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Kavli Institute for Cosmology, Cambridge

 
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Fri 10 Jun 13:15: Evidence of planet engulfment in post-main sequence stars

Fri, 10/06/2022 - 12:17
Evidence of planet engulfment in post-main sequence stars

The post-main sequence stellar evolution can have catastrophic consequences for orbiting planets. With the expansion of the star’s envelope during the red giant branch, some exoplanets are likely engulfed, producing changes in the surface chemical composition of the star. There are no clear chemical signatures that are unequivocally associated with this event, but enhancement of light elements that should be depleted on the surface of red giants can be considered indicators of engulfment. In this talk, I will discuss lithium as a signature of accretion of substellar companions in red giant branch stars. Although identifying individual engulfment events during the red giant evolutionary phase can be complicated, the death of a low-mass star provides new opportunities to study engulfment. Metals in the atmosphere of white dwarfs are signs of accretion of smaller planetary bodies. Thus, I will also show how these polluted white dwarfs offer a novel means to study the composition of rocky exoplanets and understand if they retain the same composition as the material from which they formed.

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Tue 14 Jun 13:00: Understanding the stars in our search for another Earth

Thu, 09/06/2022 - 15:38
Understanding the stars in our search for another Earth

To understand exoplanetary systems, we can study their mass-radius relationship or lack thereof. The HARPS -N Collaboration has been leading the efforts to fill and interpret the mass-radius diagram of small planets by combining space photometry, Gaia astrometry and radial velocities. Determining a precise as-well-as accurate planet mass can only be determined with well-sampled, stable, and precise observations combined with advanced computational efforts and new extraction and processing techniques. The biggest challenge remains the stellar activity processes, mimicking and hiding planetary signals. With the HARPS -N Collaboration, we have been studying the Sun-as-a-star for 6 years, providing a dataset where we truly have no planetary signals and can study stellar behaviour in more detail. In this talk, I will give an overview on the leading efforts of our collaboration to fill the mass-radius diagram, an insight in new LSD -based processing techniques, and the behaviour over time of the standard activity indicators using Solar data.

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Mon 13 Jun 13:00: Effects and uses of CMB lensing Zoom link: https://zoom.us/j/99304579109

Thu, 09/06/2022 - 12:48
Effects and uses of CMB lensing

Large-scale structure gravitationally lenses the cosmic microwave background, producing magnification, shear and rotation effects. I describe some useful and surprising effects of this, including new optimized measurements from Planck PR4 maps, lensing biases induced via masking, and how the small rotation effect may be observable using forthcoming CMB observations.

Zoom link: https://zoom.us/j/99304579109

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Thu 16 Jun 16:00: Stopping the Stars from Twinkling: monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications

Wed, 08/06/2022 - 14:50
Stopping the Stars from Twinkling: monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications

Turbulence in the Earth’s atmosphere can limit the precision of ground-based optical telescopes, both in terms of the angular resolution and the time-resolved photometry. I will present the progress in monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications. We have successfully developed a new turbulence monitor capable of operating continuously 24-hours a day, enabling support for both solar and night-time activities but also feeding into turbulence forecasting tools. The combination of these facilities allows us to model the propagation of light through the Earth’s atmosphere anywhere in the world. This is useful to select new sites, develop new instruments and optimise scheduling for existing observatories. I will also highlight the synergies between astronomical instrumentation and other exciting applications such as free-space optical communications and satellite tracking; areas where technical research staff can transfer their skills to make a significant impact in these emerging fields.

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Wed 08 Jun 13:45: Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

Mon, 06/06/2022 - 14:35
Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

In recent years, high-resolution transmission spectroscopy has emerged as one of the most successful techniques for detecting chemicals in transiting exoplanetary atmospheres. Despite many molecular detections to date, concerns have been raised about robustness when removing telluric and stellar features from the observed spectra, a step known as detrending. A robust detrending method has yet to be agreed upon, leaving previous detections inconsistent and sometimes irreproducible. We examine how overfitting detrending parameters can falsely amplify detection significances, and propose a robust methodology to select these parameters without introducing bias. To do this, we use CARMENES observations of the hot Jupiter HD189733b as a case study to investigate the robustness of different detrending optimisations. We find that selecting detrending parameters by optimising the difference between a signal-injected cross-correlation function and the observed cross-correlation function is robust against noise and spurious signals. On the other hand, optimising without this subtraction, as is often done, can induce spurious peaks and inflate detection significances. We reproduce previous detections with decreased significances reflecting more robust detrending. Our findings provide a robust framework for future homogeneous molecular surveys of exoplanetary atmospheres using high-resolution transmission spectroscopy.

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Mon 06 Jun 13:00: Surprising Dark Implications of a Supersymmetric Gravity Sector Zoom link: https://stonybrook.zoom.us/j/2816482971?pwd=TWpaN1hpd2laZzNxcGVJSkVGUVFDUT09.

Mon, 06/06/2022 - 11:32
Surprising Dark Implications of a Supersymmetric Gravity Sector

This talk explores surprises that emerge as consequences of accidental approximate scale invariances combined with a relatively supersymmetric gravity sector, both of which are argued to be robust consequences of UV physics (like string theory). Taken together these can be more than the sum of their parts, and suggest the low-energy world around us should consist of non-supersymmetric particle physics coupled to a rich dark sector built from supersymmetric gravity. A core prediction is that all particle masses arise proportional to the vev, v, of a dilaton field with the pattern where Standard Model masses, M, neutrino masses, m, and the Planck mass satisfy Mp/M \sim M/m \sim v, suggesting v is order 1e15. The framework also predicts the scalar potential for v, and this has both AdS and dS solutions without any need for problematic uplifting. The potential arises as a function of log v and so can give exponentially large values for v using only input parameters of order 70. Tantalizingly, at its minimum the potential evaluates to the fourth power of an energy E = (weak scale squared)/(Planck mass) that scales with v in the same way as a famous phenomenologically successful numerology. The prefactor is somewhat model-dependent, but in the known examples predicts the potential at its minimum to be suppressed by two powers of v (and five powers of log v), relative to the supersymmetry breaking scale in particle physics. For supersymmetry broken at 100 TeV this predicts a dark energy density of 1e(-91) in Planck units: not yet nailing the Dark Energy density—1e(-120)—but at least taping it down better than usual. Preliminary phenomenological implications are drawn assuming this framework eventually succeeds in further pushing down the minimum of V, and include intriguing cosmologies that (for free) seem to dynamically implement a recent proposal for resolving the Hubble tension (by modifying the electron mass around recombination).

Zoom link: https://stonybrook.zoom.us/j/2816482971?pwd=TWpaN1hpd2laZzNxcGVJSkVGUVFDUT09.

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Mon 06 Jun 13:00: Surprising Dark Implications of a Supersymmetric Gravity Sector Zoom link: https://zoom.us/j/93878540116.

Fri, 03/06/2022 - 10:41
Surprising Dark Implications of a Supersymmetric Gravity Sector

This talk explores surprises that emerge as consequences of accidental approximate scale invariances combined with a relatively supersymmetric gravity sector, both of which are argued to be robust consequences of UV physics (like string theory). Taken together these can be more than the sum of their parts, and suggest the low-energy world around us should consist of non-supersymmetric particle physics coupled to a rich dark sector built from supersymmetric gravity. A core prediction is that all particle masses arise proportional to the vev, v, of a dilaton field with the pattern where Standard Model masses, M, neutrino masses, m, and the Planck mass satisfy Mp/M \sim M/m \sim v, suggesting v is order 1e15. The framework also predicts the scalar potential for v, and this has both AdS and dS solutions without any need for problematic uplifting. The potential arises as a function of log v and so can give exponentially large values for v using only input parameters of order 70. Tantalizingly, at its minimum the potential evaluates to the fourth power of an energy E = (weak scale squared)/(Planck mass) that scales with v in the same way as a famous phenomenologically successful numerology. The prefactor is somewhat model-dependent, but in the known examples predicts the potential at its minimum to be suppressed by two powers of v (and five powers of log v), relative to the supersymmetry breaking scale in particle physics. For supersymmetry broken at 100 TeV this predicts a dark energy density of 1e(-91) in Planck units: not yet nailing the Dark Energy density—1e(-120)—but at least taping it down better than usual. Preliminary phenomenological implications are drawn assuming this framework eventually succeeds in further pushing down the minimum of V, and include intriguing cosmologies that (for free) seem to dynamically implement a recent proposal for resolving the Hubble tension (by modifying the electron mass around recombination).

Zoom link: https://zoom.us/j/93878540116.

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Wed 08 Jun 13:15: The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371

Wed, 01/06/2022 - 14:18
The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371

KUG 1141 +371 is a Seyfert 1 galaxy that shows a simultaneous flux increase in the optical and UV bands in the past decade. For instance, the Swift observations in 2019 show that the UVW2 flux of the AGN in KUG 1141 +371 has increased by over one order of magnitude since 2009. Meanwhile, the soft X-ray flux of KUG 1141 +371 also shows a steady increase by almost one order of magnitude from 2007 to 2019. The significant multi-wavelength luminosity change is likely due to a boost in mass accretion rate from approximately 0.6% of the Eddington limit to 3.2%, assuming a black hole mass of 100 million solar masses. I will present a detailed multi-epoch X-ray spectral analysis focusing on the variability of the X-ray continuum emission and the puzzling soft excess emission. In addition, our SED models also suggest a simultaneous increase in disc temperature and a decreasing inner disc radius along with the increasing accretion rate. Simultaneous ground-based optical observations show significant changes in the permitted line profiles and optical continuum. Finally, I will discuss the possible connection between KUG 1141 +371 and black hole transients in outburst.

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Fri 08 Jul 11:30: Title to be confirmed

Tue, 31/05/2022 - 19:33
Title to be confirmed

Abstract not available

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Tue 07 Jun 13:00: The LIFE mission - atmospheric characterization of terrestrial exoplanets in the mid-infrared with a large space-based nulling interferometer

Tue, 31/05/2022 - 13:42
The LIFE mission - atmospheric characterization of terrestrial exoplanets in the mid-infrared with a large space-based nulling interferometer

The LIFE initiative (LIFE = Large Interferometry For Exoplanets) has the goal to develop the scientific context, the technology and a roadmap for an ambitious mid-infrared nulling interferometer space mission that will allow humankind to detect and characterize the atmospheres of hundreds of nearby extrasolar planets including dozens that are similar to Earth. Additional motivation for the initiative is provided by the outcome of ESA ’s “Voyage 2050” process and the corresponding recommendations from the ESA Senior Committee: the direct detection of the thermal emission of temperate terrestrial exoplanets was given very high scientific priority and is considered as a candidate theme for a future L-class mission. In this talk I will discuss the scientific potential and unique discovery space for a mission like LIFE , in particular for the detection of atmospheric biosignatures. Synergies with, but also advantages over future NASA flagship missions will be described and an overview of ongoing technology developments and related challenges will be provided.

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Fri 03 Jun 13:00: Asymptotic Symmetries in Higher Dimensions

Tue, 31/05/2022 - 09:43
Asymptotic Symmetries in Higher Dimensions

We will briefly review some recent developments in Asymptotic Symmetries in 6 dimensions, although the results should extend to any even dimensions. We shall mainly discuss supertranslations in non-linear General Relativity and if time permits, we will also look at superrotations. Reference: https://arxiv.org/abs/2201.07813

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Mon 06 Jun 13:00: Surprising Dark Implications of a Supersymmetric Gravity Sector Zoom link: https://zoom.us/j/93878540116.

Tue, 31/05/2022 - 09:15
Surprising Dark Implications of a Supersymmetric Gravity Sector

This talk explores consequences of accidental approximate scale invariances combined with a relatively supersymmetric gravity sector, both of which are argued to be robust consequences of UV physics (like string theory). Taken together these can be more than the sum of their parts, and suggest the low-energy world around us should consist of non-supersymmetric particle physics coupled to a rich dark sector built from supersymmetric gravity. A core prediction is that all particle masses arise proportional to the vev, v, of a dilaton field with a pattern where Standard Model masses, M, neutrino masses, m, and the Planck mass satisfy Mp/M M/m v, suggesting v 10. The framework also predicts the scalar potential for v, and this has both AdS and dS solutions without any need for problematic uplifting. The potential arises as a function of log v and so can give exponentially large values for v using only input parameters of order log v 70. Tantalizingly, at its minimum the potential scales as V_min Mp4/v8, and so shares the scaling of the phenomenologically successful numerology V_min (M2/Mp)4. The prefactor is somewhat model-dependent, but in the known examples predicts V_min FF/[v2 (log v2)5], where FF = Ms4 sets the supersymmetry breaking scale in particle physics. For Ms 100 TeV and v 10{15} this predicts V_min 10 Mp4: not yet nailing the Dark Energy density (10 Mp4), but at least taping it down better than usual. Preliminary phenomenological implications are drawn assuming this framework eventually succeeds in further pushing down V_min, and include intriguing cosmologies that (for free) seem to dynamically implement a recent proposal for resolving the Hubble tension (by modifying the electron mass around recombination).

Zoom link: https://zoom.us/j/93878540116.

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Mon 06 Jun 14:15: Modelling and interpreting pulsations of rapidly rotating stars

Mon, 30/05/2022 - 11:32
Modelling and interpreting pulsations of rapidly rotating stars

The majority of intermediate mass and massive main sequence stars rotate rapidly. This affects their structure, evolution, lifetime, chemical yields, and final outcome. Modelling such stars is highly challenging due to the departure from spherical symmetry and is subject to many uncertainties. Hence, it is necessary to constrain these stars observationally in order to progress in our understanding of them. Asteroseismology, the study of stellar pulsations, is currently the only approach we have at our disposal for probing their internal structure, and is accordingly a particularly important source of information. However, as will be described in this seminar, it is necessary to overcome a number of hurdles to carry out asteroseismic investigations of such stars.

First of all, pulsation calculations must be carried out in a 2D context in order to fully include the effects of rotation. The geometry of the resultant pulsation modes can differ substantially from that of their non-rotating counterparts thus leading to a different mode classification. Likewise, the associated pulsation frequency spectra follow new patterns which are more complicated than in the non-rotating case. This leads to the next major hurdle which intervenes when trying to interpret observed pulsation spectra, namely mode identification, i.e. correctly matching theoretical modes with observed pulsation frequencies. Indeed, direct comparisons between the two typically yield multiple solutions due to the high density of theoretical frequencies compared with the observed ones. Therefore, current strategies for interpreting observed pulsations involve looking for specific frequency spacings, such as the large frequency separation and the rotation rate, and/or applying mode identification techniques based on multicolour photometric observations and spectroscopic observations of line profile variations, both of which need to be adapted to the rapidly rotating case. These interpretation strategies will be illustrated through various recent studies of observed stars.

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Wed 01 Jun 13:15: Reconstructed star-formation histories in MaNGA galaxies: Dependence on host galaxy properties and radial trends

Mon, 30/05/2022 - 09:46
Reconstructed star-formation histories in MaNGA galaxies: Dependence on host galaxy properties and radial trends

We developed a new methodology to reconstruct reliable non-parametric Star Formation Histories (SFHs) from full spectral fitting using the penalized pixel fitting code pPXF (Cappellari, 2017), and by adopting a bootstrapping re-sampling scheme in combination with weight regularization. We have applied this technique to 10,000 MaNGA SDSS galaxies and explored the SFHs as a function of galactocentric radius, host galaxy properties like stellar mass and star-formation state with high statistical significance.

Our spatially resolved analysis reveals cases of inside-out quenching in high mass galaxies and bulge building in low mass galaxies. Further, we recover the expected trends in the chemical enrichment histories of galaxies and the stellar fundamental metallicity relation (FMR). Additionally, very interestingly, our technique gives room for speculation about pristine gas accretion or lack thereof. Indeed, our analysis of MaNGA galaxies indicates the existence of young metal-poor populations (YMPP) in some populations of galaxies, potentially tracing stars formed by the recent accretion of metal-poor gas. Our spatially resolved analysis reveals cases of both centrally concentrated and extended YMPP . However, these findings are still subject to significant doubts and require further testing.

Finally, I will give a brief outlook to our planned investigation of the first quenched galaxies at high redshift from the cycle 1 observations obtained within the JWST NIR Spec GTO programme, and by using an adapted version of the methodology described above.

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Mon 30 May 14:00: Nonlinear interaction of tidal flows in the convective envelopes of low-mass stars or giant gaseous planets

Wed, 25/05/2022 - 14:04
Nonlinear interaction of tidal flows in the convective envelopes of low-mass stars or giant gaseous planets

In close exoplanetary systems, tidal interactions are known to shape the orbital architecture of the system, modify star and planet spins, and have an impact on the internal structure of the bodies through tidal heating. Most stars around which planets have been discovered are low-mass stars and thus feature a convective envelope, as is also expected in giant gaseous planets like Hot-Jupiter. The dissipation of tidal flows, and more specifically the dissipation of tidal inertial waves (restored by the Coriolis acceleration) can be particularly important in the convective envelopes, especially in the early stage of the life of the system. In parallel, the nonlinear self-interaction of inertial waves is known to affect the structure of the background flow by triggering differential rotation in convective shells, as shown in numerical and experimental hydrodynamical studies.

In this context, I will review and show how the addition of nonlinearities affects the tidal flow properties, the energy and angular momentum balances, thanks to 3D hydrodynamic nonlinear simulations of tides, in an adiabatic and incompressible convective shell. Using a realistic forcingto tidally excite inertial waves, we show that cylindrical differential rotation still develops in our model due to the non uniform deposition of angular momentum, when shear layers (straight structures where the waves are focused) are activated inside the shell. Moreover we do not observe unexpected angular momentum evolution leading to the desynchronisation of the bodies, as reported in some previous simulations. I willexplain to what extent and how the emergence of differential rotation is modifying the tidal dissipation rates, prior to linear predictions. Furthermore, nonlinear self-interactions of tidal inertial waves in the newly generated zonal flows can also trigger different kind of instabilities and resonances, when the tidal forcing is strong enough or the viscosity low enough. These various interactions between tidal inertial waves and sheared zonal flows reshape the energetic exchanges inside the shell, and also further modifies tidal dissipation rates.

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Mon 06 Jun 14:00: Modelling and interpreting pulsations of rapidly rotating stars

Wed, 25/05/2022 - 14:03
Modelling and interpreting pulsations of rapidly rotating stars

The majority of intermediate mass and massive main sequence stars rotate rapidly. This affects their structure, evolution, lifetime, chemical yields, and final outcome. Modelling such stars is highly challenging due to the departure from spherical symmetry and is subject to many uncertainties. Hence, it is necessary to constrain these stars observationally in order to progress in our understanding of them. Asteroseismology, the study of stellar pulsations, is currently the only approach we have at our disposal for probing their internal structure, and is accordingly a particularly important source of information. However, as will be described in this seminar, it is necessary to overcome a number of hurdles to carry out asteroseismic investigations of such stars.

First of all, pulsation calculations must be carried out in a 2D context in order to fully include the effects of rotation. The geometry of the resultant pulsation modes can differ substantially from that of their non-rotating counterparts thus leading to a different mode classification. Likewise, the associated pulsation frequency spectra follow new patterns which are more complicated than in the non-rotating case. This leads to the next major hurdle which intervenes when trying to interpret observed pulsation spectra, namely mode identification, i.e. correctly matching theoretical modes with observed pulsation frequencies. Indeed, direct comparisons between the two typically yield multiple solutions due to the high density of theoretical frequencies compared with the observed ones. Therefore, current strategies for interpreting observed pulsations involve looking for specific frequency spacings, such as the large frequency separation and the rotation rate, and/or applying mode identification techniques based on multicolour photometric observations and spectroscopic observations of line profile variations, both of which need to be adapted to the rapidly rotating case. These interpretation strategies will be illustrated through various recent studies of observed stars.

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Mon 30 May 13:00: Building SPT3G 2019/2020 likelihood Zoom link: https://zoom.us/j/96740399035

Wed, 25/05/2022 - 10:12
Building SPT3G 2019/2020 likelihood

The South Pole Telescope (SPT) is observing the CMB anisotropies with arcminute resolution using its state-of-the-art camera (SPT3G). Constraints on cosmological parameters from the obtained data will be as tight as Planck’s one, while remaining independent from the satellite experiment, thus allowing to test the consistency of the two dataset and investigate new physics. A reliable estimation of cosmological parameters requires accurate covariance matrices. In this talk, I will present my recent work on analytical pseudo-power spectrum covariance matrices for small survey area. First, I will introduce an efficient (but computationally expensive) exact calculation of such matrices. Then, using it as a reference, I estimate the accuracy of existing and new approximations of the covariance matrix. Finally, I will present solutions to mitigate the effect of point source masking.

Zoom link: https://zoom.us/j/96740399035

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Fri 01 Jul 11:30: Title to be confirmed

Wed, 25/05/2022 - 10:05
Title to be confirmed

Abstract not available

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Wed 15 Jun 16:00: In Search for the Next Magic Stone

Tue, 24/05/2022 - 15:38
In Search for the Next Magic Stone

Materials demarcate periods of human civilization. The current period can be argued as defined by silicon, the magic stone that transformed the way we live. In this talk, I will discuss how the concept of quantum, and the 1st wave of quantum revolution led to the rise of silicon, integrated circuit, Silicon Valley and the information age. I will then discuss the opportunities and challenges in materials where silicon class theory fails. The focus will be on modern spectroscopy tools in aiding the development of quantum many-body theory, by testing ideas, discovering surprises and benchmarking theories, aiming at a new wave of quantum, in search for the next magic stone.

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