THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
INTERNET: aavso@aavso.org
Tel. 617-354-0484 FAX 617-354-0665
AAVSO ALERT NOTICE 251 (August 28, 1998)
1903-50 SUPERNOVA 1998dq IN NGC 6754
We have been informed by the Central Bureau for Astronomical Telegrams (IAU
Circular 6998) that Brett White, Linden, New South Wales, Australia, has
visually discovered a supernova about 18" west of the nucleus of NGC 6754 on
August 23.4 UT using a 0.41-m reflector.
Visual confirmation was obtained by R. Evans, Hazelbrook, NSW, who observed the
supernova at visual magnitude 14.3. B. Schmidt, Mt. Stromlo and Siding Spring
Observatories (MSSSO), reported that B. Crook used the MSSSO 0.76-m telescope
to obtain CCD BVRI images on August 23.6 UT that showed a new blue object
18.7" west and 5" north of the galaxy nucleus. Schmidt reports a precise
position of the supernova as:
R.A. = 19h 11m 23.78s Decl. = -50 degrees 38' 25.5" (equinox 2000)
Additional observations reported (IAU Circular 6998) include T. Dobosz, Nepean
Astronomy Centre, who obtained an image on August 24 UT showing a new star 20"
west of the galaxy nucleus, and A. Gutierrez, who used the MSSSO 0.76-m
telescope on August 24.6 UT to obtain CCD images which showed the object.
The supernova, which is located about 5" from SN 1998X, is definitely a new
object and is very blue (B-V ~ 0). Inspection of the discovery images of SN
1998X show that the object was not present on March 13.9 UT down to magnitude
R = 18 (IAU Circular 6998).
Spectroscopic confirmation was reported by F. Patat and P. Leisy, European
Southern Observatory, and A. Piemonte, Pontifica Universidad Catolica (Chile),
who obtained a CCD spectrogram on August 27.00 UT using the ESO 3.6-m telescope
+EFOSC2. Their reduced spectrogram indicates that SN 1998dq is a Type Ia
around maximum light, and is very similar to SN 1998D (IAU Circular 7000).
Additional observations of SN 1998dq reported to the AAVSO include August
27.76 UT, 13.9, L. Monard, Pretoria, South Africa; 27.83, 13.9, Monard.
Accompanying is an AAVSO preliminary 'e' scale chart of NGC 6754, showing the
location of the supernova, prepared by C. Scovil. Please use this chart to
observe 1903-50 SN 1998dq, and report your observations to AAVSO Headquarters,
making sure to indicate which comparison stars you used to make your magnitude
estimates.
Congratulations to Brett White on his discovery!
RARE OUTBURST OF THE TOAD-TYPE CATACLYSMIC VARIABLE 1626+21 V592 HERCULIS
We have been informed by Timo Kinnunen, Espoo, Finland, that he observed the
cataclysmic variable V592 Her in outburst at visual magnitude 12.0 on August
26.835 UT. Confirming observations were reported by Lance Shaw, Pinole, CA,
and Gene Hansen, Cave Creek, AZ.
Observations reported to the AAVSO include Aug 24.901 UT, <15.3, G. Poyner,
Birmingham, England; 25.90, <13.2 (Guide Star Catalog sequence), P. Schmeer,
Bischmisheim, Germany; 26.835, 12.0, T. Kinnunen, Espoo, Finland; 26.862, 12.3,
Kinnunen; 26.915, 12.5, Kinnunen; 27.181, 13.0, L. Shaw, Pinole, CA; 27.1917,
13.0, G. Hanson, Cave Creek, AZ; 27.269, 13.0, Shaw; 27.852, 13.5, Poyner;
27.892, 13.2 (vsnet sequence), Kinnunen; 27.908, 13.3, Schmeer; 28.0507, 13.5,
J. Bortle, Stormville, NY; 28.233, 12.9, Shaw.
This outburst is only the third one reported for V592 Her since its discovery
as a variable star in 1968 by G. Richter. Previous confirmed outbursts
occurred in June 1968 (photographic magnitude 12.3) and May 1986 (photographic
magnitude 13.6), and were reported by G. Richter in IBVS Nos. 293 and 3619,
respectively.
V592 Her has been classified as a TOAD (Tremendous Outburst Amplitude Dwarf
Nova). TOADs are cataclysmic variables similar to SU UMa systems in that they
have superoutbursts and exhibit superhumps when in outburst; characteristics
that set them apart from other dwarf novae include having an outburst amplitude
greater than 6 magnitudes, very low luminosity at minimum, and superoutbursts
that occur at intervals of months to tens of years. Comprehensive sources of
information on TOADs include the article by S. Howell, P. Szkody, and J.
Cannizzo in Astrophys. J., 439, 337 (1995) and the web site
(URL http://wapiti.uwyo.edu/toad) created and maintained by the TOAD Group at
the University of Wyoming and directed by Dr. Steve Howell.
Observers are strongly urged to monitor V592 Her very closely visually and
photometrically throughout its rare outburst. Observers with large telescopes
and CCDs are also urged to continue to monitor this star after it returns to
quiescence.
Accompanying are revised AAVSO preliminary 'b', 'd', and 'e' scale charts of
V592 Her prepared by C. Scovil. Please use these charts to observe V592 Her
and report your observations to AAVSO Headquarters. Please be sure to indicate
which comparison stars you used to make your observations.
Congratulations to Timo Kinnunen on his discovery of the rare outburst of this
most interesting system!
FADING OF 1544+28A R CORONAE BOREALIS
We have been informed by our observers that R Coronae Borealis, the prototype
of the R CrB stars, is fading. R CrB, which is at visual magnitude 6.0 at
maximum, is reported to be at magnitude approximately 6.8 as of August 28 UT.
The nearly 100 observations of R CrB reported by 30 observers worldwide to the
AAVSO International Database since the beginning of August indicate that this
star began to fade around August 16.
The last fading of this star occurred in September 1995 - December 1996, during
which R CrB faded to visual magnitude 13.7.
Fadings of R CrB are unpredictable both in duration and in the magnitude to
which the star may fade. Please monitor R CrB closely and report your
observations of this interesting star to AAVSO Headquarters until it returns to
maximum so we may inform the astronomical community. If you need paper copies
of the AAVSO charts of R CrB, please let us know; the charts may also be
downloaded from our ftp site or via our web site (please see below).
REQUEST FOR OBSERVATIONS OF 0409-71 VW HYDRI AND 0749+22 U GEMINORUM
Astronomers at the University of Leicester, England, and the University of
Utrecht, The Netherlands, have requested our assistance in monitoring the
cataclysmic variables U Gem and VW Hyi in the coming months. During the
interval September 19-November 19, 1998, the astronomers are planning to
observe U Gem with the European x-ray satellite SAX [BeppoSAX] if the star goes into
outburst. If U Gem does not have an outburst during this interval, they plan
to observe VW Hyi in outburst instead.
From now through November, please monitor U Gem and VW Hyi closely, and inform
us immediately if you see either of them go into outburst, i.e., for U Gem, if
it becomes magnitude 13.3 or brighter, and for VW Hyi, if it becomes brighter
than magnitude 13.0. If either star goes into outburst, please monitor it
throughout the outburst and after it returns to quiescence, so we may provide
the astronomers with information about these stars' behavior throughout the
entire interval in which they are interested. Your timely notification to
AAVSO Headquarters of the start of outburst is essential to the success of
this observing run.
If you need paper copies of the AAVSO charts of U Gem, please let us know.
Regarding VW Hyi, please let us know if you need the AAVSO 'b' scale chart or
the Royal Astronomical Society of New Zealand (RASNZ) 'b' scale chart with a
letter sequence that has been converted to magnitudes down to 13.5. The charts
may also be downloaded from our ftp site or via our web site (please see below).
CHARTS AVAILABLE ON AAVSO WEB AND FTP SITES
Chart links obsolete, 11/2013: Create charts using VSP at http://www.aavso.org/vsp
Electronic copies of the AAVSO charts of SN 1998dq, V592 Her, R CrB, VW Hyi,
and U Gem and the RASNZ chart of VW Hyi mentioned in this Alert Notice are
available through our web site at the following address:
http://www.aavso.org
All of these charts may also be obtained directly from our FTP site:
ftp.aavso.org (198.116.78.5), in /pub/alerts/alert251/
Alternatively, the charts for R CrB, VW Hyi, and U Gem may be obtained from
our charts ftp site:
charts.aavso.org (198.116.78.5), in
/CRB/R_CRB/
/HYI/VW_HYI/
/GEM/U_GEM/
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
observations@aavso.org.
Many thanks for your valuable astronomical contributions and your efforts.
Good observing!
Elizabeth O. Waagen, Senior Technical Assistant
on behalf of
Janet A. Mattei, Director
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