NSV 09923 outburst!
As reported by Rod Stubbings in [vsnet-outburst 5689], a star has brightened at the position of NSV09923.
> A star has brightened at the position of NSV09923 can someone confirm? > > NSV09923 030628.446 140 Stu.RASNZ > NSV09923 030628.465 140 Stu.RASNZ (vsnet-obs 45665)This object was recognized during the identifications of NSV objects against ROSAT X-ray source (Kato 2000, vsnet-id-rosat 11). The proximity of the ROSAT position to the NSV position suggests that the object may be a dwarf nova, as we have seen in an excellent case in NSV 10934.
The "outburst" has been confirmed by Berto Monard (vsnet-outburst 5691):
> A star has obviously brightened. Its position is somewhat South of the > one given by the SIMBAD database. It's difficult to estimate the > brightness but it could be around magnitude 14CR (compared to about 16 > on the DSS image).The object has been monitored by Rod Stubbings since 2001 (54 observations), and this is the first outburst detection.
These observations seem to have confirmed the dwarf nova-type (or other kind of CV-type) nature of this object. Since the ROSAT position is slightly south to the NSV original position, Berto's finding seems to further support the identification.
NSV: 175917.1 -423504 (2000.0) NSV09923 ? 14.2 (15.5 P ROSAT: 175914.4 -423528 (2000.0) 1RXS-F_J175914.5-423529 0.095 0.83 0.08Further observations (time-resolved photometry and spectroscopy) are most urgently encouraged! We will prepare a special page when Berto's (or other observer's) images becomes available.
Regards, Taichi Kato VSNET Collaboration team
Images taken last night showed the reported object at a constant and not modulating brightness of around 14.2CR measured against reference stars from uCAC1.
Basic astrometry showed this object at position (2000)
17 59 16.53 -42 35 07.3
which is very likely coinciding with a star from the uSNO-A2.0 catalogue at position
17 59 16.521 -42 35 06.85
This catalogue gives 18.3B / 17.5R as magnitudes.
The following unfiltered CCD observations are reported:
NSV 09923 20030628.810 14.3CR MLF NSV 09923 20030628.861 14.2CR MLF Berto Monard Bronberg Observatory / CBA Pretoria
The object can be identified with a "blue" object on 2MASS images. This quiescent color probably excludes a red variable (or even a reddened usual variable). The object is likely a dwarf nova in outburst. The relatively small amplitude and the apparent lack of superhumps (still in need of further observation) seem to suggest that the object is an SS Cyg-type dwarf nova. If this is the case, the blue 2MASS color seems to suggest a short orbital period -- somewhat unusual if the recorded low outburst frequency is verified.
Regards, Taichi Kato VSNET Collaboration team
Hi,
contrary to my earlier report, it is very probable that NSV 9923 shows an oscillating light curve.
By removing unreliable run data (80% of the images were cloud affected), it is clear that the brightness points indicate a possible oscillation. For proper quantification it would be of interest that further timeseries photometry are conducted, especially at other longitudes, as CBA Pretoria might be clouded out.
Regards,
Berto Monard Bronberg Observatory / CBA Pretoria(vsnet-alert 7791)
Seven hours of unfiltered photometry show distinct superhumps in the lightcurve of NSV 09923.
The present s/h period is just under two hours (0.8285 day). The hump amplitude is around 0.3 CR.
Berto Monard Bronberg Observatory / CBA Pretoria
NSV 09923: superhump period
From Monard's data, we have yielded a superhump period of 0.0819(4) d. There is also strong indication of quasi-periodic oscillations (QPOs) with periods of 25 min near the superhump minima. The object now makes the second SU UMa-type dwarf nova discovered by the VSNET team from a systematic correlation search between NSV and ROSAT sources, and from intensive visual monitoring by Rod Stubbings. Congratulations to all!!
The measured superhump period is not particularly unusual for an SU UMa-type dwarf nova, but the apparently low outburst amplitude looks unusual, as already described in the earlier posting. It may be possible that the true quiescence is fainter than has proposed; intensive astrometry and quiescent identification is now being undertaken by Yamaoka-san.
The object, suitably situated, is the current first priority target in the south for the VSNET Collaboration!!
Regards, Taichi Kato VSNET Collaboration team
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