Timedomain astronomy on the WHT or Rare objects

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

A few thoughts about time-domain astronomy • flares (minutes – hours) • flickering (msec – minutes) • outbursts (days – months) • eruptions (months – years) • explosions (months – years) • eclipses / transits (minutes – hours) • motion (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 - 337 years later IPHAS: 6 weeks AAVSO IPHAS pre-eruption H (Wesson et al. 2008, Ap. JL 688, 21)

V 458 Vul = Nova Vulpeculae 2007 WHT/INT H 2007 -2009 IPHAS pre-eruption H (Wesson et al. 2008, Ap. JL 688, 21)

V 458 Vul = Nova Vulpeculae 2007 ISIS radial velocities shortest-period PN nucleus: Porb=98. 1 min likely a binary white dwarf (Rodríguez-Gil et al. submitted)

The evolution of compact binary stars 70% brown dwarf donors 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

SDSS 1035+0551: The first definite BD donor Twd~12000 K Sp(2)>L 2 VLT spectroscopy: eclipsing, P=82 min (Southworth et al. 2006, MNRAS 373, 687) WHT/ULTRACAM photometry: M 2=0. 055± 0. 002 (Littlefair et al. 2006, Science 314, 1578)

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

SDSS 1257+5428 – a WD + NS/BH binary cool, high-mass white dwarf with a large radial velocity amplitude unseen companion is a NS or BH, at d=48 pc, this is the closest supernova remnant known (Badenes et al. 2009, Ap. J 707, 971)

SDSS 1257+5428 – a double white dwarf ISIS spectroscopy cool, very low-mass WD with a large radial velocity amplitude, second high-mass WD visible, rapidly rotating GWR progenitor “LISA-background source” (Marsh et al. 2010, Ap. JL submitted, arxiv: 1002. 4677)

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

Eclipsing WD + low-mass companions SDSS & UKIDSS extending the observed M-R relation to very low stellar masses SDSS & UKIDSS WD+M 6 WHT/ ACAM (Burleigh et al. in prep. , Gänsicke et al. in prep)

Asteroseismology WHT/ULTRACAM PG 0014+027 (Jeffery et al. 2005, MNRAS 362, 66) Pulsation frequency spectrum provides information about mass, core composition, envelope mass, rotation rate, magnetic field…

V 455 And – the time-domain family pack V 455 And=HS 2331+3905 Porb WHT/ULTRACAM WD pulsations WD spin 2 x. WD spin -eclipsing -brown dwarf -pulsating WD -rapidly rotating WD -magnetic WD -warped accretion disc (Araujo-Betancor et al. 2005, A&A 430, 629)

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

The anomalous X-ray pulsar 4 U 0142+61 WHT/ULTRACAM RXTE g=27. 2 i=23. 7 P=8. 687 s 60000+ 0. 48 sec exposures, 0. 025 sec dead-time optical / X-ray modulation is in phase, not consistent with reprocession from a disc most likely a magnetar (Dhillon et al. 2005, MNRAS 363, 609)

X-ray reprocessing in Sco-X 1 RXTE WHT/ULTRACAM ~11 -16 sec time X-ray/optical time-delay, consistent with X-ray reprocessing on the companion star (Munoz-Diarias et al. 2007, MNRAS 379, 1637)

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

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

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 -920 nm) • intermediate spectral resolution (~2000) • complete down to V~20 (GAIA limit)

Summary • The ING caters for a large and healthy community of time-domain astronomers addressing a wide range of scientific problems • Future surveys will continuously provide rare examples of stellar evolution (SDSS-III, Pan. STARRS, and ultimately GAIA & LISA) • 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 expertise is kept …