Hyperactive brown dwarf has a companion, and may be old and heavy to boot

Stellar activity is typically attributed to magnetic field interactions, but in brown dwarfs this emission is more of a mystery.

For the most part, brown dwarfs don’t do very much; they just sit there and slowly cool off.  But a rare few are “hyperactive”, exhibiting emission lines that both vary and persist over long periods of time. The source of this activity has been a mystery for nearly a decade, but new observations we’ve conducted with the IRTF, Magellan and Keck Telescopes show that one of these hyperactive dwarfs has a very faint companion, and that it is hyperactive because it is very old and relatively massive.

First L Dwarf in the Kepler Field

An image of WISE 1906+4011 from the Kepler Observatory; the green mask marks the location of this faint source.

The Kepler Observatory is uncovering numerous planets in close orbits around distant stars.  Now it has a brown dwarf under its belt.  A search for nearby cool dwarfs by University of Delaware collaborator John Gizis uncovered the first L dwarf in Kepler, a source that may teach us much about clouds in cool brown dwarfs.

Discovery of a “wide” M dwarf-L dwarf binary

Vanderbilt University graduate student Saurav Dhital and collaborators report the discovery an unusually wide low-mass star plus brown dwarf binary. The dim pair of dwarfs, separated by over 100 AU, presents a new challenge to theories describing the formation of very low mass stars and brown dwarfs.

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

A Blue Brown Dwarf

Not all brown dwarfs are brown

We report observations of an unusually blue brown dwarf, a nearby object that may be among the coldest and oldest brown dwarfs known.  The source, ULAS J141623.94+134836.3, was originally discovered in the UKIDSS survey independently by R. Scholz and B. Burningham et al., and early results indicated its surface could be as cool as 500 K. It could even be the first Y dwarf.   Our near-infrared spectrum, obtained with the IRTF SpeX spectrograph, instead shows it to be somewhat warmer (650 K), as well as old, massive and depleted in “metals” (any element other than hydrogen and helium).  ULAS J1416+1348 is also a companion to the unusually blue L dwarf SDSS J141624.08+134826.7 discovered earlier this year by several groups.  This nearby brown dwarf pair has generated a lot of interest among astronomers, with five publications in six months.

This result was published in in the Astronomical Journal; it was also an IRTF science highlight.

June 2010