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Student Number 92249005
Author Kausharbanu Sanchawala(高莎)
Author's Email Address No Public.
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Department Graduate Institute of Astronomy
Year 2006
Semester 2
Degree Ph.D.
Type of Document Doctoral Dissertation
Language English
Title A Multiwavelength Study of the Carina Nebula
Date of Defense 2007-05-31
Page Count 123
Keyword
  • massive stars
  • Near-infrared
  • star formation
  • X-ray
  • Abstract We carried out a multiwavelength study of the central ∼400 arcmin2 area of
    the Carina Nebula that covers the star clusters, Trumpler 14 (Tr 14), and Trumpler
    16 (Tr 16). Our approach to identify the pre-main sequence (PMS) population of
    this massive star forming region is to combine the X-ray and near-infrared (NIR)
    wavelength information. NIR wavelengths, as compared to optical wavelengths, suffer
    much less problem due to extinctions which are typically high in a star-forming region
    and NIR colors of young stars provide a very useful tool to classify PMS objects. On
    the other hand, X-ray surveys provide clean samples of star forming regions as they
    suffer little contamination due to field stars and are the most efficient in identifying
    the weak-lined T Tauri population, which otherwise is difficult to be distinguished
    from unrelated field stars for its lack of classic signatures of youth, i.e., NIR excess,
    strong H emission, etc.
    We have used three archival Chandra datasets to derive a sample of ∼800 X-ray
    sources of this region, with a limiting X-ray flux of ∼ 10−14 ergs cm−2 s−1. With
    10  limiting magnitudes of ∼18.5, 17.5, and 16.5 mag, in the J, H, and Ks bands,
    respectively, our NIR imaging observations are deeper by 2–3 magnitudes than any
    existing NIR observations of this large field in the Carina Nebula. We have identified
    ∼1000 T Tauri candidates (i.e. Class II and III candidates), and some dozen Class
    I candidates using the X-ray and NIR properties of the sources, thus producing the
    most comprehensive sample of the PMS candidates of this region.
    X-ray emission is detected from all the O stars and 10% of early-B stars in our
    field. We also detected X-ray emission from several mid- or late-B stars, with their X-ray luminosities being comparable to those typical of T Tauri candidates in our
    sample, providing a circumstantial evidence that the X-ray emission could come from
    a low/intermediate-mass PMS companion. Most O and early-B stars in our sample
    satisfy the canonical relation, LX ∝ 10−7Lbol, and none of the O stars are found to
    be variable in X-ray emission—both of these findings being consistent with the windshock
    model as the X-ray emission mechanism in these massive stars. We identified
    16 candidate OB stars which have likely escaped previous detections due to larger
    extinctions they suffer in optical wavelengths.
    The spatial distribution of the PMS candidates and very red NIR sources (H −
    Ks > 2) suggests that we are apparently seeing star formation in different evolutionary
    stages. The T Tauri candidates are seen to be distributed in the direction of Tr 14
    and Tr 16, with Tr 14 containing a much larger population of Class II candidates than
    Tr 16—implying a younger age for Tr 14. The Ks band luminosity function (KLF) of
    Tr 14 shows a sharp peak, likely due to the deuterium burning PMS stars—implying
    an age of 1–2 Myr for the cluster. In contrast, the KLF of Tr 16 is seen to rise smoothly
    until it turns over at Ks ∼17 mag due to the sensitivity of our data. Most of the
    red NIR sources, on the other hand, are seen to be concentrated to the south-east
    of Tr 16, where few T Tauri candidates are found, representing a still younger and
    probably the current generation of star birth. In particular, a compact, embedded
    group of ten X-ray sources, Tr 16-SE group, where many of these sources are massive
    star candidates, with one known O4 star, is discovered. The KLF of the Tr 16-SE
    group shows that the group has a much higher number density of sources relative to
    the field, indicating that it is indeed a bona fide young star group or cluster. We also
    find strong indications of ongoing cluster formation near three mid-infrared sources,
    where we see striking correlation of some very red NIR sources (H − Ks > 2) and
    hard X-ray sources.
    Table of Content 中文摘要 i
    Abstract ii
    Acknowledgements iv
    List of Figures viii
    List of Tables x
    1 Introduction 1
    1.1 Star Formation - Overview . . . . . . . . . . . . . . . . . . . . . . . . 1
    1.2 The Classification of PMS objects . . . . . . . . . . . . . . . . . . . . 4
    1.3 Identification of PMS objects . . . . . . . . . . . . . . . . . . . . . . 8
    1.4 The Carina Nebula . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
    1.5 Motivation and Outline of Thesis . . . . . . . . . . . . . . . . . . . . 21
    2 Observations and Data Reductions 24
    2.1 X-ray Observations (Chandra) . . . . . . . . . . . . . . . . . . . . . 24
    2.1.1 Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
    2.2 Near-Infrared Observations (IRSF) . . . . . . . . . . . . . . . . . . . 29
    2.2.1 Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
    2.3 Two Micron All Sky Survey (2MASS) . . . . . . . . . . . . . . . . . . 33
    3 X-ray Young Stars in the Carina Nebula 34
    3.1 X-ray Sources and Stellar Counterparts . . . . . . . . . . . . . . . . . 34
    3.2 OB stars-X-ray Properties . . . . . . . . . . . . . . . . . . . . . . . . 39
    3.2.1 X-ray Variability . . . . . . . . . . . . . . . . . . . . . . . . . 43
    3.2.2 The LX versus Lbol Correlation . . . . . . . . . . . . . . . . . 46
    3.3 Candidate OB Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
    3.4 PMS Candidates - X-ray Luminosities . . . . . . . . . . . . . . . . . 53
    3.5 A Compact Embedded X-ray Stellar Group - Tr 16-SE . . . . . . . . 53
    3.6 The X-ray Luminosity Function of Tr 16 . . . . . . . . . . . . . . . . 59
    3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
    4 Near-infrared Study of the Carina Nebula 63
    4.1 The Color-Color Diagrams . . . . . . . . . . . . . . . . . . . . . . . . 65
    4.2 The Color-Magnitude Diagram . . . . . . . . . . . . . . . . . . . . . 71
    4.3 Estimate of Interstellar Extinction . . . . . . . . . . . . . . . . . . . . 73
    4.4 Spatial Distribution of Stellar Sources . . . . . . . . . . . . . . . . . . 73
    4.5 Stellar Mass Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . 78
    4.5.1 Tr 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
    4.5.2 Tr 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
    4.6 The Ks-band Luminosity Function . . . . . . . . . . . . . . . . . . . 85
    4.7 Individual Sources and Regions . . . . . . . . . . . . . . . . . . . . . 95
    4.7.1 IRAS 10430-5931 . . . . . . . . . . . . . . . . . . . . . . . . . 95
    4.7.2 G287.51-0.49 . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
    4.7.3 G287.47-0.54 . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
    4.7.4 Tr 16-SE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
    4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
    5 Conclusions 102
    5.1 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
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