Discovery of the Nearest Young Binary

Three-color image of the sky around TWA 30, with the faint red companion TWA 30B indicated due north.

Earlier this year, U. Hawaii Graduate student Dagny Looper reported the discovery of a young, low-mass and highly active star in the TW Hydrae Association, TWA 30.  She has now found that that star is just one component of an unusual pair.

Only 80″ (0.02 degrees) north of TWA 30 lies a faint red star just barely visible in the image above.  This source is so red that it was worth a look with the MagE spectrograph at the Magellan Telescopes.  The resulting spectrum revealed a rich set of the same forbidden emission lines the we saw in the spectrum of TWA 30, indicating accretion onto the star from a circumstellar disk and  powerful magnetically-driven jets emanating from the star’s poles.  Moreover, we found two lines of forbidden neutral carbon emission, [C I], an important probe of the gas in the disk that surrounds this source, according to a 2009 study led by Dr. Barbara Ercolano.  This is the first time these lines have been seen in the spectrum of a young star.

Two spectra (black and red lines) of TWA 30B taken with the MagE spectrograph, highlighting the bevy of emission lines arising from accretion onto and jets powered by this young star. The forbidden carbon lines are seen in the bottom panel around 8700 A and 9800 A

Like TWA 30, the new source is highly variable in the near-infrared, changing its color by over a  magnitude over the course of a few days.  However, its “direction” of variability on a near-infrared color-color plot is different from that of TWA 30, indicating that it is caused not by changes of line-of-sight reddening, but changes in how its disk is blocking starlight.  The disk, apparently viewed edge-on, has structure to it!

Variations in the near-infrared colors of TWA 30A (red stars) and TWA 30B (green stars). TWA 30A's changes are consistent with reddening caused by dust extinction (arrow at lower right), but TWA 30B's variations appear to be due to patchy obscuration by a circumstellar disk.

The motion of the new source both across the sky and radially away from us, is consistent with being both a member of the TW Hydrae association and a co-moving companion to TWA 30.  Hence, these two stars – TWA 30A and TWA 30B – are a remarkable wide young binary system, nearly 3400 AU in projected separation.  What is most surprising is that TWA 30B is about 5 magnitudes fainter than TWA 30A in the near-infrared, even though it has an earlier spectral type.  This is further evidence that the star is being obscured by an edge-on disk, much like the faint secondary in the HK Tau B binary star system.  Upcoming Hubble Space Telescope observations led by Dr. John Bochanski should reveal more about this remarkable system.

This result was published in in the Astronomical Journal. Authors include Dagny L. Looper (U. Hawaii), John J. Bochanski (MIT/Penn. State), Adam J. Burgasser (UCSD), Subhanjoy Mohanty (Imperial College), Eric E. Mamajek (U. Rochester), Jacqueline K. Faherty (SUNY Stony Brook), Andrew A. West (Boston U.), and Mark A. Pitts (U. Hawaii).

An Unsuspecting Pair

l-and-t-binary-brown-dwarf-system

Found two brown dwarfs for the effort 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

Discovery of a Wacko Star

Jets, disks and accretion in nearby low mass star

U. Hawaii Graduate student Dagny Looper reports the discovery of a young, low-mass nearby star that is both unusually active and highly variable. The star, TWA 30, is a member of the TW Hydrae Association, roughly two dozen ~8 million year-old stars located about 50 pc away. TWA 30 is the newest member of this group, and one of the most intriguing. Its optical spectrum shows classical and forbidden emission lines, indicating that it is both accreting material and emitting high-speed jets of gas. The star’s near-infrared color also varies dramatically on week-long timescales, evidence that it periodically hides behind a nearly edge-on circumstellar disk. This makes TWA 30 one of the nearest T Tauri stars to the Sun.

The paper was published in the Astrophysical Journal.

May 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