[vsnet-id 309] Re: DV Dra

[Taichi Kato <tkato>]

Dear Prof. Samus,

> I have a question concerning your paper "The 1995 Outburst of DV Dra"
> (IBVS, 1995, No. 4279). In the paper, you quote the coordinates of the
> star (18h17m24s.44 +50deg48'16".6, 2000) you report to have been observed
> in a new outburst. We possess the discovery plates used by Pavlov and
> Shugarov (Astron. Tsirk., 1985, No. 1373), clearly showing DV Dra in
> outburst at a position different from yours; our photographic astrometry
> of DV Dra gives the coordinates 18h17m23s.10 +50deg48'18".08, 2000.0, ep.
> 1984.433. Your VSNET light curve clearly shows variations. Either you
> observe another star, or your published position is in error. Can you
> kindly comment?

   The matter had been discussed in vsnet-id 182 and 183 (attached below).
Now it is evident that the true DV Dra is different from that reported
in IBVS 4279.  The most likely explanation is that the detected object
(not DV Dra) is a red star, which appeared bright on Iida's unfiltered
CCD images.  He made many negative observations in 1994 and 1995, but they
did not reach the detection magnitude.  It looks most likely this star
is at the very limit of Iida's system, which made a transient positive
detection.  The two V-band observations made at Ouda Station both showed
V=18.6 (as mentioned in IBVS 4279), which are consistent with the
likely conclusion that this star did not vary very significantly.
The single Ouda magnitude quoted in the VSNET observations (VSNET light
curve) doesn't seem to correctly reflect the published magnitude.
(The on-line light curve incorrectly referes to vsnet-obs 1595, which was
superseded by vsnet-obs 1605; I will correct this error and incorrect
Iida's entries).  In conclusion, ther was no true DV Dra outburst
in 1995 October-November.

Regards,
Taichi Kato

---

Subject: [vsnet-id 182] (fwd) On DV Dra identification

(fwd) On DV Dra identification

Date: Sun, 7 May 2000 20:51:36 +0300 (EET DST)
From: stars@personal.eunet.fi (Timo Kinnunen)
Subject: DV Dra id problem

  Hello,

  In the following message Kato-San wrote:

>[vsnet-obs 1605] DV Dra outburst, continuing?
>
>DV Dra
>
>    A 6-min V-band CCD exposure of DV Dra taken at Ouda Station last night
>clearly shows DV Dra (WZ Sge-type candidate) siginificantly brighter than
>in Downes & Shara (1993) chart.  Astrometry using 6 GSC stars (mean residual
>0".3) gives 18h17m24s.44 +50o48'16".6 (J2000.0).  This position is slightly
>different from that given in Downes & Shara (1993), but is in good agreement
>with one (18h17m24s.44 +50o48'16".3) obtained by M. Iida from his outburst
>CCD image (Iida, private communication).  Reanalysis of the Nov. 13 CCD
>image (already reported in vsnet-obs #1595, but the measurement was done
>for the coordinates by Downes & Shara (1993)) confirms this finding.


  The position given above, and also the SIMBAD position:
18 17 25.070 +50 48 14.50 (2000)
fall only a few arcseconds from an A2.0 star 1350.09592107
- at  18 17 24.71  +50 48 19.19  (2000)

  DV Dra can be very easily confused with this star - it is
certainly noteworthy, however I could not find any remarks on it
from 1995 outburst reports. Pardon me, I don't have the relevant
IBVS issue at hand, but I find it interesting that the outburst
photometry apparently was not disturbed by this A2.0 star.


>  Reexamination of POSS and the candidate by Downes &
>Shara (1993) in digitized GSC survey plate would help identifying the nature
>of this intriguing outburst.

  I checked the available POSS scans at USNO Flagstaff -
the following plate shows a DV Dra candidate some 10" due N
from this A2.0 star.
Details:

> POSSII 0229  SJ06278 1995.4976

see 5' square image at

  http://vsnet.nofs.navy.mil/tmp/fchaanCqa_sj0229.000.jpg

I believe the date is close to 1995 June 30 - about four months prior to
the outburst report by Iida, so it would be very intriguing to find out
whether the POSS-II candidate is true DV Dra, another variable,
or a plate flaw.

Regards,
Timo Kinnunen

Subject: [vsnet-id 183] Re: (fwd) On DV Dra identification

Re: (fwd) On DV Dra identification

>   DV Dra can be very easily confused with this star - it is
> certainly noteworthy, however I could not find any remarks on it
> from 1995 outburst reports.

   There was no USNO at that time, and we noticed, as already cited, a slight
difference in position from Downes & Shara (1993).  However, astrometry of
both observations were done near the limiting magnitude.  The question is
still open whether the USNO star is different from or identical with
the true DV Dra or the "outbursting object" in 1995.

   The chart in the original discovery announcement of DV Dra was not
good enough to discriminate such a subtle difference.  The second outburst
report contained no chart.

Regards,
Taichi Kato

VSNET Home Page

Return to Daisaku Nogami

---

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