85 research outputs found
CCD Photometry of Standard Stars at Maidanak Astronomical Observatory in Uzbekstan: Transformations and Comparisons
Observation of standard stars is of crucial importance in stellar photometry.
We have studied the standard transformation relations of the UBVRI CCD
photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All
observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild
486 CCD, and standard Bessell UBVRI filters from 2003 August to 2007 September.
We observed many standard stars around the celestial equator observed by SAAO
astronomers. The atmospheric extinction coefficients, photometric zero points,
and time variation of photometric zero points of each night were determined.
Secondary extinction coefficients and photometric zero points were very stable,
while primary extinction coefficients showed a distinct seasonal variation. We
also determined the transformation coefficients for each filter. For B, V, R,
and I filters, the transformation to the SAAO standard system could be achieved
with a straight line or a combination of two straight lines. However, in the
case of the U filter and Fairchild 486 CCD combination, a significant
non-linear correction term - related to the size of Balmer jump or the strength
of the Balmer lines - of up to 0.08 mags was required. We found that our data
matched well the SAAO photometry in V, B-V, V-I, and R-I. But in U-B, the
difference in zero point was about 3.6 mmag and the scatter was about 0.02 mag.
We attribute the relatively large scatter in U-B to the larger error in U of
the SAAO photometry. We confirm the mostly small differences between the SAAO
standard UBVRI system and the Landolt standard system. We also attempted to
interpret the seasonal variation of the atmospheric extinction coefficients in
the context of scattering sources in the earth's atmosphere.Comment: 14 pages, 13 figure
The Angstrom Project Alert System: real-time detection of extragalactic microlensing
The Angstrom Project is undertaking an optical survey of stellar microlensing
events across the bulge region of the Andromeda Galaxy (M31) using a
distributed network of two-meter class telescopes. The Angstrom Project Alert
System (APAS) has been developed to identify in real time candidate
microlensing and transient events using data from the Liverpool and Faulkes
North robotic telescopes. This is the first time that real-time microlensing
discovery has been attempted outside of the Milky Way and its satellite
galaxies. The APAS is designed to enable follow-up studies of M31 microlensing
systems, including searches for gas giant planets in M31. Here we describe the
APAS and we present a few example light curves obtained during its
commissioning phase which clearly demonstrate its real-time capability to
identify microlensing candidates as well as other transient sources.Comment: 4 pages, submitted to ApJ Letter
Spitzer-IRS Observations of FU Orionis Objects
We present 5-35 m spectra, taken with the Infrared Spectrograph (IRS) on
the Spitzer Space Telescope, of five FU Orionis objects: FU Ori, V1515 Cyg,
V1057 Cyg, BBW 76, and V346 Nor. All but V346 Nor reveal amorphous silicate
grains in emission at 10 m and 20 m, and show water-vapor absorption
bands at 5.8 and 6.8 m and SiO or possibly methane absorption at 8 m.
These absorption features closely match these bands in model stellar
photospheres -- signs of the gaseous photospheres of the inner regions of these
objects' accretion disks. The continuum emission at 5-8 m is also
consistent with such disks, and, for FU Orionis and BBW 76, longer-wavelength
emission may be fit by a model which includes moderate disk flaring. V1057 Cyg
and V1515 Cyg have much more emission at longer wavelengths than the others,
perhaps evidence of substantial remnant of their natal, infalling envelopes.Comment: 30 pages, 8 figures, accepted by Ap
The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004
We present results from the most recent (2002-2004) observing campaigns of
the eclipsing system KH 15D, in addition to re-reduced data obtained at Van
Vleck Observatory (VVO) between 1995 and 2000. Phasing nine years of
photometric data shows substantial evolution in the width and depth of the
eclipses. The most recent data indicate that the eclipses are now approximately
24 days in length, or half the orbital period. These results are interpreted
and discussed in the context of the recent models for this system put forward
by Winn et al. and Chiang & Murray-Clay. A periodogram of the entire data set
yields a highly significant peak at 48.37 +/- 0.01 days, which is in accord
with the spectroscopic period of 48.38 +/- 0.01 days determined by Johnson et
al. Another significant peak, at 9.6 days, was found in the periodogram of the
out-of-eclipse data at two different epochs. We interpret this as the rotation
period of the visible star and argue that it may be tidally locked in
pseudosynchronism with its orbital motion. If so, application of Hut's theory
implies that the eccentricity of the orbit is e = 0.65 +/- 0.01. Analysis of
the UVES/VLT spectra obtained by Hamilton et al. shows that the v sin(i) of the
visible star in this system is 6.9 +/- 0.3 km/sec. Using this value of v sin(i)
and the measured rotation period of the star, we calculate the lower limit on
the radius to be R = (1.3 +/- 0.1), R_Sun, which concurs with the value
obtained by Hamilton et al. from its luminosity and effective temperature. Here
we assume that i = 90 degrees since it is likely that the spin and orbital
angular momenta vectors are nearly aligned.Comment: 55 pages, 18 figures, 1 color figure, to appear the September issue
of the Astronomical Journa
Multi-wavelength observations of afterglow of GRB 080319B and the modeling constraints
We present observations of the afterglow of GRB 080319B at optical, mm and
radio frequencies from a few hours to 67 days after the burst. Present
observations along with other published multi-wavelength data have been used to
study the light-curves and spectral energy distributions of the burst
afterglow. The nature of this brightest cosmic explosion has been explored
based on the observed properties and it's comparison with the afterglow models.
Our results show that the observed features of the afterglow fits equally good
with the Inter Stellar Matter and the Stellar Wind density profiles of the
circum-burst medium. In case of both density profiles, location of the maximum
synchrotron frequency is below optical and the value of cooling break
frequency is below rays, s after the burst. Also, the
derived value of the Lorentz factor at the time of naked eye brightness is
with the corresponding blast wave size of cm. The
numerical fit to the multi-wavelength afterglow data constraints the values of
physical parameters and the emission mechanism of the burst.Comment: 8 Pages, 3 Figures, Accepted for publication to Astronomy and
Astrophysics on 02/04/200
Dependence of the state of the large intestine parietal microflora on the activity of Helicobacter Pylori associated chronic gastritis
Introduction. The aim of the study was to detect the dependence of the composition of the parietal microflora of the colon on the activity of Helicobacter pylori-associated chronic gastritis and the degree of Helicobacter pylori contamination of the gastric mucosaВведение. Целью работы являлось изучение зависимости состава пристеночной микрофлоры толстого кишечника от активности Helicobacter pylori-ассоциированного хронического гастрита и степени обсемененности Helicobacter pylori слизистой желудк
A multiwavelength study of Swift GRB 060111B constraining the origin of its prompt optical emission
In this work, we present the results obtained from a multi-wavelength
campaign, as well as from the public Swift/BAT, XRT, and UVOT data of GRB
060111B for which a bright optical emission was measured with good temporal
resolution during the prompt phase. We identified the host galaxy at R~25 mag;
its featureless spectral continuum and brightness, as well as the non-detection
of any associated supernova 16 days after the trigger and other independent
redshift estimates, converge to z~1-2. From the analysis of the early afterglow
SED, we find that non-negligible host galaxy dust extinction, in addition to
the Galactic one, affects the observed flux in the optical regime. The
extinction-corrected optical-to-gamma-ray spectral energy distribution during
the prompt emission shows a flux density ratio =0.01-0.0001
with spectral index , strongly suggesting a
separate origin of the optical and gamma-ray components. This result is
supported by the lack of correlated behavior in the prompt emission light
curves observed in the two energy domains. The properties of the prompt optical
emission observed during GRB 060111B favor interpretation of this optical light
as radiation from the reverse shock in a thick shell limit and in the slow
cooling regime. The expected peak flux is consistent with the observed one
corrected for the host extinction, likely indicating that the starting time of
the TAROT observations is very near to or coincident with the peak time. The
estimated fireball initial Lorentz factor is >260-360 at z=1-2, similar to the
Lorentz factors obtained from other GRBs. GRB 060111B is a rare, good test case
of the reverse shock emission mechanism in both the X-ray and optical energy
ranges.Comment: Accepted for publication in Astronomy and Astrophysics, 15 pages,10
figures and 7 table
The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting
more than 1 year and culminating in spring 2005. The maximum brightness
detected was R = 12.0, which represents the most luminous quasar state thus far
observed (M_B ~ -31.4). In order to follow the emission behaviour of the source
in detail, a large multiwavelength campaign was organized by the Whole Earth
Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was
performed in several bands. ToO pointings by the Chandra and INTEGRAL
satellites provided additional information at high energies in May 2005. The
historical radio and optical light curves show different behaviours. Until
about 2001.0 only moderate variability was present in the optical regime, while
prominent and long-lasting radio outbursts were visible at the various radio
frequencies, with higher-frequency variations preceding the lower-frequency
ones. After that date, the optical activity increased and the radio flux is
less variable. This suggests that the optical and radio emissions come from two
separate and misaligned jet regions, with the inner optical one acquiring a
smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index
behaviour (generally redder-when-brighter) during the outburst suggests the
presence of a luminous accretion disc. A huge mm outburst followed the optical
one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux
started to increase in early 2005 and reached a maximum at the end of our
observing period (end of September 2005). VLBA observations at 43 GHz during
the summer confirm theComment: 7 pages, 4 figures, to be published in A&
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