A New Method for Estimating Starspot Lifetimes Based on Autocorrelation Functions

Abstract We present a method that utilizes autocorrelation functions from long-term precision broadband differential light curves to estimate the average lifetimes of starspot groups for two large samples of Kepler stars: stars with and without previously known rotation periods. Our method is calibrated by comparing the strengths of the first few normalized autocorrelation peaks using ensembles of models that have various starspot lifetimes. We find that we must mix models of short and long lifetimes together (in heuristically determined ratios) to align the models with the Kepler data. Our fundamental result is that short starspot-group lifetimes (one to four rotations) are implied when the first normalized peak is weaker than about 0.4, long lifetimes (15 or greater) are implied when it is greater than about 0.7, and in between are the intermediate cases. Rotational lifetimes can be converted to physical lifetimes if the rotation period is known. Stars with shorter rotation periods tend to have longer rotational (but not physical) spot lifetimes, and cooler stars tend to have longer physical spot lifetimes than warmer stars with the same rotation period. The distributions of the physical lifetimes are log-normal for both samples and generally longer in the first sample. The shorter lifetimes in the stars without known periods probably explain why their periods are difficult to measure. Some stars exhibit longer than average physical starspot lifetimes; their percentage drops with increasing temperature from nearly half at 3000 K to nearly zero for hotter than 6000 K.

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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.

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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.

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The LCOGT NEO Follow-up Network

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006778 ◽

2015 ◽

Vol 10 (S318) ◽

pp. 321-323

Author(s):

Tim A. Lister ◽

S. Greenstreet ◽

E. Gomez ◽

E. Christensen ◽

S. Larson

Keyword(s):

Kuiper Belt ◽

Network Size ◽

Light Curves ◽

Rotation Periods ◽

Human Space Flight ◽

Sky Survey ◽

Global Coverage ◽

Imaging And Spectroscopy

AbstractLas Cumbres Observatory Global Telescope Network (LCOGT) has deployed a homogeneous telescope network of nine 1-meter telescopes to four locations in the northern and southern hemispheres, with a planned network size of twelve 1-meter telescopes at 6 locations. This network is very versatile and is designed to respond rapidly to target of opportunity events and also to perform long term monitoring of slowly changing astronomical phenomena. The global coverage of the network and the apertures of telescope available make LCOGT ideal for follow-up and characterization of Solar System objects (e.g. asteroids, Kuiper Belt Objects, comets, Near-Earth Objects (NEOs)) and additionally for the discovery of new objects.We are using the LCOGT network to confirm newly detected NEO candidates produced by the major sky surveys such as Catalina Sky Survey (CSS) and PanSTARRS (PS1&2) and several hundred targets are now being followed per year. An increasing amount of time is being spent to obtain follow-up astrometry and photometry for radar-targeted objects and those on the Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) or Asteroid Retrieval Mission (ARM) lists in order to improve the orbits, determine the light curves and rotation periods and improve the characterization. This will be extended to obtain more light curves of other NEOs which could be targets. Recent results have included the first period determinations for several of the Goldstone-targeted NEOs. We are in the process of building a NEO follow-up portal which will allow professionals, amateurs and Citizen Scientists to plan, schedule and analyze NEO imaging and spectroscopy observations and data using the LCOGT Network and to act as a co-ordination hub for the NEO follow-up efforts.

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Inflection point in the power spectrum of stellar brightness variations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936018 ◽

2020 ◽

Vol 633 ◽

pp. A32 ◽

Cited By ~ 10

Author(s):

A. I. Shapiro ◽

E. M. Amazo-Gómez ◽

N. A. Krivova ◽

S. K. Solanki

Keyword(s):

Power Spectrum ◽

Inflection Point ◽

Rotation Period ◽

Power Spectra ◽

Light Curves ◽

Stellar Rotation ◽

Space Telescopes ◽

Rotation Periods ◽

Active Stars ◽

Total Irradiance

Context. Considerable effort has gone into using light curves observed by such space telescopes as CoRoT, Kepler, and TESS for determining stellar rotation periods. While rotation periods of active stars can be reliably determined, the light curves of many older and less active stars, such as stars that are similar to the Sun, are quite irregular. This hampers the determination of their rotation periods. Aims. We aim to examine the factors causing these irregularities in stellar brightness variations and to develop a method for determining rotation periods for low-activity stars with irregular light curves. Methods. We extended the Spectral And Total Irradiance Reconstruction approach for modeling solar brightness variations to Sun-like stars. We calculated the power spectra of stellar brightness variations for various combinations of parameters that define the surface configuration and evolution of stellar magnetic features. Results. The short lifetime of spots in comparison to the stellar rotation period, as well as the interplay between spot and facular contributions to brightness variations of stars with near solar activity, cause irregularities in their light curves. The power spectra of such stars often lack a peak associated with the rotation period. Nevertheless, the rotation period can still be determined by measuring the period where the concavity of the power spectrum plotted in the log–log scale changes its sign, that is, by identifying the position of the inflection point. Conclusions. The inflection point of the (log–log) power spectrum is found to be a new diagnostic for stellar rotation periods which is shown to work even in cases where the power spectrum shows no peak at the rotation rate.

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Rotation properties in the Hilda and Main-Belt asteroid families observed by K2 and TESS

10.5194/epsc2020-810 ◽

2020 ◽

Author(s):

Gyula Szabo ◽

Csaba Kiss ◽

Róbert Szakáts ◽

András Pál ◽

László Molnár ◽

...

Keyword(s):

Solar System ◽

Internal Structure ◽

Rotation Period ◽

Light Curves ◽

High Rate ◽

Occurrence Rate ◽

First Year ◽

Main Belt ◽

Rotation Periods ◽

Asteroid Families

<p>We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C- and X-type) Hildas follow this rule. Contrary to the Main Belt, the Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P > 100 hr) is a surprising 18%, which is unique in the solar system. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of a high rate of binarity, which we can estimate as 25% within the Hilda group.&#160;</p> <p>Based on our extraction of 10 thousand full asteroid light curves from the first year observations by TESS (P\'al et al. 2020) we can compare the distribution of rotation period and shape asphericity in the most populated asteroid families overall in the Main Belt. We reveal internal structure of some asteroid families in respect to rotation statistics and signs of rotation properties evolving with age.</p>

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The GAPS programme with HARPS-N at TNG

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732234 ◽

2018 ◽

Vol 613 ◽

pp. A41 ◽

Cited By ~ 13

Author(s):

L. Mancini ◽

M. Esposito ◽

E. Covino ◽

J. Southworth ◽

K. Biazzo ◽

...

Keyword(s):

Spectral Synthesis ◽

Rotation Period ◽

Orbital Plane ◽

Orbital Evolution ◽

Photometric Data ◽

Light Curves ◽

Physical Parameters ◽

Synthesis Methods ◽

Rotation Periods ◽

Exoplanetary Systems

Context. The measurement of the orbital obliquity of hot Jupiters with different physical characteristics can provide clues to the mechanisms of migration and orbital evolution of this particular class of giant exoplanets. Aims. We aim to derive the degree of alignment between planetary orbit and stellar spin angular momentum vectors and look for possible links with other orbital and fundamental physical parameters of the star-planet system. We focus on the characterisation of five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60) and the determination of their sky-projected planet orbital obliquity through the measurement of the Rossiter–McLaughlin effect. Methods. We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the Rossiter–McLaughlin effect in the target systems and determine the sky-projected angle between the planetary orbital plane and stellar equator. The characterisation of stellar atmospheric parameters was performed by exploiting the HARPS-N spectra, using line equivalent width ratios and spectral synthesis methods. Photometric parameters of the five transiting exoplanets were re-analysed through 17 new light curves, obtained with an array of medium-class telescopes, and other light curves from the literature. Survey-time-series photometric data were analysed for determining the rotation periods of the five stars and their spin inclination. Results. From the analysis of the Rossiter–McLaughlin effect we derived a sky-projected obliquity of λ = 21.2° ± 8.7°, λ = −54°−13°+41°, λ = −2.1° ± 3.0°, λ = 0° ± 11°, and λ = −129° ± 17° for HAT-P-3 b, HAT-P-12 b, HAT-P-22 b, WASP-39 b, and WASP-60 b, respectively. The latter value indicates that WASP-60 b is moving on a retrograde orbit. These values represent the first measurements of λ for the five exoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28.7 ± 0.4 days, which allowed us to estimate the true misalignment angle of HAT-P-22 b, ψ = 24° ± 18°. The revision of the physical parameters of the five exoplanetary systems returned values that are fully compatible with those existing in the literature. The exception to this is the WASP-60 system, for which, based on higher quality spectroscopic and photometric data, we found a more massive and younger star and a larger and hotter planet.

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Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774)

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038984 ◽

2020 ◽

Vol 644 ◽

pp. A16

Author(s):

D. Gruner ◽

S. A. Barnes

Keyword(s):

Open Cluster ◽

Rotation Period ◽

Principal Component ◽

Mass Region ◽

Open Clusters ◽

Light Curves ◽

Rotating Stars ◽

Rotation Periods ◽

Periodicity Analysis ◽

Cool Stars

Context. Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K – M-type stars. Aims. We study the 2.7 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. Methods. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Results. Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6 d – 33 d, allowing for a comparison of Ruprecht 147 to both other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. Conclusions. The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru 147 favors a recently-proposed model which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.

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Decomposing Interacting Binary Light Curves: The Eclipses of the Mean Light, Secular Variability and Flickering in RW Tri

International Astronomical Union Colloquium ◽

10.1017/s0252921100038136 ◽

1996 ◽

Vol 158 ◽

pp. 33-34

Author(s):

Paul J. Bennie ◽

R. W. Hilditch ◽

Keith Horne

Keyword(s):

Light Curve ◽

Accretion Disc ◽

Light Curves ◽

New Method ◽

Secular Variability ◽

The Mean

AbstractWe describe a new method of orbital light curve decomposition which is applicable to long-term photometry of interacting binaries. This method determines the orbital dependence (including eclipses) of the mean light, secular variability and RMS flickering. We identify the true line of centres of RW Tri and find that the accretion disc is a location of secular variability and a source of flickering.

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Using planetary transits to estimate magnetic cycles lengths in Kepler stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004082 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 152-158 ◽

Cited By ~ 1

Author(s):

Raissa Estrela ◽

Adriana Valio

Keyword(s):

Cycle Length ◽

Rotation Period ◽

Activity Cycle ◽

Magnetic Activity ◽

Activity Level ◽

Light Curves ◽

Cycle Period ◽

Solar Type ◽

Magnetic Cycles

AbstractObservations of various solar-type stars along decades showed that they could have magnetic cycles, just like our Sun. These observations yield a relation between the rotation period Prot and the cycle length Pcycle of these stars. Two distinct branches for the cycling stars were identified: active and inactive, classified according to stellar activity level and rotation rate. In this work, we determined the magnetic activity cycle for 6 active stars observed by the Kepler telescope. The method adopted here estimates the activity from the excess in the residuals of the transit light curves. This excess is obtained by subtracting a spotless model transit from the light curve, and then integrating over all the residuals during the transit. The presence of long term periodicity is estimated from the analysis of a Lomb-Scargle periodogram of the complete time series. Finally, we investigate the rotation-cycle period relation for the stars analysed here.

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Horizontal and vertical motions of barotropic vortices over a submarine mountain

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.9 ◽

2012 ◽

Vol 695 ◽

pp. 173-198 ◽

Cited By ~ 11

Author(s):

L. Zavala Sansón ◽

A. C. Barbosa Aguiar ◽

G. J. F. van Heijst

Keyword(s):

Rotation Axis ◽

Vertical Plane ◽

Rotation Period ◽

Vertical Flow ◽

Rotating Fluid ◽

Physical Processes ◽

Vorticity Distribution ◽

Topographic Slope ◽

Rotation Periods

AbstractThe evolution of barotropic vortices over a topographic, axisymmetric mountain in a homogeneous rotating fluid is studied experimentally. The aim is to identify the main physical processes observed in (i) a horizontal plane of motion, perpendicular to the rotation axis of the system, and (ii) a vertical plane across the diameter of the mountain. The vortices are monopolar cyclones initially generated near or over the topography. Initially, the vortices drift towards the mountain due to the $\ensuremath{\beta} $-effect associated with the topographic slope. On arriving, they turn around the obstacle in an anticyclonic direction, whilst anticyclonic vorticity is generated over the summit. The long-term vorticity distribution is dominated by the original cyclone elongated around the topographic contours and the generated anticyclone over the tip of the topography. In the vertical plane an oscillatory uphill–downhill flow is generated, which is directly related to the drift of the cyclone around the mountain. Depending on the vortex characteristics, the period of the oscillation ranges from 4 to 10 times the rotation period of the system. The horizontal and vertical flow fields are reproduced numerically by using a shallow-water formulation, which allows a detailed view of the vertical motions, hence facilitating the interpretation of the experimental results. In addition, the cyclone–anticyclone pair over the mountain is compared with analytical solutions of topographically trapped waves. A general conclusion is that vertical motions persist for several days (or rotation periods), which implies that this mechanism might be potentially important for the vertical transport over seamounts.

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