Techniques d'observation spectroscopique d'astéroïdes
Techniques d'observation spectroscopique d'astéroïdes Techniques d'observation spectroscopique d'astéroïdes
62 CHAPTER 3. OBSERVING TECHNIQUES 1 0.8 Relative Flux 0.6 0.4 tel-00785991, version 1 - 7 Feb 2013 0.2 Asteroid Star 0 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] Figure 3.3: The raw spectra of an asteroid and standard star. The twos spectra are modulated by the absorption bands of the Earth atmosphere (essentially telluric water bands). at two separate locations along the slit (close to top - "A" and close to bottom - "B"). This is call the nodding procedure [Nedelcu, 2010]. In the low resolution mode of SpeX, spectra are acquired only in a band of 512x100 pixels of the CCD. Flat field corrections. The flat field images are made using a lamp based on Quartz- Tungsten-Halogen (T=3200 K). This procedure is applied at the beginning and at the end of the observing session, by taking 10 images each time. If a pixel value is greater than 10% of the neighboring pixels, it is considered as a bad pixel. Such pixels are replaced in all images (object images, flat fields and arc images and standard star images) with a value obtained from interpolation of neighboring pixel values. A "master flat" is obtained by combining and averaging all flat field images. The master flat field is subtracted from all images. Removing the sky background. The consecutive images A and B are subtracted (A-B and B-A) resulting new images containing two spectra: one with positive pixel values and another with negative pixel values (Fig. 3.2.3). Wavelength calibration. The wavelength calibration is made by identifying the emission lines of an Argon lamp. Thus, it results a correspondence between the pixel position on the x-axis and the wavelength (Fig. 3.2.3). Combining the images. The two spectra (corresponding to both positive and negative pixel values ) are identified in each image. The images are cut, only the positive spectrum being kept. A final spectral image (Fig. 3.2.4) is obtained for each object by gathering all its corresponding images (before summing all images they are aligned by the brightest trace). Extraction of the raw spectrum. The final point of this stage consists in summing the value
CHAPTER 3. OBSERVING TECHNIQUES 63 of the pixels from y axis corresponding to the spectrum of an object and extraction of these values in a file containing the wavelengths (in accord with the correspondence pixel position on x axis - wavelength) and the pixel values (Fig. 3.2.3). An example of such a raw spectrum is given in Fig. 4.1. The next part of the data reduction procedures consists in removing the influence of Earth atmosphere. This task is accomplished using some IDL routines that implements the atmospheric transmission (Atmospheric Transmission Model (ATRAN)) model by Lord [1992]. The final step consists in dividing the asteroid spectrum by the solar analog. In this way we obtain the relative reflectance spectrum of the asteroid. The NIR spectra presented in this thesis are normalized to 1.25 µm. tel-00785991, version 1 - 7 Feb 2013
- Page 11 and 12: tel-00785991, version 1 - 7 Feb 201
- 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
- Page 19 and 20: 7.4.2 (3623) Chaplin . . . . . . .
- Page 21 and 22: List of Tables 2.1 The emission lin
- Page 23 and 24: List of Figures 1.1 A field obtaine
- Page 25 and 26: 5.8 Asteroid spectra and the best t
- Page 27 and 28: tel-00785991, version 1 - 7 Feb 201
- Page 29 and 30: tel-00785991, version 1 - 7 Feb 201
- Page 31 and 32: 1 Why asteroids? tel-00785991, vers
- Page 33 and 34: CHAPTER 1. WHY ASTEROIDS? 33 tel-00
- Page 35 and 36: CHAPTER 1. WHY ASTEROIDS? 35 tel-00
- Page 37 and 38: CHAPTER 1. WHY ASTEROIDS? 37 tel-00
- Page 39 and 40: CHAPTER 1. WHY ASTEROIDS? 39 the fi
- Page 41 and 42: tel-00785991, version 1 - 7 Feb 201
- Page 43 and 44: 2 Why spectroscopy? spectrum. By ca
- Page 45 and 46: CHAPTER 2. WHY SPECTROSCOPY? 45 0.4
- Page 47 and 48: CHAPTER 2. WHY SPECTROSCOPY? 47 The
- Page 49 and 50: CHAPTER 2. WHY SPECTROSCOPY? 49 0.6
- Page 51 and 52: CHAPTER 2. WHY SPECTROSCOPY? 51 −
- Page 53 and 54: CHAPTER 2. WHY SPECTROSCOPY? 53 tel
- Page 55 and 56: tel-00785991, version 1 - 7 Feb 201
- Page 57 and 58: 3 Observing techniques tel-00785991
- Page 59 and 60: CHAPTER 3. OBSERVING TECHNIQUES 59
- Page 61: CHAPTER 3. OBSERVING TECHNIQUES 61
- Page 65 and 66: 4 Spectral analysis techniques tel-
- Page 67 and 68: CHAPTER 4. SPECTRAL ANALYSIS TECHNI
- Page 69 and 70: CHAPTER 4. SPECTRAL ANALYSIS TECHNI
- Page 71 and 72: CHAPTER 4. SPECTRAL ANALYSIS TECHNI
- Page 73 and 74: CHAPTER 4. SPECTRAL ANALYSIS TECHNI
- Page 75 and 76: CHAPTER 4. SPECTRAL ANALYSIS TECHNI
- Page 77 and 78: 5 M4AST - Modeling of Asteroids Spe
- Page 79 and 80: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 81 and 82: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 83 and 84: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 85 and 86: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 87 and 88: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 89 and 90: CHAPTER 5. M4AST - MODELING OF ASTE
- Page 91 and 92: tel-00785991, version 1 - 7 Feb 201
- Page 93 and 94: 6 Spectral properties of near-Earth
- Page 95 and 96: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 97 and 98: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 99 and 100: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 101 and 102: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 103 and 104: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 105 and 106: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 107 and 108: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 109 and 110: CHAPTER 6. SPECTRAL PROPERTIES OF N
- Page 111 and 112: CHAPTER 6. SPECTRAL PROPERTIES OF N
CHAPTER 3. OBSERVING TECHNIQUES 63<br />
of the pixels from y axis corresponding to the spectrum of an object and extraction of these<br />
values in a file containing the wavelengths (in accord with the correspondence pixel position<br />
on x axis - wavelength) and the pixel values (Fig. 3.2.3). An example of such a raw spectrum<br />
is given in Fig. 4.1.<br />
The next part of the data reduction procedures consists in removing the influence of Earth atmosphere.<br />
This task is accomplished using some IDL routines that implements the atmospheric<br />
transmission (Atmospheric Transmission Model (ATRAN)) model by Lord [1992].<br />
The final step consists in dividing the asteroid spectrum by the solar analog. In this way we<br />
obtain the relative reflectance spectrum of the asteroid. The NIR spectra presented in this thesis<br />
are normalized to 1.25 µm.<br />
tel-00785991, version 1 - 7 Feb 2013
Change language