arXiv subjects

Paul Ripoche

Publications and source records attributed to Paul Ripoche.

7 recordsLinked to original sources

arXiv2023

Carbon stars as standard candles -- III. Un-binned maximum likelihood fitting and comparison with TRGB estimations

In the second paper of this series, we developed a new distance determination method using the median $J$ magnitude of carbon-rich asymptotic giant branch stars (CS) as standard candles and the Magellanic Clouds as the fundamental calibrators. The $J$-band CS luminosity function was modeled using a modified Lorentzian distribution whose parameters were used to determined whether the LMC or SMC was the most suitable calibrator. In this third paper of the series, we expand our sample of galaxies and introduce a more robust method to determine the parameters of the Lorentzian model. The new fitting method uses an un-binned maximum likelihood estimator to determine the parameters of the Lorentzian model resulting in parameter errors that are significantly smaller compared to the second paper. We test our method in NGC 6822, IC 1613, NGC 3109 and WLM. We also estimate the distances to the same sample of galaxies via the tip of the red giant branch (TRGB) detection method. Our results from the CS measurements agree well with those obtained from the TRGB.

astro-ph.GA↗

arXiv2021

Progress toward optimizing energy and arrival-time resolution with a transition-edge sensor from simulations of X-ray-photon events

Superconducting transition-edge sensors (TESs) carried by X-ray telescopes are powerful tools for the study of neutron stars and black holes. Several methods, such as optimal filtering or principal component analysis, have already been developed to analyse X-ray data from these sensors. However, these techniques may be hard to implement in space. Our goal is to develop a lower-computational-cost technique that optimizes energy and time resolution when X-ray photons are detected by a TES. TESs exhibit a non-linear response with photon energy. Therefore, at low energies we focus on the current-pulse height whereas at high energies we consider the current-pulse width, to retrieve energy and arrival time of X-ray photons. For energies between 0.1 keV and 30 keV and with a sampling rate of 195 kHz, we obtain an energy resolution (full width at half the maximum) between 1.32 eV and 2.98 eV. We also get an arrival-time resolution (full duration at half the maximum) between 163 ns and 3.85 ns. To improve the accuracy of these results it will be essential to get a thorough description of non-stationary noise in a TES, and to develop a robust on-board identification method of pile-up events.

astro-ph.IM↗

arXiv2020

Carbon stars as standard candles: II. The median J magnitude as a distance indicator

We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ($(J-K_{s})_0$, $J_0$) colour-magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS $J$-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fit distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median $J$ magnitude ($\overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an "LMC-like" CS luminosity function while IC 1613 is more "SMC-like". Using the values for the median absolute $J$ magnitude for the LMC and SMC found in Paper I we find a distance modulus of $μ_{0}=23.54\pm0.03$ (stat) for NGC 6822 and $μ_{0}=24.34\pm0.05$ (stat) for IC 1613.

astro-ph.GA↗

arXiv2020

Carbon stars as standard candles: I. The luminosity function of carbon stars in the Magellanic Clouds

Our goal in this paper is to derive a carbon-star luminosity function that will eventually be used to determine distances to galaxies at $50$-$60$ Mpc and hence yield a value of the Hubble constant. Cool N-type carbon stars exhibit redder near-infrared colours than oxygen-rich stars. Using Two Micron All Sky Survey near-infrared photometry and the Gaia Data Release 2, we identify carbon stars in the Magellanic Clouds (MC) and the Milky Way (MW). Carbon stars in the MC appear as a distinct horizontal feature in the near-infrared ($(J-K_s)_0$, $M_J$) colour-magnitude diagram. We build a colour selection ($1.4 < (J-K_s)_0 < 2$) and derive the luminosity function of the colour-selected carbon stars. We find the median absolute magnitude and the dispersion, in the J band, for the Large Magellanic Cloud and the Small Magellanic Cloud to be, respectively, ($\bar{M_J} = -6.284 \pm 0.004$, $σ= 0.352 \pm 0.005$) and ($\bar{M_J} = -6.160 \pm 0.015$, $σ= 0.365 \pm 0.014$). The difference between the MC may be explained by the lower metallicity of the Small Magellanic Cloud, but in any case it provides limits on the type of galaxy whose distance can be determined with this technique. To account for metallicity effects, we developed a composite magnitude, named C, for which the error-weighted mean C magnitude of both the MC are equal. Thanks to the next generation of telescopes (JWST, ELT, TMT), carbon stars could be detected in MC-type galaxies at distances out to $50$-$60$ Mpc. The final goal is to eventually try and improve the measurement of the Hubble constant while exploring the current tensions related to its value.

astro-ph.SR↗

arXiv2019

QED effects are negligible for neutron-star spin-down

The energy loss of a rotationally powered pulsar is primarily carried away as electromagnetic radiation and a particle wind. Considering that the magnetic field strength of pulsars ranges from about $10^8$ to $10^{15}$ G, one could expect quantum electrodynamics (QED) to play a role in their spin-down, especially for strongly magnetized ones (magnetars). In fact several authors have argued that QED corrections will dominate the spin-down for slowly rotating stars. They called this effect quantum vacuum friction (QVF). However, QVF was originally derived using a problematic self-torque technique, which leads to a dramatic overestimation of this spin-down effect. Here, instead of using QVF, we explicitly calculate the energy loss from rotating neutron stars using the Poynting vector and a model for a particle wind, and we include the QED one-loop corrections. We express the excess emission as QED one-loop corrections to the radiative magnetic moment of a neutron star. We do find a small component of the spin-down luminosity that originates from the vacuum polarization. However, it never exceeds one percent of the classical magnetic dipole radiation in neutron stars for all physically interesting field strengths. Therefore, we find that the radiative corrections of QED are irrelevant in the energetics of neutron-star spin-down.

astro-ph.HE↗

arXiv2019

Testing general relativity with accretion onto compact objects

The X-ray emission of neutron stars and black holes presents a rich phenomenology that can lead us to a better understanding of their nature and to address more general physics questions: Does general relativity apply in the strong gravity regime? Is spacetime around black holes described by the Kerr metric? This white paper considers how we can investigate these questions by studying reverberation mapping and quasi-periodic oscillations in accreting systems with a combination of high-spectral and high-timing resolution. In the near future, we will be able to study compact objects in the X-rays in a new way: advancements in transition-edge sensors (TES) technology will allow for electron-volt-resolution spectroscopy combined with nanoseconds-precision timing.

astro-ph.HE↗

arXiv2019

Exploring the physics of neutron stars with high-resolution, high-throughput X-ray spectroscopy

The advent of moderately high-resolution X-ray spectroscopy with Chandra and XMM promised to usher in a new age in the study of neutron stars: we thought we would study neutron stars like stars, with resolved absorption spectra revealing their surface chemical composition and physical conditions (e.g. surface gravity, pressure, temperature). Nature, however, did not cooperate in this endeavor, as observations of neutron stars have not revealed verified atomic absorption lines yet. In the near future, advancements in transition-edge sensors (TES) technology will allow for electron-volt-resolution spectroscopy combined with nanoseconds-precision timing. Combining these detectors with collector optics will also us to study neutron stars in much greater detail by achieving high-energy resolution with much larger collecting areas to uncover even weak spectral features over a wide range of the photon energies. Perhaps we will finally be able to study neutron stars like stars.

astro-ph.HE↗