50 research outputs found
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
Accretion and outflows in young stars with CUBES
The science case on studies of accretion and outflows in low-mass (<1.5M⊙) young stellar objects (YSOs) with the new CUBES instrument is presented. We show the need for a high-sensitivity, near-ultraviolet (NUV) spectrograph like CUBES, with a resolving power at least four times that of X-Shooter and combined with UVES via a fibrelink for simultaneous observations. Simulations with the CUBES exposure time calculator and the end-to-end software show that a significant gain in signal-to-noise can be achieved compared to current instruments, for both the spectral continuum and emission lines, including for relatively embedded YSOs. Our simulations also show that the low-resolution mode of CUBES will be able to observe much fainter YSOs (V ∼ 22 mag) in the NUV than we can today, allowing us extend studies to YSOs with background-limited magnitudes. The performance of CUBES in terms of sensitivity in the NUV will provide important new insights into the evolution of circumstellar disks, by studying the accretion, jets/winds and photo-evaporation processes, down to the low-mass brown dwarf regime. CUBES will also open-up new science as it will be able to observe targets that are several magnitudes fainter than those reachable with current instruments, facilitating studies of YSOs at distances of ∼ kpc scale. This means a step-change in the field of low-mass star formation, as it will be possible to expand the science case from relatively local star-forming regions to a large swathe of distances within the Milky Way
Astrocook: Your starred chef for spectral analysis
Astrocook is a software environment to analyze quasar spectra in a variety of ways. It aims to break the static pipeline paradigm by enforcing a new flexible approach to data treatment, in which complex automatic workflows are dynamically created from a wide set of atomic operations (hence the tagline: "a thousand recipes to cook a spectrum"). We will focus both on the novel algorithms that have been implemented and on the scientific validation and reproducibility of the results. To highlight the benefits of the Astrocook approach for both interactive and automatic analysis, two specific use cases are discussed (one of which was used in practice to process observational data from the QUBRICS survey)