866 research outputs found
The first three years of the outburst and light-echo evolution of V838 Mon and the nature of its progenitor
V838 Mon has undergone one of the most mysterious stellar outbursts on
record, with (a) a large amplitude (Delta B ~ 10 mag) and multi-maxima
photometric pattern, (b) a cool spectral type at maximum becoming cooler and
cooler with time during the descent, until it reached the never-seen-before
realm of L-type supergiants, never passing through optically thin or nebular
stages, (c) the development of a spectacular, monotonically expanding
light-echo in the circumstellar material, and (d) the identification of a
massive and young B3V companion, unaffected by the outburst. In this talk we
review the photometric and spectroscopic evolution during the first three full
years of outburst, the light-echo development and infer the nature of the
progenitor, which was brighter and hotter in quiescence than the B3V companion
and with an inferred ZAMS mass of about 65 Msun.Comment: to appear in the Proceedings of the Colloquium "Interacting Binaries:
Accretion, Evolution and Outcome", held in Cefalu' (Sicily) July 4-10, 2004,
L.A. Antonelli et al. eds., American Institute of Physics Conf. Proc. series,
in press. 6 pages, 4 figure
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&
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
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