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The periodic spectroscopic events in eta 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 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 eta Carinae with 5 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 Lsun) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primary's 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 ne, Comment: Two-column style; 18 pages, 10 figures, and 1 table. Accepted for publication in ApJ

The metal content of planet hosting stars is an important ingredient which 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., Comment: 41 pages, 10 figures, 6 tables, accepted for publication in ApJ

The study of chemical abundances in stars with planets is an important ingredient for the models of formation and evolution of planetary systems. In order to determine accurate abundances, it is crucial to have a reliable set of atmospheric parameters. In this work, we describe the homogeneous determination of effective temperatures, surface gravities and iron abundances for a large sample of stars with planets as well as a control sample of stars without giant planets. Our results indicate that the metallicity distribution of the stars with planets is more metal rich by ~ 0.13 dex than the control sample stars., Comment: 2 pages, 1 figure, to appear in Proceedings of IAU Symposium 265, Chemical Abundances in the Universe: Connecting First Stars to Planets

Aims. We study the geometry of the circumstellar environment of the B[e] supergiant star GG Car. Methods. We present observations acquired using the IAGPOL imaging polarimeter in combination with the Eucalyptus-IFU spectrograph to obtain spectropolarimetric measurements of GG Car across Halpha at two epochs. Polarization effects along the emission line are analysed using the Q-U diagram. In particular, the polarization position angle (PA) obtained using the line effect is able to constrain the symmetry axis of the disk/envelope. Results. By analysing the fluxes, GG Car shows an increase in its double-peaked Halpha line emission relative to the continuum within the interval of our measurements (~43 days). The depolarization line effect around Halpha is evident in the Q-U diagram for both epochs, confirming that light from the system is intrinsically polarized. A rotation of the PA along Halpha is also observed, indicating a counter-clockwise rotating disk. The intrinsic PA calculated using the line effect (~85deg) is consistent between our two epochs, suggesting a clearly defined symmetry axis of the disk., Comment: 5 pages, 3 figures, accepted by Astronomy and Astrophysics

High-resolution (R = 143,000), high signal-to-noise (S/N = 700-1100) Gemini-S bHROS spectra have been analyzed in a search for 6Li in 5 stars which host extrasolar planets. The presence of detectable amounts of 6Li in these mature, solar-type stars is a good monitor of accretion of planetary disk material, or solid bodies themselves, into the outer layers of the parent stars. Detailed profile-fitting of the Li I resonance doublet at lambda 6707.8 A reveals no detectable amounts of 6Li in any star in our sample. The list of stars analyzed includes HD 82943 for which 6Li has been previouly detected at the level of 6Li/7Li = 0.05 +/- 0.02. The typical limits in the derived isotopic fraction are 6Li/7Li <= 0.00-0.02. These upper limits constrain the amount of accreted material to less than ~ 0.02 to 0.5 Jovian masses. The presence of detectable amounts of 6Li would manifest itself as a red asymmetry in the Li I line-profile and the derived upper limits on such asymmetries are discussed in light of three-dimensional hydrodynamic model atmospheres, where convective motions also give rise to slight red asymmetries in line profiles., Comment: 33 pages, 7 figures, 6 tables, accepted for publication in ApJ

Our goal is to study the physical properties of the circumstellar environment of young stellar objetcs (YSOs). In particular, the determination of the scattering mechanism can help to constrain the optical depth of the disk and/or envelope in the near infrared. We used the IAGPOL imaging polarimeter along with the CamIV infrared camera at the LNA observatory to obtain near infrared polarimetry measurements at the H band of a sample of optically visible YSOs, namely, eleven T Tauri stars and eight Herbig Ae/Be stars. An independent determination of the disk (or jet) orientation was obtained for twelve objects from the literature. The circumstellar optical depth could be then estimated comparing the integrated polarization position angle (PA) with the direction of the major axis of the disk projected in the plane of the sky. In general, optically thin disks have polarization PA perpendicular to the disk plane. In contrast, optically thick disks produce polarization PA parallel to the disks. Among the T Tauri stars, three are consistent with optically thin disks (AS 353A, RY Tau and UY Aur) and five with optically thick disks (V536 Aql, DG Tau, DO Tau, HL Tau and LkHalpha 358). Among the Herbig Ae/Be stars, two stars show evidence of optically thin disk (Hen 3-1191 and VV Ser) and two of optically thick disks (PDS 453 and MWC 297). Our results seem consistent with the fact that optically thick disks at near infrared bands are associated more likely with younger YSOs. Marginal evidence of polarization reversal is found in RY Tau, RY Ori, WW Vul, and UY Aur. On the first three cases this feature can be associated to the UXOR phenomenon. Correlations with the IRAS colours and the spectral index yielded evidence of an evolutionary segregation with the disks tend to be optically thin when they are older., Comment: 15 pages, 15 figures, accepted in Astronomy and Astrophysics

Aims: To detect line effects using spectropolarimetry in order to find evidence of rotating disks and their respective symmetry axes in T Tauri stars. Methods: We used the IAGPOL imaging polarimeter along with the Eucalyptus-IFU to obtain spectropolarimetric measurements of the T Tauri stars RY Tau (two epochs) and PX Vul (one epoch). Evidence of line effects showing a loop on the Q-U diagram favors a compact rather than an extended source for the line photons in a rotating disk. In addition, the polarization position angle (PA) obtained using the line effect can constrain the symmetry axis of the disk. Results: RY Tau shown a variable Halpha double peak on 2004-2005 data. Polarization line effect is evident on the Q-U diagram for both epochs confirming a clockwise rotating disk. A single loop is evident on 2004 changing to a linear excursion plus a loop on 2005. Interestingly, the intrinsic PA calculated using the line effect is consistent between our two epochs (~167deg). An alternative intrinsic PA computed from the interstellar polarization corrected continuum and averaged between 2001-2005 yielded a PA 137deg. This last value is closer to be perpendicular to the observed disk direction (~25deg) as expected by single scattering in an optically thin disk. For PX Vul, we detected spectral variability in Halpha along with non-variable continuum polarization when compared with previous data. The Q-U diagram shows a well-defined loop in Halpha associated to a counter-clockwise rotating disk. The symmetry axis inferred by the line effect has a PA~91deg (with an ambiguity of 90deg). Our results confirm previous evidence that the emission line in T Tauri stars has its origin in a compact source scattered off a rotating accretion disk., Comment: 6 pages, 5 figures. Accepted for publication in Astronomy and Astrophysics

The ultraviolet spectra of all ``weak emission line central stars of planetary nebulae'' (WELS) with available IUE data are presented and discussed. We performed line identifications, equivalent width and flux measurements for several features in their spectra. We found that the WELS can be divided in three different groups regarding their UV: i) Strong P-Cygni profiles (mainly in CIV 1549); ii) Weak P-Cygni features and iii) Absence of P-Cygni profiles. The last group encompasses stars with a featureless UV spectrum or with intense emission lines and a weak continuum, which are most likely of nebular origin. We have measured wind terminal velocities for all objects presenting P-Cygni profiles in N V 1238 and/or C IV 1549. The results obtained were compared to the UV data of the two prototype stars of the [WC]-PG 1159 class, namely, A30 and A78. For WELS presenting P-Cygnis, most of the terminal velocities fall in the range ~1000-1500 km/s, while [WC]-PG 1159 stars possess much higher values, of about 3000 km/s. The [WC]-PG1159 stars are characterized by intense, simultaneous P-Cygni emissions in the 1150-2000A interval of N V 1238, O V 1371 and C IV 1549. In contrast, we found that O V 1371 is very weak or absent in the WELS spectra. On the basis of the ultraviolet spectra alone, our findings indicate that [WC]-PG 1159 stars are distinct from the WELS, contrary to previous claims in the literature., Comment: 29 pages, 5 figures. Accepted by the AJ

We derive projected rotational velocities (vsini) for a sample of 156 Galactic OB star members of 35 clusters, HII regions, and associations. The HeI lines at $\lambda\lambda$4026, 4388, and 4471A were analyzed in order to define a calibration of the synthetic HeI full-widths at half maximum versus stellar vsini. A grid of synthetic spectra of HeI line profiles was calculated in non-LTE using an extensive helium model atom and updated atomic data. The vsini's for all stars were derived using the He I FWHM calibrations but also, for those target stars with relatively sharp lines, vsini values were obtained from best fit synthetic spectra of up to 40 lines of CII, NII, OII, AlIII, MgII, SiIII, and SIII. This calibration is a useful and efficient tool for estimating the projected rotational velocities of O9-B5 main-sequence stars. The distribution of vsini for an unbiased sample of early B stars in the unbound association Cep OB2 is consistent with the distribution reported elsewhere for other unbound associations., Comment: Accepted for publication in The Astronomical Journal

Aims: To investigate the spectra and the evolutionary stages of two peculiar emission-line stars: RJHA 49 and SS73 21. Methods: We used low and high resolution optical data. Line identifications and measurements were performed for several features in their spectra. Results: For each object, we have derived the extinction and the excitation temperature from a set of [Fe II] lines, and the electron density from [N II] lines. For RJHA 49, no detailed spectroscopic study was done so far. Regarding SS73 21, our low resolution spectrum have confirmed the main characteristics found in previous works. On the other side, from our high resolution data, we have found that the Halpha line presents a double-peak, in contrast with the suggestion in the literature that it should reveal a P-Cygni profile. Surprisingly, we found a few He I transitions resembling P-Cygni profiles (e.g. He I 5876), directly suggesting that mass loss is active in SS73 21. We also discussed the nature of these two objects based on the data obtained. Although the evolutionary status of SS73 21 seems well established from previous studies (a proto-planetary nebula), the situation for RJHA 49 is not so clear mainly due to its unknown distance. However, from the strength of [N II] 5754 relative to [O I] 6300, the possibility of RJHA 49 being a LBV object is reduced, and a B[e]-supergiant or a proto-planetary nebula status is more plausible., Comment: 8 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics

The [O I] 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 than 0.1%, meaning that the disk material is predominantly neutral. The free-free emission is calculated from the polar wind, and the minimum density contrast between disk and polar wind is found to be ~10., Comment: 2 pages, to appear in Rev. Mex. Astron. Astrof. Conf. Ser., ed. P. Benaglia, G. Bosch and C.E. Cappa, Proceedings of the workshop on Massive Stars held in Carilo, Argentina, Dec. 11-14, 2006

We present far-UV to optical analyses of four hydrogen deficient central stars of planetary nebulae: BD+303639, 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(Rt)-temperature and HR diagrams. NGC 5315 showed itself as an odd object among the previously analyzed central stars. Its temperature (~76kK) is considerably lower than other early-type [WR] stars (~120-150kK). 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+303639, NGC 40 and NGC 5315 through the transitions P V 1118,1128. 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 from fits to the Si IV lines we determined a solar Si abundance for BD+303639 and NGC 40. For phosphorus, an oversolar abundance in the NGC 5315 model was preferred, while in the other stars a solar phosphorus abundance cannot be discarded. Regarding sulfur, we estimated upper limits for its abundance, since no conspicuous lines can be seen in the observed spectra. We found that Ne is overabundant in BD +30 3639. In the other stars, Ne is weak or undetectable and upper limits for its abundance were estimated. Our results are in agreement with theoretical predictions and show the usefulness of [WR] stars as testbeds for nucleosynthesis calculations in the AGB and post-AGB phases.(abridged), Comment: ApJ, in press, 44 pages, 14 figures. For full resolution version see http://www.journals.uchicago.edu/ApJ/journal/preprints/ApJ65628.preprint.pdf

HD 326823 is a peculiar emission line object. In the literature it was considered as a pre-WN candidate. Based mainly on high resolution data, obtained with the FEROS spectrograph, we made an atlas covering 3800-9200A region. This atlas confirms the presence of several strong HeI lines and numerous N lines. There is also a deficiency of H, indicating that this object is indeed in an evolved stage. In addition, with low resolution spectra, we obtained intensities of several lines., Comment: 16 pages, 10 figures, 8 tables, accepted for ApJSS

Coude spectroscopic data of a poorly-studied peculiar supergiant, HD327083, are presented. Halpha and Hbeta line profiles have been fitted employing a non-LTE code adequate for spherically expanding atmospheres. Line fits lead to estimates of physical parameters. These parameters suggest that HD327083 may be close to the Luminous Blue Variable phase but it is also possible that it could be a B[e] Supergiant., Comment: 4 pages, 4 figures, Accepted for publication in A&A Letter

A set of 45 dust envelopes of carbon stars has been modeled. Among them, 34 were selected according to their dust envelope class (as suggested by Sloan, Little-Marenin & Price, 1998) and 11 are extreme carbon stars. The models were performed using a code that describes the radiative transfer in dust envelopes considering core/mantle grains composed by an alpha-SiC core and an amorphous carbon (A.C.) mantle. In addition, we have also computed models with a code that considers two kinds of grains - alpha-SiC and A.C. - simultaneously. Core-mantle grains seem to fit dust envelopes of evolved carbon stars, while two homogeneous grains are more able to reproduce thinner dust envelopes. Our results suggest that there exists an evolution of dust grains in the carbon star sequence. In the beginning of the sequence, grains are mainly composed of SiC and amorphous carbon; with dust envelope evolution, carbon grains are coated in SiC. This phenomena could perhaps explain the small quantity of SiC grains observed in the interstellar medium. However, in this work we consider only alpha-SiC grains, and the inclusion of beta-SiC grains can perhaps change some of there results., Comment: Accepted for publication in A&A