High resolution spectroscopy of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428)

Astronomy and Astrophysics (Impact Factor: 4.48). 03/2005; 431(3). DOI: 10.1051/0004-6361:20041506

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.

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    ABSTRACT: We present FEROS high-resolution (R~45000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d<250 pc) star-forming regions (SFRs). All the candidates have IR excess. We determine the spectral type and luminosity class of the sources, derive their radial and rotational velocities, and constrain their distances employing spectroscopic parallaxes. We confirm 13 sources as Herbig Ae/Be stars and find one classical T Tauri star. Three sources are emission line early-type giants and may be Herbig Ae/Be stars. One source is a main-sequence A-type star. Fourteen sources are post-main-sequence giant and supergiant stars. Two sources are extreme emission-line stars. Most of the sources appear to be background stars at distances over 700 pc. We show that high-resolution optical spectroscopy is a crucial tool for distinguishing young stars from post-main sequence stars in samples taken from emission-line star catalogs based on low-resolution spectroscopy. Within the sample, 3 young stars (CD-38 4380, Hen 3-1145, and HD 145718) and one early-type luminosity class III giant with emission lines (Hen 3-416) are at distances closer than 300 pc and are positionally coincident with a nearby SFR. These 4 sources are likely to be nearby young stars and are interesting for follow-up observations at high-angular resolution. Furthermore, seven confirmed Herbig Ae/Be stars at d>700 pc (Hen 2-80, Hen 3-1121 N&S, HD 313571, MWC 953, WRAY 15-1435, and Th 17-35) are inside or close (<5') to regions with extended 8 micron continuum emission and in their 20' vicinity have astronomical sources characteristic of SFRs. These 7 sources are likely to be members of SFRs. These regions are attractive for future studies of their stellar content. Comment: 24 pages, 6 Figures, accepted by Astronomy and Astrophysics, in press.
    Astronomy and Astrophysics 04/2010; DOI:10.1051/0004-6361/200913800 · 4.48 Impact Factor
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    ABSTRACT: We present the results of spectroscopic and photometric observations for three hot southern-hemisphere post-AGB objects, Hen 3-1347 = IRAS 17074-1845, Hen 3-1428 = IRAS17311-4924, and LSS 4634 = IRAS 18023-3409. In the spectrograms taken with the 1.9-m telescope of the South African Astronomical Observatory (SAAO) in 2012, we have measured the equivalent widths of the most prominent spectral lines. Comparison of the new data with those published previously points to a change in the spectra of Hen 3-1428 and LSS 4634 in the last 20 years. Based on ASAS data, we have detected rapid photometric variability in all three stars with an amplitude up to 0.3 mag, 0.4 mag in the $V$ band. A similarity between the patterns of variability for the sample stars and other hot protoplanetary nebulae is pointed out. We present the results of $UBV$ observations for Hen 3-1347, according to which the star undergoes rapid irregular brightness variations with maximum amplitudes $\Delta V$=0.25 mag, $\Delta B$=0.25 mag, and $\Delta U$=0.30 mag and shows color-magnitude correlations. Based on archival data, we have traced the photometric history of the stars over more than 100 years. Hen 3-1347 and LSS 4634 have exhibited a significant fading on a long time scale. The revealed brightness and spectrum variations in the stars, along with evidence for their enhanced mass, may be indicative of their rapid post-AGB evolution.
    Astronomy Letters 10/2014; 40(8). DOI:10.1134/S1063773714080015 · 1.30 Impact Factor
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    ABSTRACT: Context. Hot post-AGB stars are luminous objects of low- and intermediate mass (0.8-8 M⊙) in the final stage of evolution, moving between the asymptotic giant branch (AGB) stars and planetary nebulae. The absorption lines observed in their spectra are typical of early-type stars and their abundance pattern may be associated with the occurence of one or more mixing processes during the previous AGB phase. Aims: To better constrain their observed chemical pattern and evolutionary status, we determined chemical abundances for a sample of hot post-AGB stars selected according to spectroscopic criteria. Methods: The observational data are high-resolution spectra obtained with the FEROS spectrograph. The stellar parameters and chemical composition were obtained from fully consistent non-LTE synthesis. Results: The general abundance pattern reveals relevant nitrogen enrichment, slight depletion in carbon and sulfur and mild excess in helium for most of the objects. One notable exception is LSE 148, with Z = 0.001, which is likely to be a metal-poor object at high galactic latitude. The atmospheric parameters and chemical abundances obtained are discussed in the context of evolutionary models. Mixing processes like the second/third dredged-up and "hot bottom-burning" are invoked to explain the obtained results. Based on observations made with the 2.2 m telescope at the European Southern Observatory (La Silla, Chile).
    Astronomy and Astrophysics 07/2012; 543:11-. DOI:10.1051/0004-6361/201117591 · 4.48 Impact Factor


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