988 research outputs found
HT Cas - eclipsing dwarf nova during its superoutburst in 2010
We present results of a world-wide observing campaign of the eclipsing dwarf
nova - HT Cas during its superoutburst in November 2010. Using collected data
we were able to conduct analysis of the light curves and we calculated
diagrams.
The CCD photometric observations enabled us to derive the superhump period
and with the timings of eclipses the orbital period was calculated. Based on
superhump and orbital period estimations the period excess and mass ratio of
the system were obtained
IX Draconis - a curious ER UMa-type dwarf nova
We report results of an extensive world-wide observing campaign devoted to a
very active dwarf nova star - IX Draconis. We investigated photometric
behaviour of the system to derive its basic outburst properties and understand
peculiarities of IX Dra as well as other active cataclysmic variables, in
particular dwarf novae of the ER Uma-type. In order to measure fundamental
parameters of the system, we carried out analyses of the light curve, O-C
diagram, and power spectra. During over two months of observations we detected
two superoutbursts and several normal outbursts. The V magnitude of the star
varied in the range 14.6 - 18.2 mag. Superoutbursts occur regularly with the
supercycle length of 58.5+/-0.5 d. When analysing data over the past 20 years,
we found that the supercycle length is increasing at a rate of P_dot = 1.8 *
10^{-3}. Normal outbursts appear to be irregular, with typical occurrence times
in the range 3.1 - 4.1 d. We detected a double-peaked structure of superhumps
during superoutburst, with the secondary maximum becoming dominant near the end
of the superoutburst. The mean superhump period observed during superoutbursts
equals 0.066982(36) d, which is constant over the last two decades of
observations. Based on the power spectrum analysis, the evaluation of the
orbital period was problematic. We found two possible values: the first one,
0.06641(3) d, which is in agreement with previous studies and our O-C analysis
(0.06646(2) d), and the second one, 0.06482(3) d, which is less likely. The
evolutionary status of the object depends dramatically on the choice between
these two values. A spectroscopic determination of the orbital period is
needed. We updated available information on ER UMa-type stars and present a new
set of their basic statistics. Thereby, we provide evidence that this class of
stars is not uniform.Comment: Accepted for publication in MNRAS; 15 pages, 15 figures, 6 tables;
typo correcte
MN Draconis - peculiar, active dwarf nova in the period gap
Context: We present results of an extensive world-wide observing campaign of
MN Draconis.
Aims: MN Draconis is a poorly known active dwarf nova in the period gap and
is one of the only two known cases of period gap SU UMa objects showing the
negative superhumps. Photometric behaviour of MN Draconis poses a challenge for
existing models of the superhump and superoutburst mechanisms. Therefore,
thorough investigation of peculiar systems, such as MN Draconis, is crucial for
our understanding of evolution of the close binary stars.
Methods: To measure fundamental parameters of the system, we collected
photometric data in October 2009, June-September 2013 and June-December 2015.
Analysis of the light curves, diagrams and power spectra was carried out.
Results: During our three observational seasons we detected four
superoutburts and several normal outbursts. Based on the two consecutive
superoutbursts detected in 2015, the supercycle length was derived P_sc = 74
+/- 0.5 days and it has been increasing with a rate of P_dot = 3.3 x 10^(-3)
during last twelve years. Based on the positive and negative superhumps we
calculated the period excess epsilon = 5.6% +/- 0.1%, the period deficit
epsilon_ = 2.5% +/- 0.6%, and in result, the orbital period P_orb = 0.0994(1)
days (143.126 +/- 0.144 min). We updated the basic light curve parameters of MN
Draconis.
Conclusions: MN Draconis is the first discovered SU UMa system in the period
gap with increasing supercycle length.Comment: 14 pages, 20 figures, 8 tables, accepted for publication in Astronomy
and Astrophysic
An anisotropic distribution of spin vectors in asteroid families
Current amount of ~500 asteroid models derived from the disk-integrated
photometry by the lightcurve inversion method allows us to study not only the
spin-vector properties of the whole population of MBAs, but also of several
individual collisional families. We create a data set of 152 asteroids that
were identified by the HCM method as members of ten collisional families, among
them are 31 newly derived unique models and 24 new models with well-constrained
pole-ecliptic latitudes of the spin axes. The remaining models are adopted from
the DAMIT database or the literature. We revise the preliminary family
membership identification by the HCM method according to several additional
criteria - taxonomic type, color, albedo, maximum Yarkovsky semi-major axis
drift and the consistency with the size-frequency distribution of each family,
and consequently we remove interlopers. We then present the spin-vector
distributions for eight asteroidal families. We use a combined orbital- and
spin-evolution model to explain the observed spin-vector properties of objects
among collisional families. In general, we observe for studied families similar
trends in the (a_p, \beta) space: (i) larger asteroids are situated in the
proximity of the center of the family; (ii) asteroids with \beta>0{\deg} are
usually found to the right from the family center; (iii) on the other hand,
asteroids with \beta<0{\deg} to the left from the center; (iv) majority of
asteroids have large pole-ecliptic latitudes (|\beta|\gtrsim 30{\deg}); and
finally (v) some families have a statistically significant excess of asteroids
with \beta>0{\deg} or \beta<0{\deg}. Our numerical simulation of the long-term
evolution of a collisional family is capable of reproducing well the observed
spin-vector properties. Using this simulation, we also independently constrain
the age of families Flora (1.0\pm0.5 Gyr) and Koronis (2.5-4 Gyr).Comment: Accepted for publication in A&A (September 16, 2013
Functional interaction of the retinoblastoma and Ini1/Snf5 tumor suppressors in cell growth and pituitary tumorigenesis
The Ini1 subunit of the SWI/SNF chromatin remodeling complex suppresses formation of malignant rhabdoid tumors in humans and mice. Transduction of Ini1 into Ini1-deficient tumor-derived cell lines has indicated that Ini1 arrests cell growth, controls chromosomal ploidy, and suppresses tumorigenesis by regulating components of the retinoblastoma (Rb) signaling pathway. Furthermore, conditional inactivation of Ini1 in mouse fibroblasts alters the expression of various Rb-E2F-regulated genes, indicating that endogenous Ini1 levels may control Rb signaling in cells. We have reported previously that loss of one allele of Ini1 in mouse fibroblasts results only in a 15% to 20% reduction in total Ini1 mRNA levels due to transcriptional compensation by the remaining Ini1 allele. Here, we examine the effects of Ini1 haploinsufficiency on cell growth and immortalization in mouse embryonic fibroblasts. In addition, we examine pituitary tumorigenesis in Rb-Ini1 compound heterozygous mice. Our results reveal that heterozygosity for Ini1 up-regulates cell growth and immortalization and that exogenous Ini1 down-regulates the growth of primary cells in a Rb-dependent manner. Furthermore, loss of Ini1 is redundant with loss of Rb function in the formation of pituitary tumors in Rb heterozygous mice and leads to the formation of large, atypical Rb(+/-) tumor cells lacking adrenocorticotropic hormone expression. These results confirm in vivo the relationship between Rb and Ini1 in tumor suppression and indicate that Ini1 plays a role in maintaining the morphologic and functional differentiation of corticotrophic cells
Episodic Star Formation Coupled to Reignition of Radio Activity in 3C 236
We present Hubble Space Telescope UV and optical imaging of the radio galaxy
3C 236, whose relic 4 Mpc radio jet lobes and inner 2 kpc CSS radio source are
evidence of multiple epochs of AGN activity. Our data confirm the presence of
four bright knots of FUV emission in an arc along the edge of the inner
circumnuclear dust disk in the galaxy's nucleus, as well as FUV emission
cospatial with the nucleus itself. We interpret these to be sites of recent or
ongoing star formation. We present photometry of these knots, as well as an
estimate for the internal extinction in the source using the Balmer decrement
from SDSS spectroscopy. We estimate the ages of the knots by comparing our
extinction-corrected photometry with stellar population synthesis models. We
find the four knots cospatial with the dusty disk to be young, of order 10^7 yr
old. The FUV emission in the nucleus is likely due to an episode of star
formation triggered ~10^9 yr ago. We argue that the young 10^7 yr old knots
stem from an episode of star formation that was roughly coeval with the event
resulting in reignition of radio activity, creating the CSS source. The 10^9 yr
old stars in the nucleus may be associated with the previous epoch of activity
that generated the 4 Mpc relic source, before it was cut off by exhaustion or
interruption. The ages of the knots, considered in context with the disturbed
morphology of the nuclear dust and the double-double morphology of the "old"
and "young" radio sources, present evidence for an episodic AGN/starburst
connection. We suggest that the AGN fuel supply was interrupted for ~10^7 yr
due to a minor merger event and has now been restored, and the resultant
non-steady flow of gas toward the nucleus is likely responsible for both the
new episode of infall-induced star formation and also the multiple epochs of
radio activity.Comment: 15 pages, 7 figures. Accepted for publication in ApJ
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