Populations of accreting white dwarfs

Hai-Liang Chen (���)chenhl@ynao.ac.cn

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).