Download Astro-tomography: CAT-scanning accretion in compact binaries

Binsim courtesy R.Hynes
The galactic population of AM CVn binaries
Danny Steeghs
University of Warwick
Tom Marsh (Warwick), G.Roelofs (CfA),
G.Nelemans, P.Groot (Nijmegen)
Danny Steeghs – Tucson 2009
The AM CVn stars
• A white dwarf
accreting from a
Hydrogen-deficient
mass donor star
– They are CVs
– They need a 2nd
common envelope
Danny Steeghs – Tucson 2009
Binary evolution towards AM CVn systems
3)
1)
2)
from Yungelson (2008)
Danny Steeghs – Tucson 2009
Formation channels and Pmin
log(Mdot)
-5
first contact
-10
evolved CV
detached double WD
2
3
4
log (binary period) [s]
1) Double WD channel, Pmin ~2-3 mins
2) He-star donor channel, Pmin ~ 10 mins
3) Evolved CV donor channel, Pmin ~ 10-60 mins
Danny Steeghs – Tucson 2009
Mass transfer and stability : merger vs accretion
• Loss of orbital angular momentum
via gravitational wave radiation:
dJGR/dt = -32/5 G3/c5 M1M2M/a4 Jorb
• Initial stability of mass transfer
determined by the response of the
mass donor to mass loss:
2 =  log R2 /  log M2 < 0
• Transfer of momentum via mass
loss:
dJ2/dt = (GM1Rh)1/2 dM2/dt
• Spin – orbit coupling : nonsynchronous rotation leads to
angular momentum transport via
tidal/magnetic or viscous torques
Courtesy
NASA/GSFC
Danny Steeghs – Tucson 2009
Mass transfer between two white dwarfs at contact
• Post common-envelope detached double white dwarfs
driven into contact by gravitational waves (P<10hrs)
donor
dynamically
unstable:
mergers
‘ q> 2/3 ‘
Type Ia
M1+m2 > Mch
DIRECT
IMPACT
accretion disk
formation ‘stable’
accretor
Danny Steeghs – Tucson 2009
Mass transfer between two white dwarfs
• Semi-detached ‘direct-impact’ birth at P~few mins
Porb = few minutes
Porb = half an hour
Webbink & Iben 1987
Nelemans et al. 2001, Marsh & Steeghs 2002, Marsh, Nelemans & Steeghs 2004
Danny Steeghs – Tucson 2009
Emission line diagnostics
• facilitate their discovery/identification
• sample the abundances of the donor star -> formation channel
• provide a detailed dynamical probe of the emission line regions
Danny Steeghs – Tucson 2009
Spectroscopic periods
• Complex photometric
behaviour of AM CVn stars
makes a solid identification
of the binary period difficult
• The stream-disk impact
localisation provides a
common beacon in the
binary frame
• Kicked off by fast
spectroscopy of AM CVn
itself
Accretion disc + bright spot emission
(Nelemans, Steeghs & Groot 2001)
Danny Steeghs – Tucson 2009
The blue variable ES Ceti with Magellan
Danny Steeghs – Tucson 2009
ES Cet, a 10.3 mins binary
HeII 4686
HeII 5411
Robust orbital periods through fast spectroscopy
Danny Steeghs – Tucson 2009
Beyond orbital periods ; tracing the accretor
Central spikes in GP Com and V396 Hya
VLT/UVES data, Steeghs et al. 2009
Danny Steeghs – Tucson 2009
Central spike from the accreting WD
1
0
orbital phase
2
K1 = 11.7 km/s
Danny Steeghs – Tucson 2009
Doppler maps
Danny Steeghs – Tucson 2009
Emission spikes from the white dwarf
• Spikes all move in phase and with
the same amplitude and flare on short
timescales
=> near WD
(Marsh 1999)
• However, spike mean velocity
changes significantly from line to line
(~ 0-50 km/s )
• Some lines show double spikes, each
moving together
• Both GP Com and V396 Hya show
the same pattern, other AM CVn
systems show spikes as well
• Spikes are narrow, though nonGaussian
• Stark effect in high-density line
formation region?
(Morales-Rueda et al. 2003)
appears not to be consistent with
DB/EHe models for Stark-shift
and split (Beauchamp et al. 1997)
Danny Steeghs – Tucson 2009
Beauchamp et al. (1997) Stark profiles
ne=1015 cm-3
1016 cm-3
-100 km/s
velocity
+100 km/s
-100 km/s
velocity
+100 km/s
Both velocity of peak and overall profile shape depends on ne
Danny Steeghs – Tucson 2009
Spikes at the accreting WD
• Single density (ne= 3-4 1015 cm-3) Stark profiles describe the
spike properties remarkably well
• Kinematics and density conditions of the spike match a slowly
rotating emission line region tied to the accreting white dwarf
• Provide us with the orbital velocity K1, the absolute binary phase
and the (Stark corrected) systemic velocity
• Unknown binary space velocity prevents us from converting the
overall velocity offset (+16-17 km/s) into a gravitational red-shift
Danny Steeghs – Tucson 2009
Doppler maps
GP Com HeI 3888
V396 HeI 5015
Danny Steeghs – Tucson 2009
Mass ratio from disk-stream impact
GP Com
q=M2/M1
V396 Hya
q
Danny Steeghs – Tucson 2009
Mass ratios from spike + impact spot
• GP Com
q = 0.019 ± 0.002
• V396 Hya
q = 0.013 ± 0.002
• SDSS J1240 (Roelofs et al. 2005)
q = 0.039 ± 0.010
• AM CVn (Roelofs et al. 2006)
q = 0.18 ± 0.01
• (SDSS J1552)
Danny Steeghs – Tucson 2009
Only one eclipser so far …
Marsh et al. ; P=28 min
Danny Steeghs – Tucson 2009
Period distribution of current AM CVn systems
young
DWDs
high Mdot
old
evolved
systems
low Mdot
theoretical
minimum for 2
WDs (~3m)
Hydrogen rich
period minimum
Danny Steeghs – Tucson 2009
Beyond periods : distances
• Relatively nearby sample (300 pc scaleheight, closest at ~70pc)
- parallax measurements possible with HST-FGS
- 50 orbit program on five AM CVn systems
GP Com
HP Lib
CR Boo
V803 Cen
AM CVn
d=
d=
d=
d=
d=
75 ± 2 pc
197 ± 13 pc
337 ± 40 pc
347 ± 30 pc
606 ± 110 pc
Roelofs et al. 2007
- space density estimate of <10-5 pc-3
- some systems must have semi-degenerate donor
(see also Deloye et al. 2007)
Danny Steeghs – Tucson 2009
Any systems undergoing direct-impact?
• Direct impact accretion first proposed to explain the 9 min
variable V407 Vul (Ramsay et al. ; Marsh & Steeghs 2002)
–
–
–
–
–
Short period
Luminous x-ray source with emission pulsed at full amplitude
No polarisation; non-magnetic
Out of phase optical pulsations
No emission lines (?)
Danny Steeghs – Tucson 2009
The not-so-cooperative; V407 Vul
• 7 hours (53 orbits) of Gemini GMOS spectroscopy of V407 Vul
Steeghs et al. 2006
Danny Steeghs – Tucson 2009
The record-holder RXJ0806 ; 5.3 mins ?
RXJ0806;
Discovered as a variable ROSAT
source, 100% modulation in Xray intensity every 5.3minutes,
same period in the optical/UV.
Twin of V407 Vul, spectroscopy
is also challenging (V>21)
Keck LRIS runs: weathered out
three times!
Barros et al. (2007)
Danny Steeghs – Tucson 2009
Gravitational wave beacons
strongest known
resolved LISA
sources ;
verification sources
Adapted from
Nelemans 2007
Roelofs et al. 2007
Danny Steeghs – Tucson 2009
The AM CVn stars and their discovery method
•
Ultra-compacts (3)
– HM Cnc / RXJ 0806.3
– V407 Vul / RXJ1914+24
– ES Cet
321s
569s
620s
X-ray (ROSAT)
X-ray (ROSAT)
blue/UV
•
High mass transfer rate systems (2)
– AM CVn
– HP Lib
1029s
1103s
blue color (HZ)
blue color (EC)
•
Intermediate systems and Helium Dwarf Novae
(8)
– KL Dra
1502s
– CR Boo
1471s
– V803 Cen
1596s
– SDSSJ0926
1699s
– CP Eri
1724s
– V406 Hya / SN2003aw
2028s
– 2QZ J142701-0123
2194s
– SDSSJ1240
2241s
‘SN’
blue (PG)
chance variable
emission lines (SDSS)
blue variable (Luyten)
‘SN’
emission lines (2QZ)
emission lines (SDSS)
•
Low mass transfer rate systems
– SDSSJ0804
– GP Com
– V396 Hya / CE-315
– SDSSJ1411+4813
– SDSSJ1552
blue color (SDSS)
proper motion
proper motion (CE)
emission lines (SDSS)
emission lines (SDSS)
•
New, no periods yet (4)
– SDSSJ0129
– SDSSJ2047
– SDSSJ1208
– SNF20060524
(5)
2670s
2790s
3906s
2760s
3376s
emission lines (SDSS)
emission lines (SDSS)
emission lines (SDSS)
‘SN’
Danny Steeghs – Tucson 2009
Need for better samples
• we need large and well selected samples to determine the
formation channels, the mass transfer stability and thus the
actual distribution of sources
• for progenitors (detached systems), accretors as well as endproducts / post-mergers
• targeted low-galactic latitude survey
-Variability ; RATS, VST
-Colours/lines ; EGAPS
-X-rays ; GBS, cross-matching
• exploit large-scale surveys
-SDSS (many filters, good coverage)
-SkyMapper, Pan-STARRS, LSST
Danny Steeghs – Tucson 2009
SDSS AM CVn search
• 6 AM CVn systems have been
discovered serendipitously in
SDSS because spectra were
taken
• AM CVn systems occupy a welldefined region in color space
that is sparsely populated
• Easy to recognise and
distinguish from white dwarfs
SDSS types
courtesy J.Girven
Danny Steeghs – Tucson 2009
SDSS AM CVn search
•
N=6 implied space
density is 1-3 10-6 pc-3
(Roelofs et al. 2007)
•
This is close to the most
pessimistic estimates
from population synthesis
calculations
(Nelemans et al. 2001:
6 10-6 – 3 10-5 pc-3 )
•
~50 systems still lurking
in this color-color region
for a wide range of r
Roelofs et al. 2007
Danny Steeghs – Tucson 2009
Summary
• AM CVn binaries form a crucial population in
testing binary evolution (abundant progenitors,
2 common envelope phases, dominate GWR)
• Initial phase of mass transfer after contact is
dominated by direct-impact geometry
(survival, mergers, explosions?)
• Sample is growing though very inhomogenous
• Fast spectroscopy on large telescopes has
delivered orbital periods, mass ratios and an
insight into (He) accretion geometries
• SDSS is benchmarking space densities,
expectation of significant increase in sample
size in the era of surveys
Danny Steeghs – Tucson 2009
Is the DD channel a significant contributor to Ia’s?
• Type Ia = degenerate Carbon ignition of ~1.4 M object =
accreting white dwarf
• Is the companion another degenerate
object? (SD versus DD channels)
• Ia’s are observed in both young and old populations, most
luminous events are young
• Delay times of few Gyr natural in DD channel, simple SD picture
take longer
• Rates seem OK as well, but the std SD is not produced enough in
current binary evolution models
• Mergers do not always explode even if M1+M2 > 1.4 M
• Does Type Ia diversity imply multiple channels and can this
diversity be linked to the variety of expected DD configurations?
Danny Steeghs – Tucson 2009
Key locations
 Donor star with velocity K2
 Accretor with velocity K1
 (Ballistic) accretion stream
 Accretion disk
 Stream-disk interaction
 Stream-accretor interaction (direct impact)
Danny Steeghs – Tucson 2009
Formation of compact WD binaries
• M < 8 Msol  evolves into a WD
• M_WD ~ 0.6 Msol , R_WD ~ 109 cm
(CO)
• Main-sequence binaries with periods of 1010,000 days evolve into compact binaries
involving white dwarfs
• Common-envelope phase required to produce
post CE binaries with P< days
• Single CE produces WD + star  CV
• After two CE sessions left with WD + WD
Danny Steeghs – Tucson 2009
Rotation
• Spikes are relatively narrow, and shapes are dominated by the
Stark broadening profile
• Need very little rotational broadening !
• From HeII 4686 (no Stark):
vsini = 60 – 85 km/s
• White dwarfs appear to be rotating
slowly, unless the spike photosphere
does not co-rotate with the white dwarf
Danny Steeghs – Tucson 2009
A multi-wavelength picture
UV
optical lines
X-rays
optical cont?
Danny Steeghs – Tucson 2009
Mass ratio from disk-stream impact
ballistic
mix
disk velocities
Danny Steeghs – Tucson 2009
Double hot-spots ; stream overflow ?
V396 Hya
not sensitive to q ?
SDSS J1240 + sn2003aw
Roelofs et al. 2005
Danny Steeghs – Tucson 2009
Spike velocity shifts
Decent match to the family of spike profiles
(both shift and shape) for ne = 3 1015 cm-3
Danny Steeghs – Tucson 2009
Observed split spike profiles
Danny Steeghs – Tucson 2009
Rotation
• Spikes are relatively narrow, and shapes are dominated by the
Stark broadening profile
• Need very little rotational broadening !
• From HeII 4686 (no Stark):
vsini = 60 – 85 km/s
• White dwarfs appear to be rotating
slowly, unless the spike photosphere
does not co-rotate with the white dwarf
Danny Steeghs – Tucson 2009
Recent theoretical developments
• Hydro simulations of initial mass transfer (and merger)
D’Souza et al. 2006, Yoon et al. 2007, Wood et al. 2008
First steps …. At 104 MEdd !
Danny Steeghs – Tucson 2009
Surviving the direct-impact phase
• Survival of the initial direct impact phase uncertain
efficient spinorbit coupling
• Crucial for using accreting systems to probe DWD progenitor population
Danny Steeghs – Tucson 2009
The AM CVn stars
• Classics ; AM CVn and GP Com known for decades
• 5 known
Danny Steeghs – Tucson 2009
The accretion geometry in ES Cet (10.3m)
constant
variable
A disk is present, though containing a strong asymmetry, most
likely the stream-disk interaction
No classic direct-impact, but how far does the stream penetrate?
Strong orbital modulations in the UV?
(HST/XMM)
Danny Steeghs – Tucson 2009
Hot donors ; He-star vs hot WD
Danny Steeghs – Tucson 2009
Growing samples; observational diagnostics
-
accretion luminosity in the X-ray/UV/optical
low frequency GWR driving the orbital evolution
hot white dwarfs heated by accretion (optical/UV)
pulsed X-ray sources for direct-impact accretors
low mass and cool donor stars ; He-core or CO WD? (IR)
post-mergers & progenitors
Danny Steeghs – Tucson 2009