Mid-infrared spectra of bulk CAI from the CV3.2 chondrite Allende are presented and compared with astronomical spectra of cometary dust, zodiacal light,the circumstellar disk of beta Pictoris and dust around the red supergiant PR Per

Bland, P. A.

Cressey, G.

Grady, M. M.

Koehler, M.

Menzies, O. N.

Morlok, A.

English

Morlok, A

Menzies, ON

Koehler, M

Bland, PA

Cressey, G

Grady, MM

Spiral - Imperial College Digital Repository

Mid-Infrared Spectroscopy of CAI and AOA from the Allende CV3.2 Chondrite.  A. Morlok1,4, O.N. Men-zies2,4, M. Koehler3,4, P. Bland2,4, G. Cressey1, M.M. Grady1,4 1The  Natural History Museum, Cromwell Road, Lon-don, SW7 5BD, UK, A.Morlok@nhm.ac.uk , 2Imperial College London, South Kensington Campus, SW7 2AZ. 3Institut fuer Planetologie, Wilhelm-Klemm-Str.10, 48149 Muenster, Germany  4IARC  Introduction:  Infrared spectroscopy of dust grains in circumstellar debris disks is the main way to obtain information about the mineralogical composition of such material. To find out what these spectra actually mean, infrared spectra of standard materials are needed for comparison. While so far mainly synthetic or ter-restrial minerals have been used for this purpose, we use mineral separates or components from primitive meteorite for this purpose. This is based on the as-sumption, that these phases formed in environments similar to those where the astronomical spectra origi-nate. Like meteorites, the astronomical dust is often not completely pristine, but represents a later genera-tion of processed material [1]. In the first part of our project, we analysed olivines and pyroxenes from unequilibrated chondrites [2,3]. Following this, we turned to Calcium-Aluminium-Rich inclusions (CAI) and Amoeboid Olivine Aggregates (AOA). These bodies represent the first step in con-densation and processing of minerals in the Solar Sys-tem. Here we present further results of the spectros-copy of these objects.  Techniques and Samples: We used bulk material of 3 powdered CAIs and one AOA from Allende.  Mineralogy: The mineralogical composition of this material was previously measured using a new micro-XRD technique [4]. With the help of this technique, it is possible to quantify the modal mineralogical compo-sition of small amounts of material. CAI 15 has been identified as a compact, type A inclusion. Its composi-tion is 77wt% gehlenite, 16wt% grossular and 7 wt% spinel. CAI 5 is a compact, type A CAI. The modal mineral abundance in the fine-grained, spinel rich CAI 2 is 47wt% anorthite, 12wt% diopside, 18wt% heden-bergite and 23wt% spinel. The composition of the AOA 3 is 5wt % akermanite, 19wt% forsterite100, 25wt% forsterite90, 30wt% forsterite80 and 21wt% he-denbergite. Also some matrix areas have been ana-lysed to get information about potential contamination with that material.  Infrared Spectroscopy: The infrared spectra of the specimens were obtained using a Perkin Elmer Auto Image infrared microscope. Small amounts of pow-dered CAI material were further compressed to a very fine grained powder using a diamond compression cell first, and then analysed under the infrared microscope. Of several measurements of the material, an average spectrum was calculated [5]. The results are presented in Fig.1.   The astronomical spectra used for comparison in Fig.1 were taken using Earth and space based tele-scopes. These were the NASA Aerospace spectrograph at the NASA Infrared Telescope Facility (IRTF) for the circumstellar dsk around β Pictoris [6], Aerospace Corp BASS (IRTF)for the res supergiant PR Per [7], the ISOCAM at the Infrared Space Observatory (ISO) for Zodiacal dust [8] and the United Kingdom Infrared Telescope (UKIRT) for comet C/2002 V1 NEAT [9]. Discussion: Small shifts of ~0.1 micron provided, comparison with a spectra of the circumstellar disc of β Pictoris [6] shows good similarity with CAI 2 for the strong bands(Fig.1a), as well as with the matrix mate-rial. The only fit for some strong bands with the red supergiant PR Per [7] would be possible with a ~0.2 micron shift of  CAI 2 (Fig.1b). Strong bands in matrix material and in CAI 2 and AOA 3 agree very well with bands of the Zodiacal light [8] (Fig.1c). Given a minor shift of ~0.2 micron, inclusion AOA 3 and CAI 5 also fit well. The spectra of comet C/2002 V1 NEAT [9] had no similarity with the laboratory spectra.Small shifts in bands composition can be accomplished in several ways: temperature effects, compositional (chemical and isotopic) differences, grain size and morphology. However, since these comparisons only take into account a narrow region in the mid-infrared, the findings have to be first confirmed by measure-ments over a wider range. For most minerals, many characteristic bands occur in the far infrared (up to ~100 micron). Also in no case could all bands in the astronomical spectra be confirmed with one of our laboratory spectra, which indicates that at least another component is missing.  Acknowledgements: This work was supported by PPARC and the EU Marie Curie program. References:  [1] Okamoto Y.K. Kataza H. and Honda M. et al. (2004) Nature, 431, 660–663. [2] Morlok A. Koehler M. Menzies O.N. et al. (2004) Workshop Chondrites and the Protoplanetary Disk, Kauai, #9022 [3] Morlok A. Koehler M. Menzies O.N. et al. (2004) Workshop Chondrites and the Protoplanetary Disk, Kauai, #9023 [4] Menzies O.N. Bland P.A. Cressey G. et al. (2004) MAPS 39, A67 [5] Morlok A. Koehler M. Bowey J. et al. (2005) Mon. Not. Roy. Astr. Soc. (Submitted) [6] . Knacke R. et al. (1993) Astrophys. Jour. 418, 440 [7] Speck A.M. et al. (2000) A&A 146, 437-464 [8] Han-ner M. et al. (1997) Earth, Moon and Planets 79, 247 [9] Reach W. et al. (2003) Icarus 164, 384  Lunar and Planetary Science XXXVI (2005) 1644.pdf Fig.1a   Fig.1b  Fig.1c  Fig.1a-c: (All spectra in relative absorbance) Compari-son of laboratory spectra with the bands of astronomi-cal spectra (grey bands). (a) comparison with the cir-cumstellar disk of β Pictoris, (b) with the red super-giant PR Per and (c) with that of Zodical dust.      Lunar and Planetary Science XXXVI (2005) 1644.pdf

Mid-infrared spectroscopy of CAI and AOA from the Allende CV3.2 chondrite

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsMid-infrared spectroscopy of CAI and AOA from theAllende CV3.2 chondriteConference or Workshop ItemHow to cite:Morlok, A.; Menzies, O. N.; Koehler, M.; Bland, P. A.; Cressey, G. and Grady, M. M. (2005). Mid-infraredspectroscopy of CAI and AOA from the Allende CV3.2 chondrite. In: 36th Lunar and Planetary Science Conference,14-18 Mar 2005, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1644.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukMid-Infrared Spectroscopy of CAI and AOA from the Allende CV3.2 Chondrite.  A. Morlok1,4, O.N. Men-zies2,4, M. Koehler3,4, P. Bland2,4, G. Cressey1, M.M. Grady1,4 1The  Natural History Museum, Cromwell Road, Lon-don, SW7 5BD, UK, A.Morlok@nhm.ac.uk , 2Imperial College London, South Kensington Campus, SW7 2AZ. 3Institut fuer Planetologie, Wilhelm-Klemm-Str.10, 48149 Muenster, Germany  4IARC  Introduction:  Infrared spectroscopy of dust grains in circumstellar debris disks is the main way to obtain information about the mineralogical composition of such material. To find out what these spectra actually mean, infrared spectra of standard materials are needed for comparison. While so far mainly synthetic or ter-restrial minerals have been used for this purpose, we use mineral separates or components from primitive meteorite for this purpose. This is based on the as-sumption, that these phases formed in environments similar to those where the astronomical spectra origi-nate. Like meteorites, the astronomical dust is often not completely pristine, but represents a later genera-tion of processed material [1]. In the first part of our project, we analysed olivines and pyroxenes from unequilibrated chondrites [2,3]. Following this, we turned to Calcium-Aluminium-Rich inclusions (CAI) and Amoeboid Olivine Aggregates (AOA). These bodies represent the first step in con-densation and processing of minerals in the Solar Sys-tem. Here we present further results of the spectros-copy of these objects.  Techniques and Samples: We used bulk material of 3 powdered CAIs and one AOA from Allende.  Mineralogy: The mineralogical composition of this material was previously measured using a new micro-XRD technique [4]. With the help of this technique, it is possible to quantify the modal mineralogical compo-sition of small amounts of material. CAI 15 has been identified as a compact, type A inclusion. Its composi-tion is 77wt% gehlenite, 16wt% grossular and 7 wt% spinel. CAI 5 is a compact, type A CAI. The modal mineral abundance in the fine-grained, spinel rich CAI 2 is 47wt% anorthite, 12wt% diopside, 18wt% heden-bergite and 23wt% spinel. The composition of the AOA 3 is 5wt % akermanite, 19wt% forsterite100, 25wt% forsterite90, 30wt% forsterite80 and 21wt% he-denbergite. Also some matrix areas have been ana-lysed to get information about potential contamination with that material.  Infrared Spectroscopy: The infrared spectra of the specimens were obtained using a Perkin Elmer Auto Image infrared microscope. Small amounts of pow-dered CAI material were further compressed to a very fine grained powder using a diamond compression cell first, and then analysed under the infrared microscope. Of several measurements of the material, an average spectrum was calculated [5]. The results are presented in Fig.1.   The astronomical spectra used for comparison in Fig.1 were taken using Earth and space based tele-scopes. These were the NASA Aerospace spectrograph at the NASA Infrared Telescope Facility (IRTF) for the circumstellar dsk around β Pictoris [6], Aerospace Corp BASS (IRTF)for the res supergiant PR Per [7], the ISOCAM at the Infrared Space Observatory (ISO) for Zodiacal dust [8] and the United Kingdom Infrared Telescope (UKIRT) for comet C/2002 V1 NEAT [9]. Discussion: Small shifts of ~0.1 micron provided, comparison with a spectra of the circumstellar disc of β Pictoris [6] shows good similarity with CAI 2 for the strong bands(Fig.1a), as well as with the matrix mate-rial. The only fit for some strong bands with the red supergiant PR Per [7] would be possible with a ~0.2 micron shift of  CAI 2 (Fig.1b). Strong bands in matrix material and in CAI 2 and AOA 3 agree very well with bands of the Zodiacal light [8] (Fig.1c). Given a minor shift of ~0.2 micron, inclusion AOA 3 and CAI 5 also fit well. The spectra of comet C/2002 V1 NEAT [9] had no similarity with the laboratory spectra.Small shifts in bands composition can be accomplished in several ways: temperature effects, compositional (chemical and isotopic) differences, grain size and morphology. However, since these comparisons only take into account a narrow region in the mid-infrared, the findings have to be first confirmed by measure-ments over a wider range. For most minerals, many characteristic bands occur in the far infrared (up to ~100 micron). Also in no case could all bands in the astronomical spectra be confirmed with one of our laboratory spectra, which indicates that at least another component is missing.  Acknowledgements: This work was supported by PPARC and the EU Marie Curie program. References:  [1] Okamoto Y.K. Kataza H. and Honda M. et al. (2004) Nature, 431, 660–663. [2] Morlok A. Koehler M. Menzies O.N. et al. (2004) Workshop Chondrites and the Protoplanetary Disk, Kauai, #9022 [3] Morlok A. Koehler M. Menzies O.N. et al. (2004) Workshop Chondrites and the Protoplanetary Disk, Kauai, #9023 [4] Menzies O.N. Bland P.A. Cressey G. et al. (2004) MAPS 39, A67 [5] Morlok A. Koehler M. Bowey J. et al. (2005) Mon. Not. Roy. Astr. Soc. (Submitted) [6] . Knacke R. et al. (1993) Astrophys. Jour. 418, 440 [7] Speck A.M. et al. (2000) A&A 146, 437-464 [8] Han-ner M. et al. (1997) Earth, Moon and Planets 79, 247 [9] Reach W. et al. (2003) Icarus 164, 384  Lunar and Planetary Science XXXVI (2005) 1644.pdf Fig.1a   Fig.1b  Fig.1c  Fig.1a-c: (All spectra in relative absorbance) Compari-son of laboratory spectra with the bands of astronomi-cal spectra (grey bands). (a) comparison with the cir-cumstellar disk of β Pictoris, (b) with the red super-giant PR Per and (c) with that of Zodical dust.      Lunar and Planetary Science XXXVI (2005) 1644.pdf

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Mid-infrared spectroscopy of CAI and AOA from the Allende CV3.2 chondrite

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