Superhumps in EG Cnc

Outburst and quiescent CCD images taken at Ouda Station

(quiescent image: 1995 Nov. 16)

(vsnet-alert 607, 1996 Dec. 4)

We obtained a continuous (four hours) CCD V-band light curve of EG Cnc last night. The observed light curve shows superhumps with a low amplitude, approximately between 0.03 and 0.04 magnitude. A preliminary analysis yielded a period of 0.058 day, which is one of the shortest known among dwarf novae.

The long interval of outbursts and the large amplitude support the WZ Sge-type classification of EG Cnc; the observed doubly-humped feature of superhumps strongly suggests that the object was observed in the earlier stage of a superoutburst. Further follow-up observations are encourged.

Regards,
Katsura Matsumoto (Osaka Kyoiku Universiry, Japan)
e-mail: katsura@quasar.cc.osaka-kyoiku.ac.jp

(vsnet-alert 610, 1996 Dec. 6)

                EG CANCRI, A SHINY NEW WZ SAGITTAE STAR

We have obtained time-series photometry of EG Cnc on each night (December 1-5) since Schmeer's exciting recovery of the star after its 19-year slumber. We used data from four stations of the Center for Backyard Astrophysics (CBA), and added brief coverage from the Cerro Tololo 1-m telescope. The star continues a linear decline at 0.12 mag/night, and was at V=12.83 on December 5.3 UT. During December 1-3, the star showed a periodic modulation at 0.0572+-0.0002 d, with ever-decreasing amplitude (averaging .03 mag peak-to-trough). On December 4-5, the signal weakened further and disappeared into the noise.

This is reminiscent of AL Com, which had a large outburst in April 1995 after a 20-year quiescence. AL Com showed an "outburst orbital hump" exactly at Porb for the first 5 days, then lost periodic signals for 4 days until the main superhumps (at Porb + 1.1%) appeared suddenly and with large amplitude on day 10. Those superhumps rumbled through the light curve for at least another month.

It's still too early to know how extensive the resemblance is. But so far, the outburst of EG Cnc is distinctive for the *smallness* of the photometric waves, and for their rapid disappearance even while the star remains bright. It's tempting to guess that the 82.4 min waves reported here (and by Matsumoto in vsnet-alert 607) aren't the real superhumps, but some sort of "warm-up" for the real thing which is still a few days away. They're really just not sufficiently "super": quite small, and no provable displacement of period from Porb since the latter is completely unknown.

I would bet dollars to doughnuts (American phrase; translates well enough, I guess, since dollars are a strong currency) that EG Cnc will grow strong genuine superhumps within a few days. This would offer a great chance to watch the growth of superhumps in real time, which is very rarely possible since there is seldom much warning for these things. At magnitude 12.8 and decently placed in the night sky, the star could provide a historic opportunity for learning the timescale of superhump growth, an important subject poorly constrained by observation or theory.

So shrug off that morning frost and get thee to a telescope! And we would be absolutely delighted to hear from observers who manage to obtain any time-series photometry.

Joe Patterson, Jonathan Kemp           David Harvey
CBA-New York                           CBA-Tucson

Tonny Vanmunster      David Skillman      Seiichiro Kiyota
CBA-Belgium           CBA-Maryland        CBA-Tsukuba

(vsnet-alert 612, 1996 Dec. 6)

Congratulations to K. Matsumoto and the CBA team on their independent discoveries of "superhumps" (regardless of oribital or genuine). The short period and large outburst amplitude (~7.2 mag) strongly favor EG Cnc as a new member of WZ Sge, while the development of "outburst (super)humps" still needs to be more carefully treated, since at least some of "more usual" SU UMa-type stars definitly show ever-decreasing -- even nearly disappering -- amplitudes of superhumps while they are still in their plateau stage. Watanabe's sighting (vsnet-alert 601), and one more sighting by N. Makiguchi may be suggestive of existence of normal outbursts -- more resembling long outburst-cycle SU UMa-type dwarf novae like V1028 Cyg? In these cases double-humped low amplotude modulations also appeared in the earliest stage of a superoutburst, which seem to differ from early superhumps in "genuine" WZ Sge stars in that the modulations do not always seem to represent orbital periods: sometimes longer than the later superhump period. Although I strongly expect and favor everything WZ Sge or AL Com in EG Cnc also, the truth should lie in the course presently ongoing. Huruhata's 1977 record suggests the star may show a plateau or a halt at around eight days after the maximum; a 0.3 mag short-term variation in his record may be indicative of fully grown superhumps, considering the accuracy of his photographic measures. The wavefront of the waited signal may be just intruding the solar system.

Regards,
Taichi Kato

(vsnet-alert 613, 1996 Dec. 6)

I had submitted the following article to IAUC.

EG CANCRI

K. Matsumoto, Osaka Kyoiku University, Japan, reports: "We obtained continuous CCD V-band light curves of EG Cnc on Dec. 2.625-2.791 UT and Dec. 3.625-3.708 UT with a 51-cm reflector at Osaka Kyoiku University. The observed light curves revealed suprehumps with a low (0.03-0.04 mag) amplitude. A preliminary analysis for combined light curves yielded a period of 0.0582 day, which is one of the shortest known among dwarf novae. The long interval (last ouburst: Nov. 1977) and large amplitude (more than 7 mag) of outbursts, together with the short superhump period, support the WZ Sge-type classification of EG Cnc."

With best wishes,
Katsura Matsumoto (Osaka Kyoiku University, Japan)

Development of "true" superhumps

(vsnet-alert 615, 1996 Dec. 7)

THEY have arrived.

The photometric waves in EG Cancri that Taichi Kato sensed as they were passing Pluto (how does he get his information?).

During a CBA-Maryland run of six hours centered on December 5.35 UT, the waves were at 0.027 mag and slightly growing. A Cerro Tololo observation on December 6.3 showed that the amplitude had grown to 0.13 mag (at V=13.0), and on December 7.3 it had grown further to 0.18 mag while the star had brightened to V=12.5. The period was probably 0.0606+-0.0002 d, with a chance of really being 0.0645 d, the one-day alias. In either case, quite a bit longer than the period(s) reported a few days earlier.

Won't you join us in watching this fascinating little star which is likely to teach us a lot during its four weeks of fame...


                 Joe Patterson, Jonathan Kemp, Dave Skillman


                          BigApple
             Centers for             Astrophysics  (CBA subsidiaries)
                          Basement

Confirmation of superhumps in EG Cnc

(vsnet-alert 616, 1996 Dec. 7)

Dear colleagues,

We (Ouda team) have carried out time-resolved photometry of EG Cnc from Dec. 7.68 to 7.81 at Ouda Station using a 60-cm reflector + CCD + Johnson V filter. A preliminary analysis using PDM method gives 0.061 (+- 0.001) d as the best estimated period, confirming the period reported by Patterson et al. (vsnet-alert 615). Superhumps have grown to 0.20 mag.

Best regards,
Daisaku Nogami

(vsnet-alert 618, 1996 Dec. 7)

We obtained a 5 hr, V-band CCD run on EG Cnc during the hours 8.4 - 13.4 UT on Dec 7. A total of 4 SH maxima and 3 SH minima (full amplitude 0.18 mag) were observed and yield a superhump period of 0.0604 (+-0.0002) days -- consistent with the periods reported in vsnet-alerts 615 and 616.

Allen Shafter (e-mail: shafter@proteus.sdsu.edu)
Scott Dahm
Hye-kyung Lee

(vsnet-alert 619, 1996 Dec. 8)

We obtained a second night (6 hr) V-band CCD run on EG Cnc during the hours 7.2 - 13.4 UT on Dec 8 using the Mount Laguna 1-m. An additional 4 maxima and 5 minima (full amplitude now 0.13 mag) were observed. When combined with last night's data (vsnet-alert 618) the SH period remains 0.0604 (+- 0.0001) days.

Allen Shafter
Scott Dahm
Hye-kyung Lee