117 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
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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
The sky lancer: 417th Bomb Group
The Sky Lancers have established an enviable record in combat against the Japanese in the Southwest Pacific Theatre of Operations. We have advanced twenty-five hundred miles since debarking at Cape Sudest, New Guinea; we have delivered destruction to the enemy over every mile of it and part of our great task still lies ahead on the road to Tokyo. Our gains have not been made easily and the price has been paid in both men and equipment.
It is to our gallant comrades who made their last flight with our organization that The SKY LANCER is dedicated, for it was they who contributed so greatly to our success and to the ultimate peace we are to gain through their courageous efforts.
Milton W. Johnson, Lt. Col., Air Corps, Commandinghttps://digicom.bpl.lib.me.us/ww_reg_his/1078/thumbnail.jp
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
RNA phage biology in a metagenomic era
The number of novel bacteriophage sequences has expanded significantly as a result of many metagenomic studies of phage populations in diverse environments. Most of these novel sequences bear little or no homology to existing databases (referred to as the “viral dark matter”). Also, these sequences are primarily derived from DNA-encoded bacteriophages (phages) with few RNA phages included. Despite the rapid advancements in high-throughput sequencing, few studies enrich for RNA viruses, i.e., target viral rather than cellular fraction and/or RNA rather than DNA via a reverse transcriptase step, in an attempt to capture the RNA viruses present in a microbial communities. It is timely to compile existing and relevant information about RNA phages to provide an insight into many of their important biological features, which should aid in sequence-based discovery and in their subsequent annotation. Without comprehensive studies, the biological significance of RNA phages has been largely ignored. Future bacteriophage studies should be adapted to ensure they are properly represented in phageomic studies
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
Tomography of X-ray Nova Muscae 1991: Evidence for ongoing mass transfer and stream-disc overflow
We present a spectroscopic analysis of the black hole binary Nova Muscae 1991
in quiescence using data obtained in 2009 with MagE on the Magellan Clay
telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las
Campanas Observatory. Emission from the disc is observed in H alpha, H beta and
Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all
three emission lines. The existence of this spot establishes ongoing mass
transfer from the donor star in 2009-2010 and, given its absence in the
1993-1995 observations, demonstrates the presence of a variable hotspot in the
system. We find the radial distance to the hotspot from the black hole to be
consistent with the circularization radius. Our tomograms are suggestive of
stream-disc overflow in the system. We also detect possible Ca II (8662 A)
absorption from the donor star.Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRA
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