The Metallicity Distribution of F/G Dwarfs Derived from BATC Survey Data

Abstract

Based on synthetic flux spectra calculated from theoretical atmospheric models, a calibration of temperature and metallicity for the dwarfs observed in the Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor photometric system is presented in this paper. According to this calibration, stellar effective temperatures can be obtained from some temperature-sensitive color indices. The sample stars have colors and magnitudes in the ranges 0.1 < d − i < 0.9 and 14.0 < i < 20.5. The photometric metallicities for these sample stars can be derived by fitting SEDs. We determine the average stellar metallicity as a function of distance from the Galactic plane. The metallicity gradient is found to be d[Fe/H]/dz = −0.37 ± 0.1 dex/kpc for z < 4 kpc and d[Fe/H]/dz = −0.06 ± 0.09 dex/kpc between 5 and 15 kpc. These results can be explained in terms of different contributions in density distribution for Galactic models 'thin disk', 'thick disk' and 'halo' components. However, for the gradient in z > 5 kpc, it could not be interpreted according to the different contributions from the three components because of the large uncertainty. So it is possible that there is little or no gradient for z > 5 kpc. The overall distribution shows a metallicity gradient d[Fe/H]/dz = −0.17 ± 0.04 dex/kpc for z < 15 kpc.

The stellar metallicity distribution in intermediate-latitude fields with BATC and SDSS data

“…Accurate determination of the properties of components of the Milky Way requires surveys with sufficient sky coverage to assess the overall geometry (De Jong et al 2010). Most previous investigations of the Galactic metallicity distribution use only one or a few selected line‐of‐sight directions (Du et al 2004; Siegel et al 2009; Karatas et al 2009). In this paper, the BATC photometry survey presented 21 intermediate‐latitude fields in multiple directions.…”

“…For each model in the library, a flux spectrum is given for the same set of 1221 wavelength points covering the range 9.1–160 000 nm, with a mean resolution of 20 Å in the visible. The spectra are thus in a format that has proved to be adequate for synthetic photometry of wide‐ and intermediate‐band systems (Du et al 2004).…”

“…Here, we synthesize colours for simulated stellar spectra with T eff and log g characteristic of main sequences (log g = 3.5, 4.0, 4.5 for dwarfs) and 19 values of metallicity ([ M /H] =−5.0, −4.5, −4.0, −3.5, −3.0, −2.5, −2.0, −1.5, −1.0, −0.5, −0.3, −0.2, −0.1, 0.0, +0.1, +0.2, +0.3, +0.5 and +1.0), where [ M /H] denotes the metallicity relative to hydrogen. The synthetic i th filter magnitude can be calculated with : where F λ is the flux per unit wavelength and φ i is the transmission curve of the i th filter of the BATC or SDSS filter system (Du et al 2004) .…”

“…The sample SED simulation with template SEDs can be used to derive the parameters of sample stars (Du et al 2004). Standard minimization, computing and minimizing the deviations between the photometric SEDs of the star and the template SEDs obtained with the same photometric system, is used in the fitting process.…”

The stellar metallicity distribution in intermediate-latitude fields

“…We use a theoretical library of synthetic stellar spectra from Lejeune, Cuisinier & Buser (1997) to derive synthetic colors of the BATC and SDSS photometric system. The sample SEDs simulation with template SEDs can be used to derive the parameter of sample stars (Du et al 2004). …”