542 research outputs found
Speckle interferometry and radiative transfer modelling of the Wolf-Rayet star WR 118
WR 118 is a highly evolved Wolf-Rayet star of the WC10 subtype surrounded by
a permanent dust shell absorbing and re-emitting in the infrared a considerable
fraction of the stellar luminosity. We present the first diffraction-limited
2.13micron speckle interferometric observations of WR 118 with 73 mas
resolution. The speckle interferograms were obtained with the 6m telescope at
the Special Astrophysical Observatory. The two-dimensional visibility function
of the object does not show any significant deviation from circular symmetry.
The visibility curve declines towards the diffraction cut-off frequency to 0.66
and can be approximated by a linear function. Radiative transfer calculations
have been carried out to model the spectral energy distribution, given in the
range of 0.5-25micron, and our 2.13micron visibility function, assuming
spherical symmetry of the dust shell. Both can be fitted with a model
containing double-sized grains (``small'' and ``large'') with the radii of a =
0.05micron and 0.38micron, and a mass fraction of the large grains greater than
65%. Alternatively, a good match can be obtained with the grain size
distribution function n(a)~a^-3, with a ranging between 0.005micron and
0.6micron. At the inner boundary of the modelled dust shell (angular diameter
(17 +/- 1)mas), the temperature of the smallest grains and the dust shell
density are 1750K +/- 100K and (1 +/- 0.2)x10^-19 g/cm^3, respectively. The
dust formation rate is found to be (1.3 +/- 0.5)x10^-7 Msol/yr assuming Vwind =
1200 km/s.Comment: 6 pages including 4 PostScript figures, also available from
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.html;
accepted for publication in Astronomy & Astrophysic
The massive Wolf-Rayet Binary LSS1964 (=WR29), II: the V light curve
Context. WR 29 is a known WN7h+O double-lined binary system with a rather short period (3.164 days). Aims. We search for light variations to determine the inclination of the system and thus the absolute masses of both components. Methods. We observed photometrically the field of WR 29 between December, 2002, and February, 2006. Results. We find that the V light of WR 29 varies in phase with the spectroscopic period of 3.16412 days, presenting two minima corresponding to the conjunctions of the binary components. Numerical models fitted to the light curve indicate an orbital inclination of about 44◦, and masses of 53 M and 42 M for the O- and WN-type components, respectively.Fil: Gamen, Roberto Claudio. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Fernandez Lajus, Eduardo Eusebio. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Niemela, Virpi Sinikka. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Barba, Rodolfo Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentin
Are WC9 Wolf-Rayet stars in colliding-wind binaries?
We present results from a spectroscopic search for massive companions to
dust-making Galactic WC9 stars as a step to testing the paradigm that dust
formation in these systems requires colliding winds to produce over densities.
We find evidence for OB companions to the WC9 stars WR 59 and WR 65, but not WR
121 or WR 117. We identify lines of N III-V and possibly N II in the spectrum
of WR 88, one of the few Galactic WC9 stars which do not make circumstellar
dust, and suggest that WR 88 is a transitional WN-WC9 object and less evolved
than the other WC9 stars. On the other hand, the possible identification of a
strong emission line at 4176A in the spectrum of WR 117 with Ne I suggests that
this star is more evolved than other WC9 stars studied.Comment: 4 pages, 3 figures, contribution to "Massive Stars and High-Energy
Emission in OB Associations"; JENAM 2005, held in Liege (Belgium
A Galactic O2 If*/WN6 star possibly ejected from its birthplace in NGC3603
In this work I report the discovery of a new Galactic O2 If*/WN6 star, a rare
member of the extremely massive hydrogen core-burning group of stars that due
its high intrinsic luminosity (close to the Eddington limit), possess an
emission-line spectrum at the beginning of their main-sequence evolution,
mimicking the spectral appearance of classical WR stars. The new star is named
WR42e and is found in isolation at 2.7 arcmin (about 6 pc) from the core of the
star-burst cluster NGC3603. From the computed E(B-V) color excess and observed
visual magnitude it was possible to estimate its absolute visual magnitude as
MV =-6.3 mag, which is a value similar to those obtained by other researchers
for stars of similar spectral type both, in the Galaxy and in the Large
Magellanic Cloud. Considering the derived absolute visual magnitude, we
computed a bolometric stellar luminosity of about 3.2x106 Lsun. Finally, the
mass of the new O2If*/WN6 star was estimated by comparing its observed
magnitudes and colors with those of other probable NGC3603 cluster members,
founding that the WR42e initial mass possibly exceeds 100 Msun.Comment: Accepted for publication on MNRAS Letter
The Discovery of a Twelfth Wolf-Rayet Star in the Small Magellanic Cloud
We report the discovery of a relatively faint (V=15.5) early-type WN star in
the SMC. The line strength and width of He II lambda 4686 emission is similar
to that of the other SMC WNs, and the presense of N V lambda 4603,19 emission
(coupled with the lack of N III) suggests this star is of spectral type
WN3-4.5, and thus is similar in type to the other SMC WRs. Also like the other
SMC WN stars, an early-type absorption spectrum is weakly present. The absolute
magnitude is comparable to that of other (single) Galactic early-type WNs. The
star is located in the Hodge 53 OB association, which is also the home of two
other SMC WNs. This star, which we designate SMC-WR12, was actually detected at
a high significance level in an earlier interference-filter survey, but the
wrong star was observed as part of a spectroscopic followup, and this case of
mistaken identity resulted in its Wolf-Rayet nature not being recognized until
now.Comment: Accepted by PASP (November 2003 issue
A very large array 3.6 centimeter continuum survey of galactic wolf-rayet stars
We report the results of a survey of radio continuum emission of Galactic Wolf-Rayet (WR) stars north of δ = -46°. The observations were obtained at 8.46 GHz (3.6 cm) using the Very Large Array, with an angular resolution of ∼6″ × 9″ and typical rms noise of ∼0.04 mJy beam-1. Our survey of 34 WR stars resulted in 15 definite, and five probable detections, 13 of these for the first time at radio wavelengths. All detections are unresolved (θ ≲ 5″). Time variations in flux are confirmed in the cases of WR 98a, 104, 105, and 125. WR 79a and WR 89 are also variable in flux, and we suspect they are also nonthermal emitters. Thus, of our sample 20%30% of the detected stars are nonthermal emitters. Average mass-loss rate determinations obtained excluding definite and suspected nonthermal cases give similar values for WN (all subtypes) and WC5-7 stars [M(WN) = (4 ± 3) × 10-5 M⊙ yr-1 and M(WC5-7) = (4 ± 2) × 10-5 M⊙ yr-1], while a lower value was obtained for WC8-9 stars [M(WC8-9) = (2 ± 1) × 10-5 M ⊙ yr-1]. Uncertainties in stellar distances largely contribute to the observed scatter in mass-loss rates. Upper limits to the mass-loss rates were obtained in cases of undetected sources and for sources that probably show additional nonthermal emission.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí
Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma Velorum
We present XMM-Newton observations of gamma^2 Velorum (WR 11, WC8+O7.5III, P
= 78.53 d), a nearby Wolf-Ray binary system, at its X-ray high and low states.
At high state, emission from a hot collisional plasma dominates from about 1 to
8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma
is identified with the shock zone between the winds of the primary Wolf-Rayet
star and the secondary O giant. The absorption at low state is interpreted as
photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to
measure the absorbing column density and to derive a mass loss rate 8x10^{-6}
M_sun/yr for the WC8 star. This mass loss rate, in conjunction with a previous
Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping
factor of 16 is required. The X-ray spectra below 1 keV (12 Ang) show no
absorption and are essentially similar in both states. There is a rather clear
separation in that emission from a plasma hotter than 5 MK is heavily absorbed
in low state while the cooler plasma is not. This cool plasma must come from a
much more extended region than the hot material. The Neon abundance in the
X-ray emitting material is 2.5 times the solar value. The unexpected detection
of CV (25.3 Ang) and CVI (31.6 Ang) radiative recombination continua at both
phases indicates the presence of a cool (~40,000 K) recombination region
located far out in the binary system.Comment: 16 page
Obscured clusters.I. GLIMPSE30 - Young Milky Way Star Cluster Hosting Wolf-Rayet Stars
Young massive clusters are perfect astrophysical laboratories for study of
massive stars. Clusters with Wolf-Rayet (WR) stars are of special importance,
since this enables us to study a coeval WR population at a uniform metallicity
and known age. GLIMPSE30 (G30) is one of them. The cluster is situated near the
Galactic plane (l=298.756deg, b=-0.408deg) and we aimed to determine its
physical parameters and to investigate its high-mass stellar content and
especially WR stars. Our analysis is based on SOFI/NTT JsHKs imaging and low
resolution (R~2000) spectroscopy of the brightest cluster members in the K
atmospheric window. For the age determination we applied isochrone fits for MS
and Pre-MS stars. We derived stellar parameters of the WR stars candidates
using a full nonLTE modeling of the observed spectra. Using a variety of
techniques we found that G30 is very young cluster, with age t~4Myr. The
cluster is located in Carina spiral arm, it is deeply embedded in dust and
suffers reddening of Av~10.5+-1.1mag. The distance to the object is
d=7.2+-0.9kpc. The mass of the cluster members down to 2.35Msol is ~1600Msol.
Cluster's MF for the mass range of 5.6 to 31.6Msol shows a slope of
Gamma=-1.01+-0.03. The total mass of the cluster obtained by this MF down to
1Msol is about 3x10^3Msol. The spectral analysis and the models allow us to
conclude that in G30 are at least one Ofpe/WN and two WR stars. The WR stars
are of WN6-7 hydrogen rich type with progenitor masses more than 60Msol. G30 is
a new member of the exquisite family of young Galactic clusters, hosting WR
stars. It is a factor of two to three less massive than some of the youngest
super-massive star clusters like Arches, Quintuplet and Central cluster and is
their smaller analog.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Assisted stellar suicide in V617 Sgr
V617 Sgr is a V Sagittae star - a group of binaries thought to be the
galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. To
check this hypothesis, we measured the time derivative of its orbital period.
Observed timings of eclipse minima spanning over 30,000 orbital cycles are
presented. We found that the orbital period evolves quite rapidly: P/Pdot = 1.1
x 10^{6} years. This is consistent with the idea that V617 Sgr is a wind driven
accretion supersoft source. As the binary system evolves with a time-scale of
about one million years, which is extremely short for a low mass evolved
binary, it is likely that the system will soon end either by having its
secondary completely evaporated or by the primary exploding as a supernova of
type Ia.Comment: 4 pages, accepted for publication in A&A Letter
- …