Measuring the stellar atmosphere parameters using follow-up polarimetry microlensing observations

Elahe Khalouei

Physics Department, Sharif University of Technology

Abstract:  We present an analysis of the potential follow-up polarimetry microlensing observation to study the stellar atmospheres of the distant stars. First, we produce synthetic microlensing events using the Galactic model, stellar population, and interstellar dust toward the Galactic Bulge. We simulate the polarization microlensing light curves and pass them through the instrument specifications of FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT), and then analyze them. We find that the accuracy of the VLT telescope lets us constrain the atmosphere of cool RGB stars. Assuming detection of about 3000 microlensing events per year by the OGLE telescope, we expect to detect almost 20,~10,~8,  and 5 of polarization microlensig events for the four different criteria of being three consecutive polarimetry data points above the baseline with 1\sigma, 2\sigma, 3\sigma, and 4\sigma, respectively in the polarimetry light curves. We generalize the covariance matrix formulation and present the combination of polarimetry and photometry information that leads us to measure the scattering optical depth of the atmosphere and the inner radius of the stellar envelope of red giant stars. These two parameters could determine the dust opacity of the atmosphere of cool RGB source stars and the radius where dust can be formed.

یکشنبه 14 دی 1399، ساعت 15:00

Sunday 3 January 2021 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

A hint from Hubble: Does tension reveal the secrets of dark energy?

Abdolali Banihashemi

Physics Department of Shahid Beheshti University

Abstract: In this talk we will have a brief review on  tension and then we investigate, theoretically and observationally, a model in which dark energy emerges as a critical phenomenon.

یکشنبه 7 دی 1399، ساعت 15:00

Sunday 27 December 2020 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Dear colleagues,

We are organizing the virtual “Tehran Meeting on Cosmology at the Crossroads” for 22nd-25th February 2021. In this meeting which is the third one in its series, the challenges in LCDM will be discussed. We would appreciate it if you can circulate it with those you think are interested and encourage them to participate and or have a presentation.

Best regards,

Shant Baghram on behalf of Organizers

Dear Colleagues

Quantifying the impact of baryon-CDM perturbations on halo clustering and baryon fraction

Hasti Khoraminezhad

Scuola Internazionale Superiore di Studi Avanzati (SISSA)

Abstract: Baryons and cold dark matter (CDM) as the two dominant matter components of the Universe did not comove prior to recombination. This leads to differences in the local baryon and CDM densities, the so-called baryon-CDM isocurvature perturbations . These perturbations are usually neglected in the analysis of Large-Scale Structure data but taking them into account might become important in the era of high precision cosmology. In this talk first I will give a brief overview of isocurvature perturbations and how to measure the corresponding galaxy bias parameter . Then I will turn to various numerical tests to validate our simulation setup required for such perturbations. After that, I will present our results of the impact of such perturbations on the dark matter halos distribution through gravity-only 2-fluid simulations. I will concentrate particularly on the baryon fraction in halos as a function of mass and large-scale and also the measurements of cross-power spectrum between the halo field and  over a wide range of mass which is non-zero and negative showing that halo formation is impacted by . I will demonstrate the agreement between our measurements of the associated bias parameter  through 2-fluid simulations and the so-called separate Universe technique for only-CDM simulations. Finally, I will present the impact of these perturbations on halo-halo power spectrum and the fact that they could be degenerate with the effect of massive neutrinos for high redshift DESI-like surveys.

یکشنبه 23 آذر 1399، ساعت 19:00

Sunday 13 December 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Resolved Multi-element Stellar Chemical Abundances in Lensed Quiescent Galaxies at z ∼ 2

Marziye Jafariyazani

Carnegie Observatories & University of California, Riverside

Abstract: Measuring the chemical composition of galaxies is crucial to our understanding of galaxy formation and evolution models. However, such measurements are extremely challenging for quiescent galaxies at high redshifts, which have faint stellar continua and compact sizes, making it difficult to detect absorption lines and nearly impossible to spatially resolve them. Gravitational lensing offers the opportunity to study these galaxies with detailed spectroscopy that can be even spatially resolved. In this talk, I will first give an introduction on the chemical evolution modeling of galaxies and its current challenges. Then I will present my results on analyzing the spectra of MRG-M0138, the brightest lensed quiescent galaxy at z ~ 2. Taking advantage of full spectral fitting, I measure [Mg/Fe], [Fe/H] and, for the first time, the stellar abundances of 6 other elements in this galaxy. I further constrained, also for the first time in a z ∼ 2 galaxy, radial gradients in stellar age, [Fe/H], and [Mg/Fe]. I will discuss how these measurements challenge simple galactic chemical evolution models that vary only the star formation timescale and show the need for more elaborate models. Lastly, I will present our preliminary results on extending such measurements for a few more lensed quiescent galaxies at high redshifts.

یکشنبه 16 آذر 1399، ساعت 19:00

Sunday 6 December 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Probing the particle nature of dark matter with strong gravitational lensing

Yashar Hezaveh

Department of Physics, University of Montreal, Montreal, Canada

Abstract: The nature of dark matter is one of the most important outstanding questions in modern cosmology and astrophysics. Uncovering the properties of the dark matter particle could result in significant leaps in our understanding of fundamental physics and impact numerous astrophysical models. It is well understood that the microphysics of the dark matter particle impacts its clustering properties on different scales. The most widely accepted dark matter model, cold dark matter, has had tremendous success explaining the large-scale structure of the universe. However, it has faced many challenges for its predictions of the distribution of matter on small, sub-galactic scales, with some observations seemingly favoring a warm dark matter alternative. A definitive answer to this question can only be achieved by mapping the distribution of dark matter on small scales with a purely gravitational probe. Strong gravitational lensing is the only probe capable of doing this at cosmological distances. In this talk, I will discuss how the discovery of a new population of strong gravitational lenses, a new observatory, ALMA, and new advances in analysis methods are allowing us to map the distribution of dark matter on small scales with high precision. In the coming years, thousands of new lenses from large surveys (e.g., LSST), existing and new facilities (e.g., ALMA, JWST, TMT), and new analysis methods (machine learning) will transform this field, allowing us to understand the small-scale behavior of dark matter with unprecedented accuracy and precision, opening a new window for testing dark matter models in a previously inaccessible regime.

یکشنبه 9 آذر 1399، ساعت 17:00

Sunday 29 November 2020 – 17:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Planet demographics and atmospheres – The key to life beyond Earth?

Martin Dominik

School of Physics and Astronomy – University of St Andrews

 Abstract: It is widely portrayed that the study of planet demographics and atmospheres will provide us with crucial insight on whether biology is universal or life is a feature specific to planet Earth. This is far less straightforward than it might look like at first sight. Notably, there are substantial methodological gaps for advancing towards such goals and several current approaches might well turn out to result in a dead end.

یکشنبه 2 آذر 1399، ساعت 19:00

Sunday 22 November 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

4D Einstein-Gauss-Bonnet gravity

Zahra Haghani

School of Physics, Damghan University

Abstract: In this talk, I will consider the gravitational theory known as the “novel 4D Einstein-Gauss-Bonnet’’ gravity.  First I will have a short review on Lovelock theory and then introduce 4D Einstein-Gauss-Bonnet gravity. This theory has the same properties as GR in a maximally symmetric background and also at the perturbative level. This degeneracy will disappear in the static spherically symmetric and FLRW spacetimes.  In the static spherically symmetric space-time the Ricci scalar does not vanish due to the contributions from the Gauss-Bonnet term. In this case, we will have two branches of solutions. At large distances, one of these branches reduces to the Schwarzschild solution with positive gravitational mass. I will also consider matter perturbations and obtain the best-fit value of the model parameter using the Hubble parameter and fσ₈ observational data and compare results with the ΛCDM model.

یکشنبه 25 آبان 1399، ساعت 19:00

Sunday 15 November 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest

Baryon Acoustic Oscillations

Marc Moniez

Laboratoire de l’Accélérateur Linéaire (LAL), Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, IJCLab

Abstract: The propagation of primordial density fluctuations has given rise to the appearance of very large-scale correlations in the visible Universe. We will discuss some of the observables linked to this phenomenon, particularly in optical astronomy and radio astronomy, and we will review the impact of this cosmological probe in the determination of the cosmological parameters.

یکشنبه 18 آبان 1399، ساعت 19:00

Sunday 8 November 2020 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest