Here are the 2015 light curves for stars on the section’s programme. These are based on observations made by Matthew Barrett, Graham Taylor, Richard Livingstone, Tony Markham and David Scanlan. Apologies for the somewhat inconsistent formatting (e.g font sizes) in places – my Windows 7 laptop hit problems during the period in which I was creating the light curves and it took time to get used to the new version of Office that I’m using with the replacement Windows 10 laptop – all of the features are present in the new Office version, it just takes time to track them all down!
This Mira type variable produced two peaks during 2015, with the Jan-Feb peak being around a magnitude brighter than the autumn peak. Observations of the latter peak were hindered by Bootes becoming increasingly low in the evening sky.
This semi-regular variable star continued to vary with a range of over a magnitude and a period of around 209 days duing most of 2015. However, the brightness changes seemed to become smaller late in the year.
The light curve which follows combines all observations of RZ Cas made during 2015 near the time of primary eclipse.
If the primary eclipse was occurring in line with predictions made using the elements in the General catalogue of Variable Stars (GCVS), then it would be centred on phase 0. The observations, however, show it to be centred near (predicted) phase 0.06. This quates to the primary eclipse occurring approx 1.7 hours later than predicted by the GCVS data. Fortunately, however, we don’t rely on the GCVS for eclipse predictions and have available more recent elements for RZ Cas that prove quite reliable for predicting eclipses. Calculating phases relative to the GCVS elements does however allow us to monitor how the discrepancies between observations and GCVS predictions evolve over time.
This light curve shows all of the observations of Delta Cephei made during 2015 combined to show one (and a half) cycles of variation.
At the start of 2015, T Cephei was in a long “pause” at around mag 8.0 on gthe way to its late April maximum. This pause was somewhat longer than had been seen in recent years. Although such a long pause was unusual, there has been another long pause, starting in 2015 December, on the way to T Cephei’s spring 2016 maximum.
The light curves which follows shows all observations made in 2015 near the time of primary eclipse combined into a single light curve, with the phases being calculated using the information in the GCVS. The eclipse is clearly not centred on phase 0. It appears to be centred close to (predicted) phase 0.085. This equates to the eclipses occuring approx 5 hours later than predicted by the GCVS info.
Omicron Ceti (Mira)
The maxima of Mira are currently occurring during the spring months when Mira is not observable from the UK. By the time that Mira emerges from the morning twilight in late July, it is already fading from maximum. Minimum brightness occurs late in the year. Latest observations from 2016 show it rapidly brightening towards its (unobservable) April maximum.
R Coronae Borealis
Following a deep fade that had persisted for many years, R CrB finally returned to binocular visibility during the autumn of 2014. However, the brightening slowed and peaked near mag 7.0 in late February 2015. A new fade then set in. This was slow initially, but the brightness of R CrB then plummeted in early June and it has stayed well below binocular visibility ever since.
U Coronae Borealis
Despite U CrB being observable all year round, it can prove difficult top observe eclipses. When Corona Borealis is best placed for observation during the spring, the nights are getting rather short. By the time that the nights get longer in the autumn, Corona Borealis is only observable for a few hours at the start of the night. During the winter months, it is only visible for a few hours pre-dawn. All of this means that it is virtually impossible to observe a whole 11 hour eclipse in one night. The light curve which follows shows U CrB fading into eclipse during the evening of Sep 7th … observations being terminated when U CrB became lost in the haze.
AF Cygni is a semi-regular variable which usually varies with a period of about 3 months. During 2014 and early 2015 the light curve was more suggestive of a 6 month period, However, during the second half of 2015, the 3 month period was becoming more apparent again.
Chi Cygni had produced an unusually bright maximum (mag 3.8) in May 2013 followed by an unusually faint maximum (mag 6.5) in June 2014. In 2015, it produced a brighter than average maximum, about half a magnitude below that seen in 2013.
All of the observations this Cepheid variable made by section members during 2015 have been combined to create this light curve showing approx one and a half cycles of variation. The light curve of zeta Gem is sinusoidal, with peak brightness occurring near phase 0 and minimum brightyness near phase 0.5.
With Alpha Herculis being a rather red star, brightness estimates can differ between observers by a few tenths of a magnitude. Hence it could be misleading to show magnitudes on the vertical axis in this light curve. Suffice to say that the star has spent most of 2015 near the top of its brightness range.
68 (u) Herculis
The light curve which follows combines all observations of u Herculis made during 2015 into a single light curve. Although the primary eclipse can (just) be made out near phase 0, the level of scatter shows how tricky it can be to observe this star. From most UK locations, this eclipsing variable is too faint to be followed using the naked eye, but it is also a bit on the bright side for common binocular sizes such as 10×50. All of this tends to make the scatter quite large compared with the star’s 0.7 magnitude range.
2015 was not an easy year in which to observe this Mira type variable. It passed through minimum during the spring and was at maximum just as it was emerging from the morning twilight in September.
This light curve shows all observations of Beta Lyrae made during 2015 into a single light curve showing one (and a half) cycles of variation. The primary eclipse can be seen near phase 0, with the shallower secondary eclipse being visible near phase 0.5 .
The brightness variations of RR Lyrae are almost (but not quite) as predictable as those of Delta cephei. Nevertheless, it is still feasible to combine all observations made during 2015 into a single light curve showing one (and a half) cycles of variation. The period of variation is approx 13 hours.
Alpha Orionis (Betelgeuse)
Betelgeuse spent 2015 near the top of its brightness range. There is the inevitable scatter that occurs when observing Betegeuse due to it being located some distance away on the sky fom its comparison stars. The mid year gap occurs when Orion is not observable in the night sky.
With the period of this Mira type variable being about a week longer than a year, maxima occur at a similar time from one year to the next but become progressively later over the years. In recent decades, they have moved from the late autumn through to the early spring. A consequence of this is that they are starting to occur close to the time in early May when U Ori is sinking into the evening twilight. Hence, although we can still see the maximum that occurs during April, we lose sight of U Ori during its fade from maximum. Observsations were fairly sparse in 2015, but do indicate a peak brightness near mag 7.0 in mid April.
Beta Persei (Algol)
Despite being easyto locate, Algol can prove quite a tricky star to observe. From mid spring until August it is only fairly low in the sky during the hours of darkness and this makes it harder to compare its brightness with that of its comparison stars whose apparent brightness may be affected differently by haze. During the autumn and winter, Algol is better placed for observation, but it can be a matter of luck as to whether the sky is clear when Algol is in eclipse – and a bright Moon in the Aries/Taurus/Gemini area can also seriously hinder observations.
In the event, only six observations during eclipses (three different eclipses) were made during 2015 and these are shown in this light curve. These suggest that primary eclipse is centred near (GCVS predicted) phase 0.05, corresponding to the eclipses occurring about three hours later than predicted by the orbital elements listed in the GCVS.
The 2015 minima of R Scuti was not as deep as those of 2013 and 2014 (some of which dropped below mag 8.0), but there was still a good amount of brightness variation to be followed by observers.
The period of this Mira type variable is only about a week short of a year and so the maxima occur at a similar time each year, but over time become progressively earlier. In the early 1990s, they were occurring with R Ser only observable in the winter morning sky. Now, however, they are more conveniently timed and observations in 2015 showed R Ser peaking near mag 6.4 at the end of July.
This Mira type variable was the only star on the section’s programme to not be observed during 2015. Fading from its autumn 2014 maximum, it dropped below binocular visibility in December 2014. The 2015 maximum in the late spring was then very unfavourable, with R Tri being close to conjunction with the Sun. It was brightening again in late 2015, but didn’t reach binocular visibility until January 2016.
R Ursae Majoris
R UMa, another Mira type variable, produced two maxima during 2015. As these light curves show, the autumn maximum was around a magnitude fainter than the January peak.
S Ursae Majoris
This is a very red star and one consequence of this shows up in the early 2015 peak. The sensitivity of the eyes to red light varies from observer to observer. As a result, some observers will see red stars brighter than do other observers. Normally this only amounts to a few tenths of a magnitude, but in very red stars such as S UMa the differences tend to be bigger – in some cases this can amount to as much as a magnitude. During the early 2015 peak, one observer saw the peak brightness as being around mag 7.8, while the other saw it around mag 8.4. However, both observers saw the peak occurring on approx the same date – and it is this latter figure which is the most important.
T Ursae Majoris
This Mira variable reached its peak brightness during the mid spring. This was a much brighter than usual – about a magnitude brighter than the average peak. Having been too faint to be seen in binoculars during the summer and autumn, it had brightened back to around mag 8.8 by late December, on the way to its January 2016 maximum.
Z Ursae Majoris
The six monthly brightness variations of Z UMa are very apparent in this light curve. Of particular note during 2015 was that the minima were unusually deep – below the mag 9.3 faint limit generally quoted for Z UMa.