Data Set Overview
  =================
    All spectral observations were obtained using the SpeX instrument
    on the NASA IRTF in low-resolution prism mode. Observations were
    made remotely and in classical mode on site. SpeX in low resolution
    mode has resolving powers of R~100 across the wavelength region
    from ~0.7 to 2.5 microns.  An infrared guider is available to
    guide on calibration stars (sidereal rates) and asteroids
    (non-sidereal rates). The main spectrograph uses a 1024x1024
    Aladdin 3 InSb array and the guider uses a 512x512 Aladdin 2 InSb
    array [RAYNERETAL2004]. Low-resolution spectrographs like SpeX are
    ideal for resolving broad absorption features produced by abundant
    mafic minerals like olivine and pyroxene that make up many asteroid
    surface assemblages. The low resolution prism mode also helps in
    obtaining spectra with higher signal-to-noise-ratios (SNR) and
    asteroids as faint as Vmag~17.5 are routinely observed.

    Spectral observations for this data set were made by taking nodded
    spectral image pairs of the asteroid, local standard star (for
    telluric correction), solar-analog stars, and calibration
    flat-field and argon arc-lamp images. The placement of these
    stellar observations, temporally and spatially on the sky, in
    relation to the asteroid is important for producing good quality
    spectra. If the atmosphere over Mauna Kea is stable throughout the
    observing run (photometric), then the log of the flux (apparent
    magnitude) of the object will decrease linearly with increasing
    airmass. Hence, all objects are typically observed at airmasses
    less than 1.5, which corresponds to a zenith angle of less than 50
    degrees. However, if the atmosphere is unstable over Mauna Kea,
    whether due to an orographic cap cloud or rapid variability of
    water vapor content, it often produces a non-linear magnitude-
    airmass relationship.

    Local (or extinction) standard stars close to the asteroid are
    observed to correct for the terrestrial atmospheric water vapor
    features. Generally, the greater the distance between the local
    standard star and the asteroid, the poorer the monitoring of the
    sky conditions for the asteroid. During a typical observing run, a
    local standard star with spectral properties similar to our Sun
    (i.e., G-type, main sequence stars) is paired with an asteroid and
    is observed over a wide airmass range that bracket the airmass
    range of the asteroid observations. Solar analog stars are observed
    to remove the solar continuum from the asteroid spectrum. At least
    two solar analog stars should be observed each night to eliminate
    the possibility of systematic errors that may be present in a
    single solar analog star spectrum.

    SpeX prism data was reduced using the IDL-based Spextool provided
    by the NASA IRTF [CUSHINGETAL2004]. The steps followed in the
    reduction process include: (1) sky background removal by subtracting the
    image pairs, (2) flat-fielding, (3) cosmic ray and
    spurious hit removals, (4) wavelength calibration, (5) division of
    asteroid spectra by the spectrum of the solar analog star, and (6)
    co-adding of individual spectra.

    NOTE: Definitions for keywords which may appear in the labels:
    IMAGE_COUNT is the number of individual observations which have
    been combined to produce the final spectrum. APPARENT_MAGNITUDE is
    the apparent V magnitude of the target. FILTER_NAME (always V) is
    the filter of the APPARENT_MAGNITUDE. STAR_NAME is the name of the
    solar analog star used to reduce the observation. PHASE_ANGLE,
    SOLAR_DISTANCE, and AIRMASS all refer to the target.

    Plots with all the NIR spectra are provided in a pdf file located in the
    document directory. Numbers in the plots refer to the asteroid number.
    Error bars are not included in the plots.

Confidence Level Overview
  =========================
    Uncertainties in spectral parameters for near-IR data are crucial for
    detecting and quantifying surface composition. The average wavelength
    resolution of the Spextool data is ~ 0.0035 microns. This is just due to
    spectral resolution based on the wavelength calibration. When spectra were
    combined the statistic used was the robust weighted mean. For this,
    Spextool makes use of a sigma clipping algorithm to identify outliers. The
    value at each pixel is then the weighted average of the good pixels and
    the uncertainty is given by the propagated variance. Uncertainties in the
    data arise primarily due to low SNR of the final average spectrum,
    incomplete correction of telluric absorption features, and variable
    sky/weather conditions.

    Data corresponding to asteroids (45) Eugenia, (213) Lilaea, (256)
    Walpurga, (308) Polyxo, (389) Industria, (442) Eichsfeldia, (1145)
    Robelmonte, (1284) Latvia, (1329) Eliane have error values much larger
    than might be expected given the scatter in the spectrum data points. The
    cause for these large uncertainties was not identified, but could be
    related to the small number of individual spectra that were combined to
    obtain the final spectrum. For these spectra the point-to-point scatter of
    the data provides a better estimate of the uncertainty associated with
    these measurements.