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A Time Series Study of Rigel, a B8ia Supergiant

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A Thesis entitled A time series study of Rigel, a B8Ia supergiant by Sara Rother As partial ful¯llment of the requirements for the Master of Science in Physics Advisor: Dr. Nancy D. Morrison Committee: Dr. Steven Federman Committee: Dr. Rupali Chandar Dr. Michael Bisesi, Senior Associate Dean College of Graduate Studies The University of Toledo August 2009 An Abstract of A time series study of Rigel, a B8Ia supergiant Sara Rother Submitted in partial ful¯llment of the requirements for the Master of Science in Physics The University of Toledo August 2009 Rigel is a B8Ia spectral type, massive, supergiant star that is experiencing mass loss in the stellar wind. The study was done with data on Rigel that was taken over the course of 10 seasons, with 192 total observations. All observations were taken with the 1.06 meter telescope at the University of Toledo's Ritter Astrophysical Research Center. I looked for a periodic variation in the H® line by looking at the equivalent widths and radial velocities, as well as classifying the pro¯les into seven categories and determining the frequency of occurrence of each. I also measured the radial velocities of a singly ionized carbon line. A high velocity absorption event, such as the 2 seen by Kaufer et. al. in 1993 and 1994, was also seen in 2006 in this study. No single, dominant periodic component was found in the radial velocity measurements of either line. ii Contents Abstract ii Contents iii List of Figures v List of Tables vii 1 Introduction 1 1.1 Previous Work .............................. 5 2 Observations 11 3 Reduction and Analysis 16 4 Results 21 5 Discussion and Conclusions 31 5.1 Future Work ............................... 33 iii A Journal of Observations 34 B Radial Velocities of Carbon II lines 43 C Radial Velocities of H® lines in absorption 52 D Radial Velocities of H® lines in Emission 61 References 70 iv List of Figures 1-1 P Cygni pro¯le .............................. 8 1-2 Mg II lines from Selvelli et. al. ...................... 8 1-3 Mg II lines from Kaufer et al. ...................... 9 1-4 High velocity absorption event seen by Israelian et al. (1997) . 10 3-1 Water Line Removal ........................... 20 4-1 High velocity absorption event seen on 4 November 2006 . 22 4-2 High velocity absorption event seen on 10 November 2006 . 25 4-3 H® in P Cygni pro¯le .......................... 25 4-4 H® in double Emission ......................... 26 4-5 H® in Absorption ............................ 26 4-6 H® in Inverse P Cygni pro¯le ..................... 27 4-7 H® in Double Absorption ........................ 27 4-8 H® in Emission .............................. 28 4-9 H® in triple absorption ......................... 28 v 4-10 How often Rigel is in each of the pro¯les . 29 4-11 typical graph of theta vs period ..................... 30 5-1 Theoretical Pro¯le ............................ 32 vi List of Tables 2.1 Wavelength range of each Echelle¶ order . 12 4.1 How often each pro¯le type is seen in the observations . 23 A.1 Journal of Observations ......................... 34 A.1 Journal of Observations ......................... 35 A.1 Journal of Observations ......................... 36 A.1 Journal of Observations ......................... 37 A.1 Journal of Observations ......................... 38 A.1 Journal of Observations ......................... 39 A.1 Journal of Observations ......................... 40 A.1 Journal of Observations ......................... 41 A.1 Journal of Observations ......................... 42 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 43 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 44 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 45 vii B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 46 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 47 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 48 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 49 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 50 B.1 Radial Velocity of Carbon II lines at 6578 Aº and 6582 Aº . 51 C.1 Radial Velocity of H® lines in absorption . 52 C.1 Radial Velocity of H® lines in absorption . 53 C.1 Radial Velocity of H® lines in absorption . 54 C.1 Radial Velocity of H® lines in absorption . 55 C.1 Radial Velocity of H® lines in absorption . 56 C.1 Radial Velocity of H® lines in absorption . 57 C.1 Radial Velocity of H® lines in absorption . 58 C.1 Radial Velocity of H® lines in absorption . 59 C.1 Radial Velocity of H® lines in absorption . 60 D.1 Radial Velocity of H® lines in Emission . 61 D.1 Radial Velocity of H® lines in Emission . 62 D.1 Radial Velocity of H® lines in Emission . 63 D.1 Radial Velocity of H® lines in Emission . 64 D.1 Radial Velocity of H® lines in Emission . 65 viii D.1 Radial Velocity of H® lines in Emission . 66 D.1 Radial Velocity of H® lines in Emission . 67 D.1 Radial Velocity of H® lines in Emission . 68 D.1 Radial Velocity of H® lines in Emission . 69 ix Chapter 1 Introduction Rigel is a well-known, bright star in the constellation of Orion. It is the brightest star in Orion, at a visual magnitude of 0.12. It has a spectral type of B8Ia. The luminosity class shows that it is a bright supergiant. It has a scienti¯c name of ¯ Orionis A. It also has the names of HR 1713, HD 34085, 19 Ori, as well as the common names of Algebar and Elgebar. Rigel is located close to the celestial equator; its coordinates are Right Ascension: 05h14m32s Declination: ¡08± 1200500 for epoch 2000.0. Its galactic coordinates are 209± longitude and ¡25± latitude. Rigel is important in many ways. It is a supergiant star, which means that it is one of the most massive stars. Massive stars are important because when they end their lives they form supernovae, which can then enrich the interstellar medium by releasing heavy elements. Massive stars also have mass loss during their lifetimes, which can a®ect the precise nature of the supernova. The supernova is very sensitive to end mass, and will a®ect how many elements heavier than helium are released. Rigel is near the end of its life, which is typically very short; for this type of star, the main sequence lifetime is around 50 million years. It is also a variable star. Its 1 2 H-alpha pro¯le varies over a short range of time, as short as 1 day. Some of the basic properties of Rigel have been established in the literature (Is- raelian et al. 1997 and Kaufer et al. 1996a,b). The stellar radius is around 130 R¯. The e®ective temperature is 13000 § 500 K. The luminosity is 105:63§0:06 times the solar luminosity. It now has a mass of around 24 M¯, but when it was at its zero age main sequence point, its mass was about 31 M¯. It is losing mass at a rate of about 1 £ 10¡6§0:5 solar masses per year, although this rate is not constant, and has not always been the same. The B-V value is -0.03 and its color excess E (B-V) is 0.00. Rigel has a parallax angle of 4.22 § 0.81 milliarcseconds, which gives it a distance of around 237 § 57 parsecs, or around 775 lightyears. This was estimated using the Hipparchos data from Perryman (1997). The projected equatorial rotational velocity (v sin i) is 40 km s¡1, which has been found from the line width by Israelian et al. (1997). Rigel has a gravity of log g [cm s¡1] of 1.6, which was found by Israelian et al. (1997). This is the gravitational acceleration. The value on the surface of the earth is 980 cm s¡1, which would give a log g of around 3. The supergiant's gravity is much lower because it has such a large radius, and is not very dense, and the atmosphere 39 3 is not compact. Using the radius of 130 R¯, the volume of the star is 3:10 £ 10 m . This gives a density of 1.54£10¡5 g cm¡3. Severny (1970) found a magnetic ¯eld of 130 Gauss in Rigel, which was the ¯rst detection of a magnetic ¯eld in a non-main sequence star. Rigel is not alone in its orbit; it is part of at least a triple star system. The secondary star has been resolved, as a main sequence star, with a spectral type of B9, and a visual magnitude of 7.6. They have an angular separation of 9.6 arcseconds, which gives a true separation of 2275§536 AU. The tertiary star is too close to the 3 secondary to resolve; it was seen spectroscopically. These stars are so far from Rigel that they will not a®ect it on the timescale of this study, since the period of the second and third stars around Rigel is about 1£105 years. I studied a line from the hydrogen atom. The electron in an atom can be excited to get into di®erent states, when a photon with that speci¯c energy interacts with it. If the electron is in the ground state, and a 10.2 eV photon interacts with it, it moves from level n=1 to level n=2 (where n is the principal quantum number), and will absorb the photon, obtaining the energy.
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