Abundances of 23 field RR Lyrae stars

We present stellar parameters and abundances of 15 elements （Na, Mg, A1, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Y and Ba） for 23 field RR Lyrae variables based on high-resolution （R ~ 60 000） and high signal-to-noise （S/N~ 200） spectra obtained using the High Dispersion Spectrograph on the Subaru Telescope. Six stars in the sample have more than one spectrum observed at different pulsation phases. The derived abundance ratios of [X/Fe] for 14 elements （except for Ba） do not vary during the pulsation cycle. An interesting curve of [Ba/Fe] versus phase is detected for the first time and it shows decreasing [Ba/Fe] with increasing temperature at a given metallicity. Combining with data in the literature, abundances of most RR Lyrae stars as a function of [Fe/H] follow the same trends as those of dwarf stars, but [Sc/Fe] and [Y/Fe] ratios of RR Lyrae stars at solar metallicity are lower than those of dwarf stars. The kinematics of RR Lyrae stars indicate that three comparatively metal-rich RR Lyrae stars might originate from the thick disk and they show higher [a/Fe] ratios than RR Lyrae stars with thin disk kinematics. Among 23 RR Lyrae stars, two special objects are found with abnormal abundances; TV Lib has high [a/Fe], [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios while TW Her has solar [a/Fe] but significantly lower [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios as compared with other RR Lyrae stars.     

A photometric study of an EW-type binary system： GV Leo

A photometric study of a contact binary system, GV Leo is presented. New observations were done using the B VR filter bands. We find that a revised orbital period is 0.26673171 d and the orbital period of this system is decreasing at a rate of dP/ dt = -4.95 × 10-7 d yr-1. The photometric solutions are fairly well fitted at a mass ratio of q = 0.1879, with a fillout factor of f = 17.74%. The results indicate that there exists mass transfer from the more massive component to the less massive one at a rate of relative mass exchange, 6zl/m = -1.09× 10-7 yr-1. It is possible that this weak- contact system, that shows a decreasing orbital period, may undergo contraction of the inner and outer critical Roche lobes and evolve into a deep-contact binary.     

Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.     

Estimating stellar atmospheric parameters based on Lasso features

With the rapid development of large scale sky surveys like the Sloan Digital Sky Survey （SDSS）, GAIA and LAMOST （Guoshoujing telescope）, stellar spectra can be obtained on an ever-increasing scale. Therefore, it is necessary to estimate stel- lar atmospheric parameters such as Teff, log g and [Fe/H] automatically to achieve the scientific goals and make full use of the potential value of these observations. Feature selection plays a key role in the automatic measurement of atmospheric parameters. We propose to use the least absolute shrinkage selection operator （Lasso） algorithm to select features from stellar spectra. Feature selection can reduce redundancy in spectra, alleviate the influence of noise, improve calculation speed and enhance the robustness of the estimation system. Based on the extracted features, stellar atmospheric param- eters are estimated by the support vector regression model. Three typical schemes are evaluated on spectral data from both the ELODIE library and SDSS. Experimental results show the potential performance to a certain degree. In addition, results show that our method is stable when applied to different spectra.     

The ROSAT bright source 1RXS J201607.0＋251645： an active Algol-type binary

1RXS J201607.0＋251645 is identified as an eclipsing binary. We present preliminary observations in the V band with the 0.6-m telescope for three years and extensive observations in the V and R bands with the 0.8-m telescope for six nights, respectively. The light curve of the system is E13 type. Five light minimum times were obtained and the orbital period of 0.388058^d（±0.00044d） is determined. The photometric solution given by the 2003-version of the Wilson-Devinney program suggests that the binary is a semidetached system with photometric mass ratio 0.895（±0.006）, which is probably comprised of a G5 primary and an oversized K5 secondary. The tess massive component has completely filled its Roche lobe, while the other one almost fills its Roche lobe with a filling factor of 93.4%. The system shows a varying O＇Connell effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous with log Lx/Lbol - -3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer that the binary may be in thermal oscillation or may evolve into a contact binary.     

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.     

The low-mass classic Algol-type binary UU Leo revisited

New multi-color photometry of the eclipsing binary UU Leo, acquired from 2010 to 2013, was carried out by using the 60-cm and 85-cm telescopes at the Xinglong station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. With the updated Wilson-Devinney code, the photometric solution was derived from BVR light curves. The results imply that UU Leo is a semi-detached Algol-type binary, with a mass ratio of q = 0.100（±0.002）. The change in orbital period was reanalyzed based on all available eclipsing times. The 0 - C curve could be described by an upward parabola superimposed on a quasi-sinusoidal curve. The period and semi-amplitudes are Pmod = 54.5（±1.1） yr and A = 0.0273d（±0.0015d）, which may be attributed to the light-time effect via the presence of an invisible third body. The long-term period increases at a rate of dR/dr=＋4.64（±0.14）×10^-7d yr^-1, which may be interpreted by the conserved mass being transferred from the secondary to the primary. With mass being transferred, the low-mass Algol-type binary UU Leo may evolve into a binary system with a main sequence star and a helium white dwarf.     

Molecular outflows and gas rotation associated with G20.08-0.14N

We present the results of a high-resolution study with the Submillimeter Array （SMA） toward the massive star-forming complex G20.08-0.14N. With the SMA data, we have detected and analyzed the transitions in the 12CO （3-2） and 12CO （2-1） molecular lines as well as CHaCN. The millimeter observations reveal highly collimated bipolar molecular outflows, traced by high-velocity 12CO （2-1） and 12CO （3-2） emissions. Using a rotation temperature diagram, we derive that the rota- tional temperature and the column density of CHaCN are 244 K and 1.2 ~ 1015 cm-2, respectively. We also suggest that the minor outflow is probably driven by the hy- percompact （HC） HII region A that is inside. We find the molecular gas （traced by ClrO, SO, CH3OH and SO2） surrounding G20.08-0.14N appears to be undergoing bulk rotation. The HCHII region A that is inside is most probably the main source of accretion and heating for G20.08-0.14N.