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Search for Gas Giants Around Late-M Dwarfs

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University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2010 Search For Gas Giants Around Late-m Dwarfs Rohit Deshpande University of Central Florida Part of the Physics Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Doctoral Dissertation (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Deshpande, Rohit, "Search For Gas Giants Around Late-m Dwarfs" (2010). Electronic Theses and Dissertations, 2004-2019. 1562. https://stars.library.ucf.edu/etd/1562 SEARCH FOR GAS GIANTS AROUND LATE-M DWARFS by ROHIT DESHPANDE´ M.S. University of Central Florida, 2006 A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics in the College of Sciences at the University of Central Florida Orlando, Florida Summer Term 2010 Major Professor: Eduardo Mart´ın c 2010 Rohit Deshpand´e ii ABSTRACT We carried out a near-infrared radial velocity search for Jupiter-mass planets around 36 late M dwarfs. This survey was the first of its kind undertaken to monitor radial velocity vari- ability of these faint dwarfs. For this unique survey we employed the 10-m Keck II on Mauna Kea in Hawaii. With a resolution of 20,000 on the near-infrared spectrograph, NIRSPEC, we monitored these stars over four epochs in 2007. In addition to the measurement of relative radial velocity we established physical properties of these stars. The physical properties of M dwarfs we determined included the identification of neutral atomic lines, the measurement of pseudo-equivalent widths, masses, surface gravity, effective temperature, absolute radial velocities, rotational velocities and rotation periods. The iden- tification of neutral atomic lines was carried out using the Vienna Atomic line Database. We were able to confirm these lines that were previously identified. We also found that some of the lines observed in the K-type stars, such as Mg I though weak, still persist in late M dwarfs. Using the measurement of pseudo-equivalent widths (p-EW) of 13 neutral atomic lines, we have established relations between p-EW and spectral type. Such relations serve as a tool in determining the spectral type of an unknown dwarf star by means of measuring its p-EW. We employed the mass-luminosity relation to compute the masses of M dwarfs. Our calculations indicate these dwarfs to be in the range of 0.1 to 0.07 solar masses. This suggests that some of the late M dwarfs appear to be in the Brown dwarf regime. Assuming their radii of 0.1 solar radii, we calculated their surface gravity. The mean surface gravity is, log g = 5.38. Finally their effective temperature was determined by using the spectral-type iii temperature relationship. Our calculations show effective temperatures in the range of 3000 2300 K. Comparison of these values with models in literature show a good agreement. The absolute radial and rotational velocities of our targets were also calculated. Values of rotational velocities indicate that M dwarfs are, in general, slow rotators. Using our result and that from literature, we extended our study of rotational velocities to L dwarfs. Our observations show an increase in rotational velocities from late M to L dwarfs. We also find that the mean periods of M dwarfs are less than 10 hours. In order to improve our precision in measuring relative radial velocity (RV), we employed the use of deconvolution method. With this method we were able to ameliorate relative RV precision from 300 m/s to 200 m/s. This was a substantial improvement in our ability to detect gas-giant planets. However none of the 15 dwarfs we monitored indicate a presence of companions. This null result was then used to compute the upper limit to the binary frequency and close-in Jupiter mass planetary frequency. We find the binary frequency to be 11% while the planetary frequency was 1.20%. iv To my parents and brother v ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Mart´ın for his guidance, support and giving me the opportunity to work in the exciting field of exoplanets detection. Thank you to my committee, Dr. Britt, Dr. Campins, and Dr. Je for reviewing my thesis, listening to my talks and making construtive suggestions in improving it. Their questions over the years has helped me think deeply about the work I carry out. I would like to thank my family, especially my mother for her strength, support and with whom I spent countless number of hours on phone. This thesis would not have been complete without the help, guidance and support of Dr. Michele M. Montgomery. Discussions with her have greatly helped me in my work. Thank you to the Physics staff, Mike Jimenez, Felix Ayala, Monika Crittenden, Jessica Brookes and Pat Korosec. They have always helped me in my administrative needs. Thank you to my fellow graduate students, particularly Kevin Bailli´efor his help with Latex, statistics and hanging out in the evenings. I would like to thank Dr. Zapatero Osorio from whom I have learnt so much in terms of stellar spectroscopy. I owe my expertise in spectroscopy to her. Thank you to Dr. Rodler for his help in teaching me the deconvolution method and the computation of relative radial velocity. Lastly, I would like to thank SIMBAD whose database were used extensively for this work. Thank you to Fitzgerald and Frank Valdes at iraf.net for answering my queries. vi TABLE OF CONTENTS LIST OF FIGURES :::::::::::::::::::::::::::::::::::: xi LIST OF TABLES ::::::::::::::::::::::::::::::::::::: xvii CHAPTER 1: INTRODUCTION ::::::::::::::::::::::::::::: 1 1.1 Historical Perspective...............................1 1.2 Physical Properties of M Dwarfs.........................3 1.2.1 Effective Temperature..........................4 1.2.2 Gravity, Mass and Radii.........................6 1.2.3 Metallicity.................................8 1.3 Formation and Evolution of M dwarfs......................8 1.3.1 Formation Process............................8 1.3.2 Post Main Sequence Evolution...................... 11 1.4 State-of-the Art at the Beginning of My Thesis................ 13 1.4.1 Radial Velocity Technique........................ 13 1.4.2 Radial Velocity Surveys......................... 16 1.5 Open Questions and Goals of My Thesis.................... 18 1.5.1 Are there planets around late-M dwarfs?................ 18 CHAPTER 2: OBSERVATIONS ::::::::::::::::::::::::::::: 20 2.1 Sample Selection................................. 21 2.2 The NIRSPEC Instrument............................ 24 2.3 Observations.................................... 27 vii 2.3.1 Observing List.............................. 29 2.4 Summary..................................... 30 CHAPTER 3: DATA REDUCTION ::::::::::::::::::::::::::: 35 3.1 Factors Affecting Stellar Flux.......................... 35 3.2 General Reduction Procedure.......................... 41 3.3 REDSPEC and IRAF comparison........................ 48 3.3.1 REDSPEC reduction procedure..................... 48 3.3.2 IRAF reduction procedure........................ 51 3.3.3 Comparing the two methods....................... 52 3.4 Summary..................................... 59 CHAPTER 4: EQUIVALENT WIDTHS AND LINE IDENTIFICATION ::::::: 61 4.1 Spectral Lines and Line Identification...................... 61 4.2 Equivalent Width................................. 65 4.3 Line Identification in the spectra of M dwarfs.................. 66 4.4 Calculations of pseudo-Equivalent Width.................... 70 4.5 Summary..................................... 73 CHAPTER 5: RELATIVE AND ABSOLUTE RADIAL VELOCITIES OF M DWARFS 74 5.1 Relative and Absolute Radial Velocity..................... 74 5.2 Self-calibration Method: Calculation of Relative Radial Velocity....... 76 5.2.1 Step 1. Modeling the PSF........................ 78 5.2.2 Step 2: Creating a Telluric -free Template............... 84 5.2.3 Step 3. Modeling (T + S) & Computation of RV........... 88 viii 5.3 Calculation of Absolute Velocity......................... 91 5.3.1 Fourier cross-correlation (FXCOR) task in IRAF........... 94 5.4 Summary..................................... 98 CHAPTER 6: RESULTS ::::::::::::::::::::::::::::::::: 99 6.1 Identified lines................................... 99 6.2 Pseudo-equivalent width............................. 103 6.3 Physical Characteristics of M dwarfs...................... 124 6.3.1 Determination of Mass.......................... 124 6.3.2 Determination of Surface Gravity (log g)................ 127 6.3.3 Determination of Effective Temperature................ 129 6.3.4 Rotational Velocity............................ 131 6.4 Absolute Radial Velocity............................. 133 CHAPTER 7: DISCUSSION ::::::::::::::::::::::::::::::: 135 7.1 Line Identification................................. 135 7.2 Pseudo-Equivalent Widths............................ 138 7.2.1 Comparison of p-EW........................... 141 7.2.2 Relation between p-EW and Spectral Type............... 148 7.3 Comparison of M dwarf physical characteristics................ 149 7.3.1 Surface Gravity.............................. 149 7.3.2 Temperature................................ 150 7.3.3 Absolute Radial Velocity......................... 152 7.3.4 Rotational Velocities........................... 154 ix 7.4 Relative Radial Velocity and Binary Frequency................
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