740 research outputs found
Spatially resolved stis spectra of WR + OB binaries with colliding winds
We present spatially resolved spectra of the visual WR + OB massive binaries WR 86, WR 146, and WR 147, obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The systems are classified as follows: WR 86 = WC 7 + BO III, WR 146 = WC 6 + O8 I-IIf, WR 147 = WN 8 + O5-7 I-II(f). Both WR 146 and WR 147 are known to have strong nonthermal radio emission arising in a wind-wind collision shock zone between the WR and OB components. We find that the spectra of their O companions show Hα profiles in emission, indicative of large mass-loss rates and consistent with the colliding-wind model. Our spectra indicate that the B component in WR 86 has a low mass-loss rate, which possibly explains the fact that WR 86, despite being a long-period WR + OB binary, was not found to be a strong nonthermal radio emitter. Because of the small mass-loss rate of the B-star component in WR 86, the wind collision region must be closer to the B star and smaller in effective area, hence generating smaller amounts of nonthermal radio emission. Absolute magnitudes for all the stars are estimated based on the spectral types of the components (based on the tables by Schmidt-Kaler for OB stars and van der Hucht for WR stars) and compared with actual, observed magnitude differences. While the derived luminosities for the WC 7 and BO III stars in WR 86 are consistent with the observed magnitude difference, we find a discrepancy of at least 1.5 mag between the observed luminosities of the components in each of WR 146 and WR 147 and the absolute magnitudes expected from their spectral types. In both cases, it looks as though either the WR components are about 2 mag too bright for their spectral types or that the O components are about 2 mag too faint. We discuss possible explanations for this apparent discrepancy.Facultad de Ciencias Astronómicas y Geofísica
Hubble Space Telescope Imaging of the WR 38/WR38a Cluster
We are conducting a high angular resolution imaging survey of Galactic
Wolf-Rayet stars using the Wide Field and Planetary Camera 2 aboard the Hubble
Space Telescope. We have found a small stellar cluster associated with the
faint, close pair WR 38 and WR 38a. We present astrometric measurements and
photometry in the wide-band F336W (U), F439W (B), and F555W (V) filter system
for these cluster and nearby stars. We compare their colors and magnitudes with
calibrated model results for reddened stars to identify seven probable main
sequence members of the cluster. A least-squares fit of the colors and
magnitudes of this set yields a cluster reddening of E(B-V) = 1.45 +/- 0.14 mag
and a distance of 3.7^{+3.8}_{-1.2} kpc. We discuss the relationship of this
cluster to other objects along the line of sight, and we argue that the
distance probably lies in the range 5 - 8 kpc (but is not as great as 14.5 kpc
distance recently advocated by Shorlin, Turner, & Pedreros). At a distance of 8
kpc, the cluster would reside in a dense region of the Carina spiral arm, close
to a giant molecular cloud and the starburst cluster NGC 3603.Comment: Submitted to AJ, 24 pages, 3 figures Content is significantly change
Hubble Space Telescope imaging of the WR 38/WR 38a cluster
We are conducting a high angular resolution imaging survey of Galactic Wolf-Rayet stars using the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope (HST). We have found a small stellar cluster associated with the faint, close pair WR 38 and WR 38a. We present astrometric measurements and photometry in the wideband F336W (U), F439W (5), and F555W (V) filter system for the cluster and nearby stars. We combine our photometry with Johnson and IR magnitudes and compare the observations with calibrated model results for reddened stars to adjust the HST zero points and to identify five probable main-sequence members of the cluster. A least-squares fit of the colors and magnitudes of this set yields a cluster reddening of E(B - V) = 1.63 ±0.05 mag and a distance of 10 -4 +12 kpc for an assumed ratio of total to selective extinction of R = 3.1. We discuss the relationship of this cluster to other objects along the line of sight. If situated at a distance of ≈8 kpc, then the cluster would reside in a dense region of the Carina spiral arm, close to a giant molecular cloud and the starburst cluster NGC 3603.Facultad de Ciencias Astronómicas y Geofísica
A High Angular Resolution Survey of Massive Stars in Cygnus OB2: Results from the Hubble Space Telescope Fine Guidance Sensors
We present results of a high angular resolution survey of massive OB stars in
the Cygnus OB2 association that we conducted with the Fine Guidance Sensor 1R
(FGS1r) on the Hubble Space Telescope. FGS1r is able to resolve binary systems
with a magnitude difference delta-V < 4 down to separations as small as 0.01
arcsec. The sample includes 58 of the brighter members of Cyg OB2, one of the
closest examples of an environment containing a large number of very young and
massive stars. We resolved binary companions for 12 targets and confirmed the
triple nature of one other target, and we offer evidence of marginally resolved
companions for two additional stars. We confirm the binary nature of 11 of
these systems from complementary adaptive optics imaging observations. The
overall binary frequency in our study is 22% to 26% corresponding to orbital
periods ranging from 20 - 20,000 years. When combined with the known
short-period spectroscopic binaries, the results supports the hypothesis that
the binary fraction among massive stars is > 60%. One of the new discoveries is
a companion to the hypergiant star MT 304 = Cyg OB2-12, and future measurements
of orbital motion should provide mass estimates for this very luminous star.Comment: accepted for AJ, 84 pages, 61 figure
Spatially resolved stis spectra of WR + OB binaries with colliding winds
We present spatially resolved spectra of the visual WR + OB massive binaries WR 86, WR 146, and WR 147, obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The systems are classified as follows: WR 86 = WC 7 + BO III, WR 146 = WC 6 + O8 I-IIf, WR 147 = WN 8 + O5-7 I-II(f). Both WR 146 and WR 147 are known to have strong nonthermal radio emission arising in a wind-wind collision shock zone between the WR and OB components. We find that the spectra of their O companions show Hα profiles in emission, indicative of large mass-loss rates and consistent with the colliding-wind model. Our spectra indicate that the B component in WR 86 has a low mass-loss rate, which possibly explains the fact that WR 86, despite being a long-period WR + OB binary, was not found to be a strong nonthermal radio emitter. Because of the small mass-loss rate of the B-star component in WR 86, the wind collision region must be closer to the B star and smaller in effective area, hence generating smaller amounts of nonthermal radio emission. Absolute magnitudes for all the stars are estimated based on the spectral types of the components (based on the tables by Schmidt-Kaler for OB stars and van der Hucht for WR stars) and compared with actual, observed magnitude differences. While the derived luminosities for the WC 7 and BO III stars in WR 86 are consistent with the observed magnitude difference, we find a discrepancy of at least 1.5 mag between the observed luminosities of the components in each of WR 146 and WR 147 and the absolute magnitudes expected from their spectral types. In both cases, it looks as though either the WR components are about 2 mag too bright for their spectral types or that the O components are about 2 mag too faint. We discuss possible explanations for this apparent discrepancy.Facultad de Ciencias Astronómicas y Geofísica
Hubble Space Telescope imaging of the WR 38/WR 38a cluster
We are conducting a high angular resolution imaging survey of Galactic Wolf-Rayet stars using the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope (HST). We have found a small stellar cluster associated with the faint, close pair WR 38 and WR 38a. We present astrometric measurements and photometry in the wideband F336W (U), F439W (5), and F555W (V) filter system for the cluster and nearby stars. We combine our photometry with Johnson and IR magnitudes and compare the observations with calibrated model results for reddened stars to adjust the HST zero points and to identify five probable main-sequence members of the cluster. A least-squares fit of the colors and magnitudes of this set yields a cluster reddening of E(B - V) = 1.63 ±0.05 mag and a distance of 10 -4 +12 kpc for an assumed ratio of total to selective extinction of R = 3.1. We discuss the relationship of this cluster to other objects along the line of sight. If situated at a distance of ≈8 kpc, then the cluster would reside in a dense region of the Carina spiral arm, close to a giant molecular cloud and the starburst cluster NGC 3603.Facultad de Ciencias Astronómicas y Geofísica
Spatially resolved STIS spectra of WR+OB binaries with colliding winds
We present spatially resolved spectra of the visual WR+OB massive binaries
WR86, WR146, and WR147, obtained with the Space Telescope Imaging Spectrograph
on board the Hubble Space Telescope. The systems are classified as follows:
WR86 = WC7 + B0 III, WR146 = WC6 + O8 I-IIf, WR147 = WN8 + O5-7 I-II(f). Both
WR146 and WR147 are known to have strong non-thermal radio emission arising in
a wind-wind collision shock zone between the WR and OB components. We find that
the spectra of their O companions show Halpha profiles in emission, indicative
of large mass-loss rates, and consistent with the colliding-wind model. Our
spectra indicate that the B component in WR86 has a low mass-loss rate, which
possibly explains the fact that WR86, despite being a long period WR+OB binary,
was not found to be a strong non-thermal radio emitter. Because of the small
mass-loss rate of the B star component in WR86, the wind collision region must
be closer to the B star and smaller in effective area, hence generating smaller
amounts of non-thermal radio emission. Absolute magnitudes for all the stars
are estimated based on the spectral types of the components (based on the
tables by Schmidt-Kaler for OB stars, and van der Hucht for WR stars), and
compared with actual, observed magnitude differences. While the derived
luminosities for the WC7 and B0 III stars in WR86 are consistent with the
observed magnitude difference, we find a discrepancy of at least 1.5 magnitudes
between the observed luminosities of the components in each of WR146 and WR147
and the absolute magnitudes expected from their spectral types. In both cases,
it looks as though either the WR components are about 2 magnitudes too bright
for their spectral types, or that the O components are about 2 magnitudes too
faint. We discuss possible explanations for this apparent discrepancy.Comment: Accepted for publication in the Astronomical Journa
Search for Gravitational Wave Bursts from Soft Gamma Repeaters
We present the results of a LIGO search for short-duration gravitational
waves (GWs) associated with Soft Gamma Repeater (SGR) bursts. This is the first
search sensitive to neutron star f-modes, usually considered the most efficient
GW emitting modes. We find no evidence of GWs associated with any SGR burst in
a sample consisting of the 27 Dec. 2004 giant flare from SGR 1806-20 and 190
lesser events from SGR 1806-20 and SGR 1900+14 which occurred during the first
year of LIGO's fifth science run. GW strain upper limits and model-dependent GW
emission energy upper limits are estimated for individual bursts using a
variety of simulated waveforms. The unprecedented sensitivity of the detectors
allows us to set the most stringent limits on transient GW amplitudes published
to date. We find upper limit estimates on the model-dependent isotropic GW
emission energies (at a nominal distance of 10 kpc) between 3x10^45 and 9x10^52
erg depending on waveform type, detector antenna factors and noise
characteristics at the time of the burst. These upper limits are within the
theoretically predicted range of some SGR models.Comment: 6 pages, 1 Postscript figur
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