180 research outputs found
Orbital periods of cataclysmic variables identified by the SDSS. IX. NTT photometry of eight eclipsing and three magnetic systems
We report the discovery of eclipses and the first orbital period measurements
for four cataclysmic variables, plus the first orbital period measurements for
one known eclipsing and two magnetic systems. SDSS J093537.46+161950.8 exhibits
1-mag deep eclipses with a period of 92.245 min. SDSS J105754.25+275947.5 has
short and deep eclipses and an orbital period of 90.44 min. Its light curve has
no trace of a bright spot and its spectrum is dominated by the white dwarf
component, suggesting a low mass accretion rate and a very low-mass and cool
secondary star. CSS J132536+210037 shows 1-mag deep eclipses each separated by
89.821 min. SDSS J075653.11+085831.8 shows 2-mag deep eclipses on a period of
197.154 min. CSS J112634-100210 is an eclipsing dwarf nova identified in the
Catalina Real Time Transit Survey, for which we measure a period of 111.523
min. SDSS J092122.84+203857.1 is a magnetic system with an orbital period of
84.240 min; its light curve is a textbook example of cyclotron beaming. A
period of 158.72 min is found for the faint magnetic system SDSS
J132411.57+032050.4, whose orbital light variations are reminiscent of AM Her.
Improved orbital period measurements are also given for three known SDSS
cataclysmic variables. We investigate the orbital period distribution and
fraction of eclipsing systems within the SDSS sample and for all cataclysmic
variables with a known orbital period, with the finding that the fraction of
known CVs which are eclipsing is not strongly dependent on the orbital period.Comment: Accepted for publication in A&A. 12 pages, 16 figures, 5 tables. The
data are available on request and will be lodged with the CD
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
A J-band detection of the donor star in the dwarf nova OY Carinae, and an optical detection of its `iron curtain'
Purely photometric models can be used to determine the binary parameters of
eclipsing cataclysmic variables with a high degree of precision. However, the
photometric method relies on a number of assumptions, and to date there have
been very few independent checks of this method in the literature. We present
time-resolved spectroscopy of the P=90.9 min eclipsing cataclysmic variable OY
Carinae obtained with X-shooter on the VLT, in which we detect the donor star
from K I lines in the J-band. We measure the radial velocity amplitude of the
donor star K2 = 470.0 +/- 2.7 km/s, consistent with predictions based upon the
photometric method (470 +/- 7 km/s). Additionally, the spectra obtained in the
UVB arm of X-shooter show a series of Fe I and Fe II lines with a phase and
velocity consistent with an origin in the accretion disc. This is the first
unambiguous detection at optical wavelengths of the `iron curtain' of disc
material which has been previously reported to veil the white dwarf in this
system. The velocities of these lines do not track the white dwarf, reflecting
a distortion of the outer disc that we see also in Doppler images. This is
evidence for considerable radial motion in the outer disk, at up to 90 km/s
towards and away from the white dwarf.Comment: MNRAS accepted. 11 pages with 10 figures and 2 table
The evolutionary state of short-period magnetic white dwarf binaries
We present phase-resolved spectroscopy of two new short-period low accretion rate magnetic binaries, SDSS J125044.42+154957.3 (Porb= 86 min) and SDSS J151415.65+074446.5 (Porb= 89 min). Both systems were previously identified as magnetic white dwarfs from the Zeeman splitting of the Balmer absorption lines in their optical spectra. Their spectral energy distributions exhibit a large near-infrared excess, which we interpret as a combination of cyclotron emission and possibly a late-type companion star. No absorption features from the companion are seen in our optical spectra. We derive the orbital periods from a narrow, variable Hα emission line which we show to originate on the companion star. The high radial velocity amplitude measured in both systems suggests a high orbital inclination, but we find no evidence for eclipses in our data. The two new systems resemble the polar EF Eri in its prolonged low state and also SDSS J121209.31+013627.7, a known magnetic white dwarf plus possible brown dwarf binary, which was also recovered by our method
PG 1018−047 : the longest period subdwarf B binary
About 50 per cent of all known hot subdwarf B stars (sdBs) reside in close (short-period) binaries, for which common-envelope ejection is the most likely formation mechanism. However, Han et al. predict that the majority of sdBs should form through stable mass transfer leading to long-period binaries. Determining orbital periods for these systems is challenging and while the orbital periods of ∼100 short-period systems have been measured, there are no periods measured above 30 d. As part of a large programme to characterize the orbital periods of sdB binaries and their formation history, we have found that PG 1018−047 has an orbital period of 759.8 ± 5.8 d, easily making it the longest period ever detected for a sdB binary. Exploiting the Balmer lines of the subdwarf primary and the narrow absorption lines of the companion present in the spectra, we derive the radial velocity amplitudes of both stars, and estimate the mass ratio MMS/MsdB= 1.6 ± 0.2. From the combination of visual and infrared photometry, the spectral type of the companion star is determined to be mid-K
A parameter study of the eclipsing CV in the Kepler field, KIS J192748.53+444724.5
We present high-speed, three-colour photometry of the eclipsing dwarf nova KIS
J192748.53+444724.5 (KISJ1927) which is located in the Kepler field. Our data reveal
sharp features corresponding to the eclipses of the accreting white dwarf followed by the
bright spot where the gas stream joins the accretion disc. We determine the system parameters
via a parametrized model of the eclipse fitted to the observed light curve. We obtain
a mass ratio of q = 0.570 ± 0.011 and an orbital inclination of 84.
◦6 ± 0.
◦3. The primary
mass is Mw = 0.69 ± 0.07 M. The donor star’s mass and radius are found to be
Md = 0.39 ± 0.04 M and Rd = 0.43 ± 0.01 R, respectively. From the fluxes of the white
dwarf eclipse, we find a white dwarf temperature of Tw = 23000 ± 3000 K, and a photometric
distance to the system of 1600 ± 200 pc, neglecting the effects of interstellar reddening. The
white dwarf temperature in KISJ1927 implies the white dwarf is accreting at an average rate
of M˙ = 1.4 ± 0.8 × 10−9 M yr−1, in agreement with estimates of the secular mass loss rate
from the donor
Timing variations in the secondary eclipse of NN Ser
The eclipsing white dwarf plus main-sequence binary NN Serpentis provides one of the most convincing cases for the existence of circumbinary planets around evolved binaries. The exquisite timing precision provided by the deep eclipse of the white dwarf has revealed complex variations in the eclipse arrival times over the last few decades. These variations have been interpreted as the influence of two planets in orbit around the binary. Recent studies have proved that such a system is dynamically stable over the current lifetime of the binary. However, the existence of such planets is by no means proven and several alternative mechanisms have been proposed that could drive similar variations. One of these is apsidal precession, which causes the eclipse times of eccentric binaries to vary sinusoidally on many year time-scales. In this Letter, we present timing data for the secondary eclipse of NN Ser and show that they follow the same trend seen in the primary eclipse times, ruling out apsidal precession as a possible cause for the variations. This result leaves no alternatives to the planetary interpretation for the observed period variations, although we still do not consider their existence as proven. Our data limit the eccentricity of NN Ser to e < 10−3. We also detect a 3.3 ± 1.0 s delay in the arrival times of the secondary eclipses relative to the best planetary model. This delay is consistent with the expected 2.84 ± 0.04 s Rømer delay of the binary, and is the first time this effect has been detected in a white dwarf plus M dwarf system
A stellar flare during the transit of the extrasolar planet OGLE-TR-10b
We report a stellar flare occurring during a transit of the exoplanet OGLE-TR-10b, an event not previously reported in the literature. This reduces the observed transit depth, particularly in the u'-band, but flaring could also be significant in other bands and could lead to incorrect planetary parameters. We suggest that OGLE-TR-10a is an active planet-hosting star and has an unusually high X-ray luminosity
Precise mass and radius values for the white dwarf and low mass M dwarf in the pre-cataclysmic binary NN Serpentis
We derive precise system parameters for the pre-cataclysmic binary, NN Ser.
From light curve fitting we find an orbital inclination of i = 89.6 +/- 0.2
deg. From the HeII absorption line we find K_{WD}= 62.3 +/- 1.9 km/s. The
irradiation-induced emission lines from the surface of the secondary star give
a range of observed radial velocities. The corrected values give a radial
velocity of K_{sec}= 301 +/- 3 km/s, with an error dominated by the systematic
effects of the model. This leads to a binary separation of a = 0.934 +/- 0.009
R_{sun}, radii of R_{WD} = 0.0211 +/- 0.0002 R_{sun} and R_{sec} = 0.149 +/-
0.002 R_{sun} and masses of M_{WD} = 0.535 +/- 0.012 M_{sun} and M_{sec} =
0.111 +/- 0.004 M_{sun}. The masses and radii of both components of NN Ser were
measured independently of any mass-radius relation. For the white dwarf, the
measured mass, radius and temperature show excellent agreement with a `thick'
hydrogen layer of fractional mass M_{H}/{M}_{WD} = 10^{-4}. The measured radius
of the secondary star is 10% larger than predicted by models, however,
correcting for irradiation accounts for most of this inconsistency, hence the
secondary star in NN Ser is one of the first precisely measured very low mass
objects to show good agreement with models. ULTRACAM r', i' and z' photometry
taken during the primary eclipse determines the colours of the secondary star
as (r'-i')_{sec}= 1.4 +/- 0.1 and (i'-z')_{sec} = 0.8 +/- 0.1 which corresponds
to a spectral type of M4 +/- 0.5. This is consistent with the derived mass,
demonstrating that there is no detectable heating of the unirradiated face,
despite intercepting radiative energy from the white dwarf which exceeds its
own luminosity by over a factor of 20.Comment: 20 pages, 17 figures, 8 tables, minor changes, accepted for
publication in MNRA
- …