Contrast and Temperature Dependence of Multi-epoch High-resolution Cross-correlation Exoplanet Spectroscopy

Finnerty, Luke; Buzard, Cam; Pelletier, Sonia; Piskorz, Danielle; Lockwood, Alexandra; Bender, Chad F.; Benneke, Björn; Blake, Geoffrey A.

doi:10.3847/1538-3881/abd6ec

Cited by 6 publications

(17 citation statements)

References 53 publications

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“…This implies that with S/N of 2860 per pixel per epoch, the structured noise related to the combination of orbital phases dominates over random Gaussian noise. This is consistent with findings from Buzard et al (2020) and Finnerty et al (2021).…”

Section: Random Orbital Phasessupporting

confidence: 93%

“…The simulations with evenly spaced orbital phases and orbital phases near quadrature do have a peak at K p in all of the primary velocity groups, but there is often large off-peak structure at the same magnitude as, if not larger than, the true peak. Both Buzard et al (2020) and Finnerty et al (2021) found that at the S/N used in these simulations (>2500 per pixel per epoch), shot noise has very little effect on the log likelihood surface and the off-peak structure is due instead to non-random, structured noise. This structured noise is caused by a correlation between the planetary spectral model template and the stellar features in the simulated data.…”

Section: Primary Velocity Simulationsmentioning

confidence: 83%

“…This structured noise is caused by a correlation between the planetary spectral model template and the stellar features in the simulated data. Finnerty et al (2021) removed this structure in their simulations by subtracting a stellar-only log likelihood curve, which comes from simulated data generated with no planetary signal and then cross-correlated in the same two-dimensional way with a stellar and a planetary spectral model. This approach can nearly eliminate all of the off-peak structure in simulations but it would not be as effective on data due to a variety of factors including mismatches between the real and model stellar and planetary spectra and imperfect removal of tellurics from the data.…”

Section: Primary Velocity Simulationsmentioning

confidence: 99%

“…Further, we would expect that obtaining data from both quadrature positions (M = 0.25 and 0.75) would be better for constraining K p than data at just one quadrature position because having data at both quadrature positions would give us access to different velocity shifts relative to the telluric frame and so collectively more complete wavelength coverage of the planetary spectrum. Finnerty et al (2021) showed that a larger spectral grasp can drastically increase detection significance; doubling the grasp increased the significance by nearly a factor of 2. These predictions should be useful for the planning of future multi-epoch observations.…”

Section: Random Orbital Phasesmentioning

confidence: 99%

“…Our simulations considered cloud-free models and did not vary the planetary spectrum as a function of orbital phase, to account for day-to night-side differences for tidally-locked planets, though. If day-to night-side differences were considered, we would expect the day-side orbital phases (0.25 M 0.75), which should have higher effective temperatures, to allow for stronger detections (Finnerty et al 2021).…”

Section: Random Orbital Phasesmentioning

confidence: 99%

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Primary Velocity and Orbital Phase Effects on Planetary Detectability from Small Epoch Number Data Sets

Buzard

Pelletier

Piskorz

et al. 2021

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Cross-correlation analyses of high-resolution spectroscopic data have recently shown great success in directly detecting planetary signals and enabling the characterization of their atmospheres. One such technique aims to observe a system at multiple epochs and combine the measured planetary radial velocities from each epoch into a measurement of the planetary Keplerian orbital velocity K p , constituting a direct detection of the planetary signal. Recent work has shown that in few-epoch (∼5) data sets, unintended structure can arise at a high level, obscuring the planetary detection. In this work, we look to simulations to examine whether there are ways to reduce this structured noise in few-epoch data sets by careful planning of observations. The choice of observation date allows observers to select the primary (stellar) velocity through a set systemic velocity and chosen barycentric velocity and the planetary orbital phase so we focus on the effects of these two parameters. We find that epochs taken when the primary velocity is near zero and the stellar lines remain relatively fixed to the telluric rest-frame greatly reduce the level of structured noise and allow for much stronger planetary detections, on average more than twice the significance of detections made with epochs using randomly selected primary velocities. Following these results, we recommend that observers looking to build up high-resolution multi-epoch data sets target nights when their system has a near-zero primary velocity.

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Section: Random Orbital Phasessupporting

confidence: 93%

Section: Primary Velocity Simulationsmentioning

confidence: 83%

Section: Primary Velocity Simulationsmentioning

confidence: 99%

Section: Random Orbital Phasesmentioning

confidence: 99%

Section: Random Orbital Phasesmentioning

confidence: 99%

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Primary Velocity and Orbital Phase Effects on Planetary Detectability from Small Epoch Number Data Sets

Buzard

Pelletier

Piskorz

et al. 2021

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Reinvestigation of the Multiepoch Direct Detections of HD 88133 b and Upsilon Andromedae b

Buzard

Piskorz

Lockwood

et al. 2021

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We reanalyze the multiepoch direct detections of HD 88133 b and ups And b that were published in Piskorz et al. (2016) and Piskorz et al. (2017), respectively. Using simulations to attempt to reproduce the detections, we find that with the six and seven L-band Keck/NIRSPEC epochs analyzed in the original works, the planets would not have been detectable unless they had unreasonably large radii. HD88133 and ups And both have fairly large stellar radii, which contributed to the difficulty in detecting the planets. We take this opportunity to consider how these planets may have been detectable with the small number of epochs originally presented by running simulations both with the upgraded NIRSPEC instrument and with near-zero primary velocities, as recommended by Buzard et al. (2021). While seven L-band NIRSPEC2.0 epochs with near-zero primary velocities would have allowed a strong (10.8σ) detection of ups And b, many more than six L-band epochs would have been required for a strong detection of HD88133b, which could be due in part to both this system’s large stellar radius and low stellar temperature. This work stresses the importance of careful analytic procedures and the usefulness of simulations in understanding the expected sensitivity of high-resolution spectroscopic data.

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Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf

Kolecki

Ruffio

et al. 2022

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A benchmark brown dwarf (BD) is a BD whose properties (e.g., mass and chemical composition) are precisely and independently measured. Benchmark BDs are valuable in testing theoretical evolutionary tracks, spectral synthesis, and atmospheric retrievals for substellar objects. Here, we report results of atmospheric retrieval on a synthetic spectrum and a benchmark BD, HR 7672 B, with petitRADTRANS. First, we test the retrieval framework on a synthetic PHOENIX BT-Settl spectrum with a solar composition. We show that the retrieved C and O abundances are consistent with solar values, but the retrieved C/O is overestimated by 0.13–0.18, which is about four times higher than the formal error bar. Second, we perform retrieval on HR 7672 B using high spectral-resolution data (R = 35,000) from the Keck Planet Imager and Characterizer and near-infrared photometry. We retrieve [C/H], [O/H], and C/O to be −0.24 ± 0.05, −0.19 ± 0.04, and 0.52 ± 0.02. These values are consistent with those of HR 7672 A within 1.5σ. As such, HR 7672 B is among only a few benchmark BDs (along with Gl 570 D and HD 3651 B) that have been demonstrated to have consistent elemental abundances with their primary stars. Our work provides a practical procedure of testing and performing atmospheric retrieval, and sheds light on potential systematics of future retrievals using high- and low-resolution data.

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Contrast and Temperature Dependence of Multi-epoch High-resolution Cross-correlation Exoplanet Spectroscopy

Cited by 6 publications

References 53 publications

Primary Velocity and Orbital Phase Effects on Planetary Detectability from Small Epoch Number Data Sets

Primary Velocity and Orbital Phase Effects on Planetary Detectability from Small Epoch Number Data Sets

Reinvestigation of the Multiepoch Direct Detections of HD 88133 b and Upsilon Andromedae b

Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf

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