ZZ Ceti, also called R548, is a DAV. This star has been observed for the
last 3 decades. The pulsation spectrum consists mainly of 2 doublets,
one at 213 s and the other at 274 s. There are 3 objectives in observing
R548 and they are outlined below.
Both periods of the 213 s doublet
demonstrate remarkable stability; a rate of change of period with time
of only one part in a few billion years. This rate of change in period
is consistent with our theoretical cooling models. Such a great
stability in the periods makes R548 the second most stable optical
clock known, second only to G117-B15A, another DAV. White Dwarfs
like R548 and G117-B15A are more stable than atomic clocks and most
pulsars.
Observing R548 again this season will improve the current estimate
of this rate of change in period with time and more
importantly, it will reduce the error in the estimate.
However, the critical purpose in observing R548 will
be to decipher what is going on with the 274 s doublet. This doublet
has a faster rate of change of period.
There could be variations in period at shorter timescales (than evolutionary
timescales)
due to phenomena like Avoided Crossings. In order to unravel the 274 s
doublet, we need data sets separated by smaller time gaps.
We have data last year from September,
October and November 1999. We also observed it again in September 2000.
We therefore intend to get WET data in November, 2000.
So, by analysing the 1999 and 2000 data sets together, we might
be able to determine the timescale of variations affecting the 274 s
doublet. If this doublet is going through an avoided crossing, then
this detection will be the very first observational proof that such
crossings exist.
Last, but not the least, we need to detect more pulsation modes in the
star in order to probe its interior using Asteroseismology. Three
other pulsation modes have been observed in R548 at about 187 s, 318 s
and 333 s. We hope to improve our period determinations of these modes.
We also hope to search for other new pulsation modes.
Download a postscript version of this file.
Send comments to wetmaster. Last updated on 8 Oct 2000.