Galactic Variables and Transients
Danny Steeghs
University of Warwick
T.Marsh, B.Gaensicke, P.Wheatley, A.Levan et al.
Danny Steeghs – eSI Jan10
Galactic variables in surveys
Vast arrays of variable stars
(Eclipsing) Binaries
RR Lyrae
Cepheids
Pulsations
Astero-seismology
- Precision stellar parameters
- Galactic structure
- Star formation and evolution
- Role of binaries
from Howell (2007)
Danny Steeghs – eSI Jan10
Binary evolution towards Type Ia
3)
1)
2)
from Yungelson (2008)
Danny Steeghs – eSI Jan10
Galactic (plane) surveys
•
Systematic CCD based surveys in multiple filters to harvest the
diverse (binary) populations in the galaxy
IPHAS / UVES / VPHAS+VVV / SEGUE / (SDSS, PS1, SkyMapper)
•
Diagnostics both in broad-band colours, emission lines and
variability ; cross-matching
Population synthesis of ultra-compact binaries (courtesy G.Nelemans)
Danny Steeghs – eSI Jan10
Hα as a diagnostic
Strong Hα emission in an accreting binary
Hα emission in Cepheus
www.iphas.org
Flag emission line objects
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Spectral information vs variability
binaries
DA
QSO
DB
courtesy J.Girven
stars
Suitably selected broad-band colours can be an important
source discriminator to complement variability information
[inter-survey cross matching]
Danny Steeghs – eSI Jan10
White dwarfs chronometers
Cooling/age tracks
(from Drew et al. 2006)
Danny Steeghs – eSI Jan10
Binary populations: orbital periods
The evolving
population of CVs
(Gaensicke et al. 2009)
Danny Steeghs – eSI Jan10
Mass accretion and accretion states
•
Transient accretion events are observed from
a wide range of binaries containing accreting
compact objects
•
Almost all known stellar mass black-holes are
discovered through their transient outbursts
•
Represent substantial modulations in the
mass accretion rate onto the compact object,
related to instabilities in the accretion disc.
•
Observationally, transients display several
canonical states characterized by overall
spectral and variability changes
•
For black holes & neutron stars, this is mainly
driven by X-ray monitoring and timing; the
need for multi-wavelength campaigns is
increasingly recognized
Danny Steeghs – eSI Jan10
Transient Accretion
X-ray activity
A decade in the life of a transiently accreting stellar-mass black hole
(RXTE ASM monitor)
Danny Steeghs – eSI Jan10
High-energy transients
Current: GRB style strategy;
high-energy trigger, initial poor
localisation
Rapid ground-based response
at longer wavelengths
Pre-transient images ;
progenitors ‘easy’ to find
Post-transient ; if localised
quiescent counterparts can
often be found (continued
follow-up, binary parameters
etc.)
598Hz accreting pulsar
Steeghs et al. 2004
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Accreting white dwarf in Kepler field
Kepler GO highlight; few months of high cadence data
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Outbursts in variability surveys
A dwarf nova outburst
in SuperWASP
(courtesy G.Marshall)
Recurrent accretion outburst in Catalina Sky Survey
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Explosive events : He-nova
from Woudt, Steeghs et al. (2009)
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Transients ; brightness and cadence
from Kulkarni et al. (2007)
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Progenitors and remnants ; follow-up
Big advantage is that within the galaxy it is often feasible to
detect progenitors and precursors and also study the transient
after it returns to low flux levels
The transient event as trigger/discovery
Follow-up delivers a large part of the actual science results ; a
survey strategy also needs a follow-up strategy
Survey design is crucial for ensuring
science goals are met and as much can be
derived from the survey products itself
Nonetheless, the era of surveys will also
herald the era of huge follow-up efforts, in
particular growing demands for (large N)
spectroscopy
Danny Steeghs – eSI Jan10
Challenges / technical aspects
- Density of sources at low galactic latitudes
- Complex extinction, background emission
- Real-time capability including cross-matching
- Lightcurve classification + spectral constraints
- Modeling , simulating
- Multi-facility follow-up
- Data access / event sharing
- Some unique to specific science, many shared
- Computational power but also manpower and
diverse science expertise
Danny Steeghs – eSI Jan10