AAVSO Alert Notice 305

SUBJECT: Request for Monitoring of SU UMa-type Cataclysmic Variable 0409-71 VW Hydri

Object: 0409-71 VW Hydri

Event: Request for optical monitoring - visual and CCD(V)

Dr. Knox Long, Space Telescope Science Institute, has requested our assistance in monitoring the SU UMa-type cataclysmic variable 0409-71 VW Hyi. Dr. Long and his colleagues have Target-of-Opportunity (TOO) observations of VW Hyi with the NASA satellite FUSE planned for the coming months, beginning in June. The timing of the TOO observations depends on when the outbursts occur and what type of outbursts they are (normal or superoutburst), so your help is essential.

Dr. Long informs us: "During an outburst of a dwarf nova, the surface layers of the white dwarf (WD) are heated. In the intervals between outburst, the WD, which is the dominant source of radiation in the far ultraviolet, cools slowly by several thousand degrees. This summer, an international team of astronomers led by Knox Long at STScI are hoping to use the FUSE satellite to observe the cooling of the WD in VW Hyi over a full quiescent interval."

In order to plan the satellite observations, it is essential to know as soon as VW Hyi goes into outburst, and to know as soon as possible whether the outburst is a normal one or a superoutburst. Good coverage throughout the outburst, subsequent quiescence, following outburst, and following quiescence is also essential.

Presently, VW Hyi is near minimum, at approximate visual magnitude 13.4, according to observations received at the AAVSO. Its last outburst, a normal one, occurred on May 10, 2004, when it brightened to magnitude 9.5 and returned to quiescence at magnitude ~13.9 4 days later. Its last superoutburst occurred in December 2003, when VW Hyi brightened to magnitude 8.8 and stayed above quiescent magnitude for about 14 days.

We expect the next outburst to occur within the next few to several days. The outburst could be either a normal one or a superoutburst; VW Hyi does not follow the same pattern of normal outbursts and superoutbursts from cycle to cycle. However, a superoutburst is expected to occur within the next one to three outbursts.

Please monitor VW Hyi closely, and inform us immediately by phone (see below* for special phone instructions), fax, or email when it starts to brighten, i.e., becomes brighter than 12.5. Throughout the outburst, quiescence, the following outburst, and the following quiescence - that is, for two outbursts and the quiescent interval after each of them - please send in your observations daily so we may keep the astronomers informed of the star's behavior.

The success of the FUSE TOO observations very much depends on your observations and the early alerts and continuous information we can provide to our colleagues.

AAVSO Chart(s): 'b' and 'd' scale charts. VW Hyi charts may be found at: http://www.aavso.org/cgi-bin/searchcharts3.pl?name=vw%20hyi

Report Object to the AAVSO as: 0409-71 VW HYI; be sure to indicate which comparison stars you used.

SUBMIT OBSERVATIONS TO THE AAVSO

We encourage observers to submit observations via our web site (online data submission tool WebObs), or by email in AAVSO format to observations@aavso.org. If you do not have AAVSO Observer Initials, please contact Headquarters so we may assign them to you. The answering machine at AAVSO Headquarters is on nights and weekends; use our charge-free number (888-802-STAR = 888-802-7827) to report your observations, or report them via fax (617-354-0665).

*Special phone instructions: Please contact the AAVSO for more information on this.

Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Elizabeth O. Waagen
Interim Director