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 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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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
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Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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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- 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- 42 A1 --- l_EW Limit flag on EW
44- 46 I3 10-4nm EW [7/316]? Equivalent width
48- 48 A1 --- f_EW [s ] flag on EW, s=Synthetic
50- 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- 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
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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
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Jun-2018