Troubleshooting the 24 Inch Telescope and Photometric System

Troubleshooting the 24 -Inch Telescope and Photometric System at Hobbs Observatory Cole Cook and Geoffrey Root Physics and Astronomy University of Wisconsin-Eau Claire Research Advisors: Dr. Lyle Ford and Dr. George Stecher Abstract Asteroids are remnants from the formation of the Solar System. By studying the properties of asteroids, insights about this period of time and the Solar System itself can be gained. In order to study the rotational properties of asteroids, we make photometric observations using the 24 -inch telescope at Hobbs Observatory. After recent modifications to this telescope, we observed inconsistencies within our photometric data. It appeared that the pixel sensitivity of our support images differed from that of our images of the target asteroid. Support images are used to correct for varying pixel sensitivity from the images. The brightness of our target asteroids will not be accurately measured if the pixel sensitivity is not properly accounted for. In this poster, we examine the possible causes of these inconsistencies such as improper collimation and light leaks from new fan ports. The black rectangle is the filter slider that allows us to select the wavelengths of light our CCD camera detects by varying the filter in front of our camera. The amount the camera sags depends on the angle of the telescope, the angle of the derotator, and the connection between the camera and the telescope itself. Testing Our Ideas Causes Considered «Light Leaks from Fan Ports Telescopic System 24 inch Newtonian telescope Alt-Az Mount – nonstandard astronomical mount, movement about two axes De-rotator – rotates in order to keep image in the same orientation, needed for Alt-Az mounted telescope Filter Slider – allows us to select the wavelengths of light that reach our camera CCD Camera – similar to a digital camera but it is optimized for astronomical work Computer – used to control camera and telescope Performance Issues of System «Signal to noise ratio declined compared to previously obtained data «Background of images were non-uniform from CCD chip milling (ring pattern on right picture below) « Vignetting (dimming near edges) varied throughout night with both a time and space dependence though we expected no change «No problems before, why now? Could add undesired light that may vary with angle «Improper Collimation Not all light focuses into CCD camera «Camera Sagging Could change location of image on CCD chip «De-rotator Sticking Could compound problems from camera sagging and improper collimation «Inconsistency in Position of Filters Could block some light from reaching CCD camera and change vignetting pattern «Improper Communication Between Computer and Rest of System Two potential causes: hardware-strained cables, software-computer signals Proper and Improper Collimation A B Depending on altitude of the telescope, vignetting changed as did the location of greatest concentration of light. The changing angle is one possible mechanical explanation as to why our images don’t have a uniform background. «Relieved tension on strained cables No change observed «Using both the computer controls and manual controls, attempted to have filter slider fail by going to a different location than being centered After hundreds of trials, filter slider didn’t fail and consistently went back to the same location «Isolated telescope from all sources of light Ruled out light leaks as a contributing factor «Checked collimation using a laser collimator Found telescope was improperly collimated «Made mechanical adjustments to the chain of the derotator and tried warming it before making observations Sticking lessened but still present Conclusions «Eliminated Possibilities Strained cables not issue Filter slider consistently went to same place No light leaks «Investigations Remaining Move secondary mirror and recheck collimation or may have to re-machine secondary mirror support to insure proper collimation Alternative methods to prevent de-rotator sticking Camera sagging Drawing A shows a properly collimated telescope. Drawing B, however, illustrates improper light collimation. «Continue Investigating then start taking data again Want to exhaust options before re-machining secondary Research funding from Blugold Fellowship program. mirror support The printing of this poster was funded by Differential Tuition.