[vsnet-chat 3790] Re: Delta Cep period analysis of visual observations

["Stan Walker" <astroman@voyager.co.nz>]

Greetings,

So phase 0.02 * 5.366 is about 2.5 hours. That's better than I would have
thought but still translates to +/- 0.00025 over 500 cycles or 7.5 years.
Most Cepheid period changes seem to be rather smaller than this.

Perhaps the 0.3 visual to 0.005 pep is a trifle exaggerated. This supposes
two blocks of 3 x 10 second UBV measures as against a single visual measure
at around magnitude 7. If the same amount of time - 15 minutes - was spent
on the visual measure (it never is but Sebatian Otero seems to be doing this
on brighter objects) then the visual measures would, perhaps, improve to
0.05. The pep measures were made using a 50cm telescope and a very good EMI
pm tube.

Whilst on the subject of delta Cephei I seem to recollect reading that the
amplitude of Polaris had decreased around the end of the 1980s. Is this
still the case or has it gone back to normal. One of the more interesting
stars I can't see from here!

Regards,
Stan


----- Original Message -----
From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
To: <vsnet-chat@kusastro.kyoto-u.ac.jp>; <vsnet-rr@kusastro.kyoto-u.ac.jp>
Sent: Saturday, November 18, 2000 1:09 AM
Subject: [vsnet-chat 3779] Re: Delta Cep period analysis of visual
observations


> Re: Delta Cep period analysis of visual observations
>
> > Determining epochs by fitting visual measures to master light curves and
> > then plotting on O-C diagrams shows just the lack of time resolution
that
> > you would expect. Visual measures with an accuracy of +/- 0.3 magnitudes
> > produce epochs about 20-50 times less accurate than pep measures which
are
> > based on measures with accuracies of +/- 0.005 magnitudes.
>
>    I have just placed GIF figures, PDM theta plot and phase-averaged light
> curve (P=5.3660 d is used).  The phase bin in the latter figure is 0.02.
> The figures look (at least) as pretty as our usual superhump analysis :-)
> I have not yet done cross-correlation, but as inferred from the sharpness
> of the ascending branch, the error in O-C would not exceed phase 0.02.
>
>    http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/Cep/Delta_Cep/dceppdm.gif
>    http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/Cep/Delta_Cep/dcepph.gif
>
> Regards,
> Taichi Kato
>
>

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp