Data Set Overview
  =================
    This data set includes reduced composite visible and near-infrared spectra
    of 30 M-type asteroids that have been published in Fornasier et al.
    (2010).  The spectra were obtained over the years 2004-2008 at three
    different telescopes, and used to produce a single composite reduced
    visible-near-IR spectrum for each asteroid.  For one asteroid, 125
    Liberatrix, three composite spectra were produced for different times in
    the same night.  The remaining 29 asteroids are represented by a single
    composite spectrum each.
 
    The 75 individual spectra from the NTT/EMMI, NTT/SOFI, TNG/NICS, and
    TNG/Dolores instruments, which were combined to make the composite
    spectra, are also included here.  The composite spectra are in the
    subdirectory 'compspectra' and the individual spectra are in the
    subdirectory 'indivspectra' under the data directory.  The individual
    spectra from the SPeX instrument at IRTF are not included in this data set
    as they are available in another PDS data set, the IRTF NEAR-IR
    Spectroscopy of Asteroids, EAR-A-I0046-4-IRTFSPEC-V2.0.
 
    At the TNG telescope, the visible spectra were obtained with Dolores
    (Device Optimized for Low Resolution) equipped with the low resolution red
    grism (LR-R) covering the 0.51-0.95 micron range with a spectral
    dispersion of 2.9 A/pixel.  Most of the objects were also observed with
    the low resolution blue grism (LR-B, dispersion of 1.7 A/pixel, 0.4-0.7
    micron range).  The red and blue spectra in the visible range were
    separately reduced and then combined to obtain spectral coverage from 0.40
    to 0.95 microns.  The near-infrared spectra at the TNG were obtained with
    the NICS (Near Infrared Camera and Spectrometer) equipped with an Amici
    prism disperser.  The equipment covers a spectral range of 0.85-2.40
    microns with a spectral resolution of about 35 (Baffa et al. 2001).  Both
    the visible and near infrared observations were made with a 1.5 arcsecond
    slit width, oriented along the parallactic angle to minimize the effect of
    atmospheric differential refraction.
 
    At the NTT telescope, visible spectra were obtained with the EMMI
    instrument in RILD mode, using Grism #1 to cover the wavelength range
    4100-9600 Angstroms with a dispersion of 3.1 A/pixel at the first order.
    (An order-separation filter was not used for these observations, because
    tests with and without the order-separation filter showed that the
    second-order contribution was negligible.) The near-infrared spectra taken
    at the NTT telescope were taken with the instrument SOFI (Son OF Isaac) in
    the low resolution mode (Moorewood et al. 1998).  The blue grism, with
    0.95-1.64 micron range and dispersion of 6.96 A/pixel, and the red grism
    with 1.53-2.52 micron range and dispersion of 10.22 A/pixel, were used
    each with an order sorting filter.  The blue and red grisms with their
    filters are designated as GBF and GRF respectively.  The NTT observations
    were made with a 2 arsecond slit, always oriented along the parallactic
    angle.
 
    At the IRTF, the SpeX instrument was used, with wavelength range of 0.82
    to 2.49 microns (Rayner et al. 2004).  Spectra were recorded with a 0.8 x
    15 arsecond slit oriented in the north-south direction.  A dichroic lens
    reducing the signal below 0.8 microns was used for all observations.
    Objects were consistently observed near the meridian to minimize the
    airmass, but total integration time varied from 6 to 30 minutes depending
    on the strength of the signal relative to sky lines.
 
    The composite spectra are all normalized to 1.0 at a wavelength of 0.55
    microns.  The individual spectra are normalized as follows for the
    different instruments;
    NTT/SOFI gb: 1.25 micron
    NTT/SOFI gr: 2.15 micron
    NTT/EMMI: 0.55 micron
    TNG/Dolores (lrr, lrb and mrb): 0.60 micron
    TNG/NICS: 1.25 micron
 
    The thirty-two composite spectra included in this data set are plotted in
    Figures 1 through 5 in Fornasier et al (2010).  The spectra of 132 Aertha,
    125 Liberatrix, 201 Penelope, 382 Dodona, 418 Alemannia, and 558 Carmen
    cover the visible range only, while the remaining asteroids' spectra
    combine data to cover the visible and near infrared.  The plots from the
    paper are included in a pdf file (spectraplots.pdf) in the document
    directory to provide easy browsing of the spectra.
 
    Observational circumstances for each observation are given in the file
    obscirc.tab, and reproduce the information in Table 1 of the paper.  Each
    composite spectrum combines all the observations shown for the asteroid in
    obscirc.tab, except for 785 Zwetana, which used only the TNG observations,
    omitting the NTT visible observation. (Two errors in Table 1 have been
    corrected in obscirc.tab:  The SOFI observations of 369 Aeria and 498
    Tokio are shown in the paper as being both GBF observations, whereas in
    fact they were one each of GBF and GRF.)
 
    For details of the data acquisition and reduction, see Fornasier et al.
    (2010).
 
    References
    ==========
 
    Baffa, C. and 16 colleagues, NICS: The TNG near-infrared camera
    spectrometer, Astronomy and Astrophysics, 378, 722-728, 2001.
 
    Fornasier, S., B.E. Clark, E. Dotto, A. Migliorini, M. Ockert-Bell, and
    M.A. Barucci, Spectroscopic survey of M-type asteroids, Icarus 210,
    655-673, doi:10.1016/j.icarus.2010.07.001, 2010.
 
    Moorewood, A., J.-G. Cuby, and C. Lidman, SOFI sees first light at the
    NNT, Messenger 91, 9-13, 1998.
 
    Rayner, J.T., P. M. Onaka, M. C. Cushing and W. D. Vacca, Four Years of
    Good SpeX, in Ground-based Instrumentation for Astronomy, A. F. M.
    Moorwood and M. Iye, Eds., Proceedings of the SPIE, vol. 5492, pp.
    1498-1509, 2004.

Confidence Level Overview
  =========================
    Fringing associated with the Dolores chip:
 
    The Dolores chip, like most LORAL CCDs, is affected by moderate to strong
    fringing at red wavelengths.  Despite care in the the reduction process,
    some of the asteroid spectra taken with Dolores show residual fringing
    that impedes identification of absorption bands in the 0.9 micron region.
 
    Calculation of the uncertainties:
 
    Uncertainties were estimated from the signal to noise ratio of the
    observed asteroid (including the CCD quantum efficiency) plus the errors
    associate to solar analog stars used to get the relative reflectivity.
    Several solar analogs stars were observed each night and those observed at
    similar conditions were ratioed with each other. The deviation enabled
    estimation of the errors associated with the use of a given solar
    analogue.  The errors are between 1.3-1.5 percent below 0.45 micron,
    between 1-1.3 percent in the 0.45-0.90 micron region, and between 1.5-3.0
    percent in the infrared region, with higher uncertainties associated with
    the low transmission atmospheric windows.
 
    For additional information about the confidence level of these data, see
    Fornasier et al. (2010).