arXiv subjects

Paolo Molaro

Publications and source records attributed to Paolo Molaro.

At least 55 records · Page 3Linked to original sources

arXiv2010

Robust limit on a varying proton-to-electron mass ratio from a single H2 system

The variation of the dimensionless fundamental physical constant mu=m_p/m_e can be checked through observation of Lyman and Werner lines of molecular hydrogen in the spectra of distant QSOs. Our intention is to asses the accuracy of the investigation concerning a possible variation of mu and to provide more robust results for QSO 0347-383. The goal in mind is to resolve the current controversy on variation of mu and devise explanations for the different findings. We achieve this not by another single result but by providing alternative approaches to the problem. An analysis based on independent data sets of QSO 0347-383 is put forward and new approaches for some of the steps involved in the data analysis are introduced. We analyse two independent sets of observations of the same absorption system and for the first time we apply corrections for the observed offsets between discrete spectra Drawing on two independent observations of a single absorption system in QSO 0347-383 our detailed analysis yields dmu/mu = 15 +/- (9_stat + 6_sys) x 10^{-6} at z_abs=3.025. Based on the overall goodness-of-fit we estimate the limit of accuracy to about 300 m/s, consisting of roughly 180 m/s due to the uncertainty of the fit and about 120 m/s allocated to systematics This work presents alternative approaches to handle systematics and introduces methods required for precision analysis of QSO spectra available in the near future.

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arXiv2009

Calibration issues in estimating variability of the fine structure constant (alpha) with cosmic time

Laser Comb Wavelength calibration shows that the ThAr one is locally unreliable with possible deviations of up to 100 m/s within one order range, while delivering an overall 1 m/s accuracy (Wilken et al 2009). Such deviation corresponds to delta alpha/alpha ~ 7E-6 for a FeII-MgII pair. Comparison of line shifts among the 5 FeII lines, with almost identical sensitivity to fine structure constant changes, offers a clean way to directly test the presence of possible local wavelength calibration errors of whatever origin. We analyzed 5 absorption systems, with zabs ranging from 1.15 to 2.19 towards 3 bright QSOs. The results show that while some lines are aligned within 20 m/s, others reveal large deviations reaching 200 m/s or higher and corresponding to a delta alpha/alpha > 1E-5 level. The origin of these deviations is not clearly identified but could be related to the adaptation of wavelength calibration to CCD manufacturing irregularities. These results suggest that to draw conclusions from delta alpha/alpha analysis based on one or only few lines must be done with extreme care.

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arXiv2009

The mystery of the telescopes in Jan Brueghel the Elder's paintings

Several early spyglasses are depicted in five paintings by Jan Brueghel the Elder completed between 1608 and 1625, as he was court painter of Archduke Albert VII of Habsburg. An optical tube that appears in the Extensive Landscape with View of the Castle of Mariemont, dated 1608-1612, represents the first painting of a telescope whatsoever. We collected some documents showing that Albert VII obtained spyglasses very early directly from Lipperhey or Sacharias Janssen. Thus the painting likely reproduces one of the first man-made telescopes ever. Two other instruments appear in two Allegories of Sight made in the years 1617 and 1618. These are sophisticated instruments and the structure suggests that they may be keplerian, but this is about two decades ahead this mounting was in use.

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arXiv2009

On the telescopes in the paintings of J. Brueghel the Elder

We have investigated the nature and the origin of the telescopes depicted in three paintings of J. Bruegel the Elder completed between 1609 and 1618. The "tube" that appears in the painting dated 1608-1612 represents a very early dutch spyglass, tentatively attributable to Sacharias Janssen or Lipperhey, prior to those made by Galileo, while the two instruments made of several draw-tubes which appear in the two paintings of 1617 and 1618 are quite sophisticated and may represent early examples of Keplerian telescopes.

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arXiv2009

Stringent bounds to spatial variations of the electron-to-proton mass ratio in the Milky Way

The ammonia method to probe variations of the electron-to-proton mass ratio, Delta_mu/mu, is applied for the first time to dense prestellar molecular clouds in the Milky Way. Carefully selected sample of 21 NH_3/CCS pairs observed in the Perseus molecular cloud provide the offset Delta V (CCS-NH_3)= 36+/-7_{stat}+/-13.5_{sys} m/s . A similar offset of Delta V = 40.8 +/- 12.9_{stat} m/s between NH_3 (J,K) = (1,1) and N_2H+ J = 1-0 has been found in an isolated dense core L183 by Pagani et al. (2009). Overall these observations provide a safe bound of a maximum offset between ammonia and the other molecules at the level of Delta V < 100 m/s. This bound corresponds to Delta_mu/mu < 1E-7, which is an order of magnitude more sensitive than available extragalactic constraints. Taken at face value the measured Delta V shows positive shifts between the line centers of NH_3 and these two other molecules and suggest a real offset, which would imply a Delta_mu/mu about 4E-8. If Delta_mu/mu follows the gradient of the local gravitational potential, then the obtained results are in conflict with laboratory atomic clock experiments in the solar system by 5 orders of magnitude, thus requiring a chameleon-type scalar field model. New measurements involving other molecules and a wider range of objects along with verification of molecular rest frequencies are currently planned to confirm these first indications.

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arXiv2007

Science with a 16m VLT: the case for variability of fundamental constan ts

Only astronomical observations can effectively probe in space-time the variabil ity of the physical dimensionless constants such as the fine structure constant and proton-to-electron mass ratio, μ, which are related to fund amental forces of nature. Several theories beyond the Standard Model (SM) allow fundamental constants to vary, but they cannot make quantitative predictions so that only laboratory experiments and astronomical observations can show if th is is the case or set the allowed bounds. At the moment of writing there are c laims for a variability of both αand μat 5 and 4σof C.L., respectively, although for αthey are contrasted by null results. The observations are challenging and a new spectrograph such as ESPRESSO at the combined incoherent focus of 4 VLT units (a potential 16 m equivalent telescope) will allow for a significant improvement in the precision measurement clearing up the controversy. If the variations will be confirmed, the implications are far reaching, revealing new physics beyond the SM and pointing a direction for GUTs theories. A most exciting ossibility is that a variation of αis induced by quintessence through its coupling with the electromagnetic field. If this is the case an accurate measurement of the variability could provide a way for reconstructing the equation of state of Dark Energy (Avelino et al 2006).

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arXiv2007

Bounds on the fine structure constant variability from FeII absorption lines in QSO spectra

The Single Ion Differential alpha Measurement (SIDAM) method for measuring fine stucture variations (daa)and its figures of merit are illustrated together with the results produced by means of FeII absorption lines of QSO intervening systems. The method provides daa ~= -0.12(+/- 1.79) ppm (parts-per-million) at zabs = 1.15 towards HE 0515--4414 and daa = 5.66(+/-2.67) ppm at zabs= 1.84 towards Q 1101--264, which are so far the most accurate measurements for single systems. SIDAM analysis for 3 systems from the Chand et al. (2004) sample provides inconsistent results which we interpret as due to calibration errors of the Chand et al. data at the level of about 10 ppm. In one system evidence for photo-ionization Doppler shift between MgII and FeII lines is found. This evidence has important bearings on the Many Multiplet method where the signal for daa variability is carried mainly by systems involving MgII absorbers. Some correlations are also found in the Murphy et al. sample which suggest larger errors than previously reported. Thus, we consider unlikely that both the Chand et al. and Murphy et al. datasets could provide an estimate of daa with an accuracy at the level of 1 ppm. A new spectrograph like the ESPRESSO project will be crucial to make progress in the astronomical determination of daa.

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arXiv2007

Primordial Light Element Abundances

After few minutes the Universe evolved through conditions of temperature and density which permitted the first synthesis of astrophysically interesting abundances of D, 3He, 4He and 7Li. The relic abundances are sensitive probes of the nucleon density and so are the CMB acoustic oscillations, somewhat 400000 years later, which allow a stringent cross check. The CMB high precision estimate of the baryon density by WMAP is currently used as input parameter for standard big bang nucleosynthesis (SBBN) to interpret primordial bundances rather then being directly derived from the observations of light elements as was common use before. New atomic physics and identification of systematics lead to an upwards revision of the 4He primordial abundance at Yp=0.2477 +/- 0.0029 (Peimbert et al 2007) removing a major source of tension between SBBN and WMAP. The D/H as measured in QSO high redshift absorbing clouds shows an excess of scatter but the mean value is found in spectacular agreement with the WMAP prediction. The Li/H recently redetermined in halo dwarfs is more than a factor 4 lower than expected. We argue that the difference reduces to a factor 2 when the IRFM Teff scale is adopted. Diffusion has been suggested to have depleted Li in halo dwarfs by the required amount to remove the gap, however this would imply an implausible high abundance of the more fragile 6Li detected in some halo dwarfs, thus leaving the puzzle open.

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arXiv2007

Variations in the lithium abundances of turn off stars in the globular cluster 47 Tuc

aims: Our aim is to determine Li abundances in TO stars of the Globular Cluster 47 Tuc and test theories about Li variations among TO stars. method: We make use of high resolution (R~ 43000), high signal-to-noise ratio (S/N=50--70) spectra of 4 turn off (TO) stars obtained with the UVES spectrograph at the 8.2m VLT Kueyen telescope. results: The four stars observed, span the range 1.6<~A(Li)} <~ 2.14, providing a mean A(Li) = 1.84 with a standard deviation of 0.25 dex. When coupled with data of other two TO stars of the cluster, available in the literature, the full range in Li abundances observed in this cluster is 1.6<~A(Li)<~ 2.3. The variation in A(Li) is at least 0.6 dex (0.7 dex considering also the data available in the literature) and the scatter is six times larger than what expected from the observational error. We claim that these variations are real. A(Li) seems to be anti-correlated with A(Na) exactly as observed in NGC 6752. No systematic error in our analysis could produce such an anti-correlation. conclusions: Na production through p captures on 22Ne at temperatures in excess of 3x10^7 K and the contemporary Li destruction could result in this anti-correlation. However such nuclear processing cannot have taken place in the stars themselves, which do not reach such high temperatures, even at their centre. This points towards the processing in a previous generation of stars. The low N/O ratios in the observed stars and the apparent lack of correlation between N an Li abundances, place a strong constraint on the properties of this previous generation. Our results indicate a different behaviour among the Globular Clusters so far studied as far as the abundance patterns are concerned.

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arXiv2006

High-Precision Measurements of Delta alpha/alpha from QSO Absorption Spectra

Precise radial velocity measurements (delta v/c ~ 10^{-7}) of FeII lines in damped Ly-alpha systems from very high quality VLT/UVES spectra of quasars HE0515-4414 and Q1101-264 are used to probe cosmological time dependence of the fine structure constant, alpha. It is found that between two redshifts z1 = 1.15 and z2 = 1.84 the value of Delta alpha/alpha changes at the level of a few ppm: (alpha_z2 - alpha_z1)/alpha_0 = 5.43 +/- 2.52 ppm. Variations of alpha can be considered as one of the most reliable method to constrain the dark energy equation of state and improvements on the accuracy of the wavelength calibration of QSO spectra are of great importance.

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arXiv2006

Exploring variations in the fundamental constants with ELTs: The CODEX spectrograph on OWL

Cosmological variations in the fine structure constant, alpha, can be probed through precise velocity measurements of metallic absorption lines from intervening gas clouds seen in spectra of distant quasars. Data from the Keck/HIRES instrument support a variation in alpha of 6 parts per million. Such a variation would have profound implications, possibly providing a window into the extra spatial dimensions required by unified theories such as string/M-theory. However, recent results from VLT/UVES suggest no variation in alpha. The COsmic Dynamics EXperiment (CODEX) spectrograph currently being designed for the ESO OWL telescope (Pasquini et al 2005) with a resolution high enough to properly resolve even the narrowest of metallic absorption lines, R>150,000, will achieve a 2-to-3 order-of-magnitude precision increase in Deltaα/alpha. This will rival the precision available from the Oklo natural fission reactor and upcoming satellite-borne atomic clock experiments. Given the vital constraints on fundamental physics possible, the ELT community must consider such a high-resolution optical spectrograph like CODEX.

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arXiv2005

Chemical Abundances in the Secondary Star of the Neutron Star Binary Centaurus X-4

Using a high resolution spectrum of the secondary star in the neutron star binary {Cen X-4}, we have derived the stellar parameters and veiling caused by the accretion disk in a consistent way. We have used a $χ^{2}$ minimization procedure to explore a grid of 1 500 000 LTE synthetic spectra computed for a plausible range of both stellar and veiling parameters. Adopting the best model parameters found, we have determined atmospheric abundances of Fe, Ca, Ti, Ni and Al. These element abundances are super solar ($\mathrm{[Fe/H]}=0.23 \pm 0.10$), but only the abundance of Ti and Ni appear to be moderately enhanced ($\ge1σ$) as compared with the average values of stars of similar iron content. These element abundances can be explained if the secondary star captured a significant amount of matter ejected from a spherically symmetric supernova explosion of a 4 {$M_\odot$} He core progenitor and assuming solar abundances as primordial abundances in the secondary star. The kinematic properties of the system indicate that the neutron star received a natal kick velocity through an aspherical SN and/or an asymmetric neutrino emission. The former scenario might be ruled out since our model computations cannot produce acceptable fits to the observed abundances. We have also examined whether this system could have formed in the Galactic halo, and our simulations show that this possibility seems unlikely. We also report a new determination of the Li abundance consistent with previous studies that is unusually high and close to the cosmic Li abundance in the Galactic disk.

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arXiv2005

Abundances in Damped Ly-alpha Galaxies

Damped Ly_alpha galaxies provide a sample of young galaxies where chemical abundances can be derived throughout the whole universe with an accuracy comparable to that for the local universe. Despite a large spread in redshift, HI column density and metallicity, DLA galaxies show a remarkable uniformity in the elemental ratios rather suggestive of similar chemical evolution if not of an unique population. These galaxies are characterized by a moderate, if any, enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn] about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution and possibly two plateaux. In particular, the plateau at low N abundances ([N/H] < -3), is not observed in other atrophysical sites and might be evidence for primary N production by massive stars.

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arXiv2003

Hints of star fomation at z>6: the chemical abundances of the DLA system in the QSO BRI 1202-0725 (z_abs = 4.383)

The Damped Ly-alpha (DLA) absorber at redshift z_abs=4.383 observed toward QSO BRI 1202-0725 is studied by means of high resolution (FWHM ~ 7 km/s) VLT-UVES spectra. We refine a previously determined Si abundance and derive with confidence abundances for C, N and O which are poorly known in DLAs. The [O/Fe] ratio is ~0.6, but we cannot establish if iron is partially locked into dust grains. The [C/Fe]=0.08 \pm 0.13 and [Si/C]=0.31 \pm 0.07. [N/O] and [N/Si] are about -1, which is consistent with the majority of DLAs. This value is much larger than the one observed for the DLA toward QSO J0307-4945 at z_abs= 4.466. The current interpretation of the bimodal distribution of N abundances in DLAs implies that large [N/alpha] values correspond to relatively old systems. Adopting a scale time of 500 Myrs for full N production by intermediate mass stars, the onset of star formation in our DLA took place already at redshift z> 6.

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arXiv2003

CNO abundances in the Damped Ly-alpha clouds

Damped Ly alpha clouds provide information on the chemistry of distant and metal poor regions of the universe. In these clouds for observational difficulties N and O are among the last elements to be measured, and C has still to be measured with precision. In combining the extant CNO abundances, we avail of a sample which includes 33 N measurements or significant limits, a dozen of O measurements, and only few tentative measurements for C. O is found to track both S and Si rather closely without signatures of any peculiar behaviour and the few [O/Zn] ratios available show a mild alpha/iron-peak enhancement which reinforces earlier evidence. The few tentative C measurements point to roughly solar [C/Zn] and [C/Si] ratios. N abundances are rather complex with N/alpha ratios showing a bimodal distribution. The majority of the values form a first plateau at [N/Si]=-0.82 (+/- 0.13) and about 25 % form a second plateau at [N/Si]= -1.45 (+/- 0.05). The high values are at the level of the Blue Compact Dwarfs but they extend further towards lower metallicities. The lower plateau is a new feature of DLAs with no other counterparts. The two plateaux are found for different values of the N abundance with the transition at [N/H] ~ -3.0. We argue that this results from the delayed release of N between massive and intermediate mass stars with the lower plateau produced by massive stars (M> 8 M_sun) only, which accounts for the small dispersion. The systems on the lower plateau are relatively young and imply a continuous formation of the DLAs. While the interpretation of the N/O in the DLAs needs to be confirmed, these observations could ultimately prove crucial for the interpretation of the early N nucleosynthesis.

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arXiv2001

Chemical Abundances in High-Redshift Neutral Clouds

Neutral hydrogen clouds with high column density detected towards distant quasars are unique probes of elemental nucleosynthesis and chemical evolution in the low metallicity regime. They provide measurements for several elements at very early times which are unfeasible in other astrophysical environments. Comparison between refractory and non-refractory elements provides evidence for the presence of dust, and the recently measured Ar probes photoionization. A prominent characteristic is the dominance of a solar abundance pattern, which is somewhat unexpected at low metallicities. It is argued that this property and Nitrogen observations can be used to constrain the age of the Damped Ly_alpha systems and the epoch of star formation.

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arXiv2001

A new deuterium abundance measurement from a damped Ly-alpha system at z_abs = 3.025

We present the first D/H measurement in a damped Ly-alpha system at z_abs = 3.025 towards QSO 0347-3819 obtained from the UVES-VLT spectra. The DLA absorber has a metallicity of [Zn/H] = -1.25 and a relatively simple velocity structure, with two dominating components detected in several metal lines. The hydrogen Lyman series can be followed down to Ly12 thanks to the high UV-Blue efficiency of UVES. The best fit of the Lyman series lines, and in particular of Ly5, Ly8, Ly10 and Ly12, relatively free of local contamination, is obtained when the DI absorption is included in the two main components. The measured deuterium column density yields D/H = (2.24+/-0.67) 10^{-5} close to other low D/H values from Lyman limit systems. The corresponding values for the baryon to photon ratio and the baryon density derived from D/H are eta = 6 10^{-10} and Omega_b h^2 = 0.023 respectively.

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arXiv2000

UVES observations of QSO 0000-2620: Argon and Phosphorus abundances in the dust-free damped Ly-alpha system at zabs = 3.3901

The UV resonance transitions of neutral argon ArI 1066 A, and of singly ionized phosphorus PII 963 A, originated in the damped Ly_alpha system (DLA) at zabs = 3.3901 towards QSO 0000--2620 have been detected by means of the UVES spectrograph at the 8.2m ESO KUEYEN telescope. So far, this is the first measurement of ArI, and the second of PII, ever performed in damped galaxies and in high redshift objects. This DLA is well known for having one of the lowest metal abundances and dust content, and the lowest fractional abundance of molecular hydrogen H_2. The measured Ar abundance is [Ar/H] = - 1.91 (+/- 0.09) which is equal to the abundances of the other alpha-chain elements (O, S and Si). The similarity of the Ar abundance with the other alpha-chain elements implies the absence of significant photoionization by either UV background or stellar sources along the sightline throughout the damped Ly_alpha system. Both log(Ar/O) and log(Ar/S) ratios are found close to those measured in the extragalactic HII regions and in blue compact galaxies where O is more abundant by at least one order of magnitude. This strengthens the universality of the Ar/O and Ar/S ratios and lends support to the existence of a universal IMF. The abundance of the non-refractory element phosphorus [P/H] = - 2.31 (+/- 0.10) confirms the low amount of chemical evolution in the DLA. This is the measurement of P in the most metal-poor material and shows a subsolar [P/Fe] = --0.27 value. The measured ratios [P/Si] = - 0.40 (+/- 0.13) and [P/S] = - 0.33 (+/- 0.13) provide evidence for a mild odd-even effect. Finally, a stringent upper limit to the population of the 3P_1 level in the ground state of OI is derived, which provides a lower limit to the physical dimensions of the zabs = 3.3901 system of L > 7 pc.

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