Amateur Transit Light Curves

Frequent uses of a hair dryer to remove frost from the corrector plate; temp = 28 F, Dew Pt = 22 F (RH = 78%). WWV check of time tags.

The clock was checked & found to be accurate.

Air mass curvature is high due to use of a BB-filter and high air mass at the beginning.

Out-of-Transit Light Curves

These observations were a test of a new optical configuration which accounts for the short duration. Nevertheless, there seems to be mild evidence for 1 mmag variations on an hourly timescale.

Professional Transit Light Curves


Gillon et al (2007) SST observations at 8 micron wavelength, reproduced from Ribas et al (2008). Lowest panel shoes effect of a hypothetical 0.1 degree inclination change that could be produced by perturbations from a 5-Earth mass outer orbit planet in a 2:1 resonant orbit.


V-band, Observatory of Geneva 1.2-meter Euler telescope at La Silla Observatory, Chile (Gillon et al, 2007). Mid-transit at 2007 May 02, 02:41 UT. My measurements of this LC yield depth ~6.5 ± 1.0 mag, length = 0.943 ± 0.064 hr.

Finder Image

 Figure F1. Finder image with identifier star numbers (above) and J-K colors (times 100, below) selected stars. GJ 436 has V = 10.68 and Rc = 9.66.

Normally I don't present all-sky photometry results without completing a second observing session and analysis and verify compatibility between the two results. In this case I have no plans for doing this since I doubt that anyone will use any of these results.

Figure A2 and A3. Color/color scatter diagram showing the location of GJ 436 (red square) and the 9 nearby stars (gray squares) in relation to 1259 landolt stars.

If the solution for one filter band had a systematic error it would show up in these plots as a group offset in the color/color scatter diagrams involving that filter. For example, if all B-magnitudes were high by 0.05 magnitude then the goup of gray squares and the red square would be offset to the right by 0.05 magnitude. It's possible that such an offset is present in Fig. A2, but it's clear that greater vaues fo such an offset are very unlikely. An alternative for explaining the rightward shift of Fig. A2 gray squares is for there to be instead a downward shift, or values for V that are to negative by about the same 0.05 magnitude amount. This is unlikely after inspecting Fig. A3, where there is no evidence of shifts. Presumably, all 3 bands (V, R and I) are free of calibration error offsets (unless by some unlikely circumstance there are offset errors in all 3 bands that excatly compensate to produce color/color agreement with the Landolot stars). If it is true that V, R and I are free of calibration offset errors greater than ~0.03 magnitude, then what should be make of the funny location for GJ 436 in Fig. A3? I claim that it is inescapable that GJ 436 has a much greater V-I color than the Landolt stars. Since V appears to be normal (e.g., Fig. A2), we must conclude that I is anomalous. In other words, these color/color scatter diagrams show that GJ 436 has an I-magnitude that is brighter than normal by ~0.5 magnitude! I'll leave it to others to explain how this could be the case.

Note: It won't matter what magnitude you assume for reference stars for the purpose of obtaining quality light curves. These estimated values are presented for the purpose of identifying star colors that "match" GJ 436's color which can be useful in minimizing extinction related systematic errors (i.e, LC curvature that's correlated with air mass). In this table the column for R-band will be the most accurate since it is based on observations. The other magnitudes for Stars 1 through 6 are based on JK magnitudes. For GJ 436 the B and I magnitudes are based on color/color correlations for main sequence stars. All stars in the table are compatible with main sequence color/color relationships.

References

Gillon et al, 2007, Astron, & Astrophys., "Detection of Transits of the Nearby Hot Neptune GJ 436" http://babbage.sissa.it/abs/0705.2219
Butler et al, 2004, Astrophys. J. Lett.,"A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436" http://adsabs.harvard.edu/abs/2004ApJ...617..580B
Ribas et al, 2008, Astrophys. J. Lett., "A ~5_earth Super Earth Orbiting GJ 436?: The Poser of Near-Grazing Transits"  http://fr.arxiv.org/abs/0801.3230

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WebMaster: Bruce L. Gary. Nothing on this web page is copyrighted. This site opened:  July 04, 2007.  Last Update:  May 09, 2008 (UT)