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

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

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

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

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

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

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 % brown dwarf donors

SDSS : 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)

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

SDSS – 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

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

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

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

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

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… PG

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

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

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

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

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

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, 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

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 (~ nm) intermediate spectral resolution (~2000) complete down to V~20 (GAIA limit)

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