Chemical composition of A-F type post-AGB candidates

Giridhar, Sunetra; Molina, R. E.; Ferro, A. Arellano; Selvakumar, G.

doi:10.1111/j.1365-2966.2010.16696.x

Cited by 10 publications

(12 citation statements)

References 104 publications

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“…It is clear that elements with a FIP of 8 eV or lower show systematic depletion. This phenomenon has also been observed in the stars CpD–625,428 (Giridhar et al ) and IRAS 18321 − 1401 (Molina et al ). The smooth anticorrelation between the abundances and the FIP effect suggests that the removed elements systematically correspond to species with the first ionized states.…”

Section: Individual Abundancessupporting

confidence: 62%

Chemical composition of post‐AGB star candidates

2018

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We present a high-resolution detailed abundance analysis for a sample of six post-Asymptotic Giant Branch (AGB) candidate stars, five of them had not been studied spectroscopically in the optical region. All the analyzed objects are Infrared Astronomical Satellite (IRAS) sources identified as possible post-AGB on the two-color IRAS diagram. We find three objects with clear signs of evolved stars; IRAS 05338 − 3051 shows abundances similar to the RV Tauri V453 Oph; the lower-luminosity stars IRAS 18025 − 3906 are O-rich without s-process enrichment and IRAS 18386 − 1253 shows a moderate selective depletion of refractory elements generally seen in post-AGB stars (PAGBs), which show midinfrared excess; they may evolve post-Red Giant Branch (RGB) objects, in which case these would be the first Galactic counterparts of post-RGB objects observed in the Large and Small Magellanic Clouds (Kamath et al. , 2015. On the other hand, IRAS 02528 + 4350 seems to be a moderately metal-poor young object and IRAS 20259 + 4206 also seems to be a young object showing carbon deficiency; however, an analysis with better spectra might be in order to clarify its evolutionary state. Finally, our abundance calculations for the binary PAGB IRAS 17279 − 1119 are found in good agreement with those of De Smedt et al. (2016).

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Section: Individual Abundancessupporting

confidence: 62%

Chemical composition of post‐AGB star candidates

2018

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“…From this plot, we infer that the initial metallicity of the star is −0.7 dex. [Another such star showing selective depletion of refractory elements without IR excess is HD 105262 (Giridhar, Lambert & Guillermo Gonzalez 2010), which has the temperature of 8000 K and [Fe/H] of −1.8 dex. ]…”

Section: Resultsmentioning

confidence: 99%

“… 5 Giridhar et al (2010), 6 Maas et al (2005), 7 Van Winckel (1997), 8 Giridhar & Arellano Ferro (2005), …”

Section: Discussionmentioning

confidence: 99%

Chemical composition of a sample of candidate post-asymptotic giant branch stars

Rao¹,

Giridhar²,

Lambert³

2011

Monthly Notices of the Royal Astronomical Society

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We have derived elemental abundances for a sample of nine IRAS sources with colours similar to those of post-asymptotic giant branch (post-AGB) stars. For IRAS 01259+6823, IRAS 05208−2035, IRAS 04535+3747 and IRAS 08187−1905, this is the first detailed abundance analysis based upon high-resolution spectra. Mild indication of s-processing for IRAS 01259+6823, IRAS 05208−2035 and IRAS 08187−1905 has been found and a more comprehensive study of s-process-enhanced objects IRAS 17279−1119 and IRAS 22223+4327 has been carried out.We have also made a contemporary abundance analysis of the high Galactic latitude supergiants BD+39• 4926 and HD 107369. The former is heavily depleted in refractories and estimated [Zn/H] of −0.7 dex most likely gives initial metallicity of the star. For HD 107369 the abundances of α and Fe-peak elements are similar to those of halo objects and moderate deficiency of s-process elements is seen. IRAS 07140−2321, despite being a short-period binary with a circumstellar shell, does not exhibit selective depletion of refractory elements.We have compiled the stellar parameters and abundances for post-AGB stars with s-process enhancement, those showing significant depletion of condensable elements and those showing neither. The compilation shows that the s-process-enhanced group contains a very small number of binaries, and observed [α/Fe] are generally similar to thick-disc values. It is likely that they represent AGB evolution of single stars.The compilation of the depleted group contains a larger fraction of binaries and generally supports the hypothesis of dusty discs surrounding binary post-AGB stars inferred via the shape of their spectral energy distribution and mid-infrared interferometry. IRAS 07140−2321 and BD+39• 4926 are difficult to explain with this scenario and indicate the existence of an additional parameter/condition needed to explain the depletion phenomenon. However, the conditions for discernible depletion, minimum temperature of 5000 K and initial metallicity larger than −1.0 dex found from our earlier work still serve as useful criteria.

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“…Some examples of these can be seen in Fig. 1 at 4383Å and 4404Å, and correspond to Fe i species that are used as spectral type indicators due to their temperature sensitivity (Giridhar 2010). The broad peak of the Fe i lines indicate a change in temperature of the star.…”

Section: Analysis and Discussionmentioning

confidence: 99%

The changing face of α Centauri B: probing plage and stellar activity in K dwarfs

Thompson

Watson

Mooij

et al. 2017

Monthly Notices of the Royal Astronomical Society: Letters

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A detailed knowledge of stellar activity is crucial for understanding stellar dynamos, as well as pushing exoplanet radial-velocity detection limits towards Earth analogue confirmation. We directly compare archival HARPS spectra taken at the minimum in α Cen B's activity cycle to a high-activity state when clear rotational modulation of log R ′ H K is visible. Relative to the inactive spectra, we find a large number of narrow pseudo-emission features in the active spectra with strengths that are rotationally modulated. These features most likely originate from plage, spots, or a combination of both. They also display radial velocity variations of ∼300 m s −1 -consistent with an active region rotating across the stellar surface. Furthermore, we see evidence that some of the lines originating from the 'active immaculate' photosphere appear broader relative to the 'inactive immaculate' case. This may be due to enhanced contributions of e.g. magnetic bright points to these lines, which then causes additional line broadening. More detailed analysis may enable measurements of plage and spot coverage using single spectra in the future.

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Chemical composition of A-F type post-AGB candidates

Cited by 10 publications

References 104 publications

Chemical composition of post‐AGB star candidates

Chemical composition of post‐AGB star candidates

Chemical composition of a sample of candidate post-asymptotic giant branch stars

The changing face of α Centauri B: probing plage and stellar activity in K dwarfs

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