23 research outputs found
Infrared spectroscopy of cataclysmic variables: III. Dwarf novae below the period gap and novalike variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK
Lyn, T Leo, SW UMa and WZ Sge, the novalike variables DW UMa, V1315 Aql, RW
Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral
types ranging from K2-M6.
The spectra of the dwarf novae are dominated by emission lines of HI and HeI.
The large velocity and equivalent widths of these lines, in conjunction with
the fact that the lines are double-peaked in the highest inclination systems,
indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which
we obtained time-resolved data covering a complete orbital cycle, the emission
lines show modulations in their equivalent widths which are most probably
associated with the bright spot (the region where the gas stream collides with
the accretion disc). There are no clear detections of the secondary star in any
of the dwarf novae below the period gap, yielding upper limits of 10-30% for
the contribution of the secondary star to the observed K-band flux. In
conjunction with the K-band magnitudes of the dwarf novae, we use the derived
secondary star contributions to calculate lower limits to the distances to
these systems.
The spectra of the novalike variables are dominated by broad, single-peaked
emission lines of HI and HeI - even the eclipsing systems we observed do not
show the double-peaked profiles predicted by standard accretion disc theory.
With the exception of RW Tri, which exhibits NaI, CaI and 12CO absorption
features consistent with a M0V secondary contributing 65% of the observed
K-band flux, we find no evidence for the secondary star in any of the novalike
variables. The implications of this result are discussed.Comment: 13 pages, 5 figures, to appear in MNRA
UBVRI photopolarimetry of the long period eclipsing AM Herculis binary V1309
We report simultaneous UBVRI photo-polarimetric observations of the long
period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse
ingress and egress varies from night to night. We suggest this is due to the
variation in the brightness of the accretion stream. By comparing the phases of
circular polarization zero-crossovers with previous observations, we confirm
that V1309 Ori is well synchronized, and find an upper limit of 0.002 percent
for the difference between the spin and orbital periods. We model the
polarimetry data using a model consisting of two cyclotron emission regions at
almost diametrically opposite locations, and centered at colatitude 35 (deg)
and 145 (deg) on the surface of the white dwarf. We also present archive X-ray
observations which show that the negatively polarised accretion region is X-ray
bright.Comment: 11 pages, 12 figures (2 colour), Fig1 and Fig 4 are in lower
resolution than in original paper, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
The LMC supersoft X-ray binary RX J0513.9-6951
A detailed analysis of simultaneous photometric and spectroscopic observations of the optical counterpart of the LMC "supersoft" X-ray source RX J0513.9-6951 (identified with HV 5682) is presented. The spectrum is dominated by He II emission lines and H + He II blends; no He I is observed but several higher ionization emission features, especially O VI (3811, 3834, and 5290A) are prominent. Radial velocity measurements suggest a binary period of 0.76 days. If the small velocity amplitude, K~11 km/s, is interpreted as orbital motion, this implies that the binary system contains a somewhat evolved star plus a relatively massive compact object, viewed nearly pole-on. No orbital photometric variations were found, although irregular brightness changes of ~0.3 mag occurred. Unusual emission lines are observed which cannot be identified except as high velocity (4000 km/s) bipolar outflows or jets. These outflows are seen in H and He II at the same positive and negative velocities. They were relatively stable for periods of ~5 days, but their velocities appear to have been ~250 km/s smaller in 1992 than in 1993 or 1994
The Quiescent Spectrum of the AM CVn star CP Eri
We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.Comment: 12 pages, 2 figures, accepted for publication in ApJ Letter
Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840
We present simultaneous optical polarimetry and X-ray data of the near
synchronous polar RX J2115-5840. We model the polarisation data using the
Stokes imaging technique of Potter et al. We find that the data are best
modelled using a relatively high binary inclination and a small angle between
the magnetic and spin axes. We find that for all spin-orbit beat phases, a
significant proportion of the accretion flow is directed onto the lower
hemisphere of the white dwarf, producing negative circular polarisation. Only
for a small fraction of the beat cycle is a proportion of the flow directed
onto the upper hemisphere. However, the accretion flow never occurs near the
upper magnetic pole, whatever the orientation of the magnetic poles. This
indicates the presence of a non-dipole field with the field strength at the
upper pole significantly higher. We find that the brightest parts of the hard
X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200
Infrared and Optical Spectroscopy of Type Ia Supernovae in the Nebular Phase
We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13
to 338 days after maximum blue light. Some contemporary optical spectra are
also shown. All the NIR spectra exhibit considerable structure throughout the
J-, H- and K-bands. In particular they exhibit a flux `deficit' in the J-band
which persists as late as 175 days. This is responsible for the well-known red
J-H colour. To identify the emission features and test the Ni hypothesis
for the explosion and subsequent light curve, we compare the NIR and optical
nebular-phase data with a simple non-LTE nebular spectral model. We find that
many of the spectral features are due to iron-group elements and that the
J-band deficit is due to a lack of emission lines from species which dominate
the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted
for, possibly due to inaccuracies in the cobalt atomic data. For some
supernovae, blueshifts of 1000--3000 km/s are seen in infrared and optical
features at 3 months. We suggest this is due to clumping in the ejecta. The
evolution of the cobalt/iron mass ratio indicates that Co-decay
dominates the abundances of these elements. The absolute masses of iron-group
elements which we derive support the basic thermonuclear explosion scenario for
Type Ia supernovae. A core-collapse origin is less consistent with our data.Comment: 33 Latex pages, 12 Postscript figures: accepted by Monthly Notices of
the Royal Astronomical Societ
A Population of Faint Non-Transient Low Mass Black Hole Binaries
We study the thermal and viscous stability of accretion flows in Low Mass
Black Hole Binaries (LMBHBs). We consider a model in which an inner
advection-dominated accretion flow (ADAF) is surrounded by a geometrically thin
accretion disk, the transition between the two zones occurring at a radius
R_tr. In all the known LMBHBs, R_tr appears to be such that the outer disks
could suffer from a global thermal-viscous instability. This instability is
likely to cause the transient behavior of these systems. However, in most
cases, if R_tr were slightly larger than the estimated values, the systems
would be globally stable. This suggests that a population of faint persistent
LMBHBs with globally stable outer disks could be present in the Galaxy. Such
LMBHBs would be hard to detect because they would lack large amplitude
outbursts, and because their ADAF zones would have very low radiative
efficiencies, making the systems very dim. We present model spectra of such
systems covering the optical and X-ray bands.Comment: LateX, 37 pages, 11 figures; Accepted for publication in The
Astrophysical Journa