Cepheid stars help us to measure the distances of galaxies - but they are not just distance posts - they are massive, fast-evolving stars. See the Cepheid pages for a list of targets.

U MENSAE:  Alan Plummer drew attention to this star some months ago by questioning the sequence but, more importantly the flat long time the star spent around magnitude 10 each cycle.

It's clear that it is similar to R Carinae with a bluer companion, but in this case the companion is bright enough to completely flatten out the light curve at around tenth magnitude. (And cause its misclassification as an SR star!) Arne Henden of the AAVSO suggested some multicolour measures so that the system could be modelled. The ASAS measures are a help in planning observations, which would be useful in UBV and VRI. It's probably too faint in JH except near maximum

Measures of U Mensae by ASAS3 confirm the unusually shaped light curve noticed by Alan Plummer. They also suggest that the next maximum will occur around JD 2454050

A MIRA STAR CHALLENGE

The light curve of BH Crucis is presented to the right. Also shown are the colour curves which provide information about what is happening during each pulsation cycle. These curves are offset by the amounts noted: B-V colour varies from +3.5 to +2.5; U-B from +4.0 to +2.0.

The B-V curve shows that temperature varies more or less in phase with the V light curve. The second maximum is the bluer. In this it differs from R Centauri--see the Mira page--where the first maximum is bluer.

The U-B curve is interesting. Disregarding the probably misleading measures in the 0.0 to 0.25 phase, the colour curve shows a strong brightening on the rise to the secong maximum. 

There are not too many of these stars and this makes a tidy observing programme which is not too demanding and which will produce information not previously known.

Mira stars with periods of over a year are poarticularly interesting. They include most of the few with genuine period changes, the stars with dual maxima such as R Centauri, BH Crucis, R Normae and NSV 4721. The period of R Hydrae began changing about 1700, but stopped decreasing about 1940. In recent years both BH Crucis and R Centauri have changed from dual maxima objects to normal Miras, but with pronounced bumps on the ascending or descending branches. Both have changing periods and now the light curve shape is similar to R Hydrae. These stars can be observed in UBV--or perhaps VRI--every 7-14 days to provide a measure of the colour changes through each cycle.

We apologise for the scatter in the U-B light curve before phase 0.25--the star at that time is about U = 17 and as the U filter/pm tube combination is the least sensitive the readings are poor.

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