58 research outputs found
Cluster mass estimation through Fair Galaxies
We analyse a catalogue of simulated clusters within the theoretical framework
of the Spherical Collapse Model (SCM), and demonstrate that the relation
between the infall velocity of member galaxies and the cluster matter
overdensity can be used to estimate the mass profile of clusters, even though
we do not know the full dynamics of all the member galaxies. In fact, we are
able to identify a limited subset of member galaxies, the 'fair galaxies',
which are suitable for this purpose. The fair galaxies are identified within a
particular region of the galaxy distribution in the redshift (line-of-sight
velocity versus sky-plane distance from the cluster centre). This 'fair region'
is unambiguously defined through statistical and geometrical assumptions based
on the SCM. These results are used to develop a new technique for estimating
the mass profiles of observed clusters and subsequently their masses. We tested
our technique on a sample of simulated clusters; the mass profiles estimates
are proved to be efficient from 1 up to 7 virialization radii, within a typical
uncertainty factor of 1.5, for more than 90 per cent of the clusters
considered. Moreover, as an example, we used our technique to estimate the mass
profiles and the masses of some observed clusters of the Cluster Infall Regions
in the Sloan Digital Sky Survey catalogue. The technique is shown to be
reliable also when it is applied to sparse populated clusters. These
characteristics make our technique suitable to be used in clusters of large
observational catalogues.Comment: 11 pages, 11 figures, 5 tables - Slightly revised to match the
version published on MNRAS; abstract update
Field tests for the ESPRESSO data analysis software
The data analysis software (DAS) for VLT ESPRESSO is aimed to set a new
benchmark in the treatment of spectroscopic data towards the
extremely-large-telescope era, providing carefully designed, fully interactive
recipes to take care of complex analysis operations (e.g. radial velocity
estimation in stellar spectra, interpretation of the absorption features in
quasar spectra). A few months away from the instrument's first light, the DAS
is now mature for science validation, with most algorithms already implemented
and operational. In this paper, I will showcase the DAS features which are
currently employed on high-resolution HARPS and UVES spectra to assess the
scientific reliability of the recipes and their range of application. I will
give a glimpse on the science that will be possible when ESPRESSO data become
available, with a particular focus on the novel approach that has been adopted
to simultaneously fit the emission continuum and the absorption lines in the
Lyman-alpha forest of quasar spectra.Comment: 4 pages, 1 figure; proceedings of ADASS XXVI, accepted by ASP
Conference Serie
Data Analysis Software for the ESPRESSO Science Machine
ESPRESSO is an extremely stable high-resolution spectrograph which is
currently being developed for the ESO VLT. With its groundbreaking
characteristics it is aimed to be a "science machine", i.e., a fully-integrated
instrument to directly extract science information from the observations. In
particular, ESPRESSO will be the first ESO instrument to be equipped with a
dedicated tool for the analysis of data, the Data Analysis Software (DAS),
consisting in a number of recipes to analyze both stellar and quasar spectra.
Through the new ESO Reflex GUI, the DAS (which will implement new algorithms to
analyze quasar spectra) is aimed to get over the shortcomings of the existing
software providing multiple iteration modes and full interactivity with the
data.Comment: 5 pages, 2 figures; proceedings of ADASS XXI
174P/Echeclus and its Blue Coma Observed Post-outburst
It has been suggested that centaurs may lose their red surfaces and become
bluer due to the onset of cometary activity, but the way in which cometary
outbursts affect the surface composition and albedo of active centaurs is
poorly understood. We obtained consistent visual-near-infrared (VNIR)
reflectance spectra of the sporadically active centaur 174P/Echeclus during a
period of inactivity in 2014 and six weeks after its outburst in 2016 to see if
activity had observably changed the surface properties of the nucleus. We
observed no change in the surface reflectance properties of Echeclus following
the outburst compared to before, indicating that, in this case, any surface
changes due to cometary activity were not sufficiently large to be observable
from Earth. Our spectra and post-outburst imaging have revealed, however, that
the remaining dust coma is not only blue compared to Echeclus, but also bluer
than solar, with a spectral gradient of -7.7+/-0.6% per 0.1 micron measured
through the 0.61-0.88 micron wavelength range that appears to continue up to a
wavelength of around 1.3 micron before becoming neutral. We conclude that the
blue visual color of the dust is likely not a scattering effect, and instead
may be indicative of the dust's carbon-rich composition. Deposition of such
blue, carbon-rich, comatic dust onto a red active centaur may be a mechanism by
which its surface color could be neutralized.Comment: 15 pages, 4 figures, 3 tables, AJ accepted, in pres
The spectacular evolution of Supernova 1996al over 15 years: a low energy explosion of a stripped massive star in a highly structured environment
Spectrophotometry of SN 1996al carried out throughout 15 years is presented.
The early photometry suggests that SN 1996al is a Linear type-II supernova,
with an absolute peak of Mv ~ -18.2 mag. Early spectra present broad,
asymmetric Balmer emissions, with super-imposed narrow lines with P-Cygni
profile, and He I features with asymmetric, broad emission components. The
analysis of the line profiles shows that the H and He broad components form in
the same region of the ejecta. By day +142, the Halpha profile dramatically
changes: the narrow P-Cygni profile disappears, and the Halpha is fitted by
three emission components, that will be detected over the remaining 15 yrs of
the SN monitoring campaign. Instead, the He I emissions become progressively
narrower and symmetric. A sudden increase in flux of all He I lines is observed
between 300 and 600 days. Models show that the supernova luminosity is
sustained by the interaction of low mass (~1.15 Msun) ejecta, expelled in a low
kinetic energy (~ 1.6 x 10^50 erg) explosion, with highly asymmetric
circumstellar medium. The detection of Halpha emission in pre-explosion archive
images suggests that the progenitor was most likely a massive star (~25 Msun
ZAMS) that had lost a large fraction of its hydrogen envelope before explosion,
and was hence embedded in a H-rich cocoon. The low-mass ejecta and modest
kinetic energy of the explosion are explained with massive fallback of material
into the compact remnant, a 7-8 Msun black hole.Comment: 27 pages, 23 figures, Accepted for publication in MNRA
The Probabilistic Random Forest applied to the selection of quasar candidates in the QUBRICS Survey
The number of known, bright () QSOs in the
Southern Hemisphere is considerably lower than the corresponding number in the
Northern Hemisphere due to the lack of multi-wavelength surveys at .
Recent works, such as the QUBRICS survey, successfully identified new,
high-redshift QSOs in the South by means of a machine learning approach applied
on a large photometric dataset. Building on the success of QUBRICS, we present
a new QSO selection method based on the Probabilistic Random Forest (PRF), an
improvement of the classic Random Forest algorithm. The PRF takes into account
measurement errors, treating input data as probability distribution functions:
this allows us to obtain better accuracy and a robust predictive model. We
applied the PRF to the same photometric dataset used in QUBRICS, based on the
SkyMapper DR1, Gaia DR2, 2MASS, WISE and GALEX databases. The resulting
candidate list includes sources with . We estimate for our proposed
algorithm a completeness of and a purity of on the test
datasets. Preliminary spectroscopic campaigns allowed us to observe 41
candidates, of which 29 turned out to be QSOs. The performances of the
PRF, currently comparable to those of the CCA, are expected to improve as the
number of high-z QSOs available for the training sample grows: results are
however already promising, despite this being one of the first applications of
this method to an astrophysical context.Comment: Accepted for publication in MNRAS, 12 pages, 11 figures, 4 table
From ESPRESSO to the Future - Analysis of QSO Spectra with the Astrocook Package
The ESPRESSO instrument, to be commissioned in the next months at the ESO VLT, is bound to became a landmark in the field of high-resolution optical spectroscopy, both for its ground-breaking science objectives (search for Earth-like exoplanets; measure of a possible variation of fundamental constants) and for its novel approach to data treatment. For the first time for an ESO instrument, scientific information will be extracted in real time by a dedicated Data Analysis Software (DAS), which includes several interactive workflows to handle the typical analysis cases in stellar and QSO spectroscopy. Data analysis tools in the oncoming ELT era will face demanding requirements from compelling science case, such as the Sandage Test: the need of handling larger data sizes with a higher degree of accuracy, and the possibility to compare observations and simulated data on the fly. To this purpose, we are currently porting the solutions developed for ESPRESSO to a wider framework, integrating the algorithms within a full-fledged set of Python modules. The project, named "Astrocook", is aimed to provide a set of high-level, instrument-agnostic procedures to automatically extract physical information from the data
- …