publications
These selected publications are listed based on level of contribution. A more complete listing can be found in my ADS library, my Google Scholar profile , and my ORCID profile.
First Author Publications
Link to ADS Library with these.2024
- TIC 435850195: The Second Triaxial Tidally Tilted PulsatorRahul Jayaraman , Saul A. Rappaport , Brian Powell , and 8 more authorsThe Astrophysical Journal, Nov 2024
The Transiting Exoplanet Survey Satellite (TESS) has enabled the discovery of numerous tidally tilted pulsators (TTPs), which are pulsating stars in close binaries where the presence of a tidal bulge has the effect of tilting the primary star’s pulsation axes into the orbital plane. Recently, the modeling framework developed to analyze TTPs has been applied to the emerging class of triaxial pulsators, which exhibit nonradial pulsations about three perpendicular axes. In this work, we report on the identification of the second-ever discovered triaxial pulsator, with 16 robustly detected pulsation multiplets, of which 14 are dipole doublets separated by 2 \nu_orb. We jointly fit the spectral energy distribution and TESS light curve of the star, and find that the primary is slightly evolved off the zero-age main equence, while the less massive secondary still lies on the zero-age main sequence. Of the 14 doublets, we associate eight with Y_10x modes and six with novel Y_10y modes. We exclude the existence of Y_11x modes in this star and show that the observed pulsation modes must be Y_10y . We also present a toy model for the triaxial pulsation framework in the context of this star. The techniques presented here can be utilized to rapidly analyze and confirm future triaxial \ pulsator candidates.
- Gamma-Ray Bursts Observed by the Transiting Exoplanet Survey Satellite: Prompt Optical Counterparts and Afterglows of Swift-XRT-localized Gamma-Ray BurstsRahul Jayaraman , Michael Fausnaugh , George R. Ricker , and 2 more authorsThe Astrophysical Journal, Sep 2024
Very few detections have been made of optical flashes contemporaneous with prompt high-energy emission from a gamma-ray burst (GRB). In this work, we present and analyze light curves of GRB-associated optical flashes and afterglows from the Transiting Exoplanet Survey Satellite (TESS). Our sample consists of eight GRBs with arcsecond-level localizations from the X-Ray Telescope on board the Neil Gehrels Swift Observatory (Swift). For each burst, we characterize the prompt optical emission and any observed afterglow, and constrain physical parameters for four of these bursts using their TESS light curves. This work also presents a straightforward method to correct for TESS’s cosmic-ray mitigation strategy on 20 s timescales, which allows us to estimate the "true" brightness of optical flashes associated with prompt GRB emission. We also highlight TESS’s continuous wide-field monitoring capability, which provides an efficient means of identifying optical emission from GRBs and characterizing early time afterglow light curves. Based on empirical detection rates from Swift and the Fermi Gamma-ray Space Telescope, up to 10 GRBs per year may fall within the contemporaneous TESS field of view.
2022
- TIC 5724661: A Long-period Binary with a Pulsating sdB Star and δ Scuti VariableRahul Jayaraman , Saul A. Rappaport , Lorne Nelson , and 8 more authorsThe Astrophysical Journal, Sep 2022
Using TESS 20 s cadence data, we have discovered an unusual combination of pulsating stars in what we infer to be a binary system. The binary consists of a standard δ Scuti star with pulsations over the range 32-41 1/d; this is in a likely wide orbit with a hot subdwarf-B (sdB) star, which itself has a large-amplitude p-mode pulsation at 524 1/d. We establish constraints on the period of the putative binary by using radial velocity measurements of the δ Scuti star and show that any sdB companion star must orbit with a period greater than approximately thirty days. Our identification of this sdB binary serves as an important addition to the relatively small number of sdB binaries known to have orbital periods longer than a few days. We model such a binary using MESA and find that this system could be formed through stable, nonconservative mass transfer from either a low-mass or an intermediate-mass progenitor, without undergoing a common-envelope phase.
- Tidally Tilted Pulsations in HD 265435, a Subdwarf B Star with a Close White Dwarf CompanionRahul Jayaraman , Gerald Handler , Saul A. Rappaport , and 4 more authorsThe Astrophysical Journal Letters, Apr 2022
Tidally tilted pulsators (TTPs) are an intriguing new class of oscillating stars in binary systems; in such stars, the pulsation axis coincides with the line of apsides, or tidal axis, of the binary. All three TTPs discovered so far have been δ Scuti stars. In this Letter, we report the first conclusive discovery of tidally tilted pulsations in a subdwarf B (sdB) star. HD 265435 is an sdB-white dwarf binary with a 1.65 hr period that has been identified and characterized as the nearest potential Type Ia supernova progenitor. Using TESS 20 s cadence data from Sectors 44 and 45, we show that the pulsation axis of the sdB star has been tidally tilted into the orbital plane and aligned with the tidal axis of the binary. We identify 31 independent pulsation frequencies, 27 of which have between 1 and 7 sidebands separated by the orbital frequency (ν orb) or multiples thereof. Using the observed amplitude and phase variability due to tidal tilting, we assign ℓ and m values to most of the observed oscillation modes and use these mode identifications to generate preliminary asteroseismic constraints. Our work significantly expands our understanding of TTPs, as we now know that (i) they can be found in stars other than δ Scuti pulsators, especially highly evolved stars that have lost their H-rich envelopes, and (ii) tidally tilted pulsations can be used to probe the interiors of stars in very tight binaries.
- Could the Magnetic Star HD 135348 Possess a Rigidly Rotating Magnetosphere?Rahul Jayaraman , Swetlana Hubrig , Daniel L. Holdsworth , and 5 more authorsThe Astrophysical Journal Letters, Jan 2022
We report the detection and characterization of a new magnetospheric star, HD 135348, based on photometric and spectropolarimetric observations. The TESS light curve of this star exhibited variations consistent with stars known to possess rigidly rotating magnetospheres (RRMs), so we obtained spectropolarimetric observations using the Robert Stobie Spectrograph (RSS) on the South African Large Telescope (SALT) at four different rotational phases. From these observations, we calculated the longitudinal magnetic field of the star \<Bz\>, as well as the Alfven and Kepler radii, and deduced that this star contains a centrifugal magnetosphere. However, an archival spectrum does not exhibit the characteristic "double-horned" emission profile for H-alpha and the Brackett series that has been observed in many other RRM stars. This could be due to the insufficient rotational phase coverage of the available set of observations, as the spectra of these stars significantly vary with the star’s rotation. Our analysis underscores the use of TESS in photometrically identifying magnetic star candidates for spectropolarimetric follow-up using ground-based instruments. We are evaluating the implementation of a machine-learning classifier to search for more examples of RRM stars in TESS data.
2021
- Two New roAp Stars Discovered with TESSRahul Jayaraman , Donald W. Kurtz , Gerald Handler , and 2 more authorsResearch Notes of the American Astronomical Society, Nov 2021
We present two new rapidly oscillating Ap (roAp) stars, TIC 198781841 and TIC 229960986, discovered in TESS photometric data. The periodogram of TIC 198781841 has a large peak at 166.506 day-1 (1.93 mHz), with two nearby peaks at 163.412 1/d (1.89 mHz) and 169.600 1/d (1.96 mHz). These correspond to three independent high-overtone pressure modes, with alternating even and odd ℓ values. TIC 229960986 has a high-frequency triplet centered at 191.641 day-1 (2.218 mHz), with sidebands at 191.164 day-1 (2.213 mHz) and 192.119 day-1 (2.224 mHz). This pulsation appears to be a rotationally split dipole mode, with sideband amplitudes significantly larger than that of the central peak; hence, both pulsation poles are seen over the rotation cycle. Our photometric identification of two new roAp stars underscores the remarkable ability of TESS to identify high-frequency pulsators without spectroscopic observations.
Selected Major Contributions
For a full list, please see this ADS library.2024
- TIC 184 743 498: the first tri-axial stellar pulsatorValencia Zhang , Saul Rappaport , Rahul Jayaraman , and 4 more authorsMonthly Notices of the Royal Astronomical Society, Feb 2024
We have discovered a δ Scuti pulsator in a tight binary (P = 1.053 d) with nine pulsation modes whose frequencies are between 38 and 56 d-1. Each of these modes exhibits amplitude modulations and π-rad phase shifts twice per orbital cycle. Five of these modes exhibit amplitude and phase shifts that are readily explained by dipole pulsations along an axis that is aligned with the binary’s tidal axis. The novelty of the system lies in the remaining four pulsation modes, which we show are dipole pulsations along an axis that is perpendicular to both the tidal axis and the binary’s orbital angular momentum axis. There are additionally two pulsation modes whose amplitudes and phases do not change significantly with orbital phase; they are explained as dipole modes along an axis aligned with the orbital/rotation axis. Hence, we propose that TIC 184 743 498 is a tri-axial pulsator, the first of its kind.
- Transient Corotating Clumps around Adolescent Low-mass Stars from Four Years of TESSLuke G. Bouma , Rahul Jayaraman , Saul Rappaport , and 5 more authorsThe Astronomical Journal, Jan 2024
Complex periodic variables (CPVs) are stars that exhibit highly structured and periodic optical light curves. Previous studies have indicated that these stars are typically disk-free pre-main-sequence M dwarfs with rotation periods ranging from 0.2 to 2 days. To advance our understanding of these enigmatic objects, we conducted a blind search using TESS 2 minute data of 65,760 K and M dwarfs with T<16 mag and d<150 pc. We found 50 high-quality CPVs, and subsequently determined that most are members of stellar associations. Among the new discoveries are the brightest (T ≈ 9.5 mag), closest (d ≈ 20 pc), and oldest (≈200 Myr) CPVs known. One exceptional object, LP 12-502, exhibited up to eight flux dips per cycle. Some of these dips coexisted with slightly different periods, and the shortest-duration dips precisely matched the expected timescale for transiting small bodies at the corotation radius. Broadly, our search confirms that CPVs are mostly young (≲150 Myr) and low-mass (≲0.4 M ⊙). The flux dips characteristic of the class have lifetimes of ≈100 cycles, although stellar flares seem to induce a sudden dip collapse once every few months. The most plausible explanation for these phenomena remains corotating concentrations of gas or dust. The gas or dust is probably entrained by the star’s magnetic field, and the sharp features could result from a multipolar field topology, a hypothesis supported by correspondences between the light curves of CPVs and of rapidly rotating B stars known to have multipolar magnetic fields.
2023
- HD 42477: coupled r modes, g modes, and a p mode in an A0Vnne starD. W. Kurtz , R. Jayaraman , P. Sowicka , and 4 more authorsMonthly Notices of the Royal Astronomical Society, May 2023
Several studies have shown that a number of stars pulsating in p modes lie between the β Cep and δ Sct instability strips in the Hertzsprung-Russell (HR) Diagram. At present, there is no certain understanding of how p modes can be excited in this Teff range. The goal of this work is to disprove the conjecture that all stars pulsating in p modes and lying in this Teff range are the result of incorrect measurements of Teff, contamination, or the presence of unseen cooler companions lying in the δ Sct instability strip (given the high binary fraction of stars in this region of the HR Diagram). Using TESS data, we show that the A0Vnne star HD 42477 has a single p mode coupled to several r modes and/or g modes. We rule out a contaminating background star with a pixel-by-pixel examination, and we essentially rule out the possibility of a companion δ Sct star in a binary. We model the pulsations in HD 42477, and suggest that the g modes are excited by overstable convective core modes. We also conjecture that the single p mode is driven by coupling with the g modes, or that the oblateness of this rapidly-rotating star permits driving by He II ionization in the equatorial region.
- Searching for Gravitational-wave Counterparts Using the Transiting Exoplanet Survey SatelliteGeoffrey Mo , Rahul Jayaraman , Michael Fausnaugh , and 3 more authorsThe Astrophysical Journal Letters, May 2023
In 2017, the LIGO and Virgo gravitational-wave (GW) detectors, in conjunction with electromagnetic (EM) astronomers, observed the first GW multimessenger astrophysical event, the binary neutron star (BNS) merger GW170817. This marked the beginning of a new era in multimessenger astrophysics. To discover further GW multimessenger events, we explore the synergies between the Transiting Exoplanet Survey Satellite (TESS) and GW observations triggered by the LIGO-Virgo-KAGRA Collaboration (LVK) detector network. TESS’s extremely wide field of view ( 2300 deg2) means that it could overlap with large swaths of GW localizations, which often span hundreds of square degrees or more. In this work, we use a recently developed transient detection pipeline to search TESS data collected during the LVK’s third observing run, O3, for any EM counterparts. We find no obvious counterparts brighter than about 17th magnitude in the TESS bandpass. Additionally, we present end-to-end simulations of BNS mergers, including their detection in GWs and simulations of light curves, to identify TESS’s kilonova discovery potential for the LVK’s next observing run (O4). In the most optimistic case, TESS will observe up to one GW-found BNS merger counterpart per year. However, TESS may also find up to five kilonovae that did not trigger the LVK network, emphasizing that EM-triggered GW searches may play a key role in future kilonova detections. We also discuss how TESS can help place limits on EM emission from binary black hole mergers and rapidly exclude large sky areas for poorly localized GW events.
Selected Minor Contributions/Collaboration Papers
For a full list, please see this ADS Library.2024
- TESS Cycle 2 observations of roAp stars with 2-min cadence dataD. L. Holdsworth , M. S. Cunha , M. Lares-Martiz , and 47 more authorsMonthly Notices of the Royal Astronomical Society, Feb 2024
We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being α2 CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multiepoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all-known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total.
- AT2019pim: A Luminous Orphan Afterglow from a Moderately Relativistic OutflowDaniel A. Perley , Anna Y. Q. Ho , Michael Fausnaugh , and 34 more authorssubmitted, Jan 2024
Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt emission from ultra-relativistic ejecta and afterglow from shocked circumstellar material. While both components are extremely luminous in known GRBs, a variety of scenarios predict the existence of luminous afterglow emission with little or no associated high-energy prompt emission. We present AT 2019pim, the first secure example of this phenomenon to be identified. Serendipitously discovered during follow-up observations of a gravitational-wave trigger and located in a contemporaneous TESS sector, it is hallmarked by a fast-rising (t 2 hr), luminous (M_UV,peak -24.4 mag) optical transient with accompanying luminous X-ray and radio emission. No gamma-ray emission consistent with the time and location of the transient was detected by Fermi-GBM or by Konus, placing strong limits on an accompanying GRB. We investigate several independent observational aspects of the afterglow in the context of constraints on relativistic motion and find all of them are consistent with an initial Lorentz factor of Gamma_0 30-50, significantly lower than in any well-observed GRB and consistent with the theoretically-predicted "dirty fireball" scenario in which the high-energy prompt emission is stifled by pair production. However, we cannot rule out a structured jet model in which only the line-of-sight material was ejected at low-Gamma, off-axis from a classical high-Gamma jet core. This event represents a milestone in orphan afterglow searches, demonstrating that luminous afterglows with weak or no detectable gamma-ray radiation exist in nature and can be discovered by high-cadence optical surveys.
2023
- Four Years of Type Ia Supernovae Observed by TESS: Early-time Light-curve Shapes and Constraints on Companion Interaction ModelsM. M. Fausnaugh , P. J. Vallely , M. A. Tucker , and 10 more authorsThe Astrophysical Journal, Oct 2023
We present 307 type Ia supernova (SN) light curves from the first 4 yr of the Transiting Exoplanet Survey Satellite mission. We use this sample to characterize the shapes of the early-time light curves, measure the rise times from first light to peak, and search for companion star interactions. Using simulations, we show that light curves must have noise <10% of the peak flux to avoid biases in the early-time light-curve shape, restricting our quantitative analysis to 74 light curves. We find that the mean power-law index t^β_1 of the early-time light curves is β 1 = 1.93 ± 0.57, and the mean rise time to peak is 15.7 ± 3.5 days. The underlying population distribution for β 1 may instead consist of a Gaussian component with mean 2.29, width 0.34, and a long tail extending to values less than 1.0. We find that the data can rarely distinguish between models with and without companion interaction models. Nevertheless, we find three high-quality light curves that tentatively prefer the addition of a companion interaction model, but the statistical evidence for the companion interactions is not robust. We also find two SNe that disfavor the addition of a companion interaction model to a curved power-law model. Taking the 74 SNe together, we calculate 3σ upper limits on the presence of companion signatures to control for orientation effects that can hide companions in individual light curves. Our results rule out common progenitor systems with companions having Roche lobe radii >31 R ⊙ (separations >5.7 × 1012 cm, 99.9% confidence level) and disfavor companions having Roche lobe radii >10 R ⊙ (separations >1.9 × 1012 cm, 95% confidence level). Lastly, we discuss the implications of our results for the intrinsic fraction of single degenerate progenitor systems.
- A helium-burning white dwarf binary as a supersoft X-ray sourceJ. Greiner , C. Maitra , F. Haberl , and 12 more authorsNature, Mar 2023
Type Ia supernovae are cosmic distance indicators, and the main source of iron in the Universe, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed5 and suggested as Type Ia supernovae progenitors. However, observational evidence for hydrogen, which is expected to be stripped off the donor star during the supernova explosion, is lacking. Helium-accreting white dwarfs, which would circumvent this problem, have been predicted for more than 30 years, including their appearance as supersoft X-ray sources, but have so far escaped detection. Here we report a supersoft X-ray source with an accretion disk whose optical spectrum is completely dominated by helium, suggesting that the donor star is hydrogen-free. We interpret the luminous and supersoft X-rays as resulting from helium burning near the surface of the accreting white dwarf. The properties of our system provide evidence for extended pathways towards Chandrasekhar-mass explosions based on helium accretion, in particular for stable burning in white dwarfs at lower accretion rates than expected so far. This may allow us to recover the population of the sub-energetic so-called Type Iax supernovae, up to 30% of all Type Ia supernovae, within this scenario.
2021
- The TESS Objects of Interest Catalog from the TESS Prime MissionNatalia M. Guerrero , S. Seager , Chelsea X. Huang , and 102 more authorsThe Astrophysical Journal Supplement Series, Jun 2021
We present 2241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its 2 yr Prime Mission. We list these candidates in the TESS Objects of Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously known planets recovered by TESS observations. We describe the process used to identify TOIs, investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well suited for detailed follow-up observations. The TESS data products for the Prime Mission (sectors 1-26), including the TOI catalog, light curves, full-frame images, and target pixel files, are publicly available at the Mikulski Archive for Space Telescopes.