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Near-Infrared Spectra: Specific Molecules Chad Trujillo (Gemini Observatory). Introduction Part 1: Background - Why ices and why the near-infrared? - Detections on KBOs and KBO analogues: Water, Methane, and other molecules Part 2: How to end an Easter egg hunt

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slide1

Near-Infrared Spectra: Specific Molecules

Chad Trujillo (Gemini Observatory)

slide2

Introduction

Part 1: Background

- Why ices and why the near-infrared?

- Detections on KBOs and KBO analogues:

Water, Methane, and other molecules

Part 2: How to end an Easter egg hunt

- For the first time, we can count the bright KBOs

- Required signal for detection and physical interest

- List of KBOs that have been well-studied

- List of KBOs we can (reasonably) study

- Summary of population-wide spectroscopic results

correcting for signal to noise bias

slide4

Theorists

Observers

slide5

Why the near-infrared?

There are two reasons to study KBOs:

1) Dynamics of an old (but not primordial) population

2) Ices

- tracer of pristine thermal history

- possible geologic effects

- sensitive to ion bombardment

- reservoir for atmosphere

- very difficult to study in other solar system populations

due to thermal alteration

- compositions can constrain models (i.e. Nice, etc.)

- very deep transitions in the near-infrared

- almost completely neutral in the visible

slide6

Why the near-infrared?

1998 Cruikshank et al.

slide7

Detections (water ice)

2003 EL61, Orcus, Quaoar, 1996 TO66, 1999 DE9,

2002 AW197, 2002 TX300?, Charon, Phoebe, Triton

-Where signal/resolution allow, crystalline water ice

seen.

-Crystalline water ice may have a lifetime shorter

than the age of the solar system

-Transition shape is somewhat sensitive to temperature

-All have 0.1 < e < 0.2 except Quaoar (0.035) and DE9 (0.4)

-But, what is the fraction of KBOs with water, really?

slide8

Detections (water ice)

Example:

2003 EL61

can be crudely

fit with

100% water ice

and nothing else

(Trujillo et al.

submitted)

slide9

Detections (methane ice)

2003 UB313, 2005 FY9, Sedna, Pluto, Triton

-Methane has a high vapor pressure

-It may only be present on the largest bodies

-Has been found to be pure (2003 UB313) as well

as dissolved in N2 (Pluto)

-Line position is sensitive to temperature and

environment

-But, what is the fraction of KBOs with methane, really?

slide10

Detections (methane ice)

2003UB313 can

be crudely fit

with 100% pure

methane ice

and nothing

else

(Brown et al. 2005)

slide11

Detections (other)

Ammonia hydrate: Quaoar, Charon

Cyanides: Phoebe, 2003 EL61?

Methanol: VE95, Pholus

Nitrogen: Pluto, Triton

CO: Pluto, Triton

CO2: Phoebe, Triton

Ethane: 2005FY9

Propane: 2005FY9?

-But, what is the fraction of KBOs, really?

slide12

Detections (other)

2003EL61 as

water ice only

slide13

Detections (other)

2003EL61 as

water ice +

HCN.

This is not an

HCN detection,

since there are

no transitions

seen.

Note 2.35um

drop, which is

seen in other

bodies and may

be triple-CN.

slide14

Simulation

Made a simple monte-carlo simulation of ice observations:

-Model near-infrared spectral observations comparing

science goal to control spectrum

-Assume albedo is unknown and neutral material may

be present in control spectrum

-Simulated H and K, but found that signal requirements

are similar for both.

-Want to determine the required signal-to-noise

ratios (S/N) for detection / non-detection

-Relate this to S/N achievable at large (8m – 10m)

telescopes

slide15

Simulation

Water ice

detection

requires

S/N~20

for a

3 sigma

detection

of 100%

pure ice

Really want

S/N~40

slide16

Simulation

Crystalline

water ice

detection

requires

S/N~40

for a

3 sigma

detection

of 100%

pure ice

Really want

S/N~80

slide17

Simulation

Estimate

of surface

fraction

to 10% for

water ice

requires

S/N~200

slide18

Simulation

Estimate

of temp

for water

requires

S/N~500

slide19

Simulation

Methane ice

detection

requires

S/N~20

for a

3 sigma

detection

of 100%

pure ice

Really want

S/N~40

slide20

Simulation

Estimate

of surface

fraction

to 10% for

pure

methane

requires

S/N~200

slide21

Simulation

Estimate

of temp

for methane

requires

S/N~200

slide22

Simulation

Methanol

detection

requires

S/N~70

for a

3 sigma

detection

of 100%

pure ice

Really want

S/N~140

slide23

Simulation

Ammonia

detection

requires

S/N~125

for a

3 sigma

detection

of 100%

pure ice

Really want

S/N~250

slide24

Simulation Summary

S/N Ice

40 water/methane detection

80 xwater detection

200 methanol/ammonia detection

200 water/methane fraction to 10%

500 water/methane temp, N2/CO/CO2/Ethane limits

water: 7/16 EL61,Q.,O.,AW197,DE9,TO66,TX300

methane: 3/15 FY9,UB313,Sedna

xwater: 4/4 EL61,Q.,O.,TO66,AW197?,DE9?

mthnl/NH3: 2/4 Q.=NH3:H2O,VE95=methanol

Ethane: 1/1 FY9

temp: 0/1?

N2/CO/CO2: 0/1

No CH4/H2O: 6/15 CS29,TL66,GN171,WR106,Huya,Ixion

Pluto: Methane, N2, CO, Ethane?

Charon: xwater, NH3, NH3:H2O

Triton: Methane, N2, CO, CO2, 13CO

Phoebe: xwater, CO2, OH, CH, CN, Fe2+, metal-OH, phyllosilicate

slide25

What\'s Left?

Combining all our resources in an international

collaboration, we can probably get about

15 nights / year of 8m – 10m telescope time

~ 70 hours / year of integration time

~ 200 hours over next 3 years

Much more time than this is wasted every year

outside the solar system.

Assume Keck=VLT=Gemini:

S/N~100 in 1 hour for a K=18 object

What can we do?

slide26

What\'s Left?

The 7

brightest

KBOs have

at least

S/N=80

completed

There are

about 8

KBOs left

that are

“easy” H2O/CH4

detections

slide27

What\'s Left?

These have

S/N~250

These have

S/N~100

About 4 of

these have

S/N~50

About 4

of these have

S/N~40

slide28

What\'s Left?

The Good News:

- There are about 40 KBOs left that could use 8 hours

of exposure time, 8 of which could use 1 hour for marginal results

- About 25 KBOs could be observed by an international

team of collaborators using the world\'s largest

telescopes.

- Such an effort would produce ~8 X/H2O detections,

~5 CH4 detections, a few temperatures, a few good

N2/CO limits, tripling our knowledge of KBO surfaces

The Bad News:

- Don\'t bother observing any of the brightest 15 KBOs

unless you spend at least 4 hours of exposure time

on a 8m – 10m telescope in good conditions.

slide29

Your Results So Far...

After taking into account S/N issues:

For KBOs

-100% (4) of water ice is crystalline

-44% (7/16) of KBOs show water ice

-50% (2/4) of KBOs show ammonia hydrate or methanol

-20% (3/15) of KBOs show methane ice

-Only the biggest KBOs have methane ice, is this

physical or small number statistics?

-Only 1 KBO has been observed deeply enough to

detect N2/CO/CO2/Ethane (FY9, Ethane only)

-40% (6/15) of KBOs are featureless

-No clear correlation between surface and orbital parameters

-Results are similar with inclusion of KBO analogues (Pluto,Charon,etc.)

Tips for observers:

-Don\'t repeat objects that are already done!

-Observe in good conditions and at low airmass!

-Take high (80-100) S/N spectra!

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