The Project
The following objects have been detected as exhibiting some variability. (In all instances this variability has now been confirmed.) These objects are believed to be eclipsing systems because of the nature of their observed light variation. However, in most cases only one "eclipse" was observed and periods have not been determined. The detection of any possible eclipse for these systems could lead to a period determination. Any observations can be used to try to confirm the initially proposed type of variability, and can help in the determination of a period.
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One should try to observe these fields once or twice a night whenever CCD images are obtained. Even one observation of one field might reveal an eclipse in progress when compared with observations on another night.
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BD+63 537 |
4h 50m 25.1s |
+63o 19' 58.6" |
10.5 |
0.9 |
K7 |
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SAO 41956 |
7h 43m 6.43s |
+48o 41' 9.9" |
9.8 |
0.7 |
F2 |
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HD 97422 |
11h 12m 45.9s |
+00o 20' 52" |
8.47 |
0.5 |
F8 |
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GSC 1383-600 |
8h 29m 39.36s |
+17o 17' 1.8" |
10.8 |
0.6 |
G0 |
The links on the variable star names are links to POSS images centered on each object. Each image is approximately 14 arcminutes across. In these images north is up and east is toward the left. These images were obtained using the Aladin Preview system.
Some alternate names are also included for these objects. For this project the Hipparcos designation (HIP) can be particularly useful since the Hipparcos database contains all photometric measures obtained by the spacecraft during the mission. For the first three objects on this list, these are the observations that led to the discovery of these objects as being variable. This data may be examined by going to the Hipparcos web site and using the Hipparcos Epoch Photometry Viewer. For FF Cnc, the IBVS reference (Information Bulletin for Variable Stars) is to the publication that announced the discovery of the variability for this object. The publication includes the original photometric measurements.
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These objects are "bright" so reasonable exposure times are likely to be only a number of seconds for an unfiltered CCD. Unfiltered exposures will certainly be less than one minute. A 20 second exposure time for an unfiltered exposure is adequate for the brighter objects with the SSUO CCD system. For the brighter object (FM Leo) we use 10 second exposures. You will want the pixel counts in the target objects to be high, but well below saturation levels. Ideally, You would like to have at least one comparison or sequence star in the field that is brighter than the target object and not saturated. Since the target objects may become as faint as one magnitude below their nominal values during an eclipse, you will want exposures to go deep enough so that faint sequence stars at least one magnitude fainter than the target objects will be well exposed with good signal-to-noise. It is somewhat of an art to select appropriate exposure times.
And then your perfect exposure time may need to be adjusted due to changing conditions. Such conditions may include the brightness of the moon, position in the sky with respect to the horizon, and the clarity of the atmosphere. For surveilance observations it is even safe to work through high clouds or thin fog. Surveilance observations may always be made differentially within the image.
Observations using filters must be longer by the appropriate filter factors. Filtered observations are required to determine standard magnitudes and colors (BVRI) and for professional quality light curves. However, to detect eclipses, determine times of minima, and determine periods, unfiltered observations are perfectly acceptable.
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To check on the surveillance observations at the telescope, it will be necessary to determine or establish the magnitude for at least one non-variable star in the field for each object. (Simbad can help identify such stars.) A selected non-variable star may become the primary comparison star for the field. In order to check or track possible variability, or to detect a possible eclipse event, you will need to monitor the magnitude difference bewteen the target object and the primary comparison star. To determine approximate magnitudes at SSUO, consult the CCDOPS documentation for Determining Approximate Magnitudes. Consult the appropriate manual for your system if you are not working at SSUO.
While at the telescope, if you believe you may have detected an eclipse event (or variability of any kind), you should begin taking data to document the event. Taking an image once a minute or so over several hours would not be an unreasonable approach. In such an instance, calling the SSUO Observatory Director at home (whatever the hour) would not be unacceptable. Sending email to the Observatory Director as soon as possible to report any possible eclipse detection would be greatly appreciated. Such information can be an important contribution to this research program.
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Working together can increase our chances of catching an eclipse and ultimately determining periods and the detailed nature of these recently discovered variable stars. If you would be interested in working with us, we would be happy to have your collaboration. As indicated above, any observations can be potentially useful. We would be willing to help you reduce your data, or would be willing to accept a copy of your data for reduction here at SSU. Contact the Observatory Director if you are interested in participating in this project (spear@sonoma.edu).
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