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Deep photometric survey of zenith sky atNainital and study of optically variablecelestial eventsSYNOPSISSubmitted toSCHOOL OF STUDIES IN PHYSICS AND ASTROPHYSICSPT. RAVISHANKAR SHUKLA UNIVERSITY, RAIPUR(CHHATTISGARH), INDIAOn the Partial fulfillment of the requirement for the registrationinDoctor of Philosophy in PhysicsSupervisorDr. Brijesh KumarScientist-E,ARIES, Manora Peak,Nainital 263002, Uttarakhand, IndiaSubmitted byPankaj SanwalARIES, Manora PeakNainital – 263002, Uttrakhand, IndiaResearch CenterARYABHATTA RESEARCH INSTITUTE OF OBSERVATIONAL SCIENCES(ARIES), MANORA PEAKNAINITAL 263002, UTTARAKHAND, INDIA2016Work proposed to be done for the Ph.D degree in Physics of the Pt.Ravishankar Shukla University, RaipurbyMr. Pankaj SanwalAryabhatta Research Institute of Observational Sciences(ARIES), Manora PeakNainital 263002, Uttarakhand, India1. Thesis title : Deep photometric survey of zenith sky at Nainital and study ofoptical variable celestial events.2. Name of the Supervisor : Dr. Brijesh KumarScientist-E,ARIES, Manora Peak,Nainital- 263002, Uttarakhand,India3. Name of Research Institute : Aryabhatta Research Institute of Observational Sciences(ARIES), Manora PeakNainital- 263002, Uttarakhand, India1IntroductionAstronomical events that show brightness changes at optical wavelengths ranging froma thousandth of a magnitude to as much as twenty magnitudes over periods of a fractionof a second to years, are called optically variable events. Such events provide uniqueopportunity to study stellar properties, such as mass, radius, luminosity, temperature,internal and external structure, composition, and evolution. Variable stars are classifiedas either extrinsic, wherein variability is caused by the eclipse of one star by another,the transit of an extrasolar planet or by the effects of stellar rotation (e.g. non sphericalstars), or intrinsic, wherein variability is caused by physical changes such as eruptionor pulsation in the star or stellar system (e.g. Supernovae, Active Galactic Nuclie,Cepheids).Supernovae are exploding stars, the very final stages of evolution for some stars,that releases tremendous energy. All supernovae are produced via one of two differentexplosion mechanisms. The thermonuclear explosion of a white dwarf which has beenaccreting matter from a companion is known as a Type Ia Supernova, while the core-collapse of massive stars produce Type II, Type Ib and Type Ic supernovae. Supernovaeplay a key role in the synthesis of heavy elements and also signal the birth of neutronstars and black holes. These important and enigmatic astrophysical objects form fromthe cooling post supernova remnant and are the basic building blocks of other astrophys-ical systems such as pulsars and x-ray binaries. Supernovae produce and disseminatemost of the nuclei found in the Universe. Elements heavier than helium, through theiron group, are synthesized during the course of stellar evolution, and via supernovae,are disseminated into the interstellar medium to be reprocessed later in new stars, solarsystems, and other astrophysical systems. Supernovae have been of great physical sig-nificance as there are many physical processes involved, however many questions remainunanswered such as the various interconnections between different supernovae types, var-ious physical properties of different subclasses of supernovae. Furthure,it was assumedthat these Supernovae explosions are spherically symmetric. Since we cannot spatiallyresolve the average extragalactic supernova, polarization is the most powerful tool whichallows to judge the shape of the ejecta.Observational set-up play a fundamental role in discovery and charactereization ofoptically variable events. Since the beginning of the observational astronomy, differentobservers were trying to compare results with each other. However, in absolute sense,every observational setup has different response functions, so the same astronomicalobjects will not be observed to have the same flux with any other observational setup.Differences in response come from many factors: size and condition of the telescope op-tics, bandpass and quality of the filters, response of the CCD. Thus, it is almost difficultto infer true fluxes. To deal with such problems, an accurate, internally consistent andreadily accesible standard star photometric sequences were necessary for the calibrationof the intensity and color data that astronomers obtain at the telescope. In early at-tempts, A.U. Landolt(1992) observed such standard stars mostly in an approximatelytwo degree band centered on the celestial equatorial systems so that observers around theglobe can calibrate any new observations against the known brightnesses of the standardstars. Such sources that are used in calibration and standardization of astronomical datacan be found everywhere within the sky, but with minimum extinction such sources areonly available at any observer’s zenith.2A brief review of work already done in the field(A) In 2011, the physics Nobel prize was awarded for the discovery of the acceleratingexpansion of the Universe through observations of distant supernovae. To find distancesin space, we use objects such as Supernovae as ‘standard candles’. As we know the truebrightness of such objects, we can measure their distance by analyzing how faint theyappear. Type Ia supernovae (SNe Ia) have been intensively investigated due to its greathomogeneity and high luminosity, which make it possible to use them as standardizablecandles for the determination of cosmological parameters.(B)A diverse class of type II events: IIP and IIL Type II Supernovae(SNe) havebeen essentially divided, based on the light curve shape, into Type IIL (showing a lineardecline) and Type IIP (showing a pronounced plateau over a long time). The plateauseen in SNe IIP lasts for up-to 100 days with a near constant brightness and is dom-inated by the hydrogen recombination phase. Type IIL have a steep decline in theirlight curve as compared to type IIP. Type IIL SNe on an average are more luminous,less pronounced P-Cygni profile and relatively small amount of Hydrogen. However,Anderson et al. (2014) and Sanders et al. (2014) suggested that the distinction couldbe solely due to the poor number of observed SNe. Also, historical distinction betweenIIP and IIL is insufficient for a complete mapping of SNe-II diversity. Anderson et al.(2014) suggested that if all SNIIL are followed for a long time,they will exhibit afterlinear decay a significant drop in the light curve. Based on a statistical analysis of IILevents Faran et al. (2014) suggested that any event having a decline of 0.5 mag in theV-band light curve in the first 50 days can be classified as IIL. In light of this recent de-velopment, a large number of SNe IIP may now be classified as IIL. This would providefurther evidence that IIL and IIP share the same underlying physics. Thus extensivemonitoring of both IIP and IIL events need to be done so as to estimate observable pa-rameters and progenitors properties of both the events and draw a correlation betweenthem.(C) Observations of Type IIP SNe have also been used to determine distances to theirhost galaxies by using the expanding photosphere method (EPM) by Bose & Kumar(2013), which is a variant of BaadeWesselink method, developed and implemented firstby Kirshner & Kwan (1974) for two SNe. The EPM provides an estimate of cosmologicaldistances, independent of the extragalactic distance ladder, and offers an alternative toverifying results obtained with other tools, e.g., SN Ia. Type IIP supernovae (SNe) arerecognized as independent extragalactic distance indicators; however, keeping in mindthe diverse nature of their observed properties as well as the availability of good qualitydata, more and newer events need to be tested for their applicability as reliable distanceindicators. We use early photometric and spectroscopic data of eight Type IIP SNe to de-rive distances to their host galaxies by using the expanding photosphere method (EPM).(D)Core Collapse Supernovae are often found to show a significant degree of po-larization in optical and infrared (IR) wavelengths (Wang & Wheeler1996; Leonard etal. 2001; Leonard & Filippenko 2001; Wang et al.2002a; Pereyra et al. 2006). SNe witha hydrogen envelope stripped (Type Ib/c) or partially stripped (Type IIb or IIn) exhibita higher level of polarization compared to SNe with an intact H envelope, such as SNeIIP (typically about 0.5 to 0.8 % polarization). The thick Hydrogen envelope obscuresthe observed asymmetry, whereas probing deeper towards the central part of the ex-plosion, more polarization is observed, which implies a higher degree of asymmetry inthe electron scattering atmosphere (Leonard & Filippenko 2005). However, in SNe IIP,polarization enhancement is observed towards the end of the plateau as the SN starts toenter the nebular phase, where the hydrogen recombination is close to completion and,with decreasing opacity, the inner asymmetric core is being revealed (e.g. SN 2004dj;Leonard et al. 2006). Generally, a moderate asphericity of 20 per cent would result in alinear polarization of 1 percent (Leonard & Filippenko 2005). Besides asphericity in theelectron scattering atmosphere, some amount of polarization might also originate fromscattering by the dust environment (Wang & Wheeler 1996), clumps in ejecta, the asym-metric distribution of radioactive 56Ni (Chugai 2006) or the asymmetric ionization of theouter envelope due to shock produced in the circumstellar medium (CSM) interaction.The explosion mechanism imposes some axial symmetry. Thus, extensive monitoringof CCSNe using polarimetry is necessary to yield the asphericity of the explosion andasymmetry alignment of the explosion.3Objectives1. As the Supernovae do not form a homogeneous class of objects, there is no satisfactoryexplanation about the explosion mechanism, neither we have the clear answer about theprogenitor properties. We propose to carry out optical analysis of Supernovae andintend to characterize the progenitor properties i.e. the peak absolute magnitude, Ni-56mass,ejecta mass, kinetic energy of the ejecta, photospheric velocity by studying thelight curves by performing analytic model fits (Arnett model,1982) to the bolometricluminosity light curves.For the Polarimetric observations of Supernovae, the longer we see the closer we seeto the centre, the larger is the asymmetry. We think that this suggests that asymmetryis not some incidental aspect of the progenitors surrounding environment that is causingthe polarization, but something deep in the heart of the explosion. The implication isthat the explosion mechanism itself is asymmetric. We expect that the Polarimetricobservations will unveil the mystery behind the explosion mechanism .2. We aim to produce a unique database that will allow to accurately calibrate ourdata using high quality standards obtained at zenith sky of Nainital. This sky surveywill also be helpful for the upcoming “International Liquid Mirror Telescope (ILMT)”which will continuously monitor the strip of sky passing through the Zenith and huntfor optical variable events. ILMT will be installed at Devasthal (India) where it willmonitor a strip of sky of 0.5 ? at the declination equal to Devasthal(29.4 ? ). As the bothsites ARIES Manora Peak and Devasthal share same latitude, they share the same skyhence the data obtained using 104cm ST, 130cm DFOT and ILMT will be standardizedand calibrated by using our zenith sky survey. If any optically variable event occurs inthe sky survey strip, this survey will also be useful in obtaining template subtraction.4Noteworthy contribution in the field of proposedwork and current statusFor our proposed work we have been continously observing the zenith strip. The datahas been taken in UBVRI filters and it ranges in Right Ascension between 21 hours to14 hours whereas the declination of all frames is fixed i.e. 29.4 ? . Thus, so far we haveobserved 21 different zenith fields with Landolt standards using 104cm SampurnanadTelescope and 130cm Devasthal Fast Optical Telescope.We have observed some cluster fields which are listed below :Cluster NameRight Ascension DeclinationKing 2 00h 51m 00s 58d 11m 00sNGC 609 01h 36m 23s 64d 32m 00sBerkeley 67 04h 37m 49s 50d 46m 00sNGC 1896 05h 25m 40s 29d 17m 59sCzernik 23 05h 49m 42s 28d 56m 00sNGC 2165 06h 11m 04s 51d 40m 36sNGC 6866 20h 03m 55s 44d 09m 30sAlong with this work, we are continously monitoring a Supernona 2016gkg discoveredon 2016/09/20.248 at Right Ascension = 01h 34m 14s.460, Declination = -29d 26m 25s,Located 49″.1 west and 78”.4 south of the center of NGC 613. We are observing this Su-pernovae with an observing frequency of atleast twice a week in Johnson-Kron-CousinsUBVRI filters using ARIES 104cm and 130cm Telescopes. The Data is being analysedusing standard data reduction (IRAF) and plotting (SM) packages.5Proposed methodology1. For the proper follow-up of Supernovae in optical band, we will be using variousnational and international facilities.(i) For Photometric properties we will be using1.04m-Sampurnanad Telescope(ST), ARIES1.3m-Devastal Fast Optical Telescope(DFOT), ARIES.(ii) For spectral and polarisation properties of Supernovae will be studied using :1.04m-Sampurnanad Telescope(ST), ARIES3.6m-Devsathal Optical telescope(DOT),ARIES.2. For the Deep photometric survey of zenith sky at Nainital, during observationsthe telescope will be kept at the constant declination equal to the latitute of the ob-servatory(i.e. 29.4 ? same for ARIES ST and ARIES DFOT) and the strip of sky willbe observed in Johnson-Kron-Cousins Broadband UBVRI photometric system. For thissurvey, we will be using following facilities1.04m-Sampurnanad Telescope(ST), ARIES1.3m-Devastal Fast Optical Telescope(DFOT), ARIES.6Expected outcome of the proposed workWe will be able to characterize the progenitor properties by studying the light curves ofvarious Supernovae. Polarimetric analysis will provide details about explosion mecha-nism of Supernovae. Zenith sky survey will provide an unique database that will allow toaccurately calibrate our data using quality standards obtained at zenith sky of Nainital.7ReferencesAnderson, J. P., Dessart, L., Gutierrez, C. P., et al. 2014a, MNRAS, 441, 671Arnett W.D et al., 1982, ApJ, 263L, 55ABose & Kumar et al. 2013 MNRAS 433, 18711891Bose et al. 2015, ApJ 806, 160Chevalier et al. 2006, ApJ 651, 381-391Chugai et al. 2006, Astronomy Letters, Vol. 32, Issue 11, p.739-746Faran et al. 2014, MNRAS 442, 844-861Fillipenko et al. 1993 ApJ 415, L103-L106Landolt A. U et al., 1992, AJ, 104, 340Leonard et al. 2001, PASP, Volume 113, Issue 786, pp. 920-936Turatto et al. 2014 IAUWang et al. 1996 Astrophysical Journal Letters v.462, p.L27Wheeler et al. MNRAS 450, 12951307 (2015)Signature of SupervisorSignature of CandidateForwardedDirectorARIES, Nainital

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