Light Curve Period Research Articles

More Rapidly Rotating PMS M Dwarfs with Light Curves Suggestive of Orbiting Clouds of Material

Abstract In a previous paper, using data from K2 Campaign 2, we identified 11 very low mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability and phased light curves showing multiple scallops or undulations. All of the stars with the “scallop-shell” light curve morphology are mid-to-late M dwarfs without evidence of active accretion and with photometric periods generally <1 day. Their phased light curves have too much structure to be attributed to non-axisymmetrically distributed photospheric spots and rotational modulation. We have now identified an additional eight probable members of the same star-forming region plus three stars in the Taurus star-forming region with this same light curve morphology and sharing the same period and spectral type range as the previous group. We describe the light curves of these new stars in detail and present their general physical characteristics. We also examine the properties of the overall set of stars in order to identify common features that might help elucidate the causes of their photometric variability.

APO Time-resolved Color Photometry of Highly Elongated Interstellar Object 1I/‘Oumuamua

Abstract We report on g-, r-, and i-band observations of the Interstellar Object 1I/‘Oumuamua (1I) taken on 2017 October 29 from 04:28 to 08:40 UTC by the Apache Point Observatory (APO) 3.5 m telescope’s ARCTIC camera. We find that 1I’s colors are and , consistent with visible spectra and most comparable to the population of solar system C/D asteroids, Trojans, or comets. We find no evidence of any cometary activity at a heliocentric distance of 1.46 au, approximately 1.5 months after 1I’s closest approach distance to the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter toward the end of the run. By combining our APO photometric time series data with the Discovery Channel Telescope data of Knight et al., taken 20 hr later on 2017 October 30, we construct an almost complete lightcurve with a most probable single-peaked lightcurve period of . Our results imply a double-peaked rotation period of 8.1 ± 0.02 hr, with a peak-to-trough amplitude of 1.5–2.1 mag. Assuming that 1I’s shape can be approximated by an ellipsoid, the amplitude constraint implies that 1I has an axial ratio of 3.5–10.3, which is strikingly elongated. Assuming that 1I is rotating above its critical break up limit, our results are compatible with 1I having modest cohesive strength and may have obtained its elongated shape during a tidal distortion event before being ejected from its home system.

Magnetic Activity Discrepancies of Solar-Type Stars Revealed byKeplerLight Curves

AbstractMagnetic activity information is concealed in the shape of stellar light curves owing to the process of rotational modulation. We developed approaches to extract magnetic activity characteristics from stellar light curves, and applied the method to a solar-type star observed withKeplerspace telescope and also to the Sun for comparison. The result reveals distinct magnetic activity discrepancies between the solar-type star and the Sun. (1) The light-curve periodicity of the solar-type star is generally stronger than that of the Sun. (2) For the solar-type star, when the range of light-curve fluctuation is larger, the periodicity is also higher; while for the Sun, only during the solar minima with minimal range of fluctuation, the light curves show some periodicity. We propose that on the solar-type star, it is the large-scale magnetic field that leads to the light curves with both high periodicity and large range of fluctuation.

DISCOVERY OF ROTATIONAL MODULATIONS IN THE PLANETARY-MASS COMPANION 2M1207b: INTERMEDIATE ROTATION PERIOD AND HETEROGENEOUS CLOUDS IN A LOW GRAVITY ATMOSPHERE

ABSTRACT Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution. Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We present here, for the first time, time-resolved high-precision photometric measurements of a planetary-mass companion, 2M1207b. We observed the binary system with Hubble Space Telescope/Wide Field Camera 3 in two bands and with two spacecraft roll angles. Using point-spread function-based photometry, we reach a nearly photon-noise limited accuracy for both the primary and the secondary. While the primary is consistent with a flat light curve, the secondary shows modulations that are clearly detected in the combined light curve as well as in different subsets of the data. The amplitudes are 1.36% in the F125W and 0.78% in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period of 10.7 − 0.6 + 1.2 ?> hr and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b is very similar to a field brown dwarf that has identical spectral type but different J–H color. Importantly, our study also measures, for the first time, the rotation period for a directly imaged extra-solar planetary-mass companion.

The synodic rotational period of asteroid 4332 Milton

The results of our new photometric observations of the main-belt asteroid 4332 Milton are presented. These observations were obtained on two successive nights in August 2012 at Çanakkale University Observatory. The bimodal light curve amplitude and period were determined to be 0.16 ± 0.01 mag and 3.295 ± 0.005 h, respectively.

NEPTUNE'S DYNAMIC ATMOSPHERE FROM KEPLER K2 OBSERVATIONS: IMPLICATIONS FOR BROWN DWARF LIGHT CURVE ANALYSES.

Observations of Neptune with the Kepler Space Telescope yield a 49 day light curve with 98% coverage at a 1 minute cadence. A significant signature in the light curve comes from discrete cloud features. We compare results extracted from the light curve data with contemporaneous disk-resolved imaging of Neptune from the Keck 10-m telescope at 1.65 microns and Hubble Space Telescope visible imaging acquired nine months later. This direct comparison validates the feature latitudes assigned to the K2 light curve periods based on Neptune's zonal wind profile, and confirms observed cloud feature variability. Although Neptune's clouds vary in location and intensity on short and long timescales, a single large discrete storm seen in Keck imaging dominates the K2 and Hubble light curves; smaller or fainter clouds likely contribute to short-term brightness variability. The K2 Neptune light curve, in conjunction with our imaging data, provides context for the interpretation of current and future brown dwarf and extrasolar planet variability measurements. In particular we suggest that the balance between large, relatively stable, atmospheric features and smaller, more transient, clouds controls the character of substellar atmospheric variability. Atmospheres dominated by a few large spots may show inherently greater light curve stability than those which exhibit a greater number of smaller features.

An explorative approach for inspectingKeplerdata

The Kepler survey has provided a wealth of astrophysical knowledge by continuously monitoring over 150,000 stars. The resulting database contains thousands of examples of known variability types and at least as many that cannot be classified yet. In order to reveal the knowledge hidden in the database, we introduce a new visualisation method that allows us to inspect time series exploratively. To that end, we propose dimensionality reduction on the parameters of a model capable of representing time series as fixed-length vector representation. We show that a more refined objective function can be chosen by minimising the prediction error of the data reconstruction instead of the reconstruction of the model parameters. The proposed visualisation exhibits a strong correlation between the variability behaviour of the light curves and their physical properties. As a consequence, temperature and surface gravity can, for some stars, be directly inferred from non- (or quasi-) periodic light curves.

ACTIVITY ANALYSES FOR SOLAR-TYPE STARS OBSERVED WITH KEPLER . I. PROXIES OF MAGNETIC ACTIVITY

Light curves of solar-type stars often show gradual fluctuations due to rotational modulation by magnetic features (starspots and faculae) on stellar surfaces. Two quantitative measures of modulated light curves are employed as the proxies of magnetic activity for solar-type stars observed with Kepler telescope. The first is named autocorrelation index $i_{AC}$, which describes the degree of periodicity of the light curve, the second is the effective fluctuation range of the light curve $R_{eff}$, which reflects the depth of rotational modulation. The two measures are complementary and depict different aspects of magnetic activities on solar-type stars. By using the two proxies $i_{AC}$ and $R_{eff}$, we analyzed activity properties of two carefully selected solar-type stars observed with Kepler (Kepler ID: 9766237 and 10864581), which have distinct rotational periods (14.7 vs. 6.0 days). We also applied the two measures to the Sun for a comparative study. The result shows that both the measures can reveal cyclic activity variations (referred to as $i_{AC}$-cycle and $R_{eff}$-cycle) on the two Kepler stars and the Sun. For the Kepler star with the faster rotation rate, $i_{AC}$-cycle and $R_{eff}$-cycle are in the same phase, while for the Sun (slower rotator), they are in the opposite phase. By comparing the solar light curve with simultaneous photospheric magnetograms, it is identified that the magnetic feature that causes the periodic light curve during solar minima is the faculae of the enhanced network region, which can also be a candidate of magnetic features that dominate the periodic light curves on the two Kepler stars.

Periodicity in some light curves of the solar analogue V352 Canis Majoris

Our aim was to study the light curve periodicity of the solar analogue V352 CMa and in particular show that the presence or absence of periodicity in low amplitude light curves can be modelled with the Continuous Period Search (CPS) method. We applied the CPS method to 14 years of V-band photometry of V352 CMa and obtained estimates for the mean, amplitude, period and minima of the light curves in the selected datasets. We also applied the Power Spectrum Method (PSM) to these datasets and compared the performance of this frequently applied method to that of CPS. We detected signs of a $11.7 \pm 0.5$ year cycle in in the mean brightness. The long-term average photometric rotation period was $7.24 \pm 0.22$ days. The lower limit for the differential rotation coefficient would be $|k| > 0.12$, if the law of solar surface differential rotation were valid for V352 CMa and the period changes traced this phenomenon. Signs of stable active longitudes rotating with a period of $7.157 \pm 0.002$ days were detected from the epochs of the light minima with the Kuiper method. CPS performed better than the traditional PSM, because the latter always used a sinusoidal model for the data even when this was clearly not the correct model.

Discovery of four periodic methanol masers and updated light curve for a further one

We report the discovery of 6.7 GHz methanol maser periodic flares in four massive star forming regions and the updated light curve for the known periodic source G22.357+0.066. The observations were carried out with the Torun 32 m radio telescope between June 2009 and April 2014. Flux density variations with period of 120 to 245 d were detected for some or all spectral features. A variability pattern with a fast rise and relatively slow fall on time-scale of 30-60 d dominated. A reverse pattern was observed for some features of G22.357+0.066, while sinusoidal-like variations were detected in G25.411+0.105. A weak burst lasting ~520 d with the velocity drift of 0.24 km/s/yr occurred in G22.357+0.066. For three sources for which high resolution maps are available, we found that the features with periodic behaviour are separated by more than 500 au from those without any periodicity. This suggests that the maser flares are not triggered by large-scale homogeneous variations in either the background seed photon flux or the luminosity of the exciting source and a mechanism which is able to produce local changes in the pumping conditions is required.

Seventy new non-eclipsing BEER binaries discovered in CoRoT lightcurves and confirmed by RVs from AAOmega

We applied the BEER algorithm to the CoRoT lightcurves from the first five LRc fields and identified $481$ non-eclipsing BEER candidates with periodic lightcurve modulations and amplitudes of $0.5-87$ mmag. Medium-resolution spectra of $281$ candidates were obtained in a seven-night AAOmega radial-velocity (RV) campaign, with a precision of $\sim1$ km/s. The RVs confirmed the binarity of $70$ of the BEER candidates, with periods of $0.3-10$ days.

New light curve analysis and period changes of the overcontact binary EQ Tauri

A photometric CCD study of EQ Tauris was carried out in the R, V and B bands. These new data were analyzed by using the PHOEBE and Binary Marker 3 programs, which yielded the geometrical system parameters and mass and radius of both stars. We find these to confirm the results of Pribulla and Vanko (2002). Using these new data together with data from the literature, the orbital period variations were studied by using the Kalimeris method. We find the same timescale of variability of the orbital period as Pribulla and Vanko (2002), namely about 49years.

A DETAILED PHOTOMETRIC AND SPECTROSCOPIC STUDY OF THE 2011 OUTBURST OF THE RECURRENT NOVA T Pyxidis FROM 0.8 TO 250 DAYS AFTER DISCOVERY

We investigated the optical lightcurve of T Pyx during its 2011 outburst by compiling a database of SMEI and AAVSO observations. The SMEI lightcurve, providing unprecedented detail covering 1.5-49d post-discovery, was divided into four phases based on the idealised CN optical lightcurve; the initial rise (1.5-3.3d), the pre-maximum halt (3.3-13.3d), the final rise (14.7-27.9d), and the early decline (27.9d-). The SMEI lightcurve contains a strongly detected period of 1.44+/-0.05d during the pre-maximum phase. These oscillations resemble those found in TNR models arising from instabilities in the expanding envelope. No spectral variation mirroring the lightcurve periodicity was found. A marked dip at 22-24d just before maximum light (27.9d) may represent the same phenomenon seen in novae observed by SMEI. Spectra from the Liverpool Telescope and SMARTS 1.5m were obtained from 0.8-80.7 and 155.1-249.9d, covering the major phases of development. A distinct high velocity ejection phase was evident during the early rise (V~4000 km/s). A marked drop at 5.7d, and then a gradual increase occurred in the ejection velocity which stabilised at ~1500 km/s at the pre-maximum halt. Here we propose two stages of mass loss, a short-lived phase occurring immediately after outburst, lasting ~6d, followed by a steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a CN and comparison with the photometric behaviour reveals consistencies with the evolving pseudo-photosphere model of a CN outburst. Comparing optical spectra to X-ray and radio lightcurves, weak [Fe X] 6375 Angstrom emission was marginally detected before the X-ray rise and was clearly present during the brightest phase of X-ray emission. If the onset of the X-ray phase and the start of the optical final decline are related to the cessation of significant mass loss, then this occurred at 90-110d.

Observable Signatures of Classical T Tauri Stars Accreting in an Unstable Regime

We discuss key observational signatures of Classical T Tauri stars (CTTSs) accreting through Rayleigh-Taylor instability, which occurs at the interface between an accretion disk and a stellar magnetosphere. In this study, the results of global 3-D MHD simulations of accretion flows, in both stable and unstable regimes, are used to predict the variability of hydrogen emission lines and light curves associated with those two distinctive accretion flow patterns. In the stable regime, a redshifted absorption component (RAC) periodically appears in some hydrogen lines, but only during a fraction of a stellar rotation period. In the unstable regime, the RAC is present rather persistently during a whole stellar rotation period, and its strength varies non-periodically. The latter is caused by multiple accreting streams, formed randomly due to the instability, passing across the line of sight to an observer during one stellar rotation. This results in the quasi-stationarity appearance of the RAC because at least one of the accretion stream is almost always in the line of sight to an observer. In the stable regime, two stable hot spots produce a smooth and periodic light curve that shows only one or two peaks per stellar rotation. In the unstable regime, multiple hot spots formed on the surface of the star, produce the stochastic light curve with several peaks per rotation period.

Light Curve Stability and Period Behavior of the Contact Binary TZ Boo

New CCD observations of the eclipsing binary TZ Boo in BVR bands were carried out in 2006 (presented three new minima) and used together with all published minima to study and update the orbital period of the system TZ Boo by means of an (O–C) diagram. The period variation from 1926 to 2011 is represented by polynomial of eighth degree and indicates period variation of about 9.752 × 10 − 10 days/yr. We studied light curve stability over 85 yr covering all published observations in the V band and confirm the cyclic light curve variations.

EXPLORING THE VARIABLE SKY WITH LINEAR. III. CLASSIFICATION OF PERIODIC LIGHT CURVES

We describe the construction of a highly reliable sample of approximately 7,000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 sq.deg of northern sky. Majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than for most other wide-angle surveys; the photometric errors range from ~0.03 mag at $r=15$ to ~0.20 mag at r=18. Light curves include on average 250 data points, collected over about a decade. Using SDSS-based photometric recalibration of the LINEAR data for about 25 million objects, we selected ~200,000 most probable candidate variables and visually confirmed and classified approximately 7,000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a SDSS Stripe 82 region variable star catalog, and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3,900 RR Lyrae stars and 2,700 eclipsing binary stars of all subtypes, and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. We discuss the distribution of these mostly uncataloged variables in various diagrams constructed with optical-to-infrared SDSS, 2MASS and WISE photometry, and with LINEAR light curve features. An interesting side result is a robust and precise quantitative description of a strong correlation between the light-curve period and color/spectral type for close and contact eclipsing binary stars. These large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars, and we make them publicly available.

Determination of Disposed-Upper-Stage Attitude Motion by Ground-Based Optical Observations

The results of an observation campaign devoted to the determination of the rotational state of uncontrolled disposed upper stages by ground-based optical observations are presented. The photometric analysis is performed to extract light curves from photographs obtained by a camera based on charge-coupled devices. The rotation-axis direction and rotation period are determined comparing measurements with theoretical predictions obtained in the simplifying assumption of cylindrical diffusely reflecting cylinders. The angular speed is evaluated by the light-curve period. The direction of rotation axis is evaluated by measuring the difference between the maximum and minimum apparent magnitude of disposed upper stages. This evaluation can be performed from a single observing site by combining measurements collected during a suitable observation time span. The results achieved for two orbiting objects are reported showing a good agreement between determinations obtained in completely different observation geometries.

Light-curve analysis and orbital period change of the extreme mass-ratio overcontact binary AW CrB

Extreme mass-ratio contact binaries with a high degree of overcontact may be in the late evolutionary stages of the contact phase. Detailed photometric analyses and orbital period studies of those systems can provide invaluable information for the coalescence scenario of close binary systems, as recently observed in V1309 Sco. In this paper the first light curve analysis and period study for the totally eclipsing contact binary AW CrB is presented. The VRcIc CCD photometric light curves are analysed by means of the WD code. The asymmetry of the light curves is modelled by a cool star spot on the primary component. It is shown that AW CrB has a high degree of overcontact f=75% and an extreme mass-ratio of q=0.10, placing it among the few contact binaries with the lowest known mass-ratios. The mean density of the primary component suggest that it has evolved away from the ZAMS. Eighty-four times of minimum light are reported, derived from observations available in public archives, the literature, and the observations presented in this paper. The orbital period study shows a continuously increasing period, at a rate of dP/dt=3.58x10^-7 d yr^-1, suggesting a mass transfer from the secondary component to the primary one, implying a further decreasing mass-ratio.

J-band variability of M dwarfs in the WFCAM Transit Survey

We present an analysis of the photometric variability of M dwarfs in the WFCAM Transit Survey. Although periodic lightcurve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has not been as thoroughly investigated as at visible wavelengths. Spectral type estimates for a sample of over 200,000 objects are made using spectral type-colour relations, and over 9600 dwarfs (J<17) with spectral types later than K7 were found. The light curves of the late-type sample are searched for periodicity using a Lomb-Scargle periodogram analysis. A total of 68 periodic variable M dwarfs are found in the sample with periods ranging from 0.16 days to 90.33 days, with amplitudes in the range of ~0.009 to ~0.115 in the J band. We simulate active M dwarfs with a range of latitude-independent spot coverages and estimate a periodically variable fractions of 1-3 per cent for stars where spots cover more than 10 per cent of the star's surface. Our simulated spot distributions indicate that operating in the J band, where spot contrast ratios are minimised, enables variability in only the most active of stars to be detected. These findings affirm the benefits of using the $J$ band for planetary transit searches compared to visible bands. We also serendipitously find a \Delta J>0.2 mag flaring event from an M4V star in our sample.

An Information Theoretic Algorithm for Finding Periodicities in Stellar Light Curves

We propose a new information theoretic metric for finding periodicities in stellar light curves. Light curves are astronomical time series of brightness over time, and are characterized as being noisy and unevenly sampled. The proposed metric combines correntropy (generalized correlation) with a periodic kernel to measure similarity among samples separated by a given period. The new metric provides a periodogram, called Correntropy Kernelized Periodogram (CKP), whose peaks are associated with the fundamental frequencies present in the data. The CKP does not require any resampling, slotting or folding scheme as it is computed directly from the available samples. CKP is the main part of a fully-automated pipeline for periodic light curve discrimination to be used in astronomical survey databases. We show that the CKP method outperformed the slotted correntropy, and conventional methods used in astronomy for periodicity discrimination and period estimation tasks, using a set of light curves drawn from the MACHO survey. The proposed metric achieved 97.2% of true positives with 0% of false positives at the confidence level of 99% for the periodicity discrimination task; and 88% of hits with 11.6% of multiples and 0.4% of misses in the period estimation task.