Calibration Hardware and Methodology for Large Photometric Surveys

Abstract

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 $ \lambda $ 700 nm, and at the $\sim10$\% level for 700 nm $ \lambda $ 1000 nm. The current limiting systematic uncertainty term in the CBP measurements is the internal calibration of the CBP itself.

We present also the construction details of the LSST Atmospheric Transmission and Slitless Spectrograph Instrument (LATISS), which will be used to monitor the chromatic variability of the Earth's atmosphere throughout the duration of the decade-long survey. The instrument uses a Ronchi grating placed in the converging beam of the telescope as a disperser, which has the advantage of suppressing second order contamination up to manufacturing defects. We give an overview of the design, electro-optical parameters, and show a first-light spectrum taken during commissioning in Spring 2020. Slitless spectrophotometry from the instrument will be used alongside atmospheric models from libRadTran and MODTRAN to determine the effective bandpass on a per-exposure basis for LSST.

Finally, we present a study of the connection between flaring and rotation in fully convective, mid-to-late M dwarfs using time-series photometry from the MEarth survey. We find that intermediate rotators, with Rossby numbers between $0.04$ and $0.44$ are more likely to flare relative to the low Rossby number population ($R_o 0.04$, rapid rotators) at the 99.85 \% level. Additionally, slow rotators ($R_o > 0.44$) 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.