[vsolj-alert 20] Outburst of RX J0757.0+6306

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Outburst of RX J0757.0+6306

RX J0757.0+6306 のアウトバースト

　伊藤　弘さん（東京）の報告によれば、ROSAT衛星の発見した激変星で、軌道周期
　が非常に短いことから、WZ Sge型矮新星（アウトバーストのきわめてまれなSU UMa
　型矮新星）の可能性が指摘されていた RX J0757.0+6306 がアウトバーストしてい
　る模様です。もし確認されればこの天体のアウトバーストの記録としては初めて
　のものになります。

　以下 vsnet-alert への情報です。

Outburst of RX J0757.0+6306

   H. Itoh (Tokyo, Japan) communicates that the cataclysmic variable
(possible SU UMa-type or DQ Her-type) RX J0757.0+6306 is undergoing an
outburst.  Recent observations:

  YYMMDD(UT)   mag  observer
  971202.672  <137  (T. Watanabe)
  971202.794  <146  (H. Itoh)
  971203.015  <155  (G. Poyner)
  971203.674  <135  (T. Watanabe)
  971204.530  <133  (T. Watanabe)
  971205.667  <142  (T. Watanabe)
  971205.860  <131  (H. Itoh)
  971212.866   129  (H. Itoh)

  The following information is from the vsnet-chat log.

(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-chat/msg00662.html)
> Date: Thu, 9 Oct 1997 12:22:48 +0900 (JST)
> From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
> Subject: [vsnet-chat 662] RX J0757.0+6306
> 
>   According to "Astronomical Time Series" (ed Maoz et al. 1997, Kluwer
> Academic Press) p.195, Tovmassian et al. identified the ROSAT source
> RX J0757.0+6306 (=1RXS J075700.5+630602) as a new, ultrashort-period
> cataclysmic variable.  The orbital period is 75+/-1.4 min.  The optical
> spectrum shows strong hydrogen emission lines, resembling that of WZ Sge.
> Tovmassian et al. discussed in this paper the possibility of a DQ Her type.
> This star may be worth monitoring for possible future outbursts.
> 
>   The paper did not mention the accurate coordinates, but watching at
> the ROSAT position (07h 57m 00s.5, +63o 06' 02" 2000.0) might be sufficient.

(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-chat/msg00663.html)
> Date: Thu, 9 Oct 97 23:38:25 PDT
> From: Gaghik Tovmassian <gag@bufadora.astrosen.unam.mx>
> Subject: [vsnet-chat 663] RX J0757+6306 (Tovmassian)
> 
> Dear VSNET fans,
> 
> I'm readily support Taichi's call for monitoring 
> RX J0757+6306. Indeed this system has all chances to
> turn into another WZ Sge system or proof to be 
> the shortest period Intermediate Polar.
> Briefly what we know about this system:
> a. It is X-ray source, not much known about spectra or variability in X-rays.
> b. Optical Spectroscopy indicates CV nature with prominent accretion disk 
> 	and hot spot.
> c. Period derived from the S-wave radial velocity variations is
> 	most probably 81 minutes (+/- 5 min are not excluded).
> d. The limitted photometry shows no eclipsing, high amplitude flickering
> 	light curves. On 4 ocassions out of 5, significant signal was recorded
> 	at frequency corresponding to 8.5 min  oscillations.
> e. No outburst history is available at the moment.
> 
> The POSS measurments of coordinates and magnitude are as follows:
> RA 07h57m01.3s  DEC +63d06m01s   2000.0   16.06 (red)
> 
> The identification chart is posted to VSNET separately.
> The system was reported by Tovmassian et al. in  Proceedings of 
> Symp. dedicated to 25th aniversary of Wise observatory
> "Astronomical Time Series" (ed Maoz et al. 1997, Kluwer Academic 
> Press) p.195
> and 13th NorthAmerican Workshop on Cataclysmic Variables,
> in press.
> 
> Regards, Gaghik Tovmassian
>  OAN, IAUNAM, Mexico

(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-chat/msg00664.html)
> Date: Fri, 10 Oct 1997 16:25:06 +0900 (JST)
> From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
> Subject: [vsnet-chat 664] RX J0757+6306 chart
> 
> Dear Colleagues,
> 
>     I have put the finding chart of RX J0757+6306 kindly provided by
> Dr. Tovmassian on the VSNET WWW/ftp.  The JPEG file is at the URL:
> 
> http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/CVs/RXJ0757/rxj0757p63_fchart.jpg
> 
>     Please monitor this object, and report your (either positive or negative)
> observations to vsnet-obs.
> 
> Best regards,
> Taichi Kato

   Confirmation is most urgently requested; follow-up high-speed photometry
is also urgently requested.

Regards,
Taichi Kato

　軌道周期の発見者自らの情報によれば、軌道周期は８１分と、通常の激変星軌道
　周期としては最短のグループに入ります。今回のアウトバーストが、静穏光度
　（16等）より３等しか明るくない点はやや気がかりですが、もしスーパーアウト
　バーストであるならば、８１分よりもやや長い周期のスーパーハンプ現象が観測
　できると期待されます。確認観測と、ＣＣＤ等による連続測光が望まれます。
　光度は十分明るいので、積分時間は２０−３０秒程度が適当でしょう。

　天体同定用チャートは

http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/CVs/RXJ0757/rxj0757p63_fchart.jpg

　にあります。

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　加藤太一

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