A statistical search for supermetallicity in F, G and K stars

Taylor, Benjamin J.

doi:10.1046/j.1365-8711.2002.05046.x

Cited by 11 publications

(13 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These differences are all within the estimated uncertainties presented here and indicate that there are not large systematic differences between this study and those published previously. This result is encouraging, given the challenging nature of characterizing the relatively rare "super-metal rich" stars with their enhanced line absorption (e.g., Cayrel de Strobel et al 1999;Taylor 2002;Gonzalez & Vanture 1998;Feltzing & Gonzalez 2001). Clearly, 55 Cnc is a well-established metal-rich star that happens to be nearby, hosts a multiple-planet system, and exhibits planetary transits.…”

Section: Resultsmentioning

confidence: 88%

Carbon and Oxygen Abundances in Cool Metal-Rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri

Teske

Cunha

Schuler

et al. 2013

ApJ

View full text Add to dashboard Cite

The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300Å [O I] line and two C I lines suggest that 55 Cnc has a carbon-rich composition (C/O=1.12±0.09). However oxygen abundances derived using the 6300Å [O I] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H]=0.34±0.18). Here, we further investigate 55 Cnc's composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300Å [O I] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78±0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (>0.8) versus low (<0.8) C/O ratios. This study illustrates the caution that must applied when determining planet host star C/O ratios, particularly in cool, metal-rich stars. Recently Madhusudhan et al. (2012) suggest an alternative and carbon-rich composition of 55 Cnc e, garnering the super-Earth popular attention as "the diamond planet." Measurements of the carbon and oxygen abundances from two C I lines (5052Å, 5135Å) and one forbidden [O I] line (6300Å) indicate a C/O 1 ratio of 1.12±0.19 (Delgado Mena et al. 2010), i.e., a highly carbon-rich star compared to the solar C/O∼0.50 (Asplund et al. 2005). If the disk shared the host star's composition, and the host star is carbon-rich, then the planetesimals accreted during the formation of 55 Cnc e were likely Fe-and C-rich (Bond et al. 2010; Madhusudhan et al. 2012). To investigate the composition of the possibly carbon-rich exoplanet, Madhusudhan et al. (2012) consider two families of carbon-rich interior models of 55 Cnc e, consisting of layers, from inner to outer, of Fe-SiC-C and Fe-MgSiO 3 -C. Included in their carbon equation of state (EOS) are the graphite EOS at low pressures, the phase transition to diamond between 10 GPa

show abstract

Section: Resultsmentioning

confidence: 88%

Carbon and Oxygen Abundances in Cool Metal-Rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri

Teske

Cunha

Schuler

et al. 2013

ApJ

View full text Add to dashboard Cite

show abstract

“…Curiously, the most metal-rich stars are mainly dwarfs and subgiants with spectral types F or later (e.g. Taylor 2002). Figure 12 shows clearly that the most metal-rich stars in our volume-limited sample are also the coolest.…”

Section: Kinematics and Metallicity Distributionmentioning

confidence: 79%

“…Buzzoni et al 2001;Taylor 2002;Chen et al 2003). The Fe II-based metallicity of this star is about one dex higher than solar but, given the inconsistency between Fe I and Fe II abundances, and the much higher sensitivity of the Fe II lines to temperature changes, we think such a higher abundance is unlikely.…”

Section: Kinematics and Metallicity Distributionmentioning

confidence: 81%

S$\mathsf{^4}$N: A spectroscopic survey of stars in the solar neighborhood

Prieto¹,

Barklem²,

Lambert³

et al. 2004

A&A

294

View full text Add to dashboard Cite

Abstract. We report the results of a high-resolution spectroscopic survey of all the stars more luminous than M V = 6.5 mag within 14.5 pc from the Sun. The Hipparcos catalog's completeness limits guarantee that our survey is comprehensive and free from some of the selection effects in other samples of nearby stars. The resulting spectroscopic database, which we have made publicly available, includes spectra for 118 stars obtained with a resolving power of R 50 000, continuous spectral coverage between ∼362−921 nm, and typical signal-to-noise ratios in the range 150−600. We derive stellar parameters and perform a preliminary abundance and kinematic analysis of the F-G-K stars in the sample. The inferred metallicity ([Fe/H]) distribution is centered at about −0.1 dex, and shows a standard deviation of 0.2 dex. A comparison with larger samples of Hipparcos stars, some of which have been part of previous abundance studies, suggests that our limited sample is representative of a larger volume of the local thin disk. We identify a number of metal-rich K-type stars which appear to be very old, confirming the claims for the existence of such stars in the solar neighborhood. With atmospheric effective temperatures and gravities derived independently of the spectra, we find that our classical LTE model-atmosphere analysis of metal-rich (and mainly K-type) stars provides discrepant abundances from neutral and ionized lines of several metals. This ionization imbalance could be a sign of departures from LTE or inhomogeneous structure, which are ignored in the interpretation of the spectra. Alternatively, but seemingly unlikely, the mismatch could be explained by systematic errors in the scale of effective temperatures. Based on transitions of majority species, we discuss abundances of 16 chemical elements. In agreement with earlier studies we find that the abundance ratios to iron of Si, Sc, Ti, Co, and Zn become smaller as the iron abundance increases until approaching the solar values, but the trends reverse for higher iron abundances. At any given metallicity, stars with a low galactic rotational velocity tend to have high abundances of Mg, Si, Ca, Sc, Ti, Co, Zn, and Eu, but low abundances of Ba, Ce, and Nd. The Sun appears deficient by roughly 0.1 dex in O, Si, Ca, Sc, Ti, Y, Ce, Nd, and Eu, compared to its immediate neighbors with similar iron abundances.

show abstract

“…Another problem is posed by the fact that sample G has an upper metallicity limit that may not be realistic. That limit exists because at present, no giants are known for which [Fe/H] > +0.2 dex at 95 per cent confidence or better (see section 5 of Taylor 2002). Without high‐dispersion data for these ‘super‐metal‐rich’ or ‘SMR’ stars, photometric metallicity calibrations for giants cannot be extended above +0.2 dex (see the notes to table 3 of Taylor 1999c).…”

Section: Samples and Sampling Problemsmentioning

confidence: 97%

The widths and peak metallicities of thin-disc metallicity distributions for solar neighbourhood dwarfs and giants

Taylor

Croxall

2005

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

For dwarfs near the Sun, published metallicity distributions commonly have peak metallicities that are a few tenths of a dex below the solar value. However, Haywood has recently used data from photometric calibrations to obtain a peak metallicity of about −0.05 dex. Haywood argues that uncorrected sampling biases explain the difference between his result and previous results. To check Haywood's peak metallicity, a statistical analysis is applied to Haywood's sample and also to a set of averaged high-dispersion metallicities for nearby dwarfs. In addition, a magnitude-limited sample of evolved stars is considered. Care is taken to make sure that all the data in these samples have a common zero-point which there is good reason to regard as reliable. In addition, sampling biases are duly considered, and full allowance is made for the contribution of the thick-disc population. Only statistical analysis is used; no conclusions are drawn by inspecting data or histograms without the aid of statistical analysis.The analysis yields a best-fitting Gaussian for dwarfs whose peak metallicity is fully consistent with Haywood's results. The 2σ width of that Gaussian is 0.37 dex, and its peak falls at a metallicity of −0.041 ± 0.013 dex. Although that peak differs detectably from zero, the difference is not appreciable when compared with a number of previous results. For evolved stars, a problem appears: their mean metallicity turns out to be significantly lower than that for dwarfs (by 0.054 ± 0.016 dex). In addition, the metallicity distribution for evolved stars is found to be narrower than its counterpart for dwarfs. It is suggested that these discrepancies can be traced to the present lack of knowledge about giants with [Fe/H] > +0.2 dex. This suggestion is supported (although not proven) by analysing an augmented test sample which includes data for a number of high-metallicity dwarfs. It is suggested that this problem should be examined further when more has been learned about the numbers of high-metallicity giants in the solar neighbourhood.

show abstract

A statistical search for supermetallicity in F, G and K stars

Cited by 11 publications

References 56 publications

Carbon and Oxygen Abundances in Cool Metal-Rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri

Carbon and Oxygen Abundances in Cool Metal-Rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri

S$\mathsf{^4}$N: A spectroscopic survey of stars in the solar neighborhood

The widths and peak metallicities of thin-disc metallicity distributions for solar neighbourhood dwarfs and giants

Contact Info

Product

Resources

About