201 research outputs found
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
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 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
Laboratory and On-sky Testing of an InGaAs Detector for Infrared Imaging
We describe the results of testing a shortwave infrared CMOS camera using an indium gallium arsenide (InGaAs) detector. The new generation of InGaAs detectors offers a cost-effective alternative to mercury cadmium telluride (HgCdTe) for astronomy research, with current, off-the-shelf cameras requiring no modification before use. Testing was conducted in the laboratory and on-sky while mounted to the robotic, 2 m Liverpool Telescope using a H-band filter. The camera exhibits a dark current of 821 e- s-1 pix-1 and a bias level of 864 e- pix-1. The dark current associated shot noise is of similar size to the read noise of 32 e- pix-1 in one-second exposures. Linearity within the count region where readout noise and bit-depth saturation effects are not dominant is within a few tenths of a per cent. After field-compression by fore optics, the plate-scale yields 0.″3 pix-1, near perfect for Nyquist sampling at the La Palma site. The sky background for the H-band filter dominates the other noise sources for the instrument for one-second exposures producing sky-limited photometry. On-sky observations show that milli-magnitude precision is achieved for sources <10.7 mag and a signal-to-noise ratio of 10 is achievable for 16th magnitude with a 3 minutes total exposure time, making it an ideal follow-up instrument for sources detected in current and upcoming IR surveys
Hot subdwarf stars in close-up view IV. Helium abundances and the 3He isotopic anomaly of subdwarf B stars
Atmospheric parameters and helium abundances of 44 bright subdwarf B stars have been determined. More than half of our sample
consists of newly discovered stars from the Edinburgh Cape survey. We showed that effective temperatures and surface gravities can
be derived from high resolution echelle spectra with sufficient accuracy. Systematic uncertainties have been determined by comparing
the parameters derived from the high resolution data with the ones derived from medium resolution spectra. Helium abundances have
been measured with high accuracy. Besides the known correlation of helium abundance with temperature, two distinct sequences in
helium abundance have been confirmed. Significant isotopic shifts of helium lines due to an enrichment in 3He have been found in
the spectra of 8 subluminous B stars (sdBs). Most of these stars cluster in a small temperature range between 27 000K and 31 000K
very similar to the known 3He-rich main sequence B stars, which also cluster in such a small strip, but at different temperatures. Both
the helium sequences and the isotopic anomaly are discussed.Web of Scienc
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
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