arXiv subjects

Salvatore Scuderi

Publications and source records attributed to Salvatore Scuderi.

32 records · Page 2Linked to original sources

arXiv2020

Development status of the UV-VIS detector system of SOXS for the ESO-NTT telescope

SOXS will be the new spectroscopic facility for the ESO NTT telescope able to cover the optical and NIR bands by using two different arms: the UV-VIS (350-850 nm), and the NIR (800-2000 nm). In this article, we describe the development status of the visible camera cryostat, the architecture of the acquisition system and the progress in the electronic design. The UV-VIS detector system is based on a CCD detector 44-82 from e2v, a custom detector head, coupled with the ESO continuous flow cryostats (CFC), a custom cooling system, based on a Programmable Logic Controller (PLC), and the New General Controller (NGC) developed by ESO. This paper outlines the development status of the system, describes the design of the different parts that make up the UV-VIS arm and is accompanied by a series of information describing the SOXS design solutions in the mechanics and in the electronics parts. The first tests of the detector system with the UV-VIS camera will be shown.

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arXiv2020

Development status of the SOXS instrument control software

SOXS (Son Of X-Shooter) is a forthcoming instrument for ESO-NTT, mainly dedicated to the spectroscopic study of transient events and is currently starting the AIT (Assembly, Integration, and Test) phase. It foresees a visible spectrograph, a near-Infrared (NIR) spectrograph, and an acquisition camera for light imaging and secondary guiding. The optimal setup and the monitoring of SOXS are carried out with a set of software-controlled motorized components and sensors. The instrument control software (INS) also manages the observation and calibration procedures, as well as maintenance and self-test operations. The architecture of INS, based on the latest release of the VLT Software (VLT2019), has been frozen; the code development is in an advanced state for what concerns supported components and observation procedures, which run in simulation. In this proceeding we present the INS current status, focusing in particular on the ongoing efforts in the support of two non-standard, "special" devices. The first special device is the piezoelectric slit exchanger for the NIR spectrograph; the second special device is the piezoelectric tip-tilt corrector used for active compensation of mechanical flexures of the instrument.

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arXiv2020

Design and development of the SOXS calibration unit

SOXS is a new spectrograph for the New Technology Telescope (NTT), optimized for transient and variable objects, covering a wide wavelength range from 350 to 2000 nm. SOXS is equipped with a calibration unit that will be used to remove the instrument signatures and to provide wavelength calibration to the data. The calibration unit will employ seven calibration lamps: a quartz-tungsten-halogen and a deuterium lamp for the flat-field correction, a ThAr lamp and four pencil-style rare-gas lamps for the wavelength calibration. The light from the calibration lamps is injected into the spectrograph mimicking the f/11 input beam of the NTT, by using an integrating sphere and a custom doublet. The oversized illumination patch covers the length of the spectrograph slit homogeneously, with $< 1\%$ variation. The optics also supports the second mode of the unit, the star-simulator mode that emulates a point source by utilizing a pinhole mask. Switching between the direct illumination and pinhole modes is performed by a linear stage. A safety interlock switches off the main power when the lamp box cover is removed, preventing accidental UV exposure to the service personnel. All power supplies and control modules are located in an electronic rack at a distance from the telescope platform. In this presentation we describe the optical, mechanical, and electrical designs of the SOXS calibration unit, and report the status of development in which the unit is currently in the test and verification stage.

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arXiv2018

MITS: the Multi-Imaging Transient Spectrograph for SOXS

The Son Of X-Shooter (SOXS) is a medium resolution spectrograph R~4500 proposed for the ESO 3.6 m NTT. We present the optical design of the UV-VIS arm of SOXS which employs high efficiency ion-etched gratings used in first order (m=1) as the main dispersers. The spectral band is split into four channels which are directed to individual gratings, and imaged simultaneously by a single three-element catadioptric camera. The expected throughput of our design is >60% including contingency. The SOXS collaboration expects first light in early 2021. This paper is one of several papers presented in these proceedings describing the full SOXS instrument.

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arXiv2018

The VIS detector system of SOXS

SOXS will be a unique spectroscopic facility for the ESO NTT telescope able to cover the optical and NIR bands thanks to two different arms: the UV-VIS (350-850 nm), and the NIR (800-1800 nm). In this article, we describe the design of the visible camera cryostat and the architecture of the acquisition system. The UV-VIS detector system is based on a e2v CCD 44-82, a custom detector head coupled with the ESO continuous ow cryostats (CFC) cooling system and the NGC CCD controller developed by ESO. This paper outlines the status of the system and describes the design of the different parts that made up the UV-VIS arm and is accompanied by a series of contributions describing the SOXS design solutions.

astro-ph.IM↗

arXiv2018

Architecture of the SOXS instrument control software

SOXS (Son Of X-Shooter) is a new spectrograph for the ESO NTT telescope, currently in the final design phase. The main instrument goal is to allow the characterization of transient sources based on alerts. It will cover from near-infrared to visible bands with a spectral resolution of $R \sim 4500$ using two separate, wavelength-optimized spectrographs. A visible camera, primarily intended for target acquisition and secondary guiding, will also provide a scientific "light" imaging mode. In this paper we present the current status of the design of the SOXS instrument control software, which is in charge of controlling all instrument functions and detectors, coordinating the execution of exposures, and implementing all observation, calibration and maintenance procedures. Given the extensive experience of the SOXS consortium in the development of instruments for the VLT, we decided to base the design of the Control System on the same standards, both for hardware and software control. We illustrate the control network, the instrument functions and detectors to be controlled, the overall design of SOXS Instrument Software (INS) and its main components. Then, we provide details about the control software for the most SOXS-specific features: control of the COTS-based imaging camera, the flexures compensation system and secondary guiding.

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arXiv2018

Optical design of the SOXS spectrograph for ESO NTT

An overview of the optical design for the SOXS spectrograph is presented. SOXS (Son Of X-Shooter) is the new wideband, medium resolution (R>4500) spectrograph for the ESO 3.58m NTT telescope expected to start observations in 2021 at La Silla. The spectroscopic capabilities of SOXS are assured by two different arms. The UV-VIS (350-850 nm) arm is based on a novel concept that adopts the use of 4 ion-etched high efficiency transmission gratings. The NIR (800- 2000 nm) arm adopts the '4C' design (Collimator Correction of Camera Chromatism) successfully applied in X-Shooter. Other optical sub-systems are the imaging Acquisition Camera, the Calibration Unit and a pre-slit Common Path. We describe the optical design of the five sub-systems and report their performance in terms of spectral format, throughput and optical quality. This work is part of a series of contributions describing the SOXS design and properties as it is about to face the Final Design Review.

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arXiv2017

A method to measure the transverse magnetic field and orient the rotational axis of stars

Direct measurements of the stellar magnetic fields are based on the splitting of spectral lines into polarized Zeeman components. With few exceptions, Zeeman signatures are hidden in data noise and a number of methods have been developed to measure the average, over the visible stellar disk, of longitudinal components of the magnetic field. As to faint stars, at present observable only with low resolution spectropolarimetry, a method is based on the regression of the Stokes V signal against the first derivative of Stokes I. Here we present an extension of this method to obtain a direct measurement of the transverse component of stellar magnetic fields by the regression of high resolution Stokes Q and U as a function of the second derivative of Stokes I. We also show that it is possible to determine the orientation in the sky of the rotation axis of a star on the basis of the periodic variability of the transverse component due to its rotation. The method is applied to data, obtained with the Catania Astrophysical Observatory Spectropolarimeter, along the rotational period of the well known magnetic star \b{eta} CrB.

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arXiv2008

The World Space Observatory (WSO-UV) - Current status

This paper reports on the current status of the World Space Observatory WSO-UV, a space mission for UV astronomy, planned for launch at the beginning of next decade. It is based on a 1.7 m telescope, with focal plane instruments including high resolution spectrographs, long slit low resolution spectrographs and imaging cameras.

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arXiv2005

Low Mass Pre-Main Sequence stars in the Large Magellanic Cloud - II: HST-WFPC2 observations of two fields in the 30 Doradus region

As a part of an ongoing effort to characterise the young stellar populations in the Large Magellanic Cloud, we present HST-WFPC2 broad and narrow band imaging of two fields with recent star formation activity in the Tarantula region. A population of objects with Halpha and/or Balmer continuum excess was identified. On account of the intense Halpha emission (equivalent widths up to several tens of Angstroms), its correlation with the Balmer continuum excess and the stars' location on the HR diagram, we interpret them as low mass (~1-2 Mo) Pre-Main Sequence stars. In this framework, the data show that coeval high and low mass stars have significantly different spatial distributions, implying that star formation processes for different ranges of stellar masses are rather different and/or require different initial conditions. We find that the overall slope of the mass function of the young population is somewhat steeper than the classical Salpeter value and that the star formation density of this young component is 0.2-0.4 Mo/yr/kpc2, i.e. intermediate between the value for an active spiral disk and that of a starburst region. The uncertainties associated with the determination of the slope of the mass function and the star formation density are thoroughly discussed.

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arXiv2001

Accurate Stellar Population Studies from Multiband Photometric Observations

We present a new technique based on multi-band near ultraviolet and optical photometry to measure both the stellar intrinsic properties, ie luminosity and effective temperature, and the interstellar dust extinction along the line of sight to hundreds of stars per square arcminute. The yield is twofold. On the one hand, the resulting reddening map has a very high spatial resolution, of the order of a few arcseconds, and can be quite effectively used in regions where the interstellar material is patchy, thus producing considerable differential extinction on small angular scales. On the other hand, combining the photometric information over a wide baseline in wavelength provides an accurate determination of temperature and luminosity for thousands of stars. As a test case, we present the results for the region around Supernova 1987A in the Large Magellanic Cloud imaged with the WFPC2 on board the Hubble Space Telescope.

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arXiv2001

TTauri Stars in the Large Magellanic Cloud: a combined HST and VLT effort

The combination of the unprecedented spatial resolution attainable with WFPC2 on board HST and of the large collecting area of the VLT makes it possible to study in detail the low mass pre-Main Sequence stars in galaxies other than our own. Here we present the results of our studies of two star forming environments in our closest galactic neighbor, the Large Magellanic Cloud: the region around Supernova 1987A and the double cluster NGC 1850.

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arXiv2000

Young Stellar Populations Around SN1987A

We present the results of a study of the stellar population in a region of 30 pc radius around SN1987A, based on an analysis of multi-band HST-WFPC2 images. The effective temperature, radius and, possibly, reddening of each star were determined for 21,955 stars by fitting the measured broad band magnitudes to the ones calculated with model atmospheres. In addition, we have identified all stars with Halpha equivalent widths in excess of 8 A, amounting to a total of 492 stars. An inspection to the HR diagram reveals the presence of several generations of young stars, with ages between 1 and 150 Myrs, superposed on a much older field population (0.6-6 Gyrs). A substantial fraction of young stars have ages around 12 Myrs which is the stellar generation coeval to SN 1987A progenitor. The youngest stars in the field appear to be strong-line T Tauri stars. This constitute the first positive detection of low mass (about 1-2 Mo) Pre Main Sequence (PMS) stars outside the Milky Way. Their positions in the HR diagram appear to require that star formation in the LMC occurs with accretion rates about 10 times higher than in the Milky Way, i.e. ~10^{-4} Mo/yr. SN1987A appears to belong to a loose, young cluster 12+/-2 Myrs old, in which the slope of the present mass function is almost identical to Salpeter's for masses above 3 Mo, but becomes much flatter for lower masses. On a large scale, we find that the spatial distribution of massive stars and low-mass PMS stars are conclusively different. This results casts doubts on the validity of an IMF concept on a small scale (say, less than 10 pc). A preliminary analysis, done for the whole field as a single entity, shows that the IMF slope for the young population present over the entire region is steeper than Gamma ~ -1.7.

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arXiv1999

HST study of the Stellar Populations within 30 pc of SN 1987A

We have studied the stellar populations in a region of 30 pc around SN 1987A in the Large Magellanic Cloud using multi-band HST-WFPC2 images. The effective temperature, luminosity and reddening of each detected star were determined by fitting the measured broad band magnitudes to the ones calculated with model atmospheres. The resulting HR diagram reveals the presence of stars with ages between 1 and 150 Myrs, superposed on a much older field population. The youngest stars in the field appear to be T Tauri stars, characterized by strong Halpha excesses. The Star Formation Rate has increased monotonically in the last 8 Gyrs and the star formation activity is still very high at present. Young stars of low and high mass have different spatial distributions. The latter ones are strongly concentrated in the vicinities of the Supernova, whereas the previous ones are more evenly distributed on the field. Hence, the Mass Function varies on a scale of a few parsecs. However, averaging over the entire area, one can define an Initial Mass Function, well fitted by a power-law with a slope alpha<-2.55. The uncertainty on the IMF due to incompleteness in identifying T Tauri stars is discussed.

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