to recap uh what I’m talking about young stars are variable they are variable not only photometrically that I I’ve been talking about so far but also spectroscopically and uh but they they have different time scales and different amplitudes and this graph basically summarizes um what are the typical um variability amplitudes and typical variability time scales for uh a whole range of phenomena that we can for young stars and then the color coding um basically shows the different phenomena like the the blue bubbles are accuration related abenes and then there’s a some longer time scale smaller routing variab are slow changes in in the disc there are Extinction related behaviors with the red bubbles there are some events like when when there’s a binary and then one has a disc that obscure the other one or you have two stars and then they exlipse each other so those are binary related things and then there are small amplitude variability which are related to the star itself like the spots or the flash or even pulsations young Stars maybe pulsating variables so this is kind of a an overview and um and now I’m going to focus on accuration because again and this is where the field I’m I’m studying and just to to repeat again accretion is the mass transport within the disc and from the disc to the protoy and uh this is again very complicated it depends on density it depends in temperature ionization magnetic field and it varies with time and location in the disk and in this series of figures I’m I’m showing kind of an evolution of of how our knowledge about this uh about phell creation develop so this is like you know a simple uh artist VI uh which may not be very precise but then you can just sketch out um different parts like you have the disc and then the dust disc and then you have a gas disc and then you have a creation columns then in the material is diverted by the magnetic field of of the young star and then the material lands on the on the St surface you have the accre shock and then you may have dis you have Stellar all kinds of various things and but then that’s again just a concept uh conceptual sketch uh but nowadays um there are some groups who who really do like 3D magnet hypnic simulations of the accretion process H so this is the result of such a numerical simulation so uh these are very Advanced uh things um so um I will focus on the rest of my talk on on aeration variability so I will focus on the blue bubbles uh and you can see that there are like very dramatic evens which which is very large amplitude like four to six magnitudes these accuration Outburst these are these are so violent that they’re important for dis Evolution Planet formation they they have long lasting effects on on the properties of the this they may even affect radius and then there are less traumatic events like smaller smaller time scale burst then like typical fluctuations of of the magnetospheric aeration which which may have less significant effects but are still important to to understand underly physics and then what is important to keep in mind that the creation rate varies through our premium sequence Evolution so we find a variable equation class Z class one class objects as well so it’s very important to understand this to know how Stars gain their Mass uh there are many open questions in in this field and some of some of these questions motivate my my own science uh for example what is the role of varri accuration in in building the Stellar mass and how that will affect the observed properties of the prot Stars it’s a question whether all young Stars experience this large UD the outburst or or these require some kind of special circumstances it’s a question what triggers these these large accuration burst and Outburst this is still debated there are different theories about this and in some objects like this one the 1647 orus you can see that the star brighten stayed bright for a while and then went back to question and then went into Outburst again so there are events where where you can switch off decoration and then switch it on again so it’s a question what can uh what kind of process can do that and and how we can use this kind of observations to constrain what kind of instabilities is like what kind of physical phenomena lead to these bursts and of course in this case it’s also a question how we can how precisely we can measure the Luminosity of such a system which at the top of this burst may be dominated by a creation just by taking a light curve at a single wavelength probably not very well and then what is what I’m particularly interested in is the influence of of the accuration variability on for example disk structure or the chemical minical property the processes that are ongoing in these discs which is important because that will that may affect Planet formation that is actually happening right when these bursts and urst happen in the this so how can we start to answer these questions well we have to observe these systems and what is important I already mentioned in the previous slide that uh it’s important to observe them at multiple way lengths so use multi wavelength topometry for example and not only like different Optical filters but it’s actually important to measure from the X-ray through UV Optical friend to the friend to the radio it’s very important to be precise so space telescopes for example you can do microm magnitude photometry spray but even from the ground there are facilities now with which you can you can reach M magnitude level Precision level easily it’s also important to do spectroscopic monitoring because Spectra reveal a lot about the physics that are going in this object again there are very interesting lines that Trace different uh parts of the disk and different physical phenomena in the UV or the optical infr mimer but it’s also very very helpful if it takes facely resol images with the Adaptive Optics system or you use interfinger and then if you’re very lucky and then the uh committees like your proposal then you may be even to you may be even able to return to a previously observed object and observe it again and try to uh make an interform monitoring for example super useful and then all those are the observations but to interpret them of course you will need a UND dependent models which is again something that is quite recent now people in theory groups start working on on Time dependent modeling so what kind of parameters can we constraint so time is a key parameter of course we talking about variability and if you want to study variability then basically you have two main avenues that you can follow and either you make kind of a large statistical study of a star froming region You observe dozens or hundreds or even thousands of objects in a certain star froming region and then you do the same for different regions with different age and then in this way you can uh you can follow what’s going on as a function of a population age or and then you can do this uh you can follow what what’s happening for millions of years or the other thing is that um you can do is you focus on a few specific objects and then you study their variability on an hourly daily weekly monthly or even yearly time scale if if your contract allows you to do that so and then then you can observe variable ACC Creation in action so what is important to understand or to keep in mind is that if you make a snap snapshot observation of St forming region or or one specific object then you measure uh properties that are characteristic in that instant but that doesn’t mean that those properties are constant or stady state you may assume that they are but but they’re they’re probably not so you have to measure uh measure this as a function of time and then I mentioned that I’m interested in bursts and Outburst so for these we need to measure their amplitude how what is the accuration rate at the peak how long they last how often they repeat and and what is very important is basically the ACC created material over one event um and I really we would need to know this for all events and then uh of course you you need to observe the deted light CS um but you also need a spectroscopic sampling at least at Key phases like in the quiet sense at the peak of the Outburst maybe in between as well because this will help you understand the physics so let me just show this graph again and let me clean it up so then we only focus on the blue bubble the creation related event and let’s talk a little bit about them let’s start from the bottom left corner where we have the shest time SC small temped variability which is the fluctuations of the magneet accuration so typically this is what the light curve of a classical accting T star looks like and and then we we make this kind of individual studies of of various young Stars particular Inon or in cus in different close by star forming regions we have a series of of papers um on on these uh various various individual Stars so what can we learn from from analyzing these kind of light curves and and Spectra basically this uh this is the uh the idea is that uh the modeling of of the accuration shows that young Stars can accrate basically in two different ways one is a stable accuration where you basically have two well formed accuration columns uh which L the materials from the disc on basically on the magnetic close to the magnetic po of the star and then in such a and and that is what it stayes for a long time and then as the star rotates then you can have a kind of a periodic light curve and by also periodic changes in the um profiles of the accuration Tracer emission lines and then the other way uh is the unstable accretion there you basically have these smaller tongs of material that can touch the star surface at various places and then they come and go and reform and in this case your light Curve will be more stochastic and then so the profiles of the of the emission Lin change in a more complicated way and whether like that or like this depends on its rotational period its magnetic field it’s the strength of the magnetic field or whether it’s dipole luminated or octopole luminated it may depend also on dis properties on many different things so basically by monitoring light curves and Spectra you can learn about the way that the star is a creating and then one more very interesting thing I’m very excited about now is that you can use this kind of light curs of young stars to try uh to measure in a radius so that does this this is called a light Eco or reverberation experiment and this is actually a routing technique in in studies of AG so some of you might be an expert in this but as far as I understand what they do there is then you have your which the creating changes its brightness and then the um light travels uh during some time to this dust thus that is is there in the agss and then you can measure that um this tus uh also changes its brightness with some time delay which is typically weeks or months in case of a super massive black H but essentially you can do the same experiment in case of young star you have your part of start of the central changes its brightness because uh the changing accuration and then the light will travel to the inner edge of the Dust dis it will heat up the dust dust there and and that heating is actually quite fast it’s almost instantaneous and and then you can observe that basically You observe you trace the accuration optical wavelength you trace the brightness of the inner dis do dis at some longer wavelength let’s say in front and then there will be a time delay between their variability which is on the order of 1 minute because those are the spatial STS there but you can try to measure this time delay and this was actually done once so far in this specific Young Star while be 16 B um but now we’re tring do trying to do this for second time uh using one specific Young Star which is called Dr to and then we are trying to do this with with the t space telescope using the nearest instrument so this instrument covers the 0.9 to 2.7 Micron range and we complemented this monitoring with the optical light curves like 05 point4 micr so we have B and and G B measurements and we measure we measure this star for several hours simultaneously James SW and uh we were lucky enough because the star shows significant variability more than half magnitude just in in a few hours and now we have this kind of light curs at 248 different wavelengths in this wavelength range we are trying to do this Echo experiment I don’t have definite results yet but I think this this will work out but this is still work in progress so very neat okay let’s move on to next bubble which are be decoration bursters these These are objects which spend some time some of their time in Co but then they they become brighter for from time to time by a factor of few so again we have a couple of papers on on these kind of objects some of the GU alerts show these burst but one specific system I mentioned briefly earlier dto I want highlight because these show very interesting burst this is a very specific system because this is a binary star uh it’s it’s consist of two ID almost identical 6 solar mass stars uh they orbit each other with a period of about two weeks 15.8 days and they’re on an eccentric orbit quite High eccentricity actually that means that as they orbit each other sometimes they are very close to each other they approach each other to within eight star radi and then uh other times they are farther from each other and during parest what we can observe is uh that the the system shows flares so really brief like few hour long brightenings in B UV and x-ray wavelengths and then in the infra Optical it should longer brightenings like they last for a few days that’s because what what’s happening is at least what you can observe in Optical infrance is p creation so this means that as the two stars orbit each other when when they are at Upp spot they are farther from each other they’re closer to the circum stellis they pull some material from the inner disc that will sometime later during are from eventually land on the two stars and then the rate increases this shows a numerical simulation coming from from this paper uh a coration rate as a function of time for the primary and for the secondary and uh their distance so you can see that when the stars are closes to each other then there’s a peak in the accretion rate so that’s the numerical prediction and what we actually observe in my paper we measur this using multi ometry and that indeed during peras most of each F you see a peak in the operation r so it really does that and then with Al we had another close look at this system not only using photometry but also spectroscopy we had eight Spectra taken at different orbital phases so in this figure we summarize the ACC creation rate as the fal orbital phase and then continuous lines of photometry based results with DOT spectroscopy based results and red dots are our results and shows that theary went after significantly close to par asron and what is the new in this uh study is that us using these line profiles uh we could actually discern which starre because this had high enough resolution to resolve the movement of the two stars and then from looking at by looking at the acction Tracer lines we could follow whether the primary or the secondary ACC more and what we saw is that it changes it changes from Orit orbit it’s not always the same star which actually uh is what the numerical simulation show because here you see that one star is supposed to create more the we less and then they switch here so very neat it does what it should do so and then one more thing about this system is that of course um I mentioned that they approach each other the two stars approach each other very close by during perest and that’s that’s interesting from another point of view because they have magnetic fields and then when they approach each other these magnetic fields merge they are so close to each other and then some time decade ago we had some n ideas of of how this merging and separation of the magnetic fields happened at that time you had no idea about the magnetic field of the stars now thanks to spectr Prometric observations we could do a kind of a mapping of of the brownness and also the radial meridin as the components of the magnetic field for the two components separately so it’s very nice another interesting thing that we discovered is that if you measure if you do these radio velocity measurements from from the spectroscopic observation then of course you can measure the the RV curve for the two components and that actually changes with time so this is work going back to a couple of yeah maybe a decade or so and then this AR curve that you can fit with the capillarian solution and then you can get the orbital parameters then that changes with time and that’s because the uh this orbit of the of the star uh changes and that’s what we call abidal motion so I need to speed up because I only have five minutes uh so next bubble is the ex type Outburst these are objects which show smaller burst and larger Outburst again we have a series of papers for the prototype exm for some other objects among the GU that turned out to be exra um again I’m showing the light curve from ex which is very interesting because it goes back to the 1890s um and then you see larger Outburst you see smaller burst um these are distinction between them during large urst the creation rate goes up by about 40 during smaller burst it’s only goes up factor of few and then you can see how the spectral energy distribution of spect spectral properties change it goes from absorption to emission for example and then we could study specifically during the large Outburst the effect of of the released heat on on to on on the circum disc because both in at the surface and in the mid play the the dis heated up and temperature went up during an outburst and the temperature is high enough to actually crystallize part of the or amorph D grains um that uh are located in the dis and then if you that we did with spiter a long time ago now you can do the same with James web much more precisely and you can also see these kind of spectral features for different uh solids but also lots of different molecules we could detect so you have this is interesting because you have all the ingredients that you need to make planets and plan planetary atmospheres it’s really fascinating and then next bubble be 1647 Oran type objects I showed you this live curve which goes up and down and up and down these are multiple eruptions intermediate duration spectral properties a convenient place to park objects that we cannot put either into this bubble or that bubble so this one specifically we did some study earlier and that I’m mentioning because this is a first example where we had repeated int Prometric observations with the vti at that time we use midi and then at different times we managed to measure different visibilities which uh with which we could fit different um parameters for the inner edge of the dis and the envelope because this is an embedded system and we could see that on a few Au scale um these the inner inner part of the this and envelope changed because of the outburst and then the largest burst or outbursts are the urinous object here you can see some life Cur of the first three objects that were discovered the per F Fury this was the first and then 1057 sign second one 155 sign third one and then the black parts are historical like from the literature and then the red parts are the ones that we we ourselves collect Ed and analyzed with my colleagues in a series of papers and then again some of the gers that we are studying turned out to be few hours so here you can see that the lights curs can be very very different the common property that their Luminosity goes up a lot of P magnitude brighten but also the overall Luminosity goes up to hundreds of solar luminosities and then the creation rate goes up by orders of magnitude and then they’re long for example the FR F can has been in our burst for more than 90 years so if you consider how much material is it created that’s like one Jupiter Mass huge amount of material and then they also show smaller fluctuations um one important distinction between fures and other types of citar or or other types of eruptive objects is that FES are hot in the discr plane while other types of stars are hot at the surface so that causes very pronounced differ and there Spectra that we can use to identify and characterize them as I mentioned there are long-term variability in fers they’re slowly fading there you can create a different wavelength they also have score time variability that you can trace with light person like these may be interpreted as like a signs of binarity or some inhomogeneities in the dis that are orbiting they also shows some spectral variability because they uh these objects may have a variably strong winds this Queens they may also bury in in their minim light uh millimeter lines because when such a big Outburst happens then you heat up the whole disc and for example the snow line which separates the icy grains from the bare grains uh moves and then you may expect a lot of changes in the lines we have some numerical assimilations for this we didn’t manage to yeah observing time to check this yet but uh there are some measurements at least for the closer objects they are really really rich different kinds of molecules which are released from the ice pH because of the outbursts and then I’m studying the properties of these diss here I’m showing just how massive they are and how large they are because I wanted to see whether they’re different from normal T stars and they see seem to be more massive and smaller than normal stars and that’s interesting because then you can check whether they are gravitationally stable or unstable and this graph shows everything in this blue region may be gravitationally unstable so what happens with those discs they fragment and then we indeed managed to to see this kind of spiral structure and then this fragments of and SC like as well in case of v96 one of the objects that are that is supp supp to be unstable so that’s neat so yeah I just have two more slides because I talked about Intermediate Ms yet but they are also variable and then this specific case what we saw with again interferometric monitoring is that a new ring appeared in the system uh which is interesting because we think that this is due to Giant Collision that produce Fresh D and this is a young star but apparently the inner disc behaves like a breis and you can see this kind of variability also in the bre discs which are called Extreme debr discs which change significantly their infrared brightness again because we think that we have planet asms that Collide and then you produce lots of fragments and actually also like vaporized part of these that that condense and then uh you get rid of that material and then it fades back so you can actually see in idual collisions in this system um and then these are my takeaway messages because I run out of time variability I hope I could convince you that that it’s a powerful tool like a fourth dimension to study this strong young Stars it really otherwise unattainable information about the circums parameter if you ignore it you’re probably making a mistake thank you very much [Music] um questions from [Music] from CH from the how are they what the and how do they stop when they stop basically so that main idea of a creation is that you have some kind of way to get rid of angular momentum uh and then you have a slow spiral in within the this which um uh eventually stops because at some point there the the pressure from the incoming material becomes equal to the magnetic pressure and then from that point on uh the magnetic field will dominate uh will determine how the material moves so that’s why it follows uh the magnetic field lines and then you have this Channel and that at that point on mostly it’s just gas partly ionized okay so is mainly yes yes yes at least for normally accreting young stars for the largest Outburst the F orines Type Stars we think that um the accretion rate is so high that the material completely crushes the magnetic field of the star and then the material uh is incoming uh from the dis on to the star all the way in the mid plane so it’s a very different process is question yeah actually question these objects produce a lot of s use low because production of crystals molecules and so on so I was wondering what is the effect on the interpretation ofation Lo and how you can with the second one um is about the impact of this kind of Si because as far I can understand you need a quite continuous uh observation of your objects while will have some C in so I was wondering yes for the first question how we deal with the local rening is difficult especially I mean Ella knows it very well because we are doing this followup of of these gu alerts where B basically you have an object you have a light curve we have a fuse Spectra and then sometimes we have from Gaia a certain distance which is sometimes well measured sometimes very very uncertain like it can be anywhere between one kilop and three kilop who knows where it is exactly in these cases I mean what we try to use the Spectra H to to determine uh the circumstellar ring by by measuring line fluxes and then basically we try to minimize and you can use these lines to um convert the line linity to accuration linity there are like empirical relations between the two and then if you do this for several lines spanning a certain wavelength range then you may get different results from the different lines and if there’s a trend in that that then maybe because a lines shorter wavelengths are more extincted lines longer wavelengths are less extincted because that’s the the rening low so you can correct for a certain rening and then you can minimize um this the kind of a the determine the red theing which minimizes the difference of the accuration rates you get from different lines so that’s one way to determine this other if you if you don’t have these kind of lines or you don’t have Spectra then you can try to do this by just um projecting back um your object to to the tary locus if it’s a tar if it’s not very rened and then or very embedded then you can do this uh near infra color diagram so that’s that’s the way and uh yeah in in case of the most embedded object it’s it’s really difficult so we basically don’t see directly the the central object and then yeah we just we just assume that okay um most of of what what we observe as a Luminosity comes from reprocessed uh the creation as it the second yes so so for the Cadence I think I mean we try to use everything so even if it’s one minute Cadence perfect even if it’s like few years Cadence we try to use it um because it it traces different different kinds of um time scales time scales so and then basically if you have lots of observations which we had for example for Dr to if we are working on now and then one of the other papers CR I think we have this graph where you plot like the amplitude of the accretion rate changes as a function of time scale and then you have the smallest ones at short time scales which a just rotational modulated and then then it increases and then it flattens out typically because like these these Stars can vary as much as let’s say half magnitude in in a few hours or in a few days but then it’s the same phenomena if you you look at them like 10 years difference you just catch them at different states but they’re doing they’re always doing [Music] that well it’s useful if I mean it’s it’s super useful if you have some consistent data set that where you can match the different filters because if you change telescopes if you if you have different like spatial resolutions then that can that can be difficult espe yeah yes yes yes so I mean once you have information on uh the colors of the different processes like like for example the flares are very very blue so that their amplitude is very high UV in the UV and then it it drops quickly but like ACC creation rate variations are more gray they’re a bit blue because it’s hot material that you add but but it’s if you go to red opticle or near infrared then it’s it’s mostly gray so if you see less wavelength dependence then you can assign that to to a creational rate variation so once you have the idea about how to translate one light curve to another then then you can try to do this it’s in my opinion it’s very dangerous because there can be like delays that and then there’s there was one of these figures that I where I cited on MAR Cod paper they had a study where they had a this huge um survey for different sof forming regions in Chia loopus tus that they compare the optical and infrar light cures and you could classify the objects these are the objects where the two lighters correlate and these are the objects have nothing to do with each other it does something completely different in the optical and in thre in that case I mean if you have very different uh wavelength measurements then then you you can’t combine them so yeah that’s why it’s important to use the same telescope over and over again it’s difficult to get time other questions uh I didn’t see any question more so if we don’t have more questions for I think that we can thank her again and she will be around today and maybe also tomorrow um we are staying in the first floor office if you want to pass by and also around and