[vsnet 866] Re: BD+24 719: New RR Lyr-type star ?

[Toshihito Ishida <ishida@nhao.go.jp>]

Dear VSNET members; 

In the VSNET 863 issue, Prof. Andronov have drawn our attention 
to the interesting new variable BD+24 719.  

In his report, he reported that this star did not show variations 
during JD 2459418-44256, and after that it seems to start its variation.  
Because observation of the starting pulsation is important but 
very rare, I would like to inform you here on the present status 
of the observations on starting and stopping of variations due 
to stellar pulsation, which may call more attention of you all 
to this interesting new RR Lyrae candicate.  

Observations of starting and stopping of the stellar pulsation 
is very important, because it will fix the blue and red edges 
of the instability strip,  and will bring us information to 
check our understandings of the stellar interior.  

However, for observing the START of the pulsation, we need to 
monitor a non-pulsating, hence non-variable star, and need to 
wait until it evolves and enters into the instability strip.  
For this situation, we have only very poor information on 
this subject.  We only have a tip of evidence by Barlai 
(cited in Waelkens 1995: Unfortunately, I could not attend 
the IAU Colloq. 155 and missed a chance to see her presentation).  
Regrettably, we have obtained no convincing observation of 
the start of the pulsation at all.  

When we turn to the observation of STOPPING pulsation,  we have 
interesting observations on a beta Cephei star alpha Vir (Spica), 
and observations of the decreasing of the pulsation amplitudes of 
two classical Cepheids, Polaris, and Y Oph.  However,  latter 
two stars may not indicate the position of the red edge, because 
colors of the Polaris and Y Oph seems to indicate that both of the 
two star is in the middle of the Cepheid strip.  

The observations reported by Prof. Andronov may indicate that we've 
got finally a chance to observe this very rare phenomenon.  
As well as new observations to confirm variation and clearify period
of this star,  checking your plate and CCD flames to confirm 
non-variablity will also be invaluable data.  

Hoping fruitfull observations to you all. 

regards, 

References: 
 Brown and Bochonko, 1994, PASP 106, 964
 Fernie, et al. 1993, ApJ 416, 820
 Fernie 1990 PASP 102, 905 
 Odell and Pesnell, 1995, in "Stellar Evolution: What should be done", 
  32nd Liege International Astrophysical Colloq. p417-422. 
 Shobbrook, et al. 1972, MN 156, 165. 
 Waelkens, 1995, in "Astrophysical Applications of Stellar Pulsation" 
  (ASP Conf. Ser. 83), p24-30. (and references there in)

-- 
%  Toshihito ISHIDA, Ph. D., Astrophysicist                               %
%  Nishi-Harima Astronomical Observatory, Sayo-cho, Hyogo 679-53, JAPAN   %
%  Tel:     +81-790-82-3886 ext. 142      Telefax: +81-790-82-3514        %
%  e-mail: ishida@nhao.go.jp (usual) HQA01560@niftyserve.or.jp (off time) %

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