158 research outputs found
Photometry of the SW Sex-type nova-like BH Lyncis in high state
Aims: We present a photometric study of the deeply eclipsing SW Sex-type
nova-like cataclysmic variable star BH Lyn
Methods: Time-resolved V-band CCD photometry was obtained for seven nights
between 1999 and 2004.
Results: We determined 11 new eclipse timings of BH Lyn and derived a refined
orbital ephemeris with an orbital period of 0.155875577(14) day. During the
observations, BH Lyn was in high-state with V~15.5 mag. The star presents ~1.5
mag deep eclipses with mean full-width at half-flux of 0.0683(+/-0.0054)P_orb.
The eclipse shape is highly variable, even changing form cycle to cycle. This
is most likely due to accretion disc surface brightness distribution
variations, most probably caused by strong flickering. Time-dependent accretion
disc self-occultation or variations of the hot spot(s) intensity are also
possible explanations. Negative superhumps with period of ~0.145 day are
detected in two long runs in 2000. A possible connection between SW Sex and
negative superhump phenomena through the presence of tilted accretion disc is
discussed, and a way to observationally test this is suggested
Photometric study of selected cataclysmic variables II. Time-series photometry of nine systems
We present time-series photometry of nine cataclysmic variables: EI UMa,
V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12,
V1315 Aql and LN UMa. The observations were conducted at various observatories,
covering 170 hours and comprising 7,850 data points in total.
For the majority of targets we confirm previously reported periodicities and
for some of them we give, for the first time, their spectroscopic orbital
periods. For those dwarf-nova systems which we observed during both quiescence
and outburst, the increase in brightness was followed by a decrease in the
amount of flickering. Quasi-periodic oscillations have either been discovered,
or were confirmed. For the eclipsing system V1315 Aql we have covered 9
eclipses, and obtained a refined orbital ephemeris. We find that, during its
long baseline of observations, no change in the orbital period of this system
has occurred. V1315 Aql also shows eclipses of variable depth.Comment: 30 pages, 16 figures, 4 tables. Submitted to JA
H-alpha variability of the recurrent nova T Coronae Borealis
We analyze H-alpha observations of the recurrent nova T CrB obtained during
the last decade. For the first time the H-alpha emission profile is analyzed
after subtraction of the red giant contribution. Based on our new radial
velocity measurements of the H-alpha emission line we estimate the component
masses of T CrB. It is found that the hot component is most likely a massive
white dwarf. We estimate the inclination and the component masses to be i~67
deg, Mwd = 1.37 +/-0.13 Msun and Msec=1.12 +/-0.23 Msun, respectively. The
radial velocity of the central dip in the H-alpha profile changes nearly in
phase with that of the red giant's absorption lines. This suggests that the dip
is most likely produced by absorption in the giant's wind.
Our observations cover an interval when the H-alpha and the U-band flux vary
by a factor of ~6, while the variability in B and V is much smaller. Based on
our observations, and archival ultraviolet and optical data we show that the
optical, ultraviolet and H-alpha fluxes strongly correlate. We argue that the
presence of an accretion disc can account for most of the observed properties
of T CrB.Comment: 8 pages, 6 EPS figures, to appear in A&
The peculiar extinction law of SN2014J measured with The Hubble Space Telescope
The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby
galaxy M82 has been measured using UV to near-IR photometry obtained with the
Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu
Infrared Telescope. This is the first time that the reddening of a SN Ia is
characterized over the full wavelength range of - microns. A
total-to-selective extinction, , is ruled out with high
significance. The best fit at maximum using a Galactic type extinction law
yields . The observed reddening of SN2014J is also compatible
with a power-law extinction, as expected from multiple scattering of light, with
. After correction for differences in reddening, SN2014J appears
to be very similar to SN2011fe over the 14 broad-band filter light curves used
in our study.Comment: Accepted for publication in ApJ
Type Ia supernova Hubble diagram with near-infrared and optical observations
We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature. The
analysis of 45 well-sampled NIR LCs shows that a single template accurately
describes them if its time axis is stretched with the optical stretch
parameter. This allows us to estimate the NIR peak magnitudes even with one
observation obtained within 10 days from B-band maximum. We find that the NIR
Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first
time we report a possible dependence on the J_max-H_max color. The intrinsic
NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is
smaller than what can be derived for a similarly heterogeneous sample at
optical wavelengths. In conclusion, we find that SNe Ia are at least as good
standard candles in the NIR as in the optical. We showed that it is feasible to
extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the
NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that
the most efficient way to extend the NIR Hubble diagram to high redshift would
be to obtain a single observation close to the NIR maximum. (abridged)Comment: 39 pages, 15 figures, accepted by A&
Comparative Direct Analysis of Type Ia Supernova Spectra. IV. Postmaximum
A comparative study of optical spectra of Type Ia supernovae (SNe Ia)
obtained near 1 week, 3 weeks, and 3 months after maximum light is presented.
Most members of the four groups that were defined on the basis of maximum light
spectra in Paper II (core normal, broad line, cool, and shallow silicon)
develop highly homogeneous postmaximum spectra, although there are interesting
exceptions. Comparisons with SYNOW synthetic spectra show that most of the
spectral features can be accounted for in a plausible way. The fits show that 3
months after maximum light, when SN Ia spectra are often said to be in the
nebular phase and to consist of forbidden emission lines, the spectra actually
remain dominated by resonance scattering features of permitted lines, primarily
those of Fe II. Even in SN 1991bg, which is said to have made a very early
transition to the nebular phase, there is no need to appeal to forbidden lines
at 3 weeks postmaximum, and at 3 months postmaximum the only clear
identification of a forbidden line is [Ca II] 7291, 7324. Recent studies of SN
Ia rates indicate that most of the SNe Ia that have ever occurred have been
"prompt" SNe Ia, produced by young (100,000,000 yr) stellar populations, while
most of the SNe Ia that occur at low redshift today are "tardy", produced by an
older (several Gyrs) population. We suggest that the shallow silicon SNe Ia
tend to be the prompt ones.Comment: Accepted by PAS
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