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J/ApJ/847/127    Abundance analyses of V652 Her and HD 144941    (Pandey+, 2017)

Non-local thermodynamic equilibrium abundance analyses of the extreme helium stars V652 Her and HD 144941. Pandey G., Lambert D.L. <Astrophys. J., 847, 127 (2017)> =2017ApJ...847..127P
ADC_Keywords: Abundances; Stars, peculiar; Equivalent widths; Spectra, optical Keywords: stars: abundances ; stars: atmospheres ; stars: chemically peculiar ; stars: evolution ; stars: fundamental parameters Abstract: Optical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C/He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. Defining atmospheric parameters were obtained from a grid of non-LTE atmospheres and a variety of spectroscopic indicators including HeI and HeII line profiles, and the ionization equilibrium of ion pairs such as CII/CIII and NII/NIII. The various indicators provide a consistent set of atmospheric parameters: Teff=25000±300K, logg=3.10±0.12(cgs), and ξ=13±2km/s are provided for V652 Her, and Teff=22000±600K, logg=3.45±0.15(cgs), and ξ=10km/s are provided for HD 144941. In contrast to the non-LTE analyses, the LTE analyses-LTE atmospheres and an LTE line analysis-with the available indicators do not provide a consistent set of atmospheric parameters. The principal non-LTE effect on the elemental abundances is on the neon abundance. It is generally considered that these extreme helium stars with their very low C/He ratio result from the merger of two helium white dwarfs. Indeed, the derived composition of V652 Her is in excellent agreement with predictions by Zhang & Jeffery (2012MNRAS.419..452Z), who model the slow merger of helium white dwarfs; a slow merger results in the merged star having the composition of the accreted white dwarf. In the case of HD 144941, which appears to have evolved from metal-poor stars, a slow merger is incompatible with the observed composition but variations of the merger rate may account for the observed composition. More detailed theoretical studies of the merger of a pair of helium white dwarfs are to be encouraged. Description: High-resolution optical spectra of V652 Her and HD 144941 were obtained on 2011 May 13 at the coude focus of the W.J. McDonald Observatory's Harlan J. Smith 2.7m telescope with the Robert G. Tull cross-dispersed echelle spectrograph at a resolving power of R=60000. Three thirty-minute exposures were recorded for each of these stars. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 16 09 24.55 -27 13 38.2 HD 144941 = TYC 6788-284-1 16 48 04.69 +13 15 42.4 V652 Her = V* V652 Her ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table145.dat 104 5 Summary of atmospheric parameters and photospheric abundances (tables 1, 4 and 5) table2.dat 72 196 Measured equivalent widths (EW) and NLTE/LTE photospheric line for V652 Her table3.dat 72 68 Measured equivalent widths (EW) and NLTE/LTE photospheric line for HD 144941
See also: B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-2014) J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016) J/AJ/143/28 : Analysis of B6-A9 stars from INES UV spectra (Freire+, 2012) J/MNRAS/420/757 : STEREO magnetic chemically peculiar stars (Wraight+, 2012) J/A+A/469/799 : Torun catalog of post-AGB and related objects (Szczerba+, 2007) Byte-by-byte Description of file: table145.dat
Bytes Format Units Label Explanations
1- 9 A9 --- Name Star name 11- 17 A7 --- Ana "non-LTE" or "LTE" analyses 19- 23 I5 K Teff [21000/25300]? Effective temperature 25- 27 I3 K e_Teff [300/600]? Teff uncertainty 29- 32 F4.2 [cm/s2] logg [3.1/3.5]? log of surface gravity 34- 37 F4.2 [cm/s2] e_logg [0.1/0.2]? logg uncertainty 39- 40 I2 km/s Vt [10/13]? Microturbulent velocity 42 I1 km/s e_Vt [2]? Vt uncertainty 44- 45 I2 km/s vsini [10]? Rotational velocity (or lower range) 46 A1 --- --- [- ] 47- 48 I2 km/s vsini2 ? Upper range of vsini 50- 53 F4.1 --- H [9.5/12] H abundance 55- 58 F4.1 --- He [10.9/11.5] He abundance 60- 62 F3.1 --- C [6.6/8.4] C abundance 64- 66 F3.1 --- N [6.4/9] N abundance 68- 70 F3.1 --- O [7/8.7] O abundance 72- 74 F3.1 --- Ne [7.2/8.6] Ne abundance 76- 78 F3.1 --- Mg [5.8/7.6] Mg abundance 80- 82 F3.1 --- Al [5.1/6.5]? Al abundance 84- 86 F3.1 --- Si [6/7.5] Si abundance 88- 90 F3.1 --- P [5.4/5.5]? P abundance 92- 94 F3.1 --- S [6/7.4] S abundance 96- 98 F3.1 --- Ar [6.4/7]? Ar abundance 100-101 A2 --- l_Fe [≤ ] Limit flag on Fe 102-104 F3.1 --- Fe [6.2/7.5] Fe abundance
Byte-by-byte Description of file: table[23].dat
Bytes Format Units Label Explanations
1- 4 A4 --- Type Measurement type: "Line" or "Mean" 6- 11 A6 --- Ion Ion 13- 20 F8.3 0.1nm lambda [3796/7033]? wavelength, Angstroms 22 A1 --- f_lambda Flag on lambda (1) 24- 29 F6.3 eV ExPot [8.2/35.7]? Excitation potential 31- 36 F6.3 [-] log(gf) [-3,1.2]? Logarithm of oscillator strength 39 A1 --- r_log(gf) [c] Source for log(gf) (2) 42 A1 --- l_EW Limit flag on EW 44- 46 I3 10-4nm EW [7/316]? Equivalent width 48 A1 --- f_EW [s ] flag on EW, s=Synthetic 50 A1 --- l_eps-nlte Limit flag on eps-nlte 51- 55 F5.2 --- eps-nlte [5.7/10.5]? Abundance derived from this line (3) 57- 60 F4.2 --- e_eps-nlte [0/0.3]? 1σ scatter in mean value 62 A1 --- l_eps-lte Limit flag on eps-lte 63- 67 F5.2 --- eps-lte [4.9/10.5]? Abundance derived from this line (4) 69- 72 F4.2 --- e_eps-lte [0/0.4]? 1σ scatter in mean value
Note (1): * = The lines covered by the adopted model atom, including the extended model atom with more levels, for the ions providing the ionization balance and some other ions Note (2): c = Kurucz gf-value. Note (3): Parameters for NLTE: Teff, log(g), ξ=25000, 3.10, 13.0 Note (4): Parameters for LTE: Teff, log(g), ξ=25300, 3.25, 13.0
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Jun-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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