@misc{oai:ir.soken.ac.jp:00000368,
 author = {姜, 碧〓[水+為] and チアン, ビウェイ and JIANG, Biwei},
 month = {2016-02-17, 2016-02-17},
 note = {Asymptotic Giant Branch (AGB) stars are low- and intermediate-mass stars that have developed an electron-degenerate C-O core after the exhaustion of central helium.   They are detected in large amount by IRAS due to the strong middle- and far-infrared radiation from their cold circumstellar envelopes which are resulted from the mass loss at a rate of about 10-7 to 10-5 M〓 yr-1.  The third dredge-up process in AGB phase digs out the newly produced C (and/or N) in the burning shells and transforms some stars into C-rich.  Because these stars play an important role to recruit the interstellar medium as well as the evolution to the end of a stellar life, observations in multi-wavelength and by versatile methods have been made.  This thesis puts emphasis on these AGB stars in the outer disk of the Galactic plane.
  The survey in SiO maser lines was performed to the IRAS PSC sources in the outer disk of the Galaxy, which are candidates for AGB stars according to their IRAS colors.  In May of 1994, 1995 and 1996, 244 AGB stars in the second and third quadrants of the Galactic plane were searched for the 28SiO J=1-0, v=1 and v=2 transitions and the isotopic 29SiO J=1-0, v=0 transition simultaneously by taking the wide-band advantage of the 45m telescope system.  The SiO maser emission stronger than 1Jy was detectable at 5 sigma level and at a velocity resolution of 0.3 km s-1.  76 stars were detected the 28SiO maser emissions with 64 new detections.  It's found that the v=1 and v=2 lines appear simultaneously in most cases as also shown in the bulge SiO maser emitters.  The 29SiO maser emission was detected in 12 stars, adding 10 new members to the previously known 20 such rare stars partly due to that the 29SiO is only about 1-20th abundant as 28SiO in the circumstellar envelopes of AGB stars.  The isotopic maser lines are found to be detectable only in strong Si0 maser sources, located at the same velocity and about 1-10th to 1-100th strong in terms of integrated intensity as the normal SiO maser lines.
  The SiO maser sources are mostly associated with long-period large-amplitude variables.  Except several of them, the others are all optically identified in the observations made at V and I  bands by using the Kiso Schimdt telescope.  By taking the CCD images about once a month for more than one year that started from 1994 August, these stars are found to be as red as V-I  > 2mag and their amplitudes of variability are > 2mag at I band.  The low resolution spectra taken by using the 216cm telescope in 1995 October at Beijing Astronomical Observatory (BAD) showed that all the 10 observed SiO maser sources are late-M5-type stars.  They could be Mira-type or semi-regular variables as the bulge SiO maser stars are.  In spite that there is no clear difference in the properties of SiO maser spectra or SiO maser stars when compared with that in the bulge, the survey in the outer disk was out of expected high detection rate.  Previously a survey in the SiO maser lines towards the bulge direction yielded the historically highest detection rate (66%) and it's attributed to the good sensitivity of the 45m telescope system at Nobeyama Radio Observatory and appropriate selection of sources in IRAS colors.  The sample of the outer disk survey was selected under similar criteria and the same sensitivity was reached as in the bulge survey.  However the detection rate, 31%, is less than half that of the bulge survey.
  The outer disk sample was suspected to be consisted of more C-rich AGB stars responsible for the much lower detection rate.  As is known that the non-detection of SiO maser emission in AGB stars can be caused by the weakness of SiO maser line beyond the detection limit or no emission intrinsically as in case of a C-rich AGB star.  While the former reason could not bring about big difference since the same detection limit was achieved in both the bulge and the outer disk surveys and the outer disk sample stars are even averagely closer.  In order to investigate how much proportion of C-rich AGB stars is in the AGB stars in the outer disk, optical spectroscopy and near-infrared photometry were carried out to 19 and 95 sources respectively, a subsample of the SiO maser-searched.  The optical spectroscopy to 9 SiO non-detections revealed 4 C-rich stars.  Because many of the stars are optically invisible, near-infrared identification and photometry were supplemented by using the 126cm infrared telescope at BAD and the 188cm telescope at Okayama Astrophysical Observatory in the fall of 1995.  Combining the data of molecular lines, IRAS LRS spectra and optical spectroscopy, we found that the separation of C-rich from O-rich AGBs is feasible based on their near-infrared colors J-K and H-K.  About half of the stars are then of typical near-infrared colors of C-rich AGB stars.  Though this proportion of C-rich stars is quite high compared with the value of 10% among the neighborhood late-type stars, it is consistent with the low metallicity in the outer disk since the proportion of C-rich stars is high in metal poor environment as seen in external galaxies.  The content of 50% C stars can explain the major difference in SiO maser detection rate between the outer disk sample and the bulge sample.  It is also in agreement with the results of Arecibo OH maser survey towards a similar sample of AGB stars in the outer disk., application/pdf, 総研大甲第266号},
 title = {Observational Study of AGB stars in the outer Galactic disk},
 year = {}
}