Sep 11 Mon 15:00-16:30 Solar and Space Plasma Seminar
hybrid; Central Building (North) / 310 or Zoom
Sep 13 Wed 14:30-15:30 ALMA-J seminar
ALMA building #102 / Zoom (hybrid)
詳細は下記からご覧ください。
=============== Sep 11 Mon===============
Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：Sep 11th (Sep), 15:00-16:30
Place： hybrid; Central Building (North) / 310 or Zoom
Speaker：Teodora Mihailescu
Affiliation：Mullard Space Science Laboratory, University College London
Title：Intriguing Plasma Composition Pattern in a Solar Active Region: a Result of Non-Resonant Alfvén Waves?
Abstract：The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionisation potential (FIP) are preferentially transported to the corona and, therefore, show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. The highest FIP bias values are typically observed in active regions, but they also vary at sub-active region level. In this work, we use data from the EUV Imaging Spectrometer (EIS) on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the pre-existing magnetic environment of the active region. We use two FIP bias diagnostics: Si X 258.375 Å/S X 264.233 Å (formation temperature of 1.5 MK) and Ca XIV 193.874 Å /Ar XIV 194.396 Å (formation temperature of 4 MK). We observe different plasma composition patterns in the newly emerging loops and the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the enhancement of low-FIP elements in the corona is generally driven by Alfvén waves. We suggest that the low-FIP elements enhancement pattern observed in the emerging loops could be driven by resonant waves originating in the active region core loops. Conversely, we suggest that the pattern observed in preexisting loops could be driven by non-resonant waves and we discuss potential sources of these waves. This different type of wave activity is what could explain the different patterns of low-FIP elements enhancement in these two sets of loops.
Facilitator
Name：Takayoshi oba
Comment：in English
=============== Sep 13 Wed==============
Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday
Date and time: September 13, 2023 (Wed), 14:30-15:30
Place: ALMA building #102 / Zoom (hybrid)
Speaker: Kaho Morii
Affiliation: The University of Tokyo/NAOJ
Title: Unveiling Early Stages of High-Mass Star Formation: Insights from Infrared Dark Clouds
Abstract:
Physical properties in infrared dark clouds (IRDCs) provide insights into the initial conditions of high-mass star and stellar cluster formation. We have conducted the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES) on thirty-nine high-mass clumps, which are the dense parts of IRDCs. These targets are dark at 24 µm and 70 µm and have low temperatures, high masses, and high density, best candidates to investigate the earliest stages of high-mass star formation. Our ALMA observations reveal their internal structure and have identified an unprecedented number of 839 cores from dust continuum emission. We find that less than 1% (7/839) of the cores possess masses exceeding 27 Msun. All of these cores are gravitationally bound and associated with molecular outflows. No high-mass prestellar core has been observed. Furthermore, among our sample, 90% (35 out of 39) only host low- to intermediate-mass cores, indicating the necessity of additional mass input for high-mass star formation. Observed core properties generally follow the thermal Jeans fragmentation of the clumps. In this talk, I will present the first results of the statistical study of the 839 cores as well as a summary of the pilot survey, and discuss the characteristics of the initial stages of high-mass star formation.
Facilitator: Bunyo Hatsukade and Kouichiro Nakanishi