Comparison of Deterministic Methods to Estimate Sidereal Rotation Period from Light Curves

Context. In addition to stellar data, Gaia Data Release 2 (DR2) also contains accurate astrometry and photometry of about 14 000 asteroids covering 22 months of observations. Aims. We used Gaia asteroid photometry to reconstruct rotation periods, spin axis directions, and the coarse shapes of a subset of asteroids with enough observations. One of our aims was to test the reliability of the models with respect to the number of data points and to check the consistency of these models with independent data. Another aim was to produce new asteroid models to enlarge the sample of asteroids with known spin and shape. Methods. We used the lightcurve inversion method to scan the period and pole parameter space to create final shape models that best reproduce the observed data. To search for the sidereal rotation period, we also used a simpler model of a geometrically scattering triaxial ellipsoid. Results. By processing about 5400 asteroids with at least 10 observations in DR2, we derived models for 173 asteroids, 129 of which are new. Models of the remaining asteroids were already known from the inversion of independent data, and we used them for verification and error estimation. We also compared the formally best rotation periods based on Gaia data with those derived from dense lightcurves. Conclusions. We show that a correct rotation period can be determined even when the number of observations N is less than 20, but the rate of false solutions is high. For N > 30, the solution of the inverse problem is often successful and the parameters are likely to be correct in most cases. These results are very promising because the final Gaia catalogue should contain photometry for hundreds of thousands of asteroids, typically with several tens of data points per object, which should be sufficient for reliable spin reconstruction.

Download Full-text

Detecting activity cycles of late-type dwarfs in Kepler data

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002142 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 224-227

Author(s):

Krisztián Vida ◽

Katalin Oláh

Keyword(s):

Active Region ◽

Frequency Analysis ◽

Rotation Period ◽

Light Curves ◽

Late Type ◽

Dwarf Stars ◽

Time Frequency ◽

Activity Cycles ◽

Using Data ◽

Fast Rotating

AbstractUsing data of fast-rotating active dwarf stars in the Kepler database, we perform time-frequency analysis of the light curves in order to search for signs of activity cycles. We use the phenomenon that the active region latitudes vary with the cycle (like the solar butterfly diagram), which causes the observed rotation period to change as a consequence of differential rotation. We find cycles in 8 cases of the 39 promising targets with periods between of 300–900 days.

Download Full-text

Long rotation period main-sequence stars from Kepler SAP light curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2432 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5513-5529 ◽

Cited By ~ 3

Author(s):

Kaiming Cui ◽

Jifeng Liu ◽

Shuhong Yang ◽

Qing Gao ◽

Huiqin Yang ◽

...

Keyword(s):

Light Curve ◽

Main Sequence ◽

Rotation Period ◽

Light Curves ◽

Stellar Rotation ◽

Main Sequence Stars ◽

Found Objects ◽

Period Detection ◽

Search Data

ABSTRACT Stellar rotation plays a key role in stellar activity. The rotation period could be detected through light curve variations caused by star-spots. Kepler provides two types of light curves: one is the Pre-search Data Conditioning (PDC) light curves, and the other is the Simple Aperture Photometer (SAP) light curves. Compared with the PDC light curves, the SAP light curves keep the long-term trend, relatively suitable for searches of long-period signals. However, SAP data are inflicted by some artefacts such as quarterly rolls and instrumental errors, making it difficult to find the physical periods in the SAP light curves. We explore a systematic approach based on the light curve pre-processing, period detection, and candidate selection. We also develop a simulated light curve test to estimate our detection limits for the SAP-like LCs. After applying our method to the raw SAP light curves, we found more than 1000 main-sequence stars with periods longer than 30 d; 165 are newly discovered. Considering the potential flaw of the SAP, we also inspect the newly found objects with photometry methods, and most of our periodical signals are confirmed.

Download Full-text

Asteroid models reconstructed from the Lowell Photometric Database and WISE data

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833437 ◽

2018 ◽

Vol 617 ◽

pp. A57 ◽

Cited By ~ 11

Author(s):

J. Ďurech ◽

J. Hanuš ◽

V. Alí-Lagoa

Keyword(s):

Joint Inversion ◽

Rotation Period ◽

Thermal Infrared ◽

Light Curves ◽

Physical Models ◽

Infrared Light ◽

Inversion Method ◽

Significant Discrepancy ◽

Wide Range ◽

New Models

Context. Information about the spin state of asteroids is important for our understanding of the dynamical processes affecting them. However, spin properties of asteroids are known for only a small fraction of the whole population. Aims. To enlarge the sample of asteroids with a known rotation state and basic shape properties, we combined sparse-in-time photometry from the Lowell Observatory Database with flux measurements from NASA’s WISE satellite. Methods. We applied the light curve inversion method to the combined data. The thermal infrared data from WISE were treated as reflected light because the shapes of thermal and visual light curves are similar enough for our purposes. While sparse data cover a wide range of geometries over many years, WISE data typically cover an interval of tens of hours, which is comparable to the typical rotation period of asteroids. The search for best-fitting models was done in the framework of the Asteroids@home distributed computing project. Results. By processing the data for almost 75 000 asteroids, we derived unique shape models for about 900 of them. Some of them were already available in the DAMIT database and served us as a consistency check of our approach. In total, we derived new models for 662 asteroids, which significantly increased the total number of asteroids for which their rotation state and shape are known. For another 789 asteroids, we were able to determine their sidereal rotation period and estimate the ecliptic latitude of the spin axis direction. We studied the distribution of spins in the asteroid population. Apart from updating the statistics for the dependence of the distribution on asteroid size, we revealed a significant discrepancy between the number of prograde and retrograde rotators for asteroids smaller than about 10 km. Conclusions. Combining optical photometry with thermal infrared light curves is an efficient approach to obtaining new physical models of asteroids. The amount of asteroid photometry is continuously growing and joint inversion of data from different surveys could lead to thousands of new models in the near future.

Download Full-text

Characterizing Sparse Asteroid Light Curves with Gaussian Processes

The Astronomical Journal ◽

10.3847/1538-3881/ac3079 ◽

2021 ◽

Vol 163 (1) ◽

pp. 29

Author(s):

Christina Willecke Lindberg ◽

Daniela Huppenkothen ◽

R. Lynne Jones ◽

Bryce T. Bolin ◽

Mario Jurić ◽

...

Keyword(s):

Gaussian Processes ◽

Time Series Data ◽

Rotation Period ◽

Light Curves ◽

Series Data ◽

Model Parameters ◽

Wide Field ◽

Pulse Profile ◽

Rotation Periods ◽

Period Detection

Abstract In the era of wide-field surveys like the Zwicky Transient Facility and the Rubin Observatory’s Legacy Survey of Space and Time, sparse photometric measurements constitute an increasing percentage of asteroid observations, particularly for asteroids newly discovered in these large surveys. Follow-up observations to supplement these sparse data may be prohibitively expensive in many cases, so to overcome these sampling limitations, we introduce a flexible model based on Gaussian processes to enable Bayesian parameter inference of asteroid time-series data. This model is designed to be flexible and extensible, and can model multiple asteroid properties such as the rotation period, light-curve amplitude, changing pulse profile, and magnitude changes due to the phase-angle evolution at the same time. Here, we focus on the inference of rotation periods. Based on both simulated light curves and real observations from the Zwicky Transient Facility, we show that the new model reliably infers rotational periods from sparsely sampled light curves and generally provides well-constrained posterior probability densities for the model parameters. We propose this framework as an intermediate method between fast but very limited-period detection algorithms and much more comprehensive but computationally expensive shape-modeling based on ray-tracing codes.

Download Full-text

Finding flares in Kepler data using machine-learning tools

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833194 ◽

2018 ◽

Vol 616 ◽

pp. A163 ◽

Cited By ~ 10

Author(s):

Krisztián Vida ◽

Rachael M. Roettenbacher

Keyword(s):

Machine Learning ◽

Rotation Period ◽

Light Curves ◽

Consensus Algorithm ◽

Data Sets ◽

Learning Tools ◽

Stellar Rotation ◽

Data Set ◽

Single Target ◽

Long Time

Context. Archives of long photometric surveys, such as the Kepler database, are a great basis for studying flares. However, identifying the flares is a complex task; it is easily done in the case of single-target observations by visual inspection, but is nearly impossible for several year-long time series for several thousand targets. Although automated methods for this task exist, several problems are difficult (or impossible) to overcome with traditional fitting and analysis approaches. Aims. We introduce a code for identifying and analyzing flares based on machine-learning methods, which are intrinsically adept at handling such data sets. Methods. We used the RANSAC (RANdom SAmple Consensus) algorithm to model light curves, as it yields robust fits even in the case of several outliers, such as flares. The light curves were divided into search windows, approximately on the order of the stellar rotation period. This search window was shifted over the data set, and a voting system was used to keep false positives to a minimum: only those flare candidate points were kept that were identified as a flare in several windows. Results. The code was tested on short-cadence K2 observations of TRAPPIST-1 and on long-cadence Kepler data of KIC 1722506. The detected flare events and flare energies are consistent with earlier results from manual inspections.

Download Full-text

Photometric and H-Alpha Variability in Some Be Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100116124 ◽

1987 ◽

Vol 92 ◽

pp. 101-103

Author(s):

S. Catalano ◽

G. Umana

Keyword(s):

Magnetic Fields ◽

Time Scales ◽

Time Scale ◽

Small Amplitude ◽

Rotation Period ◽

Light Curves ◽

Radial Pulsation ◽

Be Stars ◽

Relative Movement ◽

Short Term

Short-term variations, typically with small amplitude (Δm < 0.1 mag.), time-scales of hours or near one day and in many cases correlated with the rotation period have been found to be commonplace among Be stars (see Harmanec and Pavlovski 1983 for review and papers). Radial and non-radial pulsation modes have been proposed to explain this variability. However, the light curves are often double-peaked, at first suggesting the stars may have large organized dipole magnetic fields and spots not unlike those in the Ap or Bp stars (Harmanec 1983). These rotationally modulated variations are not stable, and seem to vary in both amplitude and period in the sense that intervals with well defined light curves alternate with intervals when variations are absent. This phenomenon is very reminiscent of formation and apparent relative movement in longitude of spots (groups) in some RS CVn binaries (Catalano 1983, Rodono 1986), but on a much more rapid time scale.

Download Full-text

PTF11mnb: First analog of supernova 2005bf

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629874 ◽

2018 ◽

Vol 609 ◽

pp. A106 ◽

Cited By ~ 10

Author(s):

F. Taddia ◽

J. Sollerman ◽

C. Fremling ◽

E. Karamehmetoglu ◽

R. M. Quimby ◽

...

Keyword(s):

Light Curve ◽

Rotation Period ◽

Supernova Explosion ◽

Light Curves ◽

Main Peak ◽

Optical Photometry ◽

Early Peak ◽

Envelope Model ◽

Analytic Models ◽

Rayet Star

Aims. We study PTF11mnb, a He-poor supernova (SN) whose light curves resemble those of SN 2005bf, a peculiar double-peaked stripped-envelope (SE) SN, until the declining phase after the main peak. We investigate the mechanism powering its light curve and the nature of its progenitor star. Methods. Optical photometry and spectroscopy of PTF11mnb are presented. We compared light curves, colors and spectral properties to those of SN 2005bf and normal SE SNe. We built a bolometric light curve and modeled this light curve with the SuperNova Explosion Code (SNEC) hydrodynamical code explosion of a MESA progenitor star and semi-analytic models. Results. The light curve of PTF11mnb turns out to be similar to that of SN 2005bf until ~50 d when the main (secondary) peaks occur at −18.5 mag. The early peak occurs at ~20 d and is about 1.0 mag fainter. After the main peak, the decline rate of PTF11mnb is remarkably slower than what was observed in SN 2005bf, and it traces well the 56Co decay rate. The spectra of PTF11mnb reveal a SN Ic and have no traces of He unlike in the case of SN Ib 2005bf, although they have velocities comparable to those of SN 2005bf. The whole evolution of the bolometric light curve is well reproduced by the explosion of a massive (Mej = 7.8 M⊙), He-poor star characterized by a double-peaked 56Ni distribution, a total 56Ni mass of 0.59 M⊙, and an explosion energy of 2.2 × 1051 erg. Alternatively, a normal SN Ib/c explosion (M(56Ni) = 0.11 M⊙, EK = 0.2 × 1051 erg, Mej = 1 M⊙) can power the first peak while a magnetar, with a magnetic field characterized by B = 5.0 × 1014 G, and a rotation period of P = 18.1 ms, provides energy for the main peak. The early g-band light curve can be fit with a shock-breakout cooling tail or an extended envelope model from which a radius of at least 30 R⊙ is obtained. Conclusions. We presented a scenario where PTF11mnb was the explosion of a massive, He-poor star, characterized by a double-peaked 56Ni distribution. In this case, the ejecta mass and the absence of He imply a large ZAMS mass (~85 M⊙) for the progenitor, which most likely was a Wolf-Rayet star, surrounded by an extended envelope formed either by a pre-SN eruption or due to a binary configuration. Alternatively, PTF11mnb could be powered by a SE SN with a less massive progenitor during the first peak and by a magnetar afterward.

Download Full-text

Solar activity and differential rotation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015419 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 298-302

Author(s):

Hari Om Vats ◽

Satish Chandra

Keyword(s):

Solar Activity ◽

Differential Rotation ◽

Rotation Rate ◽

Rotation Period ◽

Activity Cycle ◽

Solar Activity Cycle ◽

X Ray ◽

Sunspot Numbers ◽

Sidereal Rotation

AbstractThe coronal sidereal rotation rate as a function of latitude for each year, extending from 1992 to 2001 for soft X-ray images and from 1998 - 2005 for radio images are obtained. The present analysis reveals that the equatorial rotation rate of the corona is comparable to the photosphere and the chromosphere, However, at the higher latitudes, the corona rotation quite differently than the photosphere and chromosphere. The latitude differential obtained by both radio and X-ray images is quite variable throughout the period of the study. The equatorial rotation period seems to vary almost systematically with sunspot numbers which indicates its dependence on the phases of the solar activity cycle.

Download Full-text