|
|
| Home | History / Background | Building the Observatory | Research | Photo Album | Who Am I? |
|
AH Geminorum
(27 December 2008) |
|
AH Geminorum is a 14th-magnitude short-period variable (p = 0.3367521 days = 485 minutes) of a class of variables of which
W Ursae Majoris is the prototype. These are eclipsers with periods shorter than 1 day, consisting of
ellipsoidal components almost in contact and having light curves for which it is impossible to specify the exact
times of onset and end of eclipses. The depths of the primary and secondary minima are almost equal or differ
insignificantly. Light amplitudes are usually less than 0.8 mag in V. In this case, the amplitude is on the order of
0.35 magnitude. The components generally belong to spectral types F-G and later. The primary component is a main-sequence
star similar to the Sun, while the secondary component lies below and to the left of the main sequence in the H-R Diagram.
AH Geminorum is not a well-studied variable star principally because of its fainter magnitude. There are only six references to it in the literature, none of which is a thorough study of the system. The time of primary minimum is predicted by the equation: HJD = 2452500.1155 + 0.3367521 x CycleNo. |
|
Finding chart for AH Geminorum
AH Gem: RA(2000) = 06h 53m 17.90s Dec(2000) = +15° 59' 23.0"
|
|
Eclipse curves for AH Geminorum
Observations of AH Geminorum were carried out over several nights for a period of about three hours each night surrounding the minima. Each data point represents a 50-second integration exposure using an ST-7XME CCD camera cooled to -30°C and a "Clear" filter. Each point is separated by about one minute. The ten-second difference represents the download and processing time needed before the next exposure begins. The telescope is continuously autoguided. After observing, all of the CCD images in the series are calibrated in the standard way to remove dust donuts and vignetting. The figure below shows the eclipse curve for AH Geminorum, along with the three reference stars and one check star. This is data from 22-23 December 2008 EST (cycle no. 6900), and the observed geocentric time of minimum (middle of eclipse primary minimum) was approximately 23 Dec 2008 04:57:33 UT, or HJD = 2454823.7031. The image on the right is a single CCD frame near the time of mid-eclipse, #42 from a series of 135 images. The positions of AH Geminorum, the three reference stars and the check star are indicated in the image and on the graphic. The graphic is generated by MaxIm DL/CCD, using the photometry tool.
This next figure below shows AH Geminorum, along with the same reference stars and a different check star (for no particular reason), from data from 25-26 December 2008 EST, nine eclipse cycles (cycle no. 6909) later. The observed geocentric time of minimum was 26 Dec 2008 5:37:22 UT, or HJD = 2454826.7346. The image on the right is #159 in a series of 207 images.
This third figure of AH Geminorum shows the same reference and check stars, from 144 CCD images from 29-30 December 2008 EST, in the middle of cycle 6920, 11 cycles later than the previous observations. Additional observations during secondary eclipse will improve detail of this light curve.
Here is a fourth night of AH Geminorum observations, from 170 CCD images from 2-3 January 2009 EST, in the middle of cycle 6932. These observations capture the secondary eclipse is detail. The mid-secondary-eclipse (image #87) occurred on 03 Jan 2009, at 03:32:32 AM UT, or HJD 2454834.65323, about 4 minutes late compared to predictions.
|
|
Things to Note
These are preliminary results, based only on inspection of the light curves and corresponding CCD images. The
equations used to generate heliocentric predictions for primary minimum were corrected to get a geocentric UT
time for the predicted minima. The observed geocentric UT time of primary minimum is determined from the light curve,
and corrected again to determine the observed heliocentric Julian date of mid-eclipse.
The magnitudes shown on the graphics are instrumental magnitudes, and they have not been transformed to a standard photometric system. Nevertheless, the "constant" values for the magnitudes of the reference and check stars demonstrate that the telescope-CCD system and evening conditions were stable. The light curve is rather noisy throughout. The last evening was not especially good, and this object is rather faint, so one would expect there to be a larger error associated with each data point. Ensemble photometry does, however, enable reasonable results to be had even on less than a perfect night. More observations will be added. All available data are shown in the figure below.
|
|
References
|
|
|
|
This data and information on this page are Copyright © 2008, Richard A. Berg, Washington, DC
|
