Dongyang Gao

The Weihai Observatory search for close-in planets orbiting giant stars

Planets are known to orbit giant stars, yet there is a shortage of planets orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded enough to engulf such planets, but tidal forces can bring planets to the surface of the star far beyond the stellar radius. So the question remains: are tidal forces strong enough in these stars to engulf all the missing planets? We describe a high-cadence observational program to obtain precise radial velocities of bright giants from Weihai Observatory of Shandong University. We present data on the planet host Beta Gem (HD 62509), confirming our ability to derive accurate and precise velocities; our data achieve an rms of 7.3 m/s about the Keplerian orbit fit. This planet-search programme currently receives ~100 nights per year, allowing us to aggressively pursue short-period planets to determine whether they are truly absent.

THE FIRST PHOTOMETRIC ANALYSIS OF THE NEAR CONTACT BINARY IR Cas

The first photometric analysis of IR Cas was carried out based on the new observed BVRI light curves. The symmetric light curves and nearly flat secondary minimum indicate that very precise photometric results can be determined. We found that IR Cas is a near contact binary with the primary component filling its Roche lobe. An analysis of the O-C diagram based on all available times of light minimum reveals evidence for a periodic change with a semiamplitude of 0.0153 days and a period of 39.7 years superimposed on a secular decrease at a rate of dp/dt=-1.28(\pm0.09)\times10^{-7} d yr^{-1}. The most reasonable explanation for the periodic change is the light time-travel effect due to a third body. The period decrease may be caused by mass transfer from the primary component to the secondary. With the decreasing period, IR Cas would eventually evolve into a contact system.

A possible giant planet orbiting the cataclysmic variable LX Ser

LX Ser is a deeply eclipsing cataclysmic variable with an orbital period of 0.1584325 d. 62 new eclipse times were determined by our observations and the AAVSO International Data base. Combining all available eclipse times, we analyzed the O-C behavior of LX Ser. We found that the O-C diagram of LXSer shows a sinusoidal oscillation with a period of 22.8 yr and an amplitude of 0.00035 d. Two mechanisms (i.e., the Applegate mechanism and the light-travel time effect) are applied to explain the cyclic modulation. We found that it is difficult to apply the Applegate mechanism to explain the cyclic oscillation in the orbital period. Therefore, the cyclic period change is most likely to be caused by the light-travel time effect due to the presence of a third body. The mass of the tertiary component was determined to be M-3 similar to 7.5M(Jup). We supposed that the tertiary companion is plausibly a giant planet. The stability of the giant planet was checked, and we found that the multiple system is stable.

Astrometric calibration for space debris with a small field of view

A center-shift method is presented for astrometric calibration, which is effective for space debris astrometry in a small field of view. Its details are given, the accuracy is experimented and the result is presented. The average accuracy of astrometric calibration using center-shift method is about 0.57 arcsec. The center-shift method is applicable to images observed by equatorial mount telescopes.

WES—Weihai Echelle Spectrograph

The Weihai Echelle Spectrograph (WES) is the first fiber-fed echelle spectrograph for astronomical observation in China. It is primarily used for chemical abundance and asteroseismology studies of nearby bright stars, as well as radial velocity (RV) detections for exoplanets. The optical design of WES is based on the widely demonstrated and well-established white-pupil concept. We describe the WES in detail and present some examples of its performance. A single exposure echelle image covers the spectral region 371-1100 nm in 107 spectral orders over the rectangular CCD. The spectral resolution R = lambda/Delta lambda changes from 40,600 to 57,000 through adjusting the entrance slit width from full to 2.2 pixels sampling at the fiber-exit. The limiting magnitude scales to V = 8 with a signal-to-noise ratio of more than 100 in V for an hour exposure, at the spectral resolution R approximate to 40,000 in the median seeing of 1 7 at Weihai Observatory for the 1 m telescope. The RV measurement accuracy of WES is estimated to be <10 m s(-1) in 10 months (302 days) and better than 15 m s(-1) in 4.4 years (1617 days) in the recent data processing.

The active W UMa type binary star V781 Tau revisited

In this paper, new determined BVRcIc

Discovery of a W UMa type binary GSC 03553−00845

BVR_{c}I_{c}

Four color light curves and period changes investigation of the contact binary BX Peg

light curves and radial velocities of V781 Tau are presented. By analyzing the light curves and radial velocities simultaneously, we found that V781 Tau is a W-subtype medium contact binary star with a mass ratio of q=2.207±0.005

Sky Brightness at Weihai Observatory of Shandong University

q=2.207\pm0.005

The highest rate orbital period increasing contact binary LP UMa revisited

and a contact degree of f=21.6(±1.0)%