The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey (1702.03571v1)

Abstract: We describe a 20-year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck-I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf stars. We provide here 60,949 precision radial velocities for 1,624 stars contained in that survey. We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star. Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as "significant" signals that require confirmation by additional data before rising to classification as planet candidates. Of particular interest is our detection of a candidate planet with a minimum mass of 3.9 Earth masses and an orbital period of 9.9 days orbiting Lalande 21185, the fourth-closest main sequence star to the Sun. For each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the Keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. We also tabulate 18 Keplerian-like signals that we classify as likely arising from stellar activity.

• The paper presents a 20-year precision radial velocity survey using the iodine cell technique on HIRES/Keck to identify 357 significant exoplanet signals.
• It employs a 2004 CCD upgrade that enhanced spectral resolution to up to 85,000, markedly improving measurement precision.
• The extensive dataset of 60,949 observations across 1,624 stars provides a robust foundation for future exoplanet detection and characterization.

The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey

The paper presents an extensive 20-year survey conducted by the Lick-Carnegie Exoplanet Survey Team (LCES) using the HIRES spectrometer on the Keck-I telescope. The primary aim of the survey was to detect and characterize extrasolar planets orbiting nearby F, G, K, and M dwarf stars through precision radial velocity measurements. The survey amassed an impressive dataset comprising 60,949 precision radial velocity observations for 1,624 stars.

Methodology and Instrumentation

The researchers employed the iodine cell technique for precise radial velocity measurements. This technique involves using an iodine gaseous absorption cell to superimpose iodine lines over the stellar spectrum, providing a wavelength calibration and acting as a proxy for the spectrometer's point spread function (PSF). This method facilitated the extreme precision necessary for detecting exoplanetary signals.

Significantly, HIRES on the Keck-I telescope was not initially optimized for extreme precision radial velocity work, but modifications, such as the 2004 focal plane upgrade, improved its capabilities. The upgrade involved replacing the CCD with a more efficient MIT-Lincoln Lab 2K x 4K CCD mosaic, enhancing the spectral resolution to up to 85,000 in optimal conditions.

Results and Findings

From the extensive dataset, the researchers identified 357 significant periodic signals indicative of potential exoplanets. Of these, 225 signals had already been published in previous works, while 60 remained unpublished but were classified as strong candidates requiring photometric follow-up. Another 54 signals were labeled as significant but required further data confirmation.

One noteworthy finding is the detection of a candidate planet orbiting Lalande 21185, a nearby M dwarf, with an indicated minimum mass of 3.8 Earth masses and an orbital period of 9.9 days. This detection highlights the potential of the survey to uncover small exoplanets in the solar neighborhood.

Implications and Future Prospects

The survey's robust dataset is poised to be a significant resource for the exoplanet community, facilitating further discoveries and confirmations of exoplanets. The precision radial velocity measurements, combined with additional data from other observatories, can enhance the understanding of planetary architectures in various stellar environments.

The paper acknowledges the challenges associated with the cadence of observations at shared facilities like Keck and suggests that future improvements in observing strategies and potential instrumentation upgrades could improve the detection and characterization of exoplanets, especially small and low-mass ones.

In conclusion, the paper demonstrates the value of long-term, high-precision surveys in advancing the field of exoplanetary science. The HIRES/Keck Precision Radial Velocity Survey stands as a cornerstone in the search for and characterization of extrasolar planets, offering substantial groundwork for ongoing and future research endeavors.