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J/A+A/600/A82   VLTS. O giants and supergiants nitrogen abundances (Grin+, 2017)

The VLT-FLAMES Tarantula Survey. XXV. Surface nitrogen abundances of O-type giants and supergiants. Grin N.J., Ramirez-Agudelo O.H., de Koter A., Sana H., Puls J., Brott I., Crowther P.A., Dufton P.L., Evans C.J., Graefener G., Herrero A., Langer N., Lennon D.J., van Loon J.T., Markova N., de Mink S.E., Najarro F., Schneider F.R.N., Taylor W.D., Tramper F., Vink J.S., Walborn W.R. <Astron. Astrophys. 600, A82 (2017)> =2017A&A...600A..82G (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, O ; Abundances Keywords: stars: early-type - stars: abundances - stars: rotation - Galaxies: star clusters: individual: 30 Doradus - line: profiles - Magellanic Clouds Abstract: Theoretically, rotation-induced chemical mixing in massive stars has far reaching evolutionary consequences, affecting the sequence of morphological phases, lifetimes, nucleosynthesis, and supernova characteristics. Using a sample of 72 presumably single O-type giants to supergiants observed in the context of the VLT-FLAMES Tarantula Survey (VFTS), we aim to investigate rotational mixing in evolved core-hydrogen burning stars initially more massive than 15M by analysing their surface nitrogen abundances. Using stellar and wind properties derived in a previous VFTS study we computed synthetic spectra for a set of up to 21 N II-V lines in the optical spectral range, using the non-LTE atmosphere code FASTWIND. We constrained the nitrogen abundance by fitting the equivalent widths of relatively strong lines that are sensitive to changes in the abundance of this element. Given the quality of the data, we constrained the nitrogen abundance in 38 cases; for 34 stars only upper limits could be derived, which includes almost all stars rotating at vrot>200km/s. We analysed the nitrogen abundance as a function of projected rotation rate vrot and confronted it with predictions of rotational mixing. We found a group of N-enhanced slowly-spinning stars that is not in accordance with predictions of rotational mixing in single stars. Among O-type stars with (rotation-corrected) gravities less than loggc=3.75 this group constitutes 30-40 percent of the population. We found a correlation between nitrogen and helium abundance which is consistent with expectations, suggesting that, whatever the mechanism that brings N to the surface, it displays CNO-processed material. For the rapidly-spinning O-type stars we can only provide upper limits on the nitrogen abundance, which are not in violation with theoretical expectations. Hence, the data cannot be used to test the physics of rotation induced mixing in the regime of high spin rates. While the surface abundances of 60-70 percent of presumed single O-type giants to supergiants behave in conformity with expectations, at least 30-40 percent of our sample can not be understood in the current framework of rotational mixing for single stars. Even though we have excluded stars showing radial velocity variations, of our sample may have remained contaminated by post-interaction binary products. Hence, it is plausible that effects of binary interaction need to be considered to understand their surface properties. Alternatively, or in conjunction, the effects of magnetic fields or alternative mass-loss recipes may need to be invoked. Description: Measured surface nitrogen abundances of 72 presumably-single O-type stars in the VLT-FLAMES Tarantula Survey, with luminosity class identifiers III-I. Also included are the surface nitrogen abundances of 31 O-type stars with no luminosity class identifier. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file tablea1.dat 71 72 Table of results for the O-type giants and supergiants tablea2.dat 40 31 Table of results for the O-type stars without assigned luminosity class table2.dat 195 41 Equivalent widths
See also: J/A+A/530/A108 : VLT-FLAMES Tarantula Survey (Evans+, 2011) J/A+A/550/A107 : RV catalogue of O stars in 30 Doradus (Sana+, 2013) J/A+A/550/A108 : DIB in VLT-FLAMES Tarantula Survey (van Loon+, 2013) J/A+A/550/A109 : VLT-FLAMES Tarantula Survey: vsini measures (Dufton+ 2013) J/A+A/558/A134 : VLTS. 30 Dor luminous stars (Doran+, 2013) J/A+A/560/A29 : O-stars in VLT-FLAMES Tarantula Survey (Ramirez-Agudelo+ 2013) J/A+A/564/A39 : VLTS. OVz stars in 30 Dor (Sabin-Sanjulian+, 2014) J/A+A/564/A40 : VLTS. O-type stellar content of 30 Dor (Walborn+, 2014) J/A+A/564/L7 : VLT-FLAMES Tarantula Survey: VFTS 822 (Kalari+, 2014) J/A+A/574/A13 : VLTS. B-type stars classification and RV (Evans+, 2015) J/A+A/575/A70 : VLT-FLAMES Tarantula Survey: B supergiants (McEvoy+, 2015) J/A+A/580/A93 : VLTS. B stars multiplicity (Dunstall+, 2015) J/A+A/600/A81 : VLTS. 30Dor O giants and supergiants (Ramirez-Agudelo+, 2017) Byte-by-byte Description of file: tablea1.dat
Bytes Format Units Label Explanations
1- 3 I3 --- VFTS [16/843] VLT-FLAMES Tarantula Survey identifier 4 A1 --- n_VFTS [*] Note on VFTS (1) 6- 28 A23 --- SpType Morphological classification by Walborn et al. (2014, Cat. J/A+A/564/A40) 30- 32 I3 km/s vsini Projected rotational velocity (2) 34 A1 --- l_epsN Upper limit flag on epsN 35- 38 F4.2 [-] epsN Surface nitrogen abundance (=log(NN/NH)+12, see equation 1) 40- 43 F4.2 [-] e_epsN ? Error on surface nitrogen abundance 45 I1 --- Nlines ?=- Number of lines used for measurement (3) 47- 50 F4.2 --- YHe Surface Helium mass fraction (2) 52- 55 F4.2 [cm/s2] loggc Logarithmic surface gravity corrected for rotation (2) 57- 61 F5.2 kK Teff Effective Temperature in kilo Kelvin (2) 63- 66 F4.2 [Lsun] logL Logarithmic luminosity in terms of solar (2) 68- 69 I2 Msun Mass Mass estimate in solar masses (2)(4) 71 A1 --- EW [*] * indicates equivalent width in table2
Note (1): Note as follows: * = for newly detected binaries and are excluded from quantitative comparison to theory (see Sect. 3.4). Note (2): Parameters determined by Ramirez-Agudelo et al., (2016, in prep.). Note (3): A '-' is used in case of an upper limit on the nitrogen abundance Note (4): Masses are determined using the Bayesian tool BONNSAI (Schneider et al., 2014A&A...570A..66S).
Byte-by-byte Description of file: tablea2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- VFTS [16/843] VLT-FLAMES Tarantula Survey identifier 4 A1 --- n_VFTS [*] Note on VFTS (1) 6- 16 A11 --- SpType Morphological classification by Walborn+ (2014) 18- 20 I3 km/s vsini Projected rotational velocity (2) 22- 25 F4.2 [-] epsN Surface nitrogen abundance (= log(NN/NH)+12, see equation 1) 27 A1 --- l_epsN Upper limit on the nitrogen abundance 28- 31 F4.2 [-] e_epsN ? Error on surface nitrogen abundance 33 I1 --- Nlines ?=- Number of lines used for measurement (3) 35- 38 F4.2 [cm/s2] loggc Logarithmic surface gravity corrected for 40 A1 --- EW [*] * indicates equivalent widths in table2
Note (1): Note as follows: * = for poor quality fits and are excluded from quantitative comparison to theory (see Sect. 3.4). Note (2): Parameters determined by Ramirez-Agudelo et al. (2016, in prep.). Note (3): A '-' is used in case of an upper limit on the nitrogen abundance.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- VFTS [16/843] VLT-FLAMES Tarantula Survey identifier 7- 10 F4.1 0.1pm EWNII3995 ?=- Equivalent width of the NII3995 line (1) 13- 15 F3.1 0.1pm e_EWNII3995 ?=- Error on EWNII3995 line (1) 19- 22 F4.1 0.1pm EWNII4630 ?=- Equivalent width of the NII4630 line (1) 24- 27 F4.1 0.1pm e_EWNII4630 ?=- Error on EWNII4630 line (1) 30- 34 F5.1 0.1pm EWNIII4097 ?=- Equivalent width of the NIII4097 line (1) (2) 36- 39 F4.1 0.1pm e_EWNIII4097 ?=- Error on EWNIII4097 line (1) 43- 46 F4.1 0.1pm EWNIII4195 ?=- Equivalent width of the NIII4195 line (1) 49- 51 F3.1 0.1pm e_EWNIII4195 ?=- Error on EWNIII4195 line (1) 54- 58 F5.1 0.1pm EWNIII4379 ?=- Equivalent width of the NIII4379 line (1) 60- 63 F4.1 0.1pm e_EWNIII4379 ?=- Error on EWNIII4379 line (1) 66- 70 F5.1 0.1pm EWNIII4511 ?=- Equivalent width of the NIII4511 line (1) 72- 75 F4.1 0.1pm e_EWNIII4511 ?=- Error on EWNIII4511 line (1) 78- 82 F5.1 0.1pm EWNIII4515 ?=- Equivalent width of the NIII4515 line (1) 84- 87 F4.1 0.1pm e_EWNIII4515 ?=- Error on EWNIII4515 line (1) 91- 94 F4.1 0.1pm EWNIII4518 ?=- Equivalent width of the NIII4518 line (1) 97- 99 F3.1 0.1pm e_EWNIII4518 ?=- Error on EWNIII4518 line (1) 103-106 F4.1 0.1pm EWNIII4523 ?=- Equivalent width of the NIII4523 line (1) 109-111 F3.1 0.1pm e_EWNIII4523 ?=- Error on EWNIII4523 line (1) 115-118 F4.1 0.1pm EWNIII4535 ?=- Equivalent width of the NIII4535 line (1) 121-123 F3.1 0.1pm e_EWNIII4535 ?=- Error on EWNIII4535 line (1) 125-130 F6.1 0.1pm EWNIII4634 ?=- Equivalent width of the NIII4634 line (1) 132-135 F4.1 0.1pm e_EWNIII4634 ?=- Error on EWNIII4634 line (1) 137-142 F6.1 0.1pm EWNIII4640 ?=- Equivalent width of the NIII4640 line (1) 144-147 F4.1 0.1pm e_EWNIII4640 ?=- Error on EWNIII4640 line (1) 150-154 F5.1 0.1pm EWNIIIqua ?=- Combined equivalent width of the NIII4511-4515-4518 lines (1) 156-159 F4.1 0.1pm e_EWNIIIqua ?=- Error on EWNIIIqua (1) 161-166 F6.1 0.1pm EWNIV4058 ?=- Equivalent width of the NIV4058 line (1) 169-171 F3.1 0.1pm e_EWNIV4058 ?=- Error on EWNIV4058 line (1) 174-178 F5.1 0.1pm EWNV4603 ?=- Equivalent width of the NV4603 line (1) 181-183 F3.1 0.1pm e_EWNV4603 ?=- Error on EWNV4603 line (1) 186-190 F5.1 0.1pm EWNV4619 ?=- Equivalent width of the NV4619 line (1) 193-195 F3.1 0.1pm e_EWNV4619 ?=- Error on EWNV4619 line (1)
Note (1): 0.1pm = 1e-3 Angstrom, negative equivalent width values indicate emission. A '---' indicates the line was not used in the analysis. Note (2): Equivalent width as measured after dividing the observed profile by a Lorentzian fit to the wing of Hdelta (see Sect. 3.2).
Acknowledgements: Nathan Jan Grin, ngrin(at)astro.uni-bonn.de References: Evans et al., Paper I 2011A&A...530A.108E, Cat. J/A+A/530/108 Taylor et al., Paper II 2011A&A...530L..10T Bestenlehner et al., Paper III 2011A&A...530L..14B Bressert et al., Paper IV 2012A&A...542A..49B Dunstall et al., Paper V 2012A&A...542A..50D Henault-Brunet et al., Paper VI 2012A&A...545L...1H Henault-Brunet et al., Paper VII 2012A&A...546A..73H Sana et al., Paper VIII 2013A&A...550A.107S, Cat. J/A+A/550/A107 van Loon et al., Paper IX 2013A&A...550A.108V, Cat. J/A+A/550/A108 Dufton et al., Paper X 2013A&A...550A.109D, Cat. J/A+A/550/A109 Doran et al., Paper XI 2013A&A...558A.134D, Cat. J/A+A/558/A134 Ramirez-Agudelo et al., Paper XII 2013A&A...560A..29R, Cat. J/A+A/560/A29 Sabin-Sanjulian et al., Paper XIII 2014A&A...564A..39S, Cat. J/A+A/564/A39 Walborn et al., Paper XIV 2014A&A...564A..40W, Cat. J/A+A/564/A40 Kalari et al., Paper XV 2014A&A...564L...7K, Cat. J/A+A/564/L7 Maiz Apellaniz et al., Paper XVI 2014A&A...564A..63M Bestenlehner et al., Paper XVII 2014A&A...570A..38B Evans et al., Paper XVIII 2015A&A...574A..13E McEvoy et al., Paper XIX 2015A&A...575A..70M, Cat. J/A+A/575/A70 Clark et al., Paper XX 2015A&A...579A.131C Ramirez-Agudelo et al., Paper XXI 2015A&A...580A..92R Dunstall et al., Paper XXII 2015A&A...580A..93D, Cat. J/A+A/580/A93 Howarth et al., Paper XXIII 2015A&A...582A..73H Ramirez-Agudelo et al., Paper XXIV 2017A&A...600A..81R, Cat. J/A+A/600/A81
(End) Nathan Jan Grin [AIFA, Germany], Patricia Vannier [CDS] 27-Sep-2016
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