ExoExplorer Science Series: Federica Rescigno and Jayke Nguyen

Time: 11 AM - 12 PM Pacific Daylight Time

---

Speaker: Federica Rescigno

Title: Hunting for exoearths: Sun-as-a-star RVs to study stellar variability and the BiSON recalibration

Abstract: As the precision and stability of our instruments improve, the intrinsic variability of host stars now represents the greatest barrier for the detection of small exoplanets, especially in the case of Earth-twins. Magnetic activity on the surface of stars generates signals in the radial velocities (RVs) that can mimic or hide the periodic signature of a planet. Solar data have proven to be invaluable in developing targeted mitigation techniques for Extreme Precision Radial Velocity (EPRV) surveys, offering both unparalleled cadence and baselines, and the opportunity to directly link spatially resolved solar phenomena to the variability they imprint in the RVs. In this context, data observed with the Birmingham Solar Oscillations Network (BiSON) are an invaluable asset. However, BiSON's data also presents a further unique challenge in its calibration. I thus present work on the complete re-calibration and re-analysis of the 40 years of BiSON Sun-as-a-star radial-velocity data. The inclusion of simultaneous physically-motivated models describing stellar variability will allow for the investigation of stellar activity phenomena across the solar magnetic activity levels over timescales from minutes to years.

---

Speaker: Jayke Nguyen

Title: Improving Direct Imaging of Exoplanets in Ground-based Mid-IR Observations

Abstract: Mid-IR wavelengths are of particular interest to exoplanet science due to the fact they access the strongly-absorbing and well-understood CO ro-vibronic mode at ~4.6 microns. However, a significant source of uncertainty at mid-IR wavelengths is the thermal background present in ground-based observations. 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. Using an M-band direct imaging observing sequence on NIRC2, we evaluate the thermal background of the Keck II telescope. The usage of 10-m class ground-based telescopes such as Keck are necessary since we typically require high angular resolution to image close-in exoplanets. Photometry at mid-IR can greatly constrain atmospheric models but existing data is usually scarce or has significant error bars due to the difficulty of subtracting the background. This work largely aims to improve photometric error in mid-IR data by reducing systematics. We present results that improve thermal background subtraction by factoring in the systematic background component of the de-rotator. We typically are able to image exoplanets ~12.5 magnitudes fainter than the host star at M-band, and by factoring in the thermal contribution of the de-rotator, we improve our contrast and sensitivity by a factor of ~2-4. Future on-sky and engineering observations using NIRC2 will test new strategies that minimize the telescope contribution to the thermal background and we will further evaluate the thermal background environment of the telescope. Beyond NIRC2, these results also have important implications for the impact of telescope design and how to treat systematics when performing data reduction and analysis.

---

Webinar Information

Join Zoom Meeting
https://caltech.zoom.us/j/88260962807?pwd=s7GH7jVBNRNZb2aVFeAZCR35Gjm6El.1

Meeting ID: 882 6096 2807
Passcode: 697257

One tap mobile
+16699006833,,88260962807# US (San Jose)
+12133388477,,88260962807# US (Los Angeles)

Dial by your location
• +1 669 900 6833 US (San Jose)
• +1 213 338 8477 US (Los Angeles)
• +1 346 248 7799 US (Houston)
• +1 312 626 6799 US (Chicago)
• +1 646 558 8656 US (New York)
• +1 301 715 8592 US (Washington DC)

Meeting ID: 882 6096 2807

Find your local number: https://caltech.zoom.us/u/kvWVsJMNt