SHAO Astrophysics Colloquia
Title: Direct collision of white dwarfs as a major channel for type Ia supernovae explosions Speaker: Subo Dong (KIAA-PKU) Time: Wednesday, 3:00pm, October 14 Location: Room 303, the middle conference room，3rd floor Type Ia supernovae (SNe Ia) are believed to be thermonuclear explosions of white dwarfs (WDs), but to date the explosion mechanism and progenitor systems remain elusive. I will present our works on a new channel that could possibly explain the majority of type Ia supernovae. In this scenario, a SN Ia is produced from a direct, "head-on" collision of two WDs in a common field triple system. Such collisions are shown to lead to successful detonations from strong shocks. We show that the collision models reproduce several robust observational features of SNe Ia, especially establishing that the full range of Ni56 necessary for all SNe Ia can be produced by direct collisions of typical WDs. By systematically studying the SNe Ia nebular-phase spectra, we discover that bi-modal velocity distributions in Ni56 ejecta are common, which are naturally expected from the direct collision models due to the existence of two centers of explosions. Title: 高红移LAE星系 Speaker: Junxian Wang (USTC) Time: Friday, 2:00pm, October 16 Location: Room 1617 Seminar talk
Title: The use of methanol masers in understanding star formation
Speaker: Huib van Langevelde
Time: Monday, 3:00 pm, Oct 12
Location: Room 303, the middle conference room，3rd floor
Abstract:
This talk will address how observations of methanol masers can be used to distinguish between models of high mass star formation. Using Cep A as an example case, we investigate the nature of its disk and jet structure. The excitation of methanol is briefly addressed, as is the use of the masers for measuring the distance. It will be discussed how linear polarisation observations can be used to determine the geometry of the magnetic field. Ideally the Zeeman effect could be deployed for measuring the quantitative significance of the magnetic field for regulating high-mass star formation. Calibrating this delicate effect for methanol has been difficult, but some progress based on theoretical molecular models is presented.
SHAO-USTC Lecture
Title: What if a black hole devours too much
Speaker: Jifeng Liu (NAOC)
Date & Time: Oct. 26, Monday, 2pm
Location: Middle conference room
Abstract:
The formation of relativistic jets by an accreting compact object is one of the fundamental mysteries of astrophysics. While the theory is poorly understood, observations of relativistic jets from systems known as microquasars have led to a well-established phenomenology. Relativistic jets are not expected from sources with soft or supersoft X-ray spectra, although two such systems are known to produce relatively low-velocity bipolar outflows. Here we report optical spectra of an ultraluminous supersoft X-ray source (ULS) in the nearby galaxy M81 (M81 ULS-1) showing blueshifted broad Hαemission lines, characteristic of baryonic jets with relativistic speeds. The time variable jets have projected velocities ~17 per cent of the speed of light, and seem similar to those in the prototype microquasar SS 433. Such relativistic jets are not expected to be launched from white dwarfs, but an origin from a black hole or neutron star in M81 ULS-1 is hard to reconcile with its constant soft X-rays. The completely unexpected presence of relativistic jets in a ULS challenges the canonical theories for jet formation, but can be explained by a long speculated super-critically accreting black hole with optically thick outflows.
Group meetings and additional talks http://cluster.shao.ac.cn/wiki/index.php/Seminar_Plan
Title: Searching for Substructure in the Milky Way Halo Speaker: John Vicker Time: Wednesday, 10:30 am, Oct. 14 Galaxies Group Journal Club
Location: 1608; Contact: Zhi Li <lizh@shao.ac.cn>
http://hubble.shao.ac.cn/~lizy/galaxies/Home.html
no AGN structure and evolution group Seminar Location: 1617; Contact: Liang Chen<chenliang@shao.ac.cn> Title: On the magnetization of BL Lac jets Speaker: Liang Chen Time: Friday, 10:00am, October 16th Black hole accretion theory and High-energy astrophysics Seminar
Location: 1608; Contact: Qixiang Yang < qxyang@shao.ac.cn>
http://202.127.29.4/fyuan/journalclub.html
Title: Application of the coupled accretion-jet model in astrophysics
Speaker: Qixiang Yang
Time: Tuesday, 3:00 pm, Oct. 13, 2015 Stellar Cluster and Galaxy Seminar group seminar
Location: 1617; Contact: Jian Fu<fujian@shao.ac.cn>
|
|
