73 research outputs found
Cool spots on the surface of the active giant PZ Mon
Based on the multiband (BVRIJHKL) photometric observations of the active red
giant PZ Mon performed for the first time in the winter season of 2017-2018, we
have determined the main characteristics of the spotted stellar surface in a
parametric three-spot model. The unspotted surface temperature is Teff=4730 K,
the temperature of the cool spots is Tspot=3500 K, their relative area is about
41%, and the temperature of the warm spots is Twarm=4500 K with a maximum
relative area up to 20%. The distribution of spots over the stellar surface has
been modeled. The warm spots have been found to be distributed at various
longitudes in the hemisphere on the side of the secondary component and are
most likely a result of its influence.Comment: 5 pages, 7 figure
Reverberation measurement of the inner radius of the dust torus in NGC 4151 during 2008-2013
We investigate the correlation between infrared (JHKL) and optical (B) fluxes
of the variable nucleus of the Seyfert galaxy NGC 4151 using partially
published data for the last 6 years (2008-2013.). Here we are using the same
data as in Oknyansky et al. (2014), but include also optical (B) data from Guo
et al. We find that the lag of flux in all the infrared bands is the same, 40
+- 6 days, to within the measurement accuracy. Variability in the J and K bands
is not quite simultaneous, perhaps due to the differing contributions of the
accretion disk in these bands. The lag found for the K band compared with the B
band is not significantly different from earlier values obtained for the period
2000-2007. However, finding approximately the same lags in all IR bands for
2008-2013 differs from previous results at earlier epochs when the lag
increased with increasing wavelength. Examples of almost the same lag in
different IR bands are known for some other active nuclei. In the case of NGC
4151 it appears that the relative lags between the IR bands may be different in
different years. The available data, unfortunately, do not allow us to
investigate a possible change in the lags during the test interval. We discuss
our results in the framework of the standard model where the variable infrared
radiation is mainly due to thermal re-emission from the part of the dusty torus
closest to the central source. There is also a contribution of some IR emission
from the accretion disk, and this contribution increases with decreasing
wavelength. Some cosmological applications of obtained results are discussed.Comment: 3 pages, 2 figures, 14-th Odessa International Astronomical Gamow
Conference-School Astronomy and beyond: Astrophysics, Cosmology and
Gravitation, Cosmomicrophysics, Radio-astronomy and Astrobiolog
Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
V445 Pup (2000) is a unique object identified as a helium nova. Color indexes
during the outburst are consistent with those of free-free emission. We present
a free-free emission dominated light curve model of V445 Pup on the basis of
the optically thick wind theory. Our light curve fitting shows that (1) the
white dwarf (WD) mass is very massive (M_WD \gtrsim 1.35 M_\sun), and (2) a
half of the accreted matter remains on the WD, both of which suggest that the
increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia
supernova progenitor. The estimated distance to V445 Pup is now consistent with
the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star
companion is consistent with the brightness of m_v=14.5 mag just before the
outburst, if it is a little bit evolved hot (\log T (K) \gtrsim 4.5) star with
the mass of M_He \gtrsim 0.8 M_\sun. We then emphasize importance of
observations in the near future quiescent phase after the thick circumstellar
dust dissipates away, especially its color and magnitude to specify the nature
of the companion star. We have also calculated helium ignition masses for
helium shell flashes against various helium accretion rates and discussed the
recurrence period of helium novae.Comment: 8 pages including 12 figures, to appear in Ap
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Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.
Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.
Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by ~0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation
Recurrent Symbiotic Nova T Coronae Borealis Before Outburst
The results of photometric and spectral observations of T CrB obtained in a
wide range of wavelengths in 2011-2023 are presented. We use the near-IR light
curves to determine a new ephemeris for
the times of light minima when the red giant is located between the observer
and the hot component. The flux ratio H/H varied from ~3 to ~8
in 2020-2023, which may be due to a change in the flux ratio between the X-ray
and optical ranges. It is shown that the value of H/H depends on
the rate of accretion onto the hot component of the system. Based on high-speed
follow-up observations obtained on June 8, 2023, we detected a variability of
the HeII line with a characteristic time-scale of ~25 min, the
amplitude of variability in the band was ~0.07. Simulations of the
near-IR light curves accounting for the ellipsoidal effect allowed us to obtain
the parameters of the binary system: the Roche lobe filling factor of the cool
component , the mass ratio , the orbit
inclination . A comparison of the light curve obtained in
2005-2023 with the 1946 outburst template made it possible to predict the date
of the upcoming outburst - January 2024.Comment: 15 pages, 3 tables, 8 figures, submitted to Astronomy Letter
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