arXiv subjects

S. A. Rappaport

Publications and source records attributed to S. A. Rappaport.

At least 19 recordsLinked to original sources

arXiv2026

Discovery of the First Octupole Pulsation Mode in a delta Scuti Star: A Stationary l = 3 Sectoral Mode

Aims. We are attempting to better understand how stellar pulsations in close binary systems are affected, and possibly induced, by tidal, Coriolis, and centrifugal forces. Methods. We analyzed TESS data for some 50,000 potential eclipsing binaries selected by machine learning algorithms in order to search for pulsation multiplets split by integer multiples of the orbital frequency. Results. We report on the discovery of an octupole pulsation mode in the binary star system TIC 287869463, which contains a delta Scuti star. This mode is actually a combination of Y3+3 and Y3-3 modes that are perturbed into a new eigenmode of the star via tidal, Coriolis, and centrifugal forces, which we call a Y33+ mode. The mode is stationary on the star. To our knowledge, this is the first time that such an l = 3 mode identification has been securely made in any delta Scuti star, and the first stationary l = 3 sectoral mode of this type seen in any star, including the Sun. The l = 3 pulsations appear as a combination of two components at 34.94617 per day and 39.31127 per day, split by exactly six times the frequency of the orbital motion to within better than 1 part in 100,000. We extract the pulsation frequencies from the TESS data spanning more than three years, and model the system to gain a better understanding of this novel asteroseismic discovery. The pulsation frequencies are found to be steadily increasing with time, but always maintaining a split equal to six times the orbital frequency. Conclusions. We discuss the implications for the broader class of "tidally tilted pulsators" and "tri-axial pulsators" that have been discovered to date. We conclude that these previous categories can all be interpreted as linear combinations of spherical harmonics whose axes coincide with the orbital axis and form new eigenmodes of the star via tidal, Coriolis, and centrifugal perturbations

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arXiv2026

A Few Years Later: Revisiting Period Variations of Eclipsing Binaries in the Northern Continuous Viewing Zone of TESS

In our previous analysis of the eclipse timing variation patterns of eclipsing binaries located in and near the Northern Continuous Viewing Zone (NCVZ) of the TESS space telescope, 135 hierarchical triple star candidates were found. Now, two additional years of TESS observations are available and, hence, we have extended the former analysis with the use of the new observational data. We now detect 168 triple star candidates in the updated and reanalyzed sample. The majority ($\sim74\%$) of them are identical to the former triples candidates. For many of them, our new solutions are more certain than the original ones. Therefore, we can now conclude that we have identified at least 66 short-period hierarchical triple stellar systems in the NCVZ with full confidence. In the case of the majority of the remaining systems in our sample, the presence of a close third stellar component appears to be very likely. We also identify additional, longer timescale period variations in 34 systems ($20\%$ of the total sample) and conclude that in at least three systems the presence of a fourth stellar component is quite plausible. Finally, we report the complete disappearance of the eclipses in two former EBs and detect eclipse depth variations in seven other EBs as well. We interpret this effect as the consequence of changing orbital inclination caused by a non-coplanar third body.

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arXiv2025

Ten new, ultracompact triply eclipsing triple star systems

We have identified more than a hundred close triply eclipsing hierarchical triple star systems from data taken with the space telescope TESS. Many of them have outer periods less than or, close to 100 days, hence, we call them `ultracompact hierarchical triples'. These systems are noteworthy in that we can potentially determine their dynamical and astrophysical parameters with a high precision, in many cases even without radial velocity data. In the present paper we report the comprehensive study of ten new ultracompact triply eclipsing triple star systems, located in the northern ecliptic hemisphere, taken from this larger sample: TICs 198581208, 265274458, 283846096, 337993842, 351404069, 378270875, 403792414, 403916758, 405789362, 461500036. Most of the data for this study come from TESS observations, but we obtained supplemental ground-based photometric measurements for two of the systems. The eclipse timing variation curves extracted from the TESS and the ground-based follow up data, the photometric light curves, and the spectral energy distribution are combined in a complex photodynamical analysis to yield the stellar and orbital parameters of all ten systems. The outer periods are in the range of 46.8-101.4 days. We found third-body forced, rapid apsidal motion in four systems. Moreover, TIC 403916758 was found to be a double twin triple (i.e. both the inner and the outer mass ratios are close to unity). All of the systems are substantially flat, with mutual inclination angles of $<5^o$. Finally, we have taken the results for the ten systems in the present paper, and combined them with the system parameters for more than 30 other compact triples that we have reported on in previous work, in order to examine some of the global properties of these systems on a statistical basis.

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arXiv2025

EL CMi: confirmation of triaxial pulsation theory

Triaxial pulsators are a recently discovered group of oscillating stars in close binary systems that show pulsations around three axes at the same time. It has recently been theoretically shown that new types of pulsation modes, the Tidally Tilted Standing (TTS) modes, can arise in such stars. Here, we report the first detection of a quadrupole TTS oscillation mode in the pulsating component of the binary system EL CMi following an analysis of TESS space photometry. Two dipole oscillations around different axes in the orbital plane are present as well. In addition, the binary system is characterized using new radial velocity measurements, phoebe as well as simultaneous spectral energy distribution and light curve modeling. The pulsating primary component has properties typical of a Delta Scuti star but has accreted and is still accreting mass from its Roche Lobe filling companion. The donor star is predicted to evolve into a low-mass helium white dwarf. EL CMi demonstrates the potential of asteroseismic inferences of the structure of stars in close binaries before and after mass transfer and in three spatial dimensions.

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arXiv2025

Then and now: A new look at the eclipse timing variations of hierarchical triple star candidates in the primordial $Kepler$-field, revisited by TESS

In this paper we reanalyze the extended ETV curves of the formerly identified triple star candidates and many other $Kepler$ EBs. Besides the confirmations of the former findings and/or the improvements of the triple systems' orbital properties, the extended time-base allows us to identify several new, longer outer period triple systems, and it also makes possible a more detailed study of the dynamical perturbations in the tightest triple stars. We extend the ETV curves of the $Kepler$ triples with those mid-eclipse times which can be deduced from the TESS observations and, moreover, from targeted ground-based follow up observations for a number of the objects. In general, we use the same methods that were applied for the older studies, which are described in the literature. Due to the lower quality of the TESS observations, however, for the fainter systems we average light curves of the EBs for 5-20 consecutive cycles, and thereby calculate `normal' minima from these averaged light curves. In conclusion, we identified 243 hierarchical triple star candidates in the $Kepler$ sample. This sample strongly overlaps our former, nine-year-old sample, confirming the older results, or providing new solutions for 193 systems of the 2016 sample. For the remaining 28 hierarchical triple candidates of that former study, we were unable to find new solutions either because of the disappearance of the eclipses due to orbital plane precession, or due to instrumental reasons. On the other hand, due to the extended time series, we were able to identify 50 new, longer period triple star candidates, as well. We briefly discuss the main properties of each individual system and present statistical studies of the results, as well.

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arXiv2024

Characterization of the $δ$ Scuti eclipsing binary KIC 4851217 and its tertiary companion as well as detection of tidally tilted pulsations

Stellar theory enables us to understand the properties of stars at different stages of their evolution, and contributes to other fields of astrophysics such as galactic and exoplanet studies. Assessing the accuracy of stellar theories necessitates high precision, model-independent measurements of the properties of real stars, such as those obtainable for the components of double lined eclipsing binaries (DLEBs), while asteroseismology offers probing power of the stellar interior if one or both components pulsate. KIC 4851217 is a DLEB containing two late A-type stars and exhibits pulsations of the $δ$ Scuti type. By analysing high resolution HERMES and moderate resolution ISIS spectra, jointly with Kepler and TESS light curves, we measured the masses, radii and effective temperatures of the components to precisions of ~0.5, ~1.1 and ~1 per cent, respectively. We additionally report the discovery and characterisation of a tertiary M-dwarf companion. Models of the system's spectral energy distribution agree with an age of 0.82 Gyr, with the more massive and larger secondary component near the end of the main sequence lifetime. An examination of the pulsating component's pulsation frequencies reveals 39 pulsation multiplets that are split by the orbital frequency. For most of these, it is evident that the pulsation axes have been tilted into the orbital plane. This makes KIC 4851217 a tidally tilted pulsator (TTP). This precisely characterized $δ$ Scuti DLEB is an ideal candidate for advancing intermediate-mass stellar theory, contributing to our understanding of hierarchichal systems as well as to the topic of TTPs.

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arXiv2024

Seven new triply eclipsing triple star systems

We have identified nearly a hundred close triply eclipsing hierarchical triple star systems from data taken with the space telescope TESS. These systems are noteworthy in that we can potentially determine their dynamical and astrophysical parameters with a high precision. In the present paper, we report the comprehensive study of seven new compact triply eclipsing triple star systems taken from this larger sample: TICs 133771812, 176713425, 185615681, 287756035, 321978218, 323486857, and 650024463. Most of the data for this study come from TESS observations, but two of them have Gaia measurements of their outer orbits, and we obtained supplemental radial velocity (RV) measurements for three of the systems. The eclipse timing variation curves extracted from the TESS data, the photometric light curves, the RV points, and the spectral energy distribution (SED) are combined in a complex photodynamical analysis to yield the stellar and orbital parameters of all seven systems. Four of the systems are quite compact with outer periods in the range of 41-56 days. All of the systems are substantially flat, with mutual inclination angles of < ~2 degrees. Including the systems reported in this work, we have now studied in considerable detail some 30 triply eclipsing triples with TESS, and are accumulating a meaningful census of these systems.

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arXiv2024

Eclipse timing study of new hierarchical triple star candidates in the Northern Continuous Viewing Zone of TESS

We compiled a list of more than 3500 eclipsing binaries located in and near the Northern Continuous Viewing Zone (NCVZ) of the TESS space telescope that have a sufficient amount of TESS photometry to search for additional hidden components in these systems. We obtained the TESS light curves of all targets in an automated way applying convolution-aided differential photometry on the TESS Full-Frame Images from all available sectors up to Sector 60. Using a new self-developed Python GUI, we visually vetted all of these light curves, determined the eclipsing periods of the objects and calculated their eclipse timing variations (ETVs). The ETV curves were used in order to search for nonlinear variations that could be attributed to a light travel time effect (LTTE) or dynamical perturbations caused by additional components in these systems. We pre-selected 351 such candidates and tried to model their ETVs with the analytic formulae of pure LTTE or the combination of LTTE and dynamical perturbations. In total we could fit a model solution for the ETVs of 135 hierarchical triple candidates in which 10 systems were already known in the literature and the remainder of the 125 systems are new discoveries. Among these systems, there are some more noteworthy ones, such as five tight triples very close to their dynamical stability limit with a period ratio of less than 20 and three newly discovered triply eclipsing triples. We point out that dynamical perturbations are occurring in GZ Dra, which turns out to be a triple. We also made a comparison of the distributions of some orbital parameters coming from our solutions with those from the Kepler sample derived by Borkovits et al. (2016). Finally, we checked the correlations between the available parameters for systems that have Gaia Non-Single Star orbital solutions with those from our ETV solutions. (Abridged)

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arXiv2023

V994 Her: A Unique Triply Eclipsing Sextuple Star System

We report the discovery with $TESS$ of a third set of eclipses from V994 Herculis (TIC 424508303), previously only known as a doubly-eclipsing system. The key implication of this discovery and our analyses is that V994 Her is the second fully-characterized (2+2) + 2 sextuple system, in which all three binaries eclipse. In this work, we use a combination of ground-based observations and $TESS$ data to analyze the eclipses of binaries A and B in order to update the parameters of the inner quadruple's orbit (with a derived period of 1062 $\pm$ 2d). The eclipses of binary C that were detected in the $TESS$ data were also found in older ground-based observations, as well as in more recently obtained observations. The eclipse timing variations of all three pairs were studied in order to detect the mutual perturbations of their constituent stars, as well as those of the inner pairs in the (2+2) core. At the longest periods they arise from apsidal motion, which may help constraining parameters of the component stars' internal structure. We also discuss the relative proximity of the periods of binaries A and B to a 3:2 mean motion resonance. This work represents a step forward in the development of techniques to better understand and characterize multiple star systems, especially those with multiple eclipsing components.

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arXiv2023

A Study of Nine Triply Eclipsing Triples

In this work we report the independent discovery and analysis of nine new compact triply eclipsing triple star systems found with the TESS mission: TICs 47151245, 81525800, 99013269, 229785001, 276162169, 280883908, 294803663, 332521671, and 356324779. Each of these nine systems exhibits distinct third-body eclipses where the third (`tertiary') star occults the inner eclipsing binary (EB), or vice versa. We utilize a photodynamical analysis of the TESS photometry, archival photometric data, TESS eclipse timing variations of the EBs, available archival spectral energy distribution curves (SED), and, in some cases, newly acquired radial velocity observations, to solve for the parameters of all three stars, as well as most of the orbital elements. From these analyses we find that the outer orbits of all nine systems are viewed nearly edge on (i.e., within $\lesssim 4^\circ$), and 6 of the systems are coplanar to within $5^\circ$; the others have mutual inclination angles of $20^\circ$, $41^\circ$, and possibly $179^\circ$ (i.e., a retrograde outer orbit). The outer orbital periods range from 47.8 days to 604 days, with eccentricities spanning 0.004 to 0.61. The masses of all 18 EB stars are in the range of 0.9-2.6 M$_\odot$ and are mostly situated near the main sequence. By contrast, the masses and radii of the tertiary stars range from 1.4-2.8 M$_\odot$ and 1.5-13 R$_\odot$, respectively. We make use of the system parameters from these 9 systems, plus those from a comparable number of compact triply eclipsing triples published previously, to gain some statistical insight into their properties.

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arXiv2022

Von Zeipel - Lidov - Kozai cycles in action: $Kepler$ triples with eclipse depth variations: KICs 6964043, 5653126, 5731312 and 8023317

We report the results of the photodynamical analyses of four compact, tight triple stellar systems, KICs 6964043, 5653126, 5731312, 8023317, based largely on $Kepler$ and $TESS$ data. All systems display remarkable eclipse timing and eclipse depth variations, the latter implying a non-aligned outer orbit. Moreover, KIC 6964043 is also a triply eclipsing system. We combined photometry, ETV curves, and archival spectral energy distribution data to obtain the astrophysical parameters of the constituent stars and the orbital elements with substantial precision. KICs 6964043 and 5653126 were found to be nearly flat with mutual inclinations $i_{mut}=4.1$ deg and $12.3$ deg, respectively, while KICs 5731312, 8023317 ($i_{mut}=39.4$ deg and $55.7$ deg, respectively) are found to lie in the high $i_{mut}$ regime of the von Zeipel-Kozai-Lidov (ZKL) theorem. We show that currently both high inclination triples exhibit observable unusual retrograde apsidal motion. Moreover, the eclipses will disappear in all but one of the four systems within a few decades. Short-term numerical integrations of the dynamical evolution reveal that both high inclination triples are currently subject to ongoing, large amplitude ($Δe\sim0.3$) inner eccentricity variations on centuries-long timescales, in accord with the ZKL theorem. Longer-term integrations predict that two of the four systems may become dynamically unstable on $\sim$ Gyr timescales, while in the other two triples common envelope phases and stellar mergers may occur. Finally we investigate the dynamical properties of a sample of 71 KIC/TIC triples statistically, and find that the mutual inclinations and outer mass ratios are anti-correlated at the 4$σ$ level. We discuss the implications for the formation mechanisms of compact triples.

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arXiv2022

Six New Compact Triply Eclipsing Triples Found With TESS

In this work we report the discovery and analysis of six new compact triply eclipsing triple star systems found with the TESS mission: TICs 37743815, 42565581, 54060695, 178010808, 242132789, and 456194776. All of these exhibit distinct third body eclipses where the inner eclipsing binary (EB) occults the third (`tertiary') star, or vice versa. We utilized the TESS photometry, archival photometric data, and available archival spectral energy distribution curves (SED) to solve for the properties of all three stars, as well as many of the orbital elements. We describe in detail our SED fits, search of the archival data for the outer orbital period, and the final global photodynamical analyses. From these analyses we find that all six systems are coplanar to within $0^\circ$ - $5^\circ$, and are viewed nearly edge on (i.e., within a couple of degrees). The outer orbital periods and eccentricities of the six systems are {$P_{\rm out}$ (days), $e$}: {68.7, 0.36}, {123, 0.16}, {60.7, 0.01}, {69.0, 0.29}, {41.5, 0.01}, {93.9, 0.29}, respectively, in the order the sources are listed above. The masses of all 12 EB stars were in the range of 0.7-1.8 M$_\odot$ and were situated near the main sequence. By contrast, the masses and radii of the tertiary stars ranged from 1.5-2.3 M$_\odot$ and 2.9-12 R$_\odot$, respectively. We use this information to estimate the occurrence rate of compact flat triple systems.

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arXiv2021

A 2+1+1 quadruple star system containing the most eccentric, low-mass, short-period, eclipsing binary known

We present an analysis of a newly discovered 2+1+1 quadruple system with TESS containing an unresolved eclipsing binary (EB) as part of TIC 121088960 and a close neighbor TIC 121088959. The EB consists of two very low-mass M dwarfs in a highly-eccentric ($e$ = 0.709) short-period ($P$ = 3.04358 d) orbit. Given the large pixel size of TESS and the small separation (3.9$"$) between TIC 121088959 and TIC 121088960, we used light centroid analysis of the difference image between in-eclipse and out-of-eclipse data to show that the EB likely resides in TIC 121088960, but contributes only $\sim$10% of its light. Radial velocity data were acquired with iSHELL at NASA's Infrared Facility and the Coud${é}$ spectrograph at the McDonald 2.7-m telescope. For both images, the measured RVs showed no variation over the 11-day observational baseline, and the RV difference between the two images was $8 \pm 0.3$ km s$^{-1}$. The similar distances and proper motions of the two images indicate that TIC 121088959 and TIC 121088960 are a gravitationally bound pair. Gaia's large RUWE and astrometric_excess_noise parameters for TIC 121088960, further indicate that this image is the likely host of the unresolved EB and is itself a triple star. We carried out an SED analysis and calculated stellar masses for the four stars, all of which are in the M dwarf regime: 0.19 M$_\odot$ and 0.14 M$_\odot$ for the EB stars and 0.43 M$_\odot$ and 0.39 M$_\odot$ for the brighter visible stars, respectively. Lastly, numerical simulations show that the orbital period of the inner triple is likely the range 1 to 50 years.

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arXiv2021

Triply eclipsing triple stars in the northern TESS fields: TICs 193993801, 388459317 and 52041148

In this work we report the discovery and analysis of three new triply eclipsing triple star systems found with the TESS mission during its observations of the northern skies: TICs 193993801, 388459317, and 52041148. We utilized the TESS precision photometry of the binary eclipses and third-body eclipsing events, ground-based archival and follow-up photometric data, eclipse timing variations, archival spectral energy distributions, as well as theoretical evolution tracks in a joint photodynamical analysis to deduce the system masses and orbital parameters of both the inner and outer orbits. In one case (TIC 193993801) we also obtained radial velocity measurements of all three stars. This enabled us to `calibrate' our analysis approach with and without `truth' (i.e., RV) data. We find that the masses are good to 1-3% accuracy with RV data and 3-10% without the use of RV data. In all three systems we were able to find the outer orbital period before doing any detailed analysis by searching for a longer-term periodicity in the ASAS-SN archival photometry data -- just a few thousand ASAS-SN points enabled us to find the outer periods of 49.28 d, 89.86 d, and 177.0 d, respectively. From our full photodynamical analysis we find that all three systems are coplanar to within $1^\circ - 3^\circ$. The outer eccentricities of the three systems are 0.003, 0.10, and 0.62, respectively (i.e., spanning a factor of 200). The masses of the three stars {Aa, Ab, and B} in the three systems are: {1.31, 1.19, 1.34}, {1.82, 1.73, 2.19}, and {1.62, 1.48, 2.74} M$_\odot$, respectively.

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arXiv2021

BG Ind: the nearest doubly eclipsing, compact hierarchical quadruple system

BG Ind is a well studied, bright, nearby binary consisting of a pair of F stars in a 1.46-day orbit. We have discovered in the TESS lightcurve for TIC 229804573 (aka BG Ind) a second eclipsing binary in the system with a 0.53-day. Our subsequent analyses of the recent TESS and archival ground-based photometric and radial velocity data, reveal that the two binaries are gravitationally bound in a 721-day period, moderately eccentric orbit. We present the results of a joint spectro-photodynamical analysis of the eclipse timing variation curves of both binaries based on TESS and ground-based archival data, the TESS lightcurve, archival radial velocity data and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We confirm prior studies of BG Ind which found that the brighter binary A consists of slightly evolved F-type stars with refined masses of 1.32 and 1.43 $M_\odot$, and radii of 1.59 and 2.34 $R_\odot$. The previously unknown binary B has two less massive stars of 0.69 and 0.64 $M_\odot$ and radii of 0.64 and 0.61 $R_\odot$. Based on a number of different arguments which we discuss, we conclude that the three orbital planes are likely aligned to within 17$^\circ$.

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arXiv2021

A tidally tilted sectoral dipole pulsation mode in the eclipsing binary TIC 63328020

We report the discovery of the third tidally tilted pulsator, TIC 63328020. Observations with the TESS satellite reveal binary eclipses with an orbital period of 1.1057 d, and $δ$ Scuti-type pulsations with a mode frequency of 21.09533 d$^{-1}$. This pulsation exhibits a septuplet of orbital sidelobes as well as a harmonic quintuplet. Using the oblique pulsator model, the primary oscillation is identified as a sectoral dipole mode with $l = 1, |m| = 1$. We find the pulsating star to have $M_1 \simeq 2.5\, {\rm M}_\odot$, $R_1 \simeq 3 \, {\rm R}_\odot$, and $T_{\rm eff,1} \simeq 8000$ K, while the secondary has $M_2 \simeq 1.1 \, {\rm M}_\odot$, $R_2 \simeq 2 \, {\rm R}_\odot$, and $T_{\rm eff,2} \simeq 5600$ K. Both stars appear to be close to filling their respective Roche lobes. The properties of this binary as well as the tidally tilted pulsations differ from the previous two tidally tilted pulsators, HD74423 and CO Cam, in important ways. We also study the prior history of this system with binary evolution models and conclude that extensive mass transfer has occurred from the current secondary to the primary.

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arXiv2020

TIC 278825952: a triply eclipsing hierarchical triple system with the most intrinsically circular outer orbit

We report the discovery of a compact triply eclipsing triple star system in the southern continuous viewing zone of the TESS space telescope. TIC 278825952 is a previously unstudied, circular eclipsing binary with a period of 4.781 days with a tertiary component in a wider, circular orbit of 235.55 days period that was found from three sets of third-body eclipses and from light travel-time effect dominated eclipse timing variations. We performed a joint photodynamical analysis of the eclipse timing variation curves, photometric data, and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We find that the inner binary consists of slightly evolved, near twin stars of masses of 1.12 and 1.09 $M_\odot$ and radii of 1.40 and 1.31 $R_\odot$. The third, less massive star has a mass of 0.75 $M_\odot$ and radius of 0.70 $R_\odot$. The low mutual inclination and eccentricities of the orbits show that the system is highly coplanar and surprisingly circular.

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arXiv2020

The Compact Triply Eclipsing Triple Star TIC 209409435 Discovered with TESS

We report the discovery in $TESS$ Sectors 3 and 4 of a compact triply eclipsing triple star system. TIC 209409435 is a previously unknown eclipsing binary with a period of 5.717 days, and the presence of a third star in an outer eccentric orbit of 121.872 day period was found from two sets of third-body eclipses and from eclipse timing variations. The latter exhibit signatures of strong 3rd-body perturbations. After the discovery, we obtained follow-up ground-based photometric observations of several binary eclipses as well as another of the third-body eclipses. We carried out comprehensive analyses, including the simultaneous photodynamical modelling of $TESS$ and ground-based lightcurves (including both archival WASP data, and our own follow-up measurements), as well as eclipse timing variation curves. Also, we have included in the simultaneous fits multiple star spectral energy distribution data and theoretical PARSEC stellar isochrones. We find that the inner binary consists of near twin stars of mass 0.90 $M_\odot$ and radius 0.88 $R_\odot$. The third star is just 9% more massive and 18% larger in radius. The inner binary has a rather small eccentricity while the outer orbit has $e = 0.40$. The inner binary and outer orbit have inclination angles within 0.1$^\circ$ and 0.2$^\circ$ of 90$^\circ$, respectively. The mutual inclination angle is $\lesssim 1/4^\circ$. All of these results were obtained without radial velocity observations.

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