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 P orb 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+GRGR

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 P orb range - Pile-up at P min

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 in removing 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 T wd ( age ), P orb P CE, P CV, timescale AML (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<10 8 yr) low mass companions = will start mass transfer at P orb <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 ) -ESO (pilot –study, proposed ) -ESO (Large program, planed )

CA-observations Feb 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 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: