arXiv subjects

Jayadev Rajagopal

Publications and source records attributed to Jayadev Rajagopal.

At least 19 recordsLinked to original sources

arXiv2026

Shadowing the Sun I: Testing Synthetic Granulation Spectra with NEID Solar Eclipse Observations

The subtle Doppler radial velocity (RV) signature of an Earth-mass exoplanet in the Habitable Zone around a nearby Sun-like star is difficult to detect due to stellar variability. While multiple techniques aim to mitigate rotationally-modulated stellar activity, granulation, introducing 0.1-1 m s$^{-1}$ RV shifts, currently sets the floor for detecting Earth-mass RV signals for low-activity stars. Observations of the Rossiter-McLaughlin (RM) effect during a solar eclipse, with a peak-to-trough amplitude of $\sim$1.4 km s$^{-1}$, are a rigorous test of granulation and convective blueshift in the solar spectrum. Using NEID solar feed data of the October 2023 solar eclipse and GRASS-E (a geometry-modified version of GRASS), we compare the observed RVs for 22 lines with the simulated RVs from the synthetic granulation-driven spectra. Residuals of the GRASS-E Fe I 5434 angstrom model show an RMS of 13.47 m s$^{-1}$ over the RM signal. We find that a model with an optimized convective blueshift polynomial for Fe I 5434 significantly outperforms GRASS-E with an RMS of only 2.90 m s$^{-1}$, suggesting that GRASS-E is currently limited by sparse center-to-limb observations. By combining a set of spectral lines, we achieve a weighted RMS of 5.2 m s$^{-1}$ over the RM signal ($\sim$0.37\%), a level of accuracy well beyond the reach of current exoplanet transit observations. In all, we demonstrate that solar eclipse observations allow us to recover the center-to-limb variation of the convective blueshift for individual spectral lines.

astro-ph.SR↗

arXiv2026

Quantum-optimized phase closure for robust interferometric imaging

Closure phase enables imaging with ground-based interferometric arrays by canceling telescope-dependent phase errors due to atmospheric fluctuations. It can be obtained by measuring fringe phases on individual baselines forming a triangle and summing them. We show that closure phases can be measured more accurately with fewer photons by performing joint measurements on multiple photons. We first establish that at least three photons from the same atmospheric temporal phase-stability window are required for closure-phase information to survive the unknown telescope-dependent phase noise, and show that joint three-photon measurements already provide an advantage over single-photon measurements in the minimal three-telescope setting. We then turn to large arrays and consider estimating all bispectra---complex quantities whose phases are the closure phases---under a global mean-square error criterion. Although an $m$-telescope array contains $Θ(m^2)$ independent triangle bispectra, we show that physical constraints on the visibilities make the total information content grow only nearly linearly with $m$ at fixed accuracy. Exploiting this structure, we construct an efficient protocol using at most three-photon joint measurements with photon cost $\tilde{O}(m)$, whereas any sequential single-photon protocol requires $Ω(m^2)$ photons. When the number of detected photons per temporal stability window scales linearly with the array size, this allows the required exposure time to remain independent of $m$ up to logarithmic factors. We further analyze the complementary high-precision regime using multiparameter quantum metrology and find a similar advantage for collective measurements. Overall, our results show that quantum information processing techniques can substantially improve the sensitivity and robustness of optical interferometry.

quant-ph↗

arXiv2026

The NEID Earth Twin Survey. VI. Discovery of a Low-Mass Planet Orbiting HD 126053 and RV Signals Near the Rotation Periods of HD 168009 and HD 10780

Extreme precision radial velocity (EPRV) spectrographs are making strides in extending the limits of radial velocity exoplanet detection. Perhaps the best evidence for this is how readily EPRV instruments are facilitating the discovery and detailed characterization of small-amplitude planetary signals around stars that have already been intensively monitored for decades with less stable instruments. In this paper, we use data from the ongoing NEID Earth Twin Survey (NETS) to detect and confirm the planet HD 126053 b (P=10.91 d), which is among the least massive planets (m sin i = 3.60 m M_\oplus) around solar-type stars within 25 pc. We then jointly characterize the known planet HD 168009 b (P=15.14 d; m sin i = 8.64 M_\oplus) orbiting a solar analog along with a previously unreported signal at 27.8 d which we tentatively attribute to rotational modulation of stellar activity (P_rot = 30.1 d). We also analyze and discuss periodic RV variations in HD 10780 arising from a combination of rotationally-modulated activity and a long-term activity cycle. We discuss HD 126053 b and HD 168009 b in the context of the broader small planet population and our sensitivity to long-period planets in these systems, and we comment on our capacity to disambiguate planet-induced and activity-induced radial velocity signals. HD 126053 is exceptionally RV-quiet, making it a promising target for continued RV monitoring in search of low-mass exoplanets in the habitable zone.

astro-ph.EP↗

arXiv2026

Eliminating photon transport in long-baseline optical interferometry using quantum memories

In this paper, we describe the fundamental operating mechanisms of optical interferometry using quantum memory and entanglement. We show how these remove the optical delay line bottleneck. Quantum memory is not without its own set of challenges, some of which include very small bandwidths as well as limitations in storage time. We examine the influence of timing artifacts on memory photon capture probability and interferometric complex visibility. We highlight keystone areas of technology that require further development and are essential to realizing these opportunities, as well as ongoing work to overcome these challenges.

quant-ph↗

arXiv2026

Empirical H- and K-band Limb Darkening for 31 CHARA Stars: A Near-Infrared Benchmark for Stellar-Atmosphere Models

Limb darkening, the decrease in stellar intensity from the disk center to the limb, encodes the temperature structure and opacity of stellar atmospheres. Direct spatially resolved measurements of this center-to-limb variation remain scarce, especially in the near-infrared. We present interferometric limb-darkening measurements for 31 stars observed simultaneously in the $H$ and $K$ bands with the CHARA Array. The sample spans spectral types F--M and luminosity classes IV--I. The targets are well resolved in $H$ and, for most targets, also in $K$. This coverage constrains the visibility curvature associated with limb darkening in joint $H+K$ fits. We fit the combined $H{+}K$ squared visibilities with four analytic limb-darkening laws and compare the resulting coefficients with bandpass-matched predictions from five stellar-atmosphere grids (Kurucz, MPS1, MPS2, Stagger, and spherical SATLAS, with reported coefficients placed on the Rosseland-radius convention) spanning one-dimensional plane-parallel, three-dimensional radiation--hydrodynamic, and spherical low-gravity models. The associated limb-darkened angular diameters are measured with median formal precisions of $\simeq 0.2$--0.3\%. The CHARA results show expected weaker limb darkening at longer wavelengths and also with increasing $T_{\rm eff}$. The clearest discrepancy with the atmosphere grids is in the wavelength dependence: the median fractional decrease in the power-law coefficient from $H$ to $K$ is $\simeq 39\%$ in the CHARA sample, compared with only $\simeq 17$--$22\%$ with model predictions. Relative to the MPS2 comparison, the empirical coefficients are higher by $\simeq 21\%$ in $H$ and lower by $\simeq 5\%$ in $K$. These results provide multi-band interferometric limb darkening as a near-infrared benchmark for stellar-atmosphere models.

astro-ph.SR↗

arXiv2025

Discovery of a Nearby Habitable Zone Super-Earth Candidate Amenable to Direct Imaging

We present the discovery of GJ 251 c, a candidate super-Earth orbiting in the Habitable Zone (HZ) of its M dwarf host star. Using high-precision Habitable-zone Planet Finder (HPF) and NEID RVs, in conjunction with archival RVs from the Keck I High Resolution Echelle Spectrometer (HIRES), the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrograph (CARMENES), and the SPectropolarimètre InfraROUge (SPIRou), we improve the measured parameters of the known planet, GJ 251 b ($P_{b}$ = 14.2370 days; $m \sin(i)$ = 3.85$^{+0.35}_{-0.33}$ M$_{\oplus}$), and we significantly constrain the minimum mass of GJ 251 c, placing it in a plausibly terrestrial regime (P$_{c}$ = 53.647 $\pm$ 0.044 days; $ m \sin i_{c}$ = 3.84 $\pm$ 0.75 M$_{\oplus}$). Using activity mitigation techniques that leverage chromatic information content, we perform a color-dependent analysis of the system and a detailed comparison of more than 50 models that describe the nature of the planets and stellar activity in the system. Due to GJ 251's proximity to Earth (5.5 pc), next generation, thirty meter class telescopes will likely be able to image terrestrial planets in GJ 251's HZ. In fact, GJ 251 c is currently the best candidate for terrestrial, HZ planet imaging in the Northern Sky.

astro-ph.EP↗

arXiv2025

The NEID Earth Twin Survey. III. Survey Performance After Three Years on Sky

The NEID Earth Twin Survey (NETS) has been delivering a rich set of precise radial velocity (RV) measurements for 41 bright, nearby main sequence stars. Here, we describe the status of the survey after three years on sky and we present the full set of RV measurements and accompanying stellar activity indicators. We discuss intermediate survey diagnostics, including calibration of the known RV zero point offset introduced following the Contreras fire in 2022 and the identification of an undiagnosed and previously unknown zero point offset in 2021. An analysis of our data set using RVSearch demonstrates that for these target stars, NEID is independently sensitive to nearly all known planets with periods shorter than the NETS observing baseline. We also highlight a number of newly detected RV signals, which present exciting opportunities for future investigations.

astro-ph.EP↗

arXiv2025

Time-resolved p-mode oscillations for subgiant HD 142091 with NEID at WIYN

Detections of Earth-analog planets in radial velocity observations are limited by stellar astrophysical variability occurring on a variety of timescales. Current state-of-the-art methods to disentangle potential planet signals from intrinsic stellar signals assume that stellar signals introduce asymmetries to the line profiles that can therefore be separated from the pure translational Doppler shifts of planets. Here, we examine this assumption using a time series of resolved stellar p-mode oscillations in HD 142091 ($κ$ CrB), as observed on a single night with the NEID spectrograph at 2-minute cadence and with 25 cm/s precision. As an evolved subgiant star, this target has p-mode oscillations that are larger in amplitude (4-8 m/s) and occur on longer timescales (80 min.) than those of typical Sun-like stars of RV surveys, magnifying their corresponding effects on the stellar spectral profile. We show that for HD 142091, p-mode oscillations manifest primarily as pure Doppler shifts in the average line profile -- measured by the cross-correlation function (CCF) -- with "shape-driven" CCF variations as a higher-order effect. Specifically, we find that the amplitude of the shift varies across the CCF bisector, with 10% larger oscillation amplitudes closer to the core of the CCF, and 25% smaller oscillation amplitudes for bisector velocities derived near the wings; we attribute this trend to larger oscillation velocities higher in the stellar atmosphere. Using a line-by-line analysis, we verify that a similar trend is seen as a function of average line depth, with deeper lines showing larger oscillation amplitudes. Finally, we find no evidence that p-mode oscillations have a chromatic dependence across the NEID bandpass beyond that due to intrinsic line depth differences across the spectrum.

astro-ph.SR↗

arXiv2025

The NEID Earth Twin Survey. II. Dynamical Masses in Seven High-acceleration Star Systems

We present a set of companion dynamical masses and orbital parameters of seven star systems from the NEID Earth Twin Survey with significant absolute astrometric accelerations between the epochs of Hipparcos and Gaia. These include four binary star systems (HD 68017 AB, 61 Cygni AB, HD 24496 AB, and HD 4614 AB) and three planetary systems (HD 217107, HD 190360, and HD 154345). Our analyses incorporate a long baseline of RVs that includes over 1100 previously unpublished measurements from NEID and MINERVA, extending the overall RV baseline for each system by $\approx$2.5 years, as well as relative astrometry for the stellar binary systems where the positions of both stars are well-measured. In each case, the combination of astrometry and RVs constrains the three-dimensional acceleration of the host star and enables precise dynamical masses. We publish true masses for three planets whose measurements were previously entangled with their inclinations, four stellar masses with $\lesssim$1% relative precision, and improved orbital solutions for all seven systems, including the first for HD 24496 AB. These solutions not only agree with previous estimates, but also improve their fidelity. We also explore each system for evidence of periodic signals in the residuals around our best-fit models, and discuss the potential that the three planetary systems have for being directly imaged. With dynamical mass estimates and reliable orbit ephemerides, these seven star systems represent promising benchmarks for future stellar and planetary characterization efforts, and are amenable for further improvement with the upcoming release of Gaia epoch astrometry.

astro-ph.EP↗

arXiv2025

The Immediate, Exemplary, and Fleeting echelle spectroscopy of SN 2023ixf: Monitoring acceleration of slow progenitor circumstellar material, driven by shock interaction

We present high resolution WIYN/NEID echelle spectroscopy (R $\approx70$,000) of the supernova (SN) 2023ixf in M101, obtained 1.51 to 18.51 days after explosion over nine epochs. Daily monitoring for the first four days after explosion shows narrow emission features ($\leq200$ km s$^{-1}$), exhibiting predominantly blueshifted velocities, that rapidly weaken, broaden, and vanish in a manner consistent with radiative acceleration and the SN shock eventually overrunning or enveloping the full extent of dense circumstellar medium (CSM). The most rapid evolution is in the He I emission, which is visible on day 1.51 but disappears by day 2.62. We measure the maximum pre-SN speed of He I to be 25 $^{+0}_{-5} \pm2$ km s$^{-1}$, where the error is attributable to the uncertainty in how much the He I had already been radiatively accelerated, and to measurement of the emission line profile. The radiative acceleration of material is likely driven by the shock-CSM interaction, and the CSM is accelerated to $\geq200$ km s$^{-1}$ before being completely swept up by the SN shock to $\sim 2000$ km s$^{-1}$. We compare the observed spectra with spherically-symmetric r16wb HERACLES/CMFGEN model spectra and find the line evolution to generally be consistent with radiative acceleration and optical depth effects. The progenitor of SN2023ixf underwent an enhanced mass loss phase $\gtrsim 4$ year prior to core-collapse, creating a dense, asymmetric CSM region extending out to approximately $r_{CSM} = 3.7 \times 10^{14}$ ($v_\textrm{shock}$/9500 km s$^{-1}$) cm.

astro-ph.HE↗

arXiv2024

Deep learning solutions to telescope pointing and guiding

The WIYN 3.5m Telescope at Kitt Peak National Observatory hosts a suite of optical and near infrared instruments, including an extreme precision, optical spectrograph, NEID, built for exoplanet radial velocity studies. In order to achieve sub ms precision, NEID has strict requirements on survey efficiency, stellar image positioning, and guiding performance, which have exceeded the native capabilities of the telescope's original pointing and tracking system. In order to improve the operational efficiency of the telescope we have developed a novel telescope pointing system, built on a recurrent neural network, that does not rely on the usual pointing models (TPoint or other quasi physical bases). We discuss the development of this system, how the intrinsic properties of the pointing problem inform our network design, and show preliminary results from our best models. We also discuss plans for the generalization of this framework, so that it can be applied at other sites.

astro-ph.IM↗

arXiv2024

BD+44 493: Chemo-Dynamical Analysis and Constraints on Companion Planetary Masses from WIYN/NEID Spectroscopy

In this work, we present high-resolution (R~100,000), high signal-to-noise (S/N~800) spectroscopic observations for the well-known, bright, extremely metal-poor, carbon-enhanced star BD+44 493. We determined chemical abundances and upper limits for 17 elements from WIYN/NEID data, complemented with 11 abundances re-determined from Subaru and Hubble data, using the new, more accurate, stellar atmospheric parameters calculated in this work. Our analysis suggests that BD+44 493 is a low-mass (0.83Msun) old (12.1-13.2Gyr) second-generation star likely formed from a gas cloud enriched by a single metal-free 20.5Msun Population III star in the early Universe. With a disk-like orbit, BD+44 493 does not appear to be associated with any major merger event in the early history of the Milky Way. From the precision radial-velocity NEID measurements (median absolute deviation - MAD=16m/s), we were able to constrain companion planetary masses around BD+44 493 and rule out the presence of planets as small as msin(i)=2MJ out to periods of 100 days. This study opens a new avenue of exploration for the intersection between stellar archaeology and exoplanet science using NEID.

astro-ph.SR↗

arXiv2024

Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars

Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity data are needed for definitive confirmation. Here we present radial velocity follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet ($M = 11.8 \pm 0.7 \:\mathrm{M_J}$) in a $P = 571.3 \pm 1.4\:\mathrm{day}$ orbit with a projected semi-major axis $a_0=0.312 \pm 0.040\:\mathrm{mas}$ orbiting a $0.644 \pm 0.02 \:\mathrm{M_\odot}$ star. Gaia-5b is a brown dwarf ($M = 20.9 \pm 0.5\:\mathrm{M_J}$) in a $P = 358.58 \pm 0.19\:\mathrm{days}$ eccentric $e=0.6412 \pm 0.0027$ orbit with a projected angular semi-major axis of $a_0 = 0.947 \pm 0.038\:\mathrm{mas}$ around a $0.34 \pm 0.03 \mathrm{M_\odot}$ star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star.

astro-ph.EP↗

arXiv2024

The NEID Earth Twin Survey. I. Confirmation of a 31-day planet orbiting HD 86728

With close to three years of observations in hand, the NEID Earth Twin Survey (NETS) is starting to unearth new astrophysical signals for a curated sample of bright, radial velocity (RV)-quiet stars. We present the discovery of the first NETS exoplanet, HD 86728 b, a $m_p\sin i = 9.16^{+0.55}_{-0.56}\ \rm{M}_\oplus$ planet on a circular, $P=31.1503^{+0.0062}_{-0.0066}$ d orbit, thereby confirming a candidate signal identified by Hirsch et al. (2021). We confirm the planetary origin of the detected signal, which has a semi-amplitude of just $K=1.91^{+0.11}_{-0.12}$ m s$^{-1}$, via careful analysis of the NEID RVs and spectral activity indicators, and we constrain the mass and orbit via fits to NEID and archival RV measurements. The host star is intrinsically quiet at the $\sim1$ m s$^{-1}$ level, with the majority of this variability likely stemming from short-timescale granulation. HD 86728 b is among the small fraction of exoplanets with similar masses and periods that have no known planetary siblings.

astro-ph.EP↗

arXiv2024

Utilizing Photometry from Multiple Sources to Mitigate Stellar Variability in Precise Radial Velocities: A Case Study of Kepler-21

We present a new analysis of Kepler-21, the brightest (V = 8.5) Kepler system with a known transiting exoplanet, Kepler-21 b. Kepler-21 b is a radius valley planet ($R = 1.6\pm 0.2 R_{\oplus}$) with an Earth-like composition (8.38$\pm$1.62 g/cc), though its mass and radius fall in the regime of possible "water worlds." We utilize new Keck/HIRES and WIYN/NEID radial velocity (RV) data in conjunction with Kepler and TESS photometry to perform a detailed study of activity mitigation between photometry and RVs. We additionally refine the system parameters, and we utilize Gaia astrometry to place constraints on a long-term RV trend. Our activity analysis affirms the quality of Kepler photometry for removing correlated noise from RVs, despite its temporal distance, though we reveal some cases where TESS may be superior. Using refined orbital parameters and updated composition curves, we rule out a ``water world" scenario for Kepler-21 b, and we identify a long period super-Jupiter planetary candidate, Kepler-21 (c).

astro-ph.EP↗

arXiv2024

Quantifying broadband chromatic drifts in Fabry-Perot resonators for exoplanet science

The possibility of an Earth-Sun analog beyond our solar system is one of the most longstanding questions in science. At present, answering this question embodies an extremely difficult measurement problem that requires multiple coordinated advances in astronomical telescopes, fiber optics, precision spectrographs, large format detector arrays, and advanced data processing. Taken together, addressing this challenge will require the measurement and calibration of shifts in stellar spectra at the 10^-10 level over multi-year periods. The potential for such precision has recently been advanced by the introduction of laser frequency combs (LFCs) to the field of precision astronomical spectroscopy. However, the expense, complexity and lack of full spectral coverage of LFCs has limited their widespread use and ultimate impact. To address this issue, we explore simple and robust white-light-illuminated Fabry-Perot (FP) etalons as spectral calibrators for precise radial velocity measurements. We track the frequencies of up to 13,000 etalon modes of the installed FPs from two state-of-the-art astronomical spectrographs. Combining these measurements with modeling, we trace unexpected chromatic variations of the FP modes to sub-picometer changes in the dielectric layers of the broad bandwidth FP mirrors. This yields the determination of the frequencies of the FP modes with precision approaching 10^-11/day, equivalent to a radial velocity (RV) Doppler shift of 3 mm/s/day. These results represent critical progress in precision RV measurements on two fronts: first, they make FP etalons a more powerful stand-alone calibration tool, and second, they demonstrate the capability of LFCs to extend cm/s level RV measurement precision over periods approaching a year. Together, these advances highlight a path to achieving spectroscopic calibration at levels that will be critical for finding earths like our own.

physics.optics↗

arXiv2023

TOI-1670 c, a 40-day Orbital Period Warm Jupiter in a Compact System, is Well-aligned

We report the measurement of the sky-projected obliquity angle $λ$ of the Warm Jovian exoplanet TOI-1670 c via the Rossiter-McLaughlin effect as part of the Stellar Obliquities in Long-period Exoplanet Systems (SOLES) project. We observed the transit window during UT 20 April 2023 for 7 continuous hours with NEID on the 3.5 m WIYN Telescope at Kitt Peak National Observatory. TOI-1670 hosts a sub-Neptune (P ~11 days; planet b) interior to the Warm Jovian (P ~40 days; planet c), which presents an opportunity to investigate the dynamics of a Warm Jupiter with an inner companion. Additionally, TOI-1670 c is now among the longest-period planets to date to have its sky-projected obliquity angle measured. We find planet c is well-aligned to the host star, with $λ$ = -0.3 +/- 2.2 degrees. TOI-1670 c joins a growing census of aligned Warm Jupiters around single stars and aligned planets in multi-planet systems.

astro-ph.EP↗

arXiv2023

Stable fiber-illumination for extremely precise radial velocities with NEID

NEID is a high-resolution red-optical precision radial velocity (RV) spectrograph recently commissioned at the WIYN 3.5 m telescope at Kitt Peak National Observatory, Arizona, USA. NEID has an extremely stable environmental control system, and spans a wavelength range of 380 to 930 nm with two observing modes: a High Resolution (HR) mode at R $\sim$ 112,000 for maximum RV precision, and a High Efficiency (HE) mode at R $\sim$ 72,000 for faint targets. In this manuscript we present a detailed description of the components of NEID's optical fiber feed, which include the instrument, exposure meter, calibration system, and telescope fibers. Many parts of the optical fiber feed can lead to uncalibratable RV errors, which cannot be corrected for using a stable wavelength reference source. We show how these errors directly cascade down to performance requirements on the fiber feed and the scrambling system. We detail the design, assembly, and testing of each component. Designed and built from the bottom-up with a single-visit instrument precision requirement of 27 $\textrm{cm~s}^{-1}$, close attention was paid to the error contribution from each NEID subsystem. Finally, we include the lab and on-sky tests performed during instrument commissioning to test the illumination stability, and discuss the path to achieving the instrumental stability required to search for a true Earth twin around a Solar-type star.

astro-ph.IM↗