| Proposal | Good morning, I'm Sauro Gaudenzi, my observer code is GSAD. In support of AAVSO alert no. 926, I'm requesting the use of a telescope to observe the subject TT Ari. I'm requesting two photographic sessions per week, each consisting of 10 60-second exposures using a V filter, until December 31, 2026. Abstract:
Dr. Virginia Cúneo writes: I have been awarded an XMM-Newton Target of Opportunity observation in the upcoming cycle, beginning in May, to observe a cataclysmic variable (CV) of the VY Sculptoris (VY Scl) subclass during a low state. To identify when one of the sources in my sample enters such a state, I'm asking for support from observers who can provide optical photometry in the V or CV band. If possible, I would greatly appreciate monitoring every few days, or as often as feasible, with a daily cadence once a low state is detected. Because of XMM-Newton visibility constraints, only a few sources will need to be monitored at any given time, and I will announce those through the forum. Monitoring should continue until an XMM-Newton trigger is issued.Justification:
VY Scl systems are a subclass of nova-like CVs in which a white dwarf accretes matter from a donor star through an accretion disk. They spend most of their time in a high state, with a relatively stable mass-transfer rate, but occasionally undergo unpredictable low states during which their optical brightness drops by more than a magnitude. These low states are generally thought to result from a decrease in the mass-transfer rate. Traditionally, nova-like CVs have been considered non-magnetic. However, during low states, VY Scl systems are expected to fall below the disk stability threshold and should therefore show a dwarf-nova-type outburst cycle. In practice, this has been observed in only a couple of systems. This discrepancy has led to the suggestion that some VY Scl systems may host magnetic white dwarfs. One of the most direct ways to test this idea is to search for modulations at the white dwarf spin period, which can be detected most effectively at X-ray wavelengths. To investigate this magnetic scenario, I have been awarded an XMM-Newton Target of Opportunity program to observe a VY Scl system during a low state. My sample consists of 18 sources that have shown deep low states in the past and that are observable with XMM-Newton at some point during the upcoming cycle. The program will be triggered when a pronounced low state, persisting for more than a week, is identified in one of these targets. In this effort, AAVSO observations would be extremely valuable, and I would be very grateful for the support of observers in monitoring these systems and helping identify a suitable trigger. |
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