Arunas Kucinskas

Broad-band photometric colors and effective temperature calibrations for late-type giants - I. Z = 0.02

We investigate the effects of metallicity on the broad-band photometric colors of late-type giants, and make a comparison of synthetic colors with observed photometric properties of late-type giants over a wide range of effective temperatures (T-eff = 3500- 4800K) and gravities (log g = 0.0-2.5), at [M/H] = -1.0 and -2.0. The influence of metallicity on the synthetic photometric colors is small at effective temperatures above similar to 3800K, but the effects grow larger at lower T-eff,T- due to the changing effciency of molecule formation which reduces molecular opacities at lower [M/H]. To make a detailed comparison of the synthetic and observed photometric colors of late type giants in the T-eff-color and color-color planes (which is done at two metallicities, [M/H] = -1.0 and -2.0), we derive a set of new T-eff-log g-color relations based on synthetic photometric colors, at [M/H] = -0.5, -1.0, -1.5, and -2.0. These relations are based on the T-eff- log g scales that we derive employing literature data for 178 late-type giants in 10 Galactic globular clusters (with metallicities of the individual stars between [M/H] = -0.7 and -2.5), and synthetic colors produced with the PHOENIX, MARCS and ATLAS stellar atmosphere codes. Combined with the T-eff- log g-color relations at [M/H] = 0.0 (Kucinskas et al. 2005), the set of new relations covers metallicities [M/H] = 0.0... -2.0 ([M/H] = 0.5), effective temperatures T-eff = 3500... 4800 K (T-eff = 100K), and gravities log g = - 0.5... 3.0. The new T-eff- log g-color relations are in good agreement with published T-eff-color relations based on observed properties of late-type giants, both at [M/H] = -1.0 and -2.0. The differences in all T-eff- color planes are typically well within similar to 100K. We find, however, that effective temperatures predicted by the scales based on synthetic colors tend to be slightly higher than those resulting from the T-eff- color relations based on observations, with the offsets up to similar to 100 K. This is clearly seen both at [M/H] = -1.0 and -2.0, especially in the T-eff-(B - V) and T-eff-(V - K) planes. The consistency between T-eff- log g-color scales based on synthetic colors calculated with different stellar atmosphere codes is very good, with typical differences being well within. Delta T-eff similar to 70 K at [M/H] = - 1.0 and. T-eff similar to 40 K at [M/H] = -2.0. (Less)

Isocam observations of globular clusters in the Magellanic Clouds: The data

Seventeen globular clusters in the Large and Small Magellanic Clouds were observed in the mid-infrared wavelength region with the ISOCAM instrument on board the Infrared Space Observatory (ISO). Observations were made using the broadband filters LW1, LW2, and LW10, corresponding to the effective wavelengths of 4.5, 6.7, and 12 mum, respectively. We present the photometry of point sources in each cluster, as well as their precise positions and finding charts.

3D hydrodynamical CO5BOLD model atmospheres of late-type giants: stellar abundances from molecular lines

We investigate the influence of convection on the formation of molecular spectral lines in the atmospheres of late-type giants. For this purpose we use the 3D hydrodynamical CO5BOLD and classical 1D LHD stellar atmosphere codes and synthesize a number of fictitious lines belonging to a number of astrophysically relevant molecules, C2, CH, CN, CO, NH, OH. We find that differences between the abundances obtained from molecular lines using the 3D and 1D model atmospheres are generally small at [M/H]=0.0, but they quickly increase at sub-solar metallicities where for certain molecules they may reach -2.0 dex. The 3D-1D abundance differences show a significant dependence on the spectral line parameters, such as wavelength and excitation potential. Our comparison, therefore, reveals a complex interplay between the spectral line formation and convection that can not be properly accounted for with the classical 1D model atmospheres.

Chemical abundances in metal-poor giants: limitations imposed by the use of classical 1D stellar atmosphere models

In this work we have used 3D hydrodynamical (CO5BOLD) and 1D hydrostatic (LHD) stellar atmosphere models to study the importance of convection and horizontal temperature inhomogeneities in stellar abundance work related to late-type giants. We have found that for a number of key elements, such as Na, Mg, Si, Ca, Ti, Fe, Ni, Zn, Ba, Eu, differences in abundances predicted by 3D and 1D models are typically minor (< 0.1 dex) at solar metallicity. However, at [M/H] = -3 they become larger and reach to -0.5...-0.8 dex. In case of neutral atoms and fixed metallicity, the largest abundance differences were obtained for the spectral lines with lowest excitation potential, while for ionized species the largest 3D-1D abundance differences were found for lines of highest excitation potential. The large abundance differences at low metallicity are caused by large horizontal temperature fluctuations and lower mean temperature in the outer layers of the 3D hydrodynamical model compared with its 1D counterpart.

Abundances of Mg and K in the atmospheres of turn-off starsin Galactic globular cluster 47 Tucanae

We determined abundances of Mg and K in the atmospheres of 53 (Mg) and 75 (K) turn-off (TO) stars of the Galactic globular cluster 47 Tuc. The obtained abundances, together with those of Li, O, and Na, were used to search for possible relations between the abundances of K and other light elements, Li, O, Na, and Mg, as well as the connections between the chemical composition of TO stars and their kinematical properties. Abundances of Mg and K were determined using archival VLT FLAMES/GIRAFFE spectra, in combination with the 1D NLTE spectral synthesis methodology. Spectral line profiles were computed with the MULTI code, using ATLAS9 stellar model atmospheres. We also utilized 3D hydrodynamical CO5BOLD and 1D hydrostatic LHD model atmospheres for computing 3D-1D LTE abundance corrections for the spectral lines of Mg and K, in order to assess the influence of convection on their formation in the atmospheres of TO stars. The determined average abundance-to-iron ratios and their RMS variations due to star-to-star abundance spreads were

Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?

\langle{\rm[Mg/Fe]}\rangle^{\rm 1D NLTE}=0.47\pm0.12

Radiation-hydrodynamics simulations of surface convection in low-mass stars: connections to stellar structure and asteroseismology

, and

Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

\langle{\rm [K/Fe]}\rangle^{\rm 1D NLTE}=0.39\pm0.09

Convection and observable properties of late-type giants

. Although the data suggest the possible existence of a weak correlation in the [K/Fe]-[Na/Fe] plane, its statistical significance is low. No statistically significant relations between the abundance of K and other light elements were detected. Also, we did not find any significant correlations or anti-correlations between the [Mg/Fe] and [K/Fe] ratios and projected distance from the cluster center. Similarly, no relations between the absolute radial velocities of individual stars and abundances of Mg and K in their atmospheres were detected. The 3D-1D abundance corrections were found to be small (

Star Formation Histories with Gaia: the Galaxy and Beyond

\leq 0.1