Ceres Results Summarized
Webmaster: Bruce L. Gary, Hereford, AZ; USA

This web page summarizes my observations of Ceres during the 2014 opposition. I present solutions for H & G, for each of the six Framing Camera "color" filter bands. Geometric albedo versus rotation phase is presented for each band.

Recent Update History

    2015.01.13  Added link to calibration description web page: link (in progress) 
    2015.01.11  Added HG plot with rotation variation removed; scatter is slightly better
    2015.01.10  Added new data file (DR20150110), plots of H(WL) and G(WL), & plot pairs showing phase functions and brightness variation with rotation for each FC band.
    2014.09.17  Updated flux table txt-file (DR20140916); added phase function plot.
    2014.06.15  Completed observations and analysis of Ceres FC observations.

text file of Ceres fluxes: DR20150110 

H & G vs. Wavelength

The two plots are based on BLG data only. JYL plot points are based on a data file that had the wrong phase angle listed for May 8 data, so I need to update those points. The H values are in excellent agreement, while the G values are slightly different. This might be caused by the bad May 8 phase angle, so the JYL G points should be updated.

Comparing two solution sets for H vs. wavelength from same data (JYL used data with wrong phase angle for May 8 data (my fault)).

Comparing two solution sets for G vs. wavelength from same data (JYL used
data with wrong phase angle for May 8 data (my fault)).

Note that since both JYL and BLG analyses give the same H values both analyses will also yield the same geometric albedos.

Note also that the pattern of a drop in G value at 915 nm suggests that Band I effects might be responsible for the G feature.

Upper and lower traces show maximum and minimum albedos during a rotation.

Phase Functions and Rotation Variation

The following pairs of plots are based on the data file DR20150110 (downloadable from above link). They are based on chi-square solutions with re-normalized SE for fluxes (given in the data file). Re-normalization factors that yielded reduced chi-square of ~ one were typically 1.7. Outlier data were identified using the chi-square criterion of 11, usually. All brightness variation plots are fitted by a 3-term sinusoid model; some additional structure can be seen by visual inspection of these plots, which may account for part of the SE re-normalization exceeding one.








One more HG fitting is possible: since we have a rotation variation model let's remove it from the plot of HG data! This should reduce the scatter of points and be more representative of the HG relation. The next pair of plots, for 649 nm data, shows that there is a small improvement.

Before and after removal of rotation variation, showing a slight reduction of scatter.


Albedo Spectrum

Geometric albedo spectrum for selected phases from all data to date (Mar 20 to Jun 13), using a phase parameter G shown in the next graph.

Dependence of phase parameter G on wavelength (WL).

Rotation Phase-Folded Light Curves

The following phase-folded albedo light curves are based on a solution for phase effect parameter G that was solved for each band.

Transmission Grating Results

More information about these measurements are at: http://brucegary.net/SA/

Go to "calibration procedure" description
Return to main Dawn FC Calibration web page.

This site opened:  2014.04.10 by Bruce L. Gary (B L G A R Y at u m i c h dot e d u).  BGary web sites