Characterizing Cool Brown Dwarfs and Low-Mass Companions with Low-Resolution Near-Infrared Spectra PDF Download
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Author: Paige Godfrey
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Languages : en
Pages :
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Author: Paige Godfrey
Publisher:
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Languages : en
Pages :
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Author: Caleb Cañas
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In this dissertation, I present a comprehensive overview of near-infrared spectroscopy and spaced-based photometric and astrometric surveys as fundamental tools for the validation and characterization of Jupiter-sized planets and brown dwarfs orbiting main sequence stars. I begin by discussing my involvement in a spectroscopic survey of planetary candidates from Kepler that leverages the efficiency and multiplexing capabilities of the northern Apache Point Observatory Galactic Evolution Experiment (APOGEE-N) spectrograph. While APOGEE-N achieves a radial velocity precision of ~100 m/s, it has facilitated a multi-visit survey of >1600 different stars. This, coupled with its near-infrared wavelength coverage, make APOGEE-N an ideal instrument to follow-up Kepler planet candidates that are expensive observations for traditional high-precision optical instruments. This program was designed to investigate a large fraction of the planetary candidates identified in Kepler and characterize the false positive scenarios that can mimic the signal of a genuine planet. I summarize the pipeline developed to reduce APOGEE-N spectra and derive radial velocities and characterize a subset of 28 low-mass companions using the public data release from this survey. I also highlight the ability of near infrared spectrometers, such as APOGEE-N, to aid in the vetting and validation of planetary systems too faint for extensive observations with single-object optical spectrographs. I then discuss my work characterizing Jupiter-sized companions to M dwarfs discovered by NASA's TESS mission using two high-precision, high-resolution spectrographs: the Habitable-zone Planet Finder (HPF) and NEID. I summarize the framework developed to vet and confirm these systems with a combination of RVs, photometry, high-contrast imaging, and astrometric measurements from Gaia. I highlight four systems discovered with TESS: (i) TOI-1899, the first M dwarf system known to have a transiting Jupiter at a period >10 days and a lucrative target for future atmospheric characterization for a temperate gas giant, (ii) TOI-3714, an M2 dwarf system with a transiting hot Jupiter and a distant white dwarf companion, (iii) TOI-3629, an M1 dwarf system hosting a transiting hot Jupiter, and (iv) TOI-2119, an M2 dwarf with a brown dwarf companion on an eccentric orbit that is an ideal target for a measurement of the projected spin-orbit misalignment with the host star. I demonstrate that the near-infrared and extended red optical wavelength coverage of HPF and NEID, respectively, enable precise mass measurements for Jupiter-sized planets and brown dwarfs orbiting M dwarfs. Lastly, I present a discussion of the changes to come with data from two all-sky surveys, TESS and Gaia, that will revolution the discovery of large companions to M dwarfs and the synergy of these discoveries with red sensitive spectrometers to enable an ensemble of well-characterized planets and brown dwarfs that are amenable to population studies and demographic analysis to constrain their origin channels.
Author: Neill I. Reid
Publisher: Springer Science & Business Media
ISBN: 1447136632
Category : Science
Languages : en
Pages : 492
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Perhaps the most common question that a child asks when he or she sees the night sky from a dark site for the first time is: 'How many stars are there?' This happens to be a question which has exercised the intellectual skills of many astronomers over the course of most of the last century, including, for the last two decades, one of the authors of this text. Until recently, the most accurate answer was 'We are not certain, but there is a good chance that almost all of them are M dwarfs. ' Within the last three years, results from new sky-surveys - particularly the first deep surveys at near infrared wavelengths - have provided a breakthrough in this subject, solidifying our census of the lowest-mass stars and identifying large numbers of the hitherto almost mythical substellar-mass brown dwarfs. These extremely low-luminosity objects are the central subjects of this book, and the subtitle should be interpreted accordingly. The expression 'low-mass stars' carries a wide range of meanings in the astronomical literature, but is most frequently taken to refer to objects with masses comparable with that of the Sun - F and G dwarfs, and their red giant descendants. While this definition is eminently reasonable for the average extragalactic astronomer, our discussion centres on M dwarfs, with masses of no more than 60% that of the Sun, and extends to 'failed stars' - objects with insufficient mass to ignite central hydrogen fusion.
Author: Stanimir Metchev
Publisher: Universal-Publishers
ISBN: 158112290X
Category : Science
Languages : en
Pages : 255
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We present results from an adaptive optics survey conducted with the Palomar and Keck telescopes over 3 years, which measured the frequency of stellar and sub-stellar companions to Sun-like stars. The survey sample contains 266 stars in the 3-10000 million year age range at heliocentric distances between 8 and 200 parsecs and with spectral types between F5-K5. A sub-sample of 101 stars, between 3-500 million years old, were observed in deep exposures with a coronagraph to search for faint sub-stellar companions. A total of 288 candidate companions were discovered around the sample stars, which were re-imaged at subsequent epochs to determine physical association with the candidate host stars by checking for common proper motion. Benefitting from a highly accurate astrometric calibration of the observations, we were able to successfully apply the common proper motion test in the majority of the cases, including stars with proper motions as small as 20 milli-arcseconds/year. The results from the survey include the discovery of three new brown dwarf companions (HD 49197B, HD 203030B, and ScoPMS 214B), 43 new stellar binaries, and a triple system. The physical association of an additional, a priori-suspected, candidate sub-stellar companion to the star HII 1348 is astrometrically confirmed. The newly-discovered and confirmed young brown dwarf companions span a range of spectral types between M5 and T0.5, and will be of prime significance for constraining evolutionary models of young brown dwarfs and extra-solar planets. Based on the 3 new detections of sub-stellar companions in the 101 star sub-sample and following a careful estimate of the survey incompleteness, a Bayesian statistical analysis shows that the frequency of 0.012-0.072 solar-mass brown dwarfs in 30-1600 AU orbits around young solar analogs is 6.8% (-4.9%, +8.3%; 2-sigma limits). While this is a factor of 3 lower than the frequency of stellar companions to G-dwarfs in the same orbital range, it is significantly higher than the frequency of brown dwarfs in 0-3 AU orbits discovered through precision radial velocity surveys. It is also fully consistent with the observed frequency of 0-3 AU extra-solar planets. Thus, the result demonstrates that the radial-velocity "brown dwarf desert" does not extend to wide separations, contrary to previous belief.
Author: Emily Martin
Publisher:
ISBN:
Category :
Languages : en
Pages : 197
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This dissertation combines near-infrared spectroscopic and astrometric analysis of low-mass stars and brown dwarfs with instrumentation work to upgrade the NIRSPEC spectrometer for the Keck II Telescope. The scientific goals of my thesis are to discover and characterize the physical properties of brown dwarfs, the lowest-mass (
Author: Rafael Rebolo
Publisher: Cambridge University Press
ISBN: 9780521663359
Category : Science
Languages : en
Pages : 284
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This volume provides a state-of-the-art review of our current knowledge of brown dwarfs and very low-mass stars. The hunt for and study of these elusive objects is currently one of the most dynamic areas of research in astronomy for two reasons. Brown dwarfs bridge the gap between stars and planets, and they may constitute an important part of the 'dark matter' of the Universe. This volume presents review articles from a team of international authorities who gathered at a conference in La Palma to assess the spectacular progress that has been made in this field in the last few years.
Author: Viki Joergens
Publisher: Springer Science & Business Media
ISBN: 3319011626
Category : Science
Languages : en
Pages : 174
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The years 2012/2013 mark the 50th anniversary of the theoretical prediction that Brown Dwarfs, i.e. degenerate objects which are just not massive enough to sustain stable hydrogen fusion, exist. Some 20 years after their discovery, how Brown Dwarfs form is still one of the main open questions in the theory of star formation. In this volume, the pioneers of Brown Dwarf research review the history of the theoretical prediction and the subsequent discovery of Brown Dwarfs. After an introduction, written by Viki Joergens, reviewing Shiv Kumar's theoretical prediction of the existence of brown dwarfs, Takenori Nakano reviews his and Hayashi's calculation of the Hydrogen Burning Minimum Mass. Both predictions happened in the early 1960s. Jill Tarter then writes on the introduction of the term 'Brown Dwarf', before Ben Oppenheimer, Rafael Rebolo and Gibor Basri describe their first discovery of Brown Dwarfs in the 1990s. Lastly, Michael Cushing and Isabelle Baraffe describe the development of the field to the current state of the art. While the book is mainly aimed at the Brown Dwarf research community, the description of the pioneering period in a scientific field will attract general readers interested in astronomy as well.
Author: John Christian Wilson
Publisher:
ISBN:
Category :
Languages : en
Pages : 278
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Author: Hugh R.A. Jones
Publisher: Springer Science & Business Media
ISBN: 9783540423539
Category : Science
Languages : en
Pages : 222
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Once you have looked at the night sky on a moonless night it is not hard to realise why so much of our science and religion has its roots in the stars. Yet it took until 1850 to realise that fainter stars were not necessarily further away, nor the brighter ones closer. In fact within the magnitude range observable to the naked eye it is probable that the brighter star is in fact further away. Even today the measurement of stellar distances is relatively difficult and is gener ally only done using dedicated telescopes. In the early years of the 20th century Hertzsprung and Russell developed a powerful classification diagram which al lows stars to be distinguished using a plot of their colour versus magnitude. The construction of this diagram involved the use of spectroscopy which has become the cornerstone of modern astronomy. As telescopes become more powerful, de tectors more sensitive and more physics is added to astrophysics, astronomical spectroscopy becomes a more powerful tool. The concern of this book is the spectral classification of stars. With a single spectrum of a star it is possible to uniquely classify an object and find its place on the Hertzsprung-Russell diagram. This spectrum is thus equivalent to having the colour and the magnitude of the object which can in turn be related to mass and other quantities.
Author: Paul Raymond Steele
Publisher:
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Category :
Languages : en
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In this thesis I present a new near-infrared photometric search for unresolved ultracool companions and debris disks to white dwarfs in UKIDSS DR5. 24 DA white dwarfs were found with multiple excesses indicative of a low mass companion, with 7 of these having a predicted mass in the range associated with brown dwarfs. The results of this survey show that the unresolved brown dwarf companion fraction to DA white dwarfs is 0.5? fWD+BD? 1.8? 0.7%. I also calculate the unresolved L-dwarf companion fraction to be 0.5? fWD+dL? 1.5? 0.6%, which is much higher than the previous estimate of Farihi, Becklin & Zuckerman (2005). However, the results are consistent with previous estimates of the brown dwarf companion fraction to main sequence stars. I analyse the near-infrared spectra of eleven known DA white dwarf + M-dwarf binaries, and compare the spectral types assigned using optical photometry against those assigned using near-infrared spectra. I search for evidence that the known short period systems once existed in a common envelope phase. No such evidence was found. I also present the spectroscopic analysis of two particularly interesting binaries; PG 1234+ 482 and PHL 5038. PG 1234+482 is the hottest and youngest DA white dwarf with a cool companion on the stellar-substellar borderline. I discuss the possibility that the companion is a brown dwarf, and the possibility that the secondary is the source of contamination by heavy metals in the white dwarf's atmosphere. PHL 5038 was identified to have a near-infrared excess in UKIDSS, and the spectroscopic analysis in this thesis confirms that the secondary in this system can be resolved at a projected orbital separation of 55AU, and is a brown dwarf with spectral type L8-L9. This is only the second such pair found (over 20 years later) after GD165AB. The secondary in this system has the potential to be used as a benchmark brown dwarf for testing substellar atmospheric models.
