- ID:
- ivo://CDS.VizieR/J/A+A/413/343
- Title:
- RGB stars in NGC 2808
- Short Name:
- J/A+A/413/343
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the first observations, taken with FLAMES during Science Verification, of red giant branch (RGB) stars in the globular cluster NGC 2808. A total of 137 stars was observed, of which 20 at high resolution (R=47000) with UVES and the others at lower resolution (R=19000-29000) with GIRAFFE in MEDUSA mode, monitoring ~3mag down from the RGB tip. Spectra were taken of the H{alpha}, Na I D and Ca II H and K lines.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/119/413
- Title:
- RI and Teff of stars in NGC 2477
- Short Name:
- J/A+AS/119/413
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Trough photometric methods we have constructed the luminosity function for the southern open cluster NGC 2477 down to M_v_=~12. We present R-I color-magnitude diagrams and near-infrared color-color diagrams, which allow us to separate statistically the cluster stars from the field ones, numerous because of the galactic latitude of the cluster. Our luminosity function (LF) reproduces some features obtained by other authors, namely, a dip at M_v_=~7, and a probable maximum at M_v_=~12. The method developed to separate cluster stars from field stars could be of interest to other astronomical problems.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/97
- Title:
- Rotation-Activity Correlations in K-M dwarfs. I.
- Short Name:
- J/ApJ/822/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The reliable determination of rotation-activity correlations (RACs) depends on precise measurements of the following stellar parameters: T_eff_, parallax, radius, metallicity, and rotational speed vsini. In this paper, our goal is to focus on the determination of these parameters for a sample of K and M dwarfs. In a future paper (PaperII; Houdebine+, 2017, J/ApJ/837/96), we will combine our rotational data with activity data in order to construct RACs. Here, we report on a determination of effective temperatures based on the (R-I)_C_ color from the calibrations of Mann+ (2015, J/ApJ/804/64) and Kenyon & Hartmann (1995, J/ApJS/101/117) for four samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar parameters (T_eff_, log(g), and [M/H]) using the principal component analysis-based inversion technique for a sample of 105 late-K dwarfs. We compile all effective temperatures from the literature for this sample. We determine empirical radius-[M/H] correlations in our stellar samples. This allows us to propose new effective temperatures, stellar radii, and metallicities for a large sample of 612 late-K and M dwarfs. Our mean radii agree well with those of Boyajian+ (2012, J/ApJ/757/112). We analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have detected vsini in 92 stars. In combination with our previous vsini measurements in M and K dwarfs, we now derive P/sini measures for a sample of 418 K and M dwarfs. We investigate the distributions of P/sini, and we show that they are different from one spectral subtype to another at a 99.9% confidence level.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/2745
- Title:
- Rotational properties of mCP stars
- Short Name:
- J/MNRAS/468/2745
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit strong, globally organized magnetic fields that are inclined to the rotational axis and facilitate the development of surface abundance inhomogeneities resulting in photometric and spectroscopic variability. Therefore, mCP stars are perfectly suited for a direct measurement of the rotational period without the need for any additional calibrations. We have investigated the rotational properties of mCP stars based on an unprecedentedly large sample consisting of more than 500 objects with known rotational periods. Using precise parallaxes from the Hipparcos and Gaia satellite missions, well-established photometric calibrations and state-of-the-art evolutionary models, we have determined the location of our sample stars in the Hertzsprung-Russell diagram and derived astrophysical parameters such as stellar masses, effective temperature, radii, inclinations and critical rotational velocities. We have confirmed the conservation of angular momentum during the main sequence evolution; no signs of additional magnetic braking were found. The inclination angles of the rotational axes are randomly distributed, although an apparent excess of fast rotators with comparable inclination angles has been observed. We have found a rotation rate of v/v_crit_>=0.5 for several stars, whose characteristics cannot be explained by current models. For the first time, we have derived the relationship between mass and rotation rate of mCP stars, and provide an analysis that links mass and rotation with magnetic field strength. Our sample is unique and offers crucial input for forthcoming evolutionary models that include the effects of magnetic fields for upper main sequence stars.
445. Rotational tracks
- ID:
- ivo://CDS.VizieR/J/ApJ/776/67
- Title:
- Rotational tracks
- Short Name:
- J/ApJ/776/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar rotation is a strong function of both mass and evolutionary state. Missions such as Kepler and CoRoT provide tens of thousands of rotation periods, drawn from stellar populations that contain objects at a range of masses, ages, and evolutionary states. Given a set of reasonable starting conditions and a prescription for angular momentum loss, we address the expected range of rotation periods for cool field stellar populations (~0.4-2.0M_{sun}_). We find that cool stars fall into three distinct regimes in rotation. Rapid rotators with surface periods less than 10 days are either young low-mass main sequence (MS) stars, or higher mass subgiants which leave the MS with high rotation rates. Intermediate rotators (10-40 days) can be either cool MS dwarfs, suitable for gyrochronology, or crossing subgiants at a range of masses. Gyrochronology relations must therefore be applied cautiously, since there is an abundant population of subgiant contaminants. The slowest rotators, at periods greater than 40 days, are lower mass subgiants undergoing envelope expansion. We identify additional diagnostic uses of rotation periods. There exists a period-age relation for subgiants distinct from the MS period-age relations. There is also a period-radius relation that can be used as a constraint on the stellar radius, particularly in the interesting case of planet host stars. The high-mass/low-mass break in the rotation distribution on the MS persists onto the subgiant branch, and has potential as a diagnostic of stellar mass. Finally, this set of theoretical predictions can be compared to extensive datasets to motivate improved modeling.
- ID:
- ivo://CDS.VizieR/J/ApJ/732/39
- Title:
- Rotational velocities of K giant stars
- Short Name:
- J/ApJ/732/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for unusually rapidly rotating giant stars in a large sample of K giants (~1300 stars) that had been spectroscopically monitored as potential targets for the Space Interferometry Mission's Astrometric Grid. The stars in this catalog are much fainter and typically more metal-poor than those of other catalogs of red giant star rotational velocities, but the spectra generally only have signal-to-noise ratio (S/N) of ~20-60, making the measurement of the widths of individual lines difficult. To compensate for this, we have developed a cross-correlation method to derive rotational velocities in moderate S/N echelle spectra to efficiently probe this sample for rapid rotator candidates. We have discovered 28 new red giant rapid rotators as well as one extreme rapid rotator with a vsin i of 86.4km/s. Rapid rotators comprise 2.2% of our sample, which is consistent with other surveys of brighter, more metal-rich K giant stars. Although we find that the temperature distribution of rapid rotators is similar to that of the slow rotators, this may not be the case with the distributions of surface gravity and metallicity. The rapid rotators show a slight overabundance of low-gravity stars and as a group are significantly more metal-poor than the slow rotators, which may indicate that the rotators are tidally locked binaries.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/159
- Title:
- Rotation-mass-age relationship of old field stars
- Short Name:
- J/ApJ/780/159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rotation-mass-age relationship offers a promising avenue for measuring the ages of field stars, assuming the attendant uncertainties to this technique can be well characterized. We model stellar angular momentum evolution starting with a rotation distribution from open cluster M37. Our predicted rotation-mass-age relationship shows significant zero-point offsets compared to an alternative angular momentum loss law and published gyrochronology relations. Systematic errors at the 30% level are permitted by current data, highlighting the need for empirical guidance. We identify two fundamental sources of uncertainty that limit the precision of rotation-based ages and quantify their impact. Stars are born with a range of rotation rates, which leads to an age range at fixed rotation period. We find that the inherent ambiguity from the initial conditions is important for all young stars, and remains large for old stars below 0.6M_{sun}_. Latitudinal surface differential rotation also introduces a minimum uncertainty into rotation period measurements and, by extension, rotation-based ages. Both models and the data from binary star systems 61 Cyg and {alpha} Cen demonstrate that latitudinal differential rotation is the limiting factor for rotation-based age precision among old field stars, inducing uncertainties at the ~2Gyr level. We also examine the relationship between variability amplitude, rotation period, and age. Existing ground-based surveys can detect field populations with ages as old as 1-2Gyr, while space missions can detect stars as old as the Galactic disk. In comparison with other techniques for measuring the ages of lower main sequence stars, including geometric parallax and asteroseismology, rotation-based ages have the potential to be the most precise chronometer for 0.6-1.0M_{sun}_stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/250/20
- Title:
- Rotation periods in TESS objects of interest (TOIs)
- Short Name:
- J/ApJS/250/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high-quality light curves from the Transiting Exoplanet Survey Satellite (TESS) represent a unique laboratory for the study of stellar rotation, which is a fundamental observable driving stellar and planetary evolution, including planetary atmospheres and impacting habitability conditions and the genesis of life around stars. As of 2020 April 14, this mission delivered public light curves for 1000 TESS objects of interest (TOIs), observed with a 2 minute cadence during the first 20 months of the mission. Here, we present a search for rotation signatures in these TOIs, using fast Fourier transform, Lomb-Scargle, and wavelet techniques, accompanied by a rigorous visual inspection. This effort revealed 163 targets with rotation signatures, 131 of which present unambiguous rotation periods ranging from 0.321 and 13.219 days, whereas 32 of them present dubious rotation periodicities. Of these stars, 109 show flux fluctuations whose root cause is not clearly identified. For 714 TOIs, the light curves show a noisy behavior, corresponding to typically low-amplitude signals. Our analysis has also revealed 10 TOI stars with pulsation periodicities ranging from 0.049 to 2.995 days and four eclipsing binaries. With upcoming TESS data releases, our periodicity analysis will be expanded to almost all TOI stars, thereby contributing in defining criteria for follow-up strategy itself, and the study of star-planet interactions, surface dynamic of host stars, and habitability conditions in planets, among other aspects. In this context, a living catalog is maintained on the Filtergraph visualization portal at http://filtergraph.com/tess_rotation_tois
- ID:
- ivo://CDS.VizieR/J/ApJS/211/24
- Title:
- Rotation periods of Kepler MS stars
- Short Name:
- J/ApJS/211/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed three years of data from the Kepler space mission to derive rotation periods of main-sequence stars below 6500K. Our automated autocorrelation-based method detected rotation periods between 0.2 and 70 days for 34030 (25.6%) of the 133030 main-sequence Kepler targets (excluding known eclipsing binaries and Kepler Objects of Interest), making this the largest sample of stellar rotation periods to date. In this paper we consider the detailed features of the now well-populated period-temperature distribution and demonstrate that the period bimodality, first seen by McQuillan et al. (2013MNRAS.432.1203M) in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6M_{sun}_. We show that these results are globally consistent with the existing ground-based rotation-period data and find that the upper envelope of the period distribution is broadly consistent with a gyrochronological age of 4.5Gyr, based on the isochrones of Barnes (2007ApJ...669.1167B), Mamajek, & Hillenbrand (Cat. J/ApJ/687/1264) and Meibom et al. (Cat. J/ApJ/695/679). We also performed a detailed comparison of our results to those of Reinhold et al. (Cat. J/A+A/560/A4) and Nielsen et al. (Cat. J/A+A/557/L10), who measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detection rotation periods, and found a typical range between ~950 ppm (5th percentile) and ~22700ppm (95th percentile), with a median of ~5600ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ~5400K.
- ID:
- ivo://CDS.VizieR/J/A+A/634/L9
- Title:
- Rotation periods of 97 solar-like stars
- Short Name:
- J/A+A/634/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The accurate determination of stellar rotation periods is important for estimating stellar ages and for understanding stellar activity and evolution. While rotation periods can be determined for about thirty thousand stars in the Kepler field, there are over one hundred thousand stars, especially with low photometric variability and irregular pattern of variations, for which rotational periods are unknown. Here we investigate the effect of metallicity on the detectability of rotation periods. This is done by synthesising light curves of hypothetical stars that are identical to our Sun with the exception of the metallicity. These light curves are then used as an input to the period determination algorithms. We find that the success rate for recovering the rotation signal has a minimum close to the solar metallicity value. This can be explained by the compensation effect of facular and spot contributions. In addition, selecting solar-like stars with near-solar effective temperature and photometric variability, and with metallicity between M/H=-0.35 and M/H=0.35 from the Kepler sample, we analyse the fraction of stars for which rotational periods have been detected as a function of metallicity. In agreement with our theoretical estimate we find a local minimum for the detection fraction close to the solar metallicity. We further report rotation periods of 87 solar-like Kepler stars for the first time.