1,603 research outputs found
Properties, evolution and morpho-kinematical modelling of the very fast nova V2672 Oph (Nova Oph 2009), a clone of U Sco
V2672 Oph reached maximum brightness V=11.35 on 2009 August 16.5. With
observed t2(V)=2.3 and t3(V)=4.2 days decline times, it is one of the fastest
known novae, being rivalled only by V1500 Cyg (1975) and V838 Her (1991) among
classical novae, and U Sco among the recurrent ones. The line of sight to the
nova passes within a few degrees of the Galactic centre. The reddening of V2672
Oph is E(B-V)=1.6 +/-0.1, and its distance ~19 kpc places it on the other side
of the Galactic centre at a galacto-centric distance larger than the solar one.
The lack of an infrared counterpart for the progenitor excludes the donor star
from being a cool giant like in RS Oph or T CrB. With close similarity to U
Sco, V2672 Oph displayed a photometric plateau phase, a He/N spectrum
classification, extreme expansion velocities and triple peaked emission line
profiles during advanced decline. The full width at zero intensity of Halpha
was 12,000 km/s at maximum, and declined linearly in time with a slope very
similar to that observed in U Sco. We infer a WD mass close to the
Chandrasekhar limit and a possible final fate as a SNIa. Morpho-kinematical
modelling of the evolution of the Halpha profile suggests that the overall
structure of the ejecta is that of a prolate system with polar blobs and an
equatorial ring. The density in the prolate system appeared to decline faster
than that in the other components. V2672 Oph is seen pole-on, with an
inclination of 0+/-6 deg and an expansion velocity of the polar blobs of 4800
+900/-800 km/s. On the basis of its remarkable similarity to U Sco, we suspect
this nova may be a recurrent. Given the southern declination, the faintness at
maximum, the extremely rapid decline and its close proximity to the Ecliptic,
it is quite possible that previous outbursts of V2672 Oph have been missed.Comment: in press in MNRA
Discovery of a planetary nebula surrounding the symbiotic star DT Serpentis
We report the discovery of a planetary nebula centered on the poorly studied
symbiotic binary star DT Ser. In a few other symbiotic stars spatially resolved
nebulae have been discovered: however, only one of them might be a genuine
planetary nebula, while the others are likely to originate in complex mass
ejections episodes from the interacting binary central stars, possibly related
to nova-like outbursts. The rim of the planetary nebula around DT Ser is
severely distorted toward a brighter star, 5 arcsec away. In infrared WISE
data, this star shows the presence of a detached cold dust shell such as those
observed in post-AGB stars. The apparent association of the symbiotic star and
its planetary nebula with the nearby possible post-AGB object is discussed. We
also discuss the sparse and conflicting literature data that could support an
observed variability of the surface brightness of the planetary nebula. The
puzzling and intriguing characteristics displayed by DT Ser are surely worth
further and more detailed investigations.Comment: in press in A&
The new carbon symbiotic star IPHAS J205836.43+503307.2
We are performing a search for symbiotic stars using IPHAS, the INT Halpha
survey of the northern Galactic plane, and follow-up observations. Candidate
symbiotic stars are selected on the basis of their IPHAS and near-IR colours,
and spectroscopy and photometry are obtained to determine their nature. We
present here observations of the symbiotic star candidate IPHAS
J205836.43+503307.2. The optical spectrum shows the combination of a number of
emission lines, among which are the high-excitation species of [OIII], HeII,
[Ca V], and [Fe VII], and a red continuum with the features of a star at the
cool end of the carbon star sequence. The nebular component is spatially
resolved: the analysis of the spatial profile of the [NII]6583 line in the
spectrum indicates a linear size of ~2.5 arcsec along the east-west direction.
Its velocity structure suggests an aspherical morphology. The near-infrared
excess of the source, which was especially strong in 1999, indicated that a
thick circumstellar dust shell was also present in the system. The carbon star
has brightened in the last decade by two to four magnitudes at red and
near-infrared wavelengths. Photometric monitoring during a period of 60 days
from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2
magnitudes. From the observed spectrophotometric properties and variability, we
conclude that the source is a new Galactic symbiotic star of the D-type, of the
rare kind that contains a carbon star, likely a carbon Mira. Only two other
systems of this type are known in the Galaxy.Comment: 6 pages, 4 figure
Asiago eclipsing binaries program. II. V505 Per
The orbit and fundamental physical parameters of the double-lined eclipsing
binary V505 Per are derived by means of Echelle high resolution, high S/N
spectroscopy and B, V photometry. Effective temperatures, gravities, rotational
velocities and metallicities are obtained from atmospheric chi^2 analysis. An
E(B-V)<=0.01 mag reddening is derived from interstellar NaI and KI lines. The
distance to the system computed from orbital parameters (60.6 +/- 1 pc) is
identical to the newly re-reduced Hipparcos parallax (61.5 +/- 1.9 pc). The
masses of the two components (M(1) = 1.2693 +/- 0.0011 and M(2) = 1.2514 +/-
0.0012 Msun) place them in the transition region between convective and
radiative stellar cores of the HR diagram, with the more massive of the two
showing already the effect of evolution within the Main Sequence band (T(1) =
6512 +/- 21 K, T(2) = 6462 +/- 12 K, R(1) = 1.287 +/- 0.014, R(2) = 1.266 +/-
0.013 Rsun). This makes this system of particular relevance to theoretical
stellar models, as a test on the overshooting. We compare the firm
observational results for V505 Per component stars with the predictions of
various libraries of theoretical stellar models (BaSTI, Padova, Granada,
Yonsei-Yale, Victoria-Regina) as well as BaSTI models computed specifically for
the masses and chemical abundances of V505 Per. We found that the overshooting
at the masses of V505 Per component stars is already pretty low, but not null,
and described by efficiencies lambda(OV)=0.093 and 0.087 for the 1.27 and 1.25
Msun components, respectively. According to the computed BaSTI models, the age
of the system is about 0.9 Gyr and the element diffusion during this time has
reduced the surface metallicity from the initial [M/H]=-0.03 to the current
[M/H]=-0.13, in excellent agreement with observed [M/H]=-0.12 +/- 0.03.Comment: accepted in press by A&
Asiago eclipsing binaries program. I. V432 Aur
The orbit and physical parameters of the previously unsolved eclipsing binary
V432 Aur, discovered by Hipparcos, have been derived with errors better than 1%
from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral
analysis of both components has been performed, yielding T_eff and log g in
close agreement with the orbital solution, a metallicity [Z/Z_sun]=-0.60 and
rotational synchronization for both components. Direct comparison on the
theoretical L, T_eff plane with the Padova evolutionary tracks and isochrones
for the masses of the two components (1.22 and 1.08 M_sun) provides a perfect
match and a 3.75 Gyr age. The more massive and cooler component is approaching
the base of the giant branch and displays a probable pulsation activity with an
amplitude of Delta V = 0.075 mag and Delta rad.vel. = 1.5 km/sec. With a T_eff
= 6080 K it falls to the red of the nearby instability strip populated by delta
Sct and gamma Dor types of pulsating variables. Orbital modeling reveals a
large and bright surface spot on it. The pulsations activity and the large
spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They
reflect in a line broadening that at cursory inspection could be taken as
indication of a rotation faster than synchronization, something obviously odd
for an old, expanding star.Comment: A&A, 11 pages, accepted Jan 7, 200
Asiago eclipsing binaries program. III. V570 Per
The orbit and physical parameters of the previously unsolved SB2 EB V570 Per
are derived using high resolution Asiago Echelle spectroscopy and B, V
photo-electric photometry. The metallicity from chi^2 analysis is [M/H]=+0.02
+/- 0.03, and reddening from interstellar NaI and KI absorption lines is E(B-V)
=0.023 +/- 0.007. The two components have masses of 1.449 +/- 0.006 and 1.350
+/- 0.006 Msun and spectral types F3 and F5, respectively. They are both still
within the Main Sequence band (T_1 =6842 +/- 25 K, T_2 =6562 +/- 25 K from
chi^2 analysis, R_1 =1.523 +/- 0.030, R_2 =1.388 +/- 0.019 Rsun) and are
dynamically relaxed to co-rotation with the orbital motion (Vrot sin i_{1,2}
=40 and 36 (+/-1) km/sec). The distance to V570 Per obtained from the orbital
solution is 123 +/- 2 pc, in excellent agreement with the revised Hipparcos
distance of 123 +/- 11 pc. The observed properties of V570 Per components are
compared to BaSTI models computed on purpose for exactly the observed masses
and varied chemical compositions. This system is interesting since both
components have their masses in the range where the efficiency of convective
core overshooting has to decrease with the total mass as a consequence of the
decreasing size of the convective core during the central H-burning stage. Our
numerical simulations show that, a small but not null overshooting is required,
with efficiencies lambda_{OV} =0.14 and 0.11 for the 1.449 and 1.350 Msun
components, respectively. This confirms the finding of Paper II on the similar
system V505 Per. At the approx 0.8 Gyr age of the system, the element diffusion
has reduced the surface metallicity of the models from the initial [M/H]=+0.17
to [M/H]=+0.02, in perfect agreement with the spectroscopically derived
[M/H]=+0.02 +/- 0.03 value.Comment: accepted by A&A. This revised upload to astro-ph correct a formatting
error generated by uncorrect A&A style fil
Historical light curve and search for previous outbursts of Nova KT Eridani (2009)
Context. Nova Eridani (2009) caught the eye of the nova community due to its
fast decline from maximum, which was initially missed, and its subsequent
development in the radio and X-ray wavelengths. This system also exhibits
properties similar to those of the much smaller class of recurrent novae;
themselves potential progenitors of Type Ia Supernovae. Aims. We aim to
determine the nature and physical parameters of the KT Eri progenitor system.
Methods. We searched the Harvard College Observatory archive plates for the
progenitor of KT Eri to determine the nature of the system, particularly the
evolutionary stage of the secondary.We used the data obtained to search for any
periodic signal and the derived luminosity to estimate a recurrence timescale.
Furthermore, by comparing the colours of the quiescent system on a
colour-magnitude diagram we may infer the nature of the secondary star.
Results. We identified the progenitor system of KT Eri and measured a quiescent
magnitude of = 14.7 \pm 0.4. No previous outburst was found. However, we
suggest that if the nova is recurrent it should be on a timescale of centuries.
We find a periodicity at quiescence of 737 days which may arise from reflection
effects and/or eclipses in the central binary. The periodicity and the
quiescence magnitude of the system suggest that the secondary star is evolved
and likely in, or ascending, the Red Giant Branch. A second period is evident
at 376 days which has a sinusoidal like light curve. Furthermore, the outburst
amplitude of ~ 9 magnitudes is inconsistent with those expected for fast
classical novae (~ 17 magnitudes) which may lend further support for an evolved
secondary. (Abridged)Comment: 6 pages, 5 figures, accepted for publication in A&
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