Eclipse observations of DV UMa during outburst

First ever observations of eclipses of DV UMa during outburst

Discovery of the outburst

Dear Colleagues,

Tonny Vanmunster (Landen, Belgium) reports an extremely rare outburst of DV UMa. The observation has been confirmed by G. Poyner (Birmingham, England)....

Feb 25.844 UT              mv= <15.2   Poyner  40cm
    26.826                      14.6   Vanmunster  35cm
    26.840                      14.7   Poyner

TA Sequence 941025 used in all observations.

This star is on the recurrent objects programme of the UK Nova/ Supernovae patrol. Our database indicates that two outbursts have been observed in the past..

1946 Feb 14 mag 14.5
1953 Feb 13 14.6

If anyone has more historical information on outbursts, we would be very interested to hear it.

Needless to say, further photometry would be most useful.

Regards,

Gary Poyner

CVC 28 (Vanmunster)

Historical outbursts

The object was discovered by Usher et al. (1981) as an ultraviolet excess object. Following magnitude estimates from the archival plates were given. (Some of them have been already listed in CVC 28 by T. Vanmunster)

  1933 Jan 23 15.3+/-0.6   Feb 24 14:+/-1
  1938 Mar 25 <17.75       Nov 27 <17.75
  1939 Apr 15 18.4+/-0.3
  1945 Mar  7 <17.4
  1946 Feb  4 14.8+/-0.4   Feb  4 14.5+/-0.4
  1946 Feb  7 15.2+/-0.7
  1947 Mar 12 <16.7
  1948 Feb  9 18.7+/-0.4   Dec  4 <16.7
  1949 Mar 20 15.5+/-0.3
  1950 Mar  9 <16.0
  1952 Feb 29 <16.0
  1953 Feb 13 14.2+/-0.12
  1976 Jan 29 18.9+/-0.3
  1978 Feb  1 19.8+/-0.4   Feb  2 19.8+/-0.3
  1978 Feb  3 19.5+/-0.3   Dec  5 18.7+/-0.4
  1980 Apr 17 19.3+/-0.3   Apr 17 18.5+/-0.3
  1980 Apr 17 18.7+/-0.3

The object was subsequently idetified as an eclipsing cataclysmic variable by Howell et al. (1988). Their photometric observations showed deep eclipses (1.5 mag or more) with an orbital period of 0.08597 day. The quiescent magnitude outside eclipses was V=19.3, and V=18.6 at maximum of orbital humps. The eclipses lasted about 0.15 Porb ~ slightly shorter than 20 min.

The orbital period (just below the period gap!) strongly suggests that the object is an SU UMa-type dwarf nova with deep eclipses, the second known in the northern hemisphere (the first one is well-known HT Cas). Since no outbrust has been reported since the discovery, the persent outburst provides not only the long-awaited opportunity to examine the eclipses of this interesting dwarf nova during outburst, but also the long-awaited detection of superhumps if the present outburst is a super- outburst. The historical outburst in 1946 looks like a superoutburst. The magnitude reported by Vanmunster & Poyner rivals that of the 1946 outburst. Therefore there would be a good chance that the present outburst is also a superoutburst.

One thing should be mentioned concerning the outburst frequency (or the duty cycle). Howell et al. (1988) examined 15 Harvard plates and detected DV UMa brighter than 16 mag in seven occasions. Similar frequency could be found in the estimates by Usher et al. (1981). Such high frequency of outbursts seem to have never observed in recent years, as Vanmunster and Poyner have already pointed out. We have also a number of CCD photometry of this system, but an outburst was never met. Has anything occurred in this system which has modified the outburst frequency? Anyway, all sorts of observations are most emergently needed during the current rare event in order to reveal the nature of this object.

Congratulations to T. Vanmunster and G. Poyner on their excellent work!

Regards,

Taichi Kato

Observations just begun!

(vsnet-alert 49, D. Nogami)

Dear colleagues,

I am observing DV UMa using 0.6-m refl. + CCD with Johnson V-filter at the Ouda Station and an eclipse of DV UMa was caught!

The preliminary data on the eclipse based on the monitor image is that the mid-time of the eclipse was 11:10(UT) (+- 1 minutes) on Feb. 27 and the eclipse continued for about 13 minutes and the brightness at that time was fainter by at least 1 mag. than that out of the eclipse estimated to be 14.6 mag. More precise data will be reported after the reduction.

I thank T. Vanmunster and G. Poyner for notifying the current outburst.

Best regards,
Daisaku Nogami

Eclipse times

(vsnet-alert 52, T. Kato)

Dear vsnet-alert members,

As D. Nogami has already announced, the Ouda team successfully obtained V-band photometry of four consecutive eclipses of just-below-the-gap dwarf nova, DV UMa, which is currently undergoing a long-awaited outburst.

A preliminary analysis of the eclipse light curves has yielded following mid-eclipse times and eclipse depths. Due to the asymmetry of the eclipse light curves, these values would have a certain offset from the mid-eclipse times of the white dwarf.

mid-eclipse (JD-Geo) depth(V)

2449775.9651 1.6
2449776.0509 1.7
2449776.1365 1.9
2449776.2224 2.0

It is interesting to note that the period obtained from these eclipse times (0.08575 +/- 0.00005 day; the error includes the internal error only) is significantly different from Porb (0.08597 day).

It is also interesting to note that the eclipse depth is indeed increasing. Has the disk already started shrinking? The superhumps had not been grown yet (less than 0.1 mag in amplitude) at the time of our observation.

Regards,

Taichi Kato

Rapid decline

Dear colleagues,

The magnitude of DV UMa estimated with the maxmum count of the CCD image is about 15.8 at Mar. 1.55(UT), fainter by about 1.0 mag. than that two days before. Very rapid decline! The current outburst is normal one?

Close monitoring is highly encouraged.

Best regards,

Daisaku Nogami

Revised ephemeris

Dear vsnet-alert members,

As D. Nogami has already announced, the Ouda team successfully obtained V-band photometry of additional three eclipses of DV UMa, an SU UMa candidate currently in rapid decline from a short (normal) outburst.

A preliminary analysis of the eclipse light curves has yielded following mid-eclipse times and eclipse depths. This table also contains the eclipse times on Feb. 27 for convenience. The eclipse times were not calculated for Feb. 28 and Mar. 1 observations due to the very poor photometric condition. Note that the asymmetry of the eclipse light curves may have resulted a certain offset from the mid-eclipse times of the white dwarf.

A least-sqares fit to the observed times of eclipse yieded a period of 0.08585 +/- 0.00001 day (again internal error only), which is two sigma longer than that obtained from Feb. 27 observations, but is still significantly shorter than the published orbital period of 0.08597 day. More observations (esp. in quiescence) are clearly needed whether this discrepancy is caused by any asymmetric feature in the outbursting disk, or by the error in the orbital period.

We hope these eclipse times and period determination would be of any help in scheduling the further observations.