Xiaotian Xu

Hi, I’m Xu Xiaotian (徐啸天), a master-degree student at School of Astronomy and Space Science, Nanjing University. I am also a reviewer for the journal Research in Astronomy and Astrophysics (RAA). I work on accretion physics and X-ray binary. My research is carried out with Fortran, Python, bash, MESA, and emcee.

Email: [email protected]

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My work:

1. millisecond pulsar (MSP):

It is widely accepted that MSPs are formed via accretion triggered by binary evolution. We develop a spin-evolution model taking into account radiation pressure, irradiation, and accretion-induced field decay to study the spin period distribution of MSP through the Monte Carlo simulation. Our work was accepted by AcASn (Chinese journal), which later recommended our work to ChA&A.

ref:

Xu & Zhu, 2016, AcASn, 57 ,631

Xu & Zhu, 2018, ChA&A, 42, 30

2. orbital evolution of black hole low-mass X-ray binary (BHLMXB):

Three BHLMXBs show very fast orbital shrinkage. Based on the possible detection of a circumbinary disk in two BHLMXBs, we propose that this phenomenon can be understood through the resonant interaction between the disk and the binary. Our simulation (performed with the MESA code) shows that, with reasonable parameters, this model can explain the fast shrinkage without invoking large mass transfer rate.

ref:

Xu & Li, 2018, ApJ, 859, 46

3. formation of pre-main-sequence BHLMXB (pre-MS/BHLMXB):

Since the lifetime of the progenitor of BH is about 1 - 10 Myr and the pre-MS lifetime of 1 solar mass star is about 10 Myr, it is quite interesting to ask the question: can we observe a BHLMXB hosting a pre-MS donor? We use MESA to simulate the evolution of the pre-MS star and the orbital evolution of the binary. Our calculation shows that tidal torque is not always able to lock the rotation of the donor, and pre-MS/BHLMXBs are short-lived system if formed.

ref:

Xu & Li, 2018, accepted by MNRAS

4. bimodal distribution of Be/X-ray pulsar (BeXP):

Knigge et al. (2011) found that there are two populations of BeXP. Cheng et al. (2014) statistically showed that these two populations are generated by different accretion mode. We propose a spin evolution model taking into account the properties of BeXPs. We adopt the Markov Chain Monte Carlo method (software: emcee) to fit our model to the observed distribution. We obtain reasonable parameters and a constraint on the properties of the type II outburst.

ref:

Xu & Li, 2018 submitted