Formation of Silicates at Cryogenic Temperatures

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1 1 Max-Planck-Institut für Astronomie Heidelberg Friedrich-Schiller- Universität Jena Formation of Silicates at Cryogenic Temperatures Gaël Rouillé Laboratory Astrophysics and Cluster Physics Group

2 Collaborators and Sponsors 2 Thomas Henning Cornelia Jäger Serge A. Krasnokutski Svitlana Zhukovska (MPIA) Melinda Krebsz (Eötvös Loránd University, Budapest) Max Planck Institute for Astronomy (Heidelberg) Friedrich Schiller University (Jena) Deutsche Forschungsgemeinschaft (DFG): Priority Program 1573 "Physics of the Interstellar Medium" (ISM-SPP)

3 Cosmic dust 3 Main components - amorphous silicates: crystallinity < 2.2% (Kemper et al. 2004, 2005; Min et al. 2007) - carbonaceous grains Formation - condensation in stellar envelopes and - growth in the interstellar medium (ISM): under discussion (e.g. Jones & Nuth 2011) - necessary to obtain a steady population of cosmic grains - consistent with observations: elemental depletions and extinction curves in the Milky Way (e.g. Hirashita & Voshchinnikov 2014) > Need for data on the formation of carbonaceous and silicate grains at ISM temperatures (< 100 K)

4 Precursors of silicate grains 4 Interstellar abundances (Colangeli et al. 2003) - O > 300 per 10 6 H atoms - Si ~30 - Mg ~30 - Fe ~30 - Al ~3 > The abundances are compatible with the formation of Mg x Fe y SiO z type silicates Another form for interstellar Si in the gas phase is SiO - dense clouds: SiO ~ per 10 6 H atoms (Herbst et al. 1989) - translucent clouds: < 10% of the Si population (Turner 1998) > Experiments on the low-temperature condensation and accretion of the precursors of silicates including SiO

5 Laboratory methods for low-t condensation studies 5

6 Matrix isolation spectroscopy apparatus 6 UV/vis/IR absorption spectroscopy Transparent substrate: CaF 2 or KBr Laser source: pulsed Nd:YAG, 266 or 532 nm, 5 ns pulse duration, 10 Hz, 1 to 25 mj per pulse

7 Condensation of SiO grains at cryogenic temperatures (1) 7

8 Condensation of SiO grains at cryogenic temperatures (2) 8

9 Laser vaporization of Mg 2 SiO 4 9 Synthetic amorphous Mg 2 SiO 4 target 532 nm mj per pulse 20 1 min shooting Mg 2 SiO 4 target c131212

10 Laser vaporization of Mg 2 SiO 4 Ne matrix at 6 K UV 10 Synthetic amorphous Mg 2 SiO 4 target 532 nm mj per pulse 20 min deposition Rouillé et al. (2014) > Mg atoms and SiO molecules in the Ne matrix > No Si atoms

11 Laser vaporization of Mg 2 SiO 4 Ne matrix at 6 K FTIR 11 Synthetic amorphous Mg 2 SiO 4 target 532 nm mj per pulse 20 min deposition Rouillé et al. (2014) > Isolated molecules in the Ne matrix * O 3 * O 4 + * SiO * H 2 (H 3 O + or H 2 O 5+ ) (?) *? > Relevance to ISM?

12 Accretion of the products of laser vaporization FTIR 12 Heating of the doped Ne matrix: up to 13 K Rouillé et al. (2014) > Rise of a band at ~1020 cm -1 (9.8 μm)

13 Condensate using the Mg 2 SiO 4 target (1) 13 Using the Mg 2 SiO 4 target Using the Mg 2 SiO 4 target c c131212

14 Condensate using the Mg 2 SiO 4 target (2) 14 > TEM: - aggregates with fluffy morphology - grains with amorphous, homogeneous structure - no obvious sign of domains > EDX: - composition: Mg1 Si O2.79

15 Laser vaporization of Mg 0.4 Fe 0.6 SiO 3 15 Synthetic amorphous Mg 0.4 Fe 0.6 SiO 3 target 532 nm mj per pulse 40 1 min shooting Mg 0.4 Fe 0.6 SiO 3 target Ø 0.45 mm c c Mg 0.4 Fe 0.6 SiO 3 target

16 Laser vaporization of Mg 0.4 Fe 0.6 SiO 3 Ne matrix at 6 K UV 16 Synthetic amorphous Mg 0.4 Fe 0.6 SiO 3 target 532 nm mj per pulse 20 min deposition Rouillé et al. (accepted) > Fe and Mg atoms in the Ne matrix

17 Laser vaporization of Mg 0.4 Fe 0.6 SiO 3 Ne matrix at 6 K FTIR 17 Synthetic amorphous Mg 0.4 Fe 0.6 SiO 3 target 532 nm mj per pulse 40 min deposition Rouillé et al. (accepted) > Isolated molecules in the Ne matrix * O 3 * O 4 + * SiO * H 2 H x O y + * SiO 2 (?) * SiO 3 (?) * FeO (?) * OFeO (?) *?

18 Condensate using the Mg 0.4 Fe 0.6 SiO 3 target (1) 18 Using the Mg 0.4 Fe 0.6 SiO 3 target Using the Mg 0.4 Fe 0.6 SiO 3 target c c131206

19 Condensate using the Mg 0.4 Fe 0.6 SiO 3 target (2) 19 c c n m 5 n m > TEM: - aggregates with fluffy morphology - grains with amorphous, homogeneous structure - no obvious sign of domains EDX: - composition: Mg0.28 Fe0.91 Si O3.58

20 Comparison with observational spectrum 20 Object: WR 98a (Chiar & Tielens 2006) ~990 cm -1 (10.1 μm) ~1020 cm -1 (9.8 μm) Rouillé et al. (accepted) > The spectra of the synthetic grains can be compared with astronomical data > The experiment can be improved: - cleaner - larger amounts for a stronger signal - production of the precursors

21 Summary and outlook 21 > Amorphous silicate grains can be formed by accretion of precursors at T relevant to the ISM (as low as 13 K) - amorphous structure like interstellar silicates - homogeneous structure > The spectra of the synthetic grains can be compared with astronomical data > Improvements: - cleaner experiment (less water) - laser vaporization of silicate targets with higher energies - deposition of larger amounts to increase the strength of the absorption spectra > Accretion under VUV photon bombardment > New ISM-SPP project (see also poster): separation of carbonaceous and siliceous matters in cosmic dust

22 Next: separation of carbonaceous and siliceous matters? 22