1998A&A...332..928D


Query : 1998A&A...332..928D

1998A&A...332..928D - Astronomy and Astrophysics, volume 332, 928-938 (1998/4-3)

Photospheric composition of the carbon-rich 21 µm post-AGB stars IRAS 22223+4327 and IRAS 04296+3429.

DECIN L., VAN WINCKEL H., WAELKENS C. and BAKKER E.J.

Abstract (from CDS):

We present a detailed chemical analysis on the basis of high-resolution, high signal-to-noise optical spectra of two post-AGB objects IRAS 22223+4327 and IRAS 04296+3429. Both display the unidentified 21µm feature in their IR-spectra. The analysis is performed using HR 1865(F0Ib) and HR 1017(F5Iab) as reference stars. The spectroscopic indicators provide accurate atmospheric parameters of Teff=6500K, logg=1.0 and ξt=5.5km/s for IRAS 22223+4327 and Teff=7000K, logg=1.0 and ξt=4.0km/s for IRAS 04296+3429. Our high-resolution data are inconsistent with the significantly lower temperatures deduced from spectral-type determinations in the literature based on low resolution spectra and highlight the need of high-resolution spectroscopy for the determination of accurate fundamental parameters of chemically peculiar supergiants. Both photospheres are found to be metal-deficient with [Fe/H]=-0.4 and -0.7 respectively. C and N are found to be overabundant. Useful O-lines were only detected in the brighter IRAS 22223+4327 and the O abundance is found to follow the Fe deficiency: the C/O photospheric abundance is about 1.3, but due to the lack of oxygen lines it is difficult to determine accurately. This corroborates the fact that the carriers of the 21µm feature are formed in a carbon rich circumstellar chemistry. Moreover, these IRAS-stars have large overabundances of s-process-elements. The mean abundance of all the measured s-process-elements is [s/Fe]=+1.0 for IRAS 22223+4327 and +1.4 for IRAS 04296+3429. The distribution of the s-process elements can best be described as due to a distribution of neutron exposures with a low mean neutron exposure of τ0=0.2mbarn–1. The 21 µm stars form an interesting sub-group in the total post-AGB sample of stars, not only for their IR characteristics, but also in a broader context of stellar (chemical) evolution theory. They show, in contrast to other post-AGB stars, that the 3rd dredge-up has been efficient during their AGB evolution. The mean neutron exposure is lower than expected for their metallicity. The spectroscopic parameters found for the massive spectral analogues (Teff=7500K, logg=2.0 and ξt=3.0km/s for HR 1865 and Teff=6500K, logg=2.0 and ξt=3.5km/s for HR 1017) agree well with the values found in the literature. Both stars display an enrichment in Na, which is commonly observed in massive supergiants but theoretically not well understood.

Abstract Copyright:

Journal keyword(s): stars: individual: HR 1017, HR 1865, IRAS 04296+3429, IRAS 22223+4327 - stars: post-AGB - stars: abundances

Simbad objects: 16

goto View the references in ADS

Number of rows : 16
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 * alf Per V* 03 24 19.3700924 +49 51 40.245455 2.64 2.27 1.79     F5Ib 818 1
2 IRAS 04296+3429 pA* 04 32 56.9743899192 +34 36 12.459816288   16.13 14.09 13.64 11.64 G0Ia 139 0
3 IRAS 05113+1347 pA* 05 14 07.7664787608 +13 50 28.200887160   14.54 11.51   10.26 G5I 62 0
4 * alf Lep V* 05 32 43.8161188 -17 49 20.241380 3.02 2.77 2.57 2.35 2.14 F0Ib 274 0
5 IRAS 05341+0852 pA* 05 36 55.0511076432 +08 54 08.656315452   15.37 13.45 12.95 11.43 F6I 109 0
6 HD 56126 pA* 07 16 10.2590823192 +09 59 47.954735376   9.20 8.32     F0/5Ia 310 0
7 CD-53 4543 pA* 12 20 15.0622728552 -53 55 31.444773420 10.29 9.74 9.36 9.69   A7I 42 0
8 V* LN Hya pA* 12 56 30.1302499344 -26 27 37.047715704   9.104 8.697   9.291 F3Ia 111 0
9 HD 133656 pA* 15 07 27.4396006536 -48 17 53.894056668 8.09 7.88 7.58 8.45   A5Iab 49 0
10 HD 187885 pA* 19 52 52.7033593752 -17 01 50.289441096   9.25 8.68 8.32   F2/6Ia 174 0
11 IRAS 20000+3239 LP* 20 01 59.5133268456 +32 47 32.799122916   16.13 13.39 11.80 10.32 ~ 75 0
12 V* V1610 Cyg pA* 21 02 18.27 +36 41 37.0           F5Iae 853 1
13 V* V448 Lac pA* 22 24 31.4283564864 +43 43 10.978781916 11.22 10.61 9.69     F7I 103 0
14 HD 235858 pA* 22 29 10.3748806056 +54 51 06.344572284   11.40 9.52 8.47 7.34 G5Ia 244 0
15 IRAS 22574+6609 pA* 22 59 18.3496246536 +66 25 47.940897972       19.2   A1-6I 55 0
16 IRAS 23304+6147 pA* 23 32 44.7858431592 +62 03 49.090372272   15.36 12.99 12.23 10.50 G2Ia 110 0

To bookmark this query, right click on this link: simbad:objects in 1998A&A...332..928D and select 'bookmark this link' or equivalent in the popup menu


2022.05.19-17:06:09

© Université de Strasbourg/CNRS

    • Contact