Effective temperatures, rotational velocities, microturbulent velocities and abundances in the atmospheres of the Sun, HD 1835 and HD 10700★

Abstract

We describe the procedure to determine effective temperatures, rotational velocities, microturbulent velocities and chemical abundances in the atmospheres of Sun-like stars. We use independent determinations of iron abundances using the fits to the observed Fe I and Fe II atomic absorption lines. We choose the best solution from the fits to these spectral features for the model atmosphere that provides the best confidence in the determined log N(Fe), V t and v sin i. Computations were performed in the framework of local thermodynamic equilibrium. Blending effects were accounted for explicitly. First, we compute the abundance of iron for a set of adopted microturbulent velocities. In some cases, a few points of log N(Fe I) = log N(Fe II) can be found. To determine the most self-consistent effective temperature and microturbulent velocity in any star's atmosphere, we used an additional constraint where we minimize the dependence of the derived abundances of Fe I and Fe II on the excitation potential of the corresponding lines. Using this procedure we analyse the spectra of the Sun and two well-known solar-type stars, HD 1835 and HD 10700, to determine their abundances, microturbulent velocity and rotational velocity. Our approach allows us to determine self-consistent values for the effective temperatures, abundances, V t and v sin i. For the Sun, we obtain the best agreement for a model atmosphere of T eff /log g/[Fe/H] = 5777/4.44/0.0, iron abundances and microturbulent velocities of log N(Fe) = 4.44, V t = 0.75 km s −1 , for the Fe I lines, and log N(Fe) = −4.47 and V t = 1.5 km s −1 for the Fe II lines. Furthermore, abundances of other elements obtained from the fits of their absorption features agree well enough (±0.1 dex) with the known values for the Sun. We determined a rotational velocity of v sin i = 1.6 ± 0.3 km s −1 for the spectrum of the Sun as a star. For HD 1835, the self-consistent solution for Fe I and Fe II lines log N(Fe) = +0.2 was obtained with a model atmosphere of 5807/4.47/+0.2 and microturbulent velocity of V t = 0.75 km s −1 , and leads to v sin i = 7.2 ± 0.5 km s −1 . For HD 10700, the self-consistent solution log N(Fe) = −4.93 was obtained using a model atmosphere of 5383/4.59/−0.6 and microturbulent velocity of V t = 0.5 km s −1 . The Fe I and Fe II lines give rise to a v sin i = 2.4 ± 0.4 km s −1 . Using T eff found from the ionization equilibrium parameters for all three stars, we found abundances of a number of other elements: Ti, Ni, Ca, Si and Cr. We show that uncertainties in the adopted values of T eff of 100 K and V t of 0.5 km s −1 change the abundances of elements up to 0.1 and 0.2 dex, respectively. Galactic abundance variations can generally be larger than this measurement precision and therefore we can study abundance variations throughout the Galaxy.

A detailed study of lithium in 107 CHEPS dwarf stars

“…For the case of the solar spectrum, the macroturbulent velocities mean that the measured widths of solar lines corresponds to a resolution, R = 70 K at 6700 Å. This formal resolution is limited by the presence in the solar atmosphere of macroturbulent motions with V mac = 1−2.6 km s −1 , see Pavlenko et al (2012) and references therein. We used this value of R for all our spectra.…”

“…Firstly, we determined the lithium abundances in the atmospheres of the stars in our sample in the framework of the thermodynamic equilibrium (LTE) approach following the Pavlenko et al (2012); Pavlenko (2017) algorithm. LTE model atmospheres and synthetic spectra were computed with the SAM12 and WITA6 programmes, respectively (see Pavlenko 1997Pavlenko , 2003.…”

Signals embedded in the radial velocity noise

“…Data from: (a) van Leeuwen (2007); (b) Teixeira et al (2009); (c) Soubiran et al (1998); (d) Mamajek & Hillebrand (2008); (e) Baliunas et al (1996); (f) Santos et al (2004); (g) Santos et al (2002); (h) Pepe et al (2011); (i) Gray et al (2006); (j) Pavlenko et al (2012). (Pavlenko et al 2012, and references therein), which could potentially make it an ideal target for searches for low-mass planets due to the relatively higher frequency of low-mass planets around low-metallicity stars (Jenkins et al 2013). Despite the fact that HD 10700 is a target star of several RV searches for planets around nearby stars (e.g.…”

Alma Observations of the Debris Disk of Solar Analog Τ Ceti

“…Tuomi et al (2013) acknowledge that the detected signals could also result from a combination of instrumental bias and stellar activity, although no further evidence is given to support these alternative interpretations. Also of note is the sub-Solar metallicity of τ Ceti, [Fe/H] = −0.55 ±0.05 dex (Pavlenko et al 2012), which makes it an interesting target for exoplanet searches due to the observed higher frequency of low-mass planets around low-metallicity stars ).…”