Showing papers by "Katia Cunha published in 2006"

A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: Variation of the Metallicity Distribution Function Along the Sagittarius Stream

Abstract: We present reliable measurements of the metallicity distribution function (MDF) at different points along the tidal stream of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy, based on high resolution, echelle spectroscopy of candidate M giant members of the Sgr system. The Sgr MDF is found to evolve significantly from a median [Fe/H] ~-0.4 in the core to ~-1.1 dex over a Sgr leading arm length representing ~2.5-3.0 Gyr of dynamical (i.e. tidal stripping) age. This is direct evidence that there can be significant chemical differences between current dSph satellites and the bulk of the stars they have contributed to the halo. Our results suggest that Sgr experienced a significant change in binding energy over the past several Gyr, which has substantially decreased its tidal boundary across a radial range over which there must have been a significant metallicity gradient in the progenitor galaxy. By accounting for MDF variation along the debris arms, we approximate the MDF Sgr would have had several Gyr ago. We also analyze the MDF of a moving group of M giants we previously discovered towards the North Galactic Cap having opposite radial velocities to the infalling Sgr leading arm stars there and propose that most of these represent Sgr trailing arm stars overlapping the Sgr leading arm in this part of the sky. If so, these trailing arm stars further demonstrate the strong MDF evolution within the Sgr stream.

Neon Abundances in B Stars of the Orion Association: Solving the Solar Model Problem?

Abstract: We report on non-LTE Ne abundances for a sample of B-type stellar members of the Orion association. The abundances were derived by means of non-LTE fully metal-blanketed model atmospheres and extensive model atoms with updated atomic data. We find that these young stars have a very homogeneous abundance of A(Ne) = 8.11 ± 0.04. This abundance is higher by ~0.3 dex than the currently adopted solar value, A(Ne) = 7.84, which is derived from lines produced in the corona and active regions. The general agreement between the abundances of C, N, and O derived for B stars with the solar abundances of these elements derived from three-dimensional hydrodynamical models atmospheres strongly suggests that the abundance patterns of the light elements in the Sun and B stars are broadly similar. If this hypothesis is true, then the Ne abundance derived here will help to reconcile solar models with helioseismological observations.

Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way

Abstract: This paper presents a homogeneous study of abundances in a sample of 79 northern Galactic planetary nebulae (PNe) whose morphological classes have been uniformly determined. Ionic abundances and plasma diagnostics were derived from selected optical line strengths in the literature, and elemental abundances were estimated with the ionization correction factor developed by Kingsbourgh & Barlow in 1994. We compare the elemental abundances to the final yields obtained from stellar evolution models of low- and intermediate-mass stars, and we confirm that most bipolar PNe have high nitrogen and helium abundance and are the likely progeny of stars with main-sequence mass greater than 3 M☉. We derive = 0.27 and discuss the implication of such a high ratio in connection with the solar neon abundance. We determine the Galactic gradients of oxygen and neon and found Δ log(O/H)/ΔR = -0.01 dex kpc-1 and Δ log(Ne/H)/ΔR = -0.01 dex kpc-1. These flat PN gradients are irreconcilable with Galactic metallicity gradients flattening with time.

Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way

Abstract: This paper presents a homogeneous study of abundances in a sample of 79 northern galactic planetary nebulae whose morphological classes have been uniformly determined. Ionic abundances and plasma diagnostics were derived from selected optical line strengths in the literature, and elemental abundances were estimated with the Ionization Correction Factor developed by Kingsbourgh & Barlow (1994). We compare the elemental abundances to the final yields obtained from stellar evolution models of low-and intermediate-mass stars, and we confirm that most Bipolar planetary nebulae have high nitrogen and helium abundance, and are the likely progeny of stars with main-sequence mass larger than 3 solar masses. We derive =0.27, and discuss the implication of such a high ratio in connection with the solar neon abundance. We determine the galactic gradients of oxygen and neon, and found Delta log (O/H)/Delta R=-0.01 dex/kpc$ and Delta log (Ne/H)/Delta R=-0.01 dex/kpc. These flat PN gradients do not reconcile with galactic metallicity gradients flattening with time.

Neon Abundances in B-Stars of the Orion Association: Solving the Solar Model Problem?

Abstract: We report on non-LTE Ne abundances for a sample of B-type stellar members of the Orion Association. The abundances were derived by means of non-LTE fully metal-blanketed model atmospheres and extensive model atoms with updated atomic data. We find that these young stars have a very homogeneous abundance of A(Ne) = 8.27 +/- 0.05. This abundance is higher by ~0.4 dex than currently adopted solar value, A(Ne)=7.84, which is derived from lines produced in the corona and active regions. The general agreement between the abundances of C, N, and O derived for B stars with the solar abundances of these elements derived from 3-D hydrodynamical models atmospheres strongly suggests that the abundance patterns of the light elements in the Sun and B stars are broadly similar. If this hypothesis is true, then the Ne abundance derived here is the same within the uncertainties as the value required to reconcile solar models with helioseismological observations.