Kepler Light Curves Research Articles

Properties of Flare Events on M Stars from LAMOST Spectral Survey Based on Kepler and TESS Light Curves

A catalog of M stars has been published from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 7 (LAMOST DR7). We cross-matched the LAMOST M catalog with Kepler, Kepler 2 (K2) and Transiting Exoplanet Survey Satellite (TESS) surveys. We obtained the light curves from the Kepler and TESS surveys. We detected 20,047 flare events from 4053 M stars and calculated their durations, amplitudes, and energies. We analyzed the distribution of the flare durations and energies. The distributions of flare duration for Kepler, K2 and TESS peak are at 3–3.5 hr, 4–6 hr and 1–1.5 hr, respectively. This may be the result of the different cadences for the three data sets. The highest regions of the flare energies of Kepler, K2 and TESS are 32–32.5, 32–32.5 and 31–31.5 erg in Log format, respectively. A linear relationship between flare duration and energy emerges from our analysis. The ratio of flare duration to total observational time is approximately 0.2%–0.3% for the Kepler, K2 and TESS surveys. The occurrence rate of a star with a flare event increases from the M0 to M4 subtypes. We also determined the spatial distribution of the flare rate of M stars in the Milky Way. It seems that the flare rate decreases as the vertical height increases. The power index of the flare energies is in the region of 1.53–2.32, which is similar to previous result for solar type star (2.0). Further, we examined the relationship between the flare amplitude and chromospheric intensity. The flare activity increases rapidly with the increase in the Hα EW at the lower values (less approximately 2 Å) and it increases slowly at the higher values.

An Ap Star Catalog Based on LAMOST DR9

We present a sample of 2700 Ap stars in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR9 catalog. The candidates are first selected to be in a temperature range typical of Ap stars by using the BP − RP color index from Gaia DR3. Then the 5200 Å flux depression features characteristic of Ap stars are visually checked in LAMOST DR9 spectra. The detailed spectral features are given by applying a modified spectral classification program, MKCLASS. The stellar parameters of these Ap stars, such as the T eff, , [Fe/H], [Si/H], and , are either extracted from a hot star catalog or derived through empirical relations and then a statistical analysis is carried out. The evolutionary stages are also discussed. Finally, we discuss the rotation and pulsation features of those that have TESS or Kepler light curves. Among these Ap stars, we find seven new rotation variables, one new roAp star, and a new δ Scuti pulsation of a previously known roAp star.

The Behavior of HgMn Stars in the Far UV—Paper 23: HD 144844

The analysis of four high resolution spectra of the Mn P Ga star HD 144844 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far ultraviolet flux of this star from 1994 July 1st to July 12th. The IUE spectra sample four different rotational phases of the rotational period derived recently from the Kepler lightcurve which shows that the far ultraviolet flux of HD 144844 is not modulated by rotation. However a previous low resolution SWP spectrum taken in August 1989 has significantly more FUV flux shortwards of 1700 Å than the spectra collected in 1994 July. On the the first spectrum of the 1994 July observations, the Al ii resonance line at 1670.79 Å is split into two components probably reflecting the orbital motions of HD 144844 and its companion.

Internal rotation and buoyancy travel time of 60 γ Doradus stars from uninterrupted TESS light curves spanning 352 days

Context. Gamma Doradus (hereafter γ Dor) stars are gravity-mode pulsators whose periods carry information about their internal structure. These periods are especially sensitive to the internal rotation and chemical mixing, two processes that are currently not well constrained in the theory of stellar evolution. Aims. We aim to identify the pulsation modes and deduce the internal rotation and buoyancy travel time for 106 γ Dor stars observed by the Transiting Exoplanet Survey Satellite (TESS) mission in its southern continuous viewing zone (hereafter S-CVZ). We rely on 140 previously detected period-spacing patterns, that is, series of (near-)consecutive pulsation mode periods. Methods. We used the asymptotic expression to compute gravity-mode frequencies for ranges of the rotation rate and buoyancy travel time that cover the physical range in γ Dor stars. Those frequencies were fitted to the observed period-spacing patterns by minimising a custom cost function. The effects of rotation were evaluated using the traditional approximation of rotation, using the stellar pulsation code GYRE. Results. We obtained the pulsation mode identification, internal rotation, and buoyancy travel time for 60 TESS γ Dor stars. For the remaining 46 targets, the detected patterns were either too short or contained too many missing modes for unambiguous mode identification, and longer light curves are required. For the successfully analysed stars, we found that period-spacing patterns from 1-yr-long TESS light curves can constrain the internal rotation and buoyancy travel time to a precision of 0.03 d-1 and 400 s, respectively, which is about half as precise as literature results based on 4-yr-long Kepler light curves of γ Dor stars.

Detectability of Rotational Modulation in Kepler Sun-like Stars as a Function of Age

We examine how the fraction f of stars for which rotational modulation has been detected in Kepler light curves depends on the stellar mass M ⋆ and age t ⋆. Our sample consists of ≈850 FGK stars hosting transiting planet candidates detected from the prime Kepler mission. For these stars, atmospheric parameters have been derived using high-resolution spectra from the California-Kepler survey, and rotational modulation has been searched in Kepler light curves homogeneously. We fit stellar models to the atmospheric parameters, Gaia parallax, and Two Micron All Sky Survey magnitude of these stars and obtain samples drawn from the posterior probability distributions for their masses and ages under a given, uninformative prior. We combine them with the result of rotational modulation search to simultaneously infer the mass–age distribution of the sample as well as f(M ⋆, t ⋆), in a manner that fully takes into account mass and age uncertainties of individual stars. We find that f remains near unity up to t ⋆ ∼ 3 Gyr and drops to almost zero by t ⋆ ∼ 5 Gyr, although the trend is less clearly detected for stars with ≲0.9 M ⊙ due to weaker age constraints. This finding is consistent with a view that the detection of rotational modulation is limited by photometric precision to younger stars that exhibit higher-amplitude modulation, and suggests that the detectability of rotational modulation in Kepler light curves is insensitive to metallicity and activity cycles for stars younger than the Sun.

Multiscale entropy analysis of astronomical time series

Context.The multiscale entropy assesses the complexity of a signal across different timescales. It originates from the biomedical domain and was recently successfully used to characterize light curves as part of a supervised machine learning framework to classify stellar variability.Aims.We aim to explore the behavior of the multiscale entropy in detail by studying its algorithmic properties in a stellar variability context and by linking it with traditional astronomical time series analysis methods and metrics such as the Lomb-Scargle periodogram. We subsequently use the multiscale entropy as the basis for an interpretable clustering framework that can distinguish hybrid pulsators with bothp- and g-modes from stars with onlyp-mode pulsations, such asδScuti (δSct) stars, or from stars with onlyg-mode pulsations, such asγDoradus (γDor) stars.Methods.We calculate the multiscale entropy for a set ofKeplerlight curves and simulated sine waves. We link the multiscale entropy to the type of stellar variability and to the frequency content of a signal through a correlation analysis and a set of simulations. The dimensionality of the multiscale entropy is reduced to two dimensions and is subsequently used as input to the HDBSCAN density-based clustering algorithm in order to find the hybrid pulsators within sets ofδSct andγDor stars that were observed byKepler.Results.We find that the multiscale entropy is a powerful tool for capturing variability patterns in stellar light curves. The multiscale entropy provides insights into the pulsation structure of a star and reveals how short- and long-term variability interact with each other based on time-domain information only. We also show that the multiscale entropy is correlated to the frequency content of a stellar signal and in particular to the near-core rotation rates ofg-mode pulsators. We find that our new clustering framework can successfully identify the hybrid pulsators with bothp- andg-modes in sets ofδSct andγDor stars, respectively. The benefit of our clustering framework is that it is unsupervised. It therefore does not require previously labeled data and hence is not biased by previous knowledge.

KIC 10417986: Spectroscopic Confirmation of the Nature of the Binary System with a δ Scuti Component

KIC 10417986 is a short orbital period (0.0737 day) ellipsoidal variable star with a δ Sct and γ Dor hybrid pulsation component discovered by Kepler. The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star. We derive the orbital parameters using the rvfit code with a result of K 1 = 29.7 ± 1.5 km s−1, γ = −18.7 ± 1.7 km s−1, and confirm an orbital period of 0.84495 day instead of the result given by Kepler. The atmospheric parameters of the primary are determined by the synthetic spectral fitting technique with the estimated values of T eff = 7411 ± 187 K, log g = 4.2 ± 0.3 dex, [M/H] = 0.08 ± 0.09 dex and vsini = 52 ± 11 km s−1. KIC 10417986 is a circular orbit binary system. From the single-lined nature and mass function of the star, the derived orbital inclination is 26° ± 6°, and the mass of the secondary is M ⊙, which should be a late-K to early-M type star. Fourteen frequencies are extracted from Kepler light curves, of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations of δ Sct star, and one independent frequency in the low-frequency region (f 2 = 1.3033 cd−1) is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.

An Attempt to Construct an Activity Cycle Catalog with Kepler Long-Cadence Light Curves

Many stars show activity cycles like the Sun. Kepler has gathered ∼200,000 light curves. Most of the Kepler stars only have long-cadence light curves, which limits their applicable methods. Some metrics, for example Sph, are effective for long-cadence light curves but require rotation periods. In order to improve the utilization of Kepler light curves, we introduce and use the smoothness metric. The smoothness metric is able to analyze stars without a measured rotation period and is applicable for long-cadence light curves. We test and validate our metric, resulting in the detection of the 11 years solar cycle and a 457 days cycle for our prototype star KIC 9017220. We analyze 92,084 Kepler long-cadence light curves, and as our main results, we detect 4455 magnetic activity cycle candidates, but about 20 percent are false cycles and 50 percent are lower limits of the real cycles, and we analyze their causes in detail. As an investigation into the performance of our method, we simulate disturbance factors and prove that the p-value test is invalid under certain circumstances.

Dust reverberation mapping and light-curve modelling of Zw229-015

ABSTRACT Multiwavelength variability studies of active galactic nuclei can be used to probe their inner regions that are not directly resolvable. Dust reverberation mapping (DRM) estimates the size of the dust emitting region by measuring the delays between the infrared (IR) response to variability in the optical light curves. We measure DRM lags of Zw229-015 between optical ground-based and Kepler light curves and concurrent IR Spitzer 3.6 and 4.5 µm light curves from 2010 to 2015, finding an overall mean rest-frame lag of 18.3 ± 4.5 d. Each combination of optical and IR light curve returns lags that are consistent with each other within 1σ, which implies that the different wavelengths are dominated by the same hot dust emission. The lags measured for Zw229-015 are found to be consistently smaller than predictions using the lag–luminosity relationship. Also, the overall IR response to the optical emission actually depends on the geometry and structure of the dust emitting region as well, so we use Markov chain Monte Carlo modelling to simulate the dust distribution to further estimate these structural and geometrical properties. We find that a large increase in flux between the 2011–2012 observation seasons, which is more dramatic in the IR light curve, is not well simulated by a single dust component. When excluding this increase in flux, the modelling consistently suggests that the dust is distributed in an extended flat disc, and finds a mean inclination angle of 49$^{+3}_{-13}$ deg.

Rotation of hot normal, peculiar and Be stars from space photometry

ABSTRACT The periods of 34 376 main-sequence stars hotter than 6000 K are derived from Kepler, K2, and TESS light curves. From the effective temperatures and GAIA DR3 luminosities, the radii, and hence the equatorial rotational velocities, can be estimated. Comparison with the projected rotational velocities shows that the photometric periods are indistinguishable from the rotational periods. Rotational light modulation in cool stars appears to continue to the hottest B stars. In fact, it is the most common type of light variation and is seen in 20–50 per cent of F, A, and B stars. The rotation rates of Am, Ap, and Bp stars do not appear to be very different from those of non-peculiar stars. Mixing of the surface layers by rotation cannot be the sole reason why element diffusion is not present in stars with normal surface abundances. The rotation rate of Be stars is well below the rate required to trigger mass-loss by non-radial pulsation. Surface activity leading to ejection of material into co-rotating clouds is suggested as the mass-loss mechanism. The rotational amplitudes of non-Be stars increases rapidly with effective temperature, possibly due to an increasing proportion of incipient Be stars in the sample. The simplest way to explain these results is to assume that surface convection is present in all main-sequence stars, from the coolest M star to the hottest B star.

Transit Hunt for Young and Maturing Exoplanets (THYME). VIII. A Pleiades-age Association Harboring Two Transiting Planetary Systems from Kepler

Young planets provide a window into the early stages and evolution of planetary systems. Ideal planets for such research are in coeval associations, where the parent population can precisely determine their ages. We describe a young association (MELANGE-3) in the Kepler field, which harbors two transiting planetary systems (KOI-3876 and Kepler-970). We identify MELANGE-3 by searching for kinematic and spatial overdensities around Kepler planet hosts with high levels of lithium. To determine the age and membership of MELANGE-3, we combine new high-resolution spectra with archival light curves, velocities, and astrometry of stars near KOI-3876 spatially and kinematically. We use the resulting rotation sequence, lithium levels, and color–magnitude diagram of candidate members to confirm the presence of a coeval 105 ± 10 Myr population. MELANGE-3 may be part of the recently identified Theia 316 stream. For the two exoplanet systems, we revise the stellar and planetary parameters, taking into account the newly determined age. Fitting the 4.5 yr Kepler light curves, we find that KOI-3876b is a 2.0 ± 0.1 R ⊕ planet on a 19.58 day orbit, while Kepler-970 b is a 2.8 ± 0.2 R ⊕ planet on a 16.73 day orbit. KOI-3876 was previously flagged as an eclipsing binary, which we rule out using radial velocities from APOGEE and statistically validate the signal as planetary in origin. Given its overlap with the Kepler field, MELANGE-3 is valuable for studies of spot evolution on year timescales, and both planets contribute to the growing work on transiting planets in young stellar associations.

Detached eclipsing binaries from the Kepler field: radii and photometric masses of components in short-period systems

ABSTRACT The characterization of detached eclipsing binaries with low-mass components has become important when verifying the role of convection in stellar evolutionary models, which requires model-independent measurements of stellar parameters with great precision. However, spectroscopic characterization depends on single-target radial velocity observations and only a few tens of well-studied low-mass systems have been diagnosed in this way. We characterize eclipsing detached systems from the Kepler field with low-mass components by adopting a purely photometric method. Based on an extensive multicolour data set, we derive effective temperatures and photometric masses of individual components using clustering techniques. We also estimate the stellar radii from additional modelling of the available Kepler light curves. Our measurements confirm the presence of an inflation trend in the mass–radius diagram against theoretical stellar models in the low-mass regime.

The Physical Properties and Starspot Activity of the Triple System KIC 6525196

We present the results of photometric and spectroscopic analyses for the triple-lined system KIC 6525196, an eclipsing binary accompanied by a third star. By modeling the Kepler light curves and radial velocities from LAMOST and HIDES observations, absolute parameters of the system are determined. Both components of the eclipsing binary are found to be solar-like stars with masses and radii of M 1 = 1.0286 ± 0.0026 M ⊙, R 1 = 1.127 ± 0.008 R ⊙, and M 2 = 0.9667 ± 0.0024 M ⊙, R 2 = 0.963 ± 0.007 R ⊙. The mass of the third star is determined to be M 3 = 0.772 ± 0.010 M ⊙. With the out-of-eclipse light residuals, we measure rotation period and decay timescale of an active region by using the autocorrelation function. In comparison to the Sun, the activity level of the system is significantly stronger. In addition, a possible short photometric activity cycle of ∼244 days is detected.

Classifying Kepler light curves for 12 000 A and F stars using supervised feature-based machine learning

ABSTRACT With the availability of large-scale surveys like Kepler and TESS, there is a pressing need for automated methods to classify light curves according to known classes of variable stars. We introduce a new algorithm for classifying light curves that compares 7000 time-series features to find those that most effectively classify a given set of light curves. We apply our method to Kepler light curves for stars with effective temperatures in the range 6500–10 000 K. We show that the sample can be meaningfully represented in an interpretable 5D feature space that separates seven major classes of light curves (δ Scuti stars, γ Doradus stars, RR Lyrae stars, rotational variables, contact eclipsing binaries, detached eclipsing binaries, and non-variables). We achieve a balanced classification accuracy of 82 per cent on an independent test set of Kepler stars using a Gaussian mixture model classifier. We use our method to classify 12 000 Kepler light curves from Quarter 9 and provide a catalogue of the results. We further outline a confidence heuristic based on probability density to search our catalogue and extract candidate lists of correctly classified variable stars.

Eclipse Timing the Milky Way’s Gravitational Potential

Abstract We show that a small but measurable shift in the eclipse midpoint time of eclipsing binary (EBs) stars of ∼0.1 s over a decade baseline can be used to directly measure the Galactic acceleration of stars in the Milky Way at ∼kiloparsec distances from the Sun. We consider contributions to the period drift rate from dynamical mechanisms other than the Galaxy’s gravitational field and show that the Galactic acceleration can be reliably measured using a sample of Kepler EBs with orbital and stellar parameters from the literature. The contribution from tidal decay we estimate here is an upper limit assuming the stars are not tidally synchronized. We find there are about 200 detached EBs that have estimated timing precision better than 0.5 s, and for which other dynamical effects are subdominant to the Galactic signal. We illustrate the method with a prototypical, precisely timed EB using an archival Kepler light curve and a modern synthetic HST light curve (which provides a decade baseline). This novel method establishes a realistic possibility to constrain dark matter substructure and the Galactic potential using eclipse timing to measure Galactic accelerations, along with other emerging new methods, including pulsar timing and extreme-precision radial velocity observations. This acceleration signal grows quadratically with time. Therefore, given baselines established in the near future for distant EBs, we can expect to measure the period drift in the future with space missions like JWST and the Roman Space Telescope.

The Spectroscopic Binaries from the LAMOST Medium-resolution Survey. I. Searching for Double-lined Spectroscopic Binaries with a Convolutional Neural Network

Abstract We developed a convolutional neural network model to distinguish the double-lined spectroscopic binaries (SB2s) from others based on single-exposure medium-resolution spectra (R ∼ 7500). The training set consists of a large set of mock spectra of single stars and binaries synthesized based on the MIST stellar evolutionary model and ATLAS9 atmospheric model. Our model reaches a novel theoretic false-positive rate by adding a proper penalty on the negative sample (e.g., 0.12% and 0.16% for the blue/red arm when the penalty parameter Λ = 16). Tests show that the performance is as expected and favors FGK-type main-sequence (MS) binaries with high mass ratio (q ≥ 0.7) and large radial velocity separation (Δv ≥ 50 km s−1). Although the real false-positive rate cannot be estimated reliably, validating on eclipsing binaries identified from Kepler light curves indicates that our model predicts low binary probabilities at eclipsing phases (0, 0.5, and 1.0) as expected. The color–magnitude diagram also helps illustrate its feasibility and capability of identifying FGK MS binaries from spectra. We conclude that this model is reasonably reliable and can provide an automatic approach to identify SB2s with period ≲10 days. This work yields a catalog of binary probabilities for over 5 million spectra of 1 million sources from the LAMOST medium-resolution survey (MRS) and a catalog of 2198 SB2 candidates whose physical properties will be analyzed in a follow-up paper. Data products are made publicly available online, as well as our Github website.

Spot and Facula Activity Variations of the Eccentric Detached Eclipsing Binary KIC 8098300 Based on the Time-series Orbital Solutions

The LAMOST spectra and Kepler light curves are combined to investigate the detached eclipsing binary KIC 8098300, which shows the O’Connell effect caused by spot/facula modulation. The radial velocity (RV) measurements are derived by using the tomographic spectra disentangling technology. The mass ratio q = K 1/K 2 = 0.812 ± 0.007, and the orbital semimajor axis are obtained by fitting the RV curves. We optimize the binary model concerning the spot/facula activity with the code PHOEBE and obtain precise parameters of the orbit including the eccentricity e = 0.0217 ± 0.0008, the inclination i = 87.°71 ± 0.°04, and the angle of periastron ω = 284.°1 ± 0.°5. The masses and radii of the primary and secondary star are determined as M 1 = 1.3467 ± 0.0001 M ⊙, R 1 = 1.569 ± 0.003 R ⊙, and M 2 = 1.0940 ± 0.0001 M ⊙, R 2 = 1.078 ± 0.002 R ⊙, respectively. The ratio of temperatures of the two component stars is r teff = 0.924 ± 0.001. We also obtain the periastron precession speed of 0.000024 ± 0.000001 day cycle−1. The residuals of out-of-eclipse are analyzed using the auto-correlation function and the discrete Fourier transform. The spot/facula activity is relatively weaker, but the lifetime is longer than that of most single main sequence stars in the same temperature range. The average rotation period of the spots P rot = 4.32 days is slightly longer than the orbital period, which may be caused by either the migration of spots/faculae along the longitude or the latitudinal differential rotation. The activity may be spot-dominated for the secondary star and facula-dominated for the primary star. The method of this work can be used to analyze more eclipsing binaries with the O’Connell effect in the Kepler field to obtain the precise parameters and investigate the difference of spot behavior between binaries and single stars. It is helpful for a deeper understanding of the stellar magnetic activity and dynamo theory.

Inferring the rotation period distribution of stars from their projected rotation velocities and radii: Application to late-F/early-G Kepler stars

ABSTRACT While stellar rotation periods Prot may be measured from broad-band photometry, the photometric modulation becomes harder to detect for slower rotators, which could bias measurements of the long-period tail of the Prot distribution. Alternatively, the Prot distribution of stars can be inferred from their projected rotation velocities vsin i and radii R, without being biased against photometrically quiet stars. We solve this inference problem using a hierarchical Bayesian framework, which (i) is applicable to heteroscedastic measurements of vsin i and R with non-Gaussian uncertainties and (ii) does not require a simple parametric form for the true Prot distribution. We test the method on simulated data sets and show that the true Prot distribution can be recovered from ≳ 100 sets of vsin i and R measured with precisions of $1\, \mathrm{km\, s}^{-1}$ and 4 per cent, respectively, unless the true distribution includes sharp discontinuities. We apply the method to a sample of 144 late-F/early-G dwarfs in the Kepler field with vsin i measured from Keck/HIRES spectra, and find that the typical rotation periods of these stars are similar to the photometric periods measured from Kepler light curves: we do not find a large population of slow rotators that are missed in the photometric sample, although we find evidence that the photometric sample is biased for young, rapidly rotating stars. Our results also agree with asteroseismic measurements of Prot for Kepler stars with similar ages and effective temperatures, and show that $\approx 1.1\, \mathrm{M}_\odot$ stars beyond the middle of their main-sequence lifetimes rotate faster than predicted by standard magnetic braking laws.

The Nature of Micro-Variability in Blazars

We present the results of a long-term study designed to investigate the nature of micro-variability in blazars carried out primarily at the Southeastern Association for Research in Astronomy (SARA) observatories. We analyzed micro-variability data of fifteen OVV quasars and BL Lac sources collected from 1995 to 2021. The data set consists of single-band light curves interspersed with multi-color and micro-variability observations. This paper reports over 900 nights of CCD observations. We also incorporated observations from other observers as well as observations gleaned from the literature into our analysis. We employed differential photometry to measure magnitudes and then construct the long-term and micro-variability light curves. Our results indicate that there is no correlation between the presence of micro-variations and the brightness of the source. We present a viable theory to explain the intermittent micro-variability as pulses of radiation emitted by individual turbulent cells in the relativistic jet, which are stimulated by a passing shock wave. We present model fits and test results for various data sets, including WEBT light curves, Kepler light curves and a TESS light curve. Although the consensus in the community is that blazar jets must be turbulent, the identification of micro-variations as manifestations of actual turbulent cells is important for modeling these turbulent jets. We can obtain estimates of cell sizes (assuming a shock speed), and the distribution of cell sizes derived from observations is consistent with numerical simulation predictions.

SN 2018agk: A Prototypical Type Ia Supernova with a Smooth Power-law Rise in Kepler (K2)

Abstract We present the 30 minutes cadence Kepler/K2 light curve of the Type Ia supernova (SN Ia) SN 2018agk, covering approximately one week before explosion, the full rise phase, and the decline until 40 days after peak. We additionally present ground-based observations in multiple bands within the same time range, including the 1 day cadence DECam observations within the first ∼5 days after the first light. The Kepler early light curve is fully consistent with a single power-law rise, without evidence of any bump feature. We compare SN 2018agk with a sample of other SNe Ia without early excess flux from the literature. We find that SNe Ia without excess flux have slowly evolving early colors in a narrow range (g − i ≈ −0.20 ± 0.20 mag) within the first ∼10 days. On the other hand, among SNe Ia detected with excess, SN 2017cbv and SN 2018oh tend to be bluer, while iPTF16abc’s evolution is similar to normal SNe Ia without excess in g − i. We further compare the Kepler light curve of SN 2018agk with companion-interaction models, and rule out the existence of a typical nondegenerate companion undergoing Roche lobe overflow at viewing angles smaller than 45°.