T. L. Esplin

A WISE survey of circumstellar disks in Taurus

We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ~M8 (M 0.03 M ☉).

A CENSUS OF YOUNG STARS AND BROWN DWARFS IN IC 348 AND NGC 1333

We have obtained optical and near-infrared spectra of candidate members of the star-forming clusters IC 348 and NGC 1333. We classify 100 and 42 candidates as new members of the clusters, respectively, which brings the total numbers of known members to 478 and 203. We also have performed spectroscopy on a large majority of the previously known members of NGC 1333 in order to provide spectral classifications that are measured with the same scheme that has been applied to IC 348 in previous studies. The new census of members is nearly complete for Ks<16.8 at Aj<1.5 in IC 348 and for Ks<16.2 at Aj<3 in NGC 1333, which correspond to masses of <=0.01 Msun for ages of 3 Myr according to theoretical evolutionary models. The faintest known members extend below these completeness limits and appear to have masses of ~0.005 Msun. In extinction-limited samples of cluster members, NGC 1333 exhibits a higher abundance of objects at lower masses than IC 348. It would be surprising if the initial mass functions of these clusters differ significantly given their similar stellar densities and formation environments. Instead, it is possible that average extinctions are lower for less massive members of star-forming clusters, in which case extinction-limited samples could be biased in favor of low-mass objects in the more heavily embedded clusters like NGC 1333. In the H-R diagram, the median sequences of IC 348 and NGC 1333 coincide with each other for the adopted distances of 300 and 235 pc, which would suggest that they have similar ages. However, NGC 1333 is widely believed to be younger than IC 348 based on its higher abundance of disks and protostars and its greater obscuration. Errors in the adopted distances may be responsible for this discrepancy.

A NEW PARALLAX MEASUREMENT FOR THE COLDEST KNOWN BROWN DWARF

WISE J085510.83-071442.5 was recently discovered as the coldest known brown dwarf based on four epochs of images from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope. We have improved the accuracy of its parallax measurement by obtaining two additional epochs of Spitzer astrometry. We derive a parallactic distance of 2.31+/-0.08 pc, which continues to support its rank as the fourth closest known system to the Sun when compared to WISE J104915.57-531906.1 AB (2.02+/-0.02 pc) and Wolf 359 (2.386+/-0.012 pc). The new constraint on the absolute magnitude at 4.5um indicates an effective temperature of 235-260 K based on four sets of theoretical models. We also show the updated positions of WISE J085510.83-071442.5 in two color-magnitude diagrams. Whereas Faherty and coworkers cited its location in MW2 versus J-W2 as evidence of water clouds, we find that those data can be explained instead by cloudless models that employ non-equilibrium chemistry.

PHOTOMETRIC MONITORING OF THE COLDEST KNOWN BROWN DWARF WITH THE SPITZER SPACE TELESCOPE

Because WISE J085510.83

MEASURING HIGH-PRECISION ASTROMETRY WITH THE INFRARED ARRAY CAMERA ON THE SPITZER SPACE TELESCOPE*

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The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy

071442.5 (hereafter WISE 0855-0714) is the coldest known brown dwarf (

A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions

\sim250

A Survey for Planetary-mass Brown Dwarfs in the Chamaeleon I Star-forming Region

K) and one of the Suns closest neighbors (2.2 pc), it offers a unique opportunity for studying a planet-like atmosphere in an unexplored regime of temperature. To detect and characterize inhomogeneities in its atmosphere (e.g., patchy clouds, hot spots), we have performed time-series photometric monitoring of WISE 0855-0714 at 3.6 and 4.5 micron with the Spitzer Space Telescope during two 23~hr periods that were separated by several months. For both bands, we have detected variability with peak-to-peak amplitudes of 4-5% and 3-4% in the first and second epochs, respectively. The light curves are semi-periodic in the first epoch for both bands, but are more irregular in the second epoch. Models of patchy clouds have predicted a large increase in mid-IR variability amplitudes (for a given cloud covering fraction) with the appearance of water ice clouds at

New Young Stars and Brown Dwarfs in the Upper Scorpius Association

T_{\rm eff}<

A WISE Survey of Circumstellar Disks in the Upper Scorpius Association

375 K, so if such clouds are responsible for the variability of WISE 0855-0714, then its small amplitudes of variability indicate a very small deviation in cloud coverage between hemispheres. Alternatively, the similarity in mid-IR variability amplitudes between WISE 0855-0714 and somewhat warmer T and Y dwarfs may suggest that they share a common origin for their variability (i.e., not water clouds). In addition to our variability data, we have examined other constraints on the presence of water ice clouds in the atmosphere of WISE 0855-0714, including the recent mid-IR spectrum from \citet{ske16}. We find that robust evidence of such clouds is not yet available.