2,193 research outputs found
BVRcIc photometric evolution and flickering during the 2010 outburst of the recurrent nova U Scorpii
CCD BVRcIc photometric observations of the 2010 outburst of the recurrent
nova U Scorpii are presented. The light-curve has a smooth development
characterized by t2(V)=1.8 and t3(V)=4.1 days, close to the t2(V)=2.2 and
t3(V)=4.3 days of 1999 outburst. The plateau phase in 2010 has been brighter,
lasting shorter and beginning earlier than in the 1999 outburst. Flickering,
with an amplitude twice larger in than in band, was absent on
day +4.8 and +15.7, and present on day +11.8, with a time scale of about half
an hour.Comment: published March 1
V496 Scuti: An Fe II nova with dust shell accompanied by CO emission
We present near-infrared and optical observations of the nova V496 Scuti 2009
covering various phases - pre-maximum, early decline and nebular - during the
first 10 months of its discovery followed by limited observations in early part
of 2011 April. The spectra follow the evolution of the nova when the lines had
strong P Cygni profiles to a phase dominated by prominent emission lines. The
notable feature of the near-IR spectra in the early decline phase is the rare
presence of first overtone bands of carbon monoxide in emission. Later about
150 days after the peak brightness the IR spectra show clear dust formation in
the expanding ejecta. Dust formation in V496 Sct is consistent with the
presence of lines of elements with low ionization potentials like Na and Mg in
the early spectra and the detection of CO bands in emission. The light curve
shows a slow rise to the maximum and a slow decline indicating a prolonged mass
loss. This is corroborated by the strengthening of P Cygni profiles during the
first 30 days. In the spectra taken close to the optical maximum brightness,
the broad and single absorption component seen at the time of discovery is
replaced by two sharper components. During the early decline phase two sharp
dips that show increasing outflow velocities are seen in the P Cygni absorption
components of Fe II and H I lines. The spectra in 2010 March showed the onset
of the nebular phase. Several emission lines display saddle-like profiles
during the nebular phase. In the nebular stage the observed fluxes of [O III]
and H-beta lines are used to estimate the electron number densities and the
mass of the ejecta. The optical spectra show that the nova evolved in the P_fe
A_o spectral sequence. The physical conditions in the ejecta are estimated. The
absolute magnitude and the distance to the nova are estimated to be M_V = -7.0
+/- 0.2 and d = 2.9 +/- 0.3 kpc respectively.Comment: 14 pages, 9 figures and 6 Tables, Accepted for Publication in MNRA
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&
The 2010 nova outburst of the symbiotic Mira V407 Cyg
The nova outburst experienced in 2010 by the symbiotic binary Mira V407 Cyg
has been extensively studied at optical and infrared wavelengths with both
photometric and spectroscopic observations. This outburst, reminiscent of
similar events displayed by RS Oph, can be described as a very fast He/N nova
erupting while being deeply embedded in the dense wind of its cool giant
companion. The hard radiation from the initial thermonuclear flash ionizes and
excites the wind of the Mira over great distances (recombination is observed on
a time scale of 4 days). The nova ejecta is found to progressively decelerate
with time as it expands into the Mira wind. This is deduced from line widths
which change from a FWHM of 2760 km/s on day +2.3 to 200 km/s on day +196. The
wind of the Mira is massive and extended enough for an outer neutral and
unperturbed region to survive at all outburst phases.Comment: MNRAS Letter, in pres
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
Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi
Eruptive variables are young stars that show episodic variations of
brightness: EXors/FUors variations are commonly associated with enhanced
accretion outbursts occurring at intermittent cadence of months/years (EXors)
and decades/centuries (FUors). Variations that can be ascribed to a variable
extinction along their line of sight are instead classified as UXors. We aim at
investigating the long-term photometric behaviour of three sources classified
as eruptive variables. We present data from the archival plates of the Asiago
Observatory relative to the fields where the targets are located. For the sake
of completeness we have also analysed the Harvard plates of the same regions
that cover a much longer historical period, albeit at a lower sensitivity,
however we are only able to provide upper limits. A total of 273 Asiago plates
were investigated, providing a total of more than 200 magnitudes for the three
stars, which cover a period of about 34 yr between 1958 and 1991. We have
compared our data with more recently collected literature data. Our plates
analysis of V2492 Cyg provides historical upper limits that seem not to be
compatible with the level of the activity monitored during the last decade.
Therefore, recently observed accretion phenomena could be associated with the
outbursting episodes, more than repetitive obscuration. While a pure extinction
does not seem the only mechanism responsible for the ASASSN-15qi fluctuations,
it can account quite reasonably for the recent V350 Cep variations.Comment: 12 pages, accepted by A&
- …