Model Light Curves Research Articles

Oxygen and calcium nebular emission line relationships in core-collapse supernovae and Ca-rich transients

ABSTRACT This work examines the relationships between the properties (flux ratios, full width at half-maximum velocities) of the [O i] λλ6300, 6364, [Ca ii] λλ7291, 7323, and the Ca ii near-infrared triplet, emission lines of a large sample of core-collapse supernovas (SNe) and Ca-rich transients (509 spectra of 86 transients, of which 10 transients are Ca-rich events). Line-flux ratios as a function of time were investigated with differences identified between the transient classes, in particular the Type II SNe were found to have distinct line-flux ratios compared to stripped-envelope (SE) SNe. No correlation was found between the [Ca ii]/[O i] flux ratios of SE-SNe and their ejecta masses and kinetic energies (as measured from light-curve modelling), suggesting that there may be a contribution from an additional power source in more luminous SE-SNe. We found that the mean characteristic width of the [Ca ii] emission line is less than the [O i] emission line for all SN types, indicating that the [Ca ii] emission typically originates from deeper in the ejecta than [O i]. This is in some tension with standard models for emission in Type II SNe. The emission line properties of Type II SNe were also compared to theoretical models and found to favour lower mass tracks (MZAMS< 15 M⊙), with no evidence found for significant mixing of 56Ni into the H envelope nor Ca mixed into the O shell. The flux ratios of some superluminous SNe were found to be similar to those of SE-SNe when scaling to account for their longer rise times was applied (although we caution the sample size is small).

Multiwavelength View of the Close-by GRB 190829A Sheds Light on Gamma-Ray Burst Physics

We monitored the position of the close-by (about 370 Mpc) gamma-ray burst GRB 190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the European VLBI Network and the Very Long Baseline Array, carrying out a total of nine observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of a few milliarcseconds. From a state-of-the art analysis of these data, we obtained valuable limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modeling of the multiwavelength light curves with a forward-plus-reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the HESS data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the multiwavelength, high-cadence coverage of the afterglow, inherent degeneracies in the afterglow model are broken to a large extent, allowing us to capture some unique physical insights; we find a low prompt emission efficiency of ≲10−3, a low fraction of relativistic electrons in the forward shock downstream χ e < 13% (90% credible level), and a rapid decay of the magnetic field in the reverse shock downstream after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometry is not sufficiently tight as to exclude any off-axis viewing angle, but we can exclude the line of sight to have been more than ∼2° away from the border of the gamma-ray-producing region based on compactness arguments.

Measurement of the vertical atmospheric density profile from the X-ray Earth occultation of the Crab Nebula with Insight-HXMT

Abstract. X-ray Earth occultation sounding (XEOS) is an emerging method for measuring the neutral density in the lower thermosphere. In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is investigated using the Hard X-ray Modulation Telescope (Insight-HXMT). The pointing observation data on the 30 September 2018 recorded by the low-energy X-ray telescope (LE) of Insight-HXMT are selected and analysed. The extinction light curves and spectra during the X-ray Earth occultation process are extracted. A forward model for the XEO light curve is established, and the theoretical observational signal for light curve is predicted. The atmospheric density model is built with a scale factor to the commonly used Mass Spectrometer Incoherent Scatter Radar Extended model (MSIS) density profile within a certain altitude range. A Bayesian data analysis method is developed for the XEO light curve modelling and the atmospheric density retrieval. The posterior probability distribution of the model parameters is derived through the Markov chain–Monte Carlo (MCMC) algorithm with the NRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions, and the respective best-fit density profiles are retrieved. It is found that in the altitude range of 105–200 km, the retrieved density profile is 88.8 % of the density of NRLMSISE-00 and 109.7 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 1.0–2.5 keV based on the XEOS method. In the altitude range of 95–125 km, the retrieved density profile is 81.0 % of the density of NRLMSISE-00 and 92.3 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 2.5–6.0 keV based on the XEOS method. In the altitude range of 85–110 km, the retrieved density profile is 87.7 % of the density of NRLMSISE-00 and 101.4 % of the density of NRLMSIS 2.0 by fitting the light curve in the energy range of 6.0–10.0 keV based on the XEOS method. Goodness-of-fit testing is carried out for the validation of the results. The measurements of density profiles are compared to the NRLMSISE-00 and NRLMSIS 2.0 model simulations and the previous retrieval results with NASA's Rossi X-ray Timing Explorer (RXTE) satellite. For further confirmation, we also compare the measured density profile to the ones by a standard spectrum retrieval method with an iterative inversion technique. Finally, we find that the retrieved density profile from Insight-HXMT based on the NRLMSISE-00 and NRLMSIS 2.0 models is qualitatively consistent with the previous retrieved results from RXTE. The results of light curve fitting and standard energy spectrum fitting are in good agreement. This research provides a method for the evaluation of the density profiles from MSIS model predictions. This study demonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT can provide an approach for the study of the upper atmosphere. The Insight-HXMT satellite can join the family of the XEOS. The Insight-HXMT satellite with other X-ray astronomical satellites in orbit can form a space observation network for XEOS in the future.

Reverse shock forming condition for magnetized relativistic outflows: reconciling theories and simulations

ABSTRACT Reverse shock (RS) emission can be used to probe the properties of the relativistic ejecta, especially the degree of magnetization σ, in gamma-ray burst (GRB) afterglows. However, there has been confusion in the literature regarding the physical condition for the RS formation, and the role of magnetic fields in the RS dynamics in the Poynting-flux-dominated regime is not fully understood. Exploiting the shock jump conditions, we characterize the properties of a magnetized RS. We compare the RS dynamics and forming conditions from different theories and numerical simulations, and reconcile the discrepancies among them. The strict RS forming condition is found to be $\sigma \lt \sigma _\mathrm{cr}=(8/3)\gamma _4^2(n_1/n_4)$, where n4 and n1 are the rest-frame number densities of the ejecta and the ambient medium, respectively, γ4 is the bulk Lorentz factor, and σcr is the critical magnetization. Contrary to previous claims, we prove that this condition agrees with other theoretical and simulated results, which can be further applied to the setup and consistency check of future numerical simulations. Using this condition, we propose a characteristic radius for RS formation, and categorize the magnetized shell into three regimes: ‘thick shell’ (relativistic RS), ‘thin shell’ (trans-relativistic RS), and ‘no RS’ regimes. The critical magnetization σcr is generally below unity for thin shells, but can potentially reaches ∼100–1000 in the ‘thick shell’ regime. Our results could be applied to the dynamical evolution of Poynting-flux-dominated ejecta, with potential applications to self-consistent light-curve modelling of magnetized relativistic outflows.

Comparisons of Type Ia Supernova Light Curves in the UV and Optical with the Swift Ultra-violet/Optical Telescope

We examine the light-curve parameters of 97 nearby Type Ia supernovae (SN Ia) in the ultraviolet and optical using observations from the Swift Ultra-violet/Optical Telescope. Our light-curve models used linear combinations of templates, which were based on functional principal component analysis of the optical photometry of SN Ia. The weights for each principal component used in the fit capture certain aspects of the light-curve properties. We find that there is little difference in the overall variability of principal component scores across filters. We also find correlations between certain filters and PC components, indicating that the UV and optical properties seem to be tied together. This is a promising step in UV SN Ia analysis and suggests that UV light curves may be used to infer optical properties, paving the way for future cosmological studies.

SNAD transient miner: Finding missed transient events in ZTF DR4 using k-D trees

We report the automatic detection of 11 transients (7 possible supernovae and 4 active galactic nuclei candidates) within the Zwicky Transient Facility fourth data release (ZTF DR4), all of them observed in 2018 and absent from public catalogs. Among these, three were not part of the ZTF alert stream. Our transient mining strategy employs 41 physically motivated features extracted from both real light curves and four simulated light curve models (SN Ia, SN II, TDE, SLSN-I). These features are input to a k-D tree algorithm, from which we calculate the 15 nearest neighbors. After pre-processing and selection cuts, our dataset contained approximately a million objects among which we visually inspected the 105 closest neighbors from seven of our brightest, most well-sampled simulations, comprising 89 unique ZTF DR4 sources. Our result illustrates the potential of coherently incorporating domain knowledge and automatic learning algorithms, which is one of the guiding principles directing the SNAD team. It also demonstrates that the ZTF DR is a suitable testing ground for data mining algorithms aiming to prepare for the next generation of astronomical data.

Revisiting the secondary eclipses of KELT-1b using TESS observations

We present the characterization of the transiting planet KELT-1b using data from the Transiting Exoplanet Survey Satellite (TESS). Our light curve model includes primary transit and secondary eclipse. Here, we model the systematic noise using Gaussian processes (GPs) and fit it to the data using the Markov Chain Monte Carlo (MCMC) method. Modeling of the TESS light curve returns a planet-to-star radius ratio, p=0.07652−0.00028+0.00029 and a relatively large secondary eclipse depth of 388−13+12 ppm. The transit ephemeris of KELT-1b is updated using the MCMC method. Finally, we complement our work by searching for transit timing variations (TTVs) for KELT-1b. We do not find significant variations from the constant-period models in our transit time data.

Seasonal Variations in Leaf Maximum Photosynthetic Capacity and Its Dependence on Climate Factors Across Global FLUXNET Sites

AbstractThe maximum carboxylation rate (Vcmax) is an important parameter affecting the photosynthesis rate of plant leaves. In terrestrial ecosystem models (TEMs), Vcmax at 25°C (Vm25°) is often assigned as constants according to plant functional types (PFTs), while its variations with leaf temperature and nutrient contents are described using empirical functions. However, Vm25° could itself vary seasonally due to changes in the leaf physiological state that cannot be described by the empirical functions, potentially causing large uncertainties in simulated water and carbon fluxes. So far, the seasonal variation in Vm25° has not been systematically studied. Here, we generated a Vm25° data set of eight main biomes from 2000 to 2020 using eddy covariance (EC) measurements at globally distributed 176 sites. The boreal ecosystem productivity simulator was combined with a light response curve model (BEPS‐LRC) to invert Vm25° from EC data. We investigated seasonal variations of Vm25° and analyzed how different environmental and physiological factors, such as physiological (leaf chlorophyll content, LCC and Rubisco or RuBP) and climatic environment factors, including air temperature (Ta), solar shortwave radiation, CO2 concentration (CO2), and soil water content (SWC), influence this parameter. Vm25° values derived from flux data using BEPS‐LRC correlate well with Vm25° of the reference data set (R2 = 0.74, slope = 0.77, and root mean square error = 24.45 μmol m−2 s−1, p &lt; 0.001). Leaf Vm25° has strong seasonal variations in all PFTs except for in evergreen broadleaf forests, but its seasonal variation patterns differ greatly among eight biomes. Air temperature (Ta) is the most important determinant of Vm25°, followed by SWC. The interactive effects of Ta and SWC on Vm25° vary among different biomes. The seasonal variation of Vm25° was strongly dependent on LCC. After the correction of temperature effect, the contribution of LCC to the seasonal variation of Vm25° averaged 26% among eight biomes. These findings provide useful information for better parameterization of Vm25° in TEMs.

Evolution of a Peculiar Type Ibn Supernova SN 2019wep

We present a high-cadence short term photometric and spectroscopic monitoring campaign of a type Ibn SN 2019wep, which is one of the rare SN Ibn after SNe 2010al and 2019uo to display signatures of flash ionization (He ii, C iii, N iii). We compare the decline rates and rise time of SN 2019wep with other SNe Ibn and fast transients. The post-peak decline in all bands (0.1 mag day−1) are consistent with SNe Ibn but less than the fast transients. On the other hand, the Δm 15 values are slightly lower than the average values for SNe Ibn but consistent with the fast transients. The rise time is typically shorter than SNe Ibn but longer than fast transients. SN 2019wep lies at the fainter end of SNe Ibn but possesses an average luminosity among the fast transients sample. The peculiar color evolution places it between SNe Ib and the most extreme SNe Ibn. The bolometric light-curve modeling shows resemblance with SN 2019uo with ejecta masses consistent with SNe Ib. SN 2019wep belongs to the P cygni subclass of SNe Ibn and shows faster evolution in line velocities as compared to the emission subclass. The post-maximum spectra show close resemblance with ASASSN-15ed hinting it to be of SN Ib nature. The low He i CSM velocities and residual Hα further justifies it and provide evidence of an intermittent progenitor between Wolf-Rayet and LBV stars.

SN 2020jfo: A Short-plateau Type II Supernova from a Low-mass Progenitor

We present spectroscopic and photometric observations of the Type IIP supernova, SN 2020jfo, in ultraviolet and optical wavelengths. SN 2020jfo occurred in the spiral galaxy M61 (NGC 4303), with eight observed supernovae in the past 100 yr. SN 2020jfo exhibited a short plateau lasting < 65 days, and achieved a maximum brightness in Vband of M V = −17.4 ± 0.4 mag at about 8.0 ± 0.5 days since explosion. From the bolometric light curve, we have estimated the mass of 56Ni synthesized in the explosion to be 0.033 ± 0.006 M ⊙. The observed spectral features are typical for a Type IIP supernova except for shallow Hα absorption throughout the evolution and the presence of stable 58Ni feature at 7378 Å, in the nebular phase. Using hydrodynamical modeling in the MESA + STELLA framework, an ejecta mass of ∼5 M ⊙ is estimated. Models also indicate SN 2020jfo could be the result of a red supergiant progenitor with M ZAMS ∼ 12 M ⊙. Bolometric light-curve modeling revealed the presence of a secondary radiation source for initial ∼20 days, which has been attributed to interaction with a circumstellar material of mass ∼ 0.2 M ⊙, which most likely was ejected due to enhanced mass loss about 20 yr prior to the supernova explosion.

Detecting and Monitoring Tidal Dissipation of Hot Jupiters in the Era of SiTian

Abstract Transit Timing Variation (TTV) of hot Jupiters provides direct observational evidence of planet tidal dissipation. Detecting tidal dissipation through TTV needs high precision transit timings and long timing baselines. In this work, we predict and discuss the potential scientific contribution of the SiTian Survey in detecting and analyzing exoplanet TTV. We develop a tidal dissipation detection pipeline for the SiTian Survey that aims at time-domain astronomy with 72 1 m optical telescopes. The pipeline includes the modules of light curve deblending, transit timing acquisition and TTV modeling. SiTian is capable of detecting more than 25,000 exoplanets among which we expect ∼50 sources to show evidence of tidal dissipation. We present detection and analysis of tidal dissipating targets, based on simulated SiTian light curves of XO-3b and WASP-161b. The transit light curve modeling gives consistent results within 1σ to input values of simulated light curves. Also, the parameter uncertainties predicted by Markov Chain Monte Carlo are consistent with the distribution obtained from simulating and modeling the light curve 1000 times. The timing precision of SiTian observations is ∼0.5 minutes with one transit visit. We show that differences between TTV origins, e.g., tidal dissipation, apsidal precession and multiple planets, would be significant, considering the timing precision and baseline. The detection rate of tidal dissipating hot Jupiters would answer a crucial question of whether the planet migrates at an early formation stage or random stages due to perturbations, e.g., planet scattering or secular interaction. SiTian identified targets would be constructive given that the sample would extend tenfold.

PGIR 20eid (SN 2020qmp): A Type IIP Supernova at 15.6 Mpc discovered by the Palomar Gattini-IR survey

Aims.We present a detailed analysis of SN 2020qmp, a nearby Type IIP core-collapse supernova (CCSN) that was discovered by the Palomar Gattini-IR survey in the galaxy UGC07125 (distance of ≈15.6 ± 4 Mpc). We illustrate how the multiwavelength study of this event helps our general understanding of stellar progenitors and circumstellar medium (CSM) interactions in CCSNe. We highlight the importance of near-infrared (NIR) surveys for detections of supernovae in dusty environments.Methods.We analyze data from observations in various bands: radio, NIR, optical, and X-rays. We use optical and NIR data for a spectroscopic and spectro-polarimetric study of the supernova and to model its light curve (LC). We obtain an estimate of the zero-age main-sequence (ZAMS) progenitor mass from the luminosity of the [O I] doublet lines (λλ6300, 6364) normalized to the decay power of56Co. We also independently estimate the explosion energy and ZAMS progenitor mass through hydrodynamical LC modeling. From radio and X-ray observations, we derive the mass-loss rate and microphysical parameters of the progenitor star, and we investigate possible deviations from energy equipartition of magnetic fields and electrons in a standard CSM interaction model. Finally, we simulate a sample of CCSNe with plausible distributions of brightness and extinction, within 40 Mpc, and test what fraction of the sample is detectable at peak light by NIR surveys versus optical surveys.Results.SN 2020qmp displays characteristic hydrogen lines in its optical spectra as well as a plateau in its optical LC, hallmarks of a Type IIP supernova. We do not detect linear polarization during the plateau phase, with a 3σupper limit of 0.78%. Through hydrodynamical LC modeling and an analysis of its nebular spectra, we estimate a ZAMS progenitor mass of around 11.0M⊙and an explosion energy of around 0.8 × 1051erg. We find that the spectral energy distribution cannot be explained by a simple CSM interaction model, assuming a constant shock velocity and a steady mass-loss rate. In particular, the excess X-ray luminosity compared with the synchrotron radio luminosity suggests deviations from equipartition. Finally, we demonstrate the advantages of NIR surveys over optical surveys for the detection of dust-obscured CCSNe in the local Universe. Specifically, our simulations show that the Wide-Field Infrared Transient Explorer will detect up to 14 more CCSNe (out of the 75 expected in its footprint) within 40 Mpc over five years than would an optical survey equivalent to the Zwicky Transient Facility.Conclusions.We have determined or constrained the main properties of SN 2020qmp and its progenitor, highlighting the value of multiwavelength follow-up observations of nearby CCSNe. We have shown that forthcoming NIR surveys will enable us to improve constraints on the local CCSN rate by detecting obscured supernovae that would be missed by optical searches.

Radius Constraints from Reflection Modeling of Cygnus X-2 with NuSTAR and NICER

Abstract We present a spectral analysis of NuSTAR and NICER observations of the luminous, persistently accreting neutron star (NS) low-mass X-ray binary Cygnus X-2. The data were divided into different branches that the source traces out on the Z-track of the X-ray color–color diagram; namely, the horizontal branch, the normal branch, and the vertex between the two. The X-ray continuum spectrum was modeled in two different ways that produced comparable quality fits. The spectra showed clear evidence of a reflection component in the form of a broadened Fe K line, as well as a lower-energy emission feature near 1 keV likely due to an ionized plasma located far from the innermost accretion disk. We account for the reflection spectrum with two independent models (relxillns and rdblur*rfxconv). The inferred inclination is in agreement with earlier estimates from optical observations of ellipsoidal lightcurve modeling (relxillns: i = 67° ± 4°; rdblur*rfxconv: i = 60° ± 10°). The inner disk radius remains close to the NS (R in ≤ 1.15 R ISCO) regardless of the source position along the Z-track or how the 1 keV feature is modeled. Given the optically determined NS mass of 1.71 ± 0.21 M ⊙, this corresponds to a conservative upper limit of R in ≤ 19.5 km for M = 1.92 M ⊙ or R in ≤ 15.3 km for M = 1.5 M ⊙. We compare these radius constraints to those obtained from NS gravitational wave merger events and recent NICER pulsar lightcurve modeling measurements.

Properties of Type Ibn Supernovae: Implications for the Progenitor Evolution and the Origin of a Population of Rapid Transients

Abstract Type Ibn supernovae (SNe Ibn) show signatures of strong interaction between the SN ejecta and hydrogen-poor circumstellar matter (CSM). Deriving the ejecta and CSM properties of SNe Ibn provides a great opportunity to study the final evolution of massive stars. In the present work, we present a light-curve (LC) model for the ejecta–CSM interaction, taking into account the processes in which the high-energy photons originally created at the forward and reverse shocks are converted to the observed emission in the optical. The model is applied to a sample of SNe Ibn and “SN Ibn” rapidly evolving transients. We show that the characteristic post-peak behavior commonly seen in the SN Ibn LCs, where a slow decay is followed by a rapid decay, is naturally explained by the transition of the forward-shock property from cooling to adiabatic regime without introducing a change in the CSM density distribution. The (commonly found) slope in the rapid-decay phase indicates a steep CSM density gradient (ρ CSM ∝ r −3), inferring a rapid increase in the mass-loss rate toward the SN as a generic property of the SN Ibn progenitors. From the derived ejecta and CSM properties, we argue that massive Wolf–Rayet stars with an initial mass of ≳18 M ⊙ can be a potential class of the progenitors. The present work also indicates the existence of a currently missing population of UV-bright rapid transients for which the final mass-loss rate is lower than the optical SNe Ibn, which can be efficiently probed by future UV missions.

The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve

Context. Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. These ‘ultra-hot Jupiters’ have atmospheres made of ions and atomic species from molecular dissociation and feature strong day-to-night temperature gradients. Photometric observations at different orbital phases provide insights on the planet’s atmospheric properties. Aims. We aim to analyse the photometric observations of WASP-189 acquired with the Characterising Exoplanet Satellite (CHEOPS) to derive constraints on the system architecture and the planetary atmosphere. Methods. We implemented a light-curve model suited for an asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. We also modelled the reflective and thermal components of the planetary flux, the effect of stellar oblateness and light-travel time on transit-eclipse timings, the stellar activity, and CHEOPS systematics. Results. From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189 b, Rp = 1.600−0.016+0.017 RJ, with a precision of 1%, and the true orbital obliquity of the planetary system, Ψp = 89.6 ± 1.2deg (polar orbit). We detect no significant hotspot offset from the phase curve and obtain an eclipse depth of δecl = 96.5−5.0+4.5 ppm, from which we derive an upper limit on the geometric albedo: Ag &lt; 0.48. We also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficient energy redistribution. Finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope. Conclusions. Based on the derived system architecture, we predict the eclipse depth in the upcoming Transiting Exoplanet Survey Satellite (TESS) observations to be up to ~165 ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbands might help disentangle reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment J2 (oblateness).

New Variable Hot Subdwarf Stars Identified from Anomalous Gaia Flux Errors, Observed by TESS, and Classified via Fourier Diagnostics

Abstract Hot subdwarf stars are mostly stripped red giants that can exhibit photometric variations due to stellar pulsations, eclipses, the reflection effect, ellipsoidal modulation, and Doppler beaming. Detailed studies of their light curves help constrain stellar parameters through asteroseismological analyses or binary light-curve modeling and generally improve our capacity to draw a statistically meaningful picture of this enigmatic stage of stellar evolution. From an analysis of Gaia DR2 flux errors, we have identified around 1200 candidate hot subdwarfs with inflated flux errors for their magnitudes—a strong indicator of photometric variability. As a pilot study, we obtained 2 minute cadence TESS Cycle 2 observations of 187 candidate hot subdwarfs with anomalous Gaia flux errors. More than 90% of our targets show significant photometric variations in their TESS light curves. Many of the new systems found are cataclysmic variables, but we report the discovery of several new variable hot subdwarfs, including HW Vir binaries, reflection-effect systems, pulsating sdBV s stars, and ellipsoidally modulated systems. We determine atmospheric parameters for select systems using follow-up spectroscopy from the 3 m Shane telescope. Finally, we present a Fourier diagnostic plot for classifying binary light curves using the relative amplitudes and phases of their fundamental and harmonic signals in their periodograms. This plot makes it possible to identify certain types of variables efficiently, without directly investigating their light curves, and may assist in the rapid classification of systems observed in large photometric surveys.

The OGLE Collection of Variable Stars: One Thousand Heartbeat Stars in the Galactic Bulge and Magellanic Clouds

Abstract We present a collection of 991 heartbeat star (HBS) candidates found in the Optical Gravitational Lensing Experiment (OGLE) project data archive. We discuss the selection process of the HBS candidates and the structure of the catalog itself. It consists of 512 stars located toward the Galactic bulge, 439 stars located in the Large Magellanic Cloud, and 40 in the Small Magellanic Cloud. The collection contains two large groups of HBSs with different physical properties. The main distinction between the two groups is the evolutionary status of the primary star. The first group of about 100 systems contains a hot main-sequence or a Hertzsprung-gap primary star, while the second group of about 900 systems includes a red giant. For each star, we provide two-decade-long time-series photometry, in the Cousins I- and Johnson V-band filters, obtained by the OGLE project. We also present basic observational information as well as orbital parameters derived from the light-curve modeling.

Radiation hydrodynamics modelling of kilonovae withSNEC

ABSTRACTWe develop a method to compute synthetic kilonova light curves that combine numerical relativity simulations of neutron star mergers and the SNEC radiation–hydrodynamics code. We describe our implementation of initial and boundary conditions, r-process heating, and opacities for kilonova simulations. We validate our approach by carefully checking that energy conservation is satisfied and by comparing the SNEC results with those of two semi-analytic light-curve models. We apply our code to the calculation of colour light curves for three binaries having different mass ratios (equal and unequal mass) and different merger outcome (short-lived and long-lived remnants). We study the sensitivity of our results to hydrodynamic effects, nuclear physics uncertainties in the heating rates, and duration of the merger simulations. We find that hydrodynamics effects are typically negligible and that homologous expansion is a good approximation in most cases. However, pressure forces can amplify the impact of uncertainties in the radioactive heating rates. We also study the impact of shocks possibly launched into the outflows by a relativistic jet. None of our models match AT2017gfo, the kilonova in GW170817. This points to possible deficiencies in our merger simulations and kilonova models that neglect non-LTE effects and possible additional energy injection from the merger remnant and to the need to go beyond the assumption of spherical symmetry adopted in this work.

Efficient and Precise Transit Light Curves for Rapidly Rotating, Oblate Stars

Abstract We derive solutions to transit light curves of exoplanets orbiting rapidly rotating stars. These stars exhibit significant oblateness and gravity darkening, a phenomenon where the poles of the star have a higher temperature and luminosity than the equator. Light curves for exoplanets transiting these stars can exhibit deviations from those of slowly rotating stars, even displaying significantly asymmetric transits depending on the system’s spin–orbit angle. As such, these phenomena can be used as a protractor to measure the spin–orbit alignment of the system. In this paper, we introduce a novel semianalytic method for generating model light curves for gravity-darkened and oblate stars with transiting exoplanets. We implement the model within the code package starry and demonstrate several orders of magnitude improvement in speed and precision over existing methods. We test the model on a TESS light curve of WASP-33, whose host star displays rapid rotation ( v sin i * = 86.4 km s−1). We subtract the host’s δ-Scuti pulsations from the light curve, finding an asymmetric transit characteristic of gravity darkening. We find the projected spin–orbit angle is consistent with Doppler tomography and constrain the true spin–orbit angle of the system as φ = 108.3 − 15.4 + 19.0 °. We demonstrate the method’s uses in constraining spin–orbit inclinations of such systems photometrically with posterior inference. Lastly, we note the use of such a method for inferring the dynamical history of thousands of such systems discovered by TESS (https://github.com/rodluger/starry, https://rodluger.github.io/starry, https://github.com/shashankdholakia/gravity-dark).

Late-onset Circumstellar Medium Interactions are Rare: An Unbiased GALEX View of Type Ia Supernovae

Abstract Using ultraviolet (UV) light curves, we constrain the circumstellar environments of 1080 Type Ia supernovae (SNe Ia) within z &lt; 0.5 from archival Galaxy Evolution Explorer (GALEX) observations. All SNe Ia are required to have pre- and post-explosion GALEX observations to ensure adequate subtraction of the host-galaxy flux. Using the late-time GALEX observations, we look for the UV excess expected from any interaction between the SN ejecta and circumstellar material (CSM). Four SNe Ia are detected near maximum light, and we compare the GALEX photometry to archival data. However, we find that none of our targets show convincing evidence of CSM interaction. A recent Hubble Space Telescope (HST) survey estimates that ∼6% of SNe Ia may interact with distant CSM, but statistical inferences are complicated by the small sample size and selection effects. By injecting model light curves into our data and then recovering them, we constrain a broad range of CSM interactions based on the CSM interaction start time and the maximum luminosity. Combining our GALEX nondetections with the HST results, we constrain occurrence of late-onset CSM interaction among SNe Ia with moderate CSM interaction, similar to that observed in PTF11kx, to f CSM ≲ 5.1% between 0 and 500 days after discovery and ≲2.7% between 500 and 1000 days after discovery at 90% confidence. For weaker CSM interactions similar to SN 2015cp, we obtain limits of ≲16% and ≲4.8%, respectively, for the same time ranges.