Techniques d'observation spectroscopique d'astÃ©roÃ¯des

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60 CHAPTER 3. OBSERVING TECHNIQUES 1 Flat correction 2 tel-00785991, version 1 - 7 Feb 2013 2' 3 3' Bad pixel correction A-B Wavelength calibration 4 5 m m Figure 3.2: The data reduction procedure for NIR spectra obtained with IRTF/SpeX [Nedelcu, 2010].
CHAPTER 3. OBSERVING TECHNIQUES 61 atures. To remove this noise, an exposure is taken of similar length as the useful images,with the dome and shutter closed. These dark images can also be used to find dead or hot pixels. If dark frames are used, the CCD bias is contained within them and separate bias corrections are not necessary. Similarly, multiple dark exposures can be averaged to reduce the random readout noise by averaging them. This is called a "master dark file". Dark current is more significant in infrared arrays, and it may not be linear and scalable from different exposures [McLean, 2008]. tel-00785991, version 1 - 7 Feb 2013 Flat - Sensitivity variations from pixel to pixel arise as the result of fabrication processes and also due to optical attenuation effects such as microscopic dust particles on the surface of the CCD. A flat field image to correct for this effect is usually obtained by observing inside of the telescope dome (if it is matt or white) or place a huge white card on the dome. The dome is illuminated with a projector lamp. In this case the telescope is completely out of focus which ensures that the field is uniformly illuminated. For faint objects it is the light of the sky that dominates, and so it is better to try to use the sky itself as a flat-field. In other cases, as in photometry for instance, the flat field could be done using a sky region in the day light time (at the beginning and end of the night). Arc lamp - "arc" images are used to determine the pixel to wavelength correspondence, more exactly to make the wavelength calibration. Typically, the lamps used contain helium, neon, xenon, argon or a combination thereof. The emission lines from the spectrum of the arc lamp are at known wavelengths and can be identified. For the IRTF/SpeX a lamp with argon is available (Fig. 3.2). Standard star - A solar-like standard star spectrum taken at similar airmass is required to correct the atmospheric effects and to remove the signature of the Sun’s spectrum in order to have only the signature of the asteroid surface. The G2 stars are used with magnitudes (usually between 5 to 12) that allow to obtain a high SNR (signal to noise ratio) spectrum with a short integration time (a few seconds). If the star is too bright it will saturate the CCD, while a fainter star will require an unacceptably long integration time. The steps required for data reduction are figured in Fig. 3.2. These steps are described below: Acquisition of the images containing the spectra. The most important aspect that should be taken into account is the variation of the sky background. This effect is caused in principal by the chemical reaction of combination/recombination in ionosphere 2 . There are two techniques used to avoid this unwanted effect. First, the images are taken with an exposure time less than 120 sec. It is known that the variation of the sky background in an interval lower than 120 sec. could be neglected. Images with longer exposure time can be obtained by combining individual images with shorter exposure time. Second, the spectra are obtained alternatively 2 the most common name of these phenomena is airglow
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OBSERVATOIRE DE PARIS ÉCOLE DOCTOR
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tel-00785991, version 1 - 7 Feb 201
Page 9 and 10: Résumé: L’objectif fondamental
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Page 13 and 14: Acknowledgements tel-00785991, vers
Page 15 and 16: Dedicated to mygrandfather, IosifPo
Page 17 and 18: Contents Tables 22 Figures 27 I INT
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Page 21 and 22: List of Tables 2.1 The emission lin
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Page 65 and 66: 4 Spectral analysis techniques tel-
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CHAPTER 6. SPECTRAL PROPERTIES OF N
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7 Spectral properties of Main Belt
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CHAPTER 7. SPECTRAL PROPERTIES OF M
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8 Conclusions and perspectives tel-
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A The GuideDog and the BigDog inter
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B List of publications B.1 First Au
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APPENDIX B. LIST OF PUBLICATIONS 13
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Bibliography Adams, J. B. 1974. Vis
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BIBLIOGRAPHY 143 Brunetto, R., Vern
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BIBLIOGRAPHY 145 Donnison, J. R. 19
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BIBLIOGRAPHY 147 tel-00785991, vers
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BIBLIOGRAPHY 149 Popescu, M., Birla
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BIBLIOGRAPHY 151 tel-00785991, vers
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tel-00785991, version 1 - 7 Feb 201
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A&A 535, A15 (2011) Table 1. Log of
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A&A 535, A15 (2011) tel-00785991, v
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A&A 535, A15 (2011) Table 3. Summar
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A&A 535, A15 (2011) tel-00785991, v
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Band I center [um] 1.04 1.02 1 0.98
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A&A 544, A130 (2012) DOI: 10.1051/0
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M. Popescu et al.: M4AST - Modeling
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U.P.B. Sci. Bull., Series A, Vol. 7
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Applications of optical and infrare
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Mon. Not. R. Astron. Soc. 000, 000-
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Spectral properties of (854), (1333
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Vernazza P., Mothé-Diniz T., Baruc
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Techniques d'observation spectroscopique d'astÃ©roÃ¯des

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