896 research outputs found
The system parameters of the polars MR Ser and ST LMi
We obtain the NaI 8183,8195 absorption line radial velocity curves for the
polars ST LMi and MR Ser, from which we find the semi-amplitudes to be
K_abs=329=+/-6 kms-1 and K_abs=289+/-9 kms-1 respectively. We find that for
both systems the effects on the \NaI absorption lines due to X-rays heating the
inner face of the secondary are negligible, and so the values obtained for
K_abs can be taken as the true semi-amplitude of the secondary star. We then
determine the projected rotational velocities, vsini, to be 104+/-9 kms-1 and
66+/-13 kms-1 for ST LMi and MR Ser respectively which enables their mass
ratios to be calculated. For ST LMi and MR Ser we find the mass ratio to be
0.22+/-0.04 and 0.10+/-0.05 respectively; values which are significantly
different only at the 94 percent level. We show that ``spike'' in the orbital
period distribution of polars is a significant feature, although the discovery
of only one more system with a period outside the ``spike'' would decrease its
significance below a 99 percent confidence level. We conclude that, even if the
limb darkening coefficients for the secondary stars in ST LMi and MR Ser are
the same, we cannot rule out the two systems having identical parameters.
Therefore our observations are compatible with the theory explaining the
``spike'' in the period distribution of the AM Hers.Comment: 6 pages, accepted for MNRAS, use mn.sty, 9 postscript figures, 3
table
HST/STIS UV Spectroscopy of Two Quiescent X-ray Novae: A0620-00 and Centaurus X-4
In 1998 we made UV spectroscopic observations with HST/STIS of A0620-00 and
Cen X-4, which are two X-ray novae (aka soft X-ray transients). These binary
systems are similar in all respects except that the former contains a black
hole and the latter contains a neutron star. A UV spectrum (1700-3100A) is
presented for the quiescent state of each system in the context of previously
published UV/optical and X-ray data. The non-stellar, continuum spectrum of
black hole A0620-00 has a prominent UV/optical peak centered at about 3500A. In
contrast the spectrum of neutron-star Cen X-4 lacks a peak and rises steadily
with frequency over the entire UV/optical band. In the optical, the two systems
are comparably luminous. However, black hole A0620-00 is about 6 times less
luminous at 1700A, and about 40 times less luminous in the X-ray band. The
broadband spectrum of A0620-00 is discussed in terms of the advection-dominated
accretion flow model.Comment: 18 pages including 4 figures; tentatively scheduled for the March 10,
2000 issue of ApJ; minor revision
Inclination Effects and Beaming in Black Hole X-ray Binaries
We investigate the dependence of observational properties of black hole X-ray
binaries on the inclination angle i of their orbits. We find the following: (1)
Transient black hole binaries show no trend in their quiescent X-ray
luminosities as a function of i, suggesting that the radiation is not
significantly beamed. This is consistent with emission from an accretion disk.
If the X-rays are from a jet, then the Lorentz factor gamma of the jet is less
than 1.24 at the 90% confidence level. (2) The X-ray binary 4U1543-47 with i of
order 21 degrees has a surprisingly strong fluorescent iron line in the high
soft state. Quantifying an earlier argument by Park et al. (2004), we conclude
that if the continuum X-ray emission in this source is from a jet, then gamma <
1.04. (3) None of the known binaries has cos i 75 degrees. This
fact, plus the lack of eclipses among the 20 black hole binaries in our sample,
strongly suggests at the 99.5% confidence level that systems with large
inclination angles are hidden from view. The obscuration could be the result of
disk flaring, as suggested by Milgrom (1978) for neutron star X-ray binaries.
(4) Transient black hole binaries with i ~ 70-75 degrees have significantly
more complex X-ray light curves than systems with i < 65 degrees. This may be
the result of variable obscuration and/or variable height above the disk of the
radiating gas.Comment: 26 pages, to appear in The Astrophysical Journal, vol. 624, May 1,
200
The outburst radial velocity curve of X-Ray Nova Scorpii 1994 (=GRO J1655--40)
We present a reanalysis of the outburst radial velocity data for X-Ray Nova
Scorpii 1994. Using a model based on X-ray heating of the secondary star we
suggest a more realistic treatment of the radial velocity data. Solutions are
obtained in the (K_2,q) plane which, when combined with the published value for
the binary mass ratio and inclination, constrain the mass of the black hole to
within the region 4.1<M_1<6.6 Msun (90 per cent confidence), which is
significantly lower than the value obtained by Orosz & Bailyn (1997). This
reduced lower bound for the black hole mass together with the high space
velocity of the system is consistent with the idea that it was formed by the
post-supernova collapse of a neutron star.Comment: Accepted for MNRAS, 4 pages Latex, 4 figure
Properties of the redback millisecond pulsar binary 3FGL J0212.1+5320
Linares et al. (2016) obtained quasi-simultaneous g', r' and i-band light
curves and an absorption line radial velocity curve of the secondary star in
the redback system 3FGL J0212.1+5320. The light curves showed two maxima and
minima primarily due to the secondary star's ellipsoidal modulation, but with
unequal maxima and minima. We fit these light curves and radial velocities with
our X-ray binary model including either a dark solar-type star spot or a hot
spot due to off-centre heating from an intrabinary shock, to account for the
unequal maxima. Both models give a radial velocity semi-amplitude and
rotational broadening that agree with the observations. The observed secondary
star's effective temperature is best matched with the value obtained using the
hot spot model, which gives a neutron star and secondary star mass of =1.85 and =0.50
, respectively.Comment: 10 pages, 8 figues, accepted by MNRA
Spectroscopic Identification of the Infrared Counterpart to GX5-1
Using CGS4 on UKIRT, we have obtained a 1.95-2.45 micron infrared spectrum of
the primary candidate counterpart to the bright Z LMXB GX5-1. IR photometry by
Naylor, Charles, & Longmore (1992) and the astrometry of Jonker et al. (2000)
had previously identified this star as the most likely counterpart to GX5-1.
The spectrum presented here clearly shows Brackett gamma and He lines in
emission, for the first time confirming the identity of the counterpart.
Similar to our previous spectroscopy of the Z source LMXBs Sco X-1 and Sco X-2
(Bandyopadhyay et al. 1999), the K-band spectrum of GX5-1 shows emission lines
only. We briefly discuss the implications of this spectrum for the nature of
the Z sources.Comment: accepted for publication as a Letter in MNRA
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