J/ApJ/882/L22 Subaru obs. of Vesta in MIR spectral range (Palomba+, 2019)
Detection of crystalline and fine-grained calcic plagioclases on Vesta.
Palomba E., D'Aversa E., Sato T.M., Longobardo A., Dirri F., Aoki S.,
Orton G., Sindoni G., Oliva F., Carrozzo G., Kasaba Y.
<Astrophys. J., 882, L22 (2019)>
=2019ApJ...882L..22P 2019ApJ...882L..22P
ADC_Keywords: Minor planets; Spectra, infrared
Keywords: Infrared astronomy ; Spectroscopy ; Main belt asteroids ; Asteroids ;
Minor planets ; Meteorites ; Achondrites ; Infrared telescopes
Abstract:
Plagioclase feldspars are among the most prevalent minerals in the
solar system, and are present in many chondritic and achondritic
meteorite families. Nevertheless, spectral features of plagioclases
have never been unambiguously and directly observed in remote
observations of asteroids. We report here the detection of an
absorption band at 12.2µm on Vesta spectra provided by ground-based
spectral observations at the Subaru Telescope. This signature
represents the first direct evidence of a widespread presence of
crystalline Ca-rich plagioclase on Vesta and reveals that its regolith
is comminuted to a very fine grain size, smaller than a few tens of
microns, indicating that the mechanical brecciation process has been
very effective. The crystalline nature of plagioclase strongly
suggests that impacts alone cannot be the sole mechanism for regolith
formation on Vesta and a milder process, such as thermal fatigue,
should be invoked as an important and concomitant process Thermal
fatigue should be considered a very effective process in regolith
production and rejuvenation not only for near-Earth asteroids but even
for large asteroids located in the main belt.
Description:
We performed new observations of Vesta in the mid-IR spectral range
(8-13um) with the COMICS instrument at the 8.2m Subaru Telescope at
Mauna Kea, Hawaii. Observations were conducted in two campaigns in
2016 and 2017, obtaining a total of four full-disk spectra acquired
during four different good-seeing nights (Figure 2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
2016_23.dat 21 236 *Vesta spectral emissivity from 2016-23 data
with retrieved scalar parameters:
(Tss,glob.emiss.,glob.rough.,glob.fact.)=
(234.2,0.892,0.107,1.54)
2016_24.dat 21 234 *Vesta spectral emissivity from 2016-24 data
with retrieved scalar parameters:
(Tss,glob.emiss.,glob.rough.,glob.fact.)=
(236.5,0.875,0.107,1.53)
2017_12.dat 21 238 *Vesta spectral emissivity from 2017-12 data
with retrieved scalar parameters:
(Tss,glob.emiss.,glob.rough.,glob.fact.)=
(243.4,0.933,0.098,1.29)
2017_13.dat 21 238 *Vesta spectral emissivity from 2017-13 data
with retrieved scalar parameters:
(Tss,glob.emiss.,glob.rough.,glob.fact.)=
(244.4,0.922,0.102,1.28)
nwa7854.dat 32 1405 Absolute emissivity of eucrite NWA7854 with
grain size 25-63um (spec 2474)
nwa2698.dat 32 1405 Absolute emissivity of howardite NWA2698 with
grain size 0-25um (spec 2476)
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Note on 2016_23.dat: Retrieved by Bayesian Gauss-Newton inversion in chi2
statistics on Mon Nov 6 09:39:09 2017 with a priori:
(238.000,0.940,0.100,1.600).
Note on 2016_24.dat: Retrieved by Bayesian Gauss-Newton inversion in chi2
statistics on Mon Nov 6 09:39:33 2017 with a priori:
(238.000,0.940,0.100,1.600)
Note on 2017_12.dat: Retrieved by Bayesian Gauss-Newton inversion in chi2
statistics on Mon Nov 6 09:38:09 2017 with a priori:
(235.000,0.940,0.100,1.300)
Note on 2017_13.dat: Retrieved by Bayesian Gauss-Newton inversion in chi2
statistics on Mon Nov 6 9:23:51 2017 with a priori:
(235.000,0.94 ,0.1 ,1.300)
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See also:
J/MNRAS/456/248 : (4) Vesta adopted polarimetric light curves (Cellino+, 2016)
J/A+A/623/A6 : VLT/SPHERE/ZIMPOL images of Vesta (Fetick+, 2019)
J/AJ/159/264 : Obs. of 10 Vesta asteroids with WISE/NEOWISE (Jiang+, 2020)
Byte-by-byte Description of file: 201*.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 um lambda [7.67/13.1] Wavelength
9- 14 F6.4 --- em [0.81/0.96]? Emissivity
16- 21 F6.4 --- e_em [0.007/0.08]? Uncertainty in em
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Byte-by-byte Description of file: nwa*.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 cm-1 Wavenum [624.85/3332.56] Wavenumber
12- 21 F10.7 um lambda [3.00069/16.00372] Wavelength
23- 32 F10.8 --- em [0.874/0.992] Emissivity
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Feb-2021