arXiv subjects

Ritvik Basant

Publications and source records attributed to Ritvik Basant.

11 recordsLinked to original sources

arXiv2026

New and Updated Rossiter-McLaughlin Measurements for Three Hot Jupiter-Hosting M Dwarfs

Evidence suggests that Kozai-Lidov high-eccentricity migration (HEM) is the dominant migration channel for short-period Giant Exoplanets around M dwarf Stars (GEMS). However, it is unlikely that all short-period GEMS form via HEM, given that most systems lack known massive companions capable of driving HEM. Characterizing the stellar obliquities of GEMS via the Rossiter-McLaughlin (RM) effect can help shed light on the dynamical histories of GEMS. We present RM effect detections for the GEMS TOI-5205 b, TIC 46432937 b, and TOI-3714 b using the Gemini-North/MAROON-X spectrograph, bringing the total number of GEMS with RM detections to five. Our systems are well-aligned, with sky-projected obliquities of $\lambda = 0 \pm 6^\circ$, $3_{-3}^{+4}$$^\circ$, and $15_{-8}^{+12}$$^\circ$, respectively, and we measure a deprojected obliquity of $\psi = 24_{-8}^{+7}$ $^\circ$ for TOI-3714. We analyze archival radial velocities, astrometry, and speckle imaging data to search for additional companions around all five known GEMS with RM detections. We find tentative evidence for a new massive companion around one of these GEMS, TOI-5293 A, in Gaia DR2+DR3 data, though further follow-up is needed for confirmation. We rule out massive companions between $\sim 1-10\textrm{ AU}$ in the remaining systems, but cannot rule out all companions capable of driving HEM. Our findings present further evidence that short-period GEMS are preferentially aligned. While current results remain consistent with both primordial alignment and HEM plus tidal damping, we offer future directions for studies to further constrain the dominant migration channel for GEMS.

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arXiv2026

A Pair of Warm Saturn-mass Planets near the 2:1 Mean Motion Resonance around TOI-3850

Warm Jupiters, with orbital periods of $10$--$200~\rm{days}$ and radii exceeding $8~R_{\oplus}$, are a relatively understudied class of exoplanets occupying the parameter space between hot Jupiters and more widely separated, colder Jupiter analogs. In this work, we report the detection of a multi-planet warm Jupiter system around TOI-3850 (TIC-143008050), a moderately active, near-solar metallicity G0 dwarf star observed by TESS in Sectors 15, 21, 41, 48 and 75. Initially, a single candidate planet was discovered by TESS, displaying transit timing variations (TTVs) with an amplitude of $\sim 1~\rm hr$ and a super-period of $513~\rm days$. Through a combination of transit photometry, radial velocity observations with MAROON-X, and TTV modeling, we identify two planets: TOI-3850 b $(P_b=14.484\pm0.002~\mathrm{days},~ M_b =112\pm20~M_{\oplus},~e_b = 0.018\pm0.008, R_b = 12.07\pm0.09~R_{\oplus}, ~T_{\rm{eq}}=841\pm10~\rm{K})$, a transiting warm Jupiter, and TOI-3850 c $(P_c=29.85\pm0.01~\mathrm{days},~ M_c =90\pm15~M_{\oplus},~e_c < 0.015, ~T_{\rm{eq}}=661\pm7~\rm{K})$, a non-transiting, Saturn-mass companion. The two planets lie wide of the 2:1 mean motion resonance $(P_c/P_b \approx 2.06)$, consistent with a formation history involving disk-driven migration. $N$-body integrations indicate that TOI-3850 c may begin to transit on decadal timescales, while TOI-3850 b remains a promising target for follow-up atmospheric characterization.

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arXiv2026

RV and TTV Measurements of Two Transiting Long-Period Giants around TOI-4600

TOI-4600b and c, originally identified by the Transiting Exoplanet Survey Satellite (TESS) and reported by I. Mireles et al. (2023), are a rare pair of transiting long-period giant planets ($\rm P_b=82.7$ days, $\rm P_c=482.8$ days) orbiting an early K dwarf. In this work, we refine the orbital parameters of the TOI-4600 system by combining new TESS photometry, ground-based transit follow-up, and radial velocity (RV) observations from MAROON-X. We obtain improved constraints on planetary masses and eccentricities, and update other parameters, such as the stellar age. For TOI-4600b, we measure a mass of $M_p = 74.7^{+4.7}_{-4.4}\,M_{\oplus}$ and an eccentricity of $e=0.153^{+0.020}_{-0.018}$, and $M_p = 212.53^{+13.26}_{-13.03}\,M_{\oplus}$ and $e=0.219^{+0.015}_{-0.018}$ for TOI-4600c. We find significant transit timing variations (TTV) in both planets, with semi-amplitudes of approximately $1$\,hr. We derive Transit Spectroscopy Metric values of 16.87 for TOI-4600b and 10.09 for TOI-4600c, indicating that both planets are promising JWST targets for studying the atmospheres of temperate and cold Jupiters, a relatively poorly characterized sample thus far. These updated parameters and TTV ephemerides are important for planning and interpreting future photometric, spectroscopic, and dynamical studies of the TOI-4600 system.

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arXiv2025

Searching for GEMS: TOI-5349b is a Saturn-like planet orbiting a metal-rich early M-dwarf

We report the confirmation and analysis of TOI-5349b, a transiting, warm, Saturn-like planet orbiting an early M-dwarf with a period of $\sim$3.3 days, which we confirmed as part of the Searching for GEMS (Giant Exoplanets around M-dwarf Stars) survey. TOI-5349b was initially identified in photometry from NASA's Transiting Exoplanet Survey Satellite (TESS) mission and subsequently confirmed using high-precision radial velocity (RV) measurements from the Habitable-zone Planet Finder (HPF) and MAROON-X spectrographs, and from ground-based transit observations obtained using the 0.6-m telescope at Red Buttes Observatory (RBO) and the 1.0-m telescope at the Table Mountain Facility of Pomona College. From a joint fit of the RV and photometric data, we determine the planet's mass and radius to be $0.40\pm 0.02~\mathrm{M_J}$ ($127.4_{-5.7}^{+5.9}~M_\oplus$) and $0.91\pm 0.02~\mathrm{R_J}$ ($10.2\pm 0.3~R_\oplus$), respectively, resulting in a bulk density of $\rho_p=0.66 \pm0.06~\mathrm{g~cm^{-3}}$ ($\sim$0.96 the density of Saturn). We determine that the host star is a metal-rich M1-type dwarf with a mass and radius of $0.61 \pm 0.02~M_\odot$ and $0.58\pm 0.01~R_\odot$, and an effective temperature of $T_\mathrm{eff} = 3751 \pm 59$ K. Our analysis highlights an emerging pattern, exemplified by TOI-5349, in which transiting GEMS often have Saturn-like masses and densities and orbit metal-rich stars. With the growing sample of GEMS planets, comparative studies of short-period gas giants orbiting M-dwarfs and Sun-like stars are needed to investigate how metallicity and disk conditions shape the formation and properties of these planets.

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arXiv2025

The JWST Rocky Worlds DDT Program reveals GJ 3929b to likely be a bare rock

We report first results from the JWST Rocky Worlds Director's Discretionary Time program. Two secondary eclipses of the terrestrial exoplanet GJ 3929b were recently observed using MIRI photometric imaging at 15 um. We present a reduction of these data using the updated SPARTA pipeline. We also refine the planet mass, radius, and predicted time of secondary eclipse using a new sector of TESS data and new, high-precision radial velocities from the MAROON-X spectrograph. For the two JWST observations, we recover secondary eclipse depths of 177+47-45ppm and 143+34-35ppm at times consistent with a nearly circular orbit, as expected from the radial velocity data. A joint fit of the two visits yields a dayside brightness temperature Tp,dayside = 782+/-79K for GJ 3929b, which is consistent with the maximum brightness temperature Tmax = 737+/-14K for a bare, black rock (i.e., assuming zero Bond albedo and no heat redistribution). These results rule out CO2-rich atmospheres thicker than 100mbar at >3sigma, suggesting that GJ 3929b has lost any significant secondary atmosphere. The radial velocity data also indicate two additional non-transiting planets in the system: a previously-identified planet in a 15.0d orbit, and a newly-identified planet candidate in a 6.1d orbit.

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arXiv2025

An Earth-like Density for the Temperate Earth-sized Planet GJ 12b

While JWST has provided us with the opportunity to probe the atmospheres of potentially-habitable planets, observations of the TRAPPIST-1 system have shown us that active stars severely complicate efforts at studying their planets. GJ 12b is a newly-discovered temperate (Teq ~ 300 K), Earth-sized (Rp = 0.96 +/- 0.05 Earth radii) planet orbiting an inactive M dwarf that might be a good alternate to the TRAPPIST-1 planets for atmospheric characterization. In this paper, we use MAROON-X radial velocities to measure a mass of 0.71 +/- 0.12 Earth masses for GJ 12b. We also find moderate evidence that the planet has an eccentric (e ~ 0.16) orbit. GJ 12b's mass results in a planetary density comparable to or less dense than Earth, possibly indicating the presence of water or a low bulk iron mass fraction. With its low mass, GJ 12b is likely within reach of JWST transmission spectroscopy observations, making it an excellent target for determining the location of the cosmic shoreline. Its low mass may mean that the planet could have trouble retaining its primary atmosphere during the star's active pre-main-sequence phase. However, if it has a heightened eccentricity, it may be able to sustain a secondary atmosphere through tidally-induced volcanism.

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arXiv2025

Four sub-Earth planets orbiting Barnard's Star from MAROON-X and ESPRESSO

Barnard's Star is an old, single M dwarf star that comprises the second-closest extrasolar system. It has a long history of claimed planet detections from both radial velocities and astrometry. However, none of these claimed detections have so far withstood further scrutiny. Continuing this story, extreme precision radial velocity (EPRV) measurements from the ESPRESSO instrument have recently been used to identify four new sub-Earth-mass planet candidates around Barnard's Star. We present here 112 radial velocities of Barnard's Star from the MAROON-X instrument that were obtained independently to search for planets around this compelling object. The data have a typical precision of 30\,cm\,s$^{-1}$ and are contemporaneous with the published ESPRESSO measurements (2021 -- 2023). The MAROON-X data on their own confirm planet b ($P$\,=\,3.154\,d) and planet candidates c and d ($P$\,=\,4.124\,d and 2.340\,d, respectively). Furthermore, adding the MAROON-X data to the ESPRESSO data strengthens the evidence for planet candidate e ($P$\,=\,6.739\,d), thus leading to its confirmation. The signals from all four planets are $<$50\,cm\,s$^{-1}$, the minimum masses of the planets range from 0.19 to 0.34\,$M_{\oplus}$, and the system is among the most compact known among late M dwarfs hosting low-mass planets. The current data rule out planets with masses $>0.57\,M_{\oplus}$ (with a $99\%$ detection probability) in Barnard Star's habitable zone ($P$\,=\,10 -- 42\,d).

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arXiv2025

Calibrating the Instrumental Drift in MAROON-X using an Ensemble Analysis

MAROON-X is a state-of-the-art extreme precision radial velocity spectrograph deployed on the 8.1-meter Gemini-N telescope on Maunakea, Hawai'i. Using a stabilized Fabry-P\'erot etalon for wavelength and drift calibration, MAROON-X has achieved a short-term precision of $\sim$\,30\,cm\,s$^{-1}$. However, due to a long-term drift in the etalon (2.2\,cm\,s$^{-1}$ per day) and various interruptions of the instrument baseline over the first few years of operation, MAROON-X experiences RV offsets between observing runs several times larger than the short-term precision during any individual run, which hinders the detection of longer-period signals. In this study, we analyze RV measurements of 11 targets that either exhibit small RV scatter or have signals that can be precisely constrained using Keplerian or Gaussian Process models. Leveraging this ensemble, we calibrate MAROON-X's run offsets for data collected between September 2020 and early January 2024 to a precision of $\sim$0.5\,m\,s$^{-1}$. When applying these calibrated offsets to HD 3651, a quiet star, we obtain residual velocities with an RMS of $<$70\,cm\,s$^{-1}$ in both the Red and Blue channels of MAROON-X over a baseline of 29 months. We also demonstrate the sensitivity of MAROON-X data calibrated with these offsets through a series of injection-recovery tests. Based on our findings, MAROON-X is capable of detecting sub m\,s$^{-1}$ signals out to periods of more than 1,000 days.

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arXiv2024

Searching for GEMS: Characterizing Six Giant Planets around Cool Dwarfs

Transiting giant exoplanets around M-dwarf stars (GEMS) are rare, owing to the low-mass host stars. However, the all-sky coverage of TESS has enabled the detection of an increasingly large number of them to enable statistical surveys like the \textit{Searching for GEMS} survey. As part of this endeavour, we describe the observations of six transiting giant planets, which includes precise mass measurements for two GEMS (K2-419Ab, TOI-6034b) and statistical validation for four systems, which includes validation and mass upper limits for three of them (TOI-5218b, TOI-5616b, TOI-5634Ab), while the fourth one -- TOI-5414b is classified as a `likely planet'. Our observations include radial velocities from the Habitable-zone Planet Finder on the Hobby-Eberly Telescope, and MAROON-X on Gemini-North, along with photometry and high-contrast imaging from multiple ground-based facilities. In addition to TESS photometry, K2-419Ab was also observed and statistically validated as part of the K2 mission in Campaigns 5 and 18, which provides precise orbital and planetary constraints despite the faint host star and long orbital period of $\sim 20.4$ days. With an equilibrium temperature of only 380 K, K2-419Ab is one of the coolest known well-characterized transiting planets. TOI-6034 has a late F-type companion about 40\arcsec~away, making it the first GEMS host star to have an earlier main-sequence binary companion. These confirmations add to the existing small sample of confirmed transiting GEMS.

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arXiv2023

EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc

Earth-sized exoplanets that transit nearby, late spectral type red dwarfs will be prime targets for atmospheric characterization in the coming decade. Such systems, however, are difficult to find via wide-field transit surveys like Kepler or TESS. Consequently, the presence of such transiting planets is unexplored and the occurrence rates of short-period Earth-sized planets around late M dwarfs remain poorly constrained. Here, we present the deepest photometric monitoring campaign of 22 nearby late M dwarf stars, using data from over 500 nights on seven 1-2 meter class telescopes. Our survey includes all known single quiescent northern late M dwarfs within 15 pc. We use transit-injection-and-recovery tests to quantify the completeness of our survey, successfully identify most ($>80\%$) transiting short-period (0.5-1 d) super-Earths ($R > 1.9 R_\oplus$), and are sensitive ($\sim50\%$) to transiting Earth-sized planets ($1.0-1.2 R_\oplus$). Our high sensitivity to transits with a near-zero false positive rate demonstrates an efficient survey strategy. Our survey does not yield a transiting planet detection, yet it provides the most sensitive upper limits on transiting planets orbiting our target stars. Finally, we explore multiple hypotheses about the occurrence rates of short-period planets (from Earth-sized planets to giant planets) around late M dwarfs. We show, for example, that giant planets at short periods ($<1$ day) are uncommon around our target stars. Our dataset provides some insight into occurrence rates of short-period planets around TRAPPIST-1-like stars, and our results can help test planetary formation and system evolution models, as well as guide future observations of nearby late M dwarfs.

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arXiv2022

An Integrative Analysis of the Rich Planetary System of the Nearby Star e Eridani: Ideal Targets For Exoplanet Imaging and Biosignature Searches

e Eridani, the fifth-closest Sun-like star, hosts at least three planets and could possibly harbor more. However, the veracity of the planet candidates in the system and its full planetary architecture remain unknown. Here we analyze the planetary architecture of e Eridani via DYNAMITE, a method providing an integrative assessment of the system architecture (and possibly yet-undetected planets) by combining statistical, exoplanet-population level knowledge with incomplete but specific information available on the system. DYNAMITE predicts the most likely location of an additional planet in the system based on the Kepler population demographic information from more than 2000 planets. Additionally, we analyze the dynamical stability of e Eridani system via N-body simulations. Our DYNAMITE and dynamical stability analyses provide support for planet candidates g, c, and f, and also predict one additional planet candidate with an orbital period between 549 -- 733 days, in the habitable zone of the system. We find that planet candidate f, if it exists, would also lie in the habitable zone. Our dynamical stability analysis also shows that the e Eridani planetary eccentricities, as reported, do not allow for a stable system, suggesting that they are lower. We introduce a new statistical approach for estimating the equilibrium and surface temperatures of exoplanets, based on a prior on the planetary albedo distribution. e Eridani is a rich planetary system with a possibility of containing two potentially habitable planets, and its vicinity to our Solar System makes it an important target for future imaging studies and biosignature searches.

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