1,660 research outputs found
Evaluating GAIA performances on eclipsing binaries. I. Orbits and stellar parameters for V505 Per, V570 Per and OO Peg
The orbits and physical parameters of three detached, double-lined A-F
eclipsing binaries have been derived combining H_P, V_T, B_T photometry from
the Hipparcos/Tycho mission with 8500-8750 Ang ground-based spectroscopy,
mimicking the photometric+spectroscopic observations that should be obtained by
GAIA, the approved Cornerstone 6 mission by ESA. This study has two main
objectives, namely (a) to derive reasonable orbits for a number of new
eclipsing binaries and (b) to evaluate the expected performances by GAIA on
eclipsing binaries and the accuracy achievable on the determination of
fundamental stellar parameters like masses and radii. It is shown that a 1%
precision in the basic stellar parameters can be achieved by GAIA on well
observed detached eclipsing binaries provided that the spectroscopic
observations are performed at high enough resolution. Other types of eclipsing
binaries (including semi-detached and contact types) and different spectral
types will be investigated in following papers along this series.Comment: A&A, 11 pages, 5 figures, 5 table
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
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
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&
Discovery in IC10 of the farthest known symbiotic star
We report the discovery of the first known symbiotic star in IC10, a
starburst galaxy belonging to the Local Group, at a distance of ~750kpc. The
symbiotic star was identified during a survey of emission-line objects. It
shines at V = 24.62+-0.04, V - R_C = 2.77+-0.05 and R_C - I_C = 2.39+-0.02 and
suffers from E(B-V) = 0.85+-0.05 reddening. The spectrum of the cool component
well matches that of solar neighborhood M8III giants. The observed emission
lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low
electronic density, negligible optical depth effects and 35,000K < T_eff <
90,000K for the ionizing source. The spectrum of the new symbiotic star in IC10
is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic
star and Mira.Comment: 5 pages including 3 figures. MNRAS Letters accepted. Also available
at http://pessoais.ov.ufrj.br/denise
Symbiotic stars on Asiago archive plates. I
The rich plate archive of the Asiago observatory has been searched for plates
containing the symbiotic stars AS 323, Ap 3-1, CM Aql, V1413 Aql (=AS 338),
V443 Her, V627 Cas (=AS 501) and V919 Sgr. The program objects have been found
on 602 plates, where their brightness has been estimated against the UBVRI
photometric sequences calibrated by Henden and Munari (2000, A&AS 143, 343). AS
323 is probably eclipsing, with a preliminary P=197.6 day period. If confirmed,
it would be the shortest orbital period known among symbiotic stars. CM Aql
does not seem to undergo a series of outbursts, its lightcurve being instead
modulated by a large amplitude sinusoidal variation with a P~1058 day period.
V627 Cas presents a secular trend in agreement with the possible post-AGB
nature of its cool component.Comment: A&A in pres
The 2016-2017 peak luminosity of the pre-main sequence variable V2492 Cyg
V2492 Cyg is a young pre-main sequence star presenting repetitive brightness
variations of significant amplitude (Delta R > 5 mag) whose physical origin has
been ascribed to both extinction (UXor-type) and accretion (EXor-type)
variability, although their mutual proportion has not been clarified yet.
Recently, V2492 Cyg has reached a level of brightness ever registered in the
period of its documented activity. Optical and near-infrared photometry and
spectroscopy have been obtained in October 2016 and between March and July
2017. The source has remained bright until the end of May 2017, then it started
to rapidly fade since the beginning of June at a rate of about 0.08 mag/day. On
mid-July 2017 the source has reached the same low-brightness level as two years
before. Extinction and mass accretion rate were derived by means of the
luminosity of the brightest lines, in particular Halpha and Hbeta. A couple of
optical high-resolution spectra are also presented to derive information on the
gas kinematics. Visual extinction variations do not exceed a few magnitudes,
while the mass accretion rate is estimated to vary from less than 10^-8 up to a
few 10^-7 M_sun/yr. This latter is comparable to that estimated on the previous
high-state in 2010, likely occurred under more severe extinction conditions.
The combined analysis of the optical and near-infrared (NIR) observations
extends to the present event the original suggestion that the V2492 Cyg
variability is a combination of changing extinction and accretion.Comment: Accepted by A&
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