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Vanishing of quadratic Love numbers of Schwarzschild black holes
No full textInternational audienceThe induced conservative tidal response of self-gravitating objects in general relativity is parametrized in terms of a set of coefficients, which are commonly referred to as Love numbers. For asymptotically-flat black holes in four spacetime dimensions, the Love numbers are famously zero in the static regime. In this work, we show that this result continues to hold upon inclusion of nonlinearities in the theory for Schwarzschild black holes. We first solve the quadratic Einstein equations in the static limit to all orders in the multipolar expansion, including both even and odd perturbations. We show that the second-order solutions take simple analytic expressions, generically expressible in the form of finite polynomials. We then define the quadratic Love numbers at the level of the point-particle effective field theory. By performing the matching with the full solution in general relativity, we show that quadratic Love number coefficients are zero to all orders in the derivative expansion, like the linear ones
Precise measurements with quantum sensors based on atom interferometry: an opportunity for the geosciences
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Final Report on key comparison EURAMET.M.G-K2.2023 of absolute gravimeters
No full textInternational audienceMain text The regional key comparison of absolute gravimeters, EURAMET.M.G-K3.2023, together with a simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in between May and June 2024. This report presents the list of participants who performed measurements, the gravity results submitted by the operators and the data processing strategy. The link to CCM.G-K2.2023 was established via three participants who took part in both comparisons. Finally, the results of the least-squares adjustment, which takes into account the correlations between measurements, are presented by means of the comparison reference values (CRV) and deviations of each gravimeter from the CRV. To reach the main text of this paper, click on Final Report . Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/ . The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA)
Calibration of two mass standards with the LNE Kibble balance in 2024
No full textInternational audienceAbstract Kibble balances are complex electromechanical instruments that enable the determination of mass within the SI by linking it to the Planck constant h , the defining constant of the mass unit. The LNE has been developing its own Kibble balance since 2002, with the most recent improvements focusing on the implementation of a contactless linear motor for the dynamic phase and the fine adjustment of the beam’s orientation with respect to the horizontal plane for the static phase. In 2024, two mass calibration campaigns were carried out using the LNE Kibble balance: first with an iridium standard (DB1), and then with a platinum-iridium standard (W1). Both artefacts have a nominal mass of 500 g, and their masses were determined with relative standard uncertainties of 3.1 ⋅ 10 − 8 and 3.5 ⋅ 10 − 8 respectively ( k = 1 )
Automated Simultaneous Precise Time Calibration of White Rabbit Switches for REFIMEVE
No full textInternational audiencePrecise time and frequency signals are required for numerous applications including advanced scientific research such as High energy physics, Astronomy, Quantum telecommunications etc. In France, the national research infrastructure REFIMEVE distributes ultra-stable optical frequency reference signals over long distances for scientific applications. The reference signals are generated by the designated institute for time and frequency, LNE-OP, at Observatoire de Paris/LTE. They are distributed over the fiber-optic network of the national research and education network, RENATER, using bidirectional links over dark channels. REFIMEVE currently connects more than 30 research laboratories across France, and is also connected via cross-border links to National Physical Laboratory (NPL, UK), Physikalisch-Technische Bundesanstalt (PTB, Germany), Istituto Nazionale di Ricerca Metrologica (INRiM, Italy) and European Organization for Nuclear Research (CERN, Switzerland). In near future the network is planned to be extended to connect more than 40 French laboratories. T-REFIMEVE is a new and ongoing component of REFIMEVE, one major objective of which is to add time and microwave frequency references to the signals which are distributed, through the addition of a White Rabbit (WR) network to the infrastructure. We aim to achieve 10 ns-level time transfer accuracy over more than 80 interconnected WR nodes, over the 5000 km optical fiber network. The WR signals are transmitted as alien wavelengths on RENATER’s fibre network, using standard xWDM technology including unidirectional amplifiers, i.e. using unidirectional links. This introduces the challenge of compensating for the optical path asymmetries inherent to unidirectional links.A first key requirement of T-REFIMEVE is the accurate calibration of the instrumental delays of the White Rabbit Switches (WRS). This poster presents the calibration of dozens of WRS at LTE. We set up an independent calibration chain for T-REFIMEVE, based on unidirectional SFP transceivers at 1560.61 nm, and otherwise following the CERN calibration guidelines [2] and the EMPIR/VSL good practice guide [3]. Port 1 of a specific WRS was chosen as the Golden Calibrator of our chain, and its ingress and egress delays determined following [2]. This Golden Calibrator was then used to calibrate port 1 of a second WRS, thus creating a backup Golden Calibrator. The backup calibrator was then used to calibrate the remaining ports, 2 to 18, of the previous WRS, which we refer to as the Golden Calibrator WRS (as distinct from the Golden Calibrator port itself). This allows the Golden Calibrator WRS to be used to simultaneously calibrate 1 port each of many (up to 18) other WR switches. To calibrate the instrumental delays of more than 80 WRS efficiently, we developed an automated calibration bench for calibrating 10 switches simultaneously, by interfacing the WR switches under calibration with a datalogger containing an RF multiplexer, used to connect the PPS out signals of the WR switches successively to a single time interval counter. The programme developed to run the parallel calibrations borrowed heavily from CERN’s calibration code [4]. The PPS offsets both before calibration (i.e., using the CERN firmware default delays) and after calibration are measured when the ports of the Golden Master WRS are connected to the backup golden calibrator port. The initial synchronization was already good, with an average offset of 55 ps (σ_A=39 ps), which improved to -11 ps (σ_A=14 ps) after calibration.References:[1] O. Lopez et al., « Frequency and time transfer for metrology and beyond using telecommunication network fibres », Comptes Rendus Physique, vol. 16, no 5, p. 531 539, juin 2015, doi: 10.1016/j.crhy.2015.04.005.[2] G. Daniluk, “White Rabbit calibration procedure,” 2015 https://white-rabbit.web.cern.ch/documents/WR_Calibration-v1.1-20151109.pdf [3] Dierickx, Erik and X. Yan, “WR Good practice guide,” May 2019 https://gitlab.com/ohwr/project/white-rabbit/wikis/uploads/7df19b6a4d0e90bf6d7b8ae32b3b32c4/WR_Good_Practice_Guide.pdf [4] Link for the White Rabbit Switch Calibration Code provided by CERN: https://gitlab.com/ohwr/project/wr-switch-sw/-/tree/master/userspace/host_tools/calibratio
Rediscovering the Milky Way with an orbit superposition approach and APOGEE data V. The disc growth and history of star formation
No full textInternational audienceThe Milky Way's (MW's) star formation history (SFH) offers insight into the chronology of its assembly and the mechanisms driving its structural development. In this study, we present an inference and analysis of the spatially resolved SFH and the MW disc growth. Our approach leverages both stellar birth radii estimates and the complete reconstruction of the MW stellar disc using a novel orbit superposition method from APOGEE data, allowing us to trace the orbit-mass weighted SFH based on formation sites while taking into account stellar mass loss. We find that the MW is a typical disc galaxy exhibiting inside-out formation: it was compact at z > 2 ( kpc), had a peak in its star formation rate (SFR) 9--10 Gyr ago, and grew to a present-day size of kpc. A secondary peak in SFR Gyr ago is responsible for the onset of the outer disc, which comprises the metal-poor, low- population. We find that in-situ star formation in the solar neighbourhood started 8--9 Gyr ago. The MW disc is characterised by a negative mean age gradient, as the result of the inside-out growth, with additional flattening induced by stellar radial migration. Our work showcases the importance of accounting for radial migration and stellar sample selection function when inferring the SFH and build-up of the MW disc
Alignment and performance verification of two-mirror focal corrector optics using computer-generated holograms for balloon-borne ultraviolet Telescope FIREBall-2
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The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. VI. Evidence for Radially Evolving Icy Grains in the HD 141569A Disk via NIRCam Coronagraphic Imaging
No full textInternational audienceWe present JWST NIRCam coronagraphic observations of the HD 141569A circumstellar disk, obtained as part of the JWST Early Release Science program. The observations recover the multi-ringed structure seen in previous shorter-wavelength observations, but at filters centered on the ∼3 μm water ice absorption feature and a complementary continuum region (F300M and F360M, respectively). The observations reveal apparent absorption between the F300M and F360M filters that decreases with radius, with a notable change around 200 au, between the innermost and outermost two rings. These results are consistent whether the data is reduced via deconvolution or through a forward-modeling approach. We demonstrate that these changes suggest a radial decrease in the water ice mass fraction by a factor of ∼3-10 and possibly a change in minimum grain size. We do not detect any point sources within the system and can exclude planetary companions 2 Jupiter masses and greater beyond 1″ radius (∼111 au). These observations and the subsequent analysis illustrate a robust pathway for using JWST/NIRCam to characterize the distribution of water ice in other circumstellar disks. We highlight some of the early lessons learned from this work that we hope will be useful for future circumstellar disk observation planning and analysis.</div
Transit Timing Variations in HIP 41378: CHEOPS and TESS confirm a non-transiting sixth planet in the system
No full textInternational audienceIn multiple-planet systems, gravitational interactions of exoplanets could lead to transit timing variations (TTVs), whose amplitude becomes significantly enhanced when planets are in or near mean-motion resonances (MMRs), making them more easily detectable. In cases where both TTVs and radial velocity (RV) measurements are available, combined analysis can break degeneracies and provide robust planetary and system characterization, even detecting non-transiting planets. In this context, HIP 41378 hosts five confirmed transiting planets with periods ranging from 15 to over 542 days, providing a unique dynamical laboratory for investigating wide multi-planet systems analogous to the Solar System. In this study, we present an intensive space-based photometric follow-up of HIP 41378, combining 15 new CHEOPS observations with eight TESS sectors, alongside data from K2, Spitzer, HST, and 311 HARPS spectra. We dynamically modeled the TTVs and RV signals of the two inner sub-Neptunes via N -body integration. These planets, HIP 41378 b ( P b = 15.57 days, R b = 2.45 R ⊕ ) and HIP 41378 c ( P c = 31.71 days, R c = 2.57 R ⊕ ), are close to (Δ ~ 1.8%) a 2:1 period commensurability. We report a clear detection of TTVs with amplitudes of 20 minutes for planet b and greater than 3 hours for planet c. We dynamically confirm the planetary nature of HIP 41378 g, a non-transiting planet with a period of about 64 days and a mass of about 7 M ⊕ , close to a 2:1 commensurability with planet c, suggesting a possible mean-motion resonance chain in the inner system. Our precise determination of the masses, eccentricities, and radii of HIP 41378 b and c enabled us to investigate their possible volatile-rich compositions. Finally, by leveraging on the last TESS sectors we constrained the period of HIP 41378 d to three possible aliases ( P d = 278, 371, and 1113 days) suggesting that the system could be placed in a double quasi resonant chain, highlighting its complex dynamical architecture
