Populations of accreting white dwarfs
Hai-Liang Chen (���)[email protected]
Yunnan Observatories
Zhanwen Han, Marat Gilfanov, Tyrone Woods, Lev Yungelson, Luciano Piersanti
Accreting white dwarfs
Accretor: white dwarf
Donor: Main Sequence star Hertzsprung Gap star Red Giant star
Formation and evolution of WD binaries
Postnov&Yungelson(2014)
Semi-detached
Chen et al. 2019
Different Types of accreting WDs
• RAWDs (Rapid Accreting WDs)
Typical Teff: 104– 105K EUV emission
• SNBWD ( stable nuclear burning white dwarf)Typical Teff ~ 105 – 106K Lbol~1036-1038 erg/s
Soft X-ray and UV emission
Not all SNBWDs will be observed as supersoft X-ray sources.
• Nova
Nova properties mainly depend on:
1) WD mass. 2) accretion rates. 3) WD temperature.
Spectra of accreting WDs
Blackbody spectrum
WD atmosphere model
Rauch + 2010
RAWDs:With typical accretion rates and effective temperature, no break at He II edge (Woods&Gilfanov2013).
SNBWDs:Spectra of massive WDs (high temperature) are reasonably approximated by blackbody spectra in soft X-ray (highlighted) and UV band.
Hybrid Binary population synthesis approach
Semi-detached
BSE codeMESA code
M1i, M2i, ai
Mwd,i, Md,j, Porb,k
WD binary evolutionary Library
Mwd, Md, Porb
BSE calculation:population of semidetached WD binaries
With the binary parameters, we can select the closest tracks from the WD binary evolutionary library.
BSE� Hurley et al. (2000,2002); MESA: Paxton et al. 2011, 2013, 2015
Observable SSSs: SNBWDs with soft X-ray (0.3-0.7keV) luminosity Lx > 1036 erg/s.
Results: Number of observable SSSs
log(stellar age) log(stellar age)
elliptical galaxy spiral galaxy
Observations: Elliptical galaxy: NGC4472: 5 SSSs; NGC4697: 4 SSSsSpiral galaxy: M101: 42 SSS; M83: 28 SSSs
Di Stefano 2010
10Gyr,1011M⦿ Elliptical galaxy Spiral galaxy
SSSs number ~10-20 ~40-130
Chen et al. 2015
Soft X-ray (0.3-0.7keV) luminosity ofaccreting WDs
data: Chandra Observations Bogdan & Gilfanov 2010, Zhang + 2012
log(time from starburst)
Chen et al. 2015
The UV emission of accreting WDs is able to ionize the ISM, in particular He II.
The presence of populations of accreting white dwarfs will significantly change the spectrum of ionizing UV radiation.
Many early type galaxies host a detectable mass of HI ~ 108-109Mʘ.
Most common morphologies are HI disc and rings (Serra+2012).
We would expect some recombination lines , e.g. He II 4686 Å, in the observations of elliptical galaxies.
Serra + 2012
Other observables
HeII 4686/Hβ line ratio
log(time from starburst)
Testable prediction: a large bump around 1 Gyr.
data: stacked SDSS spectra (~10000 galaxies) Johansson et al. 2014
Chen et al. 2015
Nova populationEvolution of nova rate
elliptical galaxy spiral galaxy
log(stellar age) log(stellar age)
10 Gyr, nova rate in elliptical galaxy: (1-2)×10-10 /yr/Mʘ.10 Gyr, nova rate in spiral galaxy: (10-20)×10-10 /yr/Mʘ.
Chen et al. 2016
WD mass distribution
elliptical galaxy spiral galaxy M31 galaxy
nova
rate
Observational data of M31 galaxy: Arp 1956, Darnley + 2006, Soraisam & Gilfanov 2015, Soraisam + 2016
nova
rate
Chen et al. 2016
elliptical galaxy spiral galaxy M31 galaxy
Mass loss time distribution
Observational data of M31 galaxy: Arp 1956, Darnley + 2006, Soraisam & Gilfanov 2015, Soraisam + 2016
nova
rate
Chen et al. 2016
Recurrence period distributionelliptical galaxy spiral galaxy M31 galaxy
nova
rate
Chen et al. 2016
Peak magnitude distribution
elliptical galaxy spiral galaxy M31 galaxy
nova
rate
Possible reasons for discrepancy with M31 data: 1) Not sufficient mixing in Yaron’s nova Models. 2) The assumption of a unique spectral type for novae at the maximum luminosity may be not accurate (see Munari 2014).
Chen et al. 2016
SNe Ia rates
• Starburst case (Delay time distribution)
Delay time: time from star formation to SN Ia explosion
Milky Way Galaxy:we predict SNe Ia rate:
2*10-4/yr
Observationally inferred data: (3-4)*10-3/yr
(Cappellaro&Turatto 1997)
time from starburst(Gyr)Chen et al. 2014
Summary1) The emission of accreting WDs is an important
component of soft X-ray emission of elliptical galaxies.
2) Accreting WDs are important ionizing sources in elliptical galaxies.
3) The majority of current novae in elliptical-like galaxies have low-mass WDs, long decay times, long recurrence periods and are relatively faint. In contrast, the majority of current novae in spiral-like galaxies have massive WDs, short decay times, short recurrence periods and are relatively bright.4) The DTD of SNe Ia in SD scenario is inconsistent with observations.
Thank you for your attention!
Optically thick wind regime
l Accretion rate larger than maximum stable burning rateoptically thick wind will
occur.l Photosphere expands
modestly, effective temperature decreases
l Typical Teff: 104– 105K EUV emission
Hachisu et al. 1999
RAWD: Rapidly accreting white dwarf (Lepo & van Kerkwijk 2013)
log(temperature)
log(
accr
etio
n ra
te)
Steady burning regime
l Typical accretion rate 10-7—10-6 Mʘ/yrWDs accumulate mass efficiently.
SNBWD: stable nuclear burning white dwarf
l Typical temperature and luminosityTeff ~ 105 – 106K Lbol~1036-1038 erg/sSoft X-ray and UV emission
l Soft X-ray emission from SNBWD is easily absorbed by ISM
l Not all SNBWDs will be observed as supersoft X-ray sources (SSSs).
Wolf et al. 2013
Unstable burning regimeNova cartoon (by Bill Wolf)
Nova properties mainly depend on:1) WD mass. 2) accretion rates. 3) WD temperature(Prialnik + 1995, Yaron + 2005).
Ma et al. 2013
A model for M31 galaxyComposite stellar population:
Convolve single bursts (SSPs) with the star formation history (SFH).
Star formation history
The value of parameter Afor SSP
SFH of M31 galaxy:Based on Robertson et al. (2004) and Olsen et al. (2006).
Nova rate of M31 galaxy: Our prediction: 80 – 160 /yrObservation: 97 /yr
Observational data of M31 galaxy: Arp 1956, Darnley + 2006
Incompleteness analysis: Soraisam & Gilfanov 2015; Soraisam et al. 2016
Photoionization calculations
l MAPPINGS III code (Kewley et al. 2001, Groves, Dopita & Sutherland 2004)
1) Assuming a plane-parallel geometry.2) Hydrogen density nH = 100 cm−3 (consistent with the
observed [SII] 6717 Å/6731 Å ratio. Yan & Blanton 2012 ).3) Solar metallicity for the warm ISM. 4) The incident flux is prescribed by an input spectral shape,
normalized by the ionization parameter U = Qph/(nHc) .log(U) ~ -3.5 (well constrained by the observed ratio of
[OIII] 5007Å/Hβ).