1. Time-domain astronomy on the WHT Boris Gänsicke …or… Rare objects from wide-field surveys

2. A few thoughts about time-domain astronomy flares flickering outbursts eruptions explosions eclipses / transits motion (minutes – hours) (msec – minutes) (days – months) (months – years) (minutes – hours) (minutes – years) stellar activity stellar structure & evolution binary evolution exo-planets accretion discs/processes cosmology

3. CK Vul = Nova Vulpeculae 1670 (Hevelius 1670, Phil. Trans. 5, 2087) - classical nova? - late thermal pulse? - merger? - sub-Chandra SN?

4. Same constellation - 337 years later IPHAS pre-eruption H  AAVSO (Wesson et al. 2008, ApJL 688, 21) IPHAS: 6 weeks

5. V458 Vul = Nova Vulpeculae 2007 IPHAS pre-eruption H  WHT/INT H  2007-2009 (Wesson et al. 2008, ApJL 688, 21)

6. V458 Vul = Nova Vulpeculae 2007 (Rodríguez-Gil et al. submitted) shortest-period PN nucleus: P orb =98.1min  likely a binary white dwarf ISIS radial velocities

7. The evolution of compact binary stars White dwarf / main sequence binaries are the simplest CBs, yet population models and observations used to disagree, e.g. no brown-dwarf donor confirmed until 2006 70% brown dwarf donors

8. SDSS1035+0551: The first definite BD donor Twd~12000K Sp(2)>L2 VLT spectroscopy: eclipsing, P=82min (Southworth et al. 2006, MNRAS 373, 687) WHT/ULTRACAM photometry: M2=0.055±0.002 (Littlefair et al. 2006, Science 314, 1578)

9. Another BD donor dynamically confirmed ISIS/QUCAM (Tulloch et al. 2009, MNRAS 397L, 32) 628 spectra at 30sec exposure time WD radial velocity = 34km/s

10. SDSS1257+5428 – a WD + NS/BH binary (Badenes et al. 2009, ApJ 707, 971) cool, high-mass white dwarf with a large radial velocity amplitude  unseen companion is a NS or BH, at d=48pc, this is the closest supernova remnant known

11. SDSS1257+5428 – a double white dwarf ISIS spectroscopy (Marsh et al. 2010, ApJL submitted, arxiv:1002.4677) cool, very low-mass WD with a large radial velocity amplitude, second high-mass WD visible, rapidly rotating  GWR progenitor “LISA-background source”

12. Basic stellar physics (Ribas et al. MmSAI 79, 562 & Parsons et al. 2010, MNRAS 402, 2591) low-mass starswhite dwarfs mass-radius relations are a strong prediction of stellar structure & evolution models, but poorly probed/constrained by observations

13. Basic stellar physics (Ribas et al. MmSAI 79, 562 & Parsons et al. 2010, MNRAS 402, 2591) low-mass starswhite dwarfs mass-radius relations are a strong prediction of stellar structure & evolution models, but poorly probed/constrained by observations

14. Eclipsing WD + low-mass companions (Burleigh et al. in prep., Gänsicke et al. in prep) SDSS & UKIDSS WD+M6 WHT/ ACAM extending the observed M-R relation to very low stellar masses

15. Asteroseismology (Jeffery et al. 2005, MNRAS 362, 66) WHT/ULTRACAM Pulsation frequency spectrum provides information about mass, core composition, envelope mass, rotation rate, magnetic field… PG0014+027

16. V455 And – the time-domain family pack (Araujo-Betancor et al. 2005, A&A 430, 629) V455 And=HS2331+3905 WHT/ULTRACAM -eclipsing -brown dwarf -pulsating WD -rapidly rotating WD -magnetic WD -warped accretion disc WD spin WD pulsations Porb 2xWD spin

17. Ultrafast spectroscopy QUCam spectroscopy 67sec 15800 spectra 2sec exposure time no deadtime (Steeghs et al. in prep)

18. The anomalous X-ray pulsar 4U 0142+61 (Dhillon et al. 2005, MNRAS 363, 609) WHT/ULTRACAM RXTE P=8.687s g=27.2 i=23.7 60000+ 0.48sec exposures, 0.025sec dead-time optical / X-ray modulation is in phase, not consistent with reprocession from a disc  most likely a magnetar

19. X-ray reprocessing in Sco-X1 (Munoz-Diarias et al. 2007, MNRAS 379, 1637) WHT/ULTRACAM RXTE ~11-16sec time X-ray/optical time-delay, consistent with X-ray reprocessing on the companion star

20. Planetary debris around white dwarfs (Gänsicke et al. 2006, Science 314, 1908) metal-rich debris from a tidally disrupted asteroid, real-time evolution of the debris disc is seen on time scales of years

21. Time domain astronomy & wide-field surveys all examples discussed here are rare objects found from large-area surveys (e.g. PG, IPHAS, HQS, SDSS…) usually identified from painful long-slit spectroscopic ID programs SDSS was a paradigm shift: co-ordinated deep multi-band imaging plus MOS follow-up (10000 white dwarfs, 2000 WD+MS binaries, 290 cataclysmic variables, 40000+ M-dwarfs…) Future multi-colour surveys, in particular GAIA, need a similar follow-up strategy to achieve maximum scientific impact, but… … all time-domain science needs continued access to time-series follow-up of new discoveries

22. MOS requirements low target density (a few to a few tens per square degree)  multiplex with other target categories (as SDSS did) broad wavelength coverage (~380-920nm) intermediate spectral resolution (~2000) complete down to V~20 (GAIA limit)

23. Summary WHT is a leading and stable platform for time-domain astronomy on all time scales, with a range of excellent instruments: ISIS, ISIS/QUCAM, ACAM, ULTRACAM … need to make sure that that expertise is kept … Future surveys will continuously provide rare examples of stellar evolution (SDSS-III, PanSTARRS, and ultimately GAIA & LISA) The ING caters for a large and healthy community of time-domain astronomers addressing a wide range of scientific problems