Where are the

stripped donor stars?Insights from the φ Persei system

Image credit: Hubble ESA Information Center

Abel SchootemeijerUniversity of Amsterdam

Supervisor: Selma de MinkCollaborators: Ylva Götberg, Manos Zapartas,

Doug Gies, Hugues Sana

0 Myr

No/before

interaction:

30 Dor O star population – constant star formation

Pre-interaction binaries

Single stars*See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

binary_cFast binary evolution code*

• Uses pre-computed grid

• ~106 systems day-1

0 Myr 10 Myr

No/before after

interaction: interaction:

30 Dor O star population – constant star formation

Pre-interaction binaries

Single stars

Other post-interaction sys.

Mergers

He star systems *See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

binary_cFast binary evolution code*

• Uses pre-computed grid

• ~106 systems day-1

0 Myr 10 Myr 20 Myr

No/before after

interaction: interaction:

30 Dor O star population – constant star formation

Pre-interaction binaries

Single stars

Other post-interaction sys.

Mergers

He star systems *See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

binary_cFast binary evolution code*

• Uses pre-computed grid

• ~106 systems day-1

0 Myr 10 Myr 20 Myr 40+ Myr

No/before after

interaction: interaction:

30 Dor O star population – constant star formation

Pre-interaction binaries

Single stars

Other post-interaction sys.

Mergers

He star systems *See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

binary_cFast binary evolution code*

• Uses pre-computed grid

• ~106 systems day-1

40+ Myr

No/before after

interaction: interaction:

O star population – constant star formation

Pre-interaction binaries

Single stars

Other post-interaction sys.

Mergers

He star systems *See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

binary_cFast binary evolution code*

• Uses pre-computed grid

• ~106 systems day-1

1/3 post interaction systems

contains a stripped He star: this is in agreement with Pols+1991

Why are stripped donor

stars hard to find? Only three have been observed

Why are stripped donor

stars hard to find? Only three have been observed

Extreme mass ratio and

widening of semi-major axisLow vorb of the

brightest star

Why are stripped donor

stars hard to find? Only three have been observed

Extreme mass ratio and

widening of semi-major axisLow vorb of the

brightest star

Bright companions Stripped stars are hard to

detect in a spectrum

Why are stripped donor

stars hard to find? Only three have been observed

Extreme mass ratio and

widening of semi-major axisLow vorb of the

brightest star

Bright companions Stripped stars are hard to

detect in a spectrum

‘Stripped stars are HOT’ *

Most light is emitted in UV

Fewer lines in spectrum

*Credit: Ylva Götberg

Be star

9.6 ± 0.3 Mʘ

104.16±0.10 Lʘvrot ≈ 0.9 vcrit

sdO companion

1.2 ± 0.2 Mʘ

103.80±0.13 Lʘ53 ± 3 kK

In φ Persei a stripped companion is found:

Porb = 126 d *Campbell, 1902

**Gies+1998, Mourard+2015

• Radial velocity variations observed*

• Full orbital solution now determined**

Be star

9.6 ± 0.3 Mʘ

104.16±0.10 Lʘvrot ≈ 0.9 vcrit

sdO companion

1.2 ± 0.2 Mʘ

103.80±0.13 Lʘ53 ± 3 kK

In φ Persei a stripped companion is found:

Porb = 126 d

Why is the stripped

star so bright?

Computational method: BINARY_C

• Bayesian analysis to determine initial parameters:

Star 1: 7.2 ± 0.5 Mʘ

Star 2: 3.8 ± 0.5 Mʘ

Porb: 17 ± 5 days

Computational method: BINARY_C

• Bayesian analysis to determine initial parameters:

Star 1: 7.2 ± 0.5 Mʘ

Star 2: 3.8 ± 0.5 Mʘ

Porb: 17 ± 5 days

>99.9% probability to

fit to helium shellburning phase

Stripped helium stars of various Mʘ

• No core helium burning helium stars seem to fit

MHe*,obs = 1.2 ± 0.2 Mʘ

Stripped helium stars of various Mʘ

• No core helium burning helium stars seem to fit

MHe*,obs = 1.2 ± 0.2 Mʘ

The φ Persei family

• For similar systems, only 2% is as bright as φ Persei’s hot companion ~50 less luminous He star systems expected (φ Per)-1

The φ Persei family

• For similar systems, only 2% is as bright as φ Persei’s hot companion ~50 less luminous He star systems expected (φ Per)-1

Proposed topic of discussion:

How to systematically search for

stripped donor stars?

Emergency slide I

Emergency slide II

Is a case A mass transfer scenario possible?

From J-conservation it follows that (if mass is conserved):𝑃

𝑃0

= (𝑀1

,0𝑀2

,0

𝑀1𝑀2

)3

• Even with M1,0 = M2,0 = 5.4 Mʘ P0 = 8 d is needed to reach

P = 126 d, M1 = 1.2 Mʘ and M2 = 9.6 Mʘ

Image credit: Hubble ESA Information Center

Emergency slide III – detailed model

Observations

of He star

Onset of He

shell burning

time

Computational method: BINARY_C

Grid:• Z = 0.02

• Salpeter IMF: df ~ M1-2.35 dM1

• Flat mass ratio distribution

• fP ~ (log10(P/d))0 (Öpik’s law)

*See Hurley+00, 02

Izzard+04, 06, 09de Mink+13

Physics assumptions:• Accretion limited by 10*Macc / tthermal

• Angular momentum loss bipolar outflow

from accretor star

binary_cFast binary evolution code*

• ~106 systems day-1

• Does not solve stellar structure