THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
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AAVSO ALERT NOTICE 250 (June 18, 1998)
1726-19 NOVA OPHIUCHI 1998
We have been informed by the Central Bureau for Astronomical Telegrams (IAU
Circular 6941) that S. Nakano, Sugano, Japan, reports that Kesao Takamizawa,
Saku-machi, Nagano-ken, Japan, discovered a nova in Ophiuchus on June 15.561
UT at photographic magnitude 9.5, on two T-Max 400 exposures taken with a
0.10-m f/4.0 lens. No object was seen down to approximately magnitude 15 at
the location of the nova on 48 patrol exposures taken by Takamizawa between
17 February 1994 and 19 May 1998.
Visual confirmation was made by R. Kushida and Y. Kushida, Yatsugatake South
Base Observatory, Japan, who reported (IAU Circular 6941) that they obtained a
poor CCD image on June 16.531 UT, showing the nova at V magnitude 10.0:, and
at the following position (given with an uncertainty of 1 arcsecond or more,
average of three frames):
R.A. = 17h 31m 59.82s Decl. = -19 degrees 13' 57.0" (equinox 2000)
Positions were also reported by Takamizawa (IAU Circular 6941), Dalibor Hanzl,
Brno, Czech Republic, and R. A. Kowalski, Zephyrhills, FL (IAU Circular 6943).
These positions all agreed to within a second of Right Ascension and
Declination with the Kushidas' position above.
Spectroscopic confirmation was made by A. V. Filippenko, D. C. Leonard, and
M. Modjaz, University of California at Berkeley, and R. G. Eastman, Lawrence
Livermore National Laboratory, who obtained CCD spectra on June 18 UT using
the Shane 3-m reflector at Lick Observatory that indicated the object is a
nova. (IAU Circular 6943)
Additional observations of N Oph 98 reported (IAU Circular 6943) include:
June 17.971 UT, 10.32 CCDV, D. Hanzl (using GSC 6243.435 as comparison star);
June 18.244 UT, 10.4 CCD, R. Kowalski.
A red USNO A1.0 star of magnitude B = 18.0, R = 16.8 is located nearby at
R.A. 17h 31m 59.79s, Decl. -19 degrees 13' 55.0" (2000). Also, T. Kato, Kyoto
University, Japan, notes that the nova lies within the 16" error circle of
the ROSAT source 1RXS 173200.0-191349 (IAU Circular 6941).
Accompanying is a revised AAVSO preliminary 'b' scale chart of TW Ophiuchi,
showing the location of the nova. Please use this chart to observe 1726-19
N Oph 98, and report your observations to AAVSO Headquarters, making sure to
indicate which comparison stars you used to make your magnitude estimates.
Congratulations to Kesao Takamizawa on his discovery!
CHARTS AVAILABLE ON AAVSO FTP SITE
Chart links obsolete, 11/2013: Create charts using VSP at http://www.aavso.org/vsp 
Electronic copies of the revised AAVSO chart of TW Oph mentioned in this Alert
Notice are available from our FTP site:
ftp.aavso.org (188.8.131.52), in /pub/alerts/alert250/
ftp.aavso.org (184.108.40.206), in /pub/charts/oph/tw_oph/
The chart may also be accessed through our Web site at the following address:
The answering machine at AAVSO Headquarters is on nights and weekends for your
convenience. Please call our charge-free number (888-802-STAR = 888-802-7827)
to report your observations. We also encourage observers to send observations
by fax to 617-354-0665 or by e-mail through the Internet to
Many thanks for your valuable astronomical contributions and your efforts.
Elizabeth O. Waagen, Senior Technical Assistant
on behalf of
Janet A. Mattei, Director
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