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.
<Mon. Not. R. Astron. Soc., 465, 1227-1240 (2017)>
=2017MNRAS.465.1227D 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 σ>5-8 per cent. The only WC 8d star is variable at
a level more comparable with those associated with wind clumping,
σ=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 λ5696.
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 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
Δλ=2.91Å (3 pixels) and a spectral range of
4700-6100Å. 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 Δλ=2.67Å (3
pixels) and a spectral range of 3800-6100Å. However, the
sensitivity of the detector was too low shortward of ∼4700Å 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:
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FileName Lrecl Records Explanations
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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
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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 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
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Note (1): Spectral types and V magnitudes are from van der Hucht
(2001NewAR..45..135V 2001NewAR..45..135V, Cat. III/215).
Note (2): Notes as follows:
b = Spectral types are from Williams & van der Hucht (2000MNRAS.314...23W 2000MNRAS.314...23W).
c = Note that Crowther, De Marco & Barlow (1998MNRAS.296..367C 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 2000MNRAS.314...23W) spectral type (see their section 3.1).
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Byte-by-byte Description of file: table3.dat
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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
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Byte-by-byte Description of file: table4.dat
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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
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 03-Sep-2018