Ground-Based Mid-IR Direct Imaging: The Origin of the Thermal Background on the Keck II Telescope and Correcting Instrumental Systematics

Abstract

Mid-IR wavelengths are of particular interest to exoplanet science due to the fact they can extend the searchable parameter space to planets that are older and/or colder. However, a significant source of uncertainty at mid-IR wavelengths on ground-based telescopes is the thermal background. This background comes from blackbody radiation in the atmosphere and telescope and is therefore dependent on instrument design and atmospheric conditions. When performing imaging observations, this background manifests as a slowly varying, inhomogeneous signal throughout the image, underlying our data. Photometry at mid-IR can greatly constrain atmospheric models but existing data are usually scarce or have significant error bars due to the difficulty of subtracting the background. Using M-band direct imaging observing sequences on NIRC2, we evaluate the thermal background of the Keck II telescope and attempt to subtract the background in a more comprehensive way. For our primary science target, the forming protoplanet AB Aur b, we present a contrast upper limit of $2\times 10^{-4}$ in M-band and address the limiting factors in our observation due to the thermal background. We determine that the origin of the systematic components of the thermal background comes from the K-mirror and find that the thermal background is also strongly influenced by emission from the secondary spiders on Keck II.

arXiv comment14 pages, 14 figures, accepted to PASP

References in corpus (19)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Angular Differential Imaging: a Powerful High-Contrast Imaging Technique
• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Images of Embedded Jovian Planet Formation At A Wide Separation Around AB Aurigae
• M-band Imaging of the HR 8799 Planetary System Using an Innovative LOCI-based Background Subtraction Technique
• The LEECH Exoplanet Imaging Survey: Characterization of the Coldest Directly Imaged Exoplanet, GJ 504 b, and Evidence for Super-Stellar Metallicity
• A PCA-based approach for subtracting thermal background emission in high-contrast imaging data
• MICADO: first light imager for the E-ELT
• Mapping the merging zone of late infall in the AB Aur planet-forming system
• Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star, HIP 39017
• Mid-Infrared Imaging of the Herbig Ae Star AB Aurigae: Extended Emission on Several Scales
• The SPHERE infrared survey for exoplanets (SHINE). V. Complete observations, data reduction and analysis, detection performances, and final results
• LBT search for companions and sub-structures in the (pre)transitional disk of AB Aurigae
• Towards a physical understanding of the thermal background in large ground-based telescopes
• Liger for Next Generation Keck AO: Filter Wheel and Pupil Design