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my name is ben sargen i'm actually i'm

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from rochester institute of technology

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so other side of the state

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um so i'm a postdoc and i'm an

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observational astronomer

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and i'll be talking about studies of uh

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infrared spectral studies of

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pre-planetary disks

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um

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so first a bit of background

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um so

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when stars form

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uh they form from giant molecular clouds

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and so if if you get a cloud that's a

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little over dense it begins contracting

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under its own gravity

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and if there's any

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angular momentum there's any spin to the

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cloud

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will collapse to form the star

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what's left over that doesn't make it to

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the star forms a disk of gas and dust

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and so it collapses and becomes a

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protoplanetary disk

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and so eventually all of the cloud

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reigns on to the disk and then after a

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few million years

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our observations are finding the discs

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seem to dissipate and this is the stage

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where planets and all the other solid

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bodies of

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planetary systems form

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so i'm studying this intermediate stage

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where you still have the the massive

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disc of gas and dust

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and i'm using infrared spectroscopy to

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study the gaseous component

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so in the past maybe 20 or so years

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there's been a number of studies

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um at the sub millimeter and millimeter

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wavelengths

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studying the the molecules in the discs

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and they found such things as cn and

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hcn and formaldehyde

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and there are ongoing studies surveys of

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these protoplanetary disks

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looking for these molecules

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also in the same time

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there have been infrared studies

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of the same disks looking at various

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molecules

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so maybe in the the 90s beginning in the

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90s there were these um studies looking

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for things like uh

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carbon monoxide and water and so forth

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however it was the

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launch of the spitzer space telescope

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about a little over 10 years ago that

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allowed

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um

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protoplanetary disks

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and then a few years into the mission we

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started

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there were a number of papers here's the

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first one that began reporting a number

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of uh various molecules from the

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slightly higher resolution setting

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of the infrared spectrograph on spitzer

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finding things like water and oh

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hcn c8 c2h2 and carbon dioxide

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so this this resolution that's

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wavelength divided by the

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spectral uh

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resolution element so it's the smallest

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wavelength detail you can see on the

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spectrum

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so this isn't all that great 600 but

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that's that's the best we can do

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so people were studying things with the

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higher resolution setting there's also a

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lower resolution setting

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r of 90.

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so it's very difficult to study gases

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with such low resolution but you can

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still find lines from such gases as hcn

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and c2h2

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this study

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this talk focuses on the stuff you can

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see at short wavelengths with this low

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resolution setting there are many more

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spectra of the

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many more spectrum the low resolution

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mode than high resolution because it

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takes either a brighter source or a

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longer observation time to get a good

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spectrum at the higher resolution so we

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have many more low resolution spectra

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so here are

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sample spectra from

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from a titari star

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i call it rw riga a so this is a a star

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with a protoplanetary disk around it the

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spectrum in blue is a of an fu orionis

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star called v1057 cygni

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furiona star is a slightly earlier stage

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when there's much more material in the

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disc so that the disc is an accretion

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disc it's material that's

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being accreted towards the star

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and for effiorionis stars

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it's thought that the disc is much more

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massive there's much more accretion

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going on and so the heating for for

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those discs

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they're heated more from within than

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without and so you get absorption

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features

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and so i start so my my study focuses on

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these t tauri discs but i'll start with

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the every your own fu orionis disc

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so all of the spectral structure that

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you're seeing in this spectrum

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comes from water vapor at one

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temperature

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that's a 800 kelvin

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model that i'm using that's the orange

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that fits the spectrum the i'm using

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also some continuum but you get all of

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the structure with just a simple model

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so you see this sort of feature here at

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6.6 microns and some sort of ripples

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here at shorter wavelengths

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so this is kind of telling for what's

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going on in the titari disks

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they are systems that have less

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accretion they're heated more from

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without

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more by the star

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the radiation from the star so you get

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emission from those systems and here you

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have the same feature but it's a mirror

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image so yet so it's emission here

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so if i just had emission

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from water vapor in the spectrum

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everything else would be the same and

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here i would have the dashed line but

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that doesn't fit the data

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so it appears there's some sort of

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component

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there's something absorbing at those

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wavelengths and in this model i've used

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formaldehyde and i get a decent fit to

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so if i had very high resolution like

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perhaps i could get from a ground-based

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telescope

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this is what i would see if all i had

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were just water vapor

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over the five to seven and a half micron

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wavelength part of the spectrum

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so you can see that this 6.3 microns

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which was

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sort of a minimum here

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it's not really absorption but it's just

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a lack of emission you're seeing down

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close to the continuum of those

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wavelengths at other wavelengths the

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shorter wavelengths you see sort of a

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cluster of

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lines that get a bit more densely packed

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and stronger

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around 5.7 microns or so

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what looked like a 6.6 micron feature is

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just a whole bunch of strong lines

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close to 6.6 microns

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but we don't have high resolution we

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just have the low resolution

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so a bit about perhaps

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what might not be going on

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so there are spectra of tetori stars

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that are completely boring over these

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wavelengths they're more or less just

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sort of continuum

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nothing much going on

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and those

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spectra so um that would suggest that

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perhaps

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it's not an artifact that's responsible

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although

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you can't rule it out but you know the

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fact that you don't see the features and

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all of these stars suggest it might not

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be an artifact

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another thing that it probably is not is

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uh features from the stellar spectrum

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this the spectrum of the star itself

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typically the emission over these

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wavelengths is like five to thirty 30

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times

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that of the star

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so

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whatever spectral structure you'll see

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over these wavelengths should be drowned

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out by a lot of

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emission from the the protoplanetary

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disk what's what structure you do see is

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probably water at least in the later

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type cooler stars

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perhaps

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some solid materials have features over

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these wavelengths these are

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opacity curves of phyllosilicates so

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those are silicate dust grains

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and and such that the crystalline

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structure

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is that the

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you get the silicon

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sio4 tetrahedron that arrange themselves

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in sheets and in between the sheets you

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have various molecules

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and so you can get some spectral

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structure over these wavelengths

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but it doesn't seem to match up to the

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stuff we see in our spectra

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so probably not phylosilicates

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it could also be ices ices have features

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over these wavelengths here are ice

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opacity profiles for formaldehyde formic

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acid and water

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and although they have features that are

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close they're not

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exactly a good match

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and there are various there have been

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various studies over the past 20 plus

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years

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over

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of ices

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you might see in

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around dust grains and big molecular

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clouds and again

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not a good match to our spectra

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what does seem to be a good match

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um so there are there seem to be

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different

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types of spectra they're the ones that

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have the 6.6 micron

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peak with the shoulder at shorter

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wavelengths sort of a minimum at 6.3 and

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then

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a sort of a

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sort of a

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upward rise to shorter wavelengths

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um so the water vapor and emission like

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with the the spectrum a few slides ago

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seems to fit overall fairly well and

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then i need to include absorption from

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something and

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for these at least formaldehyde

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seems to be a good fit

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for others water vapor and emission but

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uh something different in this case

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formic acid and absorption this uh

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spectrum df tau seems especially well

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fit with the

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formaldehyde formic acid

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there are other stars that don't have

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much or they have perhaps no water

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emission discernible this one has

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perhaps a little

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but they have these

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stronger absorption bands at the shorter

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wavelengths in this case that are better

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fit by formaldehyde

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and then others with a narrower feature

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like bf towel

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that again seem to be fit better by

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formic acid but but very little water

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so i'm not going to go through the whole

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table but these are models that i've

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generated to to match the spectra

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so the main features are that the

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emitting

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areas that i need for the water vapor

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component are

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on the order of a few astronomical units

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one astronomical unit is the average

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earth sun distance okay

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so if uaeu the typical water

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temperatures are 600 to 1200 kelvin

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which are fairly consistent with

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00:11:09,910 --> 00:11:06,800
previous studies the formaldehyde seems

291
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to be fairly cool relatively speaking so

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50 to 500 kelvin and the formic acid

293
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it's not well constrained but also

294
00:11:22,150 --> 00:11:19,920
another a few hundred kelvin or so

295
00:11:25,030 --> 00:11:22,160
um i'm running short on time so i'll

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just summarize the disc so

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00:11:28,870 --> 00:11:27,279
the idea is that

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00:11:30,550 --> 00:11:28,880
if you looked at a protoplanetary disc

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00:11:31,910 --> 00:11:30,560
edge on you're looking at cooler stuff

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00:11:34,230 --> 00:11:31,920
in front of warmer stuff and you might

301
00:11:34,949 --> 00:11:34,240
expect absorption features

302
00:11:37,269 --> 00:11:34,959
but

303
00:11:39,670 --> 00:11:37,279
the few discs that have

304
00:11:43,910 --> 00:11:39,680
inclination estimates it doesn't seem

305
00:11:49,190 --> 00:11:46,389
one thing one sanity check

306
00:11:51,590 --> 00:11:49,200
is to compare the strength of the 6.6

307
00:11:54,389 --> 00:11:51,600
micron feature versus

308
00:11:56,150 --> 00:11:54,399
strengths of water vapor lines at 17

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microns from the higher resolution

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spectra where you have a better grasp on

311
00:12:03,750 --> 00:12:01,120
you can even better constrain the water

312
00:12:06,230 --> 00:12:03,760
properties and so the the two strengths

313
00:12:08,550 --> 00:12:06,240
seem to correlate so it kind of makes

314
00:12:10,790 --> 00:12:08,560
sense the stronger the water vapor one

315
00:12:13,030 --> 00:12:10,800
wavelength the stronger it is at the

316
00:12:13,910 --> 00:12:13,040
other wavelength

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00:12:18,310 --> 00:12:13,920
for

318
00:12:19,829 --> 00:12:18,320
observed at a number of other

319
00:12:21,910 --> 00:12:19,839
wavelengths

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00:12:25,670 --> 00:12:21,920
formaldehyde has been observed for one

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00:12:27,269 --> 00:12:25,680
protostar at 3.6 microns in absorption

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00:12:29,590 --> 00:12:27,279
so that would be

323
00:12:32,150 --> 00:12:29,600
a good wavelength to try to confirm the

324
00:12:35,910 --> 00:12:32,160
formaldehyde

325
00:12:38,069 --> 00:12:35,920
spectra the formic acid

326
00:12:39,269 --> 00:12:38,079
has bands at 9 and fifteen and a half

327
00:12:41,670 --> 00:12:39,279
microns

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00:12:45,350 --> 00:12:41,680
the latter is only accessible from

329
00:12:47,030 --> 00:12:45,360
uh space-based observatories

330
00:12:49,430 --> 00:12:47,040
excuse me while the

331
00:12:51,350 --> 00:12:49,440
nine micron band is probably the best

332
00:12:55,430 --> 00:12:51,360
one as it's well suited for ground-based

333
00:13:05,509 --> 00:12:57,670
and i'll leave my conclusion slide thank

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00:13:10,389 --> 00:13:06,870
questions

335
00:13:14,310 --> 00:13:12,069
and we have to give you a microphone if

336
00:13:15,990 --> 00:13:14,320
you can ask a question by the way

337
00:13:19,190 --> 00:13:16,000
so is there something that precludes

338
00:13:20,949 --> 00:13:19,200
both formaldehyde and formic acid in

339
00:13:22,790 --> 00:13:20,959
combination because they seem to overlap

340
00:13:24,550 --> 00:13:22,800
in that spectral region

341
00:13:35,190 --> 00:13:24,560
yeah there's nothing that precludes them

342
00:13:39,509 --> 00:13:36,790
uh do you have any thoughts as to what's

343
00:13:41,350 --> 00:13:39,519
going on as to why you see very cold

344
00:13:44,069 --> 00:13:41,360
formaldehyde but fairly hot water in the

345
00:13:48,710 --> 00:13:46,230
um so yeah the

346
00:13:50,150 --> 00:13:48,720
so this this uh was written up recently

347
00:13:51,430 --> 00:13:50,160
in a paper and that was a question the

348
00:13:54,069 --> 00:13:51,440
referee asked

349
00:13:56,550 --> 00:13:54,079
um so yeah perhaps um

350
00:13:58,470 --> 00:13:56,560
the water can survive but

351
00:14:00,310 --> 00:13:58,480
we could we can see water vapor and

352
00:14:03,750 --> 00:14:00,320
spectra of uh

353
00:14:04,870 --> 00:14:03,760
the coolest stars so 3000 kelvin stars

354
00:14:07,750 --> 00:14:04,880
cooler

355
00:14:09,430 --> 00:14:07,760
so it's a hearty molecule but the

356
00:14:12,230 --> 00:14:09,440
formaldehyde is

357
00:14:14,470 --> 00:14:12,240
uh apparently it dissociates

358
00:14:15,670 --> 00:14:14,480
at higher temperatures so perhaps it

359
00:14:19,509 --> 00:14:15,680
just

360
00:14:24,550 --> 00:14:22,790
co and molecular hydrogen

361
00:14:25,829 --> 00:14:24,560
that be it could be an explanation for

362
00:14:28,829 --> 00:14:25,839
why it's only

363
00:14:30,710 --> 00:14:28,839
cold you only see cold

364
00:14:32,150 --> 00:14:30,720
formaldehyde all right we gotta move on