Bibcode
Dobbie, P. D.; Baxter, R.; Külebi, B.; Parker, Q. A.; Koester, D.; Jordan, S.; Lodieu, N.; Euchner, F.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 421, Issue 1, pp. 202-212.
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3
2012
Citations
22
Refereed citations
17
Description
We report the discovery of two, new, rare, wide, double-degenerate
binaries that each contain a magnetic and a non-magnetic star. The
components of SDSS J092646.88+132134.5 + J092647.00+132138.4 and of SDSS
J150746.48+521002.1 + J150746.80+520958.0 have angular separations of
only 4.6 arcsec (a˜ 650 au) and 5.1 arcsec (a˜ 750 au),
respectively. They also appear to share common proper motions. Follow-up
optical spectroscopy has revealed each system to consist of a DA and a
H-rich high-field magnetic white dwarf (HFMWD). Our measurements of the
effective temperatures and the surface gravities of the DA components
reveal both to have larger masses than is typical of field white dwarfs.
By assuming that these degenerates have evolved essentially as single
stars, owing to their wide orbital separations, we can use them to place
limits on the total ages of the stellar systems. These suggest that in
each case the HFMWD is probably associated with an early-type progenitor
(Minit > 2 M&sun;). We find that the cooling
time of SDSS J150746.80+520958.0 (DAH) is lower than might be expected
had it followed the evolutionary path of a typical single star. This
mild discord is in the same sense as that observed for two of the small
number of other HFMWDs for which progenitor mass estimates have been
made, RE J0317-853 and EG 59. The mass of the other DAH, SDSS
J092646.88+132134.5, appears to be smaller than expected on the basis of
single-star evolution. If this object was/is a member of a hierarchical
triple system it may have experienced greater mass loss during an
earlier phase of its life as a result of its having a close companion.
The large uncertainties on our estimates of the parameters of the HFMWDs
suggest that a larger sample of these objects is required to firmly
identify any trends in their inferred cooling times and progenitor
masses. This should shed further light on their formation and on the
impact magnetic fields have on the late stages of stellar evolution. To
serve as a starting point, we highlight two further candidate young,
wide magnetic + non-magnetic double-degenerate systems within SDSS, CBS
229 and SDSS J074853.07+302543.5 + J074852.95+302543.4, which should be
subjected to detailed (resolved) spectroscopic follow-up studies.
Related projects
Very Low Mass Stars, Brown Dwarfs and Planets
Our goal is to study the processes that lead to the formation of low mass stars, brown dwarfs and planets and to characterize the physical properties of these objects in various evolutionary stages. Low mass stars and brown dwarfs are likely the most numerous type of objects in our Galaxy but due to their low intrinsic luminosity they are not so
Rafael
Rebolo López