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ALMA OBSERVATION OF THE 658 GHz VIBRATIONALLY EXCITED H<sub>2</sub>O MASER IN ORION KL SOURCE I
Hirota, Tomoya,Kim, Mi Kyoung,Honma, Mareki American Astronomical Society 2016 The Astrophysical journal Vol.817 No.2
<P>We present an observational study of the vibrationally excited H2O line at 658 GHz (v(2) = 1, 1(1,0)-1(0,1)) toward Orion KL using the Atacama Large Millimeter/Submillimeter Array (ALMA). This line is clearly detected at the position of the massive protostar candidate, Source I. The spatial structure is compact, with a size of about 100 AU, and is elongated along the northeast-southwest low-velocity (18 km(-1)) bipolar outflow traced by 22 GHz H2O masers, SiO masers, and thermal SiO lines. A velocity gradient can be seen perpendicular to the bipolar outflow. The overall spatial and velocity structure seems to be analogous to that of the 321 GHz H2O maser line previously detected with ALMA and vibrationally excited SiO maser emission. The brightness temperature of the 658 GHz H2O line is estimated to be higher than 2 x 10(4) K, implying that it is emitted via maser action. Our results suggest that the 658 GHz H2O maser line is emitted from the base of the outflow from a rotating and expanding accretion disk as observed for the SiO masers and the 321 GHz H2O maser. We also search for two other H2O lines at 646 GHz (9(7,3)-8(8,0) and 9(7,2)-8(8,1)), but they are not detected in Orion KL.</P>
ALMA BAND 8 CONTINUUM EMISSION FROM ORION SOURCE I
Hirota, Tomoya,Machida, Masahiro N.,Matsushita, Yuko,Motogi, Kazuhito,Matsumoto, Naoko,Kim, Mi Kyoung,Burns, Ross A.,Honma, Mareki American Astronomical Society 2016 The Astrophysical journal Vol.833 No.2
<P>We have measured continuum flux densities of a high-mass protostar candidate, a radio source. I in the Orion. KL region (Orion Source I) using the Atacama Large Millimeter/Submillimeter Array (ALMA) at band. 8 with an angular resolution of 0 ''.1. The continuum emission at 430, 460, and 490 GHz associated with Source. I shows an elongated structure along the northwest-southeast direction perpendicular to the so-called low-velocity bipolar outflow. The deconvolved size of the continuum source, 90 au x 20 au, is consistent with those reported previously at other millimeter/submillimeter wavelengths. The flux density can be well fitted to the optically thick blackbody spectral energy distribution, and the brightness temperature is evaluated to be 700-800 K. It is much lower than that in the case of proton-electron or H-free-free radiations. Our data are consistent with the latest ALMA results by Plambeck & Wright, in which the continuum emission was proposed to arise from the edge-on circumstellar disk via thermal dust emission, unless the continuum source consists of an unresolved structure with a smaller beam filling factor.</P>
ALMA IMAGING OF MILLIMETER/SUBMILLIMETER CONTINUUM EMISSION IN ORION KL
Hirota, Tomoya,Kim, Mi Kyoung,Kurono, Yasutaka,Honma, Mareki IOP Publishing 2015 The Astrophysical journal Vol.801 No.2
<P>We have carried out high-resolution observations with the Atacama Large Millimeter/Submillimeter Array (ALMA) of continuum emission from the Orion Kleinmann-Low (KL) region. We identify 11 compact sources at ALMA band 6 (245 GHz) and band 7 (339 GHz), including the Hot Core, Compact Ridge, SMA1, IRc4, IRc7, and a radio source I (Source I). A spectral energy distribution (SED) of each source is determined by using previous 3 mm continuum emission data. Physical properties such as size, mass, hydrogen number density, and column density are discussed based on the dust graybody SED. Among 11 identified sources, Source I, a massive protostar candidate, is a dominant energy source in Orion KL. We extensively investigate its SED from centimeter to submillimeter wavelengths. The SED of Source I can be fitted with a single power-law index of 1.97, suggesting an optically thick emission. We employ the H- free-free emission as an opacity source of this optically thick emission. The temperature, density, and mass of the circumstellar disk associated with Source I are constrained by the SED of H- free-free emission. Still, the fitting result shows a significant deviation from the observed flux densities. Combined with the thermal dust graybody SED to explain excess emission at higher frequency, a smaller power-law index of 1.60 for the H- free-free emission is obtained in the SED fitting. The power-law index smaller than two would suggest a compact source size or a clumpy structure unresolved with the present study. Future higher resolution observations with ALMA are essential to reveal more detailed spatial structure and physical properties of Source I.</P>
A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I
Hirota, Tomoya,Kim, Mi Kyoung,Kurono, Yasutaka,Honma, Mareki University of Chicago Press for the American Astro 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.782 No.2
We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H2O lines at 321 GHz (10(2,9)-9(3,6)) and 336 GHz (nu(2) = 1, 5(2,3)-6(1,6)) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0 ''.4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0 ''.2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H2O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7M(circle dot) and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of similar to 100 AU scale.
RECENT PROGRESS IN HIGH-MASS STAR-FORMATION STUDIES WITH ALMA
Tomoya Hirota 한국천문학회 2018 天文學論叢 Vol.33 No.2
Formation processes of high-mass stars have been long-standing issues in astronomy and astrophysics. This is mainly because of major diculties in observational studies such as a smaller number of high-mass young stellar objects (YSOs), larger distances, and more complex structures in young high-mass clusters compared with nearby low-mass isolated star-forming regions (SFRs), and extremely large opacity of in- terstellar dust except for centimeter to submillimeter wavelengths. High resolution and high sensitivity observations with Atacama Large Millimeter/Submillimeter Array (ALMA) at millimeter/submillimeter wavelengths will overcome these observational diculties even for statistical studies with increasing num- ber of high-mass YSO samples. This review will summarize recent progresses in high-mass star-formation studies with ALMA such as clumps and laments in giant molecular cloud complexes and infrared dark clouds (IRDCs), protostellar disks and out ows in dense cores, chemistry, masers, and accretion bursts in high-mass SFRs.
Matsumoto, Naoko,Hirota, Tomoya,Sugiyama, Koichiro,Kim, Kee-Tae,Kim, Mikyoung,Byun, Do-Young,Jung, Taehyun,Chibueze, James O.,Honma, Mareki,Kameya, Osamu,Kim, Jongsoo,Lyo, A-Ran,Motogi, Kazuhito,Oh, C IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.789 No.1
<P>We have carried out the first very long baseline interferometry (VLBI) imaging of a 44 GHz class I methanol maser (70-61A(+)) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximate to 650 km corresponding to 100 M. in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is similar to 5 mas x 2 mas, which corresponds to the linear size of similar to 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from similar to 3.5 x 10(8) to 1.0 x 10(10) K, which are higher than the estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of similar to 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.</P>
박인환,Jared Gong,Gregory L. Lyons,Tomoya Hirota,Michio Takahashi,김보라,이승연,김영신,이정수,Bennett L. Leventhal 연세대학교의과대학 2020 Yonsei medical journal Vol.61 No.11
Through this meta-analysis, we sought to examine the prevalence of, risks for, and factors associated with bullying involvement(victimization, perpetration, perpetration-victimization) among students with autism spectrum disorder (ASD). Additionally, weattempted to examine sources of variance in the prevalence and effect sizes of bullying in students with ASD across studies. Systematicdatabase and literature review identified 34 relevant studies (31 for Western countries, three for Eastern countries). Pooledprevalence estimates for victimization, perpetration, and perpetration-victimization in general were 67%, 29%, and 14%, respectively. The risk of victimization in students with ASD was significantly higher than that in typically developing students and studentswith other disabilities. Further, deficits in social interaction and communication, externalizing symptoms, internalizing symptoms,and integrated inclusive school settings were related to higher victimization, and externalizing symptoms were related to higherperpetration. Finally, moderation analyses revealed significant variations in the pooled prevalences thereof depending on culture,age, school settings, and methodological quality and in the pooled effect sizes according to publication year and methodologicalquality. Our results highlight needs for bullying intervention for students with ASD, especially those who are younger, are in aninclusive school setting, and have higher social difficulties and externalizing/internalizing symptoms; for intensive research of bullyingexperiences among students with ASD in Eastern countries; and for efforts to improve the methodological quality of suchresearch.