543 research outputs found
Efficient analysis in planet transit surveys
With the growing number of projects dedicated to the search for extrasolar
planets via transits, there is a need to develop fast, automatic, robust
methods with a statistical background in order to efficiently do the analysis.
We propose a modified analysis of variance (AoV) test particularly suitable for
the detection of planetary transits in stellar light curves. We show how
savings of labor by a factor of over 10 could be achieved by the careful
organization of computations. Basing on solid analytical statistical
formulation, we discuss performance of our and other methods for different
signal-to-noise and number of observations.Comment: 7 pages, to be published in MNRAS, downloadable software from
http://www.camk.edu.pl/~alex/#softwar
Photometric study of the variable star population in the globular cluster NGC 6397
We present the results of a photometric survey for variable stars in the
central region of the nearby globular cluster NGC 6397.Time series photometry
was obtained for 30 variable objects. The sample includes 12 new objects, of
which 6 show periodic lightcurves and 2 are eclipsing binaries of unknown
period. Six variables possess certain and three possess likely X-ray
counterparts detected with the Chandra observatory. Among them four are
cataclysmic variables and one is a foreground eclipsing binary. The cataclysmic
variable CV2 exhibited a likely dwarf nova type outburst in May 2003. The
cataclysmic variable CV3 was observed at 18.5<V<20.0 during 5 observing runs,
but went into a low state in May 2003 when it reached V>22. We have found that
thelight curve of the optical companion to the millisecond pulsar PSRJ1740-5340
exhibits noticeable changes of its amplitude on a time scale of a few months. A
shallow eclipse with Delta_V=0.03 mag was detected in one of the cluster
turnoff stars suggesting the presence of a large planet or brown dwarf in
orbit.Comment: 8 pages, 9 figures, submitted to MNRAS on 21 April 200
CCD Photometry of Faint Variable Stars in the Globular Cluster NGC 6752
We present the results of a photometric survey for variable stars in the
field of the nearby globular cluster NGC 6752. The cluster was monitored in
1996 and 1997 for a total of 54 hours with 3 different CCD cameras mounted on
the 1.0-m Swope telescope. Eleven new variables were identified: 3 SX Phe
stars, 7 contact binaries and 1 candidate detached eclipsing binary. All 3 SX
Phe variables are likely members of the cluster while only 1 out of the 7
contact binaries is a potential cluster member. As a by-product of our survey
we obtained UBV photometry for a large sample of stars in the cluster field.
Two stars with U-B \approx -1.0 and V=19.3 and V=20.6 were identified. They lie
along the extended horizontal branch of the cluster, and are likely to be faint
sdB stars from NGC 6752.Comment: 18 pages, LaTex, 9 figures (Fig. 1 not available), accepted for
publication in the Astronomical Journa
RR Lyrae Variables in the Globular Cluster M5
We present V-band CCD photometry of 65 RR Lyr variables from the globular
cluster M5. We have estimated the basic physical parameters for 16 RRc stars
and 26 RRab stars using a Fourier decomposition of the light curves of the
variables. The mean values of mass, luminosity, effective temperature and
relative helium abundance for the RRc stars are measured to be , log L = 1.69 T_{eff}=7353 K and Y=0.28, respectively.
For the RRab variables the derived mean values of absolute magnitude,
metallicity and effective temperature are: M_V=0.81, [Fe/H]=-1.23 and
T_{eff}=6465 K. We find that the V amplitude of an RRab star for a given period
is a function of metal abundance rather than Oosterhoff type. We find
significant problems with the calibration of both the zero point and the scale
of the luminosities measured with the Fourier technique. The apparent distance
modulus derived from RRc stars is equal to and it is in good
agreement with recent determinations. On the other hand distance modulus
obtained from the sample of RRab stars (calibrated by the Baade-Wesselink
observations of field RR Lyr variables) is significantly smaller and equal to
Comment: accepted for publication in Astronomy and Astrophysics, 15 pages with
6 figure
The Lick Planet Search: Detectability and Mass Thresholds
We analyse 11 years of precise radial velocities for 76 solar type stars from
the Lick survey. Eight stars in this sample have previously reported
planetary-mass companions, all with mass (m sin i) less than 8 Jupiter masses
(MJ). For the stars without a detected companion, we place upper limits on
possible companion mass. For most stars, we can exclude companions with m sin i
> 0.7 MJ (a/AU)^1/2 for orbital radii a < 5 AU.
We use our results to interpret the observed masses and orbital radii of
planetary-mass companions. For example, we show that the finite duration of the
observations makes detection of Jupiter mass companions more and more difficult
for orbital radii beyond 3 AU. Thus it is possible that the majority of solar
type stars harbor Jupiter-mass companions much like our own, and if so these
companions should be detectable in a few years.
To search for periodicities, we adopt a "floating-mean" periodogram, which
improves on the traditional Lomb-Scargle periodogram by accounting for
statistical fluctuations in the mean of a sampled sinusoid. We discuss in
detail the normalization of the periodogram, an issue which has been of some
debate in the literature.Comment: To appear in the Astrophysical Journal (50 pages, LaTeX, including 11
figures
Cluster AgeS Experiment. CCD photometry of SX Phoenicis variables in the globular cluster M 55
We present CCD photometry of SX Phe variables in the field of the globular
cluster M 55. We have discovered 27 variables, three of which are probable
members of the Sagittarius dwarf galaxy. All of the SX Phe stars in M 55 lie in
the blue straggler region of the cluster color-magnitude diagram. Using period
ratio information we have identified the radial pulsation modes for one of the
observed variables. Inspection of the period-luminosity distribution permits
the probable identifications of the pulsation modes for most of the rest of the
stars in the sample. We have determined the slope of the period-luminosity
relation for SX Phe stars in M 55 pulsating in the fundamental mode. Using this
relation and the HIPPARCOS data for SX Phe itself, we have estimated the
apparent distance modulus to M 55 to be (m-M)_V=13.86 +- 0.25 mag.Comment: A&A accepted, 11 figure
Cluster AgeS Experiment (CASE): RR Lyrae stars from the globular cluster Omega Centauri as standard candles
New photometry of RRab and RRc stars in Omega Cen is used to calibrate their
absolute magnitudes M_V as a function of: a) metallicity; and b) the Fourier
parameters of light curves in the V band. The zero point of both calibrations
relies on the distance modulus to the cluster derived earlier by the CASE
project based on observations of the detached eclipsing binary OGLE GC17. For
RRab variables we obtained a relation of M_V=(0.26\pm 0.08)[Fe/H]+(0.91\pm
0.13). A dereddened distance modulus to the LMC based on that formula is
mag. The second calibration of M_V, which is based on
Fourier coefficients of decomposed light curves, results in the LMC distance of
mag.Comment: accepted for publication in MNRAS, 13 pages, 8 figure
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