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.

FIRE Fingerprints Cold Brown Dwarfs

In this WISE false-color image, a cold brown dwarf appears green

The Folded Port Infrared Echellette (FIRE) spectrograph, commissioned in March 2010, is contributing to the discovery of some of the coldest and least luminous brown dwarfs found to date.  In a paper accepted for publication to the Astrophysical Journal, we report the discovery of five late-type T dwarfs from the WISE survey identified by FIRE.

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.

Clouds on a Young Planet: First Science Results with FIRE

A UKIDSS false color image of the Ross 458 system, composed of a pair of M dwarfs (bright star in upper left corner) and the planetary-mass brown dwarf Ross 458C (circled in lower right corner).

To study the atmospheres of young planets outside our Solar System, we need not look  far.  The first brown dwarf science with the newly-commissioned FIRE spectrograph has revealed the presence of rock clouds in the atmosphere of a planetary-mass companion to the nearby Ross 458 system.  The presence of these clouds, and the planetary nature of the source, defy prior expectations.

The source in question is Ross 458C, a brown dwarf candidate identified in the UKIDSS survey in early 2010 by two independent studies led by Drs. Rolf-Dieter Scholz and Betrand Goldman.  This source, also known as ULAS J130041.72+122114.7, is located 1.7′ (0.028 degrees) southeast of the Ross 458 system, a pair of magnetically active M dwarfs only 11.2 pc (36.5 light-years) from the Sun. The colors and faintness of Ross 458C, and that fact that it co-moves with the Ross 458 system, led both studies to conclude that it was potentially a very cool and very low-mass brown dwarf companion.  However, neither study had the necessary spectral data to probe its atmosphere.

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

FIRE is alive!

FIRE mounted on Magellan's Baade Telescope

The Folded Port Infrared Echellette was successfully delivered and commissioned at the Magellan Telescopes at Las Campanas Observatory in Chile. Led by MIT Asst. Professor Robert Simcoe and Adam Burgasser, with major contributions by postdoctoral researcher John Bochanski, FIRE is a single-object, near-infrared spectrograph capable of obtaining 0.9-2.5 μm spectroscopy of faint sources at resolutions of 300-10,000. First science results will be published later this year.

Learn more at the FIRE website and on a recent blog post.  You can even buy FIRE merchandise!.

April 2010