scholarly journals Building a Large Solar Analog Sample Using K2

2018 ◽  
Vol 13 (S340) ◽  
pp. 233-234
Author(s):  
Derek L. Buzasi
Keyword(s):  
Time Series ◽  
Spectroscopic Data ◽  
Stellar Rotation ◽  
Rotation Periods ◽  
Solar Analogs

AbstractWe have begun a project aimed at providing a large consistent set of well- vetted solar analogs in order to address questions of stellar rotation, activity, dynamos, and gyrochronology. We make use of the K2 mission fields to obtain precise photometric time series, supplemented by ground-based photometric and spectroscopic data for promising candidates. From this data we will derive rotation periods, spot coverages, and flare rates for a well- defined and well-calibrated sample of solar analogs.

scholarly journals Rotationally Modulated Winds of BA-Type Supergiants

1999 ◽  
Vol 169 ◽  
pp. 11-18
Author(s):  
Andreas Kaufer
Keyword(s):  
Time Series ◽  
High Resolution ◽  
High Velocity ◽  
Surface Structures ◽  
Stellar Rotation ◽  
Spectroscopic Monitoring ◽  
Rotation Periods ◽  
Rotating Surface ◽  
Circumstellar Environments ◽  
Potential Use

AbstractExtended spectroscopic monitoring programs with high resolution and coverage in wavelength and time have revealed a new picture of the winds and the circumstellar environments of late B- and early A-type supergiants. Dramatic line-profile variations (LPV) of the wind-sensitive Hα line with characteristic cyclical V/R variations indicate the presence of deviations of the envelopes from spherical symmetry. Time-series analysis of these LPVs suggest that the wind variations are caused by rotating surface structures which modulate the lower wind region. Occasionally observed high-velocity absorptions (HVA) indicate the presence of rotating extended and dense streakline or loop structures in the envelopes. The potential use of these circumstellar features to determine the true stellar rotation periods is discussed.

scholarly journals Inverse tides in pulsating binary stars

2020 ◽  
Vol 501 (1) ◽  
pp. 483-490
Author(s):  
Jim Fuller
Keyword(s):  
Binary Stars ◽  
Close Binary ◽  
Close Binaries ◽  
Spin Orbit ◽  
Misalignment Angle ◽  
Stellar Rotation ◽  
Transfer Energy ◽  
Pulsating Stars ◽  
Mode Amplitude ◽  
Rotation Periods

ABSTRACT In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.

scholarly journals Updated X-ray view of the Hyades cluster

2020 ◽  
Vol 640 ◽  
pp. A66 ◽  
Author(s):  
S. Freund ◽  
J. Robrade ◽  
P. C. Schneider ◽  
J. H. M. M. Schmitt
Keyword(s):  
Main Sequence ◽  
Distribution Functions ◽  
X Rays ◽  
Stellar Rotation ◽  
Detection Rates ◽  
X Ray ◽  
Rotation Periods ◽  
Hyades Cluster ◽  
Bona Fide ◽  
Tidal Tails

Aims. We revisit the X-ray properties of the main sequence Hyades members and the relation between X-ray emission and stellar rotation. Methods. As an input catalog for Hyades members, we combined three recent Hyades membership lists derived from Gaia DR2 data that include the Hyades core and its tidal tails. We searched for X-ray detections of the main sequence Hyades members in the ROSAT all-sky survey, and pointings from ROSAT, the Chandra X-Ray Observatory, and XMM-Newton. Furthermore, we adopted rotation periods derived from Kepler’s K2 mission and other resources. Results. We find an X-ray detection for 281 of 1066 bona fide main sequence Hyades members and provide statistical upper limits for the undetected sources. The majority of the X-ray detected stars are located in the Hyades core because of its generally smaller distance to the Sun. F- and G-type stars have the highest detection fraction (72%), while K- and M-type dwarfs have lower detection rates (22%). The X-ray luminosities of the detected members range from ∼2 × 1027 erg s−1 for late M-type dwarfs to ∼2 × 1030 erg s−1 for active binaries. The X-ray luminosity distribution functions formally differ for the members in the core and tidal tails, which is likely caused by a larger fraction of field stars in our Hyades tails sample. Compared to previous studies, our sample is slightly fainter in X-rays due to differences in the Hyades membership list used; furthermore, we extend the X-ray luminosity distribution to fainter luminosities. The X-ray activity of F- and G-type stars is well defined at FX/Fbol ≈ 10−5. The fractional X-ray luminosity and its spread increases to later spectral types reaching the saturation limit (FX/Fbol ≈ 10−3) for members later than spectral type M3. Confirming previous results, the X-ray flux varies by less than a factor of three between epochs for the 104 Hyades members with multiple epoch data, significantly less than expected from solar-like activity cycles. Rotation periods are found for 204 Hyades members, with about half of them being detected in X-rays. The activity-rotation relation derived for the coeval Hyades members has properties very similar to those obtained by other authors investigating stars of different ages.

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

2019 ◽  
Author(s):  
B Toledo-Padrón ◽  
J I González Hernández ◽  
C Rodríguez-López ◽  
A Suárez Mascareño ◽  
R Rebolo ◽  
...  
Keyword(s):  
Time Series ◽  
Spectroscopic Data ◽  
Rotation Period ◽  
Photometric Data ◽  
Activity Level ◽  
Slow Rotation ◽  
Activity Levels ◽  
Stellar Activity

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.

scholarly journals High-precision photometry with Ariel

2021 ◽  
Author(s):  
Gyula M. Szabó ◽  
Szilárd Kálmán ◽  
Theodor Pribulla ◽  
Antonio Claret ◽  
Lorenzo V. Mugnai ◽  
...  
Keyword(s):  
High Precision ◽  
Spectroscopic Data ◽  
Wide Band ◽  
Optical Data ◽  
Infrared Photometry ◽  
Stellar Rotation ◽  
New Science ◽  
Planetary Rotation ◽  
Orbital Precession ◽  
High Cadence

AbstractIn this paper we describe the photometry instruments of Ariel, consisting of the VISPhot, FGS1 and FGS2 photometers in the visual and mid-IR wavelength. These photometers have their own cadence, which can be independent from each other and the cadence of the spectral instruments. Ariel will be capable to do high cadence and high precision photometry in independent bands. There is also a possibility for synthetic Jsynth, Hsynth, and wide-band thermal infrared photometry from spectroscopic data. Although the cadence of the synthetic bands will be identical to that of the spectrographs, the precision of synthetic photometry in the suggested synthetic bands will be at least as precise as the optical data. We present the accuracy of these instruments. We also review selected fields of new science which will be opened up by the possibility of high cadence multiband space photometry, including stellar rotation, spin-orbit misalignment, orbital precession, planetary rotation and oblateness, tidal distortions, rings, and moons.

scholarly journals Gaia Data Release 2

2018 ◽  
Vol 616 ◽  
pp. A16 ◽  
Author(s):  
A. C. Lanzafame ◽  
E. Distefano ◽  
S. Messina ◽  
I. Pagano ◽  
A. F. Lanza ◽  
...  
Keyword(s):  
Time Series ◽  
European Space Agency ◽  
Magnetic Activity ◽  
Variable Stars ◽  
Stellar Rotation ◽  
Dynamo Action ◽  
Space Agency ◽  
Data Release ◽  
Flux Modulation ◽  
Two Populations

Context. Amongst the ≈5 × 105 sources identified as variable stars in Gaia Data Release 2 (DR2), 26% are rotational modulation variable candidates of the BY Dra class. Gaia DR2 provides their multi-band (G, GBP, and GRP) photometric time series collected by the European Space Agency spacecraft Gaia during the first 22 months of operations as well as the essential parameters related to their flux modulation induced by surface inhomogeneities and rotation. Aims. We developed methods to identify the BY Dra variable candidates and to infer their variability parameters. Methods. BY Dra candidates were pre-selected from their position in the Hertzsprung–Russel diagram, built from Gaia parallaxes, G magnitudes, and (GBP − GRP) colours. Since the time evolution of the stellar active region can disrupt the coherence of the signal, segments not much longer than their expected evolution timescale were extracted from the entire photometric time series, and period search algorithms were applied to each segment. For the Gaia DR2, we selected sources with similar periods in at least two segments as candidate BY Dra variables. Results were further filtered considering the time-series phase coverage and the expected approximate light-curve shape. Results. Gaia DR2 includes rotational periods and modulation amplitudes of 147 535 BY Dra candidates. The data unveil the existence of two populations with distinctive period and amplitude distributions. The sample covers 38% of the whole sky when divided into bins (HEALPix) of ≈0.84 square degrees, and we estimate that this represents 0.7–5% of all BY Dra stars potentially detectable with Gaia. Conclusions. The preliminary data contained in Gaia DR2 illustrate the vast and unique information that the mission is going to provide on stellar rotation and magnetic activity. This information, complemented by the exquisite Gaia parallaxes, proper motions, and astrophysical parameters, is opening new and unique perspectives for our understanding of the evolution of stellar angular momentum and dynamo action.

scholarly journals Rotation & differential rotation of the active Kepler stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 216-219
Author(s):  
Timo Reinhold ◽  
Ansgar Reiners ◽  
Gibor Basri
Keyword(s):  
Temperature Dependence ◽  
Differential Rotation ◽  
Large Scatter ◽  
Stellar Rotation ◽  
Rotation Periods ◽  
Active Stars ◽  
Magnetic Braking ◽  
The Absolute ◽  
First Time ◽  
Second Period

AbstractStellar rotation is a well-known quantity for tens of thousands of stars. In contrast, differential rotation (DR) is only known for a handful of stars because DR cannot be measured directly. We present rotation periods for more than 24,000 active stars in the Kepler field. Thereof, more than 18,000 stars show a second period, which we attribute to surface differential rotation. Our rotation periods are consistent with previous measurements and the theory of magnetic braking. Our results on DR paint a rather different picture: The temperature dependence of the absolute shear δΩ is split into two groups separated around 6000 K. For the cooler stars δΩ only slightly increases with temperature, whereas stars hotter than 6000 K show large scatter. This is the first time that DR has been measured for such a large number of stars.

scholarly journals Stellar rotation periods determined from simultaneously measured Ca II H&K and Ca II IRT lines

2017 ◽  
Vol 607 ◽  
pp. A87 ◽  
Author(s):  
M. Mittag ◽  
A. Hempelmann ◽  
J. H. M. M. Schmitt ◽  
B. Fuhrmeister ◽  
J. N. González-Pérez ◽  
...  
Keyword(s):  
Stellar Rotation ◽  
Rotation Periods

scholarly journals Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

2018 ◽  
Vol 618 ◽  
pp. A48 ◽  
Author(s):  
M. Mittag ◽  
J. H. M. M. Schmitt ◽  
K.-P. Schröder
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Turnover Time ◽  
Rossby Number ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Rotation Periods ◽  
Period Distribution ◽  
Cool Stars

The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R+HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R+HK values are derived from the respective S-indices and related to the rotation periods in various B–V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R+HK approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R+HK, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.

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