SDSS finds the period minimum spike

Boris Gänsicke

John Southworth John Thorstensen

M Dillon, P Rodríguez-Gil, A Aungwerojwit, TR Marsh, P Szkody, SCC Barros, J Casares, D de Martino, PJ Groot, P Hakala, U Kolb, SP Littlefair,

IG Martínez-Pais, G Nelemans, MR Schreiber

Ilse Decoster

CV Evolution in a nutshellH

ow

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t al. (2

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1)

• Angular momentum loss MB/GR

MBGR

• Porb decreases down to Pmin

• Donor becomes degenerate BD

• Porb increases again

Period bouncing

CV evolution in a nutshell

Howell et al. 2001, ApJ 550, 897Kolb & Baraffe 1999, MNRAS 309, 1034

70%

29%

1% • Most systems post-bounce

• Spike at Pmin

MB

GR

• Angular momentum loss MB/GR

• At Pmin: donor BD

• MB disrupted at P=3h

Ritter 5 (1990): 167 CVs

Ritter & Kolb 6 (1998): 314 CVs

Ritter & Kolb 7.2 (2004): 518 CVs

CV evolution: theory & observations

• Pmin≈65min

80 min!

(Ritter & Kolb 2004)

• Spike @ Pmin

selection effects?

Of spikes and small numbers

Hameury et al. (1990)

114min

80 polars today

The PG CVs

- 35 CVs, of which 31 new

- 31 periods determined

(Ringwald PhD 1993, Thorstensen, and others)

no spike (see Pretorius)

CVs from the Hamburg Quasar Survey

- 96 CVs, of which 53 new

- 86 periods determined

(Gänsicke, Rodríguez-Gil, Aungwerojwit, Hagen, Engels, ...)

... 24 HQS CVs with Porb=3-4h ...

spike?

SDSS CVs

(Szkody et al. 2002, 2003, 2004)

- 101 CVs, of which 90 new

- 45 periods determinedITP time 2004/5 for SDSS CV follow-up:70 nights WHT, TNG, INT, NOT & LT(Gänsicke et al.)

Recycled slide detected … recycled slide

detected …

SDSS CVs in DR7

(Szkody et al. 2002, 2003 , 2004 , 2005 , 2006 , 2007 , 2009)

- 281 CVs, of which 90 new

- 126 periods determined

?

10 years effort in 2 minutes

Period accurate to better than 3%

10 years effort in 2 minutes

Period accurate to better than 3%

10 years effort in 2 minutes

Period accurate to better than 3%

SDSS CVs differ significantly from previous samples

new SDSS CVs

old SDSS CVs

non-SDSS CVs

- old vs non: 52.2%

- new vs non: 0.065%

two-sided Kolmogorov-Smirnov test

Gänsicke et al. 2008, MNRAS, submitted

why?

Properties of SDSS CVs

“active” CVs in the spike

V844 HerT LeoSW UMaEV UMaGG Leo

Old (active) SDSS CVs with 80min<Porb<86min

SW UMa T Leo

V844 Her EV UMa

New SDSS CVs with 80min<Porb<86min

New (inactive) SDSS CVs with 80min<Porb<86min

New (inactive) SDSS CVs with 80min<Porb<86min

New (inactive) SDSS CVs with 80min<Porb<86min

eclipsing

poor data eclipsing

polar

New (inactive) SDSS CVs with Porb>86min

New (inactive) SDSS CVs with Porb>86min

Some comments on the space density

- WD-dominated, or “WZ Sge” are often considered

post-period-bounce (candidate) systems…- Yes, SDSS finds many new “WZ Sge”… but,

they are all faint (g>17.6) and far (>150pc) away…

- …yet, no bias against finding nearby “WZ Sge”…

- “WZ Sge”s, bouncers or not, are not very common

- While Littlefair found good evidence for bouncers, they are all at Pmin

- Even SDSS has not found the predicted large population of period bouncers

SDSS finds the period spike because of depth

“Palomar Green”

“Hamburg Quasar Survey”

“SDSS Quasar Survey”

“SDSS all”

Completeness: the QSO exclusion boxes

-WD box: one faint CV-A-star box: no CV-WMDS box: 5 CVs with Porb>150min

while excluded from the QSO programme, there are sufficientspectra to inspect the kind of objects they contain.

no effect on the period spike discussed here

non-SDSS-discovered CVs in the SDSS footprint

QSO survey limit

SDSS CV (re)identification efficiency

CV has re-discovered ~90% of the previously known CVs with 17<g<19

QSO survey limit

Testing CV completeness by colour proximity

i<19.1: 66% complete

19.1<i<23: 13% complete

Selecting CV candidates via p.m. from GALEX/SDSS

1437 objects with- 5 p.m.- GALEX fluxes- SDSS spectra

all WD-cut QSO-cut

CV 67 67 63 11.3%

WD 601 169 113 31.5%

WDMS 398 368 308 55.2%

QSO 371 363 74 13.3%

Total 1437 967 558

Selecting CV candidates via p.m. from GALEX/SDSS

3713 objects with- 5 p.m.- GALEX fluxes- no SDSS spectra

1689 candidates, expect- 191 CVs- 532 WDs- 932 WDMS binaries- 225 QSO

Summary

• SDSS goes deeper than any survey before, and the SDSS CV population exhibits a period spike at Pmin=80min, but need accurate orbital periods

• The spectra of the majority of “spike” CVs are WD dominated, “WZ Sge”-like, but SDSS has still not found the predicted large population of period-bouncers.

• The SDSS CV population is 66-90% complete for 17<i<19, but completeness drops quickly below i=19.1 … and that’s where the WD-dominated CVs become more numerous!

• The “missing” SDSS CV population can be targeted via a selection combining optical/UV colours and proper motion