74 research outputs found
Observations of the X-ray Nova GRO~J0422+32: II: Optical Spectra Approaching Quiescence
We present results obtained from a series of 5~\AA\ resolution spectra of the
X-ray Nova GRO~J0422+32 obtained in 1993~October, when the system was
approximately 2 magnitudes above quiescence, with . The data
were obtained in an effort to measure the orbital radial velocity curve of the
secondary, but detection of the narrow photospheric absorption lines needed to
do this proved elusive. Instead we found wide absorption bands reminiscent of
M~star photospheric features. The parameters determined by fitting accretion
disk line profiles (Smak profiles) to the H line are similar to those
found in several strong black-hole candidates. Measurements of the velocity of
the H line are consistent with an orbital period of 5.1~hours and a
velocity semi-amplitude of the primary of ~\kms. These measurements,
when combined with measurements of the velocity semi-amplitude of the secondary
made by others, indicate that the mass ratio . If the secondary
follows the empirical mass-radius relation found for CVs, the low implies a
primary mass of \mo, and a rather low (face-on) inclination. The
H EW is found to be modulated on the orbital period with a phasing that
implies a partial eclipse of the disk by the secondary, but simultaneous R~band
photometry shows no evidence for such an eclipse.Comment: Accepted for ApJ, plain latex, 5 figures available as self-extracting
uuendoced, compressed, tarfiles (from uufiles
The mass of the neutron star in the binary millisecond pulsar PSR J1012+5307
We have measured the radial velocity variation of the white dwarf secondary in the binary system containing the millisecond pulsar PSR J1012 + 5307. Combined with the orbital parameters of the radio pulsar, we infer a mass ratio q (=M-1/M-2) = 10.5 +/- 0.5 OUT optical spectroscopy has also allowed us to determine the mass of the white dwarf companion by fitting the spectrum to a grid of DA model atmospheres: we estimate M-2 = 0.16 +/- 0.02 M., and hence the mass of the neutron star is 1.64 +/- 0.22 M., where the error is dominated by that of M-2. The orbital inclination is 52 +/- 4 deg. For an initial neutron star mass of similar to 1.4 M., only a few tenths of a solar mass at most has been successfully accreted over the lifetime of the progenitor low-mass X-ray binary. If the initial mass of the secondary was similar to 1 M., our result suggests that the mass transfer may have been non-conservative
Keck Infrared Observations of GRO J0422+32 in Quiescence
We present Keck K-band photometry and low-resolution H & K-band spectroscopy
of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent
state. No clear ellipsoidal modulation is present in the light curve, which is
instead dominated by a strong flickering component. In the K-band we observe
strong Br_gamma emission, with an equivalent width of 38 +/- 5 Angstroms. From
this we conclude that the accretion disc is the most likely source of the
observed photometric contamination, and that previous infrared-based attempts
to constrain the mass of the putative black hole in this system are prone to
considerable uncertainty. We finally proceed to show how it is possible to
place meaningful constraints on some of the binary parameters of this system,
even in the presence of a relatively high level of contamination from the disc.Comment: 7 pages, 6 figures & 1 table. Accepted for publication in MNRA
Detection of hard X-ray pulsations and a strong iron K_beta emission line during an extended low state of GX 1+4
We present here results obtained from a detailed timing and spectral analysis
of three BeppoSAX observations of the binary X-ray pulsar GX 1+4 carried out in
August 1996, March 1997, and August 2000. In the middle of the August 2000
observation, the source was in a rare low intensity state that lasted for about
30 hours. Though the source does not show pulsations in the soft X-ray band
(1.0-5.5 keV) during the extended low state, pulsations are detected in
5.5-10.0 keV energy band of the MECS detector and in hard X-ray energy bands
(15-150 keV) of the PDS instrument. Comparing the 2-10 keV flux during this low
state with the previously reported low states in GX 1+4, we suggest that the
propeller regime in GX 1+4 occurs at a lower mass accretion rate than reported
earlier. Broad-band (1.0-150 keV) pulse averaged spectroscopy reveals that the
best-fit model comprises of a Comptonized continuum along with an iron K_alpha
emission line. A strong iron K_beta emission line is detected for the first
time in GX 1+4 during the extended low state of 2000 observation with
equivalent width of ~550 eV. The optical depth and temperature of the
Comptonizing plasma are found to be identical during the high and low intensity
states whereas the hydrogen column density and the temperature of the seed
photons are higher during the low state. We also present results from pulse
phase resolved spectroscopy during the high and low flux episodes.Comment: Accepted for publication in The Astrophysical Journa
Long-term photometric variations in the candidate white-dwarf pulsar AR Scorpii from K2 , CRTS, and ASAS-SN observations
We analyze long-cadence Kepler K2 observations of AR Sco from 2014, along with survey photometry obtained between 2005 and 2016 by the Catalina Real-Time Sky Survey and the All-Sky Automated Survey for Supernovae. The K2 data show the orbital modulation to have been fairly stable during the 78 days of observations, but we detect aperiodic deviations from the average waveform with an amplitude of ~2% on a timescale of a few days. A comparison of the K2 data with the survey photometry reveals that the orbital waveform gradually changed between 2005 and 2010, with the orbital maximum shifting to earlier phases. We compare these photometric variations with proposed models of this unusual system
A Dynamical Study of the Black Hole X-ray Binary Nova Muscae 1991
We present a dynamical study of the Galactic black hole binary system Nova
Muscae 1991 (GS/GRS 1124-683). We utilize 72 high resolution Magellan
Echellette (MagE) spectra and 72 strictly simultaneous V-band photometric
observations; the simultaneity is a unique and crucial feature of this
dynamical study. The data were taken on two consecutive nights and cover the
full 10.4-hour orbital cycle. The radial velocities of the secondary star are
determined by cross-correlating the object spectra with the best-match template
spectrum obtained using the same instrument configuration. Based on our
independent analysis of five orders of the echellette spectrum, the
semi-amplitude of the radial velocity of the secondary is measured to be K_2 =
406.8+/-2.7 km/s, which is consistent with previous work, while the uncertainty
is reduced by a factor of 3. The corresponding mass function is f(M) =
3.02+/-0.06 M_\odot. We have also obtained an accurate measurement of the
rotational broadening of the stellar absorption lines (v sin i = 85.0+/-2.6
km/s) and hence the mass ratio of the system q = 0.079+/-0.007. Finally, we
have measured the spectrum of the non-stellar component of emission that veils
the spectrum of the secondary. In a future paper, we will use our
veiling-corrected spectrum of the secondary and accurate values of K_2 and q to
model multi-color light curves and determine the systemic inclination and the
mass of the black hole.Comment: ApJ accepted version; minor revision; added a subsection about
systematic uncertaintie
Broad band X-ray spectrum of KS 1947+300 with BeppoSAX
We present results obtained from three BeppoSAX observations of the
accretion-powered transient X-ray pulsar KS 1947+300 carried out during the
declining phase of its 2000 November -- 2001 June outburst. A detailed spectral
study of KS 1947+300 across a wide X-ray band (0.1--100.0 keV) is attempted for
the first time here. Timing analysis of the data clearly shows a 18.7 s
pulsation in the X-ray light curves in the above energy band. The pulse profile
of KS 1947+300 is characterized by a broad peak with sharp rise followed by a
narrow dip. The dip in the pulse profile shows a very strong energy dependence.
Broad-band pulse-phase-averaged spectroscopy obtained with three of the
BeppoSAX instruments shows that the energy spectrum in the 0.1--100 keV energy
band has three components, a Comptonized component, a ~0.6 keV blackbody
component, and a narrow and weak iron emission line at 6.7 keV with a low
column density of material in the line of sight. We place an upper limit on the
equivalent width of the iron K_\alpha line at 6.4 keV of ~13 eV (for a width of
100 eV). Assuming a spherical blackbody emitting region and the distance of the
source to be 10 kpc, the radius of the emitting region is found to be in the
range of 14--22 km, which rules out the inner accretion disk as the soft X-ray
emitting region.Comment: 17 pages, 5 figures, Accepted for publication in The Astrophysical
Journa
Aql X-1 in Outburst and Quiescence
We present photometry and spectroscopy of the soft x-ray transient Aql X-1.
Optical photometry during an active state shows a strong (0.6 mag peak-to-peak)
modulation at a period of 19 hours. Infrared (K'-band) photometry during a
quiescent state limits any ellipsoidal variations to <0.07 mag (peak-to-peak),
which implies an inclination i<31 (90% limit). Spectroscopy in a quiescent
state shows at most very small radial velocity variations, which implies a very
low inclination of i<12 (90% limit). The low inclination is rather unexpected
given the large photometric modulation seen in the active state. The upper
limit to the equivalent width of the anomalous Li 6707A line is <0.3A, which is
similar to the measured strength of this line in several other x-ray
transients.Comment: Accepted for publication in ApJ, 12 pages, 5 figure
Do shorter lengths of stay increase readmissions after total joint replacements?
BackgroundEnhanced recovery after surgery protocols for total joint replacements (TJRs) emphasize early discharge, yet the impact on readmissions is not well documented. We evaluate the impact of a one-day length of stay (LOS) discharge protocol on readmissions.MethodsWe conducted a retrospective review of all primary TJRs (hip and knee) from April 2014 to March 2015. Patients who had adequate support to be discharged home were categorized into 2 groups, 1-day (n = 174) vs 2-day (n = 285) LOS groups. Patients discharged to rehabilitation were excluded (n = 196).ResultsPatients in the 1 day group were more likely to be younger (61.7 vs 64.8 years, P < .001), be male (56.3% vs 40.4%, P = .001), and have a lower body mass index (30.0 vs 31.4 kg/m2, P = .012). One-day LOS patients had shorter surgical times (79.7 vs 85.6 minutes, P = .001) and more likely had spinal anesthesia (46.0% vs 31.2%, P = .001). The overall 30-day all-cause (2.3% vs 2.5%, P = .591) and 90-day wound-related (1.1% vs 1.1%, P = .617) readmission rates were equivalent between groups.ConclusionsEarly discharge does not increase readmissions and may help attenuate costs associated with TJRs. Further refinement of protocols may allow for more patients to be safely discharged on postoperative day 1
A Catalog of Transient X-ray Sources in M31
From October 1999 to August 2002, 45 transient X-ray sources were detected in
M31 by Chandra and XMM-Newton. We have performed spectral analysis of all
XMM-Newton and Chandra ACIS detections of these sources, as well as flux
measurements of Chandra HRC detections. The result is absorption-corrected
X-ray lightcurves for these sources covering this 2.8 year period, along with
spectral parameters for several epochs of the outbursts of most of the
transient sources. We supply a catalog of the locations, outburst dates, peak
observed luminosities, decay time estimates, and spectral properties of the
transient sources, and we discuss similarities with Galactic X-ray novae. Duty
cycle estimates are possible for 8 of the transients and range from 40% to 2%;
upper limits to the duty cycles are estimated for an additional 15 transients
and cover a similar range. We find 5 transients which have rapid decay times
and may be ultra-compact X-ray binaries. Spectra of three of the transients
suggest they may be faint Galactic foreground sources. If even one is a
foreground source, this suggests a surface density of faint transient X-ray
sources of >~1 deg.Comment: 63 pages, 22 figures, 3 tables, accepted for publication in Ap
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