- ID:
- ivo://CDS.VizieR/J/MNRAS/474/2580
- Title:
- Temporal evolution of neutron-capture elements
- Short Name:
- J/MNRAS/474/2580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Important insights into the formation and evolution of the Galactic disc(s) are contained in the chemical compositions of stars. We analysed high-resolution and high signal-to-noise HARPS spectra of 79 solar twin stars in order to obtain precise determinations of their atmospheric parameters, ages ({sigma}~0.4Gyr) and chemical abundances ({sigma}<0.01dex) of 12 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd and Dy). This valuable data set allows us to study the [X/Fe]-age relations over a time interval of ~10Gyr and among stars belonging to the thin and thick discs. These relations show that (i) the s-process has been the main channel of nucleosynthesis of n-capture elements during the evolution of the thin disc; (ii) the thick disc is rich in r-process elements which suggests that its formation has been rapid and intensive. In addition, the heavy (Ba, La, Ce) and light (Sr, Y, Zr) s-process elements revealed details on the dependence between the yields of AGB stars and the stellar mass or metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be employed as stellar clocks, allowing ages of solar twin stars to be estimated with an average precision of ~0.5Gyr.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/237/17
- Title:
- Temporal frequency shifts in 87 Kepler stars
- Short Name:
- J/ApJS/237/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the Sun, the frequencies of the acoustic modes are observed to vary in phase with the magnetic activity level. These frequency variations are expected to be common in solar-type stars and contain information about the activity-related changes that take place in their interiors. The unprecedented duration of Kepler photometric time-series provides a unique opportunity to detect and characterize stellar magnetic cycles through asteroseismology. In this work, we analyze a sample of 87 solar-type stars, measuring their temporal frequency shifts over segments of 90 days. For each segment, the individual frequencies are obtained through a Bayesian peak-bagging tool. The mean frequency shifts are then computed and compared with: (1) those obtained from a cross-correlation method; (2) the variation in the mode heights; (3) a photometric activity proxy; and (4) the characteristic timescale of the granulation. For each star and 90-day sub-series, we provide mean frequency shifts, mode heights, and characteristic timescales of the granulation. Interestingly, more than 60% of the stars show evidence for (quasi-)periodic variations in the frequency shifts. In the majority of the cases, these variations are accompanied by variations in other activity proxies. About 20% of the stars show mode frequencies and heights varying approximately in phase, in opposition to what is observed for the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/452/975
- Title:
- Temporal variability of Cygnus X-1
- Short Name:
- J/A+A/452/975
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of fitting power density spectra from archived Rossi X-ray Timing Explorer (RXTE) data of the source Cygnus X-1. The data cover the observations of the source during 1996-2003, and all spectral states are included.
- ID:
- ivo://CDS.VizieR/J/AJ/157/82
- Title:
- TEMP. V. Photometry of HAT-P-9, HAT-P-32 & HAT-P-36
- Short Name:
- J/AJ/157/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the past five years, 6, 7, and 26 transit observations were carried out for the HAT-P-9b, HAT-P-32b, and HAT-P-36b systems, respectively, through the Transiting Exoplanet Monitoring Project network. Combined with the published photometric data and radial-velocity measurements, our new photometry allows us to revisit the system parameters and search for additional close-in planetary companions in these hot Jupiter systems. We measure an updated R_P_/R_*_=0.1260+/-0.0011 for HAT-P-36 system in the R band, which is 4.5{sigma} larger than the published i-band radius ratio of 0.1186+/-0.0012. We also perform a transit timing variation (TTV) analysis for each system. Because no significant TTVs were found, we place an upper mass limit on an additional planet for each system.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/1084
- Title:
- Ten new and updated multiplanet systems
- Short Name:
- J/ApJ/693/1084
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest velocities for ten multiplanet systems, including a re-analysis of archival Keck and Lick data, resulting in improved velocities that supersede our previously published measurements. We derive updated orbital fits for 10 Lick and Keck systems, including two systems (HD 11964, HD 183263) for which we provide confirmation of second planets only tentatively identified elsewhere, and two others (HD 187123 and HD 217107) for which we provide a major revision of the outer planet's orbit. We compile orbital elements from the literature to generate a catalog of the 28 published multiple-planet systems around stars within 200pc.
- ID:
- ivo://CDS.VizieR/J/ApJ/761/166
- Title:
- Terrestrial exoplanet atmospheres. I.
- Short Name:
- J/ApJ/761/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive photochemistry model for exploration of the chemical composition of terrestrial exoplanet atmospheres. The photochemistry model is designed from the ground up to have the capacity to treat all types of terrestrial planet atmospheres, ranging from oxidizing through reducing, which makes the code suitable for applications for the wide range of anticipated terrestrial exoplanet compositions. The one-dimensional chemical transport model treats up to 800 chemical reactions, photochemical processes, dry and wet deposition, surface emission, and thermal escape of O, H, C, N, and S bearing species, as well as formation and deposition of elemental sulfur and sulfuric acid aerosols. We validate the model by computing the atmospheric composition of current Earth and Mars and find agreement with observations of major trace gases in Earth's and Mars' atmospheres. We simulate several plausible atmospheric scenarios of terrestrial exoplanets and choose three benchmark cases for atmospheres from reducing to oxidizing. The most interesting finding is that atomic hydrogen is always a more abundant reactive radical than the hydroxyl radical in anoxic atmospheres. Whether atomic hydrogen is the most important removal path for a molecule of interest also depends on the relevant reaction rates. We also find that volcanic carbon compounds (i.e., CH_4_ and CO_2_) are chemically long-lived and tend to be well mixed in both reducing and oxidizing atmospheres, and their dry deposition velocities to the surface control the atmospheric oxidation states. Furthermore, we revisit whether photochemically produced oxygen can cause false positives for detecting oxygenic photosynthesis, and find that in 1 bar CO_2_-rich atmospheres oxygen and ozone may build up to levels that have conventionally been accepted as signatures of life, if there is no surface emission of reducing gases. The atmospheric scenarios presented in this paper can serve as the benchmark atmospheres for quickly assessing the lifetime of trace gases in reducing, weakly oxidizing, and highly oxidizing atmospheres on terrestrial exoplanets for the exploration of possible biosignature gases.
- ID:
- ivo://CDS.VizieR/J/A+A/321/L33
- Title:
- Terrestrial impact cratering rate
- Short Name:
- J/A+A/321/L33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most significant periodicities in the terrestrial impact crater record are due to the "human-signal": the bias of assigning integer values for the crater ages. This bias seems to have eluded the proponents and opponents of real periodicity in the occurrence of these events, as well as the theorists searching for an extraterrestrial explanation for such periodicity. The "human-signal" should be seriously considered by scientists in astronomy, geology and paleontology when searching for a connection between terrestrial major comet or asteroid impacts and mass extinctions of species.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/8
- Title:
- Terrestrial planet occurrence rates for KOI stars
- Short Name:
- J/ApJ/809/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure planet occurrence rates using the planet candidates discovered by the Q1-Q16 Kepler pipeline search. This study examines planet occurrence rates for the Kepler GK dwarf target sample for planet radii, 0.75<=Rp<=2.5R_{Earth}_, and orbital periods, 50<=Porb<=300days, with an emphasis on a thorough exploration and identification of the most important sources of systematic uncertainties. Integrating over this parameter space, we measure an occurrence rate of F_0_=0.77 planets per star, with an allowed range of 0.3<=F0<=1.9. The allowed range takes into account both statistical and systematic uncertainties, and values of F_0_ beyond the allowed range are significantly in disagreement with our analysis. We generally find higher planet occurrence rates and a steeper increase in planet occurrence rates toward small planets than previous studies of the Kepler GK dwarf sample. Through extrapolation, we find that the one year orbital period terrestrial planet occurrence rate {zeta}_1.0_=0.1, with an allowed range of 0.01<={zeta}_1.0_<=2, where {zeta}_1.0_ is defined as the number of planets per star within 20% of the Rp and Porb of Earth. For G dwarf hosts, the {zeta}_1.0_ parameter space is a subset of the larger {eta}_{Earth}_ parameter space, thus {zeta}_1.0_ places a lower limit on {eta}_{Earth}_ for G dwarf hosts. From our analysis, we identify the leading sources of systematics impacting Kepler occurrence rate determinations as reliability of the planet candidate sample, planet radii, pipeline completeness, and stellar parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/144/62
- Title:
- Tertiary companions to close spectroscopic binaries
- Short Name:
- J/AJ/144/62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first results of a multi-epoch search for wide (separations greater than a few tens of AU), low-mass tertiary companions of a volume-limited sample of 118 known spectroscopic binaries within 30pc of the Sun, using the Two Micron All Sky Survey Point Source Catalog and follow-up observations with the KPNO and CTIO 4m telescopes. Note that this sample is not volume complete but volume limited, and, thus, there is incompleteness in our reported companion rates. We are sensitive to common proper motion companions with separations from roughly 200AU to 10000AU (~10"-->~10'). From 77 sources followed-up to date, we recover 11 previously known tertiaries, 3 previously known candidate tertiaries, of which 2 are spectroscopically confirmed and 1 rejected, and 3 new candidates, of which 2 are confirmed and 1 rejected. This yields an estimated wide tertiary fraction of 19.5^+5.2^_-3.7_%. This observed fraction is consistent with predictions set out in star formation simulations where the fraction of wide, low-mass companions to spectroscopic binaries is >10%.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/101
- Title:
- Terzan 5 chemical and kinematical properties
- Short Name:
- J/ApJ/791/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of a study aimed at determining the kinematical and chemical properties of Terzan 5, we present the first characterization of the bulge stars surrounding this puzzling stellar system. We observed 615 targets located well beyond the tidal radius of Terzan 5 and found that their radial velocity distribution is well described by a Gaussian function peaked at <v_rad_> = +21.0+/-4.6 km/s with dispersion {sigma}_v_= 113.0+/-2.7 km/s. This is one of the few high-precision spectroscopic surveys of radial velocities for a large sample of bulge stars in such a low and positive latitude environment (b = +1.7{deg}). We found no evidence of the peak at <v_rad_> ~ +200 km/s found in Nidever et al. (2012ApJ...755L..25N). Strong contamination of many observed spectra by TiO bands prevented us from deriving the iron abundance for the entire spectroscopic sample, introducing a selection bias. The metallicity distribution was finally derived for a subsample of 112 stars in a magnitude range where the effect of the selection bias is negligible. The distribution is quite broad and roughly peaked at solar metallicity ([Fe/H] =~ +0.05 dex) with a similar number of stars in the super-solar and in the sub-solar ranges. The population number ratios in different metallicity ranges agree well with those observed in other low-latitude bulge fields, suggesting (1) the possible presence of a plateau for|b| < 4{deg} in the ratio between stars in the super-solar (0 < [Fe/H] <0.5 dex) and sub-solar (-0.5 < [Fe/H] <0 dex) metallicity ranges; (2) a severe drop in the metal-poor component ([Fe/H] <-0.5) as a function of Galactic latitude.