GALEX PIII
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[edit] Foreground Contamination in the GALEX Data.
[edit] Introduction
The aim of this work is to correct the GALEX data for airglow and zodiacal light effects to derive the true diffuse emission. Even though the airglow is a "noise" for us in the study of diffuse astrophysical signal from the various part of the sky but is a very useful signal for those who are working in aeronomy. However its accurate estimation is equally important for both the groups in different aspects. It is our hope that the high quality GALEX data have the potential for the high-quality airglow measurements.
[edit] Local Time at Minimum TEC Value Vs The Exposure Time of The Observation
From the following figures, it is clear that the count rate of an observation is minimum in and around the local midnight. The spread of the local time in the left hand side of the figures is due to the short exposure of the observation which is not covering the local midnight of the day.
[edit] Airglow
Each of the GALEX observation consists of foreground radiation and background astrophysical radiation. The foreground radiation is mainly due to the geocoronal emissions from oxygen atoms (airglow) in the exosphere of the Earth and the sunlight scattered from inter planetary dust (zodiacal light).
In the FUV band, the Airglow contribution in the foreground radiation is more significant than the zodiacal light contribution as Sun is a cool star. However in the NUV band, both airglow and zodiacal light contribution are equally important in the foreground radiation.
The total count rate of different visits taken at different times of a single target are plotted against the local time from midnight in the following figure. From the figure, it is clear that airglow in any of the GALEX observation consists of a constant term (AG_c) - part of the baseline of the bell-shaped curve- which is constant during an observation and a variable part (AG_v), which is not constant during the observation.
The average variable airglow contribution in any observation has to be estimated as the exposure time weighted average of AG_v of the visits of the observation. Similarly the average constant airglow contribution has to be estimated as the exposure time weighted average of (TEC_Min-Diffuse Bkgd) of the visits of that observation. Hence the sum of the above two terms is the average total airglow contribution in an observation.
[edit] Solar Activity Dependence on the Variable AG part
There are a total of 335 ELAISS1 FUV observations. The variable airglow part (AG_v) of them scaled by the exposure time is plotted against the solar flux during the observation in the following figure.
[edit] Solar Activity Dependence on the Constant AG part
[edit] ELAISS1_00
[edit] ELAISS1 FUV Observations from 00 to 15 - Solar Activity dependence plots here
From these plots it is clear that the TEC minimum variations during the visits of an observation is not simply due to the variation in the solar activity.
