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thanks Brett and Brendan for awesome

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talks on chemistry now let's take a step

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back and look at some physical

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properties turns out we don't know some

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really fundamental properties say how

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massive food aplenty distal are even up

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to order magnitude level traditionally

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this mass has been measured from dust

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emissions in submillimeter and

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millimeter so basically we're seeing

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continuum emission from dust particles

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the problem is the spar do squirrel in

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polokwane two discs into rocks and

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boulders and plant test knows whence

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they grow bigger into cited bigger in

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size they're no longer emissive in the

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wavelength of that we're observing

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therefore we're missing a lot of mass if

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you only measure mass in submillimeter a

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mission so turns out ninety-nine percent

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of the disc mass is in h2 gas to ask the

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question what about we measure the

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dispatch directly from the gas emission

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the problem is h2 doesn't have a lecture

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dipole moment so it doesn't meet in

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typical in today's environment so this

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has been done once with HD emission by

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her show super Canelo's they measure the

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HD emission level oops right here and

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then the estimated this mask to be

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roughly 2005 solar mass and that's more

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massive than Allah estimates made in

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dust emission so her show is no longer

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with us and this lie is actually fairly

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sensitive to temperature so does not

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necessarily good probe for this mess and

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luckily we have Alma so traditionally

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people have been measuring mass of

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molecular clouds in co that's just

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because co is the last and the second

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most abundant molecule in molecular cows

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so that's the first thing people look at

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when they first got all my very first

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became able to detect molecular

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emissions in those days

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and even though typical I'm commonly

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observed CEO lines from regular co-op

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Lee sick we can still observe where as a

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cop locks se13 COC 1800's c-17 oh and

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they could be ugly thin to trace the

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Disney play and therefore the entire

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mess budget however to translate our

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observation of omission to the actual

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dis mess mostly in h2 is a very

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non-trivial process so first of all the

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different fractionation processes that

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could change a ver Co to Co ratio and

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still chemistry can also deviate the co

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2 h 2 ratio away from the molecular

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cloud value so this temperature and

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density structures they determine the

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chemical processes and they also do the

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ab decide the excitation processes that

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eventually lead to the emission lines so

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our approach is to model the

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thermochemistry of an evolving poll

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century disks so we first look at the

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thermodynamical structure we follow the

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evolution of a t-tauri desk for 3

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million years that's roughly the

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lifetime of Apollo villages around the

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solar type star and then we look at

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kinetic chemistry motto so the model was

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built upon that you miss database we

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have more than 1,300 reactions including

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gas phase reactions graceful

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distractions and different photochemical

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reactions to count for fractionation

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processes so this is what we found so

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now we're seeing a cut of the polyp ng

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disk so we're only seeing the cross

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section and then the quantity plot here

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is the number density of the species

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divided by the total proton number

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density is overseeing the dependence

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here a minus 4.2 the right color here is

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the info dependence of red means a lot

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and blue means the sternness beaches is

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depleted so we're having a lower carbon

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dioxide ice and turns out that in here

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from the cloud phase chemistry model

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however co is depleted beyond 28 you

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from the central star and turns out the

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disk is hot enough for co2 stay in the

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gas phase the whole time so does not do

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to freeze out we ask the question what

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happens so if you look at one particular

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point in this case 68 you on the

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midplane the black line here is showing

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the time evolution of the abundance of

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co it drops a million-year timescale

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same for many things and is that the

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vendors of organic molecules increase

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and they pretty much plateaued after 2

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million years of evolution if it

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averages over the entire disk it turns

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out more than forty five percent in some

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models around forty five percent of

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available carbon is stored in organic

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Isis by the end of the teacher in

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evolution so we asked the cross my heart

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robust or is Elias so we tested a result

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against of different models so we have I

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see this is a different chemical network

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different input evidences and different

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dust properties so the takeaway of this

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is um we have a lot of carbon dioxide

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ice in all cases around thirty five

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percent and a lower organics roughly

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Irish forty percent of available carbon

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and the CEO at Venice is only around

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fifteen percent so unless in molecular

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cloud we think co may not be the most

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abundant molecule out there alright so

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with starting this project trying to

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find out what can I use as the probe for

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the dismay plan and it turns out seeds

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18yo sorry c7000 becomes ugly spin after

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ten ato from the central star and for

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c18 know the numbers around 15 a you

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basically that means yes we can observe

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c70 or CAT know and use those lines as a

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direct probe of the dismay

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and use the adult slides to measure this

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mess however because the chemical

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evolution happens on a million year time

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scale so turns out the obviously the

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opacity changes quite dramatically as it

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disables so the now we're looking at up

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to depths of MCO 120 line as a function

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of radius so we start with a brief lat

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pulls out and then a dependence drops at

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around fifteen twenty eight us it dis

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evolves and interesting this has been

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seen recently in the observation of teva

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hydrate so now we're again looking at

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the column density of cos the function

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of radius the line is flat if we're only

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looking at decimation but we're seeing a

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huge drop at about twenty a you just as

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what we predicted here in the bottom

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alright if we take a step back and look

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at some global properties turns out

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people are seeing really small gas to

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dust ratios Impala plenty disks just for

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reference the canonical intersil of

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value is 100 in disks people have been

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observing a whole range of values all

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the way from 10 to 70 so the blue box

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here is observed data and the yellow

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boxes here are our model predictions if

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people interpret the observation

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assuming a constant CO 2 h 2 ratio

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alright so back to the question of the

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global dis mass so are we actually

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seeing the gas depletion globally were

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just Co depletion so does it mean we're

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under estimating the gas mask just

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because your is depleted so in order to

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do that we model the line emission based

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our chemistry model and then luckily the

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co depletion does have chemical

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signature is macula line profiles so now

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we're looking at c70 no

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a three to two rotational invention for

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the end of evolution and the top panel

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we're seeing the actual spectra and then

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the lower wise normalized land profiles

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because the chemical depletion happens

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sorry mostly the outer part of this

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query capillary rotation of capillary

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velovsky is smaller so for the chemical

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evolution model busy how does it work

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the inner part were depleted I mean most

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of a mission comes from the in there

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sorry the outer part is deeply there

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most of a mission actually comes from

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the inner part of this we're on the

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Kepler the loskis much higher all right

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I notice all details so i'll leave the

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i'm going to use my privilege and ask

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you the first question right what is the

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dominant parameter in your model that

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determines where the lines go optically

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thick in terms of a you I mean you you

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have a radius out from the central star

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where they go optically thick but what

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part of the model determines where where

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that is oh very compare the lpo tests

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just based on the chemistry so we have

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the chemical evolution model is actually

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a one-point model so we follow the

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chemical evolution is a is a 50 x 40

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grade so it follows the evolution for a

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few million years for every single point

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of the disk and then we integrate to get

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off till death yeah so that estimation

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was for a facedown GL make sure we also

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have other more detailed prediction

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coming up in the Latin profile paper

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so you mentioned that the CEO depletion

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as a result of complex organic ice

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formation what's driving that reaction

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that's a great question and I look back

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like black backups life for them oh

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that's the network just flex over in

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case anyone is interested and so it

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turns out the reaction term scouts

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limited by ionization so for roughly

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about 28 you on me play so this is the

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key figure that's a contribution of

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extra ionization basically for red and

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yellow that means that's where extra

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ionization dominance and then in the

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interior I would say within one scale

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height of exist that's where cosmic ray

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and secondary huy fong house donuts and

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that's a great question because a Elsa

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and pipe organs group and four atoms

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they've been proposing that cosmic rays

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can be shouted by the magnetic field of

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the central star were the disc so if

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that happens that will turn down the

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reaction rate by law so we are testing

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of that situation too and our point 22

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else's I think her chosen five papers so

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they try to constrain the cosmic ray and

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kazmir ionization rates by observing mo

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lang co Venice it was really nice talk

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so do you expect the the time scales the

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reactions you're considering are going

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to be fast enough the dynamics aren't

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important oh that's that's a good

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question um so I see the time scales for

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freestyle and gas phase reactions are

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definitely at not and for green surface

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reactions I mean green for green surface

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reactions they happen much faster than

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the dynamic of time scale so they're

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fine and I think there is one particular

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kind of reactions now i can remember

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which kind that could be relevant so you

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might want to consider mixing or

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transportation for that but for us with

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which Richard we track the change in

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density temperature and the change of

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column densities yeah one model of one

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group they're trying to combine the

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there's one group we're trying to

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combine the dynamic and the chemistry

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together pro demo the code scoper demo

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so they have the problem is so busy they

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calculate the thermal structure like

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citation chemistry coherently the

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problem is the only have parametric

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models so in our case we actually have

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MRI turbulence in the dismal dough so

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the first paper was based on a my