Description of the REDDY NEAR-EARTH AND MARS-CROSSING      
        ASTEROIDS bundle V1.0
=====================================================

Bundle Generation Date: 2017-07-10
Peer Review: 2017b Asteroid Review, Wed May 31 00:00:00 MST 2017              
Discipline node: Small Bodies Node


Content description for the REDDY NEAR-EARTH AND MARS-CROSSING      
        ASTEROIDS bundle
==============================================================

    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. The final files have
    different numbers of rows due to the quality of the data.                 
                                                                              
    NOTE: Definitions for keywords which may appear in the labels:   EXPOSURES
    is the number of individual observations which have been combined to      
    produce the final spectrum. V_APPARENT_MAGNITUDE is the apparent V        
    magnitude of the target. FILTER_NAME (always V) is the filter of the      
    V_APPARENT_MAGNITUDE. SOLAR_ANALOG_STAR is the name of the solar analog   
    star used to reduce the observation. SOLAR_PHASE_ANGLE, HELIO_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.


Known issues or problems with the data
======================================

    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.