Processing of silicate dust grains in Herbig Ae/Be systems

被引:264
作者
Bouwman, J
Meeus, G
de Koter, A
Hony, S
Dominik, C
Waters, LBFM
机构
[1] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[2] Katholieke Univ Leuven, Inst Sterrenkunde, B-3001 Heverlee, Belgium
来源
ASTRONOMY & ASTROPHYSICS | 2001年 / 375卷 / 03期
关键词
circumstellar matter; stars : formation; stars : pre-main-sequence;
D O I
10.1051/0004-6361:20010878
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have analysed the 10 mum spectral region of a sample of Herbig Ae/Be (HAEBE) stars. The spectra are dominated by a broad emission feature caused by warm amorphous silicates, and by polycyclic aromatic hydrocarbons. In HD 163296 we find aliphatic carbonaceous dust, the first detection of this material in a HAEBE star. The silicate band shows a large variation in shape, due to variable contributions of three components: (i) a broad shoulder at 8.6 mum; (ii) a broad maximum at 9.8 mum; and (iii) a narrow feature with a broad underlying continuum at 11.3 mum. From detailed modeling these features can be identified with silica (SiO2), sub-micrometer sized amorphous olivine grains and micrometer sized amorphous olivine grains in combination with forsterite (Mg2SiO4), respectively. Typical mass fractions are 5 to 10 per cent of crystalline over amorphous olivine, and a few per cent of silica compared to the olivines. The detection of silica in emission implies that this material is heated by thermal contact with other solids that have a high absorptivity at optical to near-IR wavelengths. The observed change in peak position of the silicate band in HAEBE stars from 9.7 mum to 11.3 mum is dominated by an increase in average grain size, while changes in composition play only a minor r (o) over cap le. The HAEBE stars, beta Pic and the solar system comet Halley form a sequence of increasing crystallinity. We find that the abundance of SiO2 tends to increase with increasing crystallinity. This is consistent with the compositional changes expected from thermal annealing of amorphous grains in the inner regions of the disk. We confirm earlier studies that the timescale for crystallisation of silicates in disks is longer than that of coagulation. Our results indicate that the processes that governed grain processing in the proto-solar nebula, are also at work in HAEBE stars.
引用
收藏
页码:950 / 962
页数:13
相关论文
共 49 条
  • [1] INTERSTELLAR POLYCYCLIC AROMATIC-HYDROCARBONS - THE INFRARED-EMISSION BANDS, THE EXCITATION EMISSION MECHANISM, AND THE ASTROPHYSICAL IMPLICATIONS
    ALLAMANDOLA, LJ
    TIELENS, AGGM
    BARKER, JR
    [J]. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 1989, 71 (04) : 733 - 775
  • [2] MICROSCOPIC IRON METAL ON GLASS AND MINERALS - A TOOL FOR STUDYING REGOLITH MATURITY
    ALLEN, CC
    MORRIS, RV
    LAUER, HV
    MCKAY, DS
    [J]. ICARUS, 1993, 104 (02) : 291 - 300
  • [3] DISCOVERY OF A SHELL AROUND ALPHA-LYRAE
    AUMANN, HH
    GILLETT, FC
    BEICHMAN, CA
    DEJONG, T
    HOUCK, JR
    LOW, FJ
    NEUGEBAUER, G
    WALKER, RG
    WESSELIUS, PR
    [J]. ASTROPHYSICAL JOURNAL, 1984, 278 (01) : L23 - L27
  • [4] Beust H, 1996, ASTRON ASTROPHYS, V310, P181
  • [5] Bohren C. F., 1998, ABSORPTION SCATTERIN
  • [6] Bouwman J, 2000, ASTRON ASTROPHYS, V360, P213
  • [7] BREGMAN JD, 1987, ASTRON ASTROPHYS, V187, P616
  • [8] BROWNLEE DE, 1978, PROTOSTARS PLANETS, P134
  • [9] Calvet N., 2000, Protostars and planets 4, P377
  • [10] SUPERNOVA TRIGGER FOR FORMATION OF SOLAR-SYSTEM
    CAMERON, AGW
    TRURAN, JW
    [J]. ICARUS, 1977, 30 (03) : 447 - 461