[vsnet-alert 1127] Possible fading of DY Per

[Taichi Kato <tkato>]

Possible fading of DY Per

   The R CrB-star DY Per has possibly started fading, as reported by
Marc Biesmans in [vsnet-obs 6621]
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-obs/msg06621.html).

  YYMMDD(UT)   mag  observer
  970619.972   108  (G. Poyner)
  970623.962   108  (G. Poyner)
  970704.988   109  (G. Poyner)
  970706.980   109  (G. Poyner)
  970708.996   109  (G. Poyner)
  970709.996   108  (G. Poyner)
  970713.338   110  (R. J. Modic)
  970714.072   109  (G. Poyner)
  970719.066   110  (G. Poyner)
  970720.058   110  (G. Poyner)
  970720.749   111  (T. Watanabe)
  970722.060   110  (G. Poyner)
  970726.017   110  (G. Poyner)
  970728.080   110  (G. Poyner)
  970728.985   113  (D. Gill)
  970729.044   110  (G. Poyner)
  970802.033   110  (G. Poyner)
  970802.767   112  (T. Watanabe)
  970807.039   119  (M. Biesmans)

   Quoted below is from "Call for monitoring of DY Per" disctributed in
[vsnet-alert 708] by Brian Skiff
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-alert/msg00708.html).

>      Appended below is a note extracted from the "chemically-peculiar cool
> stars" newsletter, which may be of interest to vsnet folks.  I don't expect
> that many readers will be able to do the spectroscopy, but prompt notification
> of the start up the expected decline later this year would be beneficial to
> professional observers.
>      I see from Gary Poyner's observation report from last night that DY Per
> is about mag. 10.5 visually.  What kind of shape are the comparison stars in?
>      For those who do not know him, Phil Keenan is the "K" of the MK spectral
> classification system.
> \Brian
> 
> +++++++++++++++++++++++++++
> 
> 
>              THE NEED FOR SPECTROSCOPIC OBSERVATIONS OF THE
>                      UNUSUAL VARIABLE STAR, DY PER
> 
>      Hoffmeister noticed the large amplitude of light variation of the
> star now known as DY Per as early as 1940, but it was only in 1994
> that Alksnis showed that the light curve made it very probable that
> DY Per belongs to the R CrB variables.  Long thought to be an R star,
> the spectrum has recently been reclassified to C-Hd 4+ C2 6.5 on the
> Revised MK system.
> 
>      DY Per is perhaps the coolest R CrB variable known, though our
> knowledge of it is based on only a few spectra.  The mean period was
> established by Alksnis as 792 days, but the intervals between the deep
> minima may vary from 630 to 934 days.  Dr. Alksnis has kindly informed
> us that if DY Per continues to behave as it has during the last few
> cycles, the next sudden drop to minimum might occur near the beginning
> of October, 1997.  The decline, however, could begin as early as July,
> or as late as November.
> 
>      It is obviously difficult to catch the star just as it starts to
> fade, but observations during the first few weeks of the decline would
> be particularly valuable, for R CrB variables commonly show a spectrum
> of many sharp emission lines just at that stage.  Because the strong
> absorption by bands of C2 and CN obliterate most of the atomic lines
> in the yellow and red regions, it would be desirable to observe the
> spectrum in the blue region.  This will not be easy, since the photo-
> graphic magnitude even at maximum light is near 13.5, but observations
> at any dispersion would be valuable.
> 
>                                          Philip C. Keenan
>                                          The Ohio State University

Regards,
Taichi Kato

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