Constraining close binaries evolution with SDSS/SEGUE:a representative sample of white dwarf/main sequence

binaries

Matthias Schreiber

ESO, May 4th, 2006

The questions in compact binary evolution are…

… the questions that everyone of us has

Where do I come from?

How much time have I left?

Where will I go to?

And what am I supposed to do here?

Motivation

Understanding the formation and evolution of close binaries:

• Supernova Ia

• Binary millisecond pulsars

• Galactic black hole candidates

• Short gamma-ray bursts

• Catalysmic Variables

• Part of stellar evolution

• …

The evolution into close binaries

Parameter: “CE-efficiency” “binding energy parameter”

How strong is AML due to magnetic braking?

Example: Our non-understanding of the evolution of CVs

Ritter & Kolb (2003) V7.3: 531 systems

Porb is typically the best determined parameter of a CV

Flashback – 1983: Disrupted magnetic braking

Paczynski & Sienkiewicz; Spruit & Ritter; Rappaport et al. (1983)

Two angular momentum loss mechanisms:

magnetic wind braking & gravitational radiation

MWB+GR GR

Predictions of the standard CV evolution model

- Lack of CVs in the 2-3h Porb range

The period gap

The standard model: Predictions

- Minimum orbital period at ~65min

- Paucity of CVs in the 2-3h Porb range

Period bouncing

The orbital period minimum

80 min!

The standard model: Predictions

- Minimum orbital period at ~65min X

- Paucity of CVs in the 2-3h Porb range

- Pile-up at Pmin

Population syntheses: The period minumum

Kolb & Baraffe (1999)

The orbital period minimum

80 min!

The standard model: Predictions

- Minimum orbital period at ~65min X

- Paucity of CVs in the 2-3h Porb range

- 99% of all CVs have Porb<2h

- Pile-up at Pmin X

The orbital period distribution

207=39%250=51%

55=10%

The standard model: Predictions

- Minimum orbital period at ~65min X

- Paucity of CVs in the 2-3h Porb range

- 99% of all CVs have Porb<2h X

- CV space density ~

Observed ~ X

- Pile-up at Pmin X

Additions to the standard model (incomplete)

• The binary age postulate (Schenker & King 2002)

• Hibernation (Shara et al. 1986)

• Alternative angular momentum loss rates (e.g. Andronov et al. 2003, Taam et al. 2003)

Large number of detached white dwarf/red dwarf binaries

Too low accretion rates (Andronov), circumbinary discs (Taam)

Large number of detached white dwarf/red dwarf binaries

… what else can we do?

• Overcome observational biases and provide a statistically representative sample of close binaries to constrain the theories of CE-evolution and magnetic braking.

• Detached white dwarf/main sequence binaries are the best class of systems for this task because they are:

• intrinsically numerous

• clean (no accretion)

• accessible with 2-8m telescopes

• well understood

Members of the WD/MS population

- long orbital period systems i.e. WD/MS that will never interact

- pre-CVs i.e. PCEBs which will become a CV in less than a Hubble-time

- Post-common envelope binaries (PCEBs) i.e. WD/MS which

went through a CE-phase

Constraining CE-evolution with WD/MS binaries

Two algorithms to determine the final separation are proposed:

1. Energy conservation (Paczynski 1976)

2. Angular momentum conservation (Nelemans & Tout 2005)

Reconstructing the CE-phase for a representative sample will tell us if one algorithm works!!

How large is the gap?

- A large gap in the WD/MS distribution will indicate a low efficiency of using the binary energy (angular momentum)to expel the envelope.

- No gap will indicate that the CE-phase is very efficient inremoving the giants envelope.

(Willems & Kolb 2004)

Is magnetic braking disrupted?

PCEBs can tell us:

Politano & Weiler (2006)

The age of WD/MS systems

(Schreiber & Gänsicke 2003)

The evolution of close WD/MS systems

Twd (age), Porb PCE, PCV, timescaleAML

(Schreiber & Gänsicke 2003)

The contact orbital periods

(Schreiber & Gänsicke 2003)

Selection effects in the pre-SDSS sample

(Schreiber & Gänsicke 2003)

PG: U-B<-0.46

Selection effects in the pre-SDSS sample

(Schreiber & Gänsicke 2003)- Extremely biased sample: hot white dwarfs = young systems (t<108yr) low mass companions = will start mass transfer at Porb<4h

WD/MS systems in SDSS I and SEGUE

• Stars (white dwarfs, main sequence)

WD/MS systems in SDSS I and SEGUE

• Stars (white dwarfs, main sequence)• Quasars

WD/MS systems in SDSS I and SEGUE

• Stars (white dwarfs, main sequence)• Quasars• WD/MS from SDSS I

WD/MS systems in SDSS I and SEGUE

• Stars (white dwarfs, main sequence)• Quasars• WD/MS from SDSS I• Model WD (8-40kK) + MS (K0-M8)

WD/MS systems in SDSS I and SEGUE

• Stars (white dwarfs, main sequence)• Quasars• WD/MS from SDSS I• Model WD (8-40kK) + MS (K0-M8)• SDSSII / SEGUE WD/MS candidates

(4 fibers per field)

SEGUE WD/MS spectra

Immediate objectives:

• Space density

• Fraction of magnetic systems

• Age of the population

• Evolutionary time scale

Current success rate is ~70%: number one in SEGUE!!!

Vision: Follow-up observations of the entire sample to constrain the CE-phase and magnetic braking

Status of follow-up observations

- Calar Alto 3.5 (first pilot study, performed)

- Calar-Alto DDT (first orbital period, performed)

- WHT (6 nights July 2006, received)

- Calar-Alto Large Program (proposed 03.2006)

- ESO (pilot –study, proposed 03.2006)

- ESO (Large program, planed 09.2006)

CA-observations Feb. 2006

In agreement with BPS predictions of 15-20%

CA-Observations, March 2006

A 10 hrs orbital period PCEB:

Conclusions

- A representative sample of WD/MS binaries will allow to significantly progress with our understanding of close binary evolution:

- constrain the CE-phase- estimate the strength of magnetic braking- test the disrupted magnetic braking hypothesis

- The pre-SDSS sample and the systems identified in SDSS I are strongly biased.

- We run a very successful SEGUE project and will identify the required representative sample until 2008

- First follow-up observations give promising results!!

The Collaboration:

PI: Matthias Schreiber (Valparaiso)

Boris Gaensicke (Warwick)

Axel Schwope (Potsdam)

Ada Nebot (Potsdam)

Robert Schwarz (Potsdam)

Alberto (Warwick)

Pablo Rodriguez-Gil (IAC)

Nikolaus Vogt (Valparaiso)

Mission Members: