A powerful bursting radio source towards the Galactic Centre

Transient astronomical sources are typically powered by compact objects and usually signify highly explosive or dynamic events. While radio astronomy has an impressive record of obtaining high time resolution observations, usually it is achieved in quite narrow fields-of-view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X- and gamma-ray bands in which wide-field instruments routinely detect transient sources. Here we report a new transient source, GCRT J1745-3009, detected in 2002 during a moderately wide-field radio transient monitoring program of the Galactic center (GC) region at 0.33 GHz. The characteristics of its bursts are unlike those known for any other class of radio transient. If located in or near the GC, its brightness temperature (~10^16 K) and the implied energy density within GCRT J1745-3009 vastly exceeds that observed in most other classes of radio astronomical sources, and is consistent with coherent emission processes rarely observed. We conclude that GCRT J1745-3009 is the first member of a new class of radio transient sources, the first of possibly many new classes to be identified through current and upcoming radio surveys.Comment: 16 pages including 3 figures. Appears in Nature, 3 March 200

The CatWISE Preliminary Catalog: Motions from WISE and NEOWISE Data

CatWISE is a program to catalog sources selected from combined WISE and NEOWISE all-sky survey data at 3.4 and 4.6 μm (W1 and W2). The CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data collected from 2010 to 2016. This data set represents four times as many exposures and spans over 10 times as large a time baseline as that used for the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in coadded images created from six-month subsets of these data, each representing one coverage of the inertial sky, or epoch. The catalog includes the measured motion of sources in eight epochs over the 6.5 yr span of the data. From comparison to Spitzer, signal-to-noise ratio = 5 limits in magnitudes in the Vega system are W1 = 17.67 and W2 = 16.47, compared to W1 = 16.96 and W2 = 16.02 for AllWISE. From comparison to Gaia, CatWISE positions have typical accuracies of 50 mas for stars at W1 = 10 mag and 275 mas for stars at W1 = 15.5 mag. Proper motions have typical accuracies of 10 mas yr⁻¹ and 30 mas yr⁻¹ for stars with these brightnesses, an order of magnitude better than from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive

The First Post-Kepler Brightness Dips of KIC 8462852

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process

A global photometric analysis of 2MASS calibration data

We present results from the application of a global photometric calibration (GPC) procedure to calibration data from the first 2 years of the Two Micron All Sky Survey (2MASS). The GPC algorithm uses photometry of both primary standards and moderately bright tracer stars in 35 2MASS calibration fields. During the first 2 years of the survey, each standard was observed on approximately 50 nights, with about 900 individual measurements. Based on the photometry of primary standard stars and secondary tracer stars and under the assumption that the nightly zero-point drift is linear, the GPC ties together all calibration fields and all survey nights simultaneously, producing a globally optimized solution. Calibration solutions for the Northern and Southern Hemisphere observatories are found separately and are tested for global consistency based on common fields near the celestial equator. Several results from the GPC are presented, including establishing candidate secondary standards, monitoring of near-infrared atmospheric extinction coefficients, and verification of the global validity of the standards. The solution gives long-term averages of the atmospheric extinction coefficients (in magnitudes per air mass), AJ = 0.096, AH = 0.026, A = 0.066 (north) and AJ = 0.092, AH = 0.031, A = 0.065 (south), with formal error of 0.001. The residuals show small seasonal variations, most likely due to changing atmospheric content of water vapor. Extension of the GPC to ~100 field stars in each of the 35 calibration fields yields a catalog of more than 2000 photometric standards ranging from the 10th to 14th magnitude, with photometry that is globally consistent to ~1%

Nucleosynthetic signatures of the first stars

Original article can be found at: http://www.nature.com/nature/index.html--Copyright Nature Publishing Group --DOI : 10.1038/nature03455Peer reviewe

Music Mentoring in Action

Brightness variability of QSOs is associated with variations of the spectral energy distribution in the optical-UV range. The observed change of the spectral shape depends on the contribution of the host galaxy. Simulations, taking into account luminosities and spectra expected for the host galaxies, are compared with the observed spectral variability of a complete QSO sample.Comment: 3 pages, 1 figure, to appear in the proceedings of the workshop on "QSO hosts and their environments", IAA, Granada, 10-12 Jan 200

CWISEP J193518.59-154620.3: An Extremely Cold Brown Dwarf in the Solar Neighborhood Discovered with CatWISE

We present the discovery of an extremely cold, nearby brown dwarf in the solar neighborhood, found in the CatWISE catalog. Photometric follow-up with Spitzer reveals that the object, CWISEP J193518.59-154620.3, has ch1-ch2 = 3.24 ±0.31 mag, making it one of the reddest brown dwarfs known. Using the Spitzer photometry and the polynomial relations from Kirkpatrick et al. we estimate an effective temperature in the ∼270-360 K range, and a distance estimate in the 5.6-10.9 pc range. We combined the WISE, NEOWISE, and Spitzer data to measure a proper motion of mas yr-1, μ δ = -50 ±97 mas yr-1, which implies a relatively low tangential velocity in the range 7-22 km s-1