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Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
We present carbon and oxygen abundances for 941 FGK stars—thelargest such catalog to date. We find that planet-bearing systems areenriched in these elements. We self-consistently measure NC/NO , which is thought to play a key role in planetformation. We identify 46 stars with NC /NO >=1.00 as potential hosts of carbon-dominated exoplanets. We measure adownward trend in [O/Fe] versus [Fe/H] and find distinct trends in thethin and thick disks, supporting the work of Bensby et al. Finally, wemeasure sub-solar NC /NO = 0.40+0.11- 0.07, for WASP-12, a surprising result as this star is hostto a transiting hot Jupiter whose dayside atmosphere was recentlyreported to have NC /NO >= 1 by Madhusudhan etal. Our measurements are based on 15,000 high signal-to-noise spectrataken with the Keck 1 telescope as part of the California Planet Search.We derive abundances from the [O I] and C I absorption lines at ?= 6300 and 6587 Å using the SME spectral synthesizer.Based in part on observations obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
We present time series measurements of chromospheric activity for morethan 2600 main-sequence and subgiant stars on the California PlanetSearch (CPS) program with spectral types ranging from about F5V to M4Vfor main-sequence stars and from G0IV to about K5IV for subgiants. Thelarge data set of more than 44,000 spectra allows us to identify anempirical baseline floor for chromospheric activity as a function ofcolor and height above the main sequence. We define ?S as anexcess in emission in the Ca II H and K lines above the baselineactivity floor and define radial velocity jitter as a function of?S and B - V for main-sequence and subgiant stars. Although thejitter for any individual star can always exceed the baseline level, wefind that K dwarfs have the lowest level of jitter. The lack ofcorrelation between observed jitter and chromospheric activity in Kdwarfs suggests that the observed jitter is dominated by instrumental oranalysis errors and not astrophysical noise sources. Thus, given thelong-term precision for the CPS program, radial velocities are notcorrelated with astrophysical noise for chromospherically quiet K dwarfstars, making these stars particularly well suited for the highestprecision Doppler surveys. Chromospherically quiet F and G dwarfs andsubgiants exhibit higher baseline levels of astrophysical jitter than Kdwarfs. Despite the fact that the rms in Doppler velocities iscorrelated with the mean chromospheric activity, it is rare to seeone-to-one correlations between the individual time series activity andDoppler measurements, diminishing the prospects for correctingactivity-induced velocity variations in F and G dwarfs.Based on observations obtained at the Keck Observatory and LickObservatory, which are operated by the University of California.
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| Сазвежђа: | Лав |
| Ректацензија: | 09h40m24.71s |
| Deклинација: | +16°58'07.1" |
| Apparent магнитуда: | 9.054 |
| Proper motion RA: | -30 |
| Proper motion Dec: | -74 |
| B-T magnitude: | 9.829 |
| V-T magnitude: | 9.118 |
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