Browsing by Department "O.A. Capodimonte"

We have started a search for supernovae as a collaboration between the University of Chile and the Cerro Tololo Inter-American Observatory, with the aim of producing a moderately distant (0.01 < z <0.10) sample of Type Ia and Type II supernovae suitable for cosmological studies. The project began in mid-1990 and continues to the present. This paper reports on the Calan/Tololo discoveries in the course of 1990, and on the spectroscopic and photometric observations gathered for these objects. All of these observations were obtained with CCDs, with the extensive collaboration of visiting astronomers. Great care was exercised in the reduction of the light curves in order to properly correct for the background light of the host galaxy of each supernova. Of the four supernovae found in 1990, one proved to be a SN II-n; the remaining three were members of the Type Ia class at redshifts that ranged between z = 0.04-0.05. One of the Type Ia events, SN 1990af, was found in the elusive premaximum phase at a redshift of z = 0.0503, and was observed through maximum light. Peak magnitudes for the other two SNe Ia, which were not observed at maximum light, were derived using a χ^2^ minimization technique to fit the data with various template curves that represent a broad range of SNe Ia light curves. In future papers we will make use of these estimates in order to discuss the Hubble diagram of SNe Ia.

On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ∼-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (∼25 m s^-1) while 100 μm radius particles were detected by the GIADA dust instrument ∼1 h later at a speed of 6 m s^-1. The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.

Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this Letter we report the discovery of a wide (projected separation ∼16.0", or 2400 AU, and position angle 114.61°) companion of the GQ Lup A-B system, most likely gravitationally bound to it. A VLT/X-shooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass (∼0.15 M_⊙) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQ Lup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0.7", formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQ Lup A and 2MASS J15491331-3539118.

Based on observations collected at the European Southern Observatory at Paranal, under program 103.C-0200(A), and archive data from 074.C-0037(A) and 082.C-0390(A).

The hard X-ray source 2PBC J0658.0-1746 was proposed as an eclipsing magnetic cataclysmic variable of the polar type, based on optical follow-ups. We present the first spectral and timing analysis at X-ray energies with XMM-Newton, complemented with archival X-ray, optical, infrared (IR) photometry, and spectroscopy. The X-ray emission shows bright and faint phases and total eclipses recurring every 2.38 h, consistent with optical properties. This firmly identifies 2PBC J0658.0-1746 as an eclipsing polar, the second hard X-ray selected in the orbital period gap. The X-ray orbital modulation changes from cycle-to-cycle and the X-ray flux is strongly variable over the years, implying a non-stationary mass accretion rate both on short and long time-scales. The X-ray eclipses allow to refine the orbital ephemeris with period 0.09913398(4) d, and to constrain the binary inclination 79^{circ}≲ i ≲ 90^{circ} and the mass ratio 0.18< M_2/M_{ WD}< 0.40. A companion mass M₂=0.2-0.25 M_{\odot } with a radius R₂=0.24-0.26 R_{\odot } and spectral type ∼M4, at D=209^{+3}_{-2} pc, is derived. A lower limit to the white dwarf mass of ∼ 0.6 M_{\odot } is obtained from the X-ray spectrum. An upper limit to the magnetic colatitude, β ≲ 50^{circ}, and a shift in azimuth, ψ ∼ 14^{circ}, of the main accreting pole are also estimated. The optical/IR spectral energy distribution shows large excess in the mid-IR due to lower harmonics of cyclotron emission. A high-state mass accretion rate ∼ 0.4-1× 10^{-10} M_{\odot } yr^{-1}, lower than that of cataclysmic variables above the gap and close to that of systems below it, is estimated. With 2PBC J0658.0-1746, the number of hard X-ray-selected polars increases to 13 members, suggesting that they are not as rare as previously believed.

We present the results from a 500 ks Chandra observation of the z = 6.31 QSO SDSS J1030 + 0524. This is the deepest X-ray observation to date of a z 6 QSO. The QSO is detected with a total of 125 net counts in the full (0.500A0-7 keV) band and its spectrum can be modeled by a single power-law model with photon index of Γ = 1.81 ± 0.18 and full band flux of f = 3.95 × 10^-15 erg s^-1 cm^-2. When compared with the data obtained by XMM-Newton in 2003, our Chandra observation in 2017 shows a harder (∆Γ ≈ -0.6) spectrum and a 2.5 times fainter flux. Such a variation, in a timespan of 2 yr rest-frame, is unexpected for such a luminous QSO powered by a > 10⁹M_☉ black hole. The observed source hardening and weakening could be related to an intrinsic variation in the accretion rate. However, the limited photon statistics does not allow us to discriminate between an intrinsic luminosity and spectral change, and an absorption event produced by an intervening gas cloud along the line of sight. We also report the discovery of diffuse X-ray emission that extends for 30″ × 20″ southward of the QSO with a signal-to-noise ratio (S/N) of approximately six, hardness ratio of HR = 0.03^+0.20_-0.25, and soft band flux of f_{0.5- keV} = 1.1^+0.3_-0.3 × 10^-15 erg s^-1 cm^-2 , that is not associated to a group or cluster of galaxies. We discuss two possible explanations for the extended emission, which may be either associated with the radio lobe of a nearby, foreground radio galaxy (at z ≈ 1 - 2), or ascribed to the feedback from the QSO itself acting on its surrounding environment, as proposed by simulations of early black hole formation.

GIADA (Grain Impact Analyzer and Dust Accumulator) on-board the Rosetta space probe is designed to measure the momentum, mass and speed of individual dust particles escaping the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P). From 2014 August to 2016 June, Rosetta escorted comet 67P during its journey around the Sun. Here, we focus on GIADA data taken between 2015 January and 2016 February which included 67P's perihelion passage. To better understand cometary activity and more specifically the presence of dust structures in cometary comae, we mapped the spatial distribution of dust density in 67P's coma. In this manner, we could track the evolution of high-density regions of coma dust and their connections with nucleus illumination conditions, namely tracking 67P's seasons. We also studied the link between dust particle speeds and their masses with respect to heliocentric distance, I.e. the level of cometary activity. This allowed us to derive a global and a local correlation of the dust particles' speed distribution with respect to the H₂O production rate.

We characterized 67P/Churyumov-Gerasimenko's cometary activity during its inbound arc before perihelion (2014 August-2015 January). We focused on the geomorphological regions of the Northern hemisphere observed by the ESA/Rosetta space probe during this time period. The GIADA dust detector characterized the physical properties of the fluffy and compact particles ejected from the nucleus; the VIRTIS imaging spectrometer detected exposed water ice.

Aims: We present the X-ray imaging and spectral analysis of the diffuse emission around the radio galaxy J1140-2629 (the Spiderweb galaxy) at z = 2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation.
Methods: We obtained a robust characterization of the unresolved nuclear emission, and carefully computed the contamination in the surrounding regions due to the wings of the instrument point spread function. Then, we quantified the extended emission within a radius of 12 arcsec. We used the Jansky Very Large Array radio image to identify the regions overlapping the jets, and performed X-ray spectral analysis separately in the jet regions and in the complementary area.
Results: We find that the Spiderweb galaxy hosts a mildly absorbed quasar, showing a modest yet significant spectral and flux variability on a timescale of ∼1 year (observed frame). We find that the emission in the jet regions is well described by a power law with a spectral index of Γ ∼ 2 − 2.5, and it is consistent with inverse-Compton upscattering of the cosmic microwave background photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ∼100 kpc centered on the Spiderweb galaxy. This emission, which is not associated with the jets, is significantly softer and consistent with thermal bremsstrahlung from a hot intracluster medium (ICM) with a temperature of kT = 2.0_−0.4^+0.7 keV, and a metallicity of Z < 1.6 Z_⊙ at 1σ c.l. The average electron density within 100 kpc is n_e = (1.51 ± 0.24 ± 0.14) × 10⁻² cm⁻³, corresponding to an upper limit for the total ICM mass of ≤(1.76 ± 0.30 ± 0.17) × 10¹² M_⊙ (where error bars are 1σ statistical and systematic, respectively). The rest-frame luminosity L_{0.5 − 10 keV} = (2.0 ± 0.5) × 10⁴⁴ erg s⁻¹ is about a factor of 2 higher than the extrapolated L − T relation for massive clusters, but still consistent within the scatter. If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc) = (1.5_−0.3^+0.5) × 10¹³ M_⊙ and, extrapolating at larger radii, we estimate a total mass M₅₀₀ = (3.2_−0.6^+1.1) × 10¹³ M_⊙ within a radius of r₅₀₀ = (220 ± 30) kpc.
Conclusions: We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by inverse-Compton scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ∼100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster.

We report the search for 7Be isotope in the outbursts of the classical nova V6595 Sgr by means of high resolution UVES observations taken at the ESO VLT in April 2021, about two weeks after discovery and under difficult circumstances due to the pandemic. Narrow absorption components with velocities at about -2620 and -2820 km/s, superposed on broader and shallow absorption, are observed in the outburst spectra for the 7BeII 313.0583, 313.1228 nm doublet resonance lines, as well as in several other elements such as CaII, FeI, MgI, NaI, HI but LiI. Using CaII K line as a reference element, we infer N(7Be)/N(H) ~ 7.4 x 10^{-6}, or ~ 9.8 x 10^{-6} when the 7Be decay is taken into account. The 7Be abundance is about half of the value most frequently measured in novae. The possible presence of over-ionization in the layers where 7Be is detected is also discussed. Observations taken at the Telescopio Nazionale Galileo (TNG) in La Palma 91 days after discovery showed prominent emission lines of Oxygen and Neon which allow to classify the nova as ONe type. Therefore, although 7Be is expected to be higher in CO novae, it is found at comparable levels in both nova types.

Multimessenger astronomy received a great boost following the discovery of kilonova (KN) AT2017gfo, the optical counterpart of the gravitational wave source GW170817 associated with the short gamma-ray burst GRB 170817A. AT2017gfo was the first KN that could be extensively monitored in time using both photometry and spectroscopy. Previously, only few candidates have been observed against the glare of short GRB afterglows. In this work, we aim to search the fingerprints of AT2017gfo-like KN emissions in the optical/NIR light curves of 39 short GRBs with known redshift. For the first time, our results allow us to study separately the range of luminosity of the blue and red components of AT2017gfo-like kilonovae in short GRBs. In particular, the red component is similar in luminosity to AT2017gfo, while the blue KN can be more than 10 times brighter. Finally, we exclude a KN as luminous as AT2017gfo in GRBs 050509B and 061201.

Photometric redshifts (photo-z) are fundamental in galaxy surveys to address different topics, from gravitational lensing and dark matter distribution to galaxy evolution. The Kilo Degree Survey (KiDS), I.e. the European Southern Observatory (ESO) public survey on the VLT Survey Telescope (VST), provides the unprecedented opportunity to exploit a large galaxy data set with an exceptional image quality and depth in the optical wavebands. Using a KiDS subset of about 25000 galaxies with measured spectroscopic redshifts, we have derived photo-z using (I) three different empirical methods based on supervised machine learning; (II) the Bayesian photometric redshift model (or BPZ); and (III) a classical spectral energy distribution (SED) template fitting procedure (LE PHARE). We confirm that, in the regions of the photometric parameter space properly sampled by the spectroscopic templates, machine learning methods provide better redshift estimates, with a lower scatter and a smaller fraction of outliers. SED fitting techniques, however, provide useful information on the galaxy spectral type, which can be effectively used to constrain systematic errors and to better characterize potential catastrophic outliers. Such classification is then used to specialize the training of regression machine learning models, by demonstrating that a hybrid approach, involving SED fitting and machine learning in a single collaborative framework, can be effectively used to improve the accuracy of photo-z estimates.

The coming decades will establish the exploration of the gravitational wave (GW) Universe over a broad frequency range by ground and space interferometers. Meanwhile, wide-field, high-cadence and sensitive surveys will span the electromagnetic spectrum from radio all the way up to TeV, as well as the high-energy neutrino window. Among the numerous classes of transients, γ-ray bursts (GRBs) have direct links with most of the hot topics that will be addressed, such as the strong gravity regime, relativistic shocks, particle acceleration processes, equation of state of matter at nuclear density, and nucleosynthesis of heavy elements, just to mention a few. Other recently discovered classes of transients that are observed throughout cosmological distances include fast radio bursts (FRBs), fast blue optical transients (FBOTs), and other unidentified high-energy transients. Here we discuss how these topics can be addressed by a mission called ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics, see Frontera et al. 18). Its payload combines two instruments: (i) an array of wide-field monitors with imaging, spectroscopic, and polarimetric capabilities (WFM-IS); (ii) a narrow field telescope (NFT) based on a Laue lens operating in the 50-600 keV range with unprecedented angular resolution, polarimetric capabilities, and sensitivity.

The classical T Tauri star (CTTS) stage is a critical phase of the star and planet formation process. In an effort to better understand the mass accretion processes, which can dictate future stellar evolution and planet formation, a multiepoch, multiwavelength photometric and spectroscopic monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was carried out in 2021 and 2022/2023 as part of the Outflows and Disks around Young Stars: Synergies for the Exploration of ULLYSES Spectra program. Here we focus on the Hubble Space Telescope (HST) UV spectra obtained by the HST Director's Discretionary Time UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program. Using accretion shock modeling, we find that all targets exhibit accretion variability, varying from short increases in accretion rate by up to a factor of 3 within 48 hr to longer decreases in accretion rate by a factor of 2.5 over the course of 1 yr. This is despite the generally consistent accretion morphology within each target. Additionally, we test empirical relationships between accretion rate and UV luminosity and find stark differences, showing that these relationships should not be used to estimate the accretion rate for an individual target. Our work reinforces that future multiepoch and simultaneous multiwavelength studies are critical in our understanding of the accretion process in low-mass star formation.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

We present the discovery of the radio afterglow of the short gamma-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of z ∼ 2.4. While radio observations commenced ≲1 day after the burst, no radio emission was detected until ∼11 days. The radio afterglow subsequently brightened by a factor of ∼3 in the span of a week, followed by a rapid decay (a "radio flare"). We find that a forward shock afterglow model cannot self-consistently describe the multiwavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of ≈5. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of ≈4, or a reverse shock from a shell collision are viable solutions to match the broadband behavior. At z ∼ 2.4, GRB 210726A is among the highest-redshift short GRBs discovered to date, as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by ≲10 days after the burst, potentially missing these late-rising, luminous radio afterglows.

The road to increasingly more challenging and bigger systems in astronomy is resulting in as much bigger challenges to the safety for people and things. As well for the ELT (Extremely Large Telescope) instrumentation and modules, these big "systems" collaborate and share the same environment and spaces, and, as for the AO module MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations) and the MICADO camera (Multi-AO Imaging Camera for Deep Observations), some subsystems are strongly embedded, even if they are designed by different consortia. Therefore, the designers are thinking to even more sophisticated systems to assure the safety and communication of information between the different instruments. In this context, the MORFEO consortium is investigating on the possibility to use industrial safety modules, architecturally integrated in the overall control system. This approach can highly help in the fulfilling of even more complex requirements with the high flexibility required to grant the possibility, during the telescope life, of one or more upgrading of the instrumentation and their way to co-operate. The paper goes through a comparison between the in-house designed safety solution, widely used in the past, and the industrial safety systems and the implementation of these technologies in the ground-based astronomy.

The road to increasingly more challenging and bigger systems in astronomy is resulting in as much bigger challenges to the safety for people and things. As well for the ELT (Extremely Large Telescope) instrumentation and modules, these big "systems" collaborate and share the same environment and spaces, and, as for the AO module MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations) and the MICADO camera (Multi-AO Imaging Camera for Deep Observations), some subsystems are strongly embedded, even if they are designed by different consortia. Therefore, the designers are thinking to even more sophisticated systems to assure the safety and communication of information between the different instruments. In this context, the MORFEO consortium is investigating on the possibility to use industrial safety modules, architecturally integrated in the overall control system. This approach can highly help in the fulfilling of even more complex requirements with the high flexibility required to grant the possibility, during the telescope life, of one or more upgrading of the instrumentation and their way to co-operate. The paper goes through a comparison between the in-house designed safety solution, widely used in the past, and the industrial safety systems and the implementation of these technologies in the ground-based astronomy.

The road to increasingly more challenging and bigger systems in astronomy is resulting in as much bigger challenges to the safety for people and things. As well for the ELT (Extremely Large Telescope) instrumentation and modules, these big "systems" collaborate and share the same environment and spaces, and, as for the AO module MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations) and the MICADO camera (Multi-AO Imaging Camera for Deep Observations), some subsystems are strongly embedded, even if they are designed by different consortia. Therefore, the designers are thinking to even more sophisticated systems to assure the safety and communication of information between the different instruments. In this context, the MORFEO consortium is investigating on the possibility to use industrial safety modules, architecturally integrated in the overall control system. This approach can highly help in the fulfilling of even more complex requirements with the high flexibility required to grant the possibility, during the telescope life, of one or more upgrading of the instrumentation and their way to co-operate. The paper goes through a comparison between the in-house designed safety solution, widely used in the past, and the industrial safety systems and the implementation of these technologies in the ground-based astronomy.