Spectroscopic Observations of Ten Galactic Wolf-Rayet Stars at Bosscha Observatory:Determination of Stellar Parameters and Mass-loss Rates

We present optical spectra of 10 Galactic Wolf-Rayet(WR)stars that consist of five WN and five WC stars.The optical observation was conducted using a low-resolution spectrograph NEO-R1000(λ/Δλ~1000)at GAO-ITB RTS(27.94 cm,F/10.0),Bosscha Observatory,Lembang.We implemented stellar atmosphere Postdam Wolf-Rayet(PoWR)grid modeling to derive stellar parameters.The normalized optical spectrum can be used to find the best model from the available PoWR grid,then we could derive stellar temperature and transformation radius.To derive luminosity,stellar radius and color excess,we conducted a Spectral Energy Distribution(SED)analysis with additional data on the near-ultraviolet spectrum from the International Ultraviolet Explorer(IUE)database,and UBV and 2MASS JHK broadband filter data.Additional analysis to derive asymptotic terminal wind velocity was conducted from the P-Cygni profile analysis of the high-resolution IUE ultraviolet spectrum.With previously derived parameters,we could determine the mass loss rate of the WR stars.Furthermore,we compared our results with previous work that used PoWR code and the differences are not more than 20%.We conclude that the PoWR spectral grid is sufficient to derive WR stellar parameters quickly and could provide more accurate initial parameter input to the PoWR program code.

Spin Evolution of Neutron Stars in OB/X-ray Binaries

We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M☉ donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B0 stronger than about 3×1012 G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B0 < 3×1012 G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the Ps-Porb diagram.

12 GHz methanol maser outflow from the massive star-forming region: G35.20-0.74

We report the internal proper motions of 12 GHz methanol masers in mas-sive star-forming region G35.20-0.74 observed with the Very Long Baseline Array （VLBA） at four epochs spanning about 1.5 yr. Two groups of maser features were de-tected, groups A and B, and the latter that had a V-shaped spatial distribution is likely tracing the north outflow in G35.20-0.74. We present a three-dimensional model for the kinematics of these masers, by assuming the interstellar medium was blown by the stellar wind from the driving source （G35.2N） of the outflow. Adopting a position angle of ～ 81° for the main axis of the outflow from previous studies, we estimate an inclination of 35 ° ± 5.5°, a velocity of 8.1 ± 0.7 km s^-1 for the stellar wind along the main axis and an expansion speed gradient of 0.05 ± 0.016 km s^-1 AU^-1. From the model, we derive the age of the north outflow in G35.20-0.74 to be ～ 1.6 × 10^4 yr.

Studies of a possible new Herbig Ae/Be star in the open cluster NGC 7380

We present a study of the star 2MASS J22472238＋5801214 with the aim of identifying its true nature which has hitherto been uncertain. This object, which is a member of the young cluster NGC 7380, has been variously proposed to be a Be star, a D-type symbiotic and a Herbig Ae/Be star in separate studies. Here we present optical spectroscopy, near-IR photometry and narrow band Hα imaging of the nebulosity in its environment. Analysis of all these results, including the spectral energy distribution constructed from available data, strongly indicate the source to be a Herbig Ae/Be star. The star is found to be accompanied by a nebulosity with an interesting structure. A bow-shock shaped structure, similar to a cometary nebula, is seen very close to the star with its apex oriented towards the photoionizing source of this region （i.e. the star DH Cep）. An interesting spectroscopic finding, from the forbidden [StI] 6716, 6731A and [OI] 6300A lines, is the detection of a blue-shifted high velocity outflow （200 -t-50 km s-1） from the star.

Radiative Diffusion in a Time-dependent Outflow:a Model for Fast Blue Optical Transients

Fast Blue Optical Transients(FBOTs)are luminous transients with fast evolving(typically t;<12 days)light curve and blue color(usually-0.2>g-r>-0.3)that cannot be explained by a supernova-like explosion.We propose a radiative diffusion in a time-dependent outflow model to interpret such special transients.In this model,we assume that a central engine ejects continuous outflow during a few days.We consider the ejection of the outflow to be time-dependent.The outflow is optically thick initially and photons are frozen in it.As the outflow expands over time,photons gradually escape,and our work is to model such an evolution.Numerical and analytical calculations are considered separately,and the results are consistent.We apply the model to three typical FBOTs:PS1-10 bjp,ZTF18 abukavn,and ATLAS 19 dqr.The modeling finds the total mass of the outflow(~1-5 M;),and the total time of the ejection(~a few days)for them,leading us to speculate that they may be the result of the collapse of massive stars.

The study of proto-magnetar winds

The velocity profiles and properties of proto-magnetar winds are investigated. It is found that the corotation of wind matter with magnetic field lines significantly affects r-process nucleosynthesis and could lead to long duration γ-ray bursts and hyper-energetic supernovae.

SN 2009ip and SN 2010mc as dual-shock Quark-Novae

In recent years a number of double-humped supernovae （SNe） have been discovered. This is a feature predicted by the dual-shock Quark-Nova （QN） model where an SN explosion is followed （a few days to a few weeks later） by a QN explo- sion. SN 2009ip and SN 2010mc are the best observed examples of double-humped SNe. Here, we show that the dual-shock QN model naturally explains their light curves including the late time emission, which we attribute to the interaction between the mixed SN and QN ejecta and the surrounding circumstellar matter. Our model applies to any star （O-stars, luminous blue variables, Wolf-Rayet stars, etc.） provided that the mass involved in the SN explosion is ~ 20 Mo which provides good conditions for forming a QN.

On the variable timing behavior of PSR B0540-69:an almost excellent example to study the pulsar braking mechanism

PSR B0540-69 has a braking index measurement in its persistent state： n = 2.129± 0.012. Recently, it has been reported to have changes in its spin-down state： a sudden 36% increase in the spin- down rate. Combining the persistent state braking index measurement with different spin-down states, PSR B0540-69 is more powerful than intermittent pulsars in constraining pulsar spin-down models. The pulsar wind model is applied to explain the variable timing behavior of PSR B0540-69. The braking index of PSR B0540-69 in its persistent state results from the combined effect of magnetic dipole radiation and particle wind. The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin-down behavior. Corresponding to the 36% increase in the spin-down rate of PSR B0540-69, the relative increase in the particle density is 88% in the vacuum gap model. The braking index calculated with the model in the new state is n = 1.79. Future observations that measure the braking index of PSR B0540-69 in the new spin-down state will be very powerful in distinguishing between different pulsar spin-down models and different particle acceleration models in the wind braking scenario. The variable timing behavior of PSR J 1846-0258 is also understandable in the pulsar wind model.

A note on the puzzling spindown behavior of the Galactic center magnetar SGR J1745-2900

SGR J1745-2900 is a magnetar near the Galactic center. X-ray observations of this source found a decreasing X-ray luminosity accompanied by an enhanced spindown rate. This negative correlation between X-ray luminosity and spindown rate is hard to understand. The wind braking model of magnetars is employed to explain this puzzling spindown behavior. During the release of magnetic energy of magnetars, a system of particles may be generated. Some of these particles remain trapped in the magnetosphere and may contribute to the X-ray luminosity. The rest of the particles can flow out and take away the rotational energy of the central neutron star. A smaller polar cap angle will cause the decrease of X-ray luminosity and enhanced spindown rate of SGR J1745-2900. This magnetar is shortly expected to have a maximum spindown rate.

Hα profile variations in the spectrum of the supergiant HD14134

Variations of the Ha line in the spectra of the star HD14134 are investigated using ob- servations carried out in 2013-2014 and in 2016 with the 2-m telescope at Shamakhy Astrophysical Observatory. In the spectra of this star, the absorption and emission components of Hα are found to disappear and an inverse P Cyg profile of Ha is seen on some observational epochs. Our observations showed that when the Ha line disappeared or an inversion of the P-Cyg-type profile is observed in the spectra, the Hβ line is redshifted. When these events appeared, no synchronous variabilities were ob- served in the spectral parameters of other spectral lines formed in deeper atmospheric layers. In addition, the structures of Ha, CII （6578.05A, 6582.88A）, Sill （6347.1 A, 6371.36A） and Hβ lines are variable on a timescale of hours, but we did not detect significant variations in the other photospheric lines, as well as in the HeI （5875.72A） line. It is suggested that observational evidence for the non-stationary atmosphere of HD 14134 can be associated in part with non-spherical stellar wind.