J/MNRAS/465/1227 Nine WC 9 stars spectral variability (Desforges+, 2017) ================================================================================ The spectral variability of a sample of WC 9 stars on time-scales of days to weeks. Desforges S., St-Louis N., Chene A.-N., de la Chevrotiere A., Henault-Brunet V. =2017MNRAS.465.1227D (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Stars, Wolf-Rayet ; Equivalent widths ; Radial velocities Keywords: techniques: spectroscopic - stars: winds, outflows - stars: Wolf-Rayet Abstract: We present the results of a spectroscopic monitoring campaign of nine presumably single Wolf-Rayet (WR) stars, eight of type WC 9 and one WC 8d. We characterize their variability and search for clues to the mechanism responsible for the formation of dust in their wind. For seven out of eight WC 9s, we find a large-scale line-flux variability level of {sigma}>5-8 per cent. The only WC 8d star is variable at a level more comparable with those associated with wind clumping, {sigma}=2.2 per cent. The changes take place on a time-scale of days but in many cases, observing over longer time spans resulted in higher line-flux variability levels. The width of the substructures ranges from ~150 to 300km/s, with the widest structures corresponding to stars with the highest variability amplitude. We searched for periodicities in integrated line quantities for CIII {lambda}5696. Radial velocity changes are typically ~20km/s but never exceed 40km/s and are anticorrelated with the skewness of the line, strongly suggesting that they do not correspond to a real movement of the star. No periodicity was found in these integrated quantities, except for WR 103. Therefore, a wind-wind collision in a close binary does not seem to be responsible for the short-term variability. We cannot, however, exclude that these stars are intermediate- to long-period binaries. We estimate that for periods up to a few years, the shock-cone resulting from wind collisions would be non-adiabatic and thus unstable. We suggest that this represents a viable mechanism to explain the spectroscopic variability. Description: The observations were obtained with the 0.6-m Helen Sawyer Hogg telescope at the El Leoncito Observatory (ELO) in Argentina and the 1.6-m telescope of the Observatoire du Mont Megantic (OMM) in Quebec, Canada. We observed every WC 9 star not demonstrated to be a binary listed in the VIIth catalogue of galactic WR stars (van der Hucht, 2001NewAR..45..135V, Cat. III/215) that has a magnitude of 13.25 or brighter. Because all the WC 9 stars in our sample have negative declinations, the majority of our spectra came from the ELO campaign. For each star, we obtained ~1 spectrum every 1 or 2 d over 1 month. Only WR 106, WR 119 and WR 121, the stars with the least negative declinations, were observable from the OMM. We obtained four to five additional spectra per night for eight nights over a period of 16d. The ELO campaign was carried out during 28 nights between 2009 May 16 and June 15 using a grating giving a resolution of {Delta}{lambda}=2.91{AA} (3 pixels) and a spectral range of 4700-6100{AA}. The OMM campaign was from 2011 June 12 to June 28 for a total of eight clear nights of observations. We used a grating yielding a slightly higher resolution {Delta}{lambda}=2.67{AA} (3 pixels) and a spectral range of 3800-6100{AA}. However, the sensitivity of the detector was too low shortward of ~4700{AA} to provide a usable signal. For both observing runs, the slit width was roughly adjusted to the nightly seeing, which was typically 1.5-2arcsec in order to maximize throughput but maintain a stable spectral resolution. Details of our targets are given in Table 1, in which the stars' name, spectral type, number of spectra obtained and average S/N for each run are listed. The S/N was obtained from the standard deviation of a short continuum region around its median value. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 37 9 Our sample of WC 9 stars table3.dat 63 12 Average moments and standard deviations table4.dat 70 240 Measurements of integrated line quantities -------------------------------------------------------------------------------- See also: III/215 : 7th Catalog of Galactic Wolf-Rayet stars (van der Hucht, 2001) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 A6 --- Name Star name 9- 15 A7 --- SpType Spectral type (1) 17- 19 A3 --- n_SpType Note on SpType (2) 21- 25 F5.2 mag vmag Magnitude in Smith system (1968MNRAS.138..109S) (1) 27- 28 I2 --- NELO Number of ELO spectra 30- 31 I2 --- S/NELO Average signal-to-noise ration (continuum) for ELO run 33- 34 I2 --- NOMM ? Number of OMM spectra 36- 37 I2 --- S/NOMM ? Average signal-to-noise ration (continuum) for OMM run -------------------------------------------------------------------------------- Note (1): Spectral types and V magnitudes are from van der Hucht (2001NewAR..45..135V, Cat. III/215). Note (2): Notes as follows: b = Spectral types are from Williams & van der Hucht (2000MNRAS.314...23W). c = Note that Crowther, De Marco & Barlow (1998MNRAS.296..367C) have re-classified this star as WC 9 following their revision of the WC and WO classification criteria. Here, we retain the Williams & van der Hucht (2000MNRAS.314...23W) spectral type (see their section 3.1). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 A6 --- Name Star name 8 A1 --- --- [(] 9- 11 A3 --- Inst ELO or OMM 12 A1 --- --- [)] 16- 21 F6.1 0.1nm EW Average equivalent width 23- 26 F4.1 0.1nm s_EW Standard deviation of EW 28- 33 F6.3 --- Skew Average Skewness 35- 39 F5.3 --- s_Skew Standard deviation of Skew 41- 45 F5.3 --- Kur Average Kurtosis 47- 51 F5.3 --- s_Kur Standard deviation of Kur 53- 57 F5.2 km/s RV Average radial velocity 59- 63 F5.2 km/s s_RV Standard deviation of RV -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 A6 --- Name Star name 8 A1 --- --- [(] 9- 11 A3 --- Inst ELO or OMM 12 A1 --- --- [)] 16- 22 F7.2 d HJD Heliocentric Julian date (HJD-2451544.5) 24- 29 F6.1 0.1nm EW Equivalent width 31- 34 F4.1 0.1nm e_EW rms uncertainty on EW 36- 41 F6.3 --- Skew Skewness 43- 47 F5.3 --- e_Skew rms uncertainty on Skew 49- 53 F5.3 --- Kur Kurtosis 55- 59 F5.3 --- e_Kur rms uncertainty on Kur 61- 65 F5.1 km/s RV Radial velocity 67- 70 F4.1 km/s e_RV rms uncertainty on RV -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Patricia Vannier [CDS] 03-Sep-2018