The data analyzed in this Technical Note can be accessed via FTP at the following sites: Thanks to Arne Henden and USNO for hosting them.
MWR 7/12/2001
This page allows access to 319324 observations made both in I and V filter of 29952 stars. The observations were made by Tom Droege using his 2-camera Mark IV telescope. The location of the observatory is Batavia, Illinois. The data were taken during the following nights in 2001 (UT):
25, 27 and 28 March; 13, 16, 17, 18, 27, 28, 29, 30 April and 20 May.
The area imaged is between 10:36 < RA < 14:36 and -2.41 < DEC < 2.05.
The same fields was imaged several times simultanously in I and V filter. Images was processed using IRAF routines and star intensities were determined using fitsblink, as described in the Technical Note 67. For each pair of images, a list of stars which appeared on both images was formed. Those of the paired stars that were identified a TYCHO stars were used for the determination of the color transformation. For each TYCHO star, first Johnson V magnitude was calculated using formula
V =Vt-0.090(Bt-Vt),
where Vt and Bt are TYCHO-2 magnitudes.
Then a color transformation was made using formula
V=Vraw+a+b (Vraw-Iraw).
The raw magnitudes Vraw and Iraw are defined as
Vraw=22.5-2.5 log10g,
where g is the star intensity in ADU units. The constant term 22.5 is arbitrarily chosen to translate the raw magnitudes into a familiar range.
Unknown coefficients a (offset) and b (color term) were calculated using a two-step linear fitting routine. In the first step, a linear fit was made, then all points with deviation larger than 3 sigma were removed and a fit was made again. This procedure removed outliers. Then V magnitudes were calculated for all paired stars. Graphs of all calibration measurements are available in a separate page.
In the next step, a master observation file MasterObs.dat was made which contains stars from all 12 disks (disks 17a-17c, 18a-18d, 18f-18i) used in this analysis. Measurements of the same stars are joined together and the average coordinates and magnitude are calculated, as well as the V magnitude. This summary information is contained in a file Totals.dat. It has one line for each star with the following fields:
From Totals.dat derivative files are made:
Each of these files is 2.7 MB long.
The MasterObs.dat is 90 MB long and contains raw observations in the following format:
One of the more important information is the dependence of the magnitude uncertainty on the V magnitude. It is shown in the following image...
and the average magnitude uncertainty as a function of magnitude:
Other statistical evaluations (graphs are presented with and without data from disk17f, which is of low quality):
Average number of observations / star as a function of magnitude:
How many stars have been observed n-times:
Some known variables were found by choosing stars with large sigma and checking them against GCVS using the Guide 6.0 program. These are:
One star is offered here as a candidate for a new variable: GSC 282_0743
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