Preface: Frontiers in Astrophysics (II) — A special issue dedicated to the 20th anniversary of RAA (2001–2020)

Monthly Notices of the Royal Astronomical Society

2018

It has been suggested that the accretion-induced collapse (AIC) of an oxygen-neon white dwarf (ONe WD) to a neutron star is a theoretically predicted outcome in stellar evolution, likely relating to the formation of some neutron star systems. However, the progenitor models of AIC events are still not well studied, and recent studies indicated that CO WD+He star systems may also contribute to the formation of neutron star systems through AIC process when off-centre carbon ignition happens on the surface of the CO WD. In this work, I studied the single-degenerate (SD) model of AIC events in a systematic way, including the contribution of the CO WD+He star channel and the ONe WD+MS/RG/He star channels. Firstly, I gave the initial parameter space of these SD channels for producing AIC events in the orbital period-secondary mass plane based on detailed binary evolution computations. Then, according to a binary population synthesis approach, I gave the rates and delay times of AIC events for these SD channels based on their initial parameter space. I found that the rates of AIC events in our galaxy are in the range of ∼ 0.3 − 0.9 × 10 −3 yr −1 , and that their delay times are >30 Myr. I also found that the ONe WD+He star channel is the main way to produce AIC events, and that the CO WD+He star channel cannot be ignored when studying the progenitors of AIC events.

Section: Bps Methodsmentioning

confidence: 99%

The single-degenerate model for the progenitors of accretion-induced collapse events

Monthly Notices of the Royal Astronomical Society

2018

“…′′ near the diffraction limit of 1.8 m telescope between 700 and 900 nm, and the field of the guiding FOV is 4 ′′ , while the average seeing of Lijiang Observation is about 1.0 ′′ from 2015 to 2017 (Wang et al 2019). In this work, the tiptilt mirror technology successfully realized high precision guiding and tracking for the high resolution spectral observation.…”

Section: The Tip-tilt Tracking Systemmentioning

confidence: 77%

The Coude Echelle Spectrograph for the Lijiang 1.8m telescope

Chang

Res. Astron. Astrophys.

et al. 2020

The Coude Echelle Spectrograph (CES) was originally mounted on Xinglong 2.16 m telescope in 1994. When the High Resolution Fiber-fed Spectrograph (HRS) was commissioned at Xinglong 2.16 m telescope, the red path of CES was moved to Lijiang 1.8 m telescope, following some redesign and reinstallation. The CES of Lijiang 1.8 m telescope has the spectral resolution (R = λ/Δλ) ranging from 20000 to 50000 corresponding to different slit widths. With a 2k × 2k PI CCD, CES has a wavelength coverage between 570 nm to 1030 nm. In particular, the resolution of 37000 at 0.5 mm slit corresponds to 1.3″ on the sky. The limiting magnitude is V = 11.5 with the use of the tip-tilt feedback system, and the S/N is about 40 for 1 hour exposure at 600 nm (R = 37000). During the installation of CES, the tip-tilt mirror technology had successfully fulfilled high precision guiding and tracking for high resolution spectral observation and significantly improved the observation efficiency.

“…A few hundreds of CB-SMBH candidates have been identified from systematic searches over extensive time-domain surveys (Graham et al 2015, Charisi et al 2016, Liu et al 2016 and time series analysis of decadal AGN long term monitorings (see e.g., Kovačević et al 2017Kovačević et al , 2018Kovačević et al , 2019Kovačević et al , 2020c. From theory of the hierarchical mergers of galaxies, CB-SMBHs emerging from dual galactic cores must be formed at centers of some (if not all) galaxies for certain periods of evolution (Begelman et al 1980, Wang andIp 2020). Also, some other types of AGN such as Changing-look AGN (CL-AGNs) as a new subpopulation (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Investigating close binary supermassive black holes at high angular resolution

Kovačević

2021

SERBIAN ASTRON J

Gravitational waves (GW) in the nano-Hz domain are expected to be radiated by close-binaries of supermassive black holes (CB-SMBHs; components bound in a Keplerian binary at mutual distance less than ~ 0.1 pc), which are relicts of galaxy mergers and anticipated to be measured via the Pulsar Timing Array (PTA) technique. The challenge of present CB-SMBH investigations is that their signatures are elusive and not easily disentangled from a single SMBH. PTAs will typically have a glimpse of an early portion of the binary inspiral to catch the frequency evolution of the binary only with sufficiently high mass and initially high eccentricity. Thus, we have to make use of electromagnetic observations to determine orbital parameters of CB-SMBHs and test nano-Hz GW properties. The 2D reverberation mapping (RM) is a powerful tool for probing kinematics and geometry of ionized gas in the SMBHs (single or binary) vicinity, yet it can lose information due to projection on the line of sight of the observer. Nevertheless, spectroastrometry with AMBER, GRAVITY, and successors can provide an independent measurement of the emitting region's size, geometry, and kinematics. These two techniques combined can resolve CB-SMBHs. In this review, we focus on RM and spectroastrometry observational signatures of CB-SMBHs with non-zero eccentricity from recent simulations with particular attention to recent developments and open issues.