644 research outputs found
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
FIRST "Winged" and X-shaped Radio Source Candidates: II. New Redshifts
We report optical spectroscopic observations of X-shaped radio sources with
the Hobby-Eberly Telescope and Multiple-Mirror Telescope, focused on the sample
of candidates from the FIRST survey presented in Paper I (Cheung 2007). A total
of 27 redshifts were successfully obtained, 21 of which are new, including that
of a newly identified candidate source of this type which is presented here.
With these observations, the sample of candidates from Paper I is over 50%
spectroscopically identified. Two new broad emission-lined X-shaped radio
sources are revealed, while no emission lines were detected in about one third
of the observed sources; a detailed study of the line properties is deferred to
a future paper. Finally, to explore their relation to the Fanaroff-Riley
division, the radio luminosities and host galaxy absolute magnitudes of a
spectroscopically identified sample of 50 X-shaped radio galaxies are
calculated to determine their placement in the Owen-Ledlow plane.Comment: emulateapj style, 10 pages, 4 figures, 2 tables; ApJS accepted with
minor revision from submitted version (v1
Observation of the first gravitational microlensing event in a sparse stellar field : the Tago event
We report the observation of the first gravitational microlensing event in a
sparse stellar field, involving the brightest (V=11.4 mag) andclosest (~ 1 kpc)
source star to date. This event was discovered by an amateurastronomer, A.
Tago, on 2006 October 31 as a transient brightening, by ~4.5 mag during a ~15
day period, of a normal A-type star (GSC 3656-1328) in the Cassiopeia
constellation. Analysis of both spectroscopic observations and the light curve
indicates that this event was caused by gravitational microlensing rather than
an intrinsically variable star. Discovery of this single event over a 30 year
period is roughly consistent with the expected microlensing rate for the whole
sky down to V = 12 mag stars. However, the probability for finding events with
such a high magnification (~ 50) is much smaller, by a factor ~1/50, which
implies that the true event rate may be higher than expected. This discovery
indicates the potential of all sky variability surveys, employing frequent
sampling by telescopes with small apertures and wide fields of view, for
finding such rare transient events, and using the observations to explore
galactic disk structure and search for exo-planets.Comment: 13 pages, 2 tables, 3 figures, accepted by Ap
Chandra Observations of 3C Radio Sources with z<0.3: Nuclei, Diffuse Emission, Jets and Hotspots
We report on our Chandra Cycle 9 program to observe half of the 60
(unobserved by Chandra) 3C radio sources at z<0.3 for 8 ksec each. Here we give
the basic data: the X-ray intensity of the nuclei and any features associated
with radio structures such as hot spots and knots in jets. We have measured
fluxes in soft, medium and hard bands and are thus able to isolate sources with
significant intrinsic column density. For the stronger nuclei, we have applied
the standard spectral analysis which provides the best fit values of X-ray
spectral index and column density. We find evidence for intrinsic absorption
exceeding a column density of 10^{22} cm^{-2} for one third of our sources.Comment: 12 pages, 37 figures (the complete version of the paper with all
figures is available on line, see appendix for details), ApJ accepte
Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle
Supernova (SN) 2016bdu is an unusual transient resembling SN 2009ip. SN
2009ip-like events are characterized by a long-lasting phase of erratic
variability which ends with two luminous outbursts a few weeks apart. The
second outburst is significantly more luminous (about 3 mag) than the first. In
the case of SN 2016bdu, the first outburst (Event A) reached an absolute
magnitude M(r) ~ -15.3 mag, while the second one (Event B) occurred over one
month later and reached M(r) ~ -18 mag. By inspecting archival data, a faint
source at the position of SN 2016bdu is detectable several times in the past
few years. We interpret these detections as signatures of a phase of erratic
variability, similar to that experienced by SN 2009ip between 2008 and
mid-2012, and resembling the currently observed variability of the luminous
blue variable SN 2000ch in NGC 3432. Spectroscopic monitoring of SN 2016bdu
during the second peak initially shows features typical of a SN IIn. One month
after the Event B maximum, the spectra develop broad Balmer lines with P Cygni
profiles and broad metal features. At these late phases, the spectra resemble
those of a typical Type II SN. All members of this SN 2009ip-like group are
remarkably similar to the Type IIn SN 2005gl. For this object, the claim of a
terminal SN explosion is supported by the disappearance of the progenitor star.
The similarity with SN 2005gl suggests that all members of this family may
finally explode as genuine SNe, although the unequivocal detection of
nucleosynthesised elements in their nebular spectra is still missing.Comment: Submitted to MNRAS on April 10, 2017; re-submitted on June 23
including suggestions from the referee. 24 pages, 12 figures, 5 table
- …