An Unsuspecting Pair

Two for the price of one

Spitzer Science Center colleague Christopher Gelino and I report the identification of low-mass binary system that refuses to show itself.  The source, 2MASS J20261584–2943124, is an L dwarf which until now had seemed to be a perfectly unassuming source.  However,  low-resolution, near-infrared spectroscopy we obtained with the IRTF SpeX spectrograph revealed a peculiar absorption feature that is commonly seen in very low-mass “spectral binaries”, blends of stars with different spectral types.  Our analysis indicates that this source is an L dwarf plus T dwarf pair, with a relative brightness of roughly 4 magnitudes (or 40 times fainter) in the near-infrared.  We were unable to resolve the putative pair with the Keck Observatory laser guide star adaptive optics system, which rules a binary wider than  9 Astronomical Units (about the distance between the Sun and Saturn).  Next step: look for Doppler shifts in the spectrum that would indicate the gravitational influence of the unseen companion and allow us to measure its mass.

This research was published in the Astronomical Journal. Authors include Christopher R. Gelino (Spitzer Science Center) and Adam J. Burgasser (UCSD).

July 2010