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Spectroscopic Study Of Selected Be Stars In Our Galaxy
The optical spectroscopic monitoring observation of two Be stars namely 4 Hercules and 88 Hercules was observed with 1.02m telescope at the VBO, Tamil Nadu, India over a period of six months. The spectra were reduced using standard routines in IRAF. The equivalent width of the lines were identified have been measured. The line profile variability exhibited by H? H?and HeI lines are studied to understand the emission mechanism in the Classical Be-stars. The properties of the process can be well constrained, leaving only few options, most importantly, but not exclusively, non-radial pulsation and small scale magnetic fields. In different stars different processes may be acting. This is not only true for the disk structure, but as well for its variability, both cyclic and secular. Be stars, at lower metallicities, seem more common and more rapidly rotating. The Be phenomenon, linked with one or more mass ejection processes, acts on top of a rotation rate of about 75% of critical or above. In this work, first the definition of Be-stars is contrasted to similar classes, and common observables obtaind for Be-stars are introduced and the respective formation mechanism explained. The current state of knowledge concerning the central stars as non-radially pulsating objects and non-magnetic stars, as far as it concerns large scale. The weak magnetic fields remain possible, but are of yet unproven. In this dissertation Chapter 1 discusses the features of Be- stars and reviewed the progress made in understanding Be-stars in the recent past. Chapter 2 discusses the literature review. Chapter 3 describes the methodology carried out to study the objective. Chapter 4 explains the result and analysis part of the research. Chapter 5 is about the conclusions. -
Spectroscopic Study of Late-type Emission-line Stars Using the Data from LAMOST DR6
Low-mass emission-line stars belong to various evolutionary stages, from pre-main-sequence young stars to evolved stars. In this work, we present a catalog of late-type (F0 to M9) emission-line stars from the LAMOST Data Release 6. Using the scipy package, we created a Python code that finds the emission peak at H? in all late-type stellar spectra. A data set of 38,152 late-type emission-line stars was obtained after a rigorous examination of the photometric quality flags and the signal-to-noise ratio of the spectra. Adopting well-known photometric and spectroscopic methods, we classified our sample into 438 infrared (IR) excess sources, 4669 post-main-sequence candidates, 9718 Fe/Ge/Ke sources, and 23,264 dMe sources. From a crossmatch with known databases, we found that 29,222 sources, comprising 65 IR excess sources, 7899 Fe/Ge/Ke stars, 17,533 dMe stars, and 3725 PtMS candidates, are new detections. We measured the equivalent width of the major emission lines observed in the spectra of our sample of emission-line stars. Furthermore, the trend observed in the line strengths of major emission lines over the entire late-type spectral range is analyzed. We further classified the sample into four groups based on the presence of hydrogen and calcium emission lines. This work presents a large data set of late-type emission-line stars, which can be used to study active phenomena in late-type stars. 2024 National Astronomical Observatories, CAS and IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved. -
Spectroscopic study of Herbig Ae/Be stars in the Galactic anti-centre region from LAMOST DR5
We study a sample of 119 Herbig Ae/Be stars in the Galactic anti-centre direction using the spectroscopic data from large sky area multi-object fiber spectroscopic telescope survey program. Emission lines of hydrogen belonging to the Balmer and Paschen series, and metallic lines of species such as Fe ii, O i, Ca ii triplet are identified. A moderate correlation is observed between the emission strengths of H? and Fe ii 5169 suggesting a possible common emission region for Fe ii lines and one of the components of H?. We explored a technique for the extinction correction of the HAeBe stars using diffuse interstellar bands present in the spectrum. We estimated the stellar parameters such as age and mass of these HAeBe stars, which are found to be in the range 0.1-10 Myr and 1.5-10 M, respectively. We found that the mass accretion rate of the HAeBe stars in the Galactic anti-centre direction follows the relation ?acc ? M?3.12-0.34+0.21, which is similar to the relation derived for HAeBe stars in other regions of the Galaxy. The mass accretion rate of HAeBe stars is found to have a functional form of ?acc ? t-1.10.02 with age, in agreement with previous studies. 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. -
Spectroscopic study of Be-shell stars: 4 Her and 88 Her
We present an optical spectroscopic study based on 41 spectra of 4 Her and 32 spectra of 88 Her, obtained over a period of 6 months. We estimate the rotational velocity of these stars from HeI lines in the blue spectral region (4000-4500 . We find that these stars are likely to be rotating at a fractional critical rotation of ?0.80. We measure the average I p/I c ratio to quantify the strength of the H? line and obtain 1.63 for 4 Her and 2.06 for 88 Her. The radius of the H? emission region is estimated to be Rd/R? ?5.0, assuming a Keplerian disk. These stars are thus found to be fast rotators with a relatively small H? emission region. We detect V/R variation of the H? spectral line during the observed period. We re-estimate the periods for both stars and obtain a period of ?46 d and its harmonic of 23.095 d for 4 Her, and a period of ?86 d for 88 Her. As these two cases are shell stars with binaries and have low H? EW with the emission region closer to the central star, the V/R variation and a change in period may be an effect of the binary on the circumstellar disk. 2016 National Astronomical Observatories, Chinese Academy of Sciences and IOP Publishing Ltd. -
Spectroscopic Studies on Structurally Modified Anthraquinone Azo Hydrazone Tautomer: Theoretical and Experimental Approach
A series of unique four mono-azo substituted anthraquinone analogue were synthesized by using the anthraquinone components in the diazo-coupling technique. The FT-IR, 1H NMR, and HRMS, data were used to confirm the structure of the molecules, and spectroscopic techniques like UV-Vis, and photoluminescence spectroscopy were employed to estimate the photophysical properties of the molecules. The molecular optimized geometry and frontier molecular orbitals were estimated using density functional theory. Further, global chemical reactivity descriptors parameter was theoretically estimated using the value of the highest occupied molecular orbit and lowest unoccupied molecular orbits. The anti-tubercular action of the synthesised dyes were also examined. The results of this biological activity showed that N-isopropyl aniline combined with anthraquinone N-isopropyl aniline had superior anti-tubercular activity when compared to Rifampicin as the standard. As per molecular docking studies, the synthesized compound Q1 showed excellent binding energy (-10.0kcal/mol) among all compounds against the 3ZXR Protein. These results agreed with our in-vitro anti-TB activity results. 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature. -
Spectroscopic Studies of Galactic Field Be Stars
Be stars provide excellent opportunity to study circumstellar disks. But the disc formation mechanism of classical Be (CBe) stars- the Be phenomenon- is still poorly understood. This can be understood by studying CBe stars in various locations like clusters and fields. Spectra of Be stars show interesting emission lines of different elements like hydrogen, helium, iron, oxygen calcium, etc. These emission lines are valuable indicators in providing information about the circumstellar disks of Be stars. In the past several decades various aspects of Be stars have been studied. But literature review clearly indicates the need of further studies to frame a consolidated picture about Be phenomenon in CBe stars. It is found that especially, the region ?????? 7500 - 8800 ??? is a less studied, and thus poorly understood area in Be star research. But this area shows some interesting features like emission lines calcium, iron, oxygen and Paschen series. So, here we have studied a sample of 118 field CBe stars taken from the catalogue of Jaschek & Egret (1982) and whose medium resolution spectra were obtained in ?????? 3800 ?? 9000 ??? region during December, 2007 to January, 2009 with the 2.1-m Himalayan Chandra Telescope (HCT), located at Hanle, Ladakh, India and operated by the Indian Institute of Astrophysics (IIA), Bangalore. In this thesis, we present three works which investigate the disc properties of our 118 program Be stars by studying their spectral line features, focussing primarily on the less explored ?????? 7500 - 8800 ??? region. Firstly, we have analyzed the less studied Fe II 7712 ??? emission line for our stars to understand the possible Fe II line excitation mechanism in CBe stars. Our work predicts that Ly???fluorescence may be the possible Fe II line excitation mechanism in CBe stars. Secondly, we have studied the Ca II triplet emission lines for our stars and have developed a new technique for deblending Ca II components from their counterpart Paschen lines, thus providing a more efficient way to analyze Ca II lines. Analyzing Ca II lines through this technique, we suggest that the gas producing these lines is optically thick. This leads us to predict that Ca II lines may be an indicator of binarity in Be stars. Lastly, we have estimated the Balmer decrement values, D34 and D54 for 81 of our sample stars to shed light on opacity effects in Be star disks. Our work confirms the disc transient nature of Be stars through epoch-wise D34 and D54 variation study and also suggests that Be star disks are optically thick. -
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Spectroscopic Studies and Theoretical Analysis of Some Selected Heterocycles
Seven derivatives of heterocycles benzimidazole, benzoxazole and benzothiazole were studied, five of which were synthesized and characterized. The molecular geometry and newlinespectroscopic data of the compounds in the ground state were calculated using the density functional theory (DFT/B3LYP) method with the 6-311++G(d,p) basis set. A comparison between the experimental and calculated data was attempted. Molecular electrostatic potential (MEP) and global reactivity parameters were deduced using theoretical calculations. HOMO-LUMO energy gap for each compound was determined by DFT and cyclic voltammetry. The cyclic voltammograms were recorded in acetonitrile solvent using lithium perchlorate as the supporting electrolyte. For all the compounds experimentally determined HOMO LUMO energy gap in polar solvent was lesser than that from DFT calculated energy gap. Using the HOMO-LUMO energy gap, global reactivity parameters were calculated. The effect of solvents of varying polarity on the absorption and emission spectra of the compounds was studied. Large excitation and emission energy differences were observed for all the selected heterocycles. The excitation and fluorescence spectra of selected heterocycles were recorded in eight solvents of different solvent polarity. It is evident from the excitation spectra that on increase of the solvent polarity, a bathochromic shift takes place for and#960;-and#960;* transition, and this is attributed to the high influence of solvent polarity in the excited state of heterocycle newlinecompared to its ground state. The dipole moments in the ground and the first excited state of heterocycle derivatives were newlinecalculated using Lippert-Mataga and Kawski-Chamma-Viallet methods. Guggenheim-Debye method was adopted to calculate ground state dipole moment. The dipole moments of the compounds were also calculated using Time Dependent-Density Functional Theory (TD-DFT). The dipole moment values of the compounds suggested that the excited state has more charge separation and thus becomes more polar. -
Spectroscopic parameters of red emitting Eu3 +-doped La2Ba3B4O12 phosphor for display and forensic applications
Eu3+-activated La2Ba3B4O12 (LBBO) phosphor was synthesized by the solid-state reaction method. LBBO phosphors characterized by structural analysis (X-ray diffraction), including refinement parameters and crystallite size, morphological analysis by (Scanning Electron Microscopy and Transmission Electron Microscopy). Photoluminescence (PL) studies of synthesized phosphors monitored in the range of 450-675 nm for the LBBO phosphor doped with Eu3 +. An excitation peak was found at 254nm and several sharp emission peaks were found around 466, 541, 588, 593, 613, and 626nm with high intensities. The crystallite size of the Eu3 +-doped LBBO phosphor was around 126nm. It is found that the intense emission peak is in the red region. The detailed processes involved and a possible mechanism for the PL are studied and discussed. The phosphor can also be used in forensic science to detect fingerprints. 2021 Elsevier Ltd All rights reserved. -
Spectroscopic investigation on shuttlecock-shaped liquid crystalline trimers: Mesomorphic behaviour and its application in optical storage devices
In this paper, we discuss the synthesis and characterization of 2,3,4-tris[n-((4-(-cyanophenyl)diazenyl)phenoxy)alkyloxy]benzonitrile obtained by coupling 2,3,4-trihydroxy benzonitrile and (E)-4-((4-((n-bromoalkyl)oxy)phenyl)diazenyl)benzonitrile, pertain to shuttlecock shaped liquid crystals. The molecular structure was confirmed by NMR spectroscopic and elemental analyzer. The thermal behavior of the trimers was assessed using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The three diazo groups in the trimers enabled us to study the photo-isomerization effect and evaluate their potential applications in optical storage devices. Importantly, we found these trimers easy to synthesize and process, paving the way for cost-effective alternatives to traditional LC materials. We fabricated an optical storage device to study the light effects on shuttlecock-shaped LC trimers, demonstrating that the geometry of the trimers plays a crucial role in determining structure-property relationships. 2024 -
Spectroscopic and TDDFT investigation of highly selective fluoride sensors by substituted acyl hydrazones
In this work, we report the synthesis of two receptors for fluoride ions based on acyl hydrazone, such as N?-[(1Z)-1-(4-fluorophenyl)ethylidene]benzohydrazide (R1) and N?-[(1Z)-1-(2-hydroxyphenyl)ethylidene]benzohydrazide (R2). The receptors R1 and R2 were synthesized from the corresponding ketones and benzoic acid hydrazide and characterized spectroscopically by UVvisible, IR and 1HNMR techniques. The response of R1 and R2 towards different anions was studied colourimetrically in acetonitrile. The receptors exhibited a specific response towards fluoride ions. Further studies of 1:1 composition of receptors, R1/R2:fluoride ions by different spectroscopic techniques such as UVVisible, IR and 1HNMR spectroscopy indicated the participation of -NH proton of the receptors in the sensing action through the hydrogen bonding. To understand the mechanism, Time-Dependent Density Functional Theory (TD-DFT) studies were done using the CAM-B3LYP/6311G++ (3df,2p) with Grimme's D3BJ empirical dispersion basis set. The studies supported the role of hydrogen bonding interaction of -NH and-OH protons of the receptors with the fluoride ions. 2020 Elsevier B.V. -
Spectroscopic analysis of lead borate systems
Oxide glass systems are interesting because of their bonding like bridging and non-bridging oxygens. Depending on the modifier, the B2O3 glass system can have various Boron-Oxygen network. It is found that, PbO modifies the borate network and increases the formation of penta and diborate groups. In this work, we investigated optical properties of Lead Borate glass systems (x PbO: (1-x) B2O3) with x varying from 30-85 mol % using UV-VIS Spectra and the corresponding band gap was estimated using Tauc relation and these systems behave like direct allowed band gap systems. These results show that, Eg decreases with the addition of lead content. Further the refractive index measurements also have been carried out at various wavelengths. Many correlation is found between the band gap and refractive index for different compositions. Using different theoretical models a best fit has been tried and Ravindra's relation is found to match with our experimental results. 2018 Author(s). -
Spectrochemical and theoretical approaches for acylhydrazone-based fluoride sensors
Abstract: Acylhydrazone derivatives N?-[1-(2-fluorophenyl)ethylidene]pyridine-3-carbohydrazide (R1) and N?-[2-fluorobenzylidene]benzohydrazide (R2) were synthesized from their corresponding hydrazides and characterized by spectroscopic methods. The response of these acylhydrazones towards different anions was studied by colorimetric and spectrofluorometric methods in acetonitrile. The receptors exhibited a specific response towards fluoride ion. The binding affinity of the receptors with fluoride anion was studied by fluorescence spectroscopic techniques and abinitio density functional theory calculations with Beckers three-parameter LeeYangPar (B3LYP) exchange functional with 6-311G basis set. Graphical abstract: [Figure not available: see fulltext.]. 2018, Springer Nature B.V. -
Spectro-temporal and type I X-ray burst analysis of GX 3+1 using AstroSat observations
GX 3+1, an atoll type neutron star low-mass X-ray binary, was observed four times by Soft X-ray Telescope and The Large Area X-ray Proportional Counter on-board AstroSat between 2017 October 5 and 2018 August 9. The hardness-intensity-diagram of the source showed it to be in the soft spectral state during all the four observations. The spectra of the source could be adequately fit with a model consisting of blackbody (bbody) and powerlaw (powerlaw) components. This yielded the blackbody radius and mass accretion rate to be ?8 km and ?2 10?9 M? y?1, respectively. In one of the observations, a type I X-ray burst having a rise and e-folding time of 0.6 and 5.6 s, respectively, was detected. Time-resolved spectral analysis of the burst showed that the source underwent a photospheric radius expansion. The radius of the emitting blackbody in GX 3+1 and its distance were estimated to be 9.19 +?00.8297 km and 10.17 +?00.1807 kpc, respectively. Temporal analysis of the burst yielded upper limits of the fractional root mean square amplitude of 7 per cent, 5 per cent, and 6 per cent during burst start, burst maximum, and right after the radius expansion phase, respectively. 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. -
Spectral quasi-linearization and irreversibility analysis of magnetized cross fluid flow through a microchannel with two different heat sources and Newton boundary conditions
Fluid flow in a microchannel with heat transport effects can be seen in various applications such as micro heat collectors, mechanicalelectromechanical systems, electronic device cooling, micro-air vehicles, and micro-heat exchanger systems. However, little is known about the consequence of internal heat source modulations on the flow of fluids in a microchannel. Therefore, in this work, the heat transfer of a magnetized cross fluid is carried out in a micro-channel subjected to two different heat source modulations. Entropy production analysis is also performed. The mathematical model consists of a cross fluid model. In addition, the effects of Joule heating, external magnetism, and the boundary conditions of Newton's heating are also examined. Determinant equations are constructed under steady-state conditions and parameterized using dimensionless variables. The numerical spectral quasi-linearization (SQLM) method was developed to interpret the Bejan number, entropy production, temperature, and velocity profiles. It is established that the power-law index of the cross fluid reduces the magnitude of the entropy production, velocity, and thermal field in the entire microchannel region. Furthermore, a larger Weissenberg number is capable of producing greater entropy, velocity, and thermal fields throughout the microchannel region. The variation in temperature distribution is more noticeable for the ESHS aspect than the THS aspect. The values of the pressure gradient parameter and the Eckert number must be kept high for maximum heat transport of the cross fluid. The entropy production of the cross fluid increases significantly with the physical aspects of Joule heating and convection heating in the system. 2021, The Author(s), under exclusive licence to SocietItaliana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature. -
Spectral Properties of the Soft X-Ray Transient MAXI J0637-430 Using AstroSat
Soft X-ray transients are systems that are detected when they go into an outburst, wherein their X-ray luminosity increases by several orders of magnitude. These outbursts are markers of the poorly understood change in the spectral state of these systems from the low/hard state to the high/soft state. We report the spectral properties of one such soft X-ray transient: MAXI J0637-430, with data from the SXT and LAXPC instruments on board the AstroSat mission. The source was observed for a total of ?60 ks in two observations on 2019 November 8 and 21 soon after its discovery. Flux-resolved spectral analysis of the source indicates the presence of a multicolor blackbody component arising from the accretion disk and a thermal Comptonization component. The stable low temperature (?0.55 keV) of the blackbody component points to a cool accretion disk with an inner disk radius of the order of a few hundred kilometers. In addition, we report the presence of a relativistically broadened Gaussian line at 6.4 keV. The disk-dominated flux and photon power-law index of ?2 and a constant inner disk radius indicate the source to be in the soft state. From the study we conclude that MAXI J0637-430 is a strong candidate for a black hole X-ray binary. 2022. The Author(s). Published by the American Astronomical Society. -
Spectral characteristics of the black hole binary 4U 1957+115: a multi mission perspective
We report spectral analysis of the persistent black hole X-ray binary, 4U 1957+115, using AstroSat, Swift, and NuSTAR observations carried out between 2016 and 2019. Modelling with a disc emission, thermal Comptonization, and blurred reflection components revealed that the source was in the high-soft state with the disc flux ?87 per cent of the total and high-energy photon index ?2.6. There is an evidence that either the inner disc radius varied by ?25 per cent or the colour hardening factor changed by ?12 per cent. The values of the inner disc radius imply that for a non-spinning black hole, the black hole mass is < 7 M ? and the source is located > 30 kpc away. On the other hand, a rapidly spinning black hole would be consistent with the more plausible black hole mass of < 10 M ? and a source distance of ?10 kpc. Fixing the distance to 10 kpc and using a relativistic accretion disc model, constrained the black hole mass to 6 M? and inclination angle to 72. A positive correlation is detected between the accretion rate and inner radii or equivalently between the accretion rate and colour factor. 2022 The Author(s). -
Spectral and type I X-ray burst studies of 4U 1702?429 using AstroSat observations
4U 1702?429, an atoll-type neutron star low-mass X-ray binary, was observed twice by the AstroSat/Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counters (LAXPC-20) on 2018 April 27 and 2019 August 8. Persistent emission spectra of the source were well fitted with the model combination - constant tbabs (thcomp diskbb+powerlaw). The parameters obtained from the spectral analysis revealed the source to be in a hard spectral state during the observations. Time-resolved spectral analyses were performed on the three type I X-ray bursts detected from the source. Burst analysis showed that the source underwent a photospheric radius expansion. Consequently, the radius of the neutron star and distance to the source (with isotropic and anisotropic burst emission) were obtained as 12.65+?008690 km and 6.92+?000916 and 8.43+?001020 kpc, respectively. 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. -
Spectral and Timing Properties of Selected Black Hole Binaries
X-ray binaries hosting a black hole (accretor) and a main sequence or a post-main sequence star (companion star) are called black hole X-ray binaries (BHXBs). BHXBs are gravitationally bound systems where the matter from the companion star is accreted onto the accretor either via a Roche lobe overand#64258;ow (low-mass companion star) or stellar wind (high-mass companion star). The accreted matter spirals towards the accretor, losing its angular momentum in the process. The gravitational potential energy of the in-falling matter is converted to kinetic energy which is eventually released as X-rays. X-ray spectrum of BHXB is quite complex by nature, which is contributed by various X-ray production processes. Systematic and comprehensive investigations of the X-ray production mechanisms are essential for understanding the fundamentals of accretion physics and exploring the general relativistic effects in extreme gravity environments. Launch of several dedicated X-ray missions like Uhuru, Ginga, RXTE, Chandra, XMM-Newton, NuSTAR, Swift, etc. for over half a century have led to the discovery, classifcation and fair understanding of spectro-temporal properties of BHXBs. Despite the continuous and ongoing newlineefforts, the physics of the accretion mechanism in BHXBs, accretion disk geometry, the origin of quasi periodic oscillations (QPOs), energy-dependent time lags and coherence of X-ray photons in different energies, etc., are yet to be completely understood. Hence, there is a need for newlinerevisiting these problems using the data from more sensitive instruments, that have broadband energy coverage and have better spectral and timing resolutions than RXTE. Thus, data from the latest missions like AstroSat, Swift, NuSTAR with their broadband energy coverage, especially in the lower energy regime (and#8804; 3.0 keV), and larger effective area can help fll in the gap in the newlineexisting body of knowledge and provide a holistic understanding of these sources. -
Spectral and temporal studies of Swift J1658.24242 using AstroSat observations with the JeTCAF model
We present the X-ray spectral and temporal analysis of the black hole X-ray transient Swift J1658.2-4242 observed by AstroSat. Three epochs of data have been analysed using the JeTCAF model to estimate the mass accretion rates and to understand the geometry of the flow. The best-fitting disc mass accretion rate (? d) varies between 0.90+-000102 and 1.09+-000304 M?Edd in these observations, while the halo mass accretion rate changes from 0.15+-000101 to 0.25+-000102 M?Edd. We estimate the size of the dynamic corona that varies substantially from 64.9+-3319 to 34.5+-1250 rg and a moderately high jet/outflow collimation factor stipulates isotropic outflow. The inferred high disc mass accretion rate and bigger corona size indicate that the source might be in the intermediate to soft spectral state of black hole X-ray binaries. The mass of the black hole estimated from different model combinations is ?14 M?. In addition, we compute the quasi-periodic oscillation (QPO) frequencies from the model-fitted parameters, which match the observed QPOs. We further calculate the binary parameters of the system from the decay profile of the light curve and the spectral parameters. The estimated orbital period of the system is 4.0 0.4 h by assuming the companion as a mid or late K-type star. Our analysis using the JeTCAF model sheds light on the physical origin of the spectrotemporal behaviour of the source, and the observed properties are mainly due to the change in both the mass accretion rates and absorbing column density. 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.