References of "Hauret, Clémentine"
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See detailCosmology with type Ia supernovae : the ultraviolet 'catastroph'? Evolution with redshift of type Ia supernovae in the ultraviolet domain
Hauret, Clémentine ULiege; Magain, Pierre ULiege

Poster (2018, December 07)

To extract useful cosmological information from type Ia supernovae (SNe Ia), standardization laws have to be determined and applied assuming that these objects do not intrinsically change with redshift ... [more ▼]

To extract useful cosmological information from type Ia supernovae (SNe Ia), standardization laws have to be determined and applied assuming that these objects do not intrinsically change with redshift. Recently, to improve that standardization, attention has been drawn towards the SNe Ia UV spectra. This resulted in (what seemed as) the discovery of two subpopulations of objects, grouped by their bluer or redder UV colors. To confirm the existence of these subpopulations, we significantly enlarged the number of studied SNe Ia (going from ~100 to ~700 objects). With such a sample, SNe Ia cannot be separated in two groups anymore but they rather follow a continuum of colors. More critically, we showed that the SNe Ia UV colors display a significant evolution with redshift, resulting in a potentially important impact on subsequent cosmological measurements. [less ▲]

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See detailA cosmology-independent calibration of type Ia supernovae data
Hauret, Clémentine ULiege; Magain, Pierre ULiege; Biernaux, Judith ULiege

in Monthly Notices of the Royal Astronomical Society (2018), 479(3), 3996-4003

Recently, the common methodology used to transform type Ia supernovae (SNe Ia) into genuine standard candles has been suffering criticism. Indeed, it assumes a par- ticular cosmological model (namely the ... [more ▼]

Recently, the common methodology used to transform type Ia supernovae (SNe Ia) into genuine standard candles has been suffering criticism. Indeed, it assumes a par- ticular cosmological model (namely the flat LambdaCDM) to calibrate the standardisation corrections parameters, i.e. the dependency of the supernova peak absolute magnitude on its colour, post-maximum decline rate and host galaxy mass. As a result, this as- sumption could make the data compliant to the assumed cosmology and thus nullify all works previously conducted on model comparison. In this work, we verify the viability of these hypotheses by developing a cosmology-independent approach to standardise SNe Ia data from the recent JLA compilation. Our resulting corrections turn out to be very close to the LambdaCDM-based corrections. Therefore, even if a LambdaCDM-based calibra- tion is questionable from a theoretical point of view, the potential compliance of SNe Ia data does not happen in practice for the JLA compilation. Previous works of model comparison based on these data do not have to be called into question. However, as this cosmology-independent standardisation method has the same degree of complex- ity than the model-dependent one, it is worth using it in future works, especially if smaller samples are considered, such as the superluminous type Ic supernovae. [less ▲]

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See detailCosmological Time, Entropy and Infinity
Hauret, Clémentine ULiege; Magain, Pierre ULiege; Biernaux, Judith ULiege

in Entropy (2017), 19(7),

Time is a parameter playing a central role in our most fundamental modelling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative ... [more ▼]

Time is a parameter playing a central role in our most fundamental modelling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motion and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks (i.e., clocks at rest with respect to the expanding space). This proper time is assumed to flow at a constant rate throughout the whole history of the universe. We make the alternative hypothesis that the rate at which the cosmological time flows depends on the dynamical state of the universe. In thermodynamics, the arrow of time is strongly related to the second law, which states that the entropy of an isolated system will always increase with time or, at best, stay constant. Hence, we assume that the time measured by fundamental clocks is proportional to the entropy of the region of the universe that is causally connected to them. Under that simple assumption, we find it possible to build toy cosmological models that present an acceleration of their expansion without any need for dark energy while being spatially closed and finite, avoiding the need to deal with infinite values. [less ▲]

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See detailCan we trust Type Ia Supernovae as cosmological tools? - Critical analysis and alternative processing of SCP Supernovae data
Hauret, Clémentine ULiege; Magain, Pierre ULiege

Poster (2015, July)

Current processing to standardize Type Ia Supernovae SCP data produces a significant bias in favour of a particular cosmological model, the flat ΛCDM model. To reduce this bias, we develop an alternative ... [more ▼]

Current processing to standardize Type Ia Supernovae SCP data produces a significant bias in favour of a particular cosmological model, the flat ΛCDM model. To reduce this bias, we develop an alternative, model-independent, methodology. [less ▲]

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See detailCritical analysis and alternative treatment of Type Ia Supernovae data
Hauret, Clémentine ULiege

Conference (2015, May 20)

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See detailOn the nature of cosmological time
Hauret, Clémentine ULiege

Conference (2015, May 13)

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See detailOn the nature of cosmological time
Hauret, Clémentine ULiege

Conference (2015, May 11)

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See detailCritical analysis and alternative processing of Type Ia supernovae data
Hauret, Clémentine ULiege; Magain, Pierre ULiege

E-print/Working paper (2015)

Context: Type Ia Supernovae (SNIa) observations in the late 90’s were the first hints for an accelerated expansion of our Universe. Today, hundreds of objects have been observed and seem to confirm the ... [more ▼]

Context: Type Ia Supernovae (SNIa) observations in the late 90’s were the first hints for an accelerated expansion of our Universe. Today, hundreds of objects have been observed and seem to confirm the flat LambdaCDM model as the cosmological model best representing our Universe. Aims: We study the SNIa observations gathered in the Union 2.1 and in the JLA compilations. By analyzing correlations and different ways of comparing cosmological models to the data, we bring to light some statistical biases, due to the current way of computing SNIa luminosity corrections for light-curve shape, color and host galaxy mass. Methods: We suggest an alternative, safer and model-independent methodology to calibrate the luminosity corrections, using only nearby SNIa. Results: With our recalibrated data, biases are strongly reduced. Moreover, open cosmological models are shown to be favoured over flat models (Omega_m,0 = 0.26+-0.08, Omega_Lambda,0 = 0.66+-0.12 for the SCP compilation and Omega_m,0 = 0.20+-0.08, Omega_Lambda,0 = 0.56+- 0.13 for the JLA one). Conclusions: The usual method to process SNIa data, i.e. simultaneously determining the parameters of the cosmological model and of the luminosity corrections on the full sample, is prone to bias the data in favour of the assumed cosmology, currently a flat LambdaCDM model, as well as to bias the cosmological parameters of the assumed model. [less ▲]

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See detailOn the nature of cosmological time
Magain, Pierre ULiege; Hauret, Clémentine ULiege

E-print/Working paper (2015)

Time is a parameter playing a central role in our most fundamental modeling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative ... [more ▼]

Time is a parameter playing a central role in our most fundamental modeling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motions and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks, i.e. clocks at rest with respect to the expanding space. This proper time is assumed to flow at a constant rate throughout the whole history of the Universe. We make the alternative hypothesis that the rate at which cosmological time flows depends on the dynamical state of the Universe. In thermodynamics, the arrow of time is strongly related to the second law, which states that the entropy of an isolated system will always increase with time or, at best, stay constant. Hence, we assume that time measured by fundamental clocks is proportional to the entropy of the region of the Universe that is causally connected to them. Under that simple assumption, we build a cosmological model that explains the Type Ia Supernovae data (the best cosmological standard candles) without the need for exotic dark matter nor dark energy. [less ▲]

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See detailDo we need dark matter in cosmology?
Magain, Pierre ULiege; Hauret, Clémentine ULiege

Conference (2014, November 19)

Detailed reference viewed: 45 (16 ULiège)