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Common Proper Motion White Dwarfs in the field of MASTER OT J043915.60+424232.3

ATel #5788; D. Denisenko, V. Lipunov, P. Balanutsa, N. Shatskiy (Moscow State University, SAI)
on 22 Jan 2014; 20:25 UT
Credential Certification: Vladimir Lipunov (lipunov2007@gmail.com)

Subjects: Optical, Binary, Cataclysmic Variable, Star

Pair of White Dwarfs with Common Proper Motion in Perseus

While examining the archival DSS images of the 15'x15' area centered at new CV MASTER OT J043915.60+424232.3 (P. Balanutsa et al., ATel #5787) we have detected the pair of blue stars 5.5' North of the OT with a common proper motion between the 1st and 2nd epoch Palomar plates. The two stars are separated by 9". They are present in USNO-B catalogue with the following coordinates, proper motion and magnitudes:
USNO-B1.0 1327-0126626 04 39 23.098 +42 47 52.71 pmRA=20 pmDE=-56 B1=18.03 R1=17.94 B2=17.66 R2=17.79 I=18.10
USNO-B1.0 1328-0128717 04 39 22.885 +42 48 01.30 pmRA=18 pmDE=-46 B1=N/A R1=18.62 B2=18.35 R2=18.91 I=18.37

Errors of proper motion for the two stars are (4, 1) and (6, 5) mas/yr, respectively. Thus, proper motions can be considered equal within the formal uncertainty limits. There is a high probability that the two stars are gravitationally bound.

Color-combined (BRIR) finder chart is uploaded to http://master.sai.msu.ru/static/OT/CPM-WD-Perseus-BRIR4x4.jpg (2x zoom). The animation of POSS-I and POSS-II blue plates is available at http://master.sai.msu.ru/static/OT/CPM-WD-POSS-B-anim.gif

One of two stars is included in the Finding List of faint UV-bright stars in the galactic plane by H. Lanning and M. Meakes (PASP Vol. 113, pp. 1393-1405, 2001) as Lan 513. However, the UV star is incorrectly identified in Simbad with the northern (fainter) component of the pair, while the GALEX data are clearly showing the southern (brighter) star to be a source of UV emission: GALEX J043923.1+424753 with NUV=18.16+/-0.06. The northern component is not present in GALEX catalog, despite being 0.5-0.7m fainter in optical band. Inspection of GALEX NUV image is actually showing a faint object to the north of the brighter source which is 3-3.5m fainter (NUV~21.5).

According to the paper by J. Andrews et al. [arXiv:1209.0175], there were only 45 wide double white dwarfs known as of September, 2012. Spectral and photometric observations are required. This pair of white dwarfs is potentially a good target for measuring the parallax, proper motion and probably even the orbital motion by GAIA and future astrometric missions.

We also note that the proper motion of this pair is very similar to that of MASTER OT J042609.34+354144.8 (D. Denisenko et al., ATel #4441) - cataclysmic variable in Perseus comoving with the red dwarf (pmRA=16 pmDE=-42). It is likely that all these stars belong to the same stellar stream.