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we talk about some novel work we're

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doing trying to do understand my

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observations of Isis in a new way so I

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brought this up before but why Isis well

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of the hundred and eighty molecules

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detected in space anything you want to

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make larger than methanol probably has

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to be made on a grain surface so these

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are the places you want to look if you

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want to understand complex molecule

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formation one of the problems we run

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into now is that these are the only

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molecules we have actually detected in a

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night's these are the only molecules

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we've detected where we think they're

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frozen out in forming everything bigger

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and most of the other species are just

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not observed so far and this is a big

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this is a big impediment to actually

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understanding ice chemistry because

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interstellar observations are how we

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reconcile our theory with what's

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actually going on and if we can't detect

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bigger more complicated things this is a

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problem so I we're a terahertz

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spectroscopy group so we obviously want

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to try to solve this problem with

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terahertz spectroscopy so terahertz is

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sometimes called the far infrared it's

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very long wavelengths infrared radiation

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or verging on very high frequency

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microwave it spans the two and so the

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transitions usually see here are either

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very low frequency large amplitude

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vibrations from single molecules or

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collective vibrations of solids and it's

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the collective vibrations of solids we

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want to go after and what we want to do

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is exploit the fact that it's very long

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wavelengths so this is two optical

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images of discs and you'll notice

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they're very fuzzy and opaque so there's

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mass here it's obstructing all of the

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optical photons dust is extremely opaque

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at optical frequencies as you go lower

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and lower in frequency the disc gets

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more and more transparent and you can

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start seeing through it but all the

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really interesting stuff in the disc the

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ice especially is all completely

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obscured because the outer edge of the

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disc is just blocking all of the light

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and so this I put this light up before

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but really quickly I this is really

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important because if we want to actually

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see into the really into

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in parts of protoplanetary discs the

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interesting stuff is happening in the

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mid plane that's where ice is freezing

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out ice freeze out drives aggregation of

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small dust grains into bigger ones in

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fact ice is probably how you get over

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the centimeter problem building up

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bigger and bigger particles generally

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requires icy bodies and it also whoops

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see if it's going to change it also

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requires a mass transport so this is

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going to be what drives the composition

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of your planet's and where all your

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organics end up and all your water and

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the problem is if you want to look at

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the mid plane of the disk you're only

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going to see very little in so if you

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want to see in towards the center where

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the ice is actually freezing out you

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need a way to look at it so

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traditionally the way I observations are

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done is through trans absorption

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spectroscopy so you have starred in the

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background you have ice along the line

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of sight and then you detect absorption

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of this but the problem is as you build

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up more and more dust in the line of

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sight well it gets a fake very quickly

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at terahertz frequencies though the dust

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is completely transparent and light goes

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right through unless it's absorbed by

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the ice or at least it's far more

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transparent I and the other thing that's

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very helpful is that you need a

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background star in the infrared so to do

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an emission experiment to get ice to

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emit you'd have to heat it up to several

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hundred Kelvin if you heed nice to

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several hundred Kelvin the ice is

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evaporated already so the only way to do

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it is absorption so you have to find a

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place with ice and then a star in the

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background that hasn't desorbed your ice

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so there's a very limited number of

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places we can actually observe ice in

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space I so that's the problem we want to

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do this with terahertz but the problem

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is terahertz spectra of Isis and far

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infrared don't really exist or they're

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fairly limited turns out making

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terahertz photons is actually very

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difficult so we go through a lot of

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trouble to make them it's a big

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complicated slide but basically what we

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do is we take an ultra-fast laser so few

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tens of femtosecond long pulse we focus

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it down to a point and we generate a

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plasma so this is our little plasma it

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throws off a huge amount of optical

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night that's very pretty but sadly we

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just lock it so

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it also gives off very intense very

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broad band terahertz pulses so these

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things span many hundreds of wave

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numbers all at once and so what we're

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going to do is collect them and focus

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them through a substrate they've already

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been a couple descriptions of how we do

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how you make these but our ice chamber

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is a small little hv system it's a

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silicon substrate and cryostat so we can

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change the temperature from anything to

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about 10 Kelvin up to 300 if we want and

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then we just dose in whatever ice we

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want to form mixtures layers or just

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pure samples and we deposited on the

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substrate and then just do a fairly

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simple beers law absorption experiment

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we just look at the absorption through

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and this is sort of the band width of

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our instruments so we can see everything

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from about a few wave numbers up to 250

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and so now if we can do spectroscopy

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here we need an observatory that can

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match that and so I've mentioned almond

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a little bit with the image of HL tau it

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actually is pretty limited it only

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covers the first terahertz a bandwidth

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we do there's Herschel spire and packs

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which have ok coverage but these are

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actually now defunct they're sitting at

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l2 but they're out of liquid helium so

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they're not running anymore there's only

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one Observatory in the world that can

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cover the bandwidth we want and that's

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Sofia's Fifi instrument so to do sort of

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just testing we've never done anything

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like this the pretty obvious case is to

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go look at water water is the biggest

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component of any interstellar ice so

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you'd like to start with water so this

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is a spectra that Brett recorded of

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crystal and water ice at 10 Kelvin it's

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nice and pretty we get a very strong

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peak here and if you look at the Fifi

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coverage we have perfect over map except

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that right now Fifi is missing a filter

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so we can't actually cover this range

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and it's really sad I so just for a

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minute I want to stop and tell you what

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Fifi is it is an instrument hooked to

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the back of this telescope it's on a 747

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we fly it up to 40,000 feet and then

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open the door in flight and then use one

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meter telescope in the back to track an

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object through turbulent so it's got a

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massive cyst

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that keeps the telescope pointed even

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when the planes jumping up and down so

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we're able to track an object as we fly

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through the sky and get really nice data

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so it's a really fantastic thing but it

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doesn't quite work for water yet what it

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does work for is co to co 2 is one of

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the next most abundant constituents in a

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nice so it's another obvious place to go

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so this is actually a spectra from

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bretts thesis we can make crystal and

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co2 ice at different temperatures and we

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have two very nice modes that pop up

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right in the middle of the Sofia band so

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we can cover both we also have this

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really interesting thing which is the

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band position shift with frequency North

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temperature so anytime you observe one

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of these Isis you immediately know its

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temperature very precisely and you get

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the information for free which is very

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helpful for understanding the physics of

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whatever you're looking at I so we'd

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like to know what these are it actually

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turns out to be very important to know

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what these two modes are these are

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crystalline modes so this is the mo

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frequency one the it's crystal and co2

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ice buying layers moving back and forth

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between each other this is just an

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optical phone on and then the higher

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frequency one is there we go I co2

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molecules bands moving back and forth

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and so it's really cool but one of the

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issues here is that this requires

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crystal and co2 to work you have to have

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an ordered crystal and ice to get these

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modes to show up so we can actually

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prove that if we go through and make an

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amorphous ice if we deposit in ice at 10

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Kelvin where the molecules don't have

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enough energy to rearrange you get this

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sort of amorphous mixture that can't

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crystallize and if you try to take a

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spectra you get a flat line so this is

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good and bad for observations it means

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that we're now sensitive to composition

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two so once you heat a nice up if you

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cool it back down it'll stay crystal and

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it will not lose that crystalline

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structure but if it's if it was never

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heated up it will never make a

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crystalline structure so this is good

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and bad because now we can track the

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thermal history of the ice if you see a

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10 Kelvin ice but its crystalline you

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know at some point that ice was exposed

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to much warmer temperatures and then

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cooled off and that can be very useful

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for understanding dynamics the problem

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is if a nice never saw a temperature

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warm enough to crystal

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is it then the line of sight that has no

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co2 or amorphous co2 looks identical and

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you can't tell if you have no co2 there

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or if it's just not warm enough to

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crystallize so this is the Fifi band so

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this actually works out beautifully now

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the trick is that we want to go out and

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do something with this telescope that

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was never intended so Fifi was meant for

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small narrow spectral lines these lines

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are our lines are a few wave numbers

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wide the mines were suppose that this

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instrument was intended to see were

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tense the hundreds of wave numbers wide

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it was never meant to see something this

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broad as a observing mode that was never

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tested and so this is going to be tricky

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because like I said we're in a 747 at

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40,000 feet bouncing around now we fly

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that high to get above most of the

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Earth's water but there's still a little

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bit of atmospheric water so now you have

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a changing atmosphere in a bouncing

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telescope and what you have to do is do

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67 individual integrations across this

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band to get enough data to actually see

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this broad feature and this is something

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nobody thought we nobody ever thought

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someone would try and so this was

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totally speculative to see if you we

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could even get something that would be

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stable over the course of an observation

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and so we propose this to the Fifi

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instrument team and they were

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surprisingly excited about it and really

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wanted us to give it a go so we picked

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the target in GC 7538 it's actually got

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two different sources irs-1 it's more

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processed and has very little co2 that's

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going to be our reference source we know

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from infrared observations there is no

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real co2 ice there and then we have IRS

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9 it's dimmer but it has very abundant

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co2 I some of the most abundant co2 ice

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observed in space so what we're going to

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do is observe both of them back and

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forth simultaneously as we fly and see

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if we can actually get stable base lines

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and so this is very new we got this

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about a month ago from the Fifi team so

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this just came down I so what we do

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black in red or individual scans so we

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started in the center and then worked

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out to the outside and then filled back

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in on the edges and so each one of these

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is an individual scan and it's actually

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worked surprisingly well for us so all

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these big dips

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our atmospheric water absorption but

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everything's tracking so stuff we did 50

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minutes after this follows the pattern

297
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exactly everything lines up nicely and

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it's shockingly stable as we're bouncing

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around in the atmosphere so this is a

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really promising start it's you know it

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proves that we can actually get the

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telescope up there working and observe

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something this broad without having the

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atmosphere completely ruined the

305
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observations we can do a background

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subtraction and it's pretty clear that

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we don't correctly subtract out the

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water lines so this is going to be the

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ongoing thing is this is something

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that's known in optical and infrared

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observations is that atmospheric water

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subtraction is really tricky the models

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that they have an infrared are very good

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so the next step is going to be starting

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to apply these methods too far infrared

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observations to really subtract the

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water out and get at the very weak

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absorption features that we hope were

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here all right with that I'd like to

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thank the rest of the Blake group our

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funding sources and you guys for your

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attention so questions really exciting

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work so I was just wondering if her show

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packs covers the same spectra Herschel

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packs covers some of the same spectra so

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there's archival data and Thomas

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Hennings put up a slide where he shows

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that water ice absorption the

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calibration is really tough so we're

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going to be working with them a lot to

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figure out because packs and fefe are

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identical instruments fifi exists

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because they built a backup of packs and

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they just had it laying around and so

335
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now they put it on telescope people yep

336
00:13:01,340 --> 00:12:58,140
it's on okay i know people working on

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her show digit pack stay there trying to

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calibrate it i don't think they trust

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ice calibration yet by skating there

340
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soon yeah so Thomas Hennings got a

341
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little bit but yeah this is a tricky

342
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process this is not what this instrument

343
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was designed for so calibration is going

344
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alright well oh yeah yeah unfortunately

345
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not it's either going to be pitch black

346
00:13:38,100 --> 00:13:36,759
in here or like this we can take a vote

347
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but I figured people don't want to fall