- ID:
- ivo://CDS.VizieR/J/AJ/155/161
- Title:
- Stars nearby Robo-AO Kepler planetary candidates
- Short Name:
- J/AJ/155/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the overall statistical results from the Robo-AO Kepler planetary candidate survey, comprising of 3857 high-angular resolution observations of planetary candidate systems with Robo-AO, an automated laser adaptive optics system. These observations reveal previously unknown nearby stars blended with the planetary candidate host stars that alter the derived planetary radii or may be the source of an astrophysical false positive transit signal. In the first three papers in the survey, we detected 440 nearby stars around 3313 planetary candidate host stars. In this paper, we present observations of 532 planetary candidate host stars, detecting 94 companions around 88 stars; 84 of these companions have not previously been observed in high resolution. We also report 50 more-widely separated companions near 715 targets previously observed by Robo-AO. We derive corrected planetary radius estimates for the 814 planetary candidates in systems with a detected nearby star. If planetary candidates are equally likely to orbit the primary or secondary star, the radius estimates for planetary candidates in systems with likely bound nearby stars increase by a factor of 1.54, on average. We find that 35 previously believed rocky planet candidates are likely not rocky due to the presence of nearby stars. From the combined data sets from the complete Robo-AO KOI survey, we find that 14.5+/-0.5% of planetary candidate hosts have a nearby star with 4", while 1.2% have two nearby stars, and 0.08% have three. We find that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of Jupiter-sized planet candidates have detected nearby stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/A+ARV/17.251
- Title:
- Stars observed with Doppler imaging
- Short Name:
- J/other/A+ARV/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere. This article is an attempt to review our current knowledge of starspots.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/507
- Title:
- Stars of Lyman break galaxies at z~5
- Short Name:
- J/ApJ/693/507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectral energy distribution (SED) fitting analysis for Lyman break galaxies (LBGs) at z~5 in the Great Observatories Origins Deep Survey North (GOODS-N) and its flanking fields (the GOODS-FF). With the publicly available Infrared Array Camera (IRAC) images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of the sample LBGs. The derived stellar masses range from 10^8^ to 10^11^M_{sun}_ with a median value of 4.1x10^9^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/AJ/103/1987
- Title:
- Stars of very low metal abundance
- Short Name:
- J/AJ/103/1987
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic observations for 1044 stars located primarily in the southern Galactic hemisphere are reported; the stars were chosen from a list of candidate metal-deficient stars discovered in the HK objective-prism survey. Radial velocities and line indices based on the equivalent widths of Ca II, K, H-gamma and H-delta, and the CH G band are reported. Estimates of metallicity for 874 stars with derived abundances less than -0.5 are presented.
- ID:
- ivo://CDS.VizieR/J/AJ/90/2089
- Title:
- Stars of very low metal abundance. I
- Short Name:
- J/AJ/90/2089
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An objective-prism and a narrowband interference filter have been used in combination on the Curtis Schmidt telescope at CTIO to conduct a search for extremely metal-poor stars. The filter restricts the bandpass to the region around the H and K lines of CaII; the metal-poor candidates are those stars with weak or absent H and K. Slit spectra (1 A resolution) of some 450 candidates are used to measure equivalent widths of the CaII K line and Balmer features. A calibration of the K-line strength for giants in the metal-poor globular cluster NGC 6397 and field dwarfs and giants of known metallicity is used to identify survey candidates with metal abundance [Fe/H]<=-2.0; a list of 134 such stars is presented. UBV photometry is used to distinguish between two groups of metal-poor stars: a group with objects near the main-sequence turnoff, on the subgiant branch, and on the giant branch; and a second group with objects on the red horizontal branch (RHB) and asymptotic giant branch (AGB). The RHB-AGB stars exhibit the well-known weak G-band effect; three CH-strong objects are identified among the subgiants.
- ID:
- ivo://CDS.VizieR/J/AJ/147/136
- Title:
- Stars of very low metal abundance. VI. Abundances
- Short Name:
- J/AJ/147/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by {approx}0.25dex for red giants and {approx}0.04dex for subgiants. Our sample contains 19 stars with [Fe/H]<=-3.5, 84 stars with [Fe/H]<=-3.0, and 210 stars with [Fe/H]<=-2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H]<=-2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.
- ID:
- ivo://CDS.VizieR/J/A+A/393/225
- Title:
- Starspot cycles of six young solar analogues
- Short Name:
- J/A+A/393/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A long-term photometric monitoring of a selected sample of solar analogues has been carried out since early nineties as part of "The Sun in tim" project, which is aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of their evolution. The extended time sequence of ground-based observations collected over more than a decade as part of this program has revealed the existence of starspot cycles. Also from these data it is possible to investigate surface differential rotation of the stars. In this paper we present the photometry collected to date and report on cycles search for a selected subsample of five young single G0-G5V stars with ages between ~130Myr and 700Myr: EK Dra, {pi}^1^ UMa, HN Peg, {kappa}^1^ Cet, BE Cet. Also we include in this study the Pleiades-age (~130Myr) K0V star DX Leo (HD 82443). All the cited stars show activity cycles whose period is, furthermore, the first determined from photometric data. They are compared to those activity cycles derived from CaII H&K emission fluxes and differences are discussed. All the cycle periods, except for EK Dra, fit well the empirical relations with global stellar parameters derived from larger stellar samples. The following results are also inferred from the present study: i) the fastest rotating stars tend to have longer cycles; ii) the range in the observed cycle lengths seems to converge with stellar age from a maximum dispersion around the Pleiades' age towards the solar cycle value at the Sun's age; iii) the overall short- and long-term photometric variability increases with inverse Rossby number with very high correlation degree, indicating that the level of magnetic activity at least in photosphere is still controlled by the stellar rotation even on the longest time scales; iiii) the increase with inverse Rossby number of the long-term overall photometric variability seems to level off at the highest rotation rate, which may be interpreted as due to a saturation in the level of photospheric magnetic activity around the activity maximum.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/126
- Title:
- Star spot models for M-dwarfs in NGC 2516
- Short Name:
- J/ApJ/765/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By combining rotation periods with spectroscopic determinations of projected rotation velocity, Jackson et al. (2009MNRAS.399L..89J) have found that the mean radii for low-mass M-dwarfs in the young, open cluster NGC 2516 are larger than model predictions at a given absolute I magnitude or I-K color and also larger than measured radii of magnetically inactive M-dwarfs. The relative radius difference is correlated with magnitude, increasing from a few percent at M_I_=7 to greater than 50% for the lowest luminosity stars in their sample at M_I_~9.5. Jackson et al. have suggested that a two-temperature star spot model is capable of explaining the observations, but their model requires spot coverage fractions of at least 50% in rapidly rotating M-dwarfs. Here we examine these results in terms of stellar models that include the inhibiting effects of magnetic fields on convective energy transport, with and without the effects of star spots. We find that a pure spot model is inconsistent with the color-magnitude diagram. The observations of radii versus color and radii versus absolute magnitude in NGC 2516 are consistent with models which include only magnetic inhibition or a combination of magnetic inhibition and spots. At a given mass we find a large dispersion in the strength of the vertical component of the magnetic field in the stellar photosphere but the general trend is that the vertical field increases with decreasing mass from a few hundred Gauss at 0.65M_{sun}_ to 600-900G, depending on spot coverage, in the lowest mass stars in the sample at 0.25M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A85
- Title:
- Starspot rotation rates vs. activity cycle phase
- Short Name:
- J/A+A/622/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the solar magnetic activity cycle the emergence latitudes of sunspots change, leading to the well-known butterfly diagram. This phenomenon is poorly understood for other stars since starspot latitudes are generally unknown. The related changes in starspot rotation rates caused by latitudinal differential rotation can however be measured. Using the set of 3093 Kepler stars with activity cycles identified by Reinhold et al. (2017A&A...603A..52R, Cat. J/A+A/603/A52), we aim to study the temporal change in starspot rotation rates over magnetic activity cycles, and how this relates to the activity level, the mean rotation rate of the star, and its effective temperature. We measured the photometric variability as a proxy for the magnetic activity and the spot rotation rate in each quarter over the duration of the Kepler mission. We phase-fold these measurements with the cycle period. To reduce random errors we perform averages over stars with comparable mean rotation rates and effective temperature at fixed activity-cycle phases. We detect a clear correlation between the variation of activity level and the variation of the starspot rotation rate. The sign and amplitude of this correlation depends on the mean stellar rotation and -- to a lesser extent -- on the effective temperature. For slowly rotating stars (rotation periods between 15-28 days) the starspot rotation rates are clearly anti-correlated with the level of activity during the activity cycles. A transition is observed around rotation periods of 10-15 days, where stars with effective temperature above 4200K instead show positive correlation. Our measurements can be interpreted in terms of a stellar "butterfly diagram", but these appear different from the Sun's since the starspot rotation rates are either in phase or anti-phase with the activity level. Alternatively, the activity cycle periods observed by Kepler are short (around 2.5 years) and may therefore be secondary cycles, perhaps analogous to the solar quasi-biennial oscillations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/429
- Title:
- Starspots in short-period Kepler binaries
- Short Name:
- J/MNRAS/448/429
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a new method for tracking the phases of the orbital modulations in very short-period, near-contact, and contact binary systems in order to follow starspots. We apply this technique to Kepler light curves for 414 binary systems that were identified as having anticorrelated O-C curves for the mid-times of the primary and secondary eclipses, or in the case of non-eclipsing systems, their light-curve minima. This phase tracking approach extracts more information about starspot and binary system behaviour than may be easily obtained from the O-C curves. We confirm the hypothesis of Tran et al. that we can successfully follow the rotational motions of spots on the surfaces of the stars in these binaries. In ~34% of the systems, the spot rotation is retrograde as viewed in the frame rotating with the orbital motion, while ~13% show significant prograde spot rotation. The remaining systems show either little spot rotation or erratic behaviour, or sometimes include intervals of both types of behaviour. We discuss the possibility that the relative motions of spots are related to differential rotation of the stars. It is clear from this study that the motions of the starspots in at least 50% of these short-period binaries are not exactly synchronized with the orbits.