Monitoring Cataclysmic Variables: Hunting for Low States
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 am 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 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.
Requested Data Types:
Photometry
Targets
| Name | Magnitude | Variability Type | Photometry Notes | Spectroscopy Notes |
|---|---|---|---|---|
| VY Scl | 11.80 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| LS Peg | 11.55 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| TT Ari | 10.20 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| BB Dor | 14.30 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| V0380 Oph | 14.30 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| V1294 Tau | 14.66 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| HS 0506+7725 | 14.60 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| KR Aur | 12.70 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| BG Tri | 11.50 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| Gaia DR2 58295423607026048 | 15.80 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| V1193 Ori | 13.60 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| MASTER OT J072703.91-631952.8 | 14.10 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| GSC 07196-00489 | 13.80 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| V0504 Cen | 12.00 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| CD-35 9665 | 12.30 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| CZ Aql | 14.30 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| ASASSN-V J211014.40-242105.3 | 14.30 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
| NSV 3734 | 13.60 | NL/VY |
Cadence: Nightly Precision: 50 mmag |
Not Requested |
Spectroscopy Lines:
No spectroscopy lines provided
Photometry Filters:
B (Johnson), V (Johnson), g (Sloan)
Comparison Stars:
Finder charts with comparison stars may be created using the AAVSO Variable Star Plotter (VSP).
Co-Authorship
Observers are eligible for co-authorship.
Additional Observer Input:
I am requesting observations of each source every few days until a low state is identified. Once a low state is detected, daily observations will be needed to follow its evolution. Because each source has different visibility windows during the cycle, only a few targets will need to be monitored at any given time. As this will change throughout the campaign, I will post updates in the forum identifying which sources most need coverage. Monitoring should continue until the trigger is issued, which I will also announce through the forum.
Additional Submission Location:
Not provided
Notes:
No public notes