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We report on the first ground-based measurement of the relativistic beamingeffect (aka Doppler boosting). We observed the beaming effect in the detached,non-interacting eclipsing double white dwarf (WD) binary NLTT 11748. Ourobservations were motivated by the system's high mass ratio and low luminosityratio, leading to a large beaming-induced variability amplitude at the orbitalperiod of 5.6 hr. We observed the system during 3 nights at the 2.0m FaulkesTelescope North with the SDSS-g' filter, and fitted the data simultaneously forthe beaming, ellipsoidal and reflection effects. Our fitted relative beamingamplitude is (3.0 +/- 0.4) x 10^(-3), consistent with the expected amplitudefrom a blackbody spectrum given the photometric primary radial velocityamplitude and effective temperature. This result is a first step in testing therelation between the photometric beaming amplitude and the spectroscopic radialvelocity amplitude in NLTT 11748 and similar systems. We did not identify anyvariability due to the ellipsoidal or reflection effects, consistent with theirexpected undetectable amplitude for this system. Low-mass, helium-core WDs areexpected to reside in binary systems where in some of those systems the binarycompanion is a faint C/O WD and the two stars are detached and non-interacting,as in the case of NLTT 11748. The beaming effect can be used to search for thefaint binary companion in those systems using wide-band photometry.

A ground-based measurement of the relativistic beaming effect in a detached double WD binary