علیرضا طالبیان اشکذری (دانشکده فیزیک دانشگاه تهران)
Abstract: We study the evolution of the “non-perturbative” metric perturbations in a Bianchi background in the long-wavelength limit. By applying the gradient expansion to the equations of motion we exhibit a generalized “Separate Universe” approach to the cosmological perturbation theory. Having found this consistent separate universe picture, we introduce the δM formalism for calculating the evolution of the tensor perturbations in anisotropic inflation models in almost similar way as the so-called δN formula for the superhorizon dynamics of the curvature perturbations. Likewise its ancestor, δN formalism, this new method can substantially reduce the amount of calculations related to the evolution of the tensor modes.
Evolved stars as probes of galaxy formation and evolution
عاطفه جوادی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی -IPM)
Abstract: The evolution of galaxies is driven by the birth and death of stars. Nearby galaxies in the Local Group offer us a complete suite of galactic environments that is perfect for studying the connection between stellar populations and galaxy evolution. Therefore, the Local Group of galaxies offers a superb near-field cosmology site. Here, we can reconstruct the formation histories, and probe the structure and dynamics, of spiral galaxies as well as the many dwarf satellite galaxies surrounding the Milky Way and Andromeda, and of isolated dwarfs using the resolved stellar populations. In this talk, first I will introduce a near-IR monitoring campaign of the Local Group spiral galaxy M33, carried out with the UK IR Telescope (UKIRT). The pulsating evolved stars are identified and their distributions are used to derive the star formation rate as a function of age. I will outline the methodology and will present the results for the central square kiloparsec and for the disc of M33. Then, I will introduce an ongoing survey (started in June 2015) to monitor the Local Group dwarf galaxies accessible from La Palma with Isaac Newton Telescope (INT). We will use the luminosity distribution of the LPVs to reconstruct the star formation history – a method we have successfully applied in other Local Group galaxies.
On the origin of morphological differences in the powerful radio galaxies
حلیمه میرآقایی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی -IPM)
Abstract: Powerful radio galaxies display a very wide range of properties, both in their extended radio morphologies and in their optical spectra. We study the environment and host galaxy properties of radio galaxies with different radio morphologies from compact sources to very extended double lobed radio galaxies and with different optical spectra as high excitation (HERG; quasar-mode) and low excitation (LERG; jet-mode) radio galaxies in order to separate and distinguish the factors that drive the radio morphological variations from those responsible for the differences in spectral properties. We particularly compare i) compact sources with Fanaroff–Riley (FR) extended radio sources from the same class of excitation, ii) HERGs with the LERGs, iii) FR type I with the FR type II from the same class of excitation. We discuss the results and what causes the differences in each comparison.
نرگس جامی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی – IPM)
Abstract: Planetary systems are born in circumstellar gas and dust disks surrounding Young Stellar Objects (YSOs). To understand how planetary systems form, a detailed knowledge of the structure and evolution of these disks is required. Although, this is almost well understood for the regions of the disks observed with a spatial resolution of several AUs, the structure of these disks probed at a few AU scale and especially inward of 1 AU remains a puzzle. In recent years, it has become possible to directly spatially resolve the inner region of protoplanetary disks with optical interferometry technique, which will be detailed in my talk.
Closed FLRW model in loop quantum cosmology and its effective dynamics
آسیه کرمی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی – IPM)
Abstract: I will review the quantization and effective dynamics of closed FLRW model within loop quantum cosmology, paying special attention to the existence of an ambiguity in the quantization process. This ambiguity arises from different ways of defining the curvature operator. One definition is through closed paths and the other one is through open paths. For spatially flat models these two methods coincide and for spatially non-flat anisotropic models the first one is not admissible. However in the case of the closed FLRW model, one can apply both methods and they yield different quantum theories. In this talk I will show the different effective descriptions they provide of the bouncing cyclic universe. In particular, the most significant difference is that in the theory defined by the ‘open path’ method, there is not one, but two different bounces through which the cyclic universe alternates. Also, I will show that the quantum corrections of both theories can cure the unboundedness of matter density and expansion in effective phase space.
Convective dynamo action in a spherical shell: symmetries and modulation
Raphaël Raynaud
School of Astronomy – IPM
Abstract: We consider dynamo action driven by three-dimensional rotating anelastic convection in a spherical shell. Motivated by the behaviour of the solar dynamo, we examine the interaction of hydromagnetic modes with different symmetries and demonstrate how complicated interactions between convection, differential rotation and magnetic fields may lead to modulation of the basic cycle. For some parameters, Type 1 modulation occurs by the transfer of energy between modes of different symmetries with little change in the overall amplitude; for other parameters, the modulation is of Type 2, where the amplitude is significantly affected (leading to grand minima in activity) without significant changes in symmetry. Most importantly, we identify the presence of ‘supermodulation’ in the solutions, where the activity switches chaotically between Type 1 and Type 2 modulation; this is believed to be an important process in solar activity.
پذیرش محقق پسادکتری در گروه کیهان شناسی دانشکده فیزیک دانشگاه صنعتی شریف
بدین وسیله به اطلاع می رساند که گروه کیهان شناسی دانشکده فیزیک دانشگاه صنعتی شریف، از متقاضیان برای موقعیت محقق پسادکتری و همکاری با گروه کیهان شناسی به مدت یکسال دعوت به عمل می آورد.متقاضیان می توانند تقاضای خود را همراه شرح حال علمی (شامل مقالات)، پیشنهاد پژوهشی و دو توصیه نامه محرمانه را تا تاریخ یکم بهمن ماه 1395 به پست الکترونیکی دکتر سهراب راهوار با آدرس rahvar@sharif.edu ارسال فرمایند. موضوعات همکاری در زمینه کیهان شناسی و اخترفیزیک می باشد.
گروه کیهان شناسی دانشکده فیزیک دانشگاه صنعتی شریف
۲۵ مهرماه ۱۳۹۵
Postdoctoral Research position in Cosmology Group of SUT
Cosmology group of Physics Department – Sharif University of Technology invites applicants for a postdoctoral positions in field Astrophysics and Cosmology for one year appointment. The applicants are encouraged to send their CV including the list of publications, a statement of research interests and at least 2 confidential professional references, to Prof. Sohrab Rahvar, with the email address of rahvar@sharif.edu
The deadline of the application is 20 January 2017.
درجستجوی ناهمسانگردی با استفاده از ابرنواخترهای نوع Ia
Anisotropy search using Supernovae Type Ia
هدی قدسی (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: There are many successes regarding the standard model of cosmology but there are also problems with this model. A few of these relate to the existence of a preferred axis in the universe which undermines the assumption of isotropy and homogeneity of the standard model known as the cosmological principle. It is therefore of high importance to utilize probes such as Supernovae Type Ia, which are pretty useful for such an investigations owing to the practical redshift range they are found in. Several different methods have been employed in this field of research so far. In this talk I will go over our latest work in this regard.
مشاهدات ریزهمگرایی گرانشی: از تصاویر خام تا منحنی های نوری
Microlensing Observations: from crude images to light curves
صدیقه سجادیان (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: In a microlensing event, the light of a background source star is temporarily magnified owing to passing through the gravitational field of a massive foreground object. One of important advantages of microlensing observations is detecting cold and dark extra solar planets often located far from us. For this reason nowadays two survey and several follow up telescopes are probing ongoing microlensing events toward the Galactic centre. Consequently, many astronomers are busy to reduce the data of these events, i.e. converting crude images to light curves and then characterising the lens and source stars. In this talk, I will explain all steps for reducing the data of a microlensing event which are calibrating the images, finding a good reference images, doing difference photometry (DIA) and finally constructing a light curve. Then, I will discuss how to obtain the best fitted model to the resulted light curve through Markov Chain Monte Carlo (MCMC) simulation.
