Asymmetric migration dynamics of the tropical Asian and Australasian floras

The tropical Asian and Australasian floras have a close relationship,and is a vital distribution pattern of seed plants worldwide.As estimated,more than 81 families and 225 genera of seed plants distributed between tropical Asia and Australasia.However,the evolutionary dynamics of two floras were still vague.Here,a total of 29 plant lineages,represented the main clades of seed plants and different habits,were selected to investigate the biotic interchange between tropical Asia and Australasia by integrated dated phylogenies,biogeography,and ancestral state reconstructions.Our statistics indicated that 68 migrations have occurred between tropical Asia and Australasia since the middle Eocene except terminal migrations,and the migration events from tropical Asia to Australasia is more than 2 times of the reverse.Only 12 migrations occurred before 15 Ma,whereas the remaining56 migrations occurred after 15 Ma.Maximal number of potential dispersal events(MDE) analysis also shows obvious asymmetry,with southward migration as the main feature,and indicates the climax of bi-directional migrations occurred after 15 Ma.We speculate that the formation of island chains after the Australian-Sundaland collision and climate changes have driven seed plant migrations since the middle Miocene.Furthermore,biotic dispersal and stable habitat may be crucial for floristic interchange between tropical Asia and Australasia.

The Masses of a Sample of Radial-velocity Exoplanets with Astrometric Measurements

Being one of the most fundamental physical parameter of astronomical objects,mass plays a vital role in the study of exoplanets,including their temperature structure,chemical composition,formation,and evolution.However,nearly a quarter of the known confirmed exoplanets lack measurements of their masses.This is particularly severe for those discovered via the radial velocity(RV)technique,which alone could only yield the minimum mass of planets.In this study,we use published RV data combined with astrometric data from a cross-calibrated Hipparcos-Gaia Catalog of Accelerations to jointly constrain the masses of 115 RV-detected substellar companions,by conducting full orbital fits using the public tool orvara.Among them,9 exoplanets with M_(p)sini<13.5M_(Jup)are reclassified to the brown dwarf(BD)regime,and 16 BD candidates(13.5≤Mp sini<80M_(Jup))turn out to be low-mass M dwarfs.We point out the presence of a transition in the BD regime as seen in the distributions of host star metallicity and orbital eccentricity with respect to planet masses.We confirm the previous findings that companions with masses below 42.5 M_(Jup)might primarily form in the protoplanetary disk through core accretion or disk gravitational instability,while those with masses above 42.5 M_(Jup)formed through the gravitational instability of a molecular cloud like stars.Selection effects and detection biases,which may affect our analysis to some extent,are discussed.

A planetary companion orbiting the intermediate-mass G Giant HD 173416

The discovery of a planetary companion to the intermediate-mass late-type giant star HD173416 from precise Doppler surveys of G and K giants at Xinglong station and Okayama Astrophysical Observatory （OAO） is presented in this letter. The planet has a minimum mass of 2.7 MJ, an eccentricity of 0.21, a semimajor axis of 1.16 AU and an orbital period of 324 days.

Line profile analysis of an astronomical spectrograph with a laser frequency comb

We present a study of the spectral line shape associated with a High Resolution Spectrograph on the 2.16 m telescope at the Xinglong Observing Station of National Astronomical Observatories, Chinese Academy of Sciences. This measurement is based on modeling the instrumental line shape obtained by unresolved modes from a Yb-fiber mode-locked laser frequency comb. With the current repetition rate of 250 MHz and 26 GHz mode spacing on the spectrograph, we find the absolute variation of the line center, 0.0597 pixel in the direction of the CCDs, and 0.00275 pixel （～3 m s^-1） for relative variation in successive exposures on a short timescale. A novel double-Gaussian model is presented to improve the quality of the fit by a factor of 2.47 in a typical single exposure. We also use analysis with raw moments and central moments to characterize the change in line shape across the detector. A trend in charge transfer efficiency can be found on the E2V 4096 ×4096 CCD that provides a correction for wavelength calibration aiming to reach a level of precision for radial velocity below 1 m s^- 1.

Chemical abundance analysis of 19 barium stars

We aim at deriving accurate atmospheric parameters and chemical abundances of 19 barium（Ba） stars, including both strong and mild Ba stars, based on the high signal-to-noise ratio and high resolution Echelle spectra obtained from the 2.16 m telescope at Xinglong station of National Astronomical Observatories, Chinese Academy of Sciences. The chemical abundances of the sample stars were obtained from an LTE, plane-parallel and line-blanketed atmospheric model by inputting the atmospheric parameters（effective temperatures Teff, surface gravities log g, metallicity [Fe/H] and microturbulence velocity ξt） and equivalent widths of stellar absorption lines. These samples of Ba stars are giants as indicated by atmospheric parameters, metallicities and kinematic analysis about UVW velocity. Chemical abundances of 17 elements were obtained for these Ba stars. Their Na, Al, α- and iron-peak elements（O, Na, Mg, Al, Si, Ca,Sc, Ti, V, Cr, Mn, Ni） are similar to the solar abundances. Our samples of Ba stars show obvious overabundances of neutron-capture（n-capture） process elements relative to the Sun. Their median abundances of[Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54, 0.65 and 0.40, respectively. The Y I and Zr I abundances are lower than Ba, La and Eu, but higher than the α- and iron-peak elements for the strong Ba stars and similar to the iron-peak elements for the mild stars. There exists a positive correlation between Ba intensity and [Ba/Fe].For the n-capture elements（Y, Zr, Ba, La）, there is an anti-correlation between their [X/Fe] and [Fe/H]. We identify nine of our sample stars as strong Ba stars with [Ba/Fe]〉0.6 where seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has Ba=1.0. The remaining ten stars are classified as mild Ba stars with 0.17〈[Ba/Fe]〈0.54.

A possible substellar companion to the intermediate-mass giant HD 175679

We report the discovery of a substellar companion around the intermediate- mass giant HD 175679. Precise radial velocity data of the star from the Xinglong Station and the Okayama Astrophysical Observatory revealed a Keplerian velocity variation with an orbital period of 1366.8±5.7 d, a semiamplitude of 380.2±3.2 m s-1 and an eccentricity of 0.378± 0.008. Adopting a stellar mass of 2.7± 0.3 M, we obtain that the minimum mass of the HD 175679 b is 37.3± 2.8 M and the semimajor axis is 3.36±0.12 AU. This discovery is the second brown dwarf companion candidate from a joint planet-search program between China and Japan.