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Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements

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Research in Astronomy and Astrophysics 2013年第11期13卷 1363-1380页

作者： tapas baug Thyagarajan Chandrasekhar Physical Research Laboratory

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.

关键词： methods: analytical -- techniques: high angular resolution -- methods:lunar occultation -- infrared: stars -- stars: late type

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Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

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Research in Astronomy and Astrophysics 2024年第6期24卷 81-93页

作者： Arijit Manna Sabyasachi Pal tapas baug Sougata Mondal Department of Physics Midnapore City CollegePaschim MedinipurWest Bengal721129India S.N.Bose National Centre for Basic Sciences Block-JDSector-IIISalt Lake CityKolkata700106 India

The observation of oxygen(O)-and nitrogen(N)-bearing molecules gives an idea about the complex prebiotic chemistry in the interstellar *** millimeter and submillimeter wavelength observations have shown the presence of complex O-and N-bearing molecules in the star formation ***,the investigation of those molecules is crucial to understanding the chemical complexity in the star-forming *** this article,we present the identification of the rotational emission lines of N-bearing molecules ethyl cyanide(C_(2)H_(5)CN)and cyanoacetylene(HC_(3)N),and O-bearing molecule methyl formate(CH_(3)OCHO)toward high-mass protostar IRAS18089–1732 using the Atacama Compact *** also detected the emission lines of both the N-and O-bearing molecule formamide(NH_(2)CHO)in the envelope of IRAS 18089–*** have detected the v=0 and 1 state rotational emission lines of CH_(3)*** also detected the two vibrationally excited states of HC_(3)N(v7=1 and v7=2).The estimated fractional abundances of C_(2)H_(5)CN,HC_(3)N(v7=1),HC_(3)N(v7=2),and NH_(2)CHO toward IRAS 18089–1732 are(1.40±0.5)×10^(-10),(7.5±0.7)×10^(-11),(3.1±0.4)×10^(-11),and(6.25±0.82)×10^(-11)***,the estimated fractional abundances of CH_(3)OCHO(v=0)and CH_(3)OCHO(v=1)are(1.90±0.9)×10^(-9)and(8.90±0.8)×10^(-10),*** also created the integrated emission maps of the detected molecules,and the observed molecules may have originated from the extended envelope of the *** show that C_(2)H_(5)CNand HC_(3)N are most probably formed via the subsequential hydrogenation of the CH_(2)CHCNand the reaction between C_(2)H_(2)and CN on the grain surface of IRAS 18089–*** found that NH_(2)CHO is probably produced due to the reaction between NH_(2)and H_(2)CO in the gas ***,CH_(3)OCHO is possibly created via the reaction between radical CH_(3)O and radical HCO on the grain surface of IRAS 18089–1732.

关键词： ISM:individual objects(IRA 18089-1732)(except) ISM:abundances ISM:kinematics and dynamics stars:formation astrochemistry

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