V589 Her - A new SU UMa type dwarf nova in the period gap

V589 Her (= S 10296), located at RA = 16h22m07.19s, Dec =  +1922'36,3" (J2000.0) is classified as a UG-type cataclysmic variable with a magnitude range of 14.1p - <17.5p. The object is having infrequent outbursts, and is subject to few detailed studies only. As an illustration : only two outbursts of the object were reported in 1999 and 2000 to VSNET. The spectrum of the object was determined by Szkody & Howell (Szkody, P. and Howell, S.B. 1992, ApJS, 78, 537).

Earlier attempts to detect superhumps in this system were unsuccessful (e.g., see my July 2001 observations).

On 2002, April 4.344 UT, Mike Simonsen (USA) announced his visual detection of an outburst of V589 Her. The Kyoto observing team reported the observation of 0.1 - 0.15 mag modulations (vsnet-campaign-dn 2257), an the possible existence of an eclipse-like dip, based on a 1.4 hours run obtained on Apr 5, 2002.

I started a 3.1 h (unfiltered) CCD photometry session of V589 Her, on April 05/06, 2002 at CBA Belgium Observatory. As usual, a 0.35-m f/6.3 telescope and ST-7 CCD were the main equipment. Weather conditions during the observing session were moderate : clear skies but heavy winds. The light curve (fig below) showed a periodic modulation with a 0.12 mag amplitude, as was also announced by the Kyoto team, but did not confirm the eclipse-like dip reported by the Kyoto staff. This first observing session was too short to firmly conclude on the nature of the modulation (vsnet-campaign-dn 2265).

On April 06/07, 2002, sky conditions were perfect over Belgium, and this allowed me to follow V598 Her during 6.1 hours (unfiltered CCD photometry). This time, the light curve (below) clearly showed the presence of superhump-like modulations with an average amplitude of 0.1 mag. The object was reported at mag 15.3C, and was already fading from its superoutburst (about 0.2 mag fainter than on Apr 05/06).

I had another clear observing night on April 07/08, 2002, during which I could successfully follow V589 Her. The object again had faded compared to the previous night (average unfiltered mag : 15.6C), and I had to use substantially longer exposure times to generate sufficient 'counts'. The resulting light curve (below) still shows the existense of 3 superhumps, although less qualified than on the previous two nights.

Meanwhile, I also received two good quality data sets of V589 Her time-series photometry observations from Jerry Foote (CBA Utah).

When combining his data set with my available V589 Her data (a total of 841 observations), I obtain a firm superhump period of 0.0947 +/- 0.0005 d, using the PDM technique. This turns V589 Her into a UGSU type dwarf nova inside the so called 'period gap' ! 

The periodogram and phase diagram below are derived from the combined observations (CBA Belgium - CBA Utah)

On 2002, Apr 08.93 UT, the object had faded to (unfiltered) mag 16.2.

V589 Her period analysis based on 841 observations


V589 Her phase diagram


Note : In a recent vsnet message (vsnet-campaign-dn 2270), Taichi Kato remarks that the small amplitude of the system (about 3 mag) might be too small for an SU UMa-type of object. However, there may be a possibility that the true quiescence of V589 Her is fainter than what was inferred from DSS/USNO/ Henden magnitudes, or that the present modulations have a different nature from usual superhumps (lower amplitude, more irregular profile). In the latter case, the object might be an unusual SU UMa-type system.





Copyright © 2002 - Tonny Vanmunster.