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J/A+A/603/A56    Stellar parameters and assumed wind parameters (Cazorla+, 2017)

Chemical abundances of fast-rotating massive stars. I. Description of the methods and individual results. Cazorla C., Morel T., Naze Y., Rauw G., Semaan T., Daflon S., Oey S. <Astron. Astrophys. 603, A56 (2017)> =2017A&A...603A..56C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, OB ; Radial velocities ; Rotational velocities ; Effective temperatures ; Abundances Keywords: stars: abundances - stars: early-type - stars: fundamental parameters - stars: massive - stars: rotation Abstract: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast-rotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen because of a number of issues (e.g., presence of numerous upper limits for the nitrogen abundance, unknown multiplicity status, mix of stars with different physical properties such as their mass and evolutionary state that are known to control the amount of rotational mixing), rendering a re-investigation necessary. We have carefully selected a large sample of bright, fast-rotating early-type stars of our Galaxy (40 objects with spectral types between B0.5 and O4). Their high-quality, high-resolution optical spectra were then analysed with the stellar atmosphere modelling codes DETAIL/SURFACE or CMFGEN, depending on the temperature of the target. Several internal and external checks were performed to validate our methods, notably comparing our results with literature data for some well-known objects, studying the effect of gravity darkening, or confronting the results provided by the two codes for stars amenable to both analyses. Furthermore, we have studied the radial velocities of the stars to assess their binarity. This first part of our study presents our methods and provides the derived stellar parameters, He, CNO abundances and the multiplicity status of every star of the sample. It is the first time that He and CNO abundances of such a large number of Galactic massive fast rotators are determined in a homogeneous way. Description: Stellar parameters derived for the stars in our sample and assumed wind parameters for our hotter stars. Because macroturbulent velocities cannot be determined reliably for fast rotators (Sect. 4.2), all values in column 6 are upper limits. Column 7 provides the multiplicity status (see Sect. 4.1 for the classification criterion and Appendix C for the RV studies of each individual object). The runaway status is based on literature studies (references are given on a star-to-star basis in Appendix C). Columns 15, 16, and 17 of the table presenting the results for the hotter stars list the assumed wind parameters. For stars with the lowest temperatures (typically B0.5 stars), the carbon abundance cannot be firmly determined due to the weakness of the CIII lines at these temperatures. Besides, NII lines may also be very weak for the hottest stars studied with DETAIL/SURFACE. In these cases, we provide upper limits for both carbon and nitrogen abundances. They correspond to predicted lines becoming detectable, i.e., having a depth significantly exceeding the local noise. Similarly, CMFGEN fits may converge towards very high or very low CNO abundances. In both cases, the upper or lower limits were determined from the chi2 curves and correspond to the limit of their flat minimum. Since the CNO abundances are measured relative to the hydrogen content (assumed to be constant in our study), a correction should in principle be applied to the CNO abundances of stars that exhibit a very high helium abundance (and therefore have a reduced hydrogen abundance). However, we found this correction to be negligible (≲0.1dex) even for the most He-rich stars. The 1σ errors on the parameters are given in dedicated columns. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file cool.dat 155 17 Cooler stars stellar parameters (table F2, part 1) hot.dat 165 23 Hotter stars stellar parameters and assumed wind parameters (table F2, part 2)
Byte-by-byte Description of file: cool.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Name Star name 10 I1 --- n_Name [1/2]? Note on Name (1) 12- 14 I3 km/s vsini Projected rotational velocity 16- 17 I2 km/s e_vsini Error on vsini 19 A1 --- l_vmac Upper limit sign for vmac 21- 23 I3 km/s vmac Macroturbulence velocity 25- 36 A12 --- mult Multiplicity from spectroscopy 38- 40 A3 --- runStat [Yes No] Runaway? 42- 46 I5 K Teff Effective temperature 48- 51 I4 K e_Teff Error on Teff 53- 56 F4.2 [cm/s2] logg Surface gravity 58- 61 F4.2 [cm/s2] e_logg Error on logg 63- 66 F4.2 [cm/s2] loggC Surface gravity corrected for centrifuge forces 68- 71 F4.2 [cm/s2] e_loggC Error on loggC 73- 77 F5.3 --- Y Helium abundance 79- 83 F5.3 --- e_Y Error on Y 85 A1 --- l_logE(C) Lower/upper limit in logE(C) 87- 90 F4.2 --- logE(C) ? Carbon abundance 92- 95 F4.2 --- e_logE(C) Error on logE(C) 97 A1 --- l_logE(N) Lower/upper limit in logE(N) 99-102 F4.2 --- logE(N) Nitrogen abundance 104-107 F4.2 --- e_logE(N) Error on logE(N) 109 A1 --- l_logE(O1) Lower/upper limit in logE(O) in 4060-4082Å 111-114 F4.2 --- logE(O1) ? Oxygen abundance in 4060-4082Å 116-119 F4.2 --- logE(O2) Oxygen abundance in 4691-4709Å 121-124 F4.2 --- logE(O) Adopted oxygen abundance 126-129 F4.2 --- e_logE(O) Error on logE(O) 131 A1 --- l_[N/C] Lower/upper limit in [N/C] 133-137 F5.2 --- [N/C] ? N/C abundance ratio 139-142 F4.2 --- e_[N/C] Error on [N/C] 144 A1 --- l_[N/O] Lower/upper limit in [N/O] 146-150 F5.2 --- [N/O] N/O abundance ratio 152-155 F4.2 --- e_[N/O] Error on [N/O]
Note (1): Note on Name ars follows: 1 = because the UCLES spectrum only covers the wavelength range ∼4350-6800Å, neither Hε, Hδ, Hγ, He I 4026, nor the C and O lines in the 4060-4082Å region were used. In order to check the reliability of our results, we have determined the atmospheric parameters of HD 172367 (whose spectral type is similar to HD 53755) considering either only one (Hβ), or four (Hε, Hδ, Hγ, Hβ) Balmer lines. No significant differences were found between the two sets of results, ensuring that our parameter derivation for HD 53755 is secure. 2 = stars studied with both DETAIL/SURFACE and CMFGEN.
Byte-by-byte Description of file: hot.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Name Star name 10 I1 --- n_Name [1]? Note on Name (1) 12- 14 I3 km/s vsini Projected rotational velocity 16- 17 I2 km/s e_vsini Error on vsini 19 A1 --- l_vmac Upper limit sign for vmac 21- 23 I3 km/s vmac Macroturbulence velocity 25- 36 A12 --- mult Multiplicity from spectroscopy 38- 40 A3 --- runStat Runaway? 42- 46 I5 K Teff Effective temperature 48- 51 I4 K e_Teff Error on Teff 53- 56 F4.2 [cm/s2] logg Surface gravity 58- 61 F4.2 [cm/s2] e_logg Error on logg 63- 66 F4.2 [cm/s2] loggC Surface gravity corrected for centrifuge forces 68- 71 F4.2 [cm/s2] e_loggC Error on loggC 73- 76 F4.1 [Msun/yr] logdM/dt Mass-loss rate 78- 81 I4 km/s vinf Terminal velocity 83- 86 F4.2 --- beta Wind beta parameter 88- 92 F5.3 --- Y Helium abundance 94- 98 F5.3 --- e_Y Error on y 100-101 A2 --- l_logE(C) [<≥ ] Lower/upper limit in logE(C) 103-106 F4.2 --- logE(C) Carbon abundance 108-111 F4.2 --- e_logE(C) Error on logE(C) 113-114 A2 --- l_logE(N) [<≥ ] Lower/upper limit in logE(N) 116-119 F4.2 --- logE(N) Nitrogen abundance 121-124 F4.2 --- e_logE(N) Error on logE(N) 126-127 A2 --- l_logE(O) [<≥ ] Lower/upper limit in logE(O) 129-132 F4.2 --- logE(O) Oxygen abundance 134-137 F4.2 --- e_logE(O) Error on logE(O) 139-140 A2 --- l_[N/C] [<≥ ] Lower/upper limit in [N/C] 142-146 F5.2 --- [N/C] N/C abundance ratio 148-151 F4.2 --- e_[N/C] Error on [N/C] (2) 153-154 A2 --- l_[N/O] [<≥ ] Lower/upper limit in [N/O] 156-160 F5.2 --- [N/O] ? N/O abundance ratio 162-165 F4.2 --- e_[N/O] ? Error on [N/O] (2)
Note (1): Note on Name as follows: 1 = atmospheric parameters and surface abundances must be considered with caution, as they were derived from a low S/N spectrum that only ranges from 4075 to 4920Å (i.e., with fewer diagnostic lines). Note (2): quadratic sum of the CNO abundance uncertainties.
Acknowledgements: Constantin Cazorla, cazorla(at)astro.ulg.ac.be
(End) Constantin Cazorla [Belgium], Patricia Vannier [CDS] 16-Mar-2017
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