1. Interstellar Ices Adwin Boogert NHSC, IPAC, Caltech, Pasadena
Collaborators:
Jean Chiar (SETI)
Amanda Cook (RPI NY)
Tracy Huard (Maryland)
Claudia Knez (Maryland)
Klaus Pontoppidan (Caltech)
Ewine van Dishoeck (Leiden)
Geoff Blake (Caltech)
Sandrine Bottinelli (Leiden)
Karin Oberg (Leiden)

2. Contents Introduction: Formation of Ices
Sample Selection and Observations
Ices toward YSOs
Special Case: Ices toward IC 1396
Ices in Quiescent Cloud Material
Deriving “High Resolution” Extinction Law
Conclusions

3. Introduction: a Grain in Space
Gas phase chemistry often insufficient to explain observed abundances, and grain surface catalysis required (e.g. Bates & Spitzer ApJ 113, 441, 1951)
Ices are the main reservoir of volatile species (except H2)
More realistic:

4. Introduction: the Molecular Universe
dense molecular clouds
diffuse medium
YSOs
evolved stars
comets, planets
tori of galactic nuclei
...
Environments vary wildly, chemical processes may be common
Ehrenfreund & Charnley (ARAA 38, 427, 2000)

5. Introduction: Laboratory Simulations
Chemical processes occurring
in space can be simulated in
laboratory at low T (>=10 K)
and low pressure.
Thin films of ice condensed on
surface and absorption or reflection spectrum taken.
Temperature and irradiation by UV light or energetic particles of ice sample can be controlled.
Astrophysical laboratories: Leiden, Catania, NASA Ames/Goddard, Paris
Gerakines et al. A&A 357, 793 (2000)

6. Introduction: Laboratory Simulations
Absorption width, peak position, shape determined by ice composition and temperature (and grain shape)
Example: H2O:CO2:CH3OH=1:1:1 heated.
Double peak characteristic for
pure CO2 appears after H2O
crystallization.
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

7. Introduction: Energetic Processing
Complex species formed, some are of biological interest:
POM (polyoxymethylene, -(CH2-O)n-
HMT (hexamethylenetetramine, C6H12N4)
amino acids (glycine)
Urea (H2NCONH2)
PAHs (polycyclic aromatic hydrocarbons)
Greenberg et al. ApJ 455, L177 (1995): launched processed ice sample in earth orbit exposing directly to solar radiation (EURECA experiment). Yellow stuff turned brown: highly carbonaceous residue, also including PAH.

8. T<90 K and AV>few magn.
Observing Ices
Ices form anywhere
T<90 K and AV>few magn.
H2O
CO2
silicates
NH4+
Foreground cloud(s)
envelope
outflow
disk
star
Star-forming dense core
Background
star

9. Source Selection
Background stars selected using broad-band 2-25 μm colors from c2d catalogs. Extinction determined for many background stars, assuming average, intrinsic stellar colors (“NICE” method).
L 1014;
AV=2-35;
20” resol;
Huard et al. (ApJ 640, 391)

10. Observations
Initial survey:
Spitzer legacy program 'From Molecular Cores to Planetary Disks' (c2d; PI N. Evans) ~20h for IRS spectroscopy of ~50 known YSOs and ~15 background stars in clouds and isolated cores
Follow-up surveys of YSOs and many more background stars identified in c2d Spitzer 3-80 um mapping programs:
GO2, Boogert et al.: 30 YSOs and 33 BG stars in 26 isolated cores, 29h
GO4, Knez et al.: ~90 BG stars in Perseus, Lupus, and Serpens, 40h
GO4+GTO, Huard et al.: ~60 BG stars in 5 isolated cores, ~25h
Observations motivated by ices, but also by extinction law and dust (silicates) studies, e.g. AK/9.7 relation.
Large clouds and isolated cores well-covered
Some cores observed in dense-grid of background stars, for local studies

11. Publications So Far Initial results:
YSOs (Boogert et al., ApJS 154, 359, 2004); 2 YSOs
Background stars (Knez et al., ApJL 635, 145, 2005); 3 BG stars
Edge-on disk (Pontoppidan et al., ApJ 622, 463, 2005); 1 YSO
Survey papers:
I: H2O and the 5-8 um bands (Boogert et al., ApJ 678, 985, 2008); ~40 YSOs
II: CO2 (Pontoppidan et al., ApJ 678, 1005, 2008); ~40 YSOs
III: CH4 (Oberg et al., ApJ 678, 1032, 2008); ~40 YSOs
IV: NH3 (Bottinelli et al., in prep); ~40 YSOs

12. Ices toward YSOs silicates silicates
Ice absorption bands cover most of 2-30 μm region of YSOs and background stars and are important source of extinction, affecting broad band (IRAC) photometry
5-30 μm Spitzer spectra need to be complemented by ground-based K, L, & M-band spectra
HCOO-
NH4+
HCOOH
CH3OH
CH4
silicates
silicates
CO2
H2O
OCN-
H2O
NH3
H2O
HCOOH
CH3OH CO
CH3OH
NH3

13. Ices toward YSOs Continuum determination crucial, difficult aspect.
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

14. Ices toward YSOs: 5-8 mm Complex
Once upon a time....
CH3OH
H2O
KAO spectrum of massive YSO W33A by Tielens et al. ApJ 287, 697 (1984)
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

15. Ices toward YSOs: 5-8 mm Complex
Determine H2O column from 3.0 μm O-H stretch or 13 μm libration mode

16. Ices toward YSOs: 5-8 mm Complex
H2O does not explain everything
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

17. Ices toward YSOs: 5-8 mm Complex
Each spectrum explained by solid pure H2O and 5 additional absorption components, by at least 7 different carriers.
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

18. Ices toward YSOs: 5-8 mm Complex
Independent determination HCOOH column
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

19. Ices toward YSOs: 5-8 mm Complex
Independent determination NH3 and CH3OH columns
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

20. Ices toward YSOs: 5-8 mm Complex
Fair fraction
5-8 μm absorption
is complex blend
of simple species
CH3OH/H2O %
HCOOH/H2O 3-8%
NH3/H2O %
H2CO/H2O 6%
HCOO-/H2O 0.3%
[CH4/H2O %]

21. Ices toward YSOs: 6.85 mm Band
Profile 6.85 um band varies dramatically
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

22. Ices toward YSOs: 6.85 mm Band
YSOs with 'red' 6.85 μm bands have low H2O ice abundances, i.e. 'warm' lines of sight.
For massive YSOs confirmed by warm gas temperatures
6.85 μm band shows evidence of ice processing

23. Ices toward YSOs: 6.85 mm Band
Which species....
...has absorption band at 6.85 μm that shifts to longer wavelengths when heated?
...does not survive in diffuse ISM?
...is less volatile than H2O?
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

24. Ices toward YSOs: 6.85 mm Band
NH4+ has spectral characteristics that fit interstellar 6.85 μm band
NH4+ easily produced by warming acid/base mixture NH3+HNCO, forming a salt
UV irradiation H2O:CO2:NH3:O2 also produces NH4+, though unlikely in dense regions. Negative counter-ions do produce feature that looks like our C5 component (Schutte & Khanna A&A 398,
1049, 2003)
heated
UV-irradiated

25. Ices toward YSOs: 6.85 mm Band
IC 1396A very different environment. Globule blasted by nearby O-star. May well be more realistic early solar system analog than for example Taurus YSOs.
Reach et al. 2009, ApJ 690, 683
IC 1396A very different environment. Globule blasted by nearby O-star. May well be more realistic early solar system analog than for example Taurus YSOs (Reach et al. 2009, ).

26. Ices toward YSOs: 6.85 mm Band
Indeed, very 'red' 6.85 μm band AND low H2O ice abundance in highly processed globule IC 1396A. Confirms carrier 6.85 μm band affected by processing.

27. Ices toward YSOs
blend of absorptions by simple species (HCOOH, NH3, H2CO) in addition to H2O explains much but not all 5-8 um absorption. Likely grain surface chemistry products.
'salts' produced by acid-base chemistry: NH4+ likely, possibly suite of negative ions.
many signatures of ice heating observed. Heating affects ice structure and facilitates chemical reactions (e.g. Acid-base chemistry).
energetic processing (UV, CR) may be responsible for some absorption in 5-8 μm. Better knowledge physical conditions (radiation fields, disk inclination, disk/envelope ratio) required.
Background star observations tracing quiescent cloud material needed to separate YSO and ISM effects
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

28. Ices toward Background Stars
Isolated core L 1014; AV=2-35; Huard et al. 2006, ApJ 640, 391
YSO
Background
Star

29. Ices toward Background Stars
Continuum determination BG stars critical step in analysis and can be done more accurately than for YSOs. c2 minimization includes:
Spectral type:
CO overtone (K-band spectra)
CO fundamental (5.3 mm/IRS)
SiO (8.0 mm/IRS)
Stellar models (MARC; Decin et al.)
Extinction laws
Silicates model
L-band spectra (H2O ice)
H2O ice model
1-25 mm photometry
H2O
silicates
NH4+
CO2

30. Ices toward Background Stars Spectral Type
Spectral types can be fairly accurately determined using H- and K-band lines
Accurate spectral type needed to correct photospheric lines at longer wavelengths

31. Ices toward Background Stars Extinction Law
Broad-band extinction law flattens at 3-10 mm in dense clouds (AV>5 mag)
Well fitted by theoretical curve for larger grains (RV~5.0)
Roman-Zuniga et al. ApJ 664, 357 [2007]
Lutz et al. A&A 315, L269 [1996]
Indebetouw et al. ApJ 619, 931 [2005]
Weingartner & Draine ApJ 548, 296 [2001]
Inclusion 23 mm MIPS point: extinction flat or even increasing toward longer wavelengths.
Chapman et al., ApJ 690, 496 [2009]
Broad-band extinction laws include dust and ice features, while for background stars we need separate continuum-only extinction law......

32. Ices toward Background Stars Extinction Law
K5-III model
Derive high resolution extinction law, separating features from continuum. Assumptions:
spectral type (K5-III)
Stellar model (Decin et al. ApJS 154, 408, 2004)
J-K extinction is standard power law.
L1014 BG
L1014 BG - model

33. Ices toward Background Stars Extinction Law
How does 'high' resolution extinction law compare to broad-band extinction laws?

34. Ices toward Background Stars Extinction Law
'High' resolution extinction law confirms significant 'continuum' extinction beyond 10 μm
However, much also due to features
Needs testing on wider range of environments

35. Ices toward Background Stars
Using accurate continuum:
Same features seen for bg stars as for YSOs
In small isolated cores and cluster-forming clouds
Consequences:
Most species seen toward YSOs are not produced by YSO radiation field or conditions.
Hypothesis: Possibly Cosmic Rays produced NH4+, and subsequently YSOs process it.
To be continued:
Band profiles and strengths need to be investigated

36. Next: Hot Cores/Corinos
Cazaux et al. 2004
(sub)millimeter-wave gas phase measurements orders of
magnitude more sensitive to abundances than IR ice observations
indirectly trace the ice mantle composition in hot cores/corinos

37. Next: Hot Cores/Corinos
Have to be able to separate flowers from the weeds
SGR B2(N), ALMA Band 6 mixer at SMT
A. Wootten, “Science with ALMA” Madrid 2006.

38. Next: Herschel/HIFI
GHz ( mm) Resolving Power / up to 10 million, or <0.1 km/s

39. Next: Herschel/HIFI
CH3OH gas cell measurement using HIFI (Teyssier et al. 2005)

40. Next: Herschel/HIFI DR 21 mass star formation region (Cygnus) Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

41. Next: Herschel
Combined PACS (70, 160 mm) and SPIRE (250, 350, 500 mm) image of Galactic plane
Science Demonstration Phase ongoing
Call for Open Time proposals Feb 2010
For questions on proposals, funding, data analysis help, please contact the NASA Herschel Science Center:
Topics
- General aspects of the survey
intro to NIRSPEC
intro to M band atmosphere
- Sources, wide variety. Show example of
categories.(emission, abs., gas, ice, Pf beta,
dynamics, infall, outflow)
- Quite diverse story that is unfinished (too early)
*infall in an edge on Disk
*processing in an edge-on disk
*detection of 13CO
*implications isotope ratios
*implications chemistry (pure CO)
*CO emission from disks (AS 205)

42. Conclusions/Future Work
To first order, same ice features, abundances, and variations thereof for low and high mass YSOs, and background stars.
5-8 μm region shows complex absorption from at least 8 different carriers. Much can be explained by simple species (H2O, HCOOH, H2CO, NH3), likely grain surface chemistry products.
Any differences between low and high mass YSOs and background stars explained by thermal processing.
Identification still issue, especially for 6.85 μm band, 6.3 μm region, broad component 5. 'Salts' are promising, especially NH4+. Signs of processing.
Background stars prominent 6.85 μm band: not produced by UV or thermal processing from YSOs. Possibly Cosmic Rays produced NH4+, and subsequently YSOs process it.
“High resolution extinction law” derived from background stars confirms flat law up to at least 25 μm. Should be tested on larger extinction and cloud range