Light curves and phase diagrams of the EA type eclipsing binary RZ Cassiopeiae / RZ Cas
RZ Cas is catalogued as an EA+DSCT type system (AAVSO VSX) where one of the components, the A3V primary, is a pulsating star of the δ Scuti type, as indicated by the DSCT classification. These are small amplitude (0.003 to 0.9 mag), short period (0.01 to 0.2 day) pulsating variables. The secondary is a K0III type. Originally thought of as ‘noise’ affecting my attempts at determining the times of eclipse minima of the system, subsequent analysis has shown that at least some of this noise was due to activity of the δ Scuti type component.
Given the small amplitude, observing this variation is pushing the limits of my system but, where possible, it will be included in the following observations and discussions.
Given the small amplitude, observing this variation is pushing the limits of my system but, where possible, it will be included in the following observations and discussions.
2016 December 22
Light curve of a primary minimum of RZ Cas on 2016 December 22 from 413 unfiltered images taken with the 2" Titan (with crossed polaroids) at Somerby Observatory.
Light curve of a primary minimum of RZ Cas on 2016 December 22 from 413 unfiltered images taken with the 2" Titan (with crossed polaroids) at Somerby Observatory.
Although this curve is not quite regular, analysis failed to show any activity consistent with δ Scuti activity.
2017 October 15: secondary minimum
Light curve of a secondaty minimum of RZ Cas on 2017 October 15 from 1002 unfiltered images taken with the 2" Titan stopped down to 30mm to enable longer exposures to be used to reduce scintillation effects, 8 seconds in this case. The first diagram shows a plot of the individual magnitude estimates, while the second diagram consists of one minute bins of this plot.
Light curve of a secondaty minimum of RZ Cas on 2017 October 15 from 1002 unfiltered images taken with the 2" Titan stopped down to 30mm to enable longer exposures to be used to reduce scintillation effects, 8 seconds in this case. The first diagram shows a plot of the individual magnitude estimates, while the second diagram consists of one minute bins of this plot.
The 'sinusoidal' modulation of the curve has a semi-amplitude of approximately 0.01 magnitudes and a period of approximately 0.016d (~23 minutes) and is consistent with variations in the δ Scuti type component.
Light curve and phase diagram of RZ Cas from photometry of 33 images taken with the Cluster Camera of the Bradford Robotic Telescope, using a tri-colour green filter, between 2014 October 12 and 2016 October 1.
Combining the above three sets of data results in the following light curve and phase diagram. The Bradford observations are in black while the Somerby observations are in red (primary minimum 2016 Dec 22) and blue (secondary minimum 2017 Oct 15).
2019 February 14: primary minimum
A primary minimum observed with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2019 February 14. The images were unfiltered (ie CV).
A primary minimum observed with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2019 February 14. The images were unfiltered (ie CV).
No δ Scuti activity was discernible in the maximum after the primary minimum, but the data was too noisy to obtain an unambiguous signal.
2022 October 5
Entry into a primary minimum was observe with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2022 October 5.
Entry into a primary minimum was observe with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2022 October 5.
The 'flat' section before the onset of the eclipse shows distinct waviness. This section has been magnified (below) and then replotted in 2 minute bins.
The probable δ Scuti activity is shown here to have a semi-amplitude of about 0.01 magnitudes and a period of approximately 0.0155 days.
2022 October 8
Entry into a secondary minimum was observed with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2022 October 8. (The gap was due to passing cloud.)
Entry into a secondary minimum was observed with the 2" Titan (stopped down to 30mm) at Somerby Observatory on 2022 October 8. (The gap was due to passing cloud.)
Here we can again see evidence of the small, regular magnitude changes caused by one of the components being a δ Scuti type pulsating variable. The period of these variations is again 0.016d (~23 minutes), , but the semi-amplitude is perhaps closer to 0.015 magnitudes.
That these are 'conspicuous' during the secondary eclipse (when the cooler star is eclipsed by the hotter star) and not seen during the primary eclipse (when the hotter star is eclipsed by the cooler star) suggests that it is the hotter star which is the δ Scuti variable.
2022 November 4: primary minimum
This night was mainly clear, but a bright Moon was present. The full 50mm aperture was used, to collect as many photons from the system as possible, using exposures of 4 seconds. The prime objective was to obtain a timing of the primary minimum, which is shown below.
This night was mainly clear, but a bright Moon was present. The full 50mm aperture was used, to collect as many photons from the system as possible, using exposures of 4 seconds. The prime objective was to obtain a timing of the primary minimum, which is shown below.
Further δ Scuti type variability was again apparent, not least in the ascending branch of the above light curve, which has a slight ‘waviness’ to it with a period of approximately 0.015 days. This is less conspicuous in the fall to minimum. The following diagram illustrates this where the red line is a polynomial of degree 8 curve plotted in Peranso.
The calculated extremum is at HJD 2459888.414817 +- 0.00049. However, given this asymmetry and lack of the actual minimum, the calculated error of +- 43 seconds might be a little optimistic.
As before, δ Scuti type variability was detected in the maximum before the start of the eclipse, plotted below in 1 minute bins. Again, this has an approximate period of 0.015 days and semi-amplitude of about 0.015 magnitudes.
As before, δ Scuti type variability was detected in the maximum before the start of the eclipse, plotted below in 1 minute bins. Again, this has an approximate period of 0.015 days and semi-amplitude of about 0.015 magnitudes.
2022 November 12: maximum
The maximum section of the light curve was observed, with the aperture reduced to 30mm in order to extend the exposures to 7s.
The maximum section of the light curve was observed, with the aperture reduced to 30mm in order to extend the exposures to 7s.
Fitting a polynomial of degree five curve to this, in blue, suggests an increase of approximately 0.02 magnitudes. The calculated extremum is at HJD 2459896.457628 +- 0.01081. (This is approximately 6.73 periods after the November 4 primary minimum, ie moving from the secondary minimum to the primary minimum.)
Peranso/ANOVA suggests a period of 0.0157d for this particular activity.
The δ Scuti activity is clearer when the above is plotted in 2 minute bins, as below. Here, the semi-amplitude is again 0.01 magnitudes approximately.
2022 November 24: maximum
The maximum section of the light curve was observed. The full aperture of 50 mm was used, requiring exposures of 3.5 seconds, to compare the results with the reduced aperture sequence above.
The maximum section of the light curve was observed. The full aperture of 50 mm was used, requiring exposures of 3.5 seconds, to compare the results with the reduced aperture sequence above.
Peranso/ANOVA suggests a period of 0.0154d for this particular activity.
The results are not conclusive, but superficially there is less scatter with the longer (smaller aperture) exposures, even though less photons are captured overall. The focus, peak pixel values and fwhm were similar on both runs, but scintillation would probably be a major factor affecting the shorter exposures. More observations needed!
2023 October 22: coming out of primary minimum
Due to weather and technical issues, the actual minimum was missed, but this is the light curve of the system coming out of minimum. The 2424 unfiltered images were taken with the 2" Titan at Somerby Observatory using its full (50mm) aperture.
The δ Scuti variability can again be seen in the following light curve constructed using 210s bins.
Still not sure whether the better data is obtained with the full (50mm) aperture, or the reduced (30mm) aperture. Although less photons are collected using the smaller aperture, the seeing is more 'smoothed out' using the longer exposures with the smaller aperture compared to the shorter exposures with the larger aperture. Seeing varies, of course, from one session to the next. Next time I observe this system perhaps testing this would be a worthwhile exercise.
The current catalogue values for the period is 1.1952503d (GCVS, AAVSO VSX, Kreiner) (accessed 2023 October 29).
There is significant o-c activity with this system (GVCS, Kreiner). This is why it is not possible to combine all of the above observations into one consistent phase diagram.)
There is significant o-c activity with this system (GVCS, Kreiner). This is why it is not possible to combine all of the above observations into one consistent phase diagram.)
This is an example of a visual observation of a primary minimum I observed from Leicester, UK, with a pair of 7x50 binoculars.
[ This page updated 2023 October 29 ]