Data Set Overview  :  These tables provide maps of net counting rates of Fe gamma rays at 7.6  MeV measured by the BGO detector of Dawn's Gamma Ray and Neutron Detector acquired at the low altitude mapping orbit. The data are binned on 0.5  degree equal area pixels. The counting rates were normalized for  variations of live time, solid angle of Vesta, and galactic cosmic ray  intensity. They were also corrected for variations of neutron number  density determined by thermal and epithermal neutrons observed by  GRaND. The table contains the original Fe counting rates reported by  YAMASHITAETAL2013.   The data were acquired during the low altitude mapping orbit  (approximately 210 km from the surface) phase (LAMO). Only those when  the spacecraft is nadir pointing (less than 5 degrees between the +Z axis of the spacecraft and the center of Vesta) are used to map Fe counting  rates. At this altitude, the spatial resolution of the gamma ray  spectrometer was about 300 km (PRETTYMANETAL2011).   Parameters  :  Each row of the table provides composition information for a  single pixel. The format for each row is '(i10,6(f7.1),(1x,e13.3).  East longitude convention is used (-180 to 180 degrees) with Claudia  (double prime) coordinate systems. The column description follows:   COLUMN NAME FORMAT DESCRIPTION UNITS 0 PIXEL_INDEX (I10) N/A  1 MIN_LAT (F7.1) Pixel latitude lower boundary deg 2 MAX_LAT (F7.1) Pixel latitude upper boundary deg 3 DELTA_LAT (F7.1) Width of pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of pixel in longitude deg 7 FE_COUNTING_RATE (E13.3) Fe counting rate uncorrected count/s for neutron number density   As discussed in YAMASHITAETAL2013, a preliminary scaling factor was  derived by scaling the average corrected counting rate to the mean Fe  content of 13.8 wt% of howardites such that   Fe Abundance (wt.%) : Fe counting rate [count/s] x 189.2   which users can apply. However caution is recommended for its  applicability.

Confidence Level Overview  :   The data set is a high order data product derived from gamma ray and  neutron counting data acquired by GRaND in LAMO as described by  PRETTYMANETAL2013 and YAMASHITAETAL2013.   Review  :   This data set is in review by NASA Planetary Data System.   Data Coverage and Quality  :   The data set contains a global map of the counting rate of gamma rays  emitted from Fe within Vesta's regolith. There are no gaps in coverage.  The depth sampled by gamma rays from which Fe gamma rays are provided is  a few decimeters (for example, see PRETTYMANETAL2011).   Coordinate System:   The data were analyzed and mapped in the Claudia coordinate system, in which the prime meridian passes close to a small crater named Claudia. In this  coordinate system, the prominent Marcia crater is located at 190E longitude. Maps published by the Dawn Geochemistry Working Group in the literature are  presented in the Claudia coordinate system [PRETTYANETAL2012,  LAWRENCEETAL2013, PEPLOWSKIETAL2013, PRETTYMANETAL2013, YAMASHITAETAL2013].   Consistent with IAU guidelines, maps of GRaND data in this archive are  presented in the 'Claudia Double Prime' (CDP) coordinate system. CDP  has the same pole position as Claudia such that latitudes are the same;  however, the prime meridian of CDP is shifted by 210 degrees from that of  Claudia, passing 20 degrees to the east of Marcia. The coordinate systems  are describes in detail by J.-Y. Li in VESTA_COORDINATES_120918.pdf, which  accompanies this archive in the DOCUMENTS directory.   All of the maps use rectangular pixels with east longitudes within  -180 to 180 degrees in the Claudia system. For archiving, the longitudes  were converted to CDP as follows:   longitude_CDP : longitude_Claudia - 210 degrees. If longitude_CDP is  less than -180 degrees, add 360 degrees.   For example, if longitude_Claudia : -170 (the location of Marcia crater),  then longitude_CDP : -20.   Similarly, longitudes in the CDP system can be converted to Claudia as  follows:   longitude_Claudia : longitude_CDP + 210. If longitude_Claudia is greater  than 180 degrees, subtract 360 degrees.   Thus, the pixel longitude boundaries, which were tabulated in this archive  in the CDP system, can easily be converted back to the Claudia system, in  which the data were analyzed, by the user when desired. To further  facilitate comparison between the PDS archived maps and those published in  the literature, a 'side-by-side' display of each map in the Claudia and  CDP systems is included in the accompanying browse file (see BROWSE  directory).   For further clarification, we note that map pixels in the Claudia system  always have MIN_LON < MAX_LON; however, when transformed into the  CDP system, not all pixels will meet this condition. For example, in  some quasi-equal area maps, the polar pixels have MIN_LON : -180 and  MAX_LON : 180 in the Claudia coordinate system. These pixels span  360 degrees in longitude. When transformed to the CDP coordinate system,  these pixels have MIN_LON : -30 and MAX_LON : -30, such that MIN_LON :  MAX_LON. In addition, for some maps, a portion of the pixels will have  MIN_LON > MAX_LON when transformed into the CDP system. To avoid confusion, we included the width of each pixel in longitude as DELTA_LON. For example, for the aforementioned polar pixels, DELTA_LON : 360.   Limitations  :   Assumptions and limitations underlying the analysis of Fe gamma rays  within Vesta's regolith are described by YAMASHITAETAL2013. We note that  the tabulated values give the range of counting rates of Fe gamma rays  that are corrected for variations of number density of subsurface neutrons  that excite Fe nuclei and induce Fe gamma-ray emissions. Thus, the  corrected counting rate is the direct measure of the Fe abundance on the  surface of Vesta.   Because the Fe uncorrected counting rate data and neutron number density  data were smoothed prior to calculating the Fe corrected counting rate  (YAMASHITAETAL2013), the mapped data have high precision. Thus,  statistical uncertainties are not reported.