Mapping the emission line strengths and kinematics of supernova remnant S147 with extensive LAMOST spectroscopic observations

We present extensive spectroscopic observations of supernova remnant(SNR) S147 collected with the Large sky Area Multi-Object fiber Spectroscopic Telescope(LAMOST). The spectra were carefully sky-subtracted taking into account the complex filamentary structure of S147. We have utilized all available LAMOST spectra toward S147, including sky and stellar spectra. By measuring the prominent optical emission lines including Hα, [NⅡ]λ 6584 and [SⅡ]λλ 6717, 6731, we present maps of radial velocity and line intensity ratio covering the whole nebula of S147 with unprecedented detail. The maps spatially correlate well with the complex filamentary structure of S147. For the central 2?of S147, the radial velocity varies from-100 to 100 km s^(-1) and has peaks between～0 and 10 km s^(-1). The intensity ratios of Hα/[S Ⅱ]λλ 6717, 6731, [SⅡ]λ 6717/λ 6731 and Hα/[NⅡ]λ 6584 peak at about 0.77, 1.35 and 1.48, respectively, with a scatter of 0.17, 0.19 and 0.37, respectively. The intensity ratios are consistent with the literature values. However, the range of variations of line intensity ratios estimated here,which are representative of the whole nebula, is larger than previously estimated.

Semi-numerical simulation of reionization with semi-analytical modeling of galaxy formation

In a semi-numerical model of reionization, the evolution of ionization fraction is approximately simulated by the criterion of ionizing photon to baryon ratio. We incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semianalytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-z observations, and it also fits the high redshift luminosity function reasonably well, but its prediction about star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization cannot be completed at z ～ 6. We also consider simple modifications of the model with more top heavy initial mass functions, which can allow the reionization to occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the epoch of reionization, and the neutral regions produced by our simulations with the semi-analytical model, which appeared less poriferous than the simple halo-based models.

On fitting the full spectrum of luminous red galaxies by using ULySS and STARLIGHT

We select a sample of quiescent luminous red galaxies(LRGs) from the Sloan Digital Sky Survey Data Release 7 with a high signal-to-noise ratio(S/N) to study the consistency of fitting the full spectrum by using different packages, mainly, ULySS and STARLIGHT. The spectrum of each galaxy in the sample is fitted by the full spectrum fitting packages ULySS and STARLIGHT. We find:(1) for spectra with higher S/Ns, the ages of stellar populations obtained from ULySS are slightly older than those from STARLIGHT, and metallicities derived from ULySS are slightly richer than those from STARLIGHT. In general, both packages can give roughly consistent fitting results.(2) For low S/N spectra, it is possible that the fitting by ULySS can become trapped at some local minimum in the parameter space during execution and thus may give unreliable results, but STARLIGHT can still give reliable results. Based on the fitting results of LRGs, we further analyze their star formation history and the relation between their age and velocity dispersion, and find that they agree well with conclusions from previous works.

Discovery of two rotational modulation periods from a young hierarchical triple system

GW Ori is a young hierarchical triple system located in λ Orionis, consisting of a binary(GW Ori A and B), a tertiary star(GW Ori C) and a rare circumtriple disk. Due to the limited data with poor accuracy, several short-period signals were detected in this system, but the values from diferent studies are not fully consistent. As one of the most successful transiting surveys, the transiting exoplanet survey satellite(TESS) provides an unprecedented opportunity to make a comprehensive periodic analysis of GW Ori. In this work we discover two significant modulation signals by analyzing the light curves of GW Ori's four observations from TESS, i.e.,(3.02 ± 0.15) and(1.92 ± 0.06) d, which are very likely to be the rotational periods caused by starspot modulation on the primary and secondary components, respectively. We calculate the inclinations of GW Ori A and B according to the two rotational periods. The results suggest that the rotational plane of GW Ori A and B and the orbital plane of the binary are almost coplanar. We also discuss the aperiodic features in the light curves;these may be related to unstable accretion. The light curves of GW Ori also include a third(possible) modulation signal with a period of(2.51±0.09) d, but the third is neither quite stable nor statistically significant.