433 research outputs found
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
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 Nature of the Emission Components in the Quasar/NLS1 PG1211+143
We present the study of the emission properties of the quasar PG1211+143,
which belongs to the class of Narrow Line Seyfert 1 galaxies. On the basis of
observational data analyzed by us and collected from the literature, we study
the temporal and spectral variability of the source in the optical/UV/X-ray
bands and we propose a model that explains the spectrum emitted in this broad
energy range. In this model, the intrinsic emission originating in the warm
skin of the accretion disk is responsible for the spectral component that is
dominant in the softest X-ray range. The shape of reflected spectrum as well as
Fe K line detected in hard X-rays require the reflecting medium to be mildly
ionized (xi~500). We identify this reflector with the warm skin of the disk and
we show that the heating of the skin is consistent with the classical alpha
P_{tot} prescription, while alpha P_{gas} option is at least two orders of
magnitude too low to provide the required heating. We find that the mass of the
central black hole is relatively small (M_BH~10^7- 10^8 Msun, which is
consistent with the Broad Line Region mapping results and characteristic for
NLS1 class.Comment: 22 pages, 10 figures, accepted to Ap
Towards equation of state of dark energy from quasar monitoring: reverberation strategy
Context. High-redshift quasars can be used to constrain the equation of state of dark energy. They can serve as a complementary tool to supernovae Type Ia, especially at z > 1
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
Clusters AgeS Experiment. RR Lyr Variables in the Globular Cluster NGC 6362
We present V and B-band CCD photometry of 35 RR Lyr stars in the southern
hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves
was used to estimate the basic properties of these variables. From the analysis
of the RRc stars we obtain a mean mass of M=0.531+/-0.014 , luminosity
log L=1.656+/-0.006, effective temperature Teff=7429+/-20, and helium abundance
Y=0.292+/-0.002. The mean values of the absolute magnitude, metallicity (on
Jurcsik's scale) and effective temperature for 14 RRab stars with "regular"
light curves are: M_V=0.86+/-0.01, [Fe/H]=-0.93+/-0.04 and Teff=6555+/-25,
respectively. From the B-V colors, periods and metallicities of the RRab stars
we estimate the color excess for NGC 6362 to be equal to E(B-V)=0.08+/-0.01.
Using this value we derive the colors of the blue and red edges of the
instability strip in NGC 6362 to be and
. From the relations between the Fourier coefficients of
RRab and RRc stars and their absolute magnitudes we estimate the apparent
distance modulus to NGC 6362 to be (m-M)_V=14.46+/-0.10. From the mean value of
log L of the RRc stars we obtain 14.59+/-0.03. The V-band light curves of three
of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time scale
of around one week. Near the radial 1st overtone frequency we find one or two
peaks, which strongly suggests that these variables belong to the newly
identified group of non-radial pulsating RR Lyr stars.Comment: 17 pages, 9 figures, submitted to MNRA
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