Data and analysis

To select Solar analogs we used the Johnson MV absolute magnitudes and the (B - V) color indices compiled by Allende Prieto & Lambert (1999) for 17,219 nearby stars (d < 100 pc) included in the Hipparcos catalog. Were selected stars within 0.07 mag of the adopted values for the Sun (B - V, Mv) = (0.65, 4.85) accessible to the 9.2-m Hobby-Eberly Telescope (HET) at McDonald Observatory during the first observing period of 2005 (December 2004-March 2005), when the observations were obtained. A list of 130 stars was placed on the HET queue, and 94 were spectroscopically observed.

The observations employed the High Resolution Spectrograph (HRS) (Tull 1998), a fiber-coupled spectrograph, using the first-order diffraction grating g316 as cross disperser to give almost continuous coverage between 407.6 and 783.8 nm. A fiber with a diameter of 2 arcsec fed the 0.625-arcsec-wide slit of the spectrograph, providing a FWHM resolving power of R ~ 120,000. The data reduction was carried out with an automated pipeline within IRAF, performing bias correction, flat-fielding, scattered-light correction, extraction, and wavelength calibration based on Th-Ar hollow-cathode spectra.

The stellar effective temperatures, surface gravities, and overall metallicity were derived by a x2 fitting of the spectral order containing Hp (Allende Prieto 2003). First, the procedure was applied to the spectra of FG dwarfs included as part of the Elodie library at a resolving power of R ~ 10,000, then the residuals were fit by linear trends. After applying the linear corrections, the rms scatter between our results and those in the Elodie catalog was found to be 1.5%, 0.16 dex, and 0.07 dex for Teff, log g, and [Fe/H], respectively.

The HRS spectra were processed in exactly the same manner, after smoothing them to a resolution R = 10,000, and the resulting parameters were subjected to the linear corrections inferred from the comparison with the Elodie library.

14

12

10

a 8

6

4

2

0

5500

15

-

a

-

5

-

0

5800 5900 Teff (K)

6000 6100 4.10 4.20

5600 5700

5800 5900 Teff (K)

6000 6100 4.10 4.20

Figure 3.1. Stellar parameters for the sample. Two metallicity distributions are shown: [M/H] indicates the values derived from the analysis of the spectral order that includes Hp (used to select the model atmosphere), and [Fe/H] indicates the values subsequently derived from the analysis of equivalent widths of Fe i lines. The surface gravities shown here correspond to the spectroscopic values derived from the Hp order, but the true gravities are likely tightly concentrated around the Solar value (log g ~ 4.437), given the narrow distribution of the sample stars in MV.

Figure 3.1. Stellar parameters for the sample. Two metallicity distributions are shown: [M/H] indicates the values derived from the analysis of the spectral order that includes Hp (used to select the model atmosphere), and [Fe/H] indicates the values subsequently derived from the analysis of equivalent widths of Fe i lines. The surface gravities shown here correspond to the spectroscopic values derived from the Hp order, but the true gravities are likely tightly concentrated around the Solar value (log g ~ 4.437), given the narrow distribution of the sample stars in MV.

Figure 3.1 shows the distribution of the final atmospheric parameters. Once the basic atmospheric parameters had been constrained, we measured and made use of the equivalent widths of 46 Fe i lines to derive the appropriate value of the microturbulence and the iron abundance using MOOG (Sneden 2002). The iron linelist is a subset of that described in Ramirez et al. (2007), and for other elements we used the same lines as Allende Prieto et al. (2004). Abundances of C, Si, Ca, Ti, and Ni were also determined assuming LTE.

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