Publications (6)17.8 Total impact
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Article: Parent Stars of Extrasolar Planets VI: Abundance Analyses of 20 New Systems
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ABSTRACT: The results of new spectroscopic analyses of 20 recently reported extrasolar planet parent stars are presented. The companion of one of these stars, HD 10697, has recently been shown to have a mass in the brown dwarf regime; we find [Fe/H] $= +0.16$ for it. For the remaining sample, we derive [Fe/H] estimates ranging from -0.41 to $+0.37$, with an average value of $+0.18 \pm 0.19$. If we add the 13 stars included in the previous papers of this series and 6 other stars with companions below the 11 M$_{\rm Jup}$ limit from the recent studies of Santos et al., we derive $<$[Fe/H]$> = +0.17 \pm 0.20$. Among the youngest stars with planets with F or G0 spectral types, [Fe/H] is systematically larger than young field stars of the same Galactocentric distance by 0.15 to 0.20 dex. This confirms the recent finding of Laughlin that the most massive stars with planets are systematically more metal rich than field stars of the same mass. We interpret these trends as supporting a scenario in which these stars accreted high-Z material after their convective envelopes shrunk to near their present masses. Correcting these young star metallicities by 0.15 dex still does not fully account for the difference in mean metallicity between the field stars and the full parent stars sample. The stars with planets appear to have smaller [Na/Fe], [Mg/Fe], and [Al/Fe] values than field dwarfs of the same [Fe/H]. They do not appear to have significantly different values of [O/Fe], [Si/Fe], [Ca/Fe], or [Ti/Fe], though. Comment: 54 pages of text and tables; 12 figures; to be published in the Astronomical Journal10/2000; -
Article: The chemical composition of IRAS 05341+0852: a post-AGB F supergiant with 21 MU M emission
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ABSTRACT: An abundance analysis of the photosphere of the F-type Post-AGB candidate IRAS 05341+0852 is presented. The analysis of the spectra suggests that the atmospheric model: Teff=6500 K, log g=0.5, xi_ {t}=5 km s(-1) and [M/H]=-1.0, best represents the photosphere of the star. We find that the star is metal-poor ([Fe/H]=-0.9) and carbon-rich (C/O~1.9). Lithium, carbon, nitrogen, oxygen, aluminum and silicon are found to be overabundant. Most importantly this star has large overabundance of s-process elements which are as follows: [Y/Fe]=1.6, [Ba/Fe]=2.2, [La/Fe]=2.9, [Ce/Fe]=1.6, [Pr/Fe]=1.8, [Nd/Fe]=2.0, and [Sm/Fe]=1.7. These s-process enhancements are of similar magnitude to those seen in FG Sge. The enhancement of Li and Al are expected due to Hot Bottom Burning (HBB), in massive AGB stars. However, the low metallicity, heliocentric radial velocity (vr=25 km s(-1) ), and the high Galactic latitude (b=-12(o) ) suggest that IRAS 05341+0852 is a low-mass star. Also the [S/Fe]=0.2 indicates that the low Fe abundance is intrinsic and is not due to fractionation. The significant overabundance of lithium (log epsilon <=2.5) and aluminum ([Al/Fe]=1.4) in this star is a puzzle. Furthermore we have detected the C2 Phillips and CN Red bands in absorption. We find rotational temperatures, column densities, and expansion velocities which show that these lines are formed in the detached circumstellar dust shell (the AGB ejecta) and we find an expansion velocity of the AGB ejecta of v_exp = 10.8 +/- 1.0 km s(-1) .Astronomy and Astrophysics 11/1997; 328:331-338. · 4.59 Impact Factor -
Article: CCD Photometry and Spectroscopy of IRAS Sources Having Far-IR Colors Similar to Planetary Nebulae
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ABSTRACT: CCD imaging and BVRI photometry of 14 IRAS sources with far-IR colors similar to planetary nebulae and post-AGB stars are presented. Also results of optical and near-IR spectroscopy of 10 of these candidates are given. From the observed flux distribution from 0.4 μm to 100 μm we find the presence of hot dust component in addition to the cold dust component. The stellar temperatures, luminosities and distances are estimated. We also estimated the parameters of the circumstellar dust envelopes. These results suggest that the 14 IRAS sources considered here are associated with post-AGB supergiants.The Astronomical Journal 10/1996; 112:2053. · 4.03 Impact Factor -
Article: HD 105262: a high latitude metal-poor post-AGB. A supergiant with large proper motion.
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ABSTRACT: The large proper motion post-AGB supergiant stars are very rare. HD 105262 is a high galactic latitude (+72deg) A-type star with large proper motion (0.057arcsec/year) and high c1-index. Earlier, it was classified as a Field Horizontal Branch (FHB) star. Recently, Abt (1993) suggested that it may be a star similar to HR 4049. From an analysis of the spectra the chemical composition of HD 105262 has been determined. The elemental abundances are found to be, [Fe/H]=-2.2, [C/H]=-0.1, [N/H]=-0.2, [O/H]=-0.5, [α/H]=-1.6. The C/O=1.2 shows that HD 105262 is a carbon rich star. The chemical composition of HD 105262 indicates that it has gone through the AGB nucleosynthesis. The chemical composition, absolute magnitude, high galactic latitude and kinematics indicate that HD 105262 is a halo metal-poor post-AGB A supergiant. It is not a FHB star.Astronomy and Astrophysics 08/1996; 313:191-196. · 4.59 Impact Factor -
Article: Fading and variations in the spectrum of the central star of the very young planetary nebula SAO 244567 (Hen 1357).
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ABSTRACT: The optical spectrum of SAO 244567 obtained in 1971 shows that it was a post-AGB B1 or B2 supergiant at that time. It has turned into a planetary nebula (PN ) within the last 20 years. The IUE ultraviolet spectra obtained during the last seven years show that the central star is rapidly evolving. It is found that the central star of this young PN has faded by a factor of 2.83 within the last seven years. The terminal velocity of the stellar wind has decreased from -3500km/s in 1988 to almost zero in 1994. In 1988 the CIV (1550A) line which was a P-Cygni profile with strong absorption component has almost vanished by 1994. The UV absorption and nebular features show variations in strength. This may be due to the fading of the central star and also possibly to expansion of the nebula. These results suggest that in the central star the nuclear fuel is almost extinct as a result of post-AGB mass loss. The main stellar energy may be gravothermal energy. Typical for hydrogen-burning AGB remnants is a very fast drop in luminosity by an order of magnitude when the burning cannot be sustained any longer. These results suggest that the central star of this young PN is rapidly evolving to become a DA white dwarf. An alternative interpretation is that the present fading could be due to an episode of high mass loss, which is now just completed. If the ultraviolet fading was a factor of 2.83 from 1988 to 1995, the luminosity would remain the same if the temperature increased from 37500K to 47500K in the same period. It may b that these changes occur in steps which are triggered by episodic mass loss periods during the post-AGB evolution, and that the hydrogen burning has not stopped or stopped temporarily.Astronomy and Astrophysics 07/1995; 300:L25. · 4.59 Impact Factor -
Article: High resolution spectroscopy of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428)
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ABSTRACT: High resolution spectra covering the wavelength range 4900 Å to 8250 Å of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428) reveal absorption lines of C II, N II, O II, Al III, Si III and Fe III and a rich emission line spectrum consisting of H I, He I, C II, N I, O I, Mg II, Al II, Si II, V I, Mn I, Fe III, [Fe II] and [Cr II]. The presence of [N II] and [O I] lines and absence of [O III] indicate low excitation nebulae around these stars. The components of Na I absorption lines indicate the presence of neutral circumstellar envelopes in addition to the low excitation nebulae around these two hot post-AGB stars. The H$_\alpha$ lines show P-Cygni profiles indicating ongoing post-AGB mass loss. From the absorption lines we derived heliocentric radial velocities of 65.31 $\pm$ 0.34 km s$^{-1}$ and 27.55 $\pm$ 0.74 km s$^{-1}$ for IRAS 13266-5551 and IRAS 17311-4924 respectively. The high Galactic latitude and large radial velocity of IRAS 13266-5551 indicate that it belongs to the old disk population. Preliminary estimates for the CNO abundances in IRAS 13266-5551 are obtained.http://dx.doi.org/10.1051/0004-6361:20041506.
