The Skynet Algorithm for Single-Dish Radio Mapping

After the National Radio Astronomy Observatory’s 20-meter diameter telescope in Green Bank, West Virginia was added to the Skynet Robotic Telescope Network - which includes optical telescopes spanning four continents - a need for a radio data-processing pipeline arose. Therefore, development began to create a pipeline similar to optical Skynet’s Afterglow, and the single-dish radio mapping algorithm was born. This algorithm has a number of advantages over traditional techniques, such as basket-weaving. (1) The algorithm makes use of weighted modeling, instead of weighted averaging, to interpolate between signal measurements. This smooths the data, but without blurring it beyond instrumental resolution. Techniques that rely on weighted averaging blur point sources sometimes as much as 40%. (2) The algorithm makes use of local, instead of global, modeling to separate astronomical signal from instrumental and/or environmental signal drift along the telescope’s scans. (3) The algorithm uses a very similar, local modeling technique to separate astronomical signal from radio-frequency interference (RFI). (4) Unlike other techniques, the algorithm does not require data to be collected on a rectangular grid or regridded before processing. (5) Any pixel density may be selected for the final image. Here, the procedure is presented and evaluated using both simulated and real data. The algorithm is being integrated into the image-processing library of Skynet. Default data products will be generated on the fly, but will be customizable by the user in real time.Bachelor of Scienc

Identifying Young KeplerKepler Planet Host Stars from Keck-HIRES Spectra of Lithium

The lithium doublet at 6708 \AA\ provides an age diagnostic for main sequence FGK dwarfs. We measured the abundance of lithium in 1305 stars with detected transiting planets from the Kepler Mission using high-resolution spectroscopy. Our catalog of lithium measurements from this sample have a range of abundance from A(Li) = 3.11 $\pm$ 0.07 to an upper limit of $-$0.84 dex. For a magnitude-limited sample that comprises 960 of the 1305 stars, our Keck-HIRES spectra have a median S/N = 45 per pixel at $\sim$6700 \AA\ with spectral resolution $\frac{\lambda}{\Delta \lambda}$ = $R$ = 55,000. We identify 80 young stars that have A(Li) values greater than the Hyades at their respective effective temperatures; these stars are younger than $\sim$650 Myr old, the approximate age of the Hyades. We then compare the distribution of A(Li) with planet size, multiplicity, orbital period, and insolation flux. We find larger planets preferentially in younger systems, with an A-D two-sided test p-value = 0.002, a $>3\sigma$ confidence that the older and younger planet samples do not come from the same parent distribution. This is consistent with planet inflation/photoevaporation at early ages. The other planet parameters ($Kepler$ planet multiplicity, orbital period, and insolation flux) are uncorrelated with age.Comment: 22 pages, 15 figures, 3 tables. Accepted for publication in ApJ. For a brief video explaining this paper, see https://youtu.be/TkO-ef28Va

Planet Engulfment Detections are Rare According to Observations and Stellar Modeling

Dynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planets. Multi-star systems are excellent environments to search for such abundance trends because stellar companions form from the same natal gas cloud and are thus expected to share primordial chemical compositions to within 0.03$-$0.05 dex. Abundance measurements have occasionally yielded rocky enhancements, but few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multi-star systems where at least one star is a known planet host. We found that only HAT-P-4 exhibits an abundance pattern suggestive of engulfment, but is more likely primordial based on its large projected separation (30,000 $\pm$ 140 AU) that exceeds typical turbulence scales in molecular clouds. To understand the lack of engulfment detections among our systems, we quantified the strength and duration of refractory enrichments in stellar photospheres using MESA stellar models. We found that observable signatures from 10 $M_{\oplus}$ engulfment events last for $\sim$90 Myr in 1 $M_{\odot}$ stars. Signatures are largest and longest lived for 1.1$-$1.2 $M_{\odot}$ stars, but are no longer observable $\sim$2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old.Comment: 15 pages, 12 figures; submitted to MNRA

Identifying Young Kepler Planet Host Stars from Keck–HIRES Spectra of Lithium

The lithium doublet at 6708 Å provides an age diagnostic for main sequence FGK dwarfs. We measured the abundance of lithium in 1305 stars with detected transiting planets from the Kepler mission using high-resolution spectroscopy. Our catalog of lithium measurements from this sample has a range of abundance from A(Li) = 3.11 ± 0.07 to an upper limit of −0.84 dex. For a magnitude-limited sample that comprises 960 of the 1305 stars, our Keck–HIRES spectra have a median signal-to-noise ratio of 45 per pixel at ~6700 Å with spectral resolution λ/(Δλ) = R = 55,000. We identify 80 young stars that have A(Li) values greater than the Hyades at their respective effective temperatures; these stars are younger than ~650 Myr, the approximate age of the Hyades. We then compare the distribution of A(Li) with planet size, multiplicity, orbital period, and insolation flux. We find larger planets preferentially in younger systems, with an A–D two-sided test p-value = 0.002, a > 3σ confidence that the older and younger planet samples do not come from the same parent distribution. This is consistent with planet inflation/photoevaporation at early ages. The other planet parameters (Kepler planet multiplicity, orbital period, and insolation flux) are uncorrelated with age