3,214 research outputs found
Time-resolved photometry of the nova remnants DM Gem, CP Lac, GI Mon, V400 Per, CT Ser and XX Tau
We present the first results of a photometric survey of poorly studied nova remnants in the Northern Hemisphere.
The main results are as follows: DM Gem shows a modulation at 0.123 d (probably linked to the orbit) and rapid variations at ∼22 min. A moderate resolution spectrum taken at the time of the photometric observations shows intense He II λ4686 and Bowen emission, characteristic of an intermediate polar or a SW Sex star. Variability at 0.127 d and intense flickering (or quasi-periodic oscillations) are the main features of the light curve of CP Lac. A 0.1-mag dip lasting for ∼45 min is observed in GI Mon, which could be an eclipse. A clear modulation (probably related to the orbital motion) either at 0.179 d or 0.152 d
is observed in the B-band light curve of V400 Per. The results for CT Ser point to an orbital period close to 0.16 d. Intense flickering is also characteristic of this old nova. Finally, XX Tau shows a possible periodic signal near 0.14 d and displays fast variability at ∼24 min. Its brightness seems to be modulated at ∼5 d. We relate this long periodicity to the motion of an eccentric/tilted accretion disc in the binary
The fight for accretion: discovery of intermittent mass transfer in BB Doradus in the low state
Our long-term photometric monitoring of southern nova-like cataclysmic
variables with the 1.3-m SMARTS telescope found BB Doradus fading from V ~ 14.3
towards a deep low state at V ~ 19.3 in April 2008. Here we present
time-resolved optical spectroscopy of BB Dor in this faint state in 2009. The
optical spectrum in quiescence is a composite of a hot white dwarf with Teff =
30000 +- 5000 K and a M3-4 secondary star with narrow emission lines (mainly of
the Balmer series and HeI) superposed. We associate these narrow profiles with
an origin on the donor star. Analysis of the radial velocity curve of the
H-alpha emission from the donor star allowed the measurement of an orbital
period of 0.154095 +- 0.000003 d (3.69828 +- 0.00007 h), different from all
previous estimates. We detected episodic accretion events which veiled the
spectra of both stars and radically changed the line profiles within a
timescale of tens of minutes. This shows that accretion is not completely
quenched in the low state. During these accretion episodes the line wings are
stronger and their radial velocity curve is delayed by ~ 0.2 cycle, similar to
that observed in SW Sex and AM Her stars in the high state, with respect to the
motion of the white dwarf. Two scenarios are proposed to explain the extra
emission: impact of the material on the outer edge of a cold, remnant accretion
disc, or the combined action of a moderately magnetic white dwarf (B1 <~ 5 MG)
and the magnetic activity of the donor star.Comment: 10 pages, 10 figures, accepted by MNRA
HS 0139+0559, HS 0229+8016, HS 0506+7725, and HS 0642+5049 : four new long-period cataclysmic variables
We present time-resolved optical spectroscopy and photometry of four relatively bright (V ∼ 14.0−15.5) long-period cataclysmic variables(CVs) discovered in the Hamburg Quasar Survey: HS 0139+0559, HS 0229+8016, HS 0506+7725, and HS 0642+5049. Their respective orbital periods, 243.69
± 0.49 min, 232.550 ± 0.049 min, 212.7 ± 0.2 min, and 225.90
± 0.23 min are determined from radial velocity and photometric variability studies. HS 0506+7725 is characterised by strong Balmer and He emission lines, short-period (∼10−20 min) flickering, and weak X-ray emission in the ROSAT All Sky Survey. The detection of a deep low state (B 18.5) identifies HS 0506+7725 as a member of the VY Scl
stars. HS 0139+0559, HS 0229+8016, and HS 0642+5049 display thick-disc like spectra and no or only weak flickering activity. HS 0139+0559 and HS 0229+8016 exhibit clean quasi-sinusoidal radial velocity variations of their emission lines but no or very little orbital photometricvariability. In contrast, we detect no radial velocity variation in HS 0642+5049 but a noticeable orbital brightness variation. We identify all three systems either as UX UMa-type novalike variables or as Z Cam-type dwarf novae. Our identification of these four new systems underlines that the currently known sample of CVs is rather incomplete even for bright objects. The four new systems add to the clustering of orbital periods in the 3−4 h range found in the sample of HQS selected CVs, and we discuss the large incidence of magnetic CVs and VY Scl/SW Sex stars found in this period range among the known population of CVs
V348 Puppis: a new SW Sex star in the period gap
We present time-resolved optical spectroscopy and photometry of the nova-like
cataclysmic variable V348 Puppis. The system displays the same spectroscopic
behaviour as SW Sex stars, so we classify V348 Pup as a new member of the
class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which
lies in the period gap. The spectra exhibit enhanced HeII 4686 emission,
reminiscent of magnetic cataclysmic variables. The study of this emission line
gives a primary velocity semi-amplitude of K1 ~= 100 km/s. We have also derived
the system parameters, obtaining: M1 ~= 0.65 Msun, M2 ~= 0.20 Msun (q ~= 0.31),
i ~= 80 deg and K2 ~= 323 km/s. The spectroscopic behaviour of V348 Pup is very
similar to that of V795 Her, with the exception that V348 Pup shows deep
eclipses. We have computed the ``0.5-absorption'' spectrum of both systems,
obtaining spectra which resemble the absorption spectrum of a B0 V star. We
propose that absorption in SW Sex systems can be produced by a vertically
extended atmosphere which forms where the gas stream re-impacts the system,
either at the accretion disc or at the white dwarf's magnetosphere (assuming a
magnetic scenario).Comment: 6 pages, 10 figures, accepted for publication in MNRA
The redshift and broad band spectral energy distribution of NRAO 150
Context. NRAO 150 is one of the brightest radio and mm AGN sources on the
northern sky. It has been revealed as an interesting source where to study
extreme relativistic jet phenomena. However, its cosmological distance has not
been reported so far, because of its optical faintness produced by strong
Galactic extinction.
Aims. Aiming at measuring the redshift of NRAO 150, and hence to start making
possible quantitative studies from the source.
Methods. We have conducted spectroscopic and photometric observations of the
source in the near-IR, as well as in the optical.
Results. All such observations have been successful in detecting the source.
The near-IR spectroscopic observations reveal strong H and H
emission lines from which the cosmological redshift of NRAO 150
() has been determined for the first time. We classify the
source as a flat-spectrum radio-loud quasar, for which we estimate a large
super-massive black-hole mass . After
extinction correction, the new near-IR and optical data have revealed a
high-luminosity continuum-emission excess in the optical (peaking at
\,\AA, rest frame) that we attribute to thermal emission from the
accretion disk for which we estimate a high accretion rate, \,% of the
Eddington limit.
Conclusions. Comparison of these source properties, and its broad-band
spectral-energy distribution, with those of Fermi blazars allow us to predict
that NRAO 150 is among the most powerful blazars, and hence a high luminosity
-although not detected yet- -ray emitter.Comment: 8 pages, 4 figure
Opacity calculation for target physics using the ABAKO/RAPCAL code
Radiative properties of hot dense plasmas remain a subject of current interest since they play an important role in inertial confinement fusion (ICF) research, as well as in studies on stellar physics. In particular, the understanding of ICF plasmas requires emissivities and opacities for both hydro-simulations and diagnostics. Nevertheless, the accurate calculation of these properties is still an open question and continuous efforts are being made to develop new models and numerical codes that can facilitate the evaluation of such properties. In this work the set of atomic models ABAKO/RAPCAL is presented, as well as a series of results for carbon and aluminum to show its capability for modeling the population kinetics of plasmas in both LTE and NLTE regimes. Also, the spectroscopic diagnostics of a laser-produced aluminum plasma using ABAKO/RAPCAL is discussed. Additionally, as an interesting application of these codes, fitting analytical formulas for Rosseland and Planck mean opacities for carbon plasmas are reported. These formulas are useful as input data in hydrodynamic simulation of targets where the computation task is so hard that in line computation with sophisticated opacity codes is prohibitive
A three-dimensional view of the remnant of Nova Persei 1901 (GK Per)
We present a kinematical study of the optical ejecta of GK Per. It is based
on proper motions measurements of 282 knots from ~20 images spanning 25 years.
Doppler-shifts are also computed for 217 knots. The combination of proper
motions and radial velocities allows a unique 3-D view of the ejecta to be
obtained. The main results are: (1) the outflow is a thick shell in which knots
expand with a significant range of velocities, mostly between 600 and 1000
km/s; (2) kinematical ages indicate that knots have suffered only a modest
deceleration since their ejection a century ago; (3) no evidence for anisotropy
in the expansion rate is found; (4) velocity vectors are generally aligned
along the radial direction but a symmetric pattern of non-radial velocities is
also observed at specific directions; (5) the total Halpha+[NII] flux has been
linearly decreasing at a rate of 2.6 % per year in the last decade. The Eastern
nebular side is fading at a slower rate than the Western one. Some of the knots
displayed a rapid change of brightness during the 2004-2011 period. Over a
longer timescale, a progressive circularization and homogenization of the
nebula is taking place; (6) a kinematic distance of 400+-30 pc is determined.
These results raise some problems to the previous interpretations of the
evolution of GK Per. In particular, the idea of a strong interaction of the
outflow with the surrounding medium in the Southwest quadrant is not supported
by our data.Comment: Accepted for publication in The Astrophysical Journal (19 pages, 17
figures). Higher resolution version of this article (2.5 MB) is available at
http://www.aai.ee/~sinope/ApJ89291_liimets.pd
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