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621. Kepler study of starspot lifetimes
ID:
ivo://CDS.VizieR/J/MNRAS/472/1618
Title:
Kepler study of starspot lifetimes
Short Name:
J/MNRAS/472/1618
Date:
21 Oct 2021
Publisher:
CDS
Description:
Wide-field high-precision photometric surveys such as Kepler have produced reams of data suitable for investigating stellar magnetic activity of cooler stars. Starspot activity produces quasi-sinusoidal light curves whose phase and amplitude vary as active regions grow and decay over time. Here we investigate, first, whether there is a correlation between the size of starspots - assumed to be related to the amplitude of the sinusoid - and their decay time-scale and, secondly, whether any such correlation depends on the stellar effective temperature. To determine this, we computed the auto-correlation functions of the light curves of samples of stars from Kepler and fitted them with apodised periodic functions. The light-curve amplitudes, representing spot size, were measured from the root-mean-squared scatter of the normalized light curves. We used a Monte Carlo Markov Chain to measure the periods and decay time-scales of the light curves. The results show a correlation between the decay time of starspots and their inferred size. The decay time also depends strongly on the temperature of the star. Cooler stars have spots that last much longer, in particular for stars with longer rotational periods. This is consistent with current theories of diffusive mechanisms causing starspot decay. We also find that the Sun is not unusually quiet for its spectral type - stars with solar-type rotation periods and temperatures tend to have (comparatively) smaller starspots than stars with mid-G or later spectral types.
622. Kepler Target Search
ID:
ivo://archive.stsci.edu/kepler_fov
Title:
Kepler Target Search
Short Name:
KIC_CT
Date:
12 Feb 2020 19:50:32
Publisher:
Space Telescope Science Institute Archive
Description:
The Kepler Target Search interface provides access to a 12.5 million row table created by MAST by joining entries from the Kepler Input catalog (KIC) with the Kepler Characteristics table (CT) and merging these with "associated" entries from the United Kingdom Infrared Telescope (IRT) project, the USNOb catalog, GALEX, the Kepler Isaac Newton Telescope Survey (KIS), and the Everett KPNO (UBV) survey. The search interface allows users to find targets within the Kepler field of view (FOV) and allows searches on magnitudes, colors, and other parameters for both KIC and associated non-KIC targets. This is the recommended interface for potential guest observers to locate possible targets for observation. GO proposers however should check on the target's position by either (or both) looking to one of our posted FFI images and seeing if it is on a chip, and (2) confirming this with the GO office.
623. KIC 8462852 ASAS V-band long-term variability
ID:
ivo://CDS.VizieR/J/ApJ/853/77
Title:
KIC 8462852 ASAS V-band long-term variability
Short Name:
J/ApJ/853/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present ~800 days of photometric monitoring of Boyajian's Star (KIC8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ~4000d of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian's Star has steadily decreased at a rate of 6.3+/-1.4mmag/yr, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian's Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ~1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at >=99.4% confidence. The 2015-2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star's behavior proposed to date.
624. KIC 10670103 frequency spectrum
ID:
ivo://CDS.VizieR/J/MNRAS/440/3809
Title:
KIC 10670103 frequency spectrum
Short Name:
J/MNRAS/440/3809
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyse 2.75yr of Kepler spacecraft observations of the pulsating subdwarf B star KIC 10670103. These 1.4 million measurements have an impressive duty cycle of 93.8 per cent, a frequency resolution of 0.017{mu}Hz, and a 5{sigma} detection limit of 0.1 parts-per-thousand (ppt). We detect 278 periodicities, making KIC 10670103 the richest pulsating subdwarf B star to date. Frequencies range from 23 to 673{mu}Hz (0.4 and 11.8h), with amplitudes from the detection limit up to 14 ppt. Follow-up spectroscopic data were obtained from which it was determined that KIC 10670103 does not show significant radial velocity variations. Updated atmospheric model fits determined T_eff_=21485+/-540K, logg=5.14+/-0.05, and logN(He)/N(H) =-2.60+/-0.04. We identify pulsation modes using asymptotic period spacings and frequency multiplets. The frequency multiplets indicate a spin period of 88+/-8d. Of the 278 periodicities detected in KIC 10670103, 163 (59 per cent) have been associated with low-degree (l<=2) pulsation modes, providing tight constraints for model fitting. While the data are exquisite, amplitudes (and some frequencies) are not stable over the course of the observations, requiring tools which are non-standard for compact pulsators such as sliding Fourier transforms and Lorentzian fitting. Using the 163 identified pulsation modes, it is possible to make detailed examinations of the pulsation structure; including where the pulsation power is concentrated in radial order, over what frequency range mode trapping is inefficient, and how power switches between multiplet members.
625. KIC 11285625: list of detected frequencies
ID:
ivo://CDS.VizieR/J/A+A/556/A56
Title:
KIC 11285625: list of detected frequencies
Short Name:
J/A+A/556/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first binary modelling results for the pulsating eclipsing binary KIC 11285625, discovered by the Kepler mission. An automated method to disentangle the pulsation spectrum and the orbital variability in high quality light curves, was developed and applied. The goal was to obtain accurate orbital and component properties, in combination with essential information derived from spectroscopy. A binary model for KIC 11285625 was obtained, using a combined analysis of high-quality space-based Kepler light curves and ground-based high-resolution HERMES echelle spectra. The binary model was used to separate the pulsation characteristics from the orbital variability in the Kepler light curve in an iterative way. We used an automated procedure to perform this task, based on the JKTEBOP binary modelling code, and adapted codes for frequency analysis and prewhitening of periodic signals. Using a disentangling technique applied to the composite HERMES spectra, we obtained a higher signal-to-noise mean component spectrum for both the primary and the secondary. A model grid search method for fitting synthetic spectra was used for fundamental parameter determination for both components. Accurate orbital and component properties of KIC 11285625 were derived, and we have obtained the pulsation spectrum of the gamma Dor pulsator in the system. Detailed analysis of the pulsation spectrum revealed amplitude modulation on a time scale of a hundred days, and strong indications of frequency splittings at both the orbital frequency, and the rotational frequency derived from spectroscopy.
626. KIC 3858884: list of pulsation frequencies
ID:
ivo://CDS.VizieR/J/A+A/563/A59
Title:
KIC 3858884: list of pulsation frequencies
Short Name:
J/A+A/563/A59
Date:
21 Oct 2021
Publisher:
CDS
Description:
Analysis of eclipsing binaries containing non-radial pulsators allows i) combining two different and independent sources of information on the internal structure and evolutionary status of the components and ii) studying the effects of tidal forces on pulsations. KIC 3858884 is a bright Kepler target whose light curve shows deep eclipses, complex pulsation patterns with pulsation frequencies typical of delta Sct, and a highly eccentric orbit. We present the result of the analysis of Kepler photometry and of high resolution phase-resolved spectroscopy. Spectroscopy yielded both the radial velocity curves and, after spectral disentangling, the primary-component effective temperature and metallicity, and line-of-sight projected rotational velocities. The Kepler light curve was analyzed with an iterative procedure that was devised to disentangle eclipses from pulsations and takes the visibility of the pulsating star into account during eclipses. The search for the best set of binary parameters was performed by combining the synthetic light curve models with a genetic minimization algorithm, which yielded a robust and accurate determination of the system parameters. The binary components have very similar masses (1.88 and 1.86M_{sun}_) and effective temperatures (6800 and 6600K), but different radii (3.45 and 3.05R_{sun}_). The comparison with the theoretical models showed a somewhat different evolutionary status of the components and the need to introduce overshooting in the models. The pulsation analysis indicates the hybrid nature of the pulsating (secondary) component, where the corresponding high order g-modes might be excited by an intrinsic mechanism or by tidal forces.
627. KIC 9777062 RVs & asteroseismology in NGC6811
ID:
ivo://CDS.VizieR/J/ApJ/831/11
Title:
KIC 9777062 RVs & asteroseismology in NGC6811
Short Name:
J/ApJ/831/11
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the analysis of an eccentric, partially eclipsing long-period (P=19.23 days) binary system KIC 9777062 that contains main-sequence stars near the turnoff of the intermediate-age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a {gamma} Dor pulsator. The component masses are 1.603+/-0.006(stat.)+/-0.016(sys.) and 1.419+/-0.003+/-0.008M_{sun}_, and the radii are 1.744+/-0.004+/-0.002 and 1.544+/-0.002+/-0.002R_{sun}_. The isochrone ages of the stars are mildly inconsistent: the age from the mass-radius combination for the primary (1.05+/-0.05+/-0.09Gyr, where the last quote was systematic uncertainty from models and metallicity) is smaller than that from the secondary (1.21+/-0.05+/-0.15Gyr) and is consistent with the inference from the color-magnitude diagram (1.00+/-0.05Gyr). We have improved the measurements of the asteroseismic parameters {Delta}{nu} and {nu}_max_ for helium-burning stars in the cluster. The masses of the stars appear to be larger (or alternately, the radii appear to be smaller) than predicted from isochrones using the ages derived from the eclipsing stars. The majority of stars near the cluster turnoff are pulsating stars: we identify a sample of 28 {delta} Sct, 15 {gamma} Dor, and 5 hybrid types. We used the period-luminosity relation for high-amplitude {delta} Sct stars to fit the ensemble of the strongest frequencies for the cluster members, finding (m-M)_V_=10.37+/-0.03. This is larger than most previous determinations, but smaller than values derived from the eclipsing binary (10.47+/-0.05).
628. Kinematics of local RR lyrae stars. I.
ID:
ivo://CDS.VizieR/J/AJ/108/1016
Title:
Kinematics of local RR lyrae stars. I.
Short Name:
J/AJ/108/1016
Date:
21 Oct 2021
Publisher:
CDS
Description:
In order to study the structure and formation history of the galaxy, we have obtained low-to-moderate dispersion spectra of 302 nearby RR Lyrae variables of Bailey type "ab". We derived abundances, typically accurate to 0.15-0.20dex and calibrated to the Zinn & West (1984ApJS...55...45Z) globular cluster metallicity scale, from the pseudo-equivalent widths of the Ca II K, Hdelta, Hgamma, and Hbeta lines. Radial velocities accurate to between 2 and 30km/s were obtained from the spectra and from the literature. Distances accurate to between 5% and 20% were derived from published apparent magnitudes and Burstein & Heiles (1982AJ.....87.1165B) reddenings. The metallicity distribution of the RR Lyrae stars peaks at [Fe/H]_K_ =~ -1.5, and is narrower than that of the Ryan & Norris (1991AJ....101.1865R) subdwarfs, as expected since the most metal-rich and metal-poor progenitors preferentially appear as stable red and blue horizontal branch stars, rather than as RR Lyrae. The metal-rich tail of the RR Lyrae distribution extends to [Fe/H]_K_{approx}0, and a qualitative analysis of the distribution of distances from the galactic plane shows that the stars in this tail (i.e., [Fe/H]_K_>-1.0) are more concentrated to the plane than the more metal-poor stars. The abundance distribution of the local RR Lyrae stars is in excellent agreement with the changing abundance distributions of distant RR Lyrae stars as a function of galactocentric distance, as derived by Suntzeff et al. (1991ApJ...367..528S), who ascribed this change to systematic variations in horizontal branch morphology (probably age variations) with galactocentric distance. The abundance distribution of the local RR Lyrae stars also agrees well with those of the distant RR Lyrae stars as a function of distance from the galactic plane. There is no evidence for an abundance gradient in this direction, suggesting that gaseous dissipation did not play a major role in the formation of the outer halo.
629. Kinematics of Mira stars
ID:
ivo://CDS.VizieR/J/MNRAS/317/460
Title:
Kinematics of Mira stars
Short Name:
J/MNRAS/317/460
Date:
21 Oct 2021
Publisher:
CDS
Description:
The space motions of Mira variables are derived from radial velocities, Hipparcos (<I/239>) proper motions and a period-luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145-200d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75+/-18km/s. This, together with a lag behind the circular velocity of Galactic rotation of 98+/-19km/s, is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ~17{deg} with the Sun-Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations.
630. Kinematics of red giant and RR Lyrae stars
ID:
ivo://CDS.VizieR/J/AJ/115/168
Title:
Kinematics of red giant and RR Lyrae stars
Short Name:
J/AJ/115/168
Date:
21 Oct 2021
Publisher:
CDS
Description:
The kinematics of 122 red giant and 124 RR Lyrae stars in the solar neighborhood are studied using accurate measurements of their proper motions obtained by the Hipparcos astrometry satellite, combined with their published photometric distances, metal abundances, and radial velocities. A majority of these sample stars have metal abundances of [Fe/H]<=-1 and thus represent the old stellar populations in the Galaxy. The halo component, with [Fe/H]<=-1.6, is characterized by a lack of systemic rotation [(<U>, <V>, <W>)=(16+/-18, -217+/-21, -10+/-12)km/s] and a radially elongated velocity ellipsoid [(<U>, <V>, <W>)=(161+/-10, 115+/-7, 108+/-7)km/s]. About 16% of such metal-poor stars have low orbital eccentricities (e<0.4), and we see no evidence of a correlation between [Fe/H] and e. Based on the model for the e-distribution of orbits, we show that this fraction of low-e stars for [Fe/H]<=-1.6 is explained by the halo component alone, without introducing the extra disk component claimed by recent workers. This is also supported by the absence of a significant change in the e-distribution with height from the Galactic plane. In the intermediate-metallicity range (-1.6<[Fe/H]<=-1), we find that stars with disklike kinematics have only modest effects on the distributions of rotational velocities and e for the sample at |z|<1kpc. This disk component appears to constitute only 10% for -1.6<[Fe/H]<=-1 and 20% for -1.4<[Fe/H]<=-1. It is also verified that this metal-weak disk has a mean rotation of ~195km/s and a vertical extent of 1 kpc, which is consistent with the thick disk's dominating at [Fe/H]=-0.6 to -1. We find no metallicity gradient in the halo, whereas there is an indication of a metallicity gradient in the metal-weak tail of the thick disk. The implications of these results for the early evolution of the Galaxy are also presented.