Papers by Mariagrazia Franchini
Chemical and Dynamical Evolution of Galaxies, 2018
Astronomy and Astrophysics
We have again had sporadic e-mail problems, but hope that things are once more under control. A f... more We have again had sporadic e-mail problems, but hope that things are once more under control. A few readers have informed me that they did not receive the last issue. When I mail to the about 350 addressees which by now get the newsletter, there are always about 10 to 15 that bounce back. For these addresses I wait another week or 10 days and then I send the newsletter once more. Sometimes a few of these bounce again, and in that case I do not make any further attempts unless I receive a request. If you are missing an issue just let me know and I will send you a copy. Please inform me if your e-mail address changes, that will save a lot of time for everybody concerned. The special issue with Ph.D. thesis abstracts advertised last month is almost ready and will be mailed later this month.
The star P Cygni was discovered on August 18, 1600 AD when it brightened to about the third magni... more The star P Cygni was discovered on August 18, 1600 AD when it brightened to about the third magnitude. Several attempts to get informations on size, chemical composition and density distribution of the material around the star have been already done (see for example Leitherer and Zickgraf (1987). Barlow et al. (1994) got [Ni II] narrow band images which show a nearly circular nebula with angular diameter of about 22 arcsec and hint at the presence of nebular rings at circa 6 and 11 arcsec. On the other hand, White and Becker (1982) obtained observations which are consistent with a homogeneous, spherically symmetric, constant velocity, isothermal flow. Our aim was to analyse the circumstellar regions very close to the star (<6 arcsec) to look for material ejected in the outburst of 1600 AD taking advantage of the use of both adaptive optics and coronography. We have obtained direct CCD images with the Compensated Image System (CIS) installed on the 1.6 m telescope of Air Force Mau...
ESO ASTROPHYSICS SYMPOSIA
Differences in the chemical composition of galactic stars with similar [Fe/H], in particular in t... more Differences in the chemical composition of galactic stars with similar [Fe/H], in particular in the range -1.0 to +0.50 dex, are attributed to the presence of different stellar components in the Galaxy, in general, and in the Galactic disk, in particular (e.g. Norris, 1999). Detailed high resolution (HR) analysis is the most appropriate approach to determine individual element abundances of individual stars. This kind of approach, when not feasible, may be substituted by the study of selected low resolution absorption features. In Franchini et al. (2004a) we introduced four combinations of Lick/IDS indices, namely NaD vs Ca4227, NaD vs Mg2, NaD vs Mgb, and NaD vs CaMg, to identify Solar Scaled Abundance (SSA) and alpha-enhanced (Non Solar Scaled Abundance, NSSA) stars without previous knowledge of atmospheric parameter values. Our method was applied in Franchini et al. (2004b) to 402 stars with accurate estimates of [Fe/H]. In this paper we extend the analysis to a larger number of stars to better investigate the metallicity and kinematical properties of NSSA and SSA stars.
To fully exploit the potentialities of new generation telescopes focal plane instruments of ever ... more To fully exploit the potentialities of new generation telescopes focal plane instruments of ever increasing complexity are conceived. From the point of view of the observer the drawback of such technical development consists in the longer training needed to become familiar with the setup procedures when preparing an observing session, especially in the choice of the optimal instrumental parameters. The
Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites
The aim of this paper is to re-analyze the stars studied by AP04 with a technique which discrimin... more The aim of this paper is to re-analyze the stars studied by AP04 with a technique which discriminates α-enhanced (Non Solar Scaled Abundance, NSSA) stars from those with Solar Scaled Abundances (SSA) without requiring any assumption about the stellar atmospheric parameter values.
… HR Diagrams and …, 2002
... 20W2 Thibault Lejeune and Jodo Fernandes, eds. Stellar Surface Gravity Determinations from Sp... more ... 20W2 Thibault Lejeune and Jodo Fernandes, eds. Stellar Surface Gravity Determinations from Spectral Energy Distribution, Photometry and Evolutionary Tracks Carlo Morossi INAF Osservatorio Astronomico di Trieste, via GB Tiepolo 11, 1-34131 Trieste, Italy Miguel Chavez ...
We present a new collection of synthetic spectra finalized at the derivation of information about... more We present a new collection of synthetic spectra finalized at the derivation of information about the enhancement of alpha-process elements in the atmospheres of F-GK stars. The spectra are computed at high resolution from fully consistent models and Opacity Distribution Functions (ODFs) for [alpha/Fe]= +0.0 and +0.4. Comparisons with observed spectra at R ≈ 2000 from the STELIB library are illustrated. Synthetic photometry in the Gaia photometric system, once the filter characteristics will be definitively assessed, could be computed and analyzed for disentangling alpha-enhanced stars from solar scaled chemical abundance ones.
The Astrophysical Journal, 2010
A new synthetic library of spectral feature indices, Lick/Sloan Digital Sky Survey (SDSS), for st... more A new synthetic library of spectral feature indices, Lick/Sloan Digital Sky Survey (SDSS), for stellar population studies is presented. Lick/SDSS is computed from synthetic spectra with resolving power R = 1800 to fully exploit the content of the spectroscopic SDSS-DR7 stellar database. The Lick/SDSS system is based on the Lick/IDS one complemented with a UV index in the wavelength region of Ca II H and K lines. The system is well suited to study alpha-element abundances in F, G, and K stars. The reliability of synthetic indices in reproducing the behaviors of observational ones with effective temperature, surface gravity, overall metallicity, and alpha-element abundances is tested by using empirical stellar libraries (ELODIE, INDO-U.S., and MILES) and the SDSS-DR7 spectroscopic database. The importance of using the same temperature scale in comparing theoretical and observational indices is discussed. The full consistency between Lick/SDSS and observational indices derived from the above mentioned stellar libraries is assessed. The comparison with indices computed from SDSS-DR7 spectra evidences good consistency for "dwarf" stars and significant disagreement for "giant" stars due to systematic overestimation of the stellar T eff by the SEGUE Stellar Parameter Pipeline.
The Astrophysical Journal, 2011
We analyzed the spectra of 17,600 F, G, and K stars extracted from the seventh Sloan Digital Sky ... more We analyzed the spectra of 17,600 F, G, and K stars extracted from the seventh Sloan Digital Sky Survey Data Release (SDSS-DR7) database in order to derive lang[alpha/Fe]rang, [Ca/Fe], and [Mg/Fe] ratios. Particular attention has been devoted to estimating homogeneous and self-consistent atmospheric parameter values, T eff, log g, and [Fe/H], by comparing synthetic and observational Lick/SDSS indices. We present
Astronomy and Astrophysics
An 'automatic' curved-of-growth technique is used to derive the excitation temperature, m... more An 'automatic' curved-of-growth technique is used to derive the excitation temperature, microturbulent velocity and Fe I column density of the T Tauri star Sz 19 (G2 V). The observations were performed at the 3.6 m telescope of the European Southern Observatory with the spectrograph CASPEC in the spectral range 5690 - 6730 A. Also obtained is the spectrum of the MK star HD 70854 (G2 V) which is used as a spectral type standard.
arXiv (Cornell University), Dec 24, 2022
The remaining affiliations can be found at the end of the paper.
Software and Cyberinfrastructure for Astronomy VII
CUBES (Cassegrain U-Band Efficient Spectrograph) is the recently approved high-efficiency VLT spe... more CUBES (Cassegrain U-Band Efficient Spectrograph) is the recently approved high-efficiency VLT spectrograph aimed to observe the sky in the UV ground-based region (305-400 nm) with a high-resolution mode (∼ 20K) and a low-resolution mode (∼ 5K). In this paper we will briefly describe the requirements and the design of the several software packages involved in the project, namely the instrument control software, the exposure time calculator, the end-to-end simulator, and the data reduction software suite. We will discuss how the above mentioned blocks cooperate to build up a "software ecosystem" for the CUBES instrument, and to support the users from the proposal preparation to the science-grade data products.
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Papers by Mariagrazia Franchini