A MULTIBAND GENERALIZATION OF THE MULTIHARMONIC ANALYSIS OF VARIANCE PERIOD ESTIMATION ALGORITHM AND THE EFFECT OF INTER-BAND OBSERVING CADENCE ON PERIOD RECOVERY RATE

We present a new method of extending the single band Analysis of Variance period estimation algorithm to multiple bands. We use SDSS Stripe 82 RR Lyrae to show that in the case of low number of observations per band and non-simultaneous observations, improvements in period recovery rates of up to $\approx$60\% are observed. We also investigate the effect of inter-band observing cadence on period recovery rates. We find that using non-simultaneous observation times between bands is ideal for the multiband method, and using simultaneous multiband data is only marginally better than using single band data. These results will be particularly useful in planning observing cadences for wide-field astronomical imaging surveys such as LSST. They also have the potential to improve the extraction of transient data from surveys with few ($\lesssim 30$) observations per band across several bands, such as the Dark Energy Survey.Comment: Submitted to ApJL, comments welcome at [email protected]

Assessment of systematic chromatic errors that impact sub-1% photometric precision in large-area sky surveys

Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is stable in time and uniform over the sky to 1% precision or better. Past surveys have achieved photometric precision of 1-2% by calibrating the survey's stellar photometry with repeated measurements of a large number of stars observed in multiple epochs. The calibration techniques employed by these surveys only consider the relative frame-by-frame photometric zeropoint offset and the focal plane position-dependent illumination corrections, which are independent of the source color. However, variations in the wavelength dependence of the atmospheric transmission and the instrumental throughput induce source color-dependent systematic errors. These systematic errors must also be considered to achieve the most precise photometric measurements. In this paper, we examine such systematic chromatic errors using photometry from the Dark Energy Survey (DES) as an example. We define a natural magnitude system for DES and calculate the systematic errors on stellar magnitudes, when the atmospheric transmission and instrumental throughput deviate from the natural system. We conclude that the systematic chromatic errors caused by the change of airmass in each exposure, the change of the precipitable water vapor and aerosol in the atmosphere over time, and the non-uniformity of instrumental throughput over the focal plane, can be up to 2% in some bandpasses. We compare the calculated systematic chromatic errors with the observed DES data. For the test sample data, we correct these errors using measurements of the atmospheric transmission and instrumental throughput. The residual after correction is less than 0.3%. We also find that the errors for non-stellar objects are redshift-dependent and can be larger than those for stars at certain redshifts

Discovery of a stellar overdensity in Eridanus-Phoenix in the Dark Energy Survey

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^\circ and b˜ -60^\circ and spans at least 30° in longitude and 10° in latitude. The Poisson significance of the detection is at least 9sigma . 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

Local Monitoring of Atmospheric Transparency from the NASA MERRA-2 Global Assimilation System

International audienceGround-based astronomy has to correct astronomical observations from the impact of the atmospheric transparency and its variability. The current objective of several observatories is to achieve a sub-percent-level monitoring of atmospheric transmission. A promising approach has been to combine internal calibration of the observations with various external meteorological data sources, upon availability and depending on quality. In this paper we investigate the use of the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) which is a general circulation model (GCM) and data assimilation system that renders freely available for any given site, at any time, all the parameters constraining atmospheric transmission. This paper demonstrates the extraction of the relevant atmospheric parameters for optical astronomy at two sites: Mauna Kea in Hawaii and Cerro Tololo International Observatory in Chile. The temporal variability for the past eight years (annual, overnight, and hourly) as well as the spatial gradients of ozone, precipitable water vapor, and aerosol optical depth are presented and their respective impacts on the atmospheric transparency are analyzed

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