Another set of spectra for the BRITE/UMontreal campaign on P Cyg and Deneb. I am seriously behind in getting these data calibrated and sent. Something for the next few days as the clear weather is supposed to go away for a while.
I monitored a new (for me) object tonight at the behest of one of the CBA members (Enrico). J010742.6+484519, an eclipsing system with 2.5-magnitude eclipses. Here’s a plot from last night’s data:
All in all everything worked pretty well – the “real” magnitude scale here would be about +13.0 from what is shown (the comparison star’s V magnitude is 13.0). The standard deviation in the comparison star light curve (in blue) is only slightly above 0.005 magnitudes. Sadly I had to throw out a fair number of exposures as there were some serious issues with the tracking in declination, ruining dozens of frames when the telescope would “jump” in declination, causing double images.
Declination Gear Stiction
The problem can be seen in plots from the autoguider logs. The image, below, shows both before and after. Basically the problem turned out to be stiction due to the declination worm being too tight against its gear. Note that during guiding I had the declination motor making corrections in only one direction (southward). The mount is not yet perfectly polar aligned and so drifts slowly to the north. This is something I intentionally did for the CGE mounts but in this case it’s just me not having enough time to really get the azimuth adjustment right. Anyway, in the top frame what you’re seeing is the slow drift of the guide star’s position as measured in each 4-second guide camera exposure. As the object crosses the zero line the motor should (and did) engage to make the correction to return the star to its initial position on the chip. But the gearing was so tight it would not move until a lot of “spring” tension had built up in the gearing and then would “snap” – and since it had not moved as commanded during all the previous corrections the result was a massive over correction. Then the entire sequence would repeat. The bottom panel shows the guiding after loosening the pressure between worm and wheel. There is still a slight bit of the same phenomenon occurring, at a much smaller scale. Earlier today (writing this on 4-September) I loosened the worm and gear a bit more and added a touch of lithium grease to the spur gear assembly. In the next week or two I’ll be taking both of the motor assemblies off to clean and re-grease the main worms and gears.