Between 1997 June and 2001 February the Two Micron All Sky Survey (2MASS) collected 25.4 Tbytes of raw imagingdatacovering99.998%ofthecelestialsphereinthenear-infraredJ(1.25 � m),H(1.65 � m),andKs(2.16 � m) bandpasses. Observations were conducted from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona,andCerroTololo,Chile.The7.8sofintegrationtimeaccumulatedforeachpointontheskyandstrictquality control yielded a 10 � point-source detection level of better than 15.8, 15.1, and 14.3 mag at the J, H, and Ks bands, respectively, for virtually the entire sky. Bright source extractions have 1 � photometric uncertainty of <0.03 mag and astrometric accuracy of order 100 mas. Calibration offsets between any two points in the sky are <0.02 mag. The 2MASS All-Sky Data Release includes 4.1 million compressed FITS images covering the entire sky, 471 million source extractions in a Point Source Catalog, and 1.6 million objects identified as extended in an Extended Source Catalog.

https://iopscience.iop.org/article/10.1086/498708/pdf

The Two Micron All Sky Survey (2MASS)

We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al., we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J-H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6 µm) and W2 (4.6 µm) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the Solar Neighborhood. We present a table that updates the entire stellar and substellar constituency within 8 parsecs of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope -0.5 < α < 0.0; however, a power-law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.

/pdf/further-defining-spectral-type-y-and-exploring-the-low-mass-dl4cv0ee81.pdf

Further defining spectral type "y" and exploring the low-mass end of the field brown dwarf mass function

We present an ongoing, five-year systematic search for extragalactic infrared transients, dubbed SPIRITS—SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer/IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate-luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between −11 and −14 (Vega-mag) and [3.6]–[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from 7 mag yr^(−1). SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a protostellar merger.

/pdf/spirits-uncovering-unusual-infrared-transients-with-spitzer-3mrugq9tj1.pdf

SPIRITS: Uncovering Unusual Infrared Transients with Spitzer

We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color-magnitude and color-color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a $T_{\rm eff}$ value and judge sample completeness over bins of $T_{\rm eff}$ and spectral type. Except for types $\ge$ T8 and $T_{\rm eff} <$ 600K, our census is statistically complete to the 20-pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law ($dN/dM \propto M^{-\alpha}$) with $\alpha = 0.6{\pm}0.1$. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200K $< T_{\rm eff} <$ 1350K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs $\ge$Y0.5 and with $T_{\rm eff} <$ 400K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.

/pdf/the-field-substellar-mass-function-based-on-the-full-sky-20-vgk09eu6ho.pdf

The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs

NASA Spitzer mission grants [10136, 11063]; Royal Thai Scholarship; NASA; United States Air Force

/pdf/a-systematic-study-of-mid-infrared-emission-from-core-3pamgv0ryw.pdf

A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with SPIRITS

The two micron all sky survey (2MASS) project, currently underway, requires a camera mated to a 13 meter Cassegrain telescope that will simultaneously image the J, H and Ks spectral bands onto three separate NICMOS3 HgCdTe detector arrays Dichroic beamsplitters allow the three FPAs to view the same field simultaneously This paper reviews the development of this camera, presents a detailed analysis of the optical design, and discusses the techniques used to align the instrument and evaluate its performance The low irradiance of astronomical sources, combined with background limited performance of the detectors, mandated a reimaging configuration and the enclosure of the camera optics within the cold volume Correcting chromatic aberrations, and minimizing ghost images were additional challenges imposed by program requirements The key to achieving high performance was found to be the selection of lens materials The final F/35 optical design uses fifteen CaF2 elements and four Infrasil elements in an all-spherical configuration The design is diffraction limited over the full format in the Ks spectral band, and is nearly so in the J and H bands The tolerance environment is benign, making the design well suited for use in a cryogenic environment A single channel prototype has been built and extensively field tested at the 50-inch telescope at Kitt Peak National Observatory Each channel in the multi-spectral camera uses the same optical design successfully demonstrated in the prototype Currently, the first of two three-channel cameras is undergoing lab tests for image quality and channel registration© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Scott Milligan

Papers

Development of a three-channel SWIR camera, for ground-based astronomical imaging. (Two micron all sky survey, 2MASS)