F. X. de Araújo

STELLAR PARAMETERS AND METALLICITIES OF STARS HOSTING JOVIAN AND NEPTUNIAN MASS PLANETS: A POSSIBLE DEPENDENCE OF PLANETARY MASS ON METALLICITY*

The metal content of planet-hosting stars is an important ingredient that may affect the formation and evolution of planetary systems. Accurate stellar abundances require the determinations of reliable physical parameters, namely, the effective temperature, surface gravity, microturbulent velocity, and metallicity. This work presents the homogeneous derivation of such parameters for a large sample of stars hosting planets (N = 117), as well as a control sample of disk stars not known to harbor giant, closely orbiting planets (N = 145). Stellar parameters and iron abundances are derived from an automated analysis technique developed for this work. As previously found in the literature, the results in this study indicate that the metallicity distribution of planet-hosting stars is more metal rich by ~0.15 dex when compared to the control sample stars. A segregation of the sample according to planet mass indicates that the metallicity distribution of stars hosting only Neptunian-mass planets (with no Jovian-mass planets) tends to be more metal poor in comparison with that obtained for stars hosting a closely orbiting Jovian planet. The significance of this difference in metallicity arises from a homogeneous analysis of samples of FGK dwarfs which do not include the cooler and more problematic M dwarfs. This result would indicate that there is a possible link between planet mass and metallicity such that metallicity plays a role in setting the mass of the most massive planet. Further confirmation, however, must await larger samples.

Detailed Far-Ultraviolet to Optical Analysis of Four [WR] Stars

We present far-UV to optical analyses of four hydrogen-deficient central stars of planetary nebulae: BD +30 3639, NGC 40, NGC 5315, and NGC 6905. Using the radiative transfer code CMFGEN, we determined new physical parameters and chemical abundances for these stars. The results were analyzed in the context of the [WR] → PG 1159 evolution via the transformed radius-temperature (RT × T*) and H-R diagrams. NGC 5315 showed itself as an odd object among the previously analyzed central stars. Its temperature (~76 kK) is considerably lower than other early-type [WR] stars (~120-150 kK). From our models for NGC 5315 and NGC 6905, it is unclear if early-type [WR] stars have smaller C/He mass ratios than other spectral classes, as claimed in the literature. A ratio of ~0.8 is found for NGC 6905. We analyzed FUSE spectra of these stars for the first time and identified phosphorus in the spectra of BD +30 3639, NGC 40, and NGC 5315 through the doublet transition P V λλ1118, 1128 (3p 2Po-3s 2S). The Fe, Si, P, S, and Ne abundances were analyzed in the context of the nucleosynthesis occurring in previous evolutionary phases. We found evidence for Fe deficiency in BD +30 3639 and NGC 5315, and we determined a solar Si abundance for BD +30 3639 and NGC 40. Regarding P, an oversolar abundance in the NGC 5315 model was preferred. Upper limits for the S abundance were estimated. We found that Ne is overabundant in BD +30 3639. In the other stars, Ne is weak or undetectable. Our results are in agreement with theoretical predictions and show the usefulness of [WR] stars as test beds for nucleosynthesis calculations in the AGB and post-AGB phases.

On the hydrogen neutral outflowing disks of B[e] supergiants

The [Oi] line emission of the LMC B[e] supergiant R126 is modeled with an outflowing disk scenario. We find that hydrogen in the disk must be ionized by less...

Neutral material around the B[e] supergiant star LHA 115-S 65 - An outflowing disk or a detached Keplerian rotating disk?

Context. B[e] supergiants are surrounded by large amounts of hydrogen neutral material, traced by the emission in the optical [Oi] lines. This neutral material is most plausibly located within their dense, cool circumstellar disks, which are formed from the (probably non-spherically symmetric) wind material released by the star. Neither the formation mechanism nor the resulting structure and internal kinematics of these disks (or disk-like outflows) are well known. However, rapid rotation, lifting the material from the equatorial surface region, seems to play a fundamental role. Aims. The B[e] supergiant LHA 115-S 65 (in short: S 65) in the Small Magellanic Cloud is one of the two most rapidly rotating B[e] stars known. Its almost edge-on orientation allows a detailed kinematical study of its optically thin forbidden emission lines. With a focus on the rather strong [Oi] lines, we intend to test the two plausible disk scenarios: the outflowing and the Keplerian rotating disk. Methods. Based on high- and low-resolution optical spectra, we investigate the density and temperature structure in those disk regions that are traced by the [Oi] emission to constrain the disk sizes and mass fluxes needed to explain the observed [Oi] line luminosities. In addition, we compute the emerging line profiles expected for either an outflowing disk or a Keplerian rotating disk, which can directly be compared to the observed profiles. Results. Both disk scenarios deliver reasonably good fits to the line luminosities and profiles of the [Oi] lines. Nevertheless, the Keplerian disk model seems to be the more realistic one, because it also agrees with the kinematics derived from the large number of additional lines in the spectrum. As additional support for the presence of a high-density, gaseous disk, the spectrum shows two very intense and clearly double-peaked [Caii] lines. We discuss a possible disk-formation mechanism, and similarities between S 65 and the group of Luminous Blue Variables.

He II lambda-4686 in Eta Carinae: Collapse of the Wind-Wind Collision Region During Periastron Passage

The periodic spectroscopic events in ? Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of ? Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II ?4686 emission line (L ~ 310 L ?) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primarys wind probably explain the flare-like behavior of both the X-ray and He II ?4686 light curves. After a short-lived minimum, He II ?4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the surface of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondarys wind and the clumps in the primarys wind.

On the evolutionary stage of the unclassified B[e] star CD-42°11721

The star CD-42 ◦ 11721 is a curious B[e] star sometimes pointed as an evolved B[e] supergiant and sometimes as a young HAeBe star, due to very uncertain or even unknown stellar parameters, especially the distance. In this paper, we present new data gained from high-resolution optical spectroscopy and a detailed description of infrared (IR) data of this star. We present a qualitative study of the numerous emission lines in our optical spectra and the classification of their line profiles, which indicate a non-spherically symmetric circumstellar environment. The first real detection of numerous [Fe II] emission lines and of many other permitted and forbidden emission lines is reported. From our optical data, we derive an effective temperature of T eff = 14 000 ± 1000 K, a radius of R∗ = 17.3 ± 0.6 R� , as well as a luminosity of L∗ = (1.0 ± 0.3) × 10 4 L� . We advocate that CD-42 ◦ 11721 might be a post-main-sequence object, even though a pre-main-sequence nature cannot be ruled out due to the uncertain distance. We further found that the spectral energy distribution in the optical and IR can best be fitted with an outflowing disc-forming wind scenario rather than with a spherical symmetric envelope or with a flared disc, supporting our tentative classification as a B[e] supergiant.

The galactic unclassified B[e] star HD 50138 - I. A possible new shell phase

Context. The observed spectral variation of HD 50138 has led different authors to classify it in a very wide range of spectral types and luminosity classes (from B5 to A0 and III to Ia) and at different evolutionary stages as either HAeBe star or classical Be. Aims. Based on new high-resolution optical spectroscopic data from 1999 and 2007 associated to a photometric analysis, the aim of this work is to provide a deep spectroscopic description and a new set of parameters for this unclassified southern B[e] star and its interstellar extinction. Methods. From our high-resolution optical spectroscopic data separated by 8 years, we perform a detailed spectral description, presenting the variations seen and discussing their possible origin. We derive the interstellar extinction to HD 50138 by taking the influences of the circumstellar matter in the form of dust and an ionized disk into account. Based on photometric data from the literature and the new Hipparcos distance, we obtain a revised set of parameters for HD 50138. Results. Because of the spectral changes, we tentatively suggest that a new shell phase could have taken place prior to our observations in 2007. We find a color excess value of E(B − V) = 0.08 mag, and from the photometric analysis, we suggest that HD 50138 is a B6-7 III-V star. A discussion of the different evolutionary scenarios is also provided.

The enigmatic B[e]-star Henize 2-90: the non-spherical mass loss history from an analysis of forbidden lines

We study the optical spectrum of the exciting B[e] star Hen 2-90 based on new high-resolution observations that cover the innermost 2´´ of this object whose total extent is more than 3´´. Our investigation is split in two parts, (i) a qualitative study of the presence of the numerous emission lines and classification of their line profiles, which indicate a circumstellar environment of high complexity, (ii) and a quantitative analysis of numerous forbidden lines, e.g. [Oi], [Oii], [Oiii], [Sii], [Siii], [Ariii], [Clii], [Cliii], and [Nii]. We find correlation between the different ionization states of the elements and the velocities derived from the line profiles: the highly ionized atoms have the highest outflow velocity, while the neutral lines have the lowest. The recent HST image of Hen 2-90 (Sahai et al. 2002, ApJ, 573, L123) reveals a bipolar, highly ionized region, a neutral disk-like structure, and an intermediate region of moderate ionization. This HST image covers about the same innermost regions as our observations. When combining the velocity information with the HST image of Hen 2-90, it seems that a non-spherical stellar wind model is a good option to explain the ionization and spatial distribution of the circumstellar material. Such a wind might expand into the cavity formed during the AGB phase of the star, which is still visible as a large nebula, seen e.g. on H α plates. We modelled the forbidden lines under the assumption of a non-spherically symmetric wind that can be split into a polar, a disk forming, and an intermediate wind, based on the HST image. We find that in order to fit the observed line luminosities, the mass flux, surface temperature, and terminal wind velocities need to be latitude dependent, which might be explained in terms of a rapidly rotating central star. A rotation speed of 75–80% of the critical velocity was derived from the terminal velocities extracted from the observed line wings considering the inclination of the system as suggested from the HST image. The total mass loss rate of the star was determined to be on the order of

The

3\times 10^{-5}~M_{\odot}

\eta

yr -1 . The combination of this wind scenario and the underabundance of C, O, and N in comparison to the solar abundance of S, Ar, and Cl might be explained in terms of a rapidly rotating post-AGB star.