1,853 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
On the accuracy of GAIA radial velocities
We have obtained 782 real spectra and used them as inputs for 6700 automatic
cross-correlation runs to the aim of investigating the radial velocity accuracy
that GAIA could potentially achieve as function of spectral resolution and
signal-to-noise ratio. We have explored the dispersions 0.25, 0.5, 1 and 2
Ang/pix (bracketing the 0.75 Ang/pix currently baselined for the 8490--8740 Ang
GAIA range centered on the near-infrared CaII triplet) over S/N ranging from 10
to 110. We have carefully maintained the condition FWHM (PSF) = 2 pixels during
the acquisition of the 782 input spectra, and therefore the resolutions that we
have explored are 0.5, 1, 2 and 4 Ang corresponding to resolving powers
R=17200, 8600, 4300 and 2150. We have investigated late-F to early-M stars
(constituting the vast majority of GAIA targets), slowly rotating (V_{rot} sin
i = 4 km/sec, as for field stars at these spectral types), of solar metallicity
( = -0.07) and not binary. The results are accurately described by the
simple law: lg sigma = 0.6(lg S/N)^2 - 2.4(lg S/N) + 1.75(lg D) + 3, where
sigma is the cross-correlation standard error (in km/sec) and D is the spectral
dispersion (in Ang/pix). The spectral dispersion has turned out to be the
dominant factor governing the accuracy of radial velocities, with S/N being
less important and the spectral mis-match being a weak player. These results
are relevant not only within the GAIA context but also to ground-based
observers because the absence of telluric absorptions and proximity to the
wavelengths of peak emission make the explored 8490--8740 Ang interval an
interesting option for studies of cool stars with conventional telescopes.Comment: 12 pages, 2 figures, 5 tables, in press in Baltic Astronom
The narrow and moving HeII lines in nova KT Eri
We present outburst and quiescence spectra of the classical nova KT Eri and
discuss the appearance of a sharp HeII 4686 Ang emission line, whose origin is
a matter of discussion for those novae that showed a similar component. We
suggest that the sharp HeII line, when it first appeared toward the end of the
outburst optically thick phase, comes from the wrist of the dumbbell structure
characterizing the ejecta as modeled by Ribeiro et al. (2013). When the ejecta
turned optically thin, the already sharp HeII line became two times narrower
and originated from the exposed central binary. During the optically thin
phase, the HeII line displayed a large change in radial velocity that had no
counterpart in the Balmer lines (both their narrow cores and the broad
pedestals). The large variability in radial velocity of the HeII line continued
well into quiescence, and it remains the strongest emission line observed over
the whole optical range.Comment: in press in A&
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
Outburst evolution, historic light curve and a flash-ionized nebula around the WZ Sge-type object PNV J03093063+2638031
We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV
J03093063+2638031 for more than four months, from V=11.0 maximum brightness
down to V=18.4 mag, close to quiescence value, by obtaining BVRI photometry and
low resolution fluxed spectroscopy. The evolution was normal and no late-time
`echo' outbursts were observed. The absolute integrated flux of emission lines
kept declining along the superoutburst, and their increasing contrast with the
underlying continuum was simply the result of the faster decline of the
continuum compared to the emission lines. Inspection of historical Harvard
plates covering the 1899-1981 period did not reveal previous outbursts, neither
`normal' nor 'super'. We discovered an extended emission nebula (radius ~1
arcmin) around PNV J03093063+2638031, that became visible for a few months as
the result of photo-ionization from the superoutburst of the central star. It
is not present on Palomar I and II sky survey images and it quickly disappeared
when the outburst was over. From the rate at wich the inization front swept
through the nebula, we derive a distance of ~120 pc to the system. The nebula
is density bounded with an outer radius of 0.03 pc, and the absolute magnitude
of the central star in quiescence is M(V)~14.2 mag. The electron density in the
nebula is estimated to be 10(+5) cm(-3) from the observed recombination time
scale. Given the considerable substructures seen across the nebula, a low
filling factor is inferred. Similar nebulae have not been reported for other WZ
Sge objects and the challenges posed to models are considered.Comment: Astronomy & Astrophysic
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
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