| DATA_SET_DESCRIPTION |
Data Set Overview
=================
Near-infrared spectral observations of 52 asteroids located at ~2.5 AU were
obtained using the NASA IRTF SpeX instrument covering the 0.7 to 2.5 micron
spectral interval. The reflectance spectra were obtained using the
low-medium resolution spectrograph SpeX (RAYNER et al. 2003). SpeX was used
in the low- resolution spectrographic mode (asteroid mode) for two reasons:
1) its ability to obtain spectra with a fairly high signal to noise ratio
(SNR) even for weak signal received from asteroids and 2) its ability to
resolve broad absorption features produced by mafic silicate minerals.
The data in each asteroid spectral file contains three columns: wavelength
(in microns), relative reflectance, and uncertainty in relative reflectance.
The label also includes keywords indicating the target name (asteroid name
and number), target type (asteroid), UT start and end dates of the first and
last asteroid observations used in creating the final reduced, calibrated
average spectrum, number of exposures used in creating the final reduced,
average calibrated spectrum, net integration time, apparent V-mag, phase
angle, geocentric distance, heliocentric distance of the asteroid at the
time of the respective asteroid observations. The solar analog star used
for each asteroid's spectral calibration is listed. The listed airmass is
the airmass at the start of the first observation of the respective
asteroid.
Observations
============
During an observing run the telescope nodded between the A beam and the B
beam(For SpeX, the telescope nod distance is 7.5 arcsec, positioning the
spectrum image at 1/4 and 3/4 distance along the 15 arcsec slit), so images
were taken in spectral image pairs of the target asteroid, local standard
star, solar-analog stars, and calibration flat-field and argon arc-lamp
images. To produce high quality NIR asteroid reflectance spectra, we
empirically derived the atmospheric extinction coefficients at each
wavelength for each night or portion of the night. To model the atmospheric
extinction over Mauna Kea, the slopes/intercepts of the relationship between
the log of the flux (apparent magnitude) vs. airmass were calculated for
each local standard star observation series. The observational procedure to
produce the slopes and intercepts required pairing each asteroid with a
nearby solar type star that experienced the same atmospheric conditions
(temporally and spatially). The local standard star and the asteroid
observations were temporally and spatially related as well and were
interspersed within the same air mass range (typically observed at airmasses
less than 1.5). The IRTF SpeX instrument uses an argon lamp as its
wavelength reference. Each night several argon arc spectra were obtained for
wavelength calibration.
Data Reduction
==============
The data were reduced and analyzed at the University of North Dakota. The
obtained raw spectra were in the form of Flexible Image Transport System
(FITS) images. Two software packages were used to process the data: 1) the
Unix-based Image Reduction and Analysis Facility (IRAF) from the National
Optical Astronomy Observatories (NOAO), and 2) SpecPR a Windows-based
program for reduction and analysis of near-infrared spectra stored in
one-dimensional arrays (CLARK 1980; GAFFEY 2003). The extraction of spectra,
background sky subtraction, summing the image rows encompassing the object
flux, conversion to text files, and determination of wavelength calibration
were done using IRAF.
Spectral processing using SpecPR involved many important phases to achieve a
final, reduced spectrum. Important operations included: 1) calculation of
starpacks from standard stars, 2) channel shifting to account for
instrumental flexure, 3) averaging routines, and 4) data analysis (division
of individual asteroid spectra by the relevant starpack and solar
analog/standard star, polynomial fits, and determination of band
positions/centers/band area ratios). Detailed descriptions of this method
can be found in (FIEBER-BEYER 2010; REDDY 2009; ABELL 2003; HARDERSEN 2003;
GAFFEY 2003; GAFFEY ET AL. 2002). A brief overview of how SpecPR creates a
final, reduced averaged nightly spectrum is as follows: each asteroid
observation was divided at each wavelength by the star flux calculated from
the selected starpack, which not only encompassed the asteroid in airmass,
but also most effectively removed the 1.4 micron and 1.9 micron telluric
water vapor absorption features from the spectrum. Specifically,
atmospheric extinction coefficients (starpacks) are computed from two or
more sets of standard star observations. Extinction coefficients are
determined for all sets of standard star observations (whole night
starpacks), for portions of each night, and for individual sequential sets
of standard star observations.
Starpacks are used to calculate the standard star flux as a function of
wavelength at the same airmass as each asteroid observation. The individual
asteroid flux spectra were divided by the computed standard star flux ratio.
The asteroid/star spectrum which most accurately canceled the atmospheric
water vapor absorptions is selected as the best reduction. Since the stars
and the asteroids were measured with the same instrument, the
wavelength-dependent instrumental response was cancelled out when the
asteroid flux measurements were ratioed to the extinction-corrected standard
star flux measurements. The solar analog star data were reduced by the same
method and used to correct for any non-solar behavior of the local standard
stars producing a reflectance spectrum. Individual best spectra were reduced
by this technique then after inspection for spurious sets - averaged
together to produce a nightly average spectrum for each asteroid. The best
reductions were normalized across a spectral interval to avoid the noise
that may be associated with any individual point in the spectrum. The
normalization value was the average of the values in SpeX channels 380 to
410. (1.5 to 1.7 microns). This interval was chosen because it is
essentially unaffected by either the 1.4 or 1.9 micron atmospheric water
vapor absorptions, or by the mafic silicate absorption feature centered in
the 1.8 to 2.5 micron interval, common in asteroid spectra.
A total of 52 asteroids were included in the survey. The data have been
published in FIEBER-BEYER 2010; FIEBER-BEYER AND GAFFEY 2011; FIEBER-BEYER
ET AL. 2011a; FIEBER-BEYER ET AL. 2011b; FIEBER-BEYER ET AL. 2012;
FIEBER-BEYER AND GAFFEY 2014; FIEBER-BEYER AND GAFFEY 2015. This is an
ongoing survey and data will be added to this archive yearly as they are
published.
Parameter table and Thumbnail Plots
===================================
A table listing all the spectra with their observational parameters, called
spectraparameters.tab, is provided in the data directory.
Thumbnail plots for browsing the spectra are available in the document
directory. The file thumbnailcumulative.pdf is cumulative with the asteroid
spectra arranged in ascending numerical order.
Modification History
====================
New to V3.0 are an additional 13 unpublished asteroid spectra obtained
spanning the years 2012 through 2014. The total number of asteroids has been
amended in the data set description to reflect a total of 52. Two
publications, one for 2014 and one for 2015, have been added within the data
set description to reflect where the data can be found in literature for the
asteroids published during these years. The thumbnail.pdf file contains 52
asteroid spectra from the years 2000 through 2014.
References
==========
Abell, P.A., Near-IR reflectance spectroscopy of main belt and near-Earth
objects: A study of their composition, meteorite affinities and source
regions. Ph.D. dissertation. Rensselaer Polytechnic Institute, Troy,NY, USA,
2003.
Clark, R.N., A large-scale interactive one-dimensional array processing
system. Publ. Astron. Soc. Pac. 92, 221-224, 1980.
Fieber-Beyer, S.K., Mineralogical characterization of asteroids in/near the
3:1 Kirkwood Gap, Ph.D. Dissertation, University of North Dakota, Grand
Forks, 203 pp, 2010.
Fieber-Beyer, S.K., and M.J. Gaffey, Near-infrared Spectroscopy of 3:1
Kirkwood Gap Asteroids (3760) Poutanen and (974) Lioba. Icarus, 214,
645-651, doi:10.1016/j.icarus.2011.06.014, 2011.
Fieber-Beyer, S.K., M.J. Gaffey, and P.A. Abell, Mineralogical
characterization of Near Earth Asteroid (1036) Ganymed, Icarus, 212,
149-157, doi:10.1016/j.icarus.2010.12.013, 2011.
Fieber-Beyer, S.K., M.J. Gaffey, M.S. Kelley, V. Reddy, C.M. Reynolds, and
T. Hicks, The Maria Asteroid Family: Genetic Relationship and a Plausible
Source of Mesosiderites near the 3:1 Kirkwood Gap. Icarus, 213,
doi:10.1016/j.icarus.2011.03.009, 524-537, 2011c.
Fieber-Beyer, S.K., M.J. Gaffey, P.S. Hardersen, and V. Reddy,Near-infrared
spectroscopy of 3:1 Kirkwood Gap asteroids: Mineralogical diversity and
plausible meteorite parent bodies, Icarus 221, 593-602,
dx.doi:10.1016/j.icarus.2012.07.029, 2012.
Fieber-Beyer, S.K., and M.J. Gaffey, Near-Infrared Spectroscopy of 3:1
Kirkwood Gap Asteroids: A Battalion of Basalts, 44th Lunar and Planetary
Science Conference, LPI Contribution No. 1719, p.1352, 2013.
Fieber-Beyer, S.K., and M. J. Gaffey, M.J., Near-infrared Spectroscopy of
3:1 Kirkwood Gap asteroids II: Probable and plausible parent bodies;
primitive and differentiated, Icarus 229, 99-108,
doi:10.1016/j.icarus.2013.11.001, 2014.
Fieber-Beyer, S.K., and M.J. Gaffey, Near-infrared spectroscopy of 3:1
Kirkwood Gap asteroids III. Icarus, 257, 113-125,
doi:10.1016/j.icarus.2015.04.034, 2015.
Gaffey, M.J., Observational and Data Reduction Techniques to Optimize
Mineralogical Characterizations of Asteroid Surface Materials. Lunar.
Planet. Sci. XXXIV, [abstract 1602], 2003.
Gaffey, M.J., E.A. Cloutis, M.S. Kelley and K.L. Reed, Mineralogy of
asteroids. In Asteroids III (W. F. Bottke, A. Cellino, P. Paolicchi and R.
P. Binzel, Eds.), Univ. of Arizona Press, pp. 183-204, 2002.
Hardersen, P.S., Near-IR Reflectance Spectroscopy of Asteroids and Study the
Thermal History of the Main Asteroid Belt. Ph.D. Dissertation. Rensselaer
Polytechnic Institute, Troy, New York, USA, 2003.
Rayner, J. T., D. W. Toomey, P. M. Onaka, A. J. Denault, W. E. Stahlberger,
and 3 others, SpeX: A Medium-Resolution 0.8 - 5.5 micron Spectrograph and
Imager for the NASA Infrared Telescope Facility, PASP 115, 362, 2003.
Reddy, V., Mineralogical Survey Of Near-Earth Asteroid Population:
Implications For Impact Hazard Assessment And Sustainability Of Life On
Earth, Ph.D. dissertation. University of North Dakota, Grand Forks, 2009.
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