125 research outputs found
Radial Velocities of Six OB Stars
We present new results from a radial velocity study of six bright OB stars
with little or no prior measurements. One of these, HD 45314, may be a
long-period binary, but the velocity variations of this Be star may be related
to changes in its circumstellar disk. Significant velocity variations were also
found for HD 60848 (possibly related to nonradial pulsations) and HD 61827
(related to wind variations). The other three targets, HD 46150, HD 54879, and
HD 206183, are constant velocity objects, but we note that HD 54879 has
H emission that may originate from a binary companion. We illustrate
the average red spectrum of each target.Comment: Accepted for publication in PASP July 2007 issu
The Long Period, Massive Binaries HD 37366 and HD 54662: Potential Targets for Long Baseline Optical Interferometry
We present the results from an optical spectroscopic analysis of the massive
stars HD 37366 and HD 54662. We find that HD 37366 is a double-lined
spectroscopic binary with a period of 31.8187 +/- 0.0004 days, and HD 54662 is
also a double lined binary with a much longer period of 557.8 +/- 0.3 days. The
primary of HD 37366 is classified as O9.5 V, and it contributes approximately
two-thirds of the optical flux. The less luminous secondary is a broad-lined,
early B-type main-sequence star. Tomographic reconstruction of the individual
spectra of HD 37366 reveals absorption lines present in each component,
enabling us to constrain the nature of the secondary and physical
characteristics of both stars. Tomographic reconstruction was not possible for
HD 54662; however, we do present mean spectra from our observations that show
that the secondary component is approximately half as bright as the primary.
The observed spectral energy distributions (SEDs) were fit with model SEDs and
galactic reddening curves to determine the angular sizes of the stars. By
assuming radii appropriate for their classifications, we determine distance
ranges of 1.4 - 1.9 and 1.2 - 1.5 kpc for HD 37366 and HD 54662, respectively.Comment: 27 pages, 8 figures, Accepted for publication in Ap
Comparison of the ICare® rebound tonometer with the Goldmann tonometer in a normal population
The aim of this study was to evaluate the accuracy of measurement of intraocular pressure (IOP) using a new induction/impact rebound tonometer (ICare) in comparison with the Goldmann applanation tonometer (AT). The left eyes of 46 university students were assessed with the two tonometers, with induction tonometry being performed first. The ICare was handled by an optometrist and the Goldmann tonometer by an ophthalmologist. In this study, statistically significant differences were found when comparing the ICare rebound tonometer with applanation tonometry (AT) (p < 0.05). The mean difference between the two tonometers was 1.34 +/- 2.03 mmHg (mean +/- S.D.) and the 95% limits of agreement were +/-3.98 mmHg. A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <3 mmHg between the ICare and the AT. In the present population the ICare overestimates the IOP value by 1.34 mmHg on average when compared with Goldmann tonometer. Nevertheless, the ICare tonometer may be helpful as a screening tool when Goldmann applanation tonometry is not applicable or not recommended, as it is able to estimate IOP within a range of +/-3.00 mmHg in more than 80% of the populatio
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
Wind Accretion and State Transitions in Cygnus X-1
We present the results of a spectroscopic monitoring program (from 1998 to
2002) of the H-alpha emission strength in HDE 226868, the optical counterpart
of the black hole binary, Cyg X-1. The H-alpha profiles consist of (1) a P
Cygni component associated with the wind of the supergiant, (2) emission
components that attain high velocity at the conjunctions and that probably form
in enhanced outflows both towards and away from the black hole, and (3) an
emission component that moves in anti-phase with the supergiant's motion. We
argue that the third component forms in accreted gas near the black hole, and
the radial velocity curve of the emission is consistent with a mass ratio of
M_X / M_opt = 0.36 +/- 0.05. We find that there is a general anti-correlation
between the H-alpha emission strength and X-ray flux in the sense that when the
H-alpha emission is strong (W_\lambda < -0.5 Angstroms) the X-ray flux is
weaker and the spectrum harder. On the other hand, there is no correlation
between H-alpha emission strength and X-ray flux when H-alpha is weak. During
the low/hard X-ray state, the strong wind is fast and the accretion rate is
relatively low, while in the high/soft state the weaker, highly ionized wind
attains only a moderate velocity and the accretion rate increases. We argue
that the X-ray transitions from the normal low/hard to the rare high/soft state
are triggered by episodes of decreased mass loss rate in the supergiant donor
star.Comment: 45 pages, 16 figures, ApJ, in pres
Spectroscopic Hα and Hγ survey of field Be stars: 2004-2009
Massive O- and B-type stars are cosmic engines in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15-30% of the sample shows indications of binarity. © International Astronomical Union 2011
Joint H-alpha and X-Ray Observations of Massive X-Ray Binaries. II. The Be X-ray Binary and Microquasar LS I +61 303
We present the results of an H-alpha monitoring campaign on the BeXRB and
microquasar system LS I +61 303. We use radial velocity measurements of HeI
lines in our spectra to re-evaluate the orbital elements and to better
establish the time of periastron. We list equivalent widths and other
parameters for the H-alpha emission line and discuss the orbital phase related
variations observed. We call attention to a dramatic episode of emission
weakening that occurred in less than a day that probably resulted from exposure
to a transient source of ionizing radiation. We argue that the increase in
H-alpha and X-ray emission following periastron probably results from the
creation of an extended density wave in the disk created by tidal forces. We
also discuss estimates of the size of the disk from the H-alpha equivalent
width measurements, and we suggest that the disk radius from the average
equivalent width corresponds to a resonant truncation radius of the disk while
the maximum equivalent width corresponds to a radius limited by the separation
of the stars at periastron. We note that a nearby faint companion is probably
an unrelated foreground object.Comment: 18 pages including 7 figures and 2 tables, accepted to Ap
The Massive Runaway Stars HD 14633 and HD 15137
We present results from a radial velocity study of two runaway O-type stars,
HD 14633 (ON8.5 V) and HD 15137 (O9.5 III(n)). We find that HD 14633 is a
single-lined spectroscopic binary with an orbital period of 15.4083 days. The
second target HD 15137 is a radial velocity variable and a possible
single-lined spectroscopic binary with a period close to 1 month. Both binaries
have large eccentricity, small semiamplitude, and a small mass function. We
show the trajectories of the stars in the sky based upon an integration of
motion in the Galactic potential, and we suggest that both stars were ejected
from the vicinity of the open cluster NGC 654 in the Perseus spiral arm. The
binary orbital parameters and runaway velocities are consistent with the idea
that both these stars were ejected by supernova explosions in binaries and that
they host neutron star companions. We find that the time-of-flight since
ejection is longer than the predicted evolutionary timescales for the stars,
which may indicate that they have a lower mass than normally associated with
their spectral classifications and/or that their lives have been extended
through rapid rotation.Comment: Submitted to ApJ, 22 pages, 4 figure
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