Calibration Hardware and Methodology for Large Photometric Surveys

Photometric surveys such as the Dark Energy Survey (DES), the Legacy Survey of Space and Time (LSST), and Pan-STARRS are and will continue to be increasingly large sources of data for the astronomical community. Type Ia supernova (SNe Ia) cosmology in particular stands to make large gains in statistical power for measurements of dark energy, but this increase in statistical power must be matched by a corresponding decrease in systematic uncertainties associated with SNe Ia measurements. Flux calibration stands out as a dominant systematic uncertainty in current-generation SNe Ia cosmology. Determination of atmospheric chromatic variability and variations in instrument throughput contribute heavily to uncertainty in flux calibration. We present two calibration systems built to increase the precision of flux measurements in astronomical surveys, with the ultimate goal of reaching 1 mmag precision. The Collimated Beam Projector (CBP) projects a field of monochromatic ``stars'' of known relative brightness onto the focal plane of a telescope. By performing aperture photometry on the ``stellar'' images and comparing to an internal CBP monitoring photodiode, estimates of the telescope's throughput can be made. We have tested this system on the StarDICE telescope at the Laboratoire de Physique Nucl\'{e}aire et des Hautes \'{E}nergies (LPNHE), and achieved throughput uncertainties at the $\sim2$\% level for 400 nm $0.44$) are less likely to flare than the intermediate population (at the 99.97 \% level). It is posited that the same angular momentum loss mechanism (if it exists) that produces the bimodal population of M dwarf rotators may be responsible for powering flares in intermediate rotators, as they quickly evolve from rapidly to slowly rotating

Boletín del Servicio Meteorológico Nacional: Epoca 2.ª Número 588 - 1953 Agosto 10

We report the discovery of an excess of main-sequence turnoff stars in the direction of the constellations of Eridanus and Phoenix from the first-year data of the Dark Energy Survey (DES). The Eridanus–Phoenix (EriPhe) overdensity is centered around l ~ 285 and b ~ -60 and spans at least 30° in longitude and 10° in latitude. The Poisson significance of the detection is at least 9s. The stellar population in the overdense region is similar in brightness and color to that of the nearby globular cluster NGC 1261, indicating that the heliocentric distance of EriPhe is about d ~ 16 kpc. The extent of EriPhe in projection is therefore at least ∼4 kpc by ∼3 kpc. On the sky, this overdensity is located between NGC 1261 and a new stellar stream discovered by DES at a similar heliocentric distance, the so-called Phoenix Stream. Given their similar distance and proximity to each other, it is possible that these three structures may be kinematically associated. Alternatively, the EriPhe overdensity is morphologically similar to the Virgo overdensity and the Hercules–Aquila cloud, which also lie at a similar Galactocentric distance. These three overdensities lie along a polar plane separated by ∼120° and may share a common origin. Spectroscopic follow-up observations of the stars in EriPhe are required to fully understand the nature of this overdensity