arXiv subjects

Ivan A. Terentev

Publications and source records attributed to Ivan A. Terentev.

At least 19 recordsLinked to original sources

arXiv2026

A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2

The transit method is currently one of our best means for the detection of potentially habitable "Earth-like" exoplanets. In principle, given sufficiently high photometric precision, cool Earth-sized exoplanets orbiting Sun-like stars could be discovered via single transit detections; however, this has not previously been achieved. In this work, we report a 10-hour long single transit event which occurred on the $V=10.1$ K-dwarf HD 137010 during K2 Campaign 15 in 2017. The transit is comparatively shallow ($225\pm10$ ppm), but is detected at high signal-to-noise thanks to the exceptionally high photometric precision achieved for the target. Our analysis of the K2 photometry, historical and new imaging observations, and archival radial velocities and astrometry strongly indicate that the event was astrophysical, occurred on-target, and can be best explained by a transiting planet candidate, which we designate HD 137010 b. The single observed transit implies a radius of $1.06^{+0.06}_{-0.05}$ $R_\oplus$, and assuming negligible orbital eccentricity we estimate an orbital period of $355^{+200}_{-59}$ days ($a=0.88^{+0.32}_{-0.10}$ AU), properties comparable to Earth. We project an incident flux of $0.29^{+0.11}_{-0.13}$ $I_\oplus$, which would place HD 137010 b near the outer edge of the habitable zone. This is the first planet candidate with Earth-like radius and orbital properties that transits a Sun-like star bright enough for substantial follow-up observations.

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arXiv2025

52 Eclipsing Quadruple Star Candidates Discovered in TESS Full Frame Images

We present the discovery of 52 eclipsing quadruple star candidates detected in TESS Full Frame Image eleanor data by machine learning and citizen scientists. The uniformly-vetted and -validated targets exhibit two sets of eclipses following two distinct periods, representing quadruple systems with a 2+2 hierarchical configuration. Detailed photocenter measurements confirmed that both sets of eclipses originate within ~0.1-0.2 pixels (~2-4 arcsec) of the corresponding target, and ruled out resolved nearby field stars. The catalog includes a number of systems producing prominent eclipse timing variations and/or apsidal motion, a quadruple with an outer period of ~1,400 days, and even a 2+2 quadruple in a likely wide quintuple with a resolved co-moving star. Additionally, two systems have complete astrometric solutions for the outer orbits from Gaia. We provide the measured ephemerides, eclipse depths and durations, overall statistical properties, and highlight potentially interesting systems that merit further investigations.

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arXiv2025

NGTS-EB-8: A double-lined eclipsing M+M binary discovered by citizen scientists

We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be $M_A=0.250^{+0.005}_{-0.004}$ M$_{\odot}$, $M_B=0.208^{+0.005}_{-0.004}$ M$_{\odot}$, $R_A=0.255^{+0.004}_{-0.005}$ R$_{\odot}$, $R_B=0.233^{+0.006}_{-0.005}$ R$_{\odot}$. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars ($<0.35$ M$_{\odot}$), therefore can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries.

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arXiv2025

The HD 60779 Planetary System: A Transiting Sub-Neptune on a 30-day Orbit and a More Massive Outer World

We present the discovery of the planetary system orbiting the bright (V = 7.2), nearby (35 pc), Sun-like star HD 60779, which has a mass of 1.050 +/- 0.044 solar masses and a radius of 1.129 +/- 0.013 solar radii. We report two TESS transits and a subsequent CHEOPS transit of HD 60779 b, a sub-Neptune with a radius of 3.250 (+0.100 / -0.098) Earth radii on a 29.986175 (+0.000030 / -0.000033) day orbit. Additionally, 286 HARPS-N radial velocity measurements reveal the mass of planet b (14.7 +1.1 / -1.0 Earth masses) and the presence of an outer planet, HD 60779 c, with an orbital period of 104.25 (+0.30 / -0.29) days and a minimum mass (m sin i) of 27.7 +/- 1.6 Earth masses. Both planets' orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779's uniquely high systemic radial velocity (129.75 +/- 0.12 km/s) allows its Lyman-alpha emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third-brightest host of a sub-Neptune with orbital period greater than 25 days and with both mass and radius measured, distinguishing it in terms of accessibility to spectroscopic characterization.

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arXiv2025

The Discovery of Two Quadruple Star Systems with the Second and Third Shortest Outer Periods

We present the discovery of two quadruple star systems -- TIC 285853156 and TIC 392229331 -- each consisting of two bound eclipsing binary stars. Among the most compact quadruples known, TIC 392229331 and TIC 285853156 have the second and third shortest outer orbital periods (145 days and 152 days, respectively) after BU Canis Minoris (122 days, Pribulla et al. 2023). We demonstrate that both systems are long-term dynamically stable despite substantial outer orbital eccentricities (0.33 for TIC 285853156 and 0.56 for TIC 392229331). We previously reported these systems in Kostov et al. (2022) and Kostov et al. (2024) as 2+2 hierarchical quadruple candidates producing two sets of primary and secondary eclipses in TESS data, as well as prominent eclipse timing variations on both binary components. We combine all available TESS data and new spectroscopic observations into a comprehensive photodynamical model, proving that the component binary stars are gravitationally bound in both systems and finding accurate stellar and orbital parameters for both systems, including very precise determinations of the outer periods. TIC 285853156 and TIC 392229331 represent the latest addition to the small population of well-characterized proven quadruple systems dynamically interacting on detectable timescales.

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arXiv2024

TIC 290061484: A Triply Eclipsing Triple System with the Shortest Known Outer Period of 24.5 Days

We have discovered a triply eclipsing triple-star system, TIC 290061484, with the shortest known outer period, Pout, of only 24.5 days. This "eclipses" the previous record set by lambda Tauri at 33.02 days, which held for 68 yr. The inner binary, with an orbital period of Pin = 1.8 days, produces primary and secondary eclipses and exhibits prominent eclipse timing variations with the same periodicity as the outer orbit. The tertiary star eclipses, and is eclipsed by, the inner binary with pronounced asymmetric profiles. The inclinations of both orbits evolve on observable timescales such that the third-body eclipses exhibit dramatic depth variations in TESS data. A photodynamical model provides a complete solution for all orbital and physical parameters of the triple system, showing that the three stars have masses of 6.85, 6.11, and 7.90 MSun, radii near those corresponding to the main sequence, and Teff in the range of 21,000-23,700 K. Remarkably, the model shows that the triple is in fact a subsystem of a hierarchical 2+1+1 quadruple with a distant fourth star. The outermost star has a period of ~3200 days and a mass comparable to the stars in the inner triple. In ~20 Myr, all three components of the triple subsystem will merge, undergo a Type II supernova explosion, and leave a single remnant neutron star. At the time of writing, TIC 290061484 is the most compact triple system and one of the tighter known compact triples (i.e., Pout/Pin = 13.7).

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arXiv2024

Confirmation and Characterization of the Eccentric, Warm Jupiter TIC 393818343 b with a Network of Citizen Scientists

NASA's Transiting Exoplanet Survey Satellite (TESS) has identified over 7,000 candidate exoplanets via the transit method, with gas giants among the most readily detected due to their large radii. Even so, long intervals between TESS observations for much of the sky lead to candidates for which only a single transit is detected in one TESS sector, leaving those candidate exoplanets with unconstrained orbital periods. Here, we confirm the planetary nature of TIC 393818343 b, originally identified via a single TESS transit, using radial velocity data and ground-based photometric observations from citizen scientists with the Unistellar Network and Exoplanet Watch. We determine a period of $P$ = 16.24921 $\substack{+0.00010 \\ -0.00011}$ days, a mass $M_{P}$ = 4.34 $\pm$ 0.15 $M_{J}$, and semi-major axis $a$ = 0.1291 $\substack{+0.0021 \\ -0.0022}$ au, placing TIC 393818343 b in the "warm Jupiter" population of exoplanets. With an eccentricity $e$ = 0.6058 $\pm$ 0.0023, TIC 393818343 b is the most eccentric warm Jupiter to be discovered by TESS orbiting less than 0.15 au from its host star and therefore an excellent candidate for follow-up, as it may inform our future understanding of how hot and warm Jupiter populations are linked.

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arXiv2024

The Active Asteroids Citizen Science Program: Overview and First Results

We present the Citizen Science program Active Asteroids and describe discoveries stemming from our ongoing project. Our NASA Partner program is hosted on the Zooniverse online platform and launched on 2021 August 31, with the goal of engaging the community in the search for active asteroids -- asteroids with comet-like tails or comae. We also set out to identify other unusual active solar system objects, such as active Centaurs, active quasi-Hilda asteroids, and Jupiter-family comets (JFCs). Active objects are rare in large part because they are difficult to identify, so we ask volunteers to assist us in searching for active bodies in our collection of millions of images of known minor planets. We produced these cutout images with our project pipeline that makes use of publicly available Dark Energy Camera (DECam) data. Since the project launch, roughly 8,300 volunteers have scrutinized some 430,000 images to great effect, which we describe in this work. In total we have identified previously unknown activity on 15 asteroids, plus one Centaur, that were thought to be asteroidal (i.e., inactive). Of the asteroids, we classify four as active quasi-Hilda asteroids, seven as JFCs, and four as active asteroids, consisting of one Main-belt comet (MBC) and three MBC candidates. We also include our findings concerning known active objects that our program facilitated, an unanticipated avenue of scientific discovery. These include discovering activity occurring during an orbital epoch for which objects were not known to be active, and the reclassification of objects based on our dynamical analyses.

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arXiv2023

101 Eclipsing Quadruple Star Candidates Discovered in TESS Full Frame Images

We present our second catalog of quadruple star candidates, containing 101 systems discovered in TESS Full-Frame Image data. The targets were initially detected as eclipsing binary stars with the help of supervised machine learning methods applied to sectors Sectors 1 through 54. A dedicated team of citizen scientists subsequently identified through visual inspection two sets of eclipses following two different periods. All 101 systems presented here pass comprehensive photocenter motion tests confirming that both sets of eclipses originate from the target star. Some of the systems exhibit prominent eclipse time variations suggesting dynamical interactions between the two component binary stars. One target is an eclipsing quintuple candidate with a (2+1)+2 hierarchical configuration, such that the (2+1) subsystem produces eclipses on the triple orbit as well. Another has recently been confirmed as the second shortest period quadruple reported to date. This catalog provides ephemerides, eclipse depths and durations, sample statistics, and highlights potentially interesting targets for future studies.

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arXiv2023

BU Canis Minoris -- the Most Compact Known Flat Doubly Eclipsing Quadruple System

We have found that the 2+2 quadruple star system BU CMi is currently the most compact quadruple system known, with an extremely short outer period of only 121 days. The previous record holder was TIC 219006972 (Kostov et al. 2023), with a period of 168 days. The quadruple nature of BU CMi was established by Volkov et al. (2021), but they misidentified the outer period as 6.6 years. BU CMi contains two eclipsing binaries (EBs), each with a period near 3 days, and a substantial eccentricity of about 0.22. All four stars are within about 0.1 solar mass of 2.4 solar masses. Both binaries exhibit dynamically driven apsidal motion with fairly short apsidal periods of about 30 years, thanks to the short outer orbital period. The outer period of 121 days is found both from the dynamical perturbations, with this period imprinted on the eclipse timing variations (ETV) curve of each EB by the other binary, and by modeling the complex line profiles in a collection of spectra. We find that the three orbital planes are all mutually aligned to within 1 degree, but the overall system has an inclination angle near 83.5 degrees. We utilize a complex spectro-photodynamical analysis to compute and tabulate all the interesting stellar and orbital parameters of the system. Finally, we also find an unexpected dynamical perturbation on a timescale of several years whose origin we explore. This latter effect was misinterpreted by Volkov et al. (2021) and led them to conclude that the outer period was 6.6 years rather than the 121 days that we establish here.

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arXiv2023

TIC 219006972: A Compact, Coplanar Quadruple Star System Consisting of Two Eclipsing Binaries with an Outer Period of 168 days

We present the discovery of a new highly compact quadruple star system, TIC 219006972, consisting of two eclipsing binary stars with orbital periods of 8.3 days and 13.7 days, and an outer orbital period of only 168 days. This period is a full factor of 2 shorter than the quadruple with the shortest outer period reported previously, VW LMi, where the two binary components orbit each other every 355 days. The target was observed by TESS in Full-Frame Images in sectors 14-16, 21-23, 41, 48 and 49, and produced two sets of primary and secondary eclipses. These show strongly non-linear eclipse timing variations (ETVs) with an amplitude of $\sim$0.1 days, where the ETVs of the primary and secondary eclipses, and of the two binaries are all largely positively correlated. This highlights the strong dynamical interactions between the two binaries and confirms the compact quadruple configuration of TIC 219006972. The two eclipsing binaries are nearly circular whereas the quadruple system has an outer eccentricity of about 0.25. The entire system is nearly edge-on, with a mutual orbital inclination between the two eclipsing binary star systems of about 1 degree.

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arXiv2022

TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain

Convergent disk migration has long been suspected to be responsible for forming planetary systems with a chain of mean-motion resonances (MMR). Dynamical evolution over time could disrupt the delicate resonant configuration. We present TOI-1136, a 700-Myr-old G star hosting at least 6 transiting planets between $\sim$2 and 5 $R_\oplus$. The orbital period ratios deviate from exact commensurability by only $10^{-4}$, smaller than the $\sim$\,$10^{-2}$ deviations seen in typical Kepler near-resonant systems. A transit-timing analysis measured the masses of the planets (3-8$M_\oplus$) and demonstrated that the planets in TOI-1136 are in true resonances with librating resonant angles. Based on a Rossiter-McLaughlin measurement of planet d, the star's rotation appears to be aligned with the planetary orbital planes. The well-aligned planetary system and the lack of detected binary companion together suggest that TOI-1136's resonant chain formed in an isolated, quiescent disk with no stellar fly-by, disk warp, or significant axial asymmetry. With period ratios near 3:2, 2:1, 3:2, 7:5, and 3:2, TOI-1136 is the first known resonant chain involving a second-order MMR (7:5) between two first-order MMR. The formation of the delicate 7:5 resonance places strong constraints on the system's migration history. Short-scale (starting from $\sim$0.1 AU) Type-I migration with an inner disk edge is most consistent with the formation of TOI-1136. A low disk surface density ($Σ_{\rm 1AU}\lesssim10^3$g~cm$^{-2}$; lower than the minimum-mass solar nebula) and the resultant slower migration rate likely facilitated the formation of the 7:5 second-order MMR. TOI-1136's deep resonance suggests that it has not undergone much resonant repulsion during its 700-Myr lifetime. One can rule out rapid tidal dissipation within a rocky planet b or obliquity tides within the largest planets d and f.

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arXiv2022

A Population of Dipper Stars from the Transiting Exoplanet Survey Satellite Mission

Dipper stars are a classification of young stellar objects that exhibit dimming variability in their light curves, dropping in brightness by 10-50%, likely induced by occultations due to circumstellar disk material. This variability can be periodic, quasi-periodic, or aperiodic. Dipper stars have been discovered in young stellar associations via ground-based and space-based photometric surveys. We present the detection and characterization of the largest collection of dipper stars to date: 293 dipper stars, including 234 new dipper candidates. We have produced a catalog of these targets, which also includes young stellar variables that exhibit predominately bursting-like variability and symmetric variability (equal parts bursting and dipping). The total number of catalog sources is 414. These variable sources were found in a visual survey of TESS light curves, where dipping-like variability was observed. We found a typical age among our dipper sources of <5 Myr, with the age distribution peaking at ~2 Myr, and a tail of the distribution extending to ages older than 20 Myr. Regardless of the age, our dipper candidates tend to exhibit infrared excess, which is indicative of the presence of disks. TESS is now observing the ecliptic plane, which is rich in young stellar associations, so we anticipate many more discoveries in the TESS dataset. A larger sample of dipper stars would enhance the census statistics of light curve morphologies and dipper ages.

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arXiv2022

TIC 114936199: A Quadruple Star System with a 12-day Outer Orbit Eclipse

We report the discovery with TESS of a remarkable quadruple star system with a 2+1+1 configuration. The two unique characteristics of this system are that (i) the inner eclipsing binary (stars Aa and Ab) eclipses the star in the outermost orbit (star C), and (ii) these outer 4th body eclipses last for $\sim$12 days, the longest of any such system known. The three orbital periods are $\sim$3.3 days, $\sim$51 days, and $\sim$2100 days. The extremely long duration of the outer eclipses is due to the fact that star B slows binary A down on the sky relative to star C. We combine TESS photometric data, ground-based photometric observations, eclipse timing points, radial velocity measurements, the composite spectral energy distribution, and stellar isochones in a spectro-photodynamical analysis to deduce all of the basic properties of the four stars (mass, radius, $T_{\rm eff}$, and age), as well as the orbital parameters for all three orbits. The four masses are $M_{\rm Aa} =0.382$M$_\odot$, $M_{\rm Ab} =0.300$M$_\odot$, $M_{\rm B} =0.540$M$_\odot$ and $M_{\rm C} =0.615$M$_\odot$, with a typical uncertainty of 0.015 M$_\odot$.

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arXiv2022

The Visual Survey Group: A Decade of Hunting Exoplanets and Unusual Stellar Events with Space-Based Telescopes

This article presents the history of the Visual Survey Group (VSG) - a Professional-Amateur (Pro-Am) collaboration within the field of astronomy working on data from several space missions (Kepler, K2 and TESS). This paper covers the formation of the VSG, its survey-methods including the most common tools used and its discoveries made over the past decade. So far, the group has visually surveyed nearly 10 million light curves and authored 69 peer-reviewed papers which mainly focus on exoplanets and discoveries involving multistellar systems found using the transit method. The preferred manual search-method carried out by the VSG has revealed its strength by detecting numerous sub-stellar objects which were overlooked or discarded by automated search programs, uncovering some of the most rare stars in our galaxy, and leading to several serendipitous discoveries of unprecedented astrophysical phenomena. The main purpose of the VSG is to assist in the exploration of our local Universe, and we therefore advocate continued crowd-sourced examination of time-domain data sets, and invite other research teams to reach out in order to establish collaborating projects.

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arXiv2022

Planet Hunters TESS IV: A massive, compact hierarchical triple star system TIC 470710327

We report the discovery and analysis of a massive, compact, hierarchical triple system (TIC 470710327) initially identified by citizen scientists in data obtained by NASA's Transiting Exoplanet Survey Satellite (TESS). Spectroscopic follow-up observations obtained with the HERMES spectrograph, combined with eclipse timing variations (ETVs), confirm that the system is comprised of three OB stars, with a compact 1.10 d eclipsing binary and a non-eclipsing tertiary on a 52.04 d orbit. Dynamical modelling of the system (from radial velocity and ETVs) reveal a rare configuration wherein the tertiary star (O9.5-B0.5V; 14-17 M$_{\odot}$) is more massive than the combined mass of the inner binary (10.9-13.2 M$_{\odot}$). Given the high mass of the tertiary, we predict that this system will undergo multiple phases of mass transfer in the future, and likely end up as a double neutron star gravitational wave progenitor or an exotic Thorne-Zytkow object. Further observational characterisation of this system promises constraints on both formation scenarios of massive stars as well as their exotic evolutionary end-products.

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arXiv2022

97 Eclipsing Quadruple Star Candidates Discovered in TESS Full Frame Images

We present a catalog of 97 uniformly-vetted candidates for quadruple star systems. The candidates were identified in TESS Full Frame Image data from Sectors 1 through 42 through a combination of machine learning techniques and visual examination, with major contributions from a dedicated group of citizen scientists. All targets exhibit two sets of eclipses with two different periods, both of which pass photocenter tests confirming that the eclipses are on-target. This catalog outlines the statistical properties of the sample, nearly doubles the number of known multiply-eclipsing quadruple systems, and provides the basis for detailed future studies of individual systems. Several important discoveries have already resulted from this effort, including the first sextuply-eclipsing sextuple stellar system and the first transiting circumbinary planet detected from one sector of TESS data.

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arXiv2022

The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 day Orbit with the Automated Planet Finder Telescope

We report the discovery of TOI-2180 b, a 2.8 $M_{\rm J}$ giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8$\pm$0.6 days, revealed an orbital eccentricity of 0.368$\pm$0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.

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