arXiv subjects

S. Gaudenzi

Publications and source records attributed to S. Gaudenzi.

7 recordsLinked to original sources

arXiv2025

GOTO065054+593624: a 8.5 mag amplitude dwarf nova identified in real time via Kilonova Seekers

Dwarf novae are astrophysical laboratories for probing the nature of accretion, binary mass transfer, and binary evolution -- yet their diverse observational characteristics continue to challenge our theoretical understanding. We here present the discovery of, and subsequent observing campaign on GOTO065054+593624 (hereafter GOTO0650), a dwarf nova of the WZ Sge type, discovered in real-time by citizen scientists via the Kilonova Seekers citizen science project, which has an outburst amplitude of 8.5 mag. An extensive dataset charts the photometric and spectroscopic evolution of this object, covering the 2024 superoutburst. GOTO0650 shows an absence of visible emission lines during the high state, strong H and barely-detected HeII emission, and high-amplitude echo outbursts with a rapidly decreasing timescale. The comprehensive dataset presented here marks GOTO0650 as a candidate period bouncer, and highlights the important contribution that citizen scientists can make to the study of Galactic transients.

astro-ph.SR↗

arXiv2017

Infrared characteristics of the BIS catalog objects

We have studied several color-color infrared diagrams of the 276 late type stars of the BIS catalog. For 95 of these stars we derived spectral classification from our slit spectroscopy. From the 2MASS color diagram we derive that none of the sample stars is a dwarf. The WISE 3.4-12 vs 12-22 plot is the best to discriminate the variability type (Mira, irregular and not-variable), as well as Carbon stars: IRAS colors are less useful due to the poor quality of the data for most of the BIS stars. Mixed plots involving 2MASS, AKARI and WISE were also explored: the 2MASS-AKARI J-[S09] vs [S09]-[L18] plot is efficient to discriminate Carbon and Mira stars. From the color plots and our spectroscopy we can statistically predict that in whole BIS catalog no other dusty Carbon star is present, while a few Miras and CH or R Carbon stars could be discovered. Only about 15 percent of the BIS stars are of early M type.

astro-ph.SR↗

arXiv2017

Spectral Properties and Variability of BIS objects

Through the analysis and interpretation of newly obtained and of literature data we have clarified the nature of poorly investigated IRAS point sources classified as late type stars, belonging to the Byurakan IRAS ~Stars catalog. From medium resolution spectroscopyof 95 stars we have strongly revised 47 spectral types and newly classified 31 sources. Nine stars are of G or K types, four are N carbon stars in the Asymptotic Giant Branch, the others being M type stars. From literature and new photometric observations we have studied their variability behaviour. For the regular variables we determined distances, absolute magnitudes and mass loss rates. For the other stars we estimated the distances, ranging between 1.3 and 10~kpc with a median of 2.8~kpc from the galactic plane, indicating that BIS stars mostly belong to the halo population.

astro-ph.SR↗

arXiv2014

The role of magnetic field for quiescence-outburst models in CVs

In this paper we present the elementary assumptions of our research on the role of the magnetic field in modelling the quiescence-outbursts cycle in Cataclysmic Variables (CVs). The behaviour of the magnetic field is crucial not only to integrate the disk instability model (Osaki 1974), but also to determine the cause and effect nexus among parameters affecting the behavior of complex systems. On the ground of our interpretation of the results emerging from the literature, we suggest that in models describing DNe outbursts, such as the disk instability model, the secondary instability model (Bath 1973) and the thermonuclear runaway model (Mitrofanov 1978), the role of the magnetic field is at least twofold. On the one hand, it activates a specific dynamic pathway for the accreting matter by channelling it. On the other hand, it could be indirectly responsible for switching a particular outburst modality. In order to represent these two roles of the magnetic field, we need to integrate the disk instability model by looking at the global behaviour of the system under analysis. Stochastic resonance in dynamo models, we believe, is a suitable candidate for accomplishing this task. We shall present the MHD model including this mechanism elsewhere.

astro-ph.HE↗

arXiv2012

New Bright Carbon Stars Found In The DFBS. (Research note, submitted to Astrophysics)

Carbon rich stars of Population II, such as CH giants, can provide direct information on the role of low to intermediate mass stars of the Halo in early Galactic evolution. Moreover, accurate knowledge of the CH stellar population is a critical requirement for building up scenarios for early Galactic chemical evolution. The first list of the faint high latitude C stars (FHLCs), found in the Digitized First Byurakan Survey {http://byurakan.phys.uniroma1.it and http://www.aras.am/Dfbs/dfbs.html} (DFBS) is given in a paper recently submitted for publication in Astronomy ad Astrophysics. In the present work, we report the recent discovery of two additional CH type stars (not previously catalogued), namely DFBS J075331.98+190344.3 and DFBS J111422.94+091442.7, detected on the DFBS plates with help of the image analysis softwares (FITSView and SAOImage DS9). Medium resolution spectra confirm the C rich nature for both of them. Using infrared color magnitudes relationship, we estimated the distances and K band absolute magnitudes of the new objects.

astro-ph.SR↗

arXiv2010

UVB radiation induced effects on cells studied by FTIR spectroscopy

We have made a preliminary analysis of the results about the eVects on tumoral cell line (lymphoid T cell line Jurkat) induced by UVB radiation (dose of 310 mJ/cm^2) with and without a vegetable mixture. In the present study, we have used two techniques: Fourier transform infrared spectroscopy (FTIR) and flow cytometry. FTIR spectroscopy has the potential to provide the identiWcation of the vibrational modes of some of the major compounds (lipid, proteins and nucleic acids) without being invasive in the biomaterials. The second technique has allowed us to perform measurements of cytotoxicity and to assess the percentage of apoptosis. We already studied the induction of apoptotic process in the same cell line by UVB radiation; in particular, we looked for correspondences and correlations between FTIR spetroscopy and flow cytometry data finding three highly probable spectroscopic markers of apoptosis (Pozzi et al. in Radiat Res 168:698-705, 2007). In the present work, the results have shown significant changes in the absorbance and spectral pattern in the wavenumber protein and nucleic acids regions after the treatments.

physics.bio-ph↗

arXiv2006

Optical variability of the strong-lined and X-ray bright source 1WGA J0447.9-0322

We present the historic light curve of 1WGA J0447.9-0322, spanning the time interval from 1962 to 1991, built using the Asiago archive plates. The source shows small fluctuations of about 0.3 mag around B=16 until 1986 and a fast dimming of its average level by about 0.5 mag after that date, again with small short term variations. The variability pattern is within the values shown by other QSOs with long term monitoring, notwithstanding its high X-ray/optical ratio. We present also its overall SED using literature data and recent UV-optical SWIFT observations.

astro-ph↗