OA@INAF - Istituto Nazionale di Astrofisica
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Study of solar brightness profiles in the 18-26 GHz frequency range with INAF radio telescopes. II. Evidence of coronal emission
No full textContext. One of the most important objectives of solar physics is to gain a physical understanding of the solar atmosphere, whose structure can also be described in terms of the density (N) and temperature (T) distributions of the atmospheric matter. Several multi-frequency analyses have shown that the characteristics of these distributions are still under debate, especially for outer coronal emission.
Aims: We aim to constrain the T and N distributions of the solar atmosphere through observations in the centimetric radio domain. We employed single-dish observations from two of the INAF radio telescopes at the K-band frequencies (18-26 GHz). We investigated the origin of the significant brightness temperature (T_B) detected up to the upper corona (at an altitude of ∼800 Mm with respect to the photospheric solar surface).
Methods: To probe the physical origin of the atmospheric emission and to constrain instrumental biases, we reproduced the solar signal by convolving specific 2D antenna beam models. We performed an analysis of the solar atmosphere by adopting a physical model that assumes the thermal bremsstrahlung as the emission mechanism, with specific T and N distributions. We compared the modelled T_B profiles with those observed by averaging solar maps obtained at 18.3 and 25.8 GHz during the minimum of solar activity (2018-2020).
Results: We probed any possible discrepancies between the T and N distributions assumed from the model and those derived from our measurements. The T and N distributions are compatible (within a 25% of uncertainty) with the model up to ∼60 Mm and ∼100 Mm in altitude, respectively.
Conclusions: Our analysis of the role of the antenna beam pattern on our solar maps proves the physical nature of the atmospheric emission in our images up to the coronal tails seen in our T_B profiles. Our results suggest that the modelled T and N distributions are in good agreement (within 25% of uncertainty) with our solar maps up to altitudes of ≲100 Mm. A subsequent, more challenging analysis of the coronal radio emission at higher altitudes, together with the data from satellite instruments, will require further multi-frequency measurements
Performance evaluation of pansharpening for planetary exploration: A case study on the implementation of TGO CaSSIS with MRO HiRISE
No full textThe present study analyses the potential of pansharpening algorithms for planetary exploration studies, testing their performance with the 4-band images from the Colour and Stereo Surface Imaging System (CaSSIS) aboard the Exomars 2016 Trace Grace Orbiter (TGO) using HiRISE images from the Mars Reconnaissance Orbiter (MRO) mission as the base. Due to the lack of suitable open-source tools, a suite of scripts was developed to improve alignment between images and enable different component substitution (CS) pansharpening algorithms. The tools developed were tested on a database of images encompassing several regions of Mars to explore its vast diversity in colours, tones, and textures. Then, the resulting images were investigated using spectral and structural performance indices, comparing the results with the source images and the colour information from the HiRISE central channels. The results show that a substantial number of the tested algorithms are more than suitable for data enhancement, showing a considerable improvement in the structural characteristics of the images without sacrificing their spectral characteristics. In detail, the Gram-Schmidt method, widely used in terrestrial pansharpening, turns out to be the best compromise among the tested algorithms. Regarding the other tested algorithms, GIHS and the MMSE Brovey, a modified version of the classic Brovey, show the most significant increase in structural properties, while GHPF and GHPM show the interesting ability to maintain virtually unchanged spectral conditions of the multispectral source data. In addition, the analysis reveals the applicability of pansharpening at a ground resolution increment up to 18 times, from 4.5 up to 0.25 m/px, a broader range than is usually used in traditional pansharpening
Investigating Protostellar Accretion-driven Outflows across the Mass Spectrum: JWST NIRSpec Integral Field Unit 3–5 μm Spectral Mapping of Five Young Protostars
No full textInvestigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9–28 μm spectral cubes of five young protostars with luminosities of 0.2–10,000 L ⊙ in their primary accretion phase. This paper introduces the NIRSpec 2.9–5.3 μm data of the inner 840–9000 au with spatial resolutions from 28 to 300 au. The spectra show rising continuum emission; deep ice absorption; emission from H2, H I, and [Fe II]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe II] for the four ⊙ protostars, two of which are additionally traced in Brα. Knots of [Fe II] emission are detected toward the most luminous protostar, and knots of [Fe II] emission with dynamical times of 2, knots of H2 and CO are detected in the jets of four protostars. H2 is seen extending through the cavities, showing that they are filled by warm molecular gas. Bright H2 emission is seen along the walls of a single cavity, while in three cavities narrow shells of H2 emission are found, one of which has an [Fe II] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets
MINDS: Mid-infrared atomic and molecular hydrogen lines in the inner disk around a low-mass star
No full textContext. Understanding the physical conditions of circumstellar material around young stars is crucial to star and planet formation studies. In particular, very low-mass stars (M < 0.2 M) are interesting sources to characterize as they are known to host a diverse population of rocky planets. Molecular and atomic hydrogen lines can probe the properties of the circumstellar gas. Aims. This work aims to measure the mass accretion rate, the accretion luminosity, and more generally the physical conditions of the warm emitting gas in the inner disk of the very low-mass star 2MASS-J16053215-1933159. We investigate the source mid-infrared spectrum for atomic and molecular hydrogen line emission. Methods. We present the full James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) spectrum of the protoplanetary disk around the very low-mass star 2MASS-J16053215-1933159 from the MINDS GTO program, previously shown to be abundant in hydrocarbon molecules. We analyzed the atomic and molecular hydrogen lines in this source by fitting one or multiple Gaussian profiles. We then built a rotational diagram for the H2 lines to constrain the rotational temperature and column density of the gas. Finally, we compared the observed atomic line fluxes to predictions from two standard emission models. Results. We identify five molecular hydrogen pure rotational lines and 16 atomic hydrogen recombination lines in the 5–20 µm spectral range. The spectrum indicates optically thin emission for both species. We use the molecular hydrogen lines to constrain the mass and temperature of the warm emitting gas. We derive a total gas mass of only 2.3 × 10−5 MJup and a temperature of 635 K for the warm H2 gas component located in the very inner disk (r < 0.033 au), which only accounts for a small fraction of the upper limit for the disk mass from continuum observations (0.2 MJup). The HI (7-6) recombination line is used to measure the mass accretion rate (4.0 × 10−10 M yr−1) and luminosity (3.1 × 10−3 L) onto the central source. This line falls close to the HI (11-8) line, however at the spectral resolution of JWST MIRI we managed to measure both separately. Previous studies based on Spitzer have measured the combined flux of both lines to measure accretion rates. HI recombination lines can also be used to derive the physical properties of the gas using atomic recombination models. The model predictions of the atomic line relative intensities constrain the atomic hydrogen density to about 109−1010 cm−3 and temperatures up to 5000 K. Conclusions. The JWST-MIRI MRS observations for the very low-mass star 2MASS-J16053215-1933159 reveal a large number of emission lines, many originating from atomic and molecular hydrogen because we are able to look into the disk warm molecular layer. Their analysis constrains the physical properties of the emitting gas and showcases the potential of JWST to deepen our understanding of the physical and chemical structure of protoplanetary disks
HR 10 as seen by CHEOPS and TESS: Revealing δ Scuti pulsations, granulation-like signal and hint for transients
Full text linkContext. HR 10 has only recently been identified as a binary system. Previously thought to be an A-type shell star, it appears that both components are fast-rotating A-type stars, each presenting a circumstellar envelope. Although showing complex photometric variability, spectroscopic observations of the metallic absorption lines reveal variation explained by the binarity, but not indicative of debris-disc inhomogeneities or sublimating exocomets. On the other hand, the properties of the two stars make them potential δ Scuti pulsators. Aims. The system has been observed in two sectors by the TESS satellite, and was the target of three observing visits by CHEOPS. Thanks to these new data, we aim to further characterise the stellar properties of the two components. In particular, we aim to decipher the extent to which the photometric variability can be attributed to a stellar origin. In complement, we searched in the lightcurves for transient-type events that could reveal debris discs or exocomets. Methods. We analysed the photometric variability of both the TESS and CHEOPS datasets in detail. We first performed a frequency analysis to identify and list all the periodic signals that may be related to stellar oscillations or surface variability. The signals identified as resulting from the stellar variability were then removed from the lightcurves in order to search for transient events in the residuals. Results. We report the detection of δ Scuti pulsations in both the TESS and CHEOPS data, but we cannot definitively identify which of the components is the pulsating star. In both datasets, we find flicker noise with the characteristics of a stellar granulation signal. However, it remains difficult to firmly attribute it to actual stellar granulation from convection, given the very thin surface convective zones predicted for both stars. Finally, we report probable detection of transient events in the CHEOPS data, without clear evidence of their origin
Observations of Low and Intermediate Spectral Peak Blazars with the Imaging X-Ray Polarimetry Explorer
Full text linkWe present X-ray polarimetry observations from the Imaging X-ray Polarimetry Explorer (IXPE) of three low spectral peak and one intermediate spectral peak blazars, namely 3C 273, 3C 279, 3C 454.3, and S5 0716+714. For none of these objects was IXPE able to detect X-ray polarization at the 3σ level. However, we placed upper limits on the polarization degree at ∼10%–30%. The undetected polarizations favor models where the X-ray band is dominated by unpolarized photons upscattered by relativistic electrons in the jets of blazars, although hadronic models are not completely eliminated. We discuss the X-ray polarization upper limits in the context of our contemporaneous multiwavelength polarization campaigns
Isotopic abundance of carbon in the DLA towards QSO B1331 + 170
Full text linkChemical evolution models predict a gradual build-up of 13 C in the Universe, based on empirical nuclear reaction rates and assumptions on the properties of stellar populations. Ho we ver, old metal-poor stars within the Galaxy contain more 13 C than is predicted, suggesting that further refinements to the models are necessary. Gas at high-redshift provides important supplementary information at metallicities -2 ≲ [ Fe / H ] ≲ -1, for which there are only a few measurements in the Galaxy. We obtained new, high-quality, VLT/ESPRESSO observations of the QSO B1331 + 170 and used them to measure 12 C/ 13 C in the damped Lyman- αsystem (DLA) at z abs = 1 . 776, with [ Fe / H ] = -1.27. AI-VPFIT , an artificial intelligence tool based on genetic algorithms and guided by a spectroscopic information criterion, was used to explore different possible kinematic structures of the carbon gas. Three hundred independent AI-VPFIT models of the absorption system were produced using pre-set 12 C/ 13 C values, ranging from 4 to 500. Our results show that 12 C/ 13 C = 28 . 5 + 51 . 5 -10 . 4 , suggesting a possibility of 13 C production at low metallicity
Blind QSO reconstruction challenge: exploring methods to reconstruct the Ly α emission line of QSOs
Full text linkReconstructing the intrinsic Ly α line flux from high-z QSOs can place constraints on the neutral hydrogen content of the intergalactic medium during reionization. There are now ≳ 10 different Ly α reconstruction pipelines using different methodologies to predict the Ly α line flux from correlations with the spectral information redwards of Ly α. However, there have been few attempts to directly compare the performance of these pipelines. Therefore, we devised a blind QSO challenge to compare these reconstruction pipelines on a uniform set of objects. Each author was provided de-identified, observed rest-frame QSO spectra with spectral information only redwards of 1260 Å rest-frame to ensure unbiased reconstruction. We constructed two samples of 30 QSOs, from X-Shooter and Sloan Digital Sky Survey (SDSS) both spanning 3.5 < z < 4.5. Importantly, the purpose of this comparison study was not to champion a single, best-performing reconstruction pipeline but rather to explore the relative performance of these pipelines over a range of QSOs with broad observational characteristics to infer general trends. In summary, we find machine-learning approaches in general provide the strongest ‘best guesses’ but underestimate the accompanying statistical uncertainty, although these can be recalibrated, while pipelines that decompose the spectral information, for example principal component or factor analysis, generally perform better at predicting the Ly α profile. Further, we found that reconstruction pipelines trained on SDSS QSOs performed similarly on average for both the X-Shooter and SDSS samples indicating no discernible biases owing to differences in the observational characteristics of the training set or QSO being reconstructed, although the recovered distributions of reconstructions for X-Shooter were broader likely due to an increased fraction of outliers
Constraints on the Evolution of the Ionizing Background and Ionizing Photon Mean Free Path at the End of Reionization
Full text linkThe variations in Lyα forest opacity observed at z > 5.3 between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path at z ∼ 6, and a dramatic improvement in z > 5 Lyα forest data quality, we revisit this latter possibility. Here, we apply the likelihood-free inference technique of approximate Bayesian computation (ABC) to jointly constrain the hydrogen photoionization rate ΓHI and the mean free path of ionizing photons λ mfp from the effective optical depth distributions at z = 5.0–6.1 from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements at z ∼ 5–6, with a concomitant rapid evolution of the photoionization rate
Probing the small-scale structure of the intergalactic medium with ESPRESSO: spectroscopy of the lensed QSO UM673
Full text linkThe gravitationally lensed quasar J014516.6-094517 at z = 2.719 has been observed with the ESPRESSO instrument at the ESO VLT to obtain high-fidelity spectra of the two images A and B with a resolving power R = 70 000. At the redshifts under investigation (2.1 ≲ z ≲ 2.7), the Lyman forests along the two sightlines are separated by sub-kiloparsec physical distances and exhibit a strong correlation. We find that the two forests are indistinguishable at the present level of signal-to-noise ratio and do not show any global velocity shift, with the cross-correlation peaking at Δv = 12 ± 48 . The distribution of the difference in velocity of individual Ly α features is compatible with a null average and a mean absolute deviation of 930 . Significant differences in NH I column density are not detected, putting a limit to the RMS fluctuation in the baryon density on ≲1 proper kpc scales of Δρ/ρ ≲ 3 per cent. On the other hand, metal lines show significant differences both in velocity structure and in column density. A toy model shows that the difference in velocity of the metal features between the two sightlines is compatible with the motions of the baryonic component associated with dark matter haloes of typical mass M ≃ 2 × 1010 M⊙, also compatible with the observed incidence of the metal systems. The present observations confirm the feasibility of the Sandage test of the cosmic redshift drift with high-fidelity spectroscopy of the Lyman forest of distant, bright quasars, but also provide an element of caution about the intrinsic noise associated with the usage of metal features for the same purpose