Superoutburst of the eclipsing dwarf nova XZ Eri

(XZ Eri in superoutburst)

Background Information

XZ Eri: eclipsing dwarf nova below the period gap

According to astro-ph/0107505, Patrick Woudt and Brian Warner found that XZ Eri is an eclipsing dwarf nova with a period of 88.1m. A very excellent candidate for an eclipsing SU UMa-type system!

Please monitor this object closely, and let's start intensive photometry during outburst! Outbursts of XZ Eri (apparently superoutbursts) have been observed roughly once a year (but none was observed during the last season).

Regards,
Taichi Kato
VSNET Collaboration team

(Donn Starkey's image)

Outburst!

(vsnet-alert 7619)

Dear Colleagues,

Rod Stubbings reported that the eclipsing dwarf nova XZ Eri is undergoing an outburst.

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Subject: [vsnet-outburst 5125] XZ Eri outburst

XZ Eri is in outburst.

ERIXZ          030127.476   150  Stu.RASNZ                          
ERIXZ          030127.521   150  Stu.RASNZ 

===

The object has an orbital period of 0.0612 d (Woudt and Warner 2001, MNRAS 328, 158). The object is thus most likely an SU UMa-type dwarf nova! Although the present magnitude is fainter than the past likely superoutbursts, the lack of recent outbursts makes the present outburst a good candidate for detailed photometric observations! Please observe the target as long as possible (preferably more than 2 orbital cycles). Use short exposure times (less than 1 min) to resolve eclipses. Observers with a larger aperture may try high-speed photometry, with exposure times less than 10s.

XZ Eri is located at 04:11:25.76 -15:23:24.3 (J2000.0), so sufficient coverage can be expected even at medium northern latitudes.

The object is now the prime target for the VSNET Collaboration!

Regards,
Taichi Kato
VSNET Collaboration team

(vsnet-campaign-dn 3356) XZ Eri: the outburst continues

The Kyoto team started time-series observation at 11:20 UT on January 28. The object is still in outburst at about 15.0mag, which indicates no rapid fading. Follow-up observations are encouraged.

Regards,
Makoto Uemura

Superhumps and Eclipses!

(vsnet-alert 7620)

XZ Eri: superoutburst of the eclipsing SU UMa-type dwarf nova!

Dear Colleagues,

We have just received observations from Greg Bolt (Jan. 28). The data clearly show the presence of ~0.4 mag superhumps (having the most likely period slightly longer than the orbital period).

The data also show shallow eclipses, which resemble the eclipses observed during the first night of a superoutburst of DV UMa (see http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/dvuma9912.html). It is likely that either the maximum expansion of the disk or the slightly low orbital inclination is responsible for the shallow eclipses. Anyway, XZ Eri is now established to be an eclipsing SU UMa-type dwarf nova (UGSU+E)! Among eclipsing SU UMa-type dwarf novae, XZ Eri has the shortest orbital period (except for the shallow eclipser WZ Sge). SU UMa-type dwarf novae with similar orbital periods are known to show unusual features, such as post-superoutburst rebrihtening, increase of the superhump periods, regrowth of the superhump amplitude during the late stage of superoutbursts, etc. The discovery of an eclipsing object in this period region will provide us important clues to understand these still poorly understood phenomena, by applying spatial resolution techniques (e.g. eclipse mapping) to the outbursting or superhumping accretion disk.

We have also received reports of successful observations from Torii-san (RIKEN), Tanabe-san (VSNET Okayama Station), and naturally by the Kyoto team. We will soon be analyzing the entire data. Further observations are *most definitely* encouraged!!

We will prepare a VSNET page in due time (will be http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/xzeri.html). Please visit this page and share the wonder of the cataclysmic variable!

Regards,
Taichi Kato
VSNET Collaboration team

Flashing superhumps and eclipses!

(see vsnet-alert 7621 for a full text)

Dear Colleagues,

We have received new data from Greg Bolt. The data on January 29 very clearly show the emergence of narrow eclipses (depth ~0.4 mag) and superhumps. This observation has clearly confirmed that XZ Eri is one of rare short-period SU UMa-type dwarf novae showing deep eclipses even during a superoutburst. The light curve (will be posted on the VSNET page later) resembles that of DV UMa.

From two-night observations, we obtained a superhump period of 0.06289(6) d, which is 2.7% longer than the orbital period. If this period holds during the entire superoutburst, the fractional superhump excess is unusually large for this orbital period. However, this value needs to be treated with care, since there is increasing amount of evidence that some SU UMa-type dwarf novae show rapid period changes during the early stage of a superoutburst.

Preliminary eclipse predictions are given below. Because of the uncertainty of the period, and the systematic and random variations of the eclipse timings during a superoutburst, the ephemeris will have a substantial (minutes?) errors. I will update the ephemeris when new period determination becomes possible.

The campaign has been very successful. We have received and obtained a large amount of data, and have received successful reports. The present report only illustrates a very early part of the entire analysis!

Please continue observing XZ Eri as densely as possible - our experience shows that maximum recommended integration time is 60-90 s, in order to catch the eclipse profile (a shorter integration time is naturally preferred for a larger instrument). Good luck with your observation!