354 research outputs found
The HH34 outflow as seen in [FeII]1.64um by LBT-LUCI
Dense atomic jets from young stars copiously emit in [FeII] IR lines, which
can, therefore, be used to trace the immediate environments of embedded
protostars. We want to investigate the morphology of the bright [FeII] 1.64um
line in the jet of the source HH34 IRS and compare it with the most commonly
used optical tracer [SII]. We analyse a 1.64um narrow-band filter image
obtained with the Large Binocular Telescope (LBT) LUCI instrument, which covers
the HH34 jet and counterjet. A Point Spread Function (PSF) deconvolution
algorithm was applied to enhance spatial resolution and make the IR image
directly comparable to a [SII] HST image of the same source. The [FeII]
emission is detected from both the jet, the (weak) counter-jet, and from the
HH34-S and HH34-N bow shocks. The deconvolved image allows us to resolve jet
knots close to about 1\arcsec from the central source. The morphology of the
[FeII] emission is remarkably similar to that of the [SII] emission, and the
relative positions of [FeII] and [SII] peaks are shifted according to proper
motion measurements, which were previously derived from HST images. An analysis
of the [FeII]/[SII] emission ratio shows that Fe gas abundance is much lower
than the solar value with up to 90% of Fe depletion in the inner jet knots.
This confirms previous findings on dusty jets, where shocks are not efficient
enough to remove refractory species from grains.Comment: 5 pages, 4 figures, note accepted by A&
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&
POISSON project - III - Investigating the evolution of the mass accretion rate
As part of the POISSON project (Protostellar Optical-Infrared Spectral Survey
on NTT), we present the results of the analysis of low-resolution NIR spectra
0.9-2.4 um) of two samples of YSOs in Lupus and Serpens (52 and 17 objects),
with masses 0.1-2.0 Msun and ages from 10^5 to a few 10^7 yr. After determining
the accretion parameters of the Lup and Ser targets by analysing their HI
near-IR emission features, we added the results to those from previous regions
(investigated in POISSON with the same methodology). We obtained a final
catalogue (143 objects) of mass accretion rates (Macc) derived in a homogeneous
fashion and analysed how Macc correlates with M* and how it evolves in time. We
derived the accretion luminosity (Lacc) and Macc for Lup and Ser objects from
the Br_gamma line by using relevant empirical relationships from the literature
that connect HI line luminosity and Lacc. To minimise the biases and also for
self-consistency, we re-derived mass and age for each source using the same set
of evolutionary tracks. We observe a correlation MaccM*^2.2, similarly to what
has previously been observed in several star-forming clouds. The time variation
of Macc is roughly consistent with the expected evolution in viscous disks,
with an asymptotic decay that behaves as t^-1.6. However, Macc values are
characterised by a large scatter at similar ages and are on average higher than
the predictions of viscous models. Although part of the scattering may be
related to the employed empirical relationship and to uncertainties on the
single measurements, the general distribution and decay trend of the Macc
points are real. These findings might be indicative of a large variation in the
initial mass of the disks, of fairly different viscous laws among disks, of
varying accretion regimes, and of other mechanisms that add to the dissipation
of the disks, such as photo-evaporation.Comment: 18 pages, 10 figures, accepted by A&
On the binarity of the classical Cepheid X Sgr from interferometric observations
Optical-infrared interferometry can provide direct geometrical measurements
of the radii of Cepheids and/or reveal unknown binary companions of these
stars. Such information is of great importance for a proper calibration of
Period-Luminosity relations and for determining binary fraction among Cepheids.
We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove
the presence of the hypothesized binary companion and to directly measure the
mean stellar radius, possibly detecting its variation along the pulsation
cycle. From AMBER observations in MR mode we performed a binary model fitting
on the closure phase and a limb-darkened model fitting on the visibility. Our
analysis indicates the presence of a point-like companion at a separation of
10.7 mas and 5.6 magK fainter than the primary, whose flux and position are
sharply constrained by the data. The radius pulsation is not detected, whereas
the average limb-darkened diameter results to be 1.48+/-0.08 mas, corresponding
to 53+/-3 R_sun at a distance of 333.3 pc.Comment: 5 pages, 3 figures, research not
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&
Connection between jets, winds and accretion in T Tauri stars: the X-shooter view
We have analysed the [OI]6300 A line in a sample of 131 young stars with
discs in the Lupus, Chamaeleon and signa Orionis star forming regions, observed
with the X-shooter spectrograph at VLT. The stars have mass accretion rates
spanning from 10^{-12} to 10^{-7} Mo/yr. The line profile was deconvolved into
a low velocity component (LVC,
40 km/s ), originating from slow winds and high velocity jets, respectively.
The LVC is by far the most frequent component, with a detection rate of 77%,
while only 30% of sources have a HVC. The [OI]6300 luminosity of both the LVC
and HVC, when detected, correlates with stellar and accretion parameters of the
central sources (i.e. Lstar , Mstar , Lacc , Macc), with similar slopes for the
two components. The line luminosity correlates better with the accretion
luminosity than with the stellar luminosity or stellar mass. We suggest that
accretion is the main drivers for the line excitation and that MHD disc-winds
are at the origin of both components. In the sub-sample of Lupus sources
observed with ALMA a relationship is found between the HVC peak velocity and
the outer disc inclination angle, as expected if the HVC traces jets ejected
perpendicularly to the disc plane. Mass loss rates measured from the HVC span
from ~ 10^{-13} to ~10^{-7} Mo/yr. The corresponding Mloss/Macc ratio ranges
from ~0.01 to ~0.5, with an average value of 0.07. However, considering the
upper limits on the HVC, we infer a ratio < 0.03 in more than 40% of sources.
We argue that most of these sources might lack the physical conditions needed
for an efficient magneto-centrifugal acceleration in the star-disc interaction
region. Systematic observations of populations of younger stars, that is, class
0/I, are needed to explore how the frequency and role of jets evolve during the
pre-main sequence phase.Comment: 15 pages, 14 figures, Accepted for publication in A&
Determinants of final infarct size and incidence of aborted infarction in patients treated with primary coronary intervention and adjunctive abciximab therapy.
On the 2015 outburst of the EXor variable star V1118 Ori
After a long-lasting period of quiescence of about a decade, the source V1118
Ori, one of the most representative members of the EXor variables, is now
outbursting. Since the initial increase of the near-infrared flux of about 1
mag (JHK bands) registered on 2015 September 22, the source brightness has
remained fairly stable. We estimate DeltaV about 3 mag with respect to the
quiescence phase. An optical/near-IR low-resolution spectrum has been obtained
with the Large Binocular Telescope instruments MODS and LUCI2, and compared
with a spectrum of similar spectral resolution and sensitivity level taken
during quiescence. Together with the enhancement of the continuum, the outburst
spectrum presents a definitely higher number of emission lines, in particular
HI recombination lines of the Balmer, Paschen, and Brackett series, along with
bright permitted lines of several species, forbidden atomic lines, and CO
ro-vibrational lines. Both mass accretion and mass loss rates have
significantly increased (by to about an order of magnitude, mass accretion rate
= 1.2-4.8 10^-8 M_sun/yr, mass loss rate = 0.8-2 10^-9 M_sun/yr) with respect
to the quiescence phase. If compared with previous outbursts, the present one
appears less energetic. Alternatively, it could already be in the fading phase
(with the maximum brightness level reached when the source was not visible),
or, viceversa, still in the rising phase.Comment: Accepted ApJ Letter
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