-
[show abstract]
[hide abstract]
ABSTRACT: Extensive Hα spectroscopy of the cool, helium-strong star δ Ori C obtained over two decades has enabled a detailed analysis of the variable Hα emission observed in this sharp-lined and strongly magnetic B3V star. Radial velocity measurements from these and other spectra have also confirmed the binary nature of the star, the first detection of the secondary being provided, and permitted an improved determination of the system's orbital parameters. The amplitude of the radial velocities and a preliminary spectroscopic analysis indicate that the secondary component is an early A-type star. Disentangling the contribution of the two components to the Balmer line profiles, we determine an effective temperature for δ Ori C slightly larger than previously adopted in the literature. The Hα emission is variable with a period of 1.477 75 ± 0.000 04 d, assumed to be the rotation period of the primary component. After removal of the binary system's photospheric contribution to the Hα line, we find that the emission arises from two distinct, but asymmetrical, optically translucent circumstellar clouds. When strongest the emission peaks have intensities of approximately 15 per cent of the continuum level at about 150 km s−1 on either side of the line centre, and emission is apparent to ±225 km s−1, or 6 R* above the photosphere if we assume that the magnetic field forces the circumstellar material into rigid rotation about the star. New 6 cm Very Large Array radio measurements, when combined with archival data, suggest that the radio flux of the star is also variable. An analysis of new and previously published magnetic field observations enabled us to derive a value for the inclination of the rotation axis of i= 12°± 3° and an obliquity of the magnetic axis of β≤ 52°. The nature of the emission variability is similar to that of the prototypical helium-strong star σ Ori E, but since the latter object has an inclination of >75°, δ Ori C provides us with an opportunity to investigate the cool components of the winds and magnetospheres of the helium-strong stars from a different vantage point.
Monthly Notices of the Royal Astronomical Society 11/2009; 401(4):2739 - 2752. · 4.90 Impact Factor
-
G. A. Wade,
M. A. Smith,
D. A. Bohlender,
T. A. Ryabchikova,
C. T. Bolton,
T. Lueftinger,
J. D. Landstreet,
P. Petit,
S. Strasser,
M. Blake, G. M. Hill
[show abstract]
[hide abstract]
ABSTRACT: This paper reports the photospheric, magnetic and circumstellar gas characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival data and new polarised and unpolarised high-resolution spectra, we redetermine the basic physical properties, the rotational period and the geometry of the magnetic field, and the photospheric abundances of various elements.}{Based on magnetic and spectroscopic measurements, we infer an improved rotational period of $3.83475\pm 0.00002$ d. We determine a current epoch of the longitudinal magnetic field positive extremum (HJD 2452246.033), and provide constraints on the geometry of the dipole magnetic field ($i\geq 56\degr$, $3210 {\rm G}\leq B_{\rm d}\leq 3930$ G, $\beta$ unconstrained). We redetermine the effective temperature and surface gravity using the optical and UV energy distributions, optical photometry and Balmer line profiles ($T_{\rm eff}=13300\pm 300$ K, $\log g=3.7-4.2$), and based on the Hipparcos parallax we redetermine the luminosity, mass, radius and true rotational speed ($L=2.54\pm 0.16 L_\odot, M=4.0\pm 0.2 M_\odot, R=3.4\pm 0.7 R_\odot, v_{\rm eq}=45-61.5$ \kms). We measure photospheric abundances for 21 elements using optical and UV spectra, and constrain the presence of vertical stratification of these elements. We perform preliminary Doppler Imaging of the surface distribution of Fe, finding that Fe is distributed in a patchy belt near the rotational equator. Most remarkably, we confirm strong variations of the H$\alpha$ line core which we interpret as due to occultations of the star by magnetically-confined circumstellar gas. Comment: Accepted by Astronomy and Astrophysics
08/2006;
-
L. Lefèvre,
S. V. Marchenko,
S. Lépine,
A. F. J. Moffat,
A. Acker,
T. J. Harries,
K. Annuk,
D. A. Bohlender,
H. Demers,
Y. Grosdidier, G. M. Hill,
N. D. Morrison,
D. C. Knauth,
G. Skalkowski,
S. Viti
[show abstract]
[hide abstract]
ABSTRACT: We present the results of an optical spectroscopic study of the massive Wolf–Rayet (WR) binary HD 192641 = WR 137. These 1986–2000 data cover the dust-formation maximum in 1997. Combining all available measurements of radial velocities, we derive, for the first time, a spectroscopic orbit with period 4766 ± 66 d (13.05 ± 0.18 yr). The resulting masses, adopting i= 67 °, are MO= 20 ± 2 M⊙ for the O component and MWR= 4.4 ± 1.5 M⊙ for the WR component. These appear, respectively, approximately normal and on the low side for the given spectral types. Analysis of the intense multisite spectroscopic monitoring in 1999 shows that the C iiiλ5696 and C ivλλ5802/12 lines have the highest intrinsic variability levels. The periodogram analysis yields a small-amplitude modulation in the absorption troughs of the C ivλλ5802/12 and He iλ5876 lines with a period of 0.83 d, which could be related either to pulsations or large-scale rotating structures as seen in the WN4 star EZ Canis Majoris (WR 6). Wavelet analysis of the strong emission lines of C iiiλ5696 and C ivλλ5802/12 enabled us to isolate and follow for several hours small structures (emission subpeaks) associated with density enhancements within the wind of the Wolf–Rayet star. Cross-correlating the variability patterns seen in different lines, we find a weak but significant correlation between the variability in emission lines with different ionization potentials, i.e. in lines formed at different distances from the WR stellar core. Adopting a β wind-velocity law, from the motion of individual subpeaks we find β∼ 5, which is significantly larger than the canonical value β≃ 1 found in O star winds.
Monthly Notices of the Royal Astronomical Society 05/2005; 360(1):141 - 152. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: ABSTRACTWR 3 is the brightest very early-type WN star in the sky. Based on several years of time-resolved spectroscopy and precision photometry on various time-scales, we deduce that WR 3 is most likely a single, weak-lined star of type WN3ha (contrary to its current catalogue-type of WN3 + O4), with H lines occurring both in emission and absorption in its wind. This conclusion is confirmed and strengthened via detailed modelling of the spectrum of WR 3. Given the similarity of WR 3 with numerous H-rich WNE stars in the Large Magellanic Cloud and especially the Small Magellanic Cloud, and its location towards the metal-deficient exterior of the Galaxy, we conclude that rotationally induced meridional circulation probably led to the apparently unusual formation of this hot Galactic WN star with enhanced hydrogen. Although we cannot completely rule out the possibility of a binary with a low orbital inclination and/or long period, we regard this latter possibility as highly unlikely.
Monthly Notices of the Royal Astronomical Society 08/2004; 353(1):153 - 161. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: High signal-to-noise ratio, moderate-resolution spectra, providing full phase coverage of the 19-d WC6 + OB binary θ Mus (WR 48, HD 113904), have been obtained and show dramatic variations of the C iiiλ5696 emission-line profile. We have modelled these line profile variations using a purely geometrical model which assumes that the emission arises from two regions, an optically thin spherical shell around the WR star and a cone-shaped region that partially wraps around the OB star. The cone-shaped region represents the shock front arising from the collision between the winds of the two stars. This work builds upon our earlier study of WR 42 and WR 79, and uses a completely new code for the modelling, which includes the effects of turbulence. We now find much better agreement between the orbital inclination angles found for these stars with those determined using other methods. The fitting parameters found via modelling the C iiiλ5696 profile variations of θ Mus are used to infer that the OB companion most likely has a spectral type of O6V or O7V. The modelling presented here continues to show the exciting promise of a better understanding of WR star fundamental parameters.
Monthly Notices of the Royal Astronomical Society 09/2002; 335(4):1069 - 1078. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have obtained complete phase coverage of the WC7+O binaries WR 42 = HD 97152 and WR 79 = HD 152270 with high signal-to-noise ratio (S/N), moderate-resolution spectra. Remarkable orbital phase-locked profile variations of the C iiiλ5696 line are observed and interpreted as arising from colliding wind effects. Within this scenario, we have modelled the spectra using a purely geometrical model that assumes a cone-shaped wind–wind interaction region which partially wraps around the O star. Such modelling holds the exciting promise of revealing a number of interesting parameters for WR+O binaries, such as the orbital inclination, the streaming velocity of material in the interaction region and the ratio of wind momentum flux. Knowledge of these parameters in turn leads to the possibility of a better understanding of WR star masses, mass-loss rates and wind region characteristics.
Monthly Notices of the Royal Astronomical Society 09/2000; 318(2):402 - 410. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed investigation of the orbit, component
characteristics and magnetic field of the single spectrum (SB1), visual
Ap binary HD 81009. By simultaneously modeling new and archival radial
velocity measurements and new and archival speckle interferometric
measurements (obtained with the CHARA array) we obtain a unique model of
the orbital geometry and constraints on the component masses of HD
81009. Additional constraints provided by the Hipparcos parallax and
component magnitude difference and the optical spectral energy
distribution allow us to determine a self-consistent solution for the
basic physical properties of the components. HD 81009 is a highly
eccentric (e=0.718), long-period (P_orb=29.3 y) binary composed of two
main sequence A-type stars. While its presence is required in order to
explain the astrometric and photometric observations, the cooler
secondary component is never detected spectroscopically, and is
therefore inferred to rotate somewhat more rapidly than the hotter
component. The hotter primary component is identified as the
slowly-rotating (P_rot=33fd 984) magnetic Ap star. We have modeled the
magnetic field geometry of this star using new and archival longitudinal
magnetic field and mean magnetic field modulus observations. The
rotational variations of the magnetic quantities are consistent with a
decentered dipole surface magnetic field geometry with small magnetic
obliquity (beta < 20degr ). This is consistent with the observation
of Landstreet & Mathys (2000), who report that nearly all magnetic
Ap stars with periods longer than around 25 days exhibit beta <20degr
, implying that their magnetic fields are approximately aligned with
their rotational axes. Based on observations obtained at the European
Southern Observatory (La Silla, Chile), the Haute Provence and Pic du
Midi Observtories (France), and the Las Campanas Observatory (Chile)
Astronomy and Astrophysics 08/2000; 361:991-1000. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with the existence of an unseen (collapsed?) companion or of spatially extended wind structures as potential candidates. We present observations of WR 1 which highlight the unusual character of the variations in this object. Our narrowband photometric observations reveal a gradual increase of the stellar continuum flux amounting to Delta v = 0.09 mag followed by a decline on about the same timescale (3-4 days). Only marginal evidence for variability is found during the 11 following nights. Strong, daily line-profile variations are also observed but they cannot be easily linked to the photometric variations. Similarly to the continuum flux variations, coherent time-dependent changes are observed in 1996 in the centroid, equivalent width, and skewness of He II 4686. Despite the generally coherent nature of the variations, we do not find evidence in our data for the periods claimed in previous studies. While the issue of a cyclical pattern of variability in WR 1 is still controversial, it is clear that this object might constitute in the future a cornerstone for our understanding of the mechanisms leading to the formation of largely anisotropic outflows in Wolf-Rayet stars.
08/1999;
-
T. Morel,
S. V. Marchenko,
P. R. J. Eenens,
A. F. J. Moffat,
G. Koenigsberger,
I. I. Antokhin,
T. Eversberg,
G. H. Tovmassian, G. M. Hill,
O. Cardona,
N. St-Louis
[show abstract]
[hide abstract]
ABSTRACT: We present the results of an intensive campaign of spectroscopic and photometric monitoring of the peculiar Wolf-Rayet star WR 134 from 1989 to 1997. This unprecedentedly large data set allows us to confirm unambiguously the existence of a coherent 2.25 +/- 0.05 day periodicity in the line-profile changes of He II 4686, although the global pattern of variability is different from one epoch to another. This period is only marginally detected in the photometric data set. Assuming the 2.25 day periodic variability to be induced by orbital motion of a collapsed companion, we develop a simple model aiming at investigating (i) the effect of this strongly ionizing, accreting companion on the Wolf-Rayet wind structure, and (ii) the expected emergent X-ray luminosity. We argue that the predicted and observed X-ray fluxes can only be matched if the accretion on the collapsed star is significantly inhibited. Additionally, we performed simulations of line-profile variations caused by the orbital revolution of a localized, strongly ionized wind cavity surrounding the X-ray source. A reasonable fit is achieved between the observed and modeled phase-dependent line profiles of He II 4686. However, the derived size of the photoionized zone substantially exceeds our expectations, given the observed low-level X-ray flux. Alternatively, we explore rotational modulation of a persistent, largely anisotropic outflow as the origin of the observed cyclical variability. Although qualitative, this hypothesis leads to greater consistency with the observations. Comment: 34 pages, 16 figures. Accepted by the Astrophysical Journal
The Astrophysical Journal 01/1999; · 6.02 Impact Factor
-
T. Morel,
S. V. Marchenko,
P. R. J. Eenens,
A. F. J. Moffat,
G. Koenigsberger,
I. I. Antokhin,
T. Eversberg,
G. H. Tovmassian, G. M. Hill,
O. Cardona,
N. St-Louis
[show abstract]
[hide abstract]
ABSTRACT: Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence of an orbiting collapsed companion,
or by the rotational modulation of a largely inhomogeneous outflow.
Astrophysics and Space Science 09/1998; 260(1):173-176. · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: As a conclusion of our all-sky variability survey of the 'enigmatic'
variable WN8 stars, we have carried out coordinated multisite
photometric and spectroscopic observations of WN8 stars in 1989 and
1994-1995. We confirm the leading role of the stellar core in
restructuring the whole wind. This emerges as a statistical trend: the
higher the level of the continuum (i.e., core) light variations, the
higher the variability of the P Cygni edges of the optical emission
lines. However, the form of the correlation between the light and
profile variations is generally different for each individual star. The
high level of activity of WN8 stars may be supported/induced by
pulsational instability.
Monthly Notices of the Royal Astronomical Society 02/1998; 294:642. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A large collection of blue and yellow CCD spectra of the short-period
eclipsing binary CQ Cep allows us to improve the double-line (SB2) orbit
of Kartasheva & Snezhko and reclassify the system as WN6+O9 II-Ib.
With orbital inclination i = 78° 65°, the masses and radii are
Msun = 18-23 Msun, MWR = 15-19
Msun, R0 ≤ 10 Rsun, 2
Rsun ≤ RWR ≤ 10 Rsun. For its
spectral type, the 0 star mass and radius are smaller than values
deduced from evolutionary models but agree with recent determinations of
other O stars in binaries. The W-R star is shown to contain a small
amount of hydrogen in its wind.
Because of the rapid orbit revolution compared to the wind velocities,
the wind interaction zone is tightly wrapped around the system. We
construct a phenomenological model which explains the numerous
phase-dependent spectral variations.
The Astrophysical Journal 08/1995; 450:811. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An internally consistent set of relative oscillator strengths for 109
spectral lines of Ti II in the range 3800-5500 Å has been derived.
These oscillator strengths have been obtained by combining available
laboratory data and theoretical calculations with new astrophysical
oscillator strengths determined from both published photographic
equivalent width lists and spectral synthesis of a number of available
Reticon spectra of several sharp-lined stars. The accuracy of our
astrophysical oscillator strengths has been tested by determining
astrophysical gf-values for a number of lines of Fe II by the same
methods. The Ti II data have been normalized to the astrophysical
oscillator strengths of Kostyk & Orlova, which also places them
essentially on the scale of Danzmann & Kock, one of the most recent
and extensive experimental data sets. It appears that the accuracy of
the relative gf-values in our final mean list for Ti II is typically
about 0.08 dex. The absolute normalization is believed to be secure to
within about 0.15 dex.
Monthly Notices of the Royal Astronomical Society 03/1994; 267:697. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have determined abundances of up to 18 chemical elements using
spectrum synthesis for half a dozen narrow-lined A-type stars. Except
for Sirius (a hot Am star) and perhaps ο Peg all are classified as
normal. Our results agree fairly well with those in the literature
obtained using more traditional techniques. Considerable star-to-star
abundance variations are present, even among the apparently normal
stars. The abundance of iron varies over a range of about 0.7 dex and
the abundances of most elements seem to vary at least roughly with those
of iron. Our results are consistent with an approximately constant
helium underabundance with respect to the Sun for all six stars; carbon
exhibits an anti-correlation with iron.
Astronomy and Astrophysics 08/1993; 276:142. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We are carrying out a program of high signal-to-noise, high resolution
Hα spectroscopy of a number of magnetic helium-strong and
helium-weak stars with the Canada-France-Hawaii 3.6-m, Dominion
Astrophysical Observatory 1.8-m, and David Dunlap Observatory 1.8-m
telescopes. These observations have resulted in the discovery of several
new spectrum variables, and include the first observations of variable
Hα emission and absorption in a number of helium-weak stars. In
all cases, the spectrum variations have periods identical to the stars'
rotation periods as derived from photometric or polarimetric
observations. As has been suggested for the prototypical helium-strong
star sigma Ori E, the Hα variations apparently arise from the
changing aspect of circumstellar material trapped in the magnetospheres
of these peculiar stars.
04/1993; 25:871.
-
The Journal of the Royal Astronomical Society of Canada. Royal Astronomical Society of Canada 07/1991; 85:196-197.
