1994A&A...292..641J


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.23CEST16:00:40

1994A&A...292..641J - Astronomy and Astrophysics, volume 292, 641-655 (1994/12-2)

Steps toward interstellar silicate mineralogy. I. Laboratory results of a silicate glass of mean cosmic composition.

JAEGER C., MUTSCHKE H., BEGEMANN B., DORSCHNER J. and HENNING T.

Abstract (from CDS):

Although extrasolar silicates were detected more than 25 years ago, important questions concerning chemical composition, material properties, and grain structure are still without reliable answers. The most important of these questions are listed at the beginning of this paper because they play decisive roles as guide-posts for the silicate research program of the Jena laboratory astrophysics group. This paper communicates the first results of this program aimed at a closer mineralogical characterization of the interstellar/circumstellar silicates that have been observed in different types of objects. In this first approach, pyroxene glass samples, the cation content of which reflects mean cosmic proportions of the four most abundant metals, have been prepared and analytically characterized. They are expected to be good candidates for matching the silicate spectra of star-forming regions and young stellar objects (YSOs). For the pyroxene glass, optical constants from 250nm to 500µm have been determined. Particles having sizes within the Rayleigh limit show broad bands peaking at 9.5 and 18.8µm. For the sake of comparison, a crystalline sample of the same composition was also measured. Its narrow bands are positioned at 9.4, 10.5, 11.1, 13.7, 15.6, 18.1, 19.5, 26.5, 29.5, 37.5, and 49µm in agreement with expectations for a chemical composition corresponding to hypersthene. In addition to the vibration bands weak crystal field bands at 1 and 2µm due to Fe2+ have also been detected for the pyroxene glass. If these bands were detectable in interstellar and circumstellar sources they would offer a unique possibility of discriminating the pyroxene-type from the olivine-type silicates. The FIR absorption coefficient measured for the glass sample turned out to be proportional to λ–2. The centroids of the 10 and 19µm bands of the pyroxene glass satisfactorily match those observed in the Orion Trapezium and massive YSOs in molecular clouds. While the mean 10µm band profile derived from observations of six massive YSOs is excellently fitted by profiles calculated with the pyroxene glass data for Rayleigh grains, the Orion Trapezium profile cannot be satisfactorily represented by analogously calculated profiles. Broadening mechanisms that could give an explanation for the great width of the Orion profile are discussed. In contrast to former conclusions, the new pyroxene glasses do not satisfactorily fit silicate emission profiles observed with less massive YSOs (Herbig Ae/Be stars, T Tauri stars). This suggests that the properties of silicate grains present in circumstellar envelopes of massive YSOs could be considerably different from those of the less massive ones. Finally, the new data are compared with former results on pyroxene glasses of different composition which were derived from transmission spectra. The comparison underscores the point that the kind of preparation sensitively influences the resulting optical data.

Abstract Copyright:

Journal keyword(s): circumstellar matter - dust, extinction - infrared: interstellar: lines

Simbad objects: 17

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Number of rows : 17

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 NAME W3 IRS 5 Y*O 02 25 40.54 +62 05 51.4           B1 322 0
2 V* RY Tau TT* 04 21 57.4132838427 +28 26 35.533990877 10.82 10.34 9.30 9.67 8.87 K1IV/Ve 633 1
3 V* AB Aur Ae* 04 55 45.8459978418 +30 33 04.293281305 7.20 7.16 7.05 6.96 6.70 A0Ve 898 2
4 V* SU Aur TT* 04 55 59.3861369488 +30 34 01.499800471   10.33 9.30 9.17   G2IIIne 523 0
5 V* GW Ori TT* 05 29 08.3925564419 +11 52 12.653756566   10.83 10.10 9.52   G5/8Ve 292 2
6 NAME Trapezium Cluster As* 05 35 16.5 -05 23 14           ~ 1432 1
7 NAME Ney-Allen Nebula ISM 05 35 17.1 -05 23 18           ~ 25 0
8 M 42 HII 05 35 17.3 -05 23 28           ~ 3658 0
9 NAME Ori A MoC 05 38 -07.1           ~ 2611 0
10 * bet Pic PM* 05 47 17.0876901 -51 03 59.441135 4.13 4.03 3.86 3.74 3.58 A6V 1597 1
11 EM* LkHA 208 Ae* 06 07 49.5332262163 +18 39 26.493880740   11.78 11.30 11.39   F0Ve 116 1
12 RAFGL 2591 Y*O 20 29 25.2650 +40 11 26.532   18       ~ 562 5
13 SH 2-140 OpC 22 19 07.8 +63 17 07           ~ 628 2
14 IRAS 22176+6303 SFR 22 19 17.978 +63 18 52.92           ~ 587 0
15 [WBN74] NGC 7538 IRS 1 Y*O 23 13 45.318 +61 28 11.69           ~ 359 3
16 [WBN74] NGC 7538 IRS 9 Y*O 23 14 01.63 +61 27 20.2           ~ 336 0
17 NAME NGC 2170 IRS 3 HII ~ ~           ~ 2 0

    Equat.    Gal    SGal    Ecl

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2019.10.23-16:00:40

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