Stellar activity analysis of Barnard’s Star: Very slow rotation and evidence for long-term activity cycle

Abstract The search for Earth-like planets around late-type stars using ultra-stable spectrographs requires a very precise characterization of the stellar activity and the magnetic cycle of the star, since these phenomena induce radial velocity (RV) signals that can be misinterpreted as planetary signals. Among the nearby stars, we have selected Barnard’s Star (Gl 699) to carry out a characterization of these phenomena using a set of spectroscopic data that covers about 14.5 years and comes from seven different spectrographs: HARPS, HARPS-N, CARMENES, HIRES, UVES, APF, and PFS; and a set of photometric data that covers about 15.1 years and comes from four different photometric sources: ASAS, FCAPT-RCT, AAVSO, and SNO. We have measured different chromospheric activity indicators (Hα, Ca II HK and Na I D), as well as the FWHM of the cross-correlation function computed for a sub-set of the spectroscopic data. The analysis of Generalized Lomb-Scargle periodograms of the time series of different activity indicators reveals that the rotation period of the star is 145 ± 15 days, consistent with the expected rotation period according to the low activity level of the star and previous claims. The upper limit of the predicted activity-induced RV signal corresponding to this rotation period is about 1 m/s. We also find evidence of a long-term cycle of 10 ± 2 years that is consistent with previous estimates of magnetic cycles from photometric time series in other M stars of similar activity levels. The available photometric data of the star also support the detection of both the long-term and the rotation signals.

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Activity time series of old stars from late F to early K

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935347 ◽

2019 ◽

Vol 628 ◽

pp. A125 ◽

Cited By ~ 8

Author(s):

N. Meunier ◽

A.-M. Lagrange

Keyword(s):

Time Series ◽

Radial Velocity ◽

Spectral Type ◽

Rotation Period ◽

Activity Level ◽

Cycle Period ◽

Large Set ◽

Data Set ◽

Stellar Activity ◽

Analysis Techniques

Context. The effect of stellar activity on radial velocity (RV) measurements appears to be a limiting factor in detecting Earth-mass planets in the habitable zone of a star that is similar to the Sun in spectral type and activity level. It is crucial to estimate whether this conclusion remain true for other stars with current correction methods. Aims. We built realistic time series in radial velocity and chromospheric emission for old main-sequence F6-K4 stars. We studied the effect of the stellar parameters we investigate on exoplanet detectability. The stellar parameters are spectral type, activity level, rotation period, cycle period and amplitude, latitude coverage, and spot constrast, which we chose to be in ranges that are compatible with our current knowledge of stellar activity. Methods. This very large set of synthetic time series allowed us to study the effect of the parameters on the RV jitter and how the different contributions to the RV are affected in this first analysis of the data set. The RV jitter was used to provide a first-order detection limit for each time series and different temporal samplings. Results. We find that the coverage in latitude of the activity pattern and the cycle amplitudes have a strong effect on the RV jitter, as has stellar inclination. RV jitter trends with B–V and Log R′HK are similar to observations, but activity cannot be responsible for RV jitter larger than 2–3 m s−1 for very quiet stars: this observed jitter is therefore likely to be due to other causes (instrumental noise or stellar or planetary companions, e.g.). Finally, we show that based on the RV jitter that is associated with each time series and using a simple criterion, a planet with one Earth mass and a period of one to two years probably cannot be detected with current analysis techniques, except for the lower mass stars in our sample, but very many observations would be required. The effect of inclination is critical. Conclusions. The results are very important in the context of future RV follow-ups of transit detections of such planets. We conclude that a significant improvement of analysis techniques and/or observing strategies must be made to reach such low detection limits.

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Long-term variations in the geomagnetic activity level Part II: Ascending phases of sunspot cycles

Annales Geophysicae ◽

10.1007/s00585-994-1065-5 ◽

1994 ◽

Vol 12 (10/11) ◽

pp. 1065-1070 ◽

Cited By ~ 5

Author(s):

V. Mussino ◽

O. Borello Filisetti ◽

M. Storini ◽

H. Nevanlinna

Keyword(s):

Correlation Coefficient ◽

Geomagnetic Activity ◽

Activity Level ◽

Activity Levels ◽

Data Set ◽

The Past ◽

Long Term Trends ◽

A Minor ◽

Long Term Variations

Abstract. Monthly averages of the Helsinki Ak-values have been reduced to the equivalent aa-indices to extend the aa-data set back to 1844. A periodicity of about five cycles was found for the correlation coefficient (r) between geomagnetic indices and sunspot numbers for the ascending phases of sunspot cycles 9 to 22, confirming previous findings based on a minor number of sunspot cycles. The result is useful to researchers in topics related to solar-terrestrial physics, particularly for the interpretation of long-term trends in geomagnetic activity during the past, and to forecast geomagnetic activity levels in the future.

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Physical Activity Trends of Finnish Adolescents With Long-Term Illnesses or Disabilities From 2002–2014

Journal of Physical Activity and Health ◽

10.1123/jpah.2015-0539 ◽

2016 ◽

Vol 13 (8) ◽

pp. 816-821 ◽

Cited By ~ 11

Author(s):

Kwok Ng ◽

Pauli Rintala ◽

Jorma Tynjälä ◽

Raili Välimaa ◽

Jari Villberg ◽

...

Keyword(s):

Physical Activity ◽

Vigorous Physical Activity ◽

Binary Logistic Regression ◽

Activity Level ◽

Binary Logistic Regression Analysis ◽

Activity Levels ◽

Physically Active ◽

Sports Club ◽

Club Membership

Background:Adolescents’ physical activity level is a major source of concern. For adolescents with long-term illnesses or disabilities (LTID), being physically active can prevent secondary conditions. This is one of the first studies reporting trends in physical activity of adolescents with LTID in relation to gender, age, and sports club membership.Methods:Data were collected from the Health Behavior in School-aged Children study in Finland during 2002, 2006, 2010, and 2014. In 13- and 15-year-olds (N = 2206), 17.1% reported having LTID. Daily physical activity recall was the dependent variable. Binary logistic regression analysis was conducted eparately for sports club members (n = 936) and nonmembers (n = 1270).Results:The proportion of physically active adolescents with LTID in 2014 was higher than in 2002 for girls (15.6% vs 8.7%) and boys (26.6% vs 13.0%). Girl sports club members were 2 times more likely to be physically active in 2014 than in 2002. The largest trend between 2014 and 2002 was among boy nonmembers (odds ratio: 4.62, 95% confidence interval, 2.02–10.58).Conclusions:More adolescents with LTID took part in daily moderate-to-vigorous physical activity in 2014 than in 2002; however, physical activity levels still remain low. Sports club membership was similar to that of the general population.

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Solar rotational cycle in lightning activity in Japan during the 18–19th centuries

Annales Geophysicae ◽

10.5194/angeo-36-633-2018 ◽

2018 ◽

Vol 36 (2) ◽

pp. 633-640 ◽

Cited By ~ 1

Author(s):

Hiroko Miyahara ◽

Ryuho Kataoka ◽

Takehiko Mikami ◽

Masumi Zaiki ◽

Junpei Hirano ◽

...

Keyword(s):

Solar Activity ◽

Solar Rotation ◽

Galactic Cosmic Rays ◽

Activity Level ◽

Lightning Activity ◽

Activity Levels ◽

Rotational Period ◽

Solar Activity Level ◽

The Impact

Abstract. Thunderstorm and cloud activities sometimes show a 27-day period, and this has long been studied to uncover a possible important link to solar rotation. Because the 27-day variations in the solar forcing parameters such as solar ultraviolet and galactic cosmic rays become more prominent when the solar activity is high, it is expected that the signal of the 27-day period in meteorological phenomena may wax and wane according to the changes in the solar activity level. In this study, we examine in detail the intensity variations in the signal of the 27-day solar rotational period in thunder and lightning activity from the 18th to the 19th centuries based on 150-year-long records found in old diaries kept in Japan and discuss their relation with the solar activity levels. Such long records enable us to examine the signals of solar rotation at both high and low solar activity levels. We found that the signal of the solar rotational period in the thunder and lightning activity increases as the solar activity increases. In this study, we also discuss the possibility of the impact of the long-term climatological conditions on the signals of the 27-day period in thunder/lightning activities. Keywords. Meteorology and atmospheric dynamics (lightning)

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The Effect of Motivational Interviewing on Physical Activity in Subjects with Chronic Obstructive Pulmonary Disease

physioscience ◽

10.1055/a-0886-6759 ◽

2019 ◽

Vol 15 (02) ◽

pp. 81-91

Author(s):

Nicolas Kahrmann ◽

Mandy Scheermesser ◽

Anne-Kathrin Rausch Osthoff

Keyword(s):

Physical Activity ◽

Motivational Interviewing ◽

Activity Level ◽

Cochrane Library ◽

Chronic Obstructive ◽

Activity Levels ◽

Long Term Effects ◽

Short Term ◽

Obstructive Pulmonary Disease

Abstract Background Current guidelines emphasise the importance of physical activity in the treatment of people with COPD. In general the physical activity level of of people with COPD is lower compared to healthy subjects. Evidence of the effectiveness of counselling in helping people with COPD to increase their activity is inconclusive. The promising method of motivational interviewing (MI) increased the activity levels in people with other chronic diseases. Objective The aim of this review was to examine the effect of MI-based counselling on activity levels in people with COPD. Method A systematic review on studies addressing short-term and preferably long-term effects of MI-based counselling on activity levels in people with COPD was performed in PubMed, CINAHL, PEDro, Cochrane Library, psycINFO and Web of Science. The study quality was assessed using the PEDro scale and the TIDieR checklist. Results The review included seven randomised controlled trials (RCT). Two of the three RCT with clinically relevant between-group differences showed also statistically significant effects. Conclusion MI-counselling might have a positive short-term effect on physical activity in people with COPD. However, all studies showed no long-term impact.

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Multifractal detrended moving average analysis of Kepler stars with surface differential rotation traces

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1791 ◽

2019 ◽

Vol 488 (3) ◽

pp. 3274-3297 ◽

Cited By ~ 2

Author(s):

D B de Freitas ◽

M M F Nepomuceno ◽

J G Cordeiro ◽

M L Das Chagas ◽

J R De Medeiros

Keyword(s):

Time Series ◽

Differential Rotation ◽

Time Series Data ◽

Moving Average ◽

Rotation Period ◽

Series Data ◽

Long Term Memory ◽

The Sun ◽

Average Analysis

ABSTRACT A multifractal formalism is employed to analyse high-precision time-series data of Kepler stars with surface differential rotation (DR) traces. The multifractal detrended moving average (MFDMA) algorithm has been explored to characterize the multiscale behaviour of the observed time series from a sample of 662 stars selected with parameters close to those of the Sun (e.g. effective temperature, mass, effective gravity and rotation period). Among these stars, 141 have surface DR traces, whereas 521 have no detected DR signatures. In our sample, we also include the Sun in its active phase. Our results can be summarized in two points. First, our work suggests that star-spots for time series with and without DR have distinct dynamics. Secondly, the magnetic fields of active stars are apparently governed by two mechanisms with different levels of complexity for fluctuations. Throughout the course of the study, we identified an overall trend whereby the DR is distributed in two H regimes segregated by the degree of asymmetry A, where H-index denotes the global Hurst exponent that is used as a measure of long-term memory of time series. As a result, we show that the degree of asymmetry can be considered a segregation factor that distinguishes the DR behaviour when related to the effect of the rotational modulation on the time series. In summary, the multifractality signals in our sample are the result of magnetic activity control mechanisms leading to activity-related long-term persistent signatures.

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A scalable, satellite-transmitted data product for monitoring high-activity events in mobile aquatic animals

Animal Biotelemetry ◽

10.1186/s40317-020-00220-0 ◽

2020 ◽

Vol 8 (1) ◽

Author(s):

Rachel A. Skubel ◽

Kenady Wilson ◽

Yannis P. Papastamatiou ◽

Hannah J. Verkamp ◽

James A. Sulikowski ◽

...

Keyword(s):

Time Series ◽

High Activity ◽

Activity Level ◽

Activity Levels ◽

Accelerometer Data ◽

Data Logger ◽

Activity Data ◽

Aquatic Animals ◽

Receiver Array ◽

In The Wild

AbstractA growing number of studies are using accelerometers to examine activity level patterns in aquatic animals. However, given the amount of data generated from accelerometers, most of these studies use loggers that archive acceleration data, thus requiring physical recovery of the loggers or acoustic transmission from within a receiver array to obtain the data. These limitations have restricted the duration of tracking (ranging from hours to days) and/or type of species studied (e.g., relatively sessile species or those returning to predictable areas). To address these logistical challenges, we present and test a satellite-transmitted metric for the remote monitoring of changes in activity, measured via a pop-off satellite archival tag (PSAT) with an integrated accelerometer. Along with depth, temperature, and irradiance for geolocation, the PSAT transmits activity data as a time-series (ATS) with a user-programmable resolution. ATS is a count of high-activity events, relative to overall activity/mobility during a summary period. An algorithm is used to identify the high-activity events from accelerometer data and reports the data as a count per time-series interval. Summary statistics describing the data used to identify high-activity events accompany the activity time-series. In this study, we first tested the ATS activity metric through simulating PSAT output from accelerometer data logger archives, comparing ATS to vectorial dynamic body acceleration. Next, we deployed PSATs with ATS under captive conditions with cobia (Rachycentron canadum). Lastly, we deployed seven pop-off satellite archival tags (PSATs) able to collect and transmit ATS in the wild on adult sandbar sharks (Carcharhinus plumbeus). In the captive trials, we identified both resting and non-resting behavior for species and used logistic regression to compare ATS values with observed activity levels. In captive cobia, ATS was a significant predictor of observed activity levels. For 30-day wild deployments on sandbar sharks, satellites received 57.4–73.2% of the transmitted activity data. Of these ATS datapoints, between 21.9 and 41.2% of records had a concurrent set of temperature, depth, and light measurements. These results suggest that ATS is a practical metric for remotely monitoring and transmitting relative high-activity data in large-bodied aquatic species with variable activity levels, under changing environmental conditions, and across broad spatiotemporal scales.

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On the multi-scale nature of large geomagnetic storms: an empirical mode decomposition analysis

Nonlinear Processes in Geophysics ◽

10.5194/npg-19-667-2012 ◽

2012 ◽

Vol 19 (6) ◽

pp. 667-673 ◽

Cited By ~ 20

Author(s):

P. De Michelis ◽

G. Consolini ◽

R. Tozzi

Keyword(s):

Time Series ◽

Empirical Mode Decomposition ◽

Geomagnetic Activity ◽

Geomagnetic Storms ◽

Decomposition Analysis ◽

Activity Level ◽

Activity Levels ◽

Geomagnetic Disturbances ◽

Multi Scale ◽

Mode Decomposition

Abstract. Complexity and multi-scale are very common properties of several geomagnetic time series. On the other hand, it is amply demonstrated that scaling properties of geomagnetic time series show significant changes depending on the geomagnetic activity level. Here, we study the multi-scale features of some large geomagnetic storms by applying the empirical mode decomposition technique. This method, which is alternative to traditional data analysis and is designed specifically for analyzing nonlinear and nonstationary data, is applied to long time series of Sym-H index relative to periods including large geomagnetic disturbances. The spectral and scaling features of the intrinsic mode functions (IMFs) into which Sym-H time series can be decomposed, as well as those of the Sym-H time series itself, are studied considering different geomagnetic activity levels. The results suggest an increase of dynamical complexity and multi-scale properties for intermediate geomagnetic activity levels.

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Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732459 ◽

2018 ◽

Vol 615 ◽

pp. A69 ◽

Cited By ~ 15

Author(s):

M. Damasso ◽

A. S. Bonomo ◽

N. Astudillo-Defru ◽

X. Bonfils ◽

L. Malavolta ◽

...

Keyword(s):

Time Series ◽

Radial Velocity ◽

Rotation Period ◽

Doppler Signal ◽

Stellar Rotation ◽

Mass Measurements ◽

Stellar Activity ◽

Velocity Signal ◽

M Dwarf ◽

High Cadence

Context. M-dwarf stars are promising targets for identifying and characterizing potentially habitable planets. K2-3 is a nearby (45 pc), early-type M dwarf hosting three small transiting planets, the outermost of which orbits close to the inner edge of the stellar (optimistic) habitable zone. The K2-3 system is well suited for follow-up characterization studies aimed at determining accurate masses and bulk densities of the three planets. Aims. Using a total of 329 radial velocity measurements collected over 2.5 years with the HARPS-N and HARPS spectrographs and a proper treatment of the stellar activity signal, we aim to improve measurements of the masses and bulk densities of the K2-3 planets. We use our results to investigate the physical structure of the planets. Methods. We analysed radial velocity time series extracted with two independent pipelines using Gaussian process regression. We adopted a quasi-periodic kernel to model the stellar magnetic activity jointly with the planetary signals. We used Monte Carlo simulations to investigate the robustness of our mass measurements of K2-3 c and K2-3 d, and to explore how additional high-cadence radial velocity observations might improve these values. Results. Even though the stellar activity component is the strongest signal present in the radial velocity time series, we are able to derive masses for both planet b (Mb = 6.6 ± 1.1 M⊕) and planet c (Mc = 3.1−1.2+1.3 M⊕). The Doppler signal from K2-3 d remains undetected, likely because of its low amplitude compared to the radial velocity signal induced by the stellar activity. The closeness of the orbital period of K2-3 d to the stellar rotation period could also make the detection of the planetary signal complicated. Based on our ability to recover injected signals in simulated data, we tentatively estimate the mass of K2-3 d to be Md = 2.7−0.8+1.2 M⊕ M⊕. These mass measurements imply that the bulk densities and therefore the interior structures of the three planets may be similar. In particular, the planets may either have small H/He envelopes (<1%) or massive water layers, with a water content ≥50% of their total mass, on top of rocky cores. Placing further constraints on the bulk densities of K2-3 c and d is difficult; in particular, we would not have been able to detect the Doppler signal of K2-3 d even by adopting a semester of intense, high-cadence radial velocity observations with HARPS-N and HARPS.

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The ESO radial velocity program. Status and results

Symposium - International Astronomical Union ◽

10.1017/s0074180900217439 ◽

2004 ◽

Vol 202 ◽

pp. 36-43

Author(s):

Martin Kürster ◽

Michael Endl ◽

Sebastian Els ◽

Artie P. Hatzes ◽

Willam D. Cochran ◽

...

Keyword(s):

Radial Velocity ◽

Time Scales ◽

Rotation Period ◽

Short Term ◽

Stellar Activity ◽

Active Star ◽

Long Period

We present results from our precision radial velocity (RV) program at ESO La Silla. The achievable RV precision after the upgrade of the CES spectrograph is demonstrated. We apply the method of pooled variance diagrams to compare our short-term with our long-term precision. For the active planet-hosting star ι Hor we determine the influence of stellar activity and the rotation period, and address the question of a second long-period planet. For the RV signal in ∊ Eri we demonstrate the distinctness of the time scales present in the RV and Call data, providing further support for the planetary interpretation in this active star.

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