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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
ell e
t al. (2
00
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
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