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)

(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 - 337 years later

IPHAS pre-eruption HAAVSO

(Wesson et al. 2008, ApJL 688, 21)

IPHAS: 6 weeks

V458 Vul = Nova Vulpeculae 2007

IPHAS pre-eruption HWHT/INT H 2007-2009

(Wesson et al. 2008, ApJL 688, 21)

V458 Vul = Nova Vulpeculae 2007

(Rodríguez-Gil et al. submitted)

shortest-period PN nucleus: Porb=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, yetpopulation models and observations used to disagree, e.g.no brown-dwarf donor confirmed until 2006

70% brown dwarf donors

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)

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

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

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 radialvelocity amplitude, second high-mass WDvisible, 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 stars white dwarfs

mass-radius relations are a strongprediction of stellar structure & evolutionmodels, but poorly probed/constrainedby observations

Basic stellar physics

(Ribas et al. MmSAI 79, 562 & Parsons et al. 2010, MNRAS 402, 2591)

low-mass stars white dwarfs

mass-radius relations are a strongprediction of stellar structure & evolutionmodels, but poorly probed/constrainedby observations

Eclipsing WD + low-mass companions

(Burleigh et al. in prep., Gänsicke et al. in prep)

SDSS & UKIDSS

SDSS & UKIDSS

WD+M6

WHT/ACAM

extending the observedM-R relation to very lowstellar 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…

PG0014+027

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

Ultrafast spectroscopy

QUCam spectroscopy

67sec15800 spectra2sec exposure timeno deadtime

(Steeghs et al. in prep)

The anomalous X-ray pulsar 4U 0142+61

(Dhillon et al. 2005, MNRAS 363, 609)

WHT/ULTRACAM

RXTE

P=8.687sg=27.2i=23.7 60000+ 0.48sec exposures,

0.025sec dead-time

optical / X-ray modulation is in phase, not consistent with reprocessionfrom 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 disruptedasteroid, 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, 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 (~380-920nm)

• 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