Data Set Information
DATA_SET_NAME IRTF NEAR-IR SPECTROSCOPY OF ASTEROIDS V1.0
DATA_SET_ID EAR-A-I0046-4-IRTFSPEC-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : All observations were obtained with SpeX, the low- to medium-resolution near-IR spectrograph and imager at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. This instrument uses prism cross-dispersers and gratings to achieve resolving powers up to R~2500 across the wavelength region from 0.8 to 5.5 microns. An infrared slit-viewer allows for object acquisition and guiding. The SpeX spectrograph employs a 1024x1024 Aladdin 3 InSb array and the slit-viewing imager uses a 512x512 Aladdin 2 InSb array. [RAYNERETAL2004]. Of specific importance to asteroid studies, SpeX provides a low-resolution (R~100 when using the nominal 0.8 arcsecond slit) 'prism' mode covering the wavelength interval 0.8-2.5 microns. In prism mode, asteroids as faint as Vmag~16.5 are routinely observed, with even fainter magnitude limits being reached when good sky conditions permit. Asteroid observations are normally obtained by taking nodded spectral image pairs of the target asteroid, solar-analog stars, and (possibly) telluric standard stars, followed by calibration flat-field and arc-lamp images. The image pairs are taken by shifting the asteroid (or star) position on the slit (nodding the telescope position) by a fixed amount. In this 'A-B' image pair, the background sky spectrum is being recorded simultaneously with the target, allowing the sky to be subtracted in both the A-B and B-A pairs. After flat fielding the individual SpeX images and carrying out the pairwise sky subtraction, multiple images of the target or standard star can be stacked, and a 1-dimensional spectrum extracted, wavelength calibrated and re-binned as appropriate. Calibration of each asteroid spectrum in dimensionless units of relative reflectance is achieved by dividing the asteroid spectrum by that of a solar analog star. Because this data set contains results derived by several different research groups, there are some variations in observing strategies and reduction procedures. This is particularly the case in the final stages of spectral calibration where effects of the Earth's atmosphere (telluric absorptions) are fitted and removed. Different techniques for telluric correction include: 1) the modeling of atmospheric absorption bands using ATRAN [LORD1992] which is based on the HITRAN database of molecular absorption lines (for convenience, a .pdf copy of Lord 1992, NASA Technical Memorandum 103957 is included in the document directory), 2) using the method included in SpeXTool [VACCAETAL2003] where observations of an A0 (telluric standard) star are convolved with a high-resolution model of Vega to construct a telluric correction spectrum, and 3) the use of SpecPR, where wavelength-dependent extinction coefficients are derived from nightly standard star observations. While the application of any of these telluric calibration methods leads to very similar results, users of this data set are encouraged to refer to the original papers for specific details about the data reduction and calibration procedures used. Papers for which data are archived are: Binzel et al. (2001) M&PS 36, 1167-1172 [BINZELETAL2001] Clark et al. (2004) AJ 128, 3070-3081 [CLARKETAL2004] Rivkin et al. (2005) Icarus 175, 175-180 [RIVKINETAL2005] Sunshine et al. (2004) M&PS 39, 1343-1357 [SUNSHINEETAL2004] Sunshine et al. (2007) M&PS 42, 155-170 [SUNSHINEETAL2007B] Sunshine et al. (2008) Science 320, 514-517 [SUNSHINEETAL2008] Data File Description : Data file names have the format: AAAA_YYMMDDTHHMMSS.tab, where AAAA is the permanent number or provisional designation of the asteroid, YYMMDD is the UT start date, and HHMMSS the UT start time of the observation. This naming convention is particularly useful when a study involved rotationally resolved spectra, where multiple spectral files are being archived for a single asteroid. To determine what asteroid spectra have been archived, and to help navigate to specific files, a science index (science_index.tab) is included in the upper level of the data directory. This file lists all spectra in order of asteroid designation, and includes the data path, UT start and end times of the first and last asteroid observations used in creating the spectrum, the apparent magnitude, phase angle and heliocentric distance of the asteroid at the time(s) of the observations(s), and a listing of the solar analog stars used in calibration. Each spectrum file contains 3 columns: wavelength (in microns), relative reflectance, and error in relative reflectance. For those spectra reduced using IRAF, the output spectrum is usually re-binned to a consistent dispersion, which allows different spectra to be easily compared and combined. During the various reduction and calibration steps, if a particular spectral data point is identified as discrepant, that point is flagged and removed from the final spectrum file. All spectra have been scaled by fitting a polynomial over the region centered on the J-band (1.215 microns), and then normalizing the fitted value at 1.215 microns to 1.00. Thumbnail plots of all spectra archived in this data set are provided (pdf files) in the document directory. These plots are organized by publication (one file per publication), using the same naming scheme as the data directory structure.
DATA_SET_RELEASE_DATE 2009-06-03T00:00:00.000Z
START_TIME 2000-09-04T02:46:35.000Z
STOP_TIME 2007-08-01T12:54:11.000Z
MISSION_NAME SUPPORT ARCHIVES
MISSION_START_DATE 2004-03-22T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME 1014 SEMPHYRA
1020 ARCADIA
1039 SONNEBERGA
1098 HAKONE
110 LYDIA
1103 SEQUOIA
112 IPHIGENIA
1228 SCABIOSA
1251 HEDERA
1275 CIMBRIA
1317 SILVRETTA
1580 BETULIA
16 PSYCHE
1662 HOFFMANN
17 THETIS
1858 LOBACHEVSKIJ
2042 SITARSKI
2048 DWORNIK
209 DIDO
214 ASCHERA
216 KLEOPATRA
217 EUDORA
234 BARBARA
2401 AEHLITA
246 ASPORINA
2501 LOHJA
2504 GAVIOLA
25143 ITOKAWA
260 HUBERTA
283 EMMA
284 AMALIA
289 NENETTA
3103 EGER
317 ROXANE
322 PHAEO
3363 BOWEN
337 DEVOSA
3395 JITKA
354 ELEONORA
3819 ROBINSON
387 AQUITANIA
409 ASPASIA
4188 KITEZH
434 HUNGARIA
44 NYSA
4426 ROERICH
446 AETERNITAS
46 HESTIA
50 VIRGINIA
517 EDITH
53 KALYPSO
536 MERAPI
5840 RAYBROWN
599 LUISA
64 ANGELINA
676 MELITTA
709 FRINGILLA
71 NIOBE
739 MANDEVILLE
768 STRUVEANA
785 ZWETANA
789 LENA
808 MERXIA
844 LEONTINA
847 AGNIA
863 BENKOELA
87 SYLVIA
899 JOKASTE
909 ULLA
976 BENJAMINA
980 ANACOSTIA
984 GRETIA
ASTEROID
ASTEROID 139359
ASTEROID 26760
ASTEROID 29075
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID OBS376T3
INSTRUMENT_NAME SPEX
INSTRUMENT_ID I0046
INSTRUMENT_TYPE SPECTROMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS SUPERSEDED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The uncertainty for each spectral channel has been derived using Poisson statistics, and was based on the signal from both the object and sky, as well as the detector characteristics. The errors listed in each spectral file do not include systematic uncertainties. Examples of such systematics include uncertainties in the telluric absorption correction model, and uncertainties in the telescopic observations that can affect the average slope as measured over the length of the spectrum. By measuring several calibration stars over the course of a night and averaging the results from each asteroid / star combination, the level of systematic errors in the final asteroid spectra have been minimized.
CITATION_DESCRIPTION Bus, S. J., Ed., IRTF Near-IR Spectroscopy of Asteroids V1.0. EAR-A-I0046-4-IRTFSPEC-V1.0. NASA Planetary Data System, 2009.
ABSTRACT_TEXT This data set contains low-resolution, near-infrared (0.8 - 2.5 micron) spectra of asteroids obtained with SpeX at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. Since it was commissioned in June 2000, SpeX has been the premier instrument for producing high quality near-IR spectra of asteroids. These spectra have been used for both taxonomic studies of asteroids, and for more detailed mineralogical and compositional investigations. This data set archives the reduced, calibrated spectra that have been published in the peer-reviewed literature, and will be regularly updated as more data become publicly available.
PRODUCER_FULL_NAME SCHELTE BUS
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