4. New Close Binary Systems (WD + MS) from SDSS (DR 5) And the Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems Nicole Silvestri and a Washington - SDSS Cast of Characters ~More than 1200 spectroscopically selected close binary systems --DA + ms (usually M dwarf) --good enough quality spectrum to see Zeeman splitting to detect B ~ 2 megagauss or larger (= strongly magnetic).but… NONE of the white dwarfs are strongly magnetic 149 magnetic white dwarfs (most from SDSS) tabulated in Paper by Kawka, Vennes, Schmidt, Wickramasinge and Koch (ApJ, in press) with B = 3 MG or larger None of these has a nondegenerate companion One has a brown dwarf (hydrogen degenerate) companion (G. Schmidt, P. Szkody, N. Silvestri, M. Cushing, J. Liebert and P. Smith 2005, ApJ, 630, 173) But this one turns out to be accreting wind from the brown dwarf

5. Dozens of the binaries are close enough to be CV progenitors Of the type lacking a strongly magnetic primary star (dwarf novae, etc.) Dozens more (not from SDSS) are catalogued by Ritter and Kolb -- none of these have a strongly magnetic White dwarf.but....about 25% of known CVs harbor a strongly magnetic.accreting primary (polars, some intermediate polars) To be clear about this, a couple of caveats -- --Some precataclysmic systems show evidence that the White Dwarf has a weaker magnetic field -- V471 Tauri and its variable X-ray emission with.rotating magnetic pole --many intermediate polars have white dwarfs with.weaker fields

6. What should we expect to see? *In a magnitude-limited sample, the PG Survey of hot, bright white dwarfs, Only 2% are strongly magnetic So, naively, 2% of the 1200 primaries from SDSS, also magnitude-limited Or 24 (+/- 5) Should be magnetic *The sample of nearby white dwarfs of Holberg, Oswalt and Sion (2002 ApJ 571, 512) is well searched for companions Of the 109 WDs, 21 or 19 (+/- 4.5) have main sequence companions We might therefore expect 14-24 % of the 149 strongly magnetic WDs in the Kawka et al. catalogue -- 21 - 35 white dwarfs To have such companions *Another relevant study by Holberg and K. Magargal, presented at the 14th European WD Workshop at Kiel in 2004 Used the 2MASS Survey data on the PG white dwarfs to look for Companions producing an excess at the J,H and/or K bands Found 23% “definite” and 29% “definite + probable” WDs need a cool companion So that, out of the 149 Magnetic WDs, 34 to 43 should have companions In Six Sigma Territory here!

7. Wellhouse, Hoard, Howell, Wachter and Esin 2005 PASP 117, 1378 Found 51 known magnetic white dwarfs Detected in the Two Micron All Sky Survey (J,H, and K bands) None showed convincing evidence of an infrared excess above the R-J tail of the white dwarf. These authors, Zuckerman and Becklin, and Hollberg had previously shown that near-infrared observations can be an effective tool at finding faint, cool companions. However, only the brighter magnetic WDs listed in the Wickramasinghe and Ferrario 2000 PASP review were detected. Very few of the newly-discovered SDSS white dwarfs (Vanlandingham et al. 2005 appeared in the 2MASS list. However, six of the detections showed possible, small infrared excesses, and might be followed up with improved infrared observations. Some stars were near the 2MASS limiting magnitudes, so That the detections are not at high signal-to-noise.

8. One other caveat.. The true fraction of strongly magnetic white dwarfs In a volume-limited sample may be closer to or even exceed 10% (Kawka PhD dissertation, Liebert, Bergeron and Holberg 2005 AJ 129, 2376) Due to the fact that the mean mass of magnetic white dwarfs is higher Their radii are smaller The search volume to a given magnitude limit is much smaller (as R cubed !) The Holberg, Oswalt and Sion 2002 nearby white dwarf sample is volume limited And.. 21 of 109 local WDs are magnetic (19 +/- 4 %)

9. So… We needed to simulate what we expect To find in a MagWD + M spectrum Nicole Silvestri, Suzanne Hawley, Paula Szkody,..and the rest of us soldiered on

12. Where are the Magnetic White Dwarfs with Detached, Nondegenerate Companions? James Liebert, Dayal Wickramasinghe, Gary Schmidt, Nicole Silvestrii, Suzanne Hawley, Paula Szkody, Lilia Ferrario, Ronald Webbink, Terry Oswalt, J. Allyn Smith and Mara Lemagie A paper with no new observational data no new calculation No Figure No Table 2005 Astronomical Journal, 129, 2376