114 research outputs found
A long-lasting quiescence phase of the eruptive variable V1118 Ori
V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main
Sequence stars whose episodic outbursts are attributed to disk accretion
events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed
between two subsequent outbursts of its recent history. We present
near-infrared photometry of V1118 Ori carried out during the last eight years,
along with a complete spectroscopic coverage from 0.35 to 2.5 um. A longterm
sampling of V1118 Ori in quiescence has never been done, hence we can benefit
from the current circumstance to determine the lowest values (i.e. the zeroes)
of the parameters to be used as a reference for evaluating the physical changes
typical of more active phases. A quiescence mass accretion rate between 1--3
10 M_{\sun} yr can be derived and the difference with
previous determinations is discussed. From line emission and IR colors analysis
a visual extinction of 1-2 mag is consistently derived, confirming that V1118
Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric
luminosity of about 2.1 L_{\sun}. An anti-correlation exists between the
equivalent width of the emission lines and the underlying continuum. We
searched the literature for evaluating whether or not such a behaviour is a
common feature of the whole class. The anti-correlation is clearly recognizable
for all the available EXors in the optical range (H and H
lines), while it is not as much evident in the infrared (Pa and
Br lines). The observed anti-correlation supports the accretion-driven
mechanism as the most likely to account for continuum variations.Comment: 6 figures, 5 tables, accepted on Ap
Recent outburst of the young star V1180 Cas
We report on the ongoing outburst of the young variable V1180 Cas, which is
known to display characteristics in common with EXor eruptive variables. We
present results that support the scenario of an accretion-driven nature of the
brightness variations of the object and provide the first evidence of jet
structures around the source. We monitored the recent flux variations of the
target in the Rc, J, H, and K bands. New optical and near-IR spectra taken
during the current high state of V1180 Cas are presented, in conjunction with
H2 narrow-band imaging of the source. Observed near-IR colour variations are
analogous to those observed in EXors and consistent with excess emission
originating from an accretion event. The spectra show numerous emission lines,
which indicates accretion, ejection of matter, and an active disc. Using
optical and near-IR emission features we derive a mass accretion rate of ~3 E-8
Msun/yr, which is an order of magnitude lower than previous estimates. In
addition, a mass loss rate of ~4 E-9 and ~4 E-10 Msun/yr are estimated from
atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright
knots of emission around the source and the nearby optically invisible star
V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution
observations of the detected jet will help to clarify whether V1180 Cas is the
driving source and to determine the relation between the observed knots.Comment: Accepted as Letter in A&A; 4 pages, 3 figure
Simultaneous monitoring of the photometric and polarimetric activity of the young star PV Cep in the optical/near-infrared bands
We present the results of a simultaneous monitoring, lasting more than 2
years, of the optical and near-infrared photometric and polarimetric activity
of the variable protostar PV Cep. During the monitoring period, an outburst has
occurred in all the photometric bands, whose declining phase (J
3 mag) lasted about 120 days. A time lag of 30 days between
optical and infrared light curves has been measured and interpreted in the
framework of an accretion event. This latter is directly recognizable in the
significant variations of the near-infrared colors, that appear bluer in the
outburst phase, when the star dominates the emission, and redder in declining
phase, when the disk emission prevails. All the observational data have been
combined to derive a coherent picture of the complex morphology of the whole PV
Cep system, that, in addition to the star and the accretion disk, is composed
also by a variable biconical nebula. In particular, the mutual interaction
between all these components is the cause of the high value of the polarization
( 20%) and of its fluctuations. The observational data concur to
indicate that PV Cep is not a genuine EXor star, but rather a more complex
object; moreover the case of PV Cep leads to argue about the classification of
other recently discovered young sources in outburst, that have been considered,
maybe over-simplifying, as EXor.Comment: Accepted for publication on Ap
Optical and infrared observations of the supernova SN 1999el
Optical and near-infrared light curves of the Type IIn supernova 1999el in
NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is
covered from the first observation obtained a few days before maximum light.
Spectroscopic observations are also discussed. Using as a distance calibrator
the Type Ia SN 2000E, which occurred some months later in the same galaxy, and
fitting a blackbody law to the photometric data we obtain a maximum bolometric
luminosity for SN 1999el of erg s. In general, the
photometric properties of SN 1999el are very similar to those of SN 1998S, a
bright and well studied Type IIn SN, showing a fast decline in all observed
bands similar to those of Type II-L SNe. The differences with SN 1998S are
analyzed and ascribed to the differences in a pre-existing circumstellar
envelope in which dust was already present at the moment of the SN outburst. We
infer that light echoes may play a possibly significant role in affecting the
observed properties of the light curves, although improved theoretical models
are needed to account for the data. We conclude that mass loss in the
progenitor RG stars is episodic and occurs in an asymmetric way. This implies
that collapsing massive stars appear as normal Type II SN if this occurs far
from major mass loss episodes, whereas they appear as Type IIn SNe if a large
mass loss episode is in progress.Comment: 30 pages, 8 figures, figure 1 available as jpeg file, ApJ in pres
Supervised machine learning on Galactic filaments. Revealing the filamentary structure of the Galactic interstellar medium
Context. Filaments are ubiquitous in the Galaxy, and they host star formation. Detecting them in a reliable way is therefore key towards our understanding of the star formation process.
Aims: We explore whether supervised machine learning can identify filamentary structures on the whole Galactic plane.
Methods: We used two versions of UNet-based networks for image segmentation. We used H2 column density images of the Galactic plane obtained with Herschel Hi-GAL data as input data. We trained the UNet-based networks with skeletons (spine plus branches) of filaments that were extracted from these images, together with background and missing data masks that we produced. We tested eight training scenarios to determine the best scenario for our astrophysical purpose of classifying pixels as filaments.
Results: The training of the UNets allows us to create a new image of the Galactic plane by segmentation in which pixels belonging to filamentary structures are identified. With this new method, we classify more pixels (more by a factor of 2 to 7, depending on the classification threshold used) as belonging to filaments than the spine plus branches structures we used as input. New structures are revealed, which are mainly low-contrast filaments that were not detected before. We use standard metrics to evaluate the performances of the different training scenarios. This allows us to demonstrate the robustness of the method and to determine an optimal threshold value that maximizes the recovery of the input labelled pixel classification.
Conclusions: This proof-of-concept study shows that supervised machine learning can reveal filamentary structures that are present throughout the Galactic plane. The detection of these structures, including low-density and low-contrast structures that have never been seen before, offers important perspectives for the study of these filaments
SOXS: a wide band spectrograph to follow up transients
SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope
capable to cover the optical and NIR bands, based on the heritage of the
X-Shooter at the ESO-VLT. SOXS will be built and run by an international
consortium, carrying out rapid and longer term Target of Opportunity requests
on a variety of astronomical objects. SOXS will observe all kind of transient
and variable sources from different surveys. These will be a mixture of fast
alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term
alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by
passage of minor bodies). While the focus is on transients and variables, still
there is a wide range of other astrophysical targets and science topics that
will benefit from SOXS. The design foresees a spectrograph with a
Resolution-Slit product ~ 4500, capable of simultaneously observing over the
entire band the complete spectral range from the U- to the H-band. The limiting
magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified
from on-going imaging surveys. Light imaging capabilities in the optical band
(grizy) are also envisaged to allow for multi-band photometry of the faintest
transients. This paper outlines the status of the project, now in Final Design
Phase.Comment: 12 pages, 14 figures, to be published in SPIE Proceedings 1070
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