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RT Leonis
(3 January 2009) |
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RT Leonis is another Algol-type eclipsing systems (p = 7.447902 days). These are binaries with spherical
or slightly ellipsoidal components. It is possible to specify, for their light curves, the moments of the
beginning and end of the eclipses. Between eclipses the light remains almost constant or varies insignificantly
because of reflection effects, slight ellipsoidality of components, or physical variations. Secondary minima
may be absent. An extremely wide range of periods is observed, from 0.2 to >= 10,000 days. Light amplitudes
are also quite different and may reach several magnitudes. In the case of RT Leonis, this amplitude is only about
0.2 magnitudes. This binary is a well-studied one, with numerous references in the literature. The time of
primary minimum is predicted by the equation:
HJD = 2452503.5770 + 7.447902 x CycleNo. |
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Finding chart for RT Leonis
RT Leo: RA(2000) = 09h 45m 24.0s Dec(2000) = 19° 54' 20"
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Eclipse curves for RT Leonis
Observation of RT Leonis was carried on one night for a period of about three hours. 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 RT Leonis, along with just one reference stars. The field is rather sparse. This is data from 02-03 January 2009 EST (cycle no. 313), and the observed geocentric time of minimum (middle of eclipse minimum) was approximately 03 Jan 2009 06:18:20 UT, or HJD = 2454834.76713. The image on the right is a single CCD frame near the time of mid-eclipse, #49 from a series of 170 images. The positions of RT Leonis and the reference star are indicated in the image and on the graphic.
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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. This light curve is typical of Algol-type eclipsing binaries, but many more observations will be needed to depict the whole light curve. With a 7+ day period, and partial eclipses occurring, it could be many weeks before additional observations are forthcoming, given my three-hour observing window. It is quite possible that the minimum observed here is the secondary mininum, and not the primary minimum. In either case, it's clearly an annular eclipse since there is no observed flat bottom at minimum. All available data are shown in the figure below. The primary (secondary?) eclipse occurs about 8½ minutes earlier than predicted.
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References
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This data and information on this page are Copyright © 2009, Richard A. Berg, Washington, DC
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